Lemaitre Nolwenn
email: nolwenn.lemaitre@erdw.ethz.ch

Dehairs Frank

Planchon Frederic

Sarthou Geraldine

Gallinari Morgane

Roig Stéphane

Jeandel Catherine

Castrillejo Maxi

Nolwenn Lemaitre

Particulate Trace Element Export in the North Atlantic (GEOTRACES GA01 Transect, GEOVIDE Cruise)

Keywords: particulate trace elements, export fluxes, multiple carrier phases, residence times, GEOTRACES

Vertical export of particulate trace elements (pTEs) is a critically underconstrained aspect of their biogeochemistry. Here, we combine elemental analyses on large (>53 μm) particles and 234Th measurements to determine downward export fluxes from the upper layers (40-110 m) of pTEs (Al, Cd, Co, Cu, Fe, Mn, Ni, P, Ti, V, Zn) and mineral phases (lithogenic, Fe-and Mn-oxides, calcium carbonate, and opal) in the North Atlantic along the GEOVIDE transect (Portugal-Greenland-Canada; GEOTRACES GA01 cruise). The role of lithogenic particles in controlling TE fluxes is obvious at proximity of the Iberian margin where the highest pTE export fluxes were estimated (up to 3912 μg/m2/d for pFe). However, high lithogenic and pTE fluxes are also observed up to 1700 km off this margin in the west European and Icelandic basins (up to 931 μg/m2/d for pFe). The lowest pTE export fluxes are determined in the Labrador Sea (as low as 501 μg/m2/d for pFe). High Mn-and Fe-oxide fluxes are estimated at the open ocean stations, suggesting that authigenic particles are an important vector of pTEs. All along the transect, biogenic particles also drive the pTE export fluxes, as shown by the similar pTE/POC ratios between exports and phytoplankton quotas. The shortest residence times (dissolved + particulate) are generally observed where lithogenic particles control the pTE fluxes (as low as 2 days for Fe) whereas pTEs seem to be longer retained when the contribution of biogenic particles become greater (residence times up to 147 days for Fe).

INTRODUCTION

Bioactive trace elements (TEs: Cd, Co, Cu, Fe, Mn, Ni, Zn, etc.) are important for the marine primary productivity [START_REF] Morel | The Biogeochemical Cycles of Trace Metals in the Oceans[END_REF] , as they are required for numerous metabolic processes [START_REF] Sunda | Trace Metal Interactions with Marine Phytoplankton[END_REF][START_REF] Twining | The Trace Metal Composition of Marine Phytoplankton[END_REF] . Sometimes in line with other bioactive trace elements, depleted Fe concentrations in the surface waters can limit the phytoplankton, thus influencing the community structure and, as a result, the overall marine carbon cycle [START_REF] Boyd | A Mesoscale Phytoplankton Bloom in the Polar Southern Ocean Stimulated by Iron Fertilization[END_REF][START_REF] Moore | Processes and Patterns of Oceanic Nutrient Limitation[END_REF] . Therefore, the quantification of biogeochemical processes regulating the internal cycle of TEs is essential to better understand the carbon cycle and in particular the biological carbon pump [START_REF] Martin | Glacial-Interglacial CO2 Change: The Iron Hypothesis[END_REF][START_REF] Sigman | Glacial/Interglacial Variations in Atmospheric Carbon Dioxide[END_REF] .

Many TEs reach the ocean through particles, either via atmospheric dusts [START_REF] Jickells | Atmospheric Transport of Trace Elements and Nutrients to the Oceans[END_REF] , rivers [START_REF] De Baar | Distributions, Sources and Sinks of Iron in Seawater[END_REF] , margins [START_REF] Jeandel | Overview of the Mechanisms That Could Explain the 'Boundary Exchange' at the Land-Ocean Contact[END_REF] or sediments [START_REF] Homoky | Quantifying Trace Element and Isotope Fluxes at the Ocean-Sediment Boundary: A Review[END_REF] . Marine particles also participate in the removal of TEs, either through scavenging onto particle surfaces [START_REF] Goldberg | Chemical Scavengers of the Sea[END_REF] , precipitation of authigenic minerals such as barite [START_REF] Dehairs | Discrete Suspended Particles of Barite and the Barium Cycle in the Open Ocean[END_REF][START_REF] Bishop | The Barite-Opal-Organic Carbon Association in Oceanic Particulate Matter[END_REF][START_REF] Ganeshram | An Experimental Investigation of Barite Formation in Seawater[END_REF] and Mn-Fe oxyhydroxides [START_REF] Bruland | Controls of Trace Metals in Seawater[END_REF] , or sinking to the deep ocean due to lithogenic and biogenic ballast minerals [START_REF] Klaas | Association of Sinking Organic Matter with Various Types of Mineral Ballast in the Deep Sea: Implications for the Rain Ratio[END_REF][START_REF] Lam | The Continental Margin Is a Key Source of Iron to the HNLC North Pacific Ocean[END_REF][START_REF] Ohnemus | Exposing the Distributions and Elemental Associations of Scavenged Particulate Phases in the Ocean Using Basin-Scale Multi-Element Data Sets[END_REF] . Small (suspended; 1-53µm diameter) particles mainly trap TEs via scavenging, though they have been shown to slowly sink after coagulation to other particles [START_REF] Puigcorbé | Small Phytoplankton Drive High Summertime Carbon and Nutrient Export in the Gulf of California and Eastern Tropical North Pacific[END_REF][START_REF] Giering | High Export via Small Particles before the Onset of the Nort Atlantic Spring Bloom[END_REF] . Large (sinking; >53µm diameter) particles export TEs from the biologically active upper water column down to the interior ocean [START_REF] Fowler | Role of Large Particles in the Transport of Elements and Organic Compounds through the Oceanic Water Column[END_REF] , with the remineralization length scale controlling the release of TEs into solution and their subsequent return to the surface. Earlier studies have revealed that particulate phosphorous (pP), nickel (pNi), zinc (pZn) and organic carbon (POC) are remineralized faster than particulate iron (pFe) because of a stronger scavenging of dissolved Fe onto particles [START_REF] Frew | Particulate Iron Dynamics during FeCycle in Subantarctic Waters Southeast of New Zealand[END_REF][START_REF] Twining | Differential Remineralization of Major and Trace Elements in Sinking Diatoms[END_REF] . Thus, particle-solute interactions determine the residence times of TEs in the water column. However these residence times are presently not well known because of scarce estimates of TE inventories and fluxes into or out of the water column [START_REF] Hayes | Replacement Times of a Spectrum of Elements in the North Atlantic Based on Thorium Supply[END_REF] .

Despite an increasing number of studies addressing TE export, this process remains still poorly understood [START_REF] Frew | Particulate Iron Dynamics during FeCycle in Subantarctic Waters Southeast of New Zealand[END_REF][START_REF] Ellwood | Pelagic Iron Cycling during the Subtropical Spring Bloom, East of New Zealand[END_REF][START_REF] Black | Ironing out Fe Residence Time in the Dynamic Upper Ocean[END_REF][START_REF] Black | Insights from the 238U-234Th Method into the Coupling of Biological Export and the Cycling of Cadmium, Cobalt, and Manganese in the Southeast Pacific Ocean. Global Biogeochem[END_REF][START_REF] Ho | Trace Metal Cycling in the Surface Water of the South China Sea: Vertical Fluxes, Composition, and Sources[END_REF][START_REF] Kuss | Seasonality of Particle-Associated Trace Element Fluxes in the Deep Northeast Atlantic Ocean[END_REF][START_REF] Kuss | Particulate Trace Element Fluxes in the Deep Northeast Atlantic Ocean[END_REF][START_REF] Lamborg | Sinking Fluxes of Minor and Trace Elements in the North Pacific Ocean Measured during the VERTIGO Program[END_REF][START_REF] Lemaitre | Impact of the Natural Fe-Fertilization on the Magnitude, Stoichiometry and Efficiency of Particulate Biogenic Silica, Nitrogen and Iron Export Fluxes[END_REF][START_REF] Planquette | Fluxes of Particulate Iron from the Upper Ocean around the Crozet Islands: A Naturally Iron-Fertilized Environment in the Southern Ocean[END_REF][START_REF] Stanley | A Comparison of Major and Minor Elemental Fluxes Collected in Neutrally Buoyant and Surface-Tethered Sediment Traps[END_REF][START_REF] Weinstein | Vertical Flux of Particulate Al, Fe, Pb, and Ba from the Upper Ocean Estimated from 234Th/238U Disequilibria[END_REF] . Besides the strong temporal and spatial variability, another reason likely resides in the difficulty in measuring particulate trace element (pTE) fluxes, as TEs are present at very low concentrations in the ocean and are easily prone to contamination. Sediment traps are used to directly quantify the pTE export fluxes [START_REF] Kuss | Particulate Trace Element Fluxes in the Deep Northeast Atlantic Ocean[END_REF][START_REF] Lamborg | Sinking Fluxes of Minor and Trace Elements in the North Pacific Ocean Measured during the VERTIGO Program[END_REF][START_REF] Benitez-Nelson | Mesoscale Eddies Drive Increased Silica Export in the Subtropical Pacific Ocean[END_REF][START_REF] Conte | The Elemental Composition of the Deep Particle Flux in the Sargasso Sea[END_REF] but their deployment tends to be time-and effort-intensive. They also can be biased because of lateral advection or because of possible TE contamination from the preservative solution added into the cups to avoid zooplankton and microbial activities [START_REF] Mcdonnell | The Oceanographic Toolbox for the Collection of Sinking and Suspended Marine Particles[END_REF] . One alternative for determining particulate export fluxes is the clean but indirect 234 Th-238 U method [START_REF] Coale | Thorium-234:Uranium-238 Disequilibria within the California Current[END_REF][START_REF] Buesseler | Carbon and Nitrogen Export during the JGOFS North Atlantic Bloom Experiment Estimated from 234Th: 238U Disequilibria[END_REF][START_REF] Cochran | Short-Lived U/Th Series Radionuclides in the Ocean: Tracers for Scavenging Rates, Export Fluxes and Particle Dynamics[END_REF] . 234 Th is a highly particle-reactive element with a short half-life (t ½ = 24.1 days) compared to its radioactive parent 238 U (t ½ = 4.47 billion years). While both isotopes are usually at secular equilibrium in subsurface waters, a deficit of 234 Th relative to 238 U can be observed in the upper ocean, where sinking particles carry 234 Th downward. This deficit of 234 Th relative to 238 U can be converted into an elemental export flux when multiplied with the ratio of the element to 234 Th (element: 234 Th hereafter) in the particulate material at a given depth [START_REF] Weinstein | Vertical Flux of Particulate Al, Fe, Pb, and Ba from the Upper Ocean Estimated from 234Th/238U Disequilibria[END_REF][START_REF] Buesseler | Carbon and Nitrogen Export during the JGOFS North Atlantic Bloom Experiment Estimated from 234Th: 238U Disequilibria[END_REF] . This method has the benefit to allow flux determination at multiple stations and for a large suite of elements and mineral phases.

The presence of lithogenic and biogenic minerals, as well as oxyhydroxides, are identified as phases liable to control the settling of particles with depth [START_REF] Ohnemus | Exposing the Distributions and Elemental Associations of Scavenged Particulate Phases in the Ocean Using Basin-Scale Multi-Element Data Sets[END_REF] . In the temperate north Atlantic, advection of lithogenic material from continental margins and pronounced seasonal phytoplankton blooms strongly enhance the pTE distributions and downward export fluxes 43- 47 . However, occasional lack of nutrients such as dissolved iron (dFe) [START_REF] Nielsdottir | Iron Limitation of the Postbloom Phytoplankton Communities in the Iceland Basin[END_REF] can limit the primary productivity, the magnitude of the downward fluxes and thus the strength of the biological carbon pump [START_REF] Moore | Processes and Patterns of Oceanic Nutrient Limitation[END_REF][START_REF] Achterberg | Natural Iron Fertilization by the Eyjafjallajökull Volcanic Eruption[END_REF][START_REF] Blain | Availability of Iron and Major Nutrients for Phytoplankton in the North-East Atlantic Ocean[END_REF] . This is well illustrated in the subtropical north Atlantic, which is characterized by oligotrophic conditions leading to low primary production [START_REF] Moore | Relative Influence of Nitrogen and Phosphorus Availability on Phytoplankton Physiology and Productivity in the Oligotrophic Sub-Tropical North Atlantic Ocean[END_REF] and to low export fluxes of POC [START_REF] Owens | Thorium-234 as a Tracer of Particle Dynamics and Upper Ocean Export in the Atlantic Ocean[END_REF][START_REF] Thomalla | Particulate Organic Carbon Export from the North and South Atlantic Gyres: The 234Th/238U Disequilibrium Approach[END_REF] and pTEs [START_REF] Kuss | Spatial Variability of Particle Associated Trace Elements in Near-Surface Waters of the North Atlantic (30°N/60°W to 60°N/2°W), Derived by Large Volume Sampling[END_REF] . In this region, exports of POC [START_REF] Antia | Basin-Wide Particulate Carbon Flux in the Atlantic Ocean ' Regional Export Patterns and Potential for Atmospheric Sequestration Avan Detlef TM Jan s Susanne Regional Differences in Changes of the Export Ratio with Depth Are Related to over the Atlantic Oc[END_REF][START_REF] Billet | Seasonal Sedimentation of Phytoplankton to the Deep-Sea Benthos[END_REF][START_REF] Henson | Decadal Variability in North Atlantic Phytoplankton Blooms[END_REF][START_REF] Lampitt | Long-Term Variability of Downward Particle Flux in the Deep Northeast Atlantic: Causes and Trends[END_REF][START_REF] Peinert | Particle Flux Variability in the Polar and Atlantie Biogeoehemieal Provinees of the Nordie Seas[END_REF] and pTEs [START_REF] Kuss | Seasonality of Particle-Associated Trace Element Fluxes in the Deep Northeast Atlantic Ocean[END_REF] show episodic fluctuations along the season due to nutrient and/or light limitations but also due to lithogenic inputs mainly originating from margins or associated with atmospheric dust depositions [START_REF] Kuss | Seasonality of Particle-Associated Trace Element Fluxes in the Deep Northeast Atlantic Ocean[END_REF][START_REF] Kuss | Spatial Variability of Particle Associated Trace Elements in Near-Surface Waters of the North Atlantic (30°N/60°W to 60°N/2°W), Derived by Large Volume Sampling[END_REF][START_REF] Ohnemus | Cycling of Lithogenic Marine Particulates in the US GEOTRACES North Atlantic Transect[END_REF][START_REF] Lam | Size-Fractionated Major Particle Composition and Concentrations from the US GEOTRACES North Atlantic Zonal Transect[END_REF] . The more productive subpolar Atlantic is characterized by lower lithogenic inputs because of the decreasing influence of the Saharan dust plume [START_REF] Kuss | Spatial Variability of Particle Associated Trace Elements in Near-Surface Waters of the North Atlantic (30°N/60°W to 60°N/2°W), Derived by Large Volume Sampling[END_REF] . Nevertheless, lateral supplies of lithogenic material from continental shelves have been reported and could enhance the export fluxes [START_REF] Kuss | Seasonality of Particle-Associated Trace Element Fluxes in the Deep Northeast Atlantic Ocean[END_REF][START_REF] Weinstein | Vertical Flux of Particulate Al, Fe, Pb, and Ba from the Upper Ocean Estimated from 234Th/238U Disequilibria[END_REF] .

In this study, we aim to better understand the processes controlling the TE distributions in the upper layers of the North Atlantic Ocean by focusing on particulate TE export. The different particulate substrates (authigenic, lithogenic and biogenic) liable to carry the pTEs are investigated and the export efficiencies are evaluated by estimating the residence times of TEs within the upper ocean.

METHODS

Biogeochemical characteristics of investigated stations

Fieldwork was conducted on board the French R/V Pourquoi Pas? along the GEOTRACES GA01 section during the GEOVIDE expedition (Fig. 1). The cruise was carried out in May-June 2014. We sampled a total of 11 stations located in five different biogeochemical domains described in details in Lemaitre et al. (2018) [START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] and in Table 1. Briefly, the Iberian basin was sampled after the spring bloom and was characterized by a low primary productivity (PP) [START_REF] Fonseca-Batista | Evidence of High N2 Fixation Rates in the Temperate Northeast Atlantic[END_REF] .

Station #13 had the highest proportion of cyanobacteria (12% of phytoplankton abundance) of the all transect [START_REF] Tonnard | Cycle Biogéochimique Du Fer : Distribution et Spéciation Dans l'océan Atlantique Nord (GA01) et l'océan Austral (GIpr05)[END_REF] . Particulate organic carbon (POC) export was high at Station #1 while low at Station #13, reflecting the low nutrient availability in subtropical waters [START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] . The west European (Stations #21 and #26) and Icelandic (Stations #32 and #38) basins were sampled during the bloom development and were the most productive areas with the highest PP observed along the transect [START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] . Diatoms dominated the phytoplankton community (41% of phytoplankton abundance) but dinoflagellates and haptophytes (including coccolitophorids) also contributed significantly in the west European basin (~20% of phytoplankton abundance [START_REF] Tonnard | Cycle Biogéochimique Du Fer : Distribution et Spéciation Dans l'océan Atlantique Nord (GA01) et l'océan Austral (GIpr05)[END_REF] ). Conversely, nano-phytoplankon and mainly haptophytes dominated the community in the Icelandic basin.

High POC exports were determined in both basins and particularly at Station #32 [START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] . The Irminger basin (Stations #44 and #51) was sampled close to the bloom maximum and PP values were high, with a clear dominance of diatoms (between 55 and 77% of phytoplankton abundance [START_REF] Tonnard | Cycle Biogéochimique Du Fer : Distribution et Spéciation Dans l'océan Atlantique Nord (GA01) et l'océan Austral (GIpr05)[END_REF] ). Because of the accumulation of biomass in the surface waters, POC export fluxes were low, with Station #44 having the lowest one of the entire cruise [START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] . The Labrador basin (Stations #64, #69 and #77) was sampled after the PP peak, at the onset of the bloom decline [START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] . Productivity was relatively low compared to the other studied basins. Diatoms were also dominating, contributing up to 62% of the phytoplankton abundance [START_REF] Tonnard | Cycle Biogéochimique Du Fer : Distribution et Spéciation Dans l'océan Atlantique Nord (GA01) et l'océan Austral (GIpr05)[END_REF] . POC export fluxes were relatively high, likely because of the increasing number of rapidly sinking particles [START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] .

Particle sampling

Total 234 Th activities were determined from 4L unfiltered seawater sampled with 12L Niskin bottles mounted on CTD rosette and were processed following the method of Pike et al. ( 2005) [START_REF] Pike | Quantification of 234Th Recovery in Small Volume Seawater Samples by Inductively Coupled Plasma Mass Spectrometry[END_REF] . Samples were acidified and spiked with a 230 Th yield monitor in order to estimate the 234 Th recovery during sample processing. After a 12h equilibration, pH was increased and KMnO4 and MnCl2 solutions were added. After a further 12h equilibration, samples were filtered on quartz-microfiber discs (QMA, Sartorius, nominal porosity=1 µm, diameter=25 mm) and the 234 Th activities were measured on-board using a low-level beta counter (RISØ®, Denmark).

Residual beta activities were measured ~6 months after the cruise after which samples were processed for Th recoveries using 229 Th as a second yield tracer. Export fluxes of 234 Th were then calculated using a 1-D box model [START_REF] Savoye | 234Th Sorption and Export Models in the Water Column: A Review[END_REF] under steady state assumptions and neglecting advection and diffusion [START_REF] Buesseler | Carbon and Nitrogen Export during the JGOFS North Atlantic Bloom Experiment Estimated from 234Th: 238U Disequilibria[END_REF] . Export fluxes of 234 Th are presented in Lemaitre et al (2018) [START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] .

Particulate matter for biogenic silica (BSi), calcium carbonate (CaCO3) and pTE analyses was collected on the same in-situ pump (Challenger Oceanics® and McLane® pumps, ISP) filter, whereas particles for POC were collected using a separate filter holder. The later was mounted either on a second flow path when modified McLane ISP heads were used, or with a separate ISP unit 60 attached 10 to 50 m apart from the ISP dedicated to TEs (see Table S1). Particulate 234 Th activity in the large size particle fraction (LSF, >53µm) was determined on particles collected with each ISP system (Fig. S1).

Particulate organic carbon (POC) LSF was collected on a 53-µm mesh polyester screen (Petex), which was cut into quarters. Particles present on one quarter of the Petex screen were rinsedoff using 0.45 µm filtered seawater obtained during the cruise and subsequently collected on a silver filter (SterliTech, nominal porosity=0.45 µm, diameter=25 mm) for one quarter, and on a GF/F filter (Whatman, nominal porosity=0.7 µm, diameter=25 mm) for another quarter, before being Beta-counted on board. Back in the home laboratory, samples were prepared for POC analyses: filters were fumed with HCl vapor, dried, packed in pre-combusted silver cups and analysed with an elemental analyser (EA-IRMS, Delta V Plus, Thermo Scientific). More details on POC and particulate 234 Th (p 234 Th) analyses can be found in Lemaitre et al. (2018) [START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] .

Particulate matter for BSi, CaCO3 and pTE determinations was filtered on a 142mm-diameter 53-µm mesh polyester screen (Petex) for the LSF upstream of a 142mm-diameter 0.8-µm polyethersulfone filter (Supor®) for the small size particle fraction (SSF). Before use, filters were soaked in 1.2M HCl (Suprapur grade, Merck), heated overnight at 60°C and subsequently rinsed with Milli-Q grade water. On board, filters were processed under a laminar flow unit within a customized clean "bubble" to prevent contamination. Before and after the ISP recoveries, pump heads were protected with plastic bags to minimize contamination. After pump recoveries, filter heads were dismantled and carried inside the clean bubble.

Using a clean ceramic scalpel, one quarter of the Petex screen, dedicated to p 234 Th and BSi analyses, was cut out. Particles were washed off the Petex screen using 0.45-µm filtered seawater obtained during the cruise. Particles were then collected on polycarbonate filters (PC; Nuclepore®, porosity=0.4µm, diameter=25mm) mounted on a polysulfone filtration unit.

Filters were left to dry at room temperature inside the laminar flow unit and subsequently prepared for Beta counting. Activities of p 234 Th were also determined on a second quarter of the Petex screen: particles were washed off, using the 0.45-µm filtered seawater, and collected on a polyethersulfone filter (Supor®, porosity=0.45 µm, diameter=25 mm) mounted on a Nalgene filtration unit (Fig. S1). Because Beta counting of samples is probably incompatible with trace metal clean stringent conditions, the two last quarters of the Petex screen, dedicated to pTEs, particulate calcium (pCa) and sodium (pNa), were stored in a clean petrislide (Pall Gelman) and kept at -20°C until sample processing and analysis in the home laboratory. Since Supor filters with the SSF were not Beta counted, there are no data for the SSF p 234 Th activity.

Particulate matter analyses

The methods used here have been approved during a GEOTRACES intercalibration exercise and our elemental concentrations have been submitted to the GEOTRACES Intermediate Data Product (IDP) 2021. The concentrations obtained from ISP sampling (this study) have been compared to those obtained by GO-FLO sampling at the same locations (from Gourain et al., 2019 [START_REF] Gourain | Inputs and Processes Affecting the Distribution of Particulate Iron in the North Atlantic along the GEOVIDE (GEOTRACES GA01) Section[END_REF] and from Planquette et al., personal communication, 2019). Both datasets were obtained after using exactly the same digestion and analytical methods. Although similar element profiles were obtained from both datasets, highlighting data consistency, we note that pTE concentrations obtained from ISP sampling were generally lower than those obtained from GO-FLO bottles. This discrepancy could possibly result from particle washout during ISP recovery, since our ISPs were not systematically equipped with anti-washout systems, or due to some loss when transferring particles from the Petex screens to other filters (see above). To limit these effects, our study focuses on elemental ratios and on element: 234 Th ratios, rather than on concentrations or activities.

Trace and major elements

In the home laboratory the two remaining quarters of Petex screen saved for pTEs, pCa and pNa analyses were washed off with 0.45-µm filtered, low TE surface seawater collected during the GEOVIDE cruise (Station #77, 40m, filtered through a Supor filter, 0.45μm) and subsequently collected on acid cleaned 47-mm diameter mixed cellulose esters filters (MF-Millipore® filters, 0.8μm), using Nalgene® filtration units (Fig. S1). Then, filters were processed following the protocol of Planquette and Sherrell (2012) [START_REF] Planquette | Sampling for Particulate Trace Element Determination Using Water Sampling Bottles: Methodology and Comparison to in Situ Pumps[END_REF] . Briefly, one half of the MF filter was kept in a clean petrislide while the other half was placed along the wall of an acid cleaned Teflon vial (Savillex®) and digested with a HNO3 8 M -HF 2.3 M mix solution (Ultrapur and Suprapur grades, respectively, Merck®), refluxing at 130°C during 4h. After gentle evaporation close to near dryness, 200 µL of concentrated HNO3 (Ultrapur grade, Merck) was added in order to drive off the fluorides. The residue was brought back into solution with 0.32M HNO3 spiked with 1 μg/L of indium and stored in acid cleaned centrifuge tubes (Corning®). Measurements of pTEs were performed using a sector field inductively coupled mass spectrometer (SF-ICP-MS, Element 2, Thermo). External calibration curves were run at the start, middle and end of the sequence. The precision and accuracy of our measurements were assessed by analysing the certified reference material (CRM) BCR-414. Recoveries were typically within 10% of the certified values and the precision, given by the relative standard deviation of the five CRM analyses, was between 0.2 and 24% depending on the element (Table 2). Gourain et al. (2019) analysed two other CRM (PACS-3 and MESS-4) by using the exact same analytical method and found similar accuracy and precision results [START_REF] Gourain | Inputs and Processes Affecting the Distribution of Particulate Iron in the North Atlantic along the GEOVIDE (GEOTRACES GA01) Section[END_REF] . The reproducibility of our analyses was assessed by analytical replicates of 17 samples and differences between replicates were less than 6% from the mean value. Aluminium (Al) is usually used as a tracer of lithogenic particles because of its high crustal abundance (Upper Continental Crust or UCC Al = 8.04% by weight [START_REF] Taylor | The Continental Crust: Its Composition and Evolution[END_REF] ) and its stable concentrations among lithogenic sources. However, Al has been shown to be removed from the surface waters via scavenging onto particles, especially diatom cells [START_REF] Moran | Evidence from Mesocosm Studies for Biological Removal of Dissolved Aluminium from Sea Water[END_REF] . During GEOVIDE, scavenging onto sinking opal-containing particles was defined as a sink for Al, especially in the Irminger and Labrador basins where diatoms dominate the phytoplankton community [START_REF] Menzel Barraqueta | Aluminium in the North Atlantic Ocean and the Labrador Sea (GEOTRACES GA01 Section): Roles of Continental Inputs and Biogenic Particle Removal[END_REF] .

Removal of aluminium via other types of particles (i.e. carbonates, lithogenics, organics, fecal pellets) was not observed in this study, although it cannot be excluded [START_REF] Menzel Barraqueta | Aluminium in the North Atlantic Ocean and the Labrador Sea (GEOTRACES GA01 Section): Roles of Continental Inputs and Biogenic Particle Removal[END_REF] . Using Al as a lithogenic tracer can thus be questioned, especially for the Irminger and Labrador basins.

Another lithogenic tracer that can be used is titanium (Ti) but it is less abundant in the UCC (UCC Ti=0.3% [START_REF] Taylor | The Continental Crust: Its Composition and Evolution[END_REF] ) and its concentrations strongly vary between geological materials. We thus calculated the lithogenic mass (litho) using both tracers: Litho (µg/L) = (pAl × 27 × 10 -6 ) / 0.0804 (1) or Litho (µg/L) = (pTi × 47.9 × 10 -6 ) / 0.003 (2) where pAl and pTi are the particulate Al and Ti concentrations in pmol/L; 0.0804 and 0.003 are the mass fractions of Al and Ti in the UCC; and 27 and 47.9 are the molar masses of Al and Ti in g/mol, respectively.

The GEOVIDE transect, and the north Atlantic in general, is characterized by multiple lithogenic sources (atmospheric, sediment or continental inputs) with different geological characteristics. For example, basaltic rocks present close to Iceland and Greenland have a different Ti concentration than gabbro from the Iberian margin, potentially leading to wrong lithogenic estimations. The flux estimates of MnO2, Fe(OH)3 and CaCO3 are lower, if not negative, when Ti is used to correct the lithogenic fraction (Fig. S2). We believe that Ti significantly overestimates the lithogenic fraction when its contribution is low (i.e. at all stations except close to the Iberian margin). In the following, we therefore use Al-calculated fluxes, yet keeping in mind that our mineral fluxes might be overestimated, especially in diatom-rich areas like the Irminger and Labrador basins.

Oxyhydroxides of Fe and Mn were calculated by subtracting Fe and Mn associated with lithogenic and biogenic materials from total Fe and Mn. Assuming that Fe oxyhydroxides are ferrihydrite (Fe(OH)3 or Fe-oxides hereafter) and Mn oxyhydroxides are birnessite (MnO2 or Mn-oxides hereafter), with formula weights 106.9 g Fe(OH)3/mol Fe and 86.9 g MnO2/mol Mn [START_REF] Lam | Size-Fractionated Distributions of Suspended Particle Concentration and Major Phase Composition from the U.S. GEOTRACES Eastern Pacific Zonal Transect (GP16)[END_REF] , it is possible to calculate:

Fe(OH)3 (µg/L) = [pFe -(pAl × 0.21) -(POC × 0.042)] × 106.9 × 10 -3 (3) MnO2 (µg/L) = [pMn -(pAl × 0.00367) -(POC × 0.003)] × 86.9 × 10 -3 (4)
where pFe, pAl and pMn are the total particulate concentrations in nmol/L; POC is the particulate organic carbon concentration in µmol/L; 0.21 and 0.00367 are respectively the UCC pFe:pAl and pMn:pAl ratios in mol/mol 67 ; 0.042 and 0.003 are respectively the average Fe:C

and Mn:C quota of bulk phytoplankton in nmol/µmol in the North Atlantic (Table 5 in Twining et al., 2015 [START_REF] Twining | Metal Contents of Phytoplankton and Labile Particulate Material in the North Atlantic Ocean[END_REF] ).

Analyses of pCa and pNa were made using an inductively coupled plasma atomic emission spectrometer (ICP-AES, ULTIMA 2, Horiba Jobin Yvon). As for pTEs, the accuracy and precision were assessed by analysing the CRM BCR-414 (Table 2). Recovery for pCa reached 80%, keeping in mind that only an indicative value for the CRM reference is available.

Replicate analyses were made for 6 samples and differences from the mean value averaged 1.3 and 1.2% for pCa and pNa, respectively. As a mineral forming the shells of coccolithophorids, pteropods or foraminifers, we estimate the calcium carbonate (CaCO3) concentrations by correcting for sea-salt and lithogenic Ca:

[Ca]CaCO3 (µg/L) = [pCa -(Ca:Na)SW × pNa -(Ca:Al)UCC × pAl] × 100.1 (5)
where pCa, pNa and pAl are respectively the total particulate calcium, sodium, and aluminium concentrations in µmol/L; (Ca:Na)SW is equal to 0.022 mol/mol and represents the mean seawater ratio 72 ; (Ca:Al)UCC is equal to 0.251 mol/mol and represents the mean UCC ratio [START_REF] Taylor | The Continental Crust: Its Composition and Evolution[END_REF] ;

100.1 is the molar mass of CaCO3 in g/mol.

Biogenic silica and opal

Following the method of Ragueneau et al. (2005), BSi concentrations were estimated using an alkaline digestion with correction of the lithogenic silica (LSi) [START_REF] Ragueneau | A New Method for the Measurement of Biogenic Silica in Suspended Matter of Coastal Waters: Using Si:Al Ratios to Correct for the Mineral Interference[END_REF] . A 25mm diameter Nuclepore filter (carrying the LSF) previously counted for Beta activity was inserted in a polymethylpentene centrifuge tube and digested with a 0.2 M NaOH solution (Merck) at 95°C for 1h. After cooling, the pH was neutralized by adding 1 M HCl (Analar Normapur, Merck)

and the supernatant was separated from the remaining suspended material by centrifugation.

Silicic acid concentrations were determined following an automated acid/molybdate colorimetric method [START_REF] Aminot | Dosage Automatique Des Nutriments Dans Les Eaux Marines: Méthodes En Flux Continu[END_REF] , using an AutoAnalyzer3 Bran&Luebbe®. Dissolved aluminium released during the digestion process was determined by fluorimetric analysis of an Aluminum-Lumogallion complex (fluorimeter MITHRAS LB 940) [START_REF] Hydes | Fluorimetric Method for the Determination of Low Concentrations of Dissolved Aluminium in Natural Waters[END_REF] . At the end of the digestion, all the BSi is converted into silicic acid, but some lithogenic Si may have dissolved as well, inducing a bias in the BSi concentration. This bias was resolved by applying a second digestion, similar to the first one, allowing the determination of a Si:Al ratio exclusively related to the lithogenic material present in the samples. As a mineral forming the shells of diatoms, sponges or radiolarians, we estimate the mass of opal assuming a hydrated form of silica: SiO2.(0.4 H2O) [START_REF] Mortlock | A Simple Method for the Rapid Determination of Biogenic Opal in Pelagic Marine Sediments[END_REF] , or 67.2 g opal/mol BSi:

Opal (µg/L) = ([Si1] -[Al1] × (Si:Al)2)× 67.2 (6)
where [Si1] and [Al1] are the concentrations of silicic acid and aluminium determined during the first digestion in µmol/L; (Si:Al)2 is the ratio of the concentrations of silicic acid and aluminium determined during the second digestion; and 67.2 is the molar mass of opal in g/mol.

Component: 234 Th ratios and export fluxes

Trace element and mineral (lithogenics, Fe-and Mn-oxides, CaCO3, opal) export fluxes were determined using the 234 Th-based approach by multiplying the TE: 234 Th or mineral: 234 Th ratio of sinking particles with the total 234 Th export flux [START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] , both determined at the same depth:

Component export flux = (component: 234 Th)particulate × 234 Th flux (7) with component being either a TE or a mineral phase.

As we do not have p 234 Th activities available for the SSF, we only consider the component: 234 Th ratios from the LSF in this study. Large particles (>53µm) are generally assumed to represent the sinking particulate matter and are thus responsible for the particulate export flux [START_REF] Bishop | The Chemistry, Biology and Vertical Flux of Particulate Matter from the Upper 400m of the Equatorial Atlantic Ocean[END_REF][START_REF] Michaels | Primary Production, Sinking Fluxes and the Microbial Food Web[END_REF][START_REF] Villa-Alfageme | Seasonal and Depth Variation in Sinking Particle Speeds in the North Atlantic[END_REF] . Using the component: 234 Th ratios from the LSF to calculate export fluxes is the most common approach [START_REF] Black | Insights from the 238U-234Th Method into the Coupling of Biological Export and the Cycling of Cadmium, Cobalt, and Manganese in the Southeast Pacific Ocean. Global Biogeochem[END_REF][START_REF] Le Moigne | Export of Organic Carbon and Biominerals Derived from 234Th and 210Po at the Porcupine Abyssal Plain[END_REF][START_REF] Planchon | Carbon Export in the Naturally Iron-Fertilized Kerguelen Area of the Southern Ocean Based on the 234 Th Approach[END_REF][START_REF] Puigcorbé | Latitudinal Distributions of Particulate Carbon Export across the North Western Atlantic Ocean[END_REF][START_REF] Black | 234Th as a Tracer of Particulate Export and Remineralization in the Southeastern Tropical Pacific[END_REF] . However, recent studies have shown that the SSF could also contribute to the export flux of particulate carbon or nitrogen in oligotrophic regions [START_REF] Puigcorbé | Small Phytoplankton Drive High Summertime Carbon and Nutrient Export in the Gulf of California and Eastern Tropical North Pacific[END_REF][START_REF] Giering | High Export via Small Particles before the Onset of the Nort Atlantic Spring Bloom[END_REF][START_REF] Durkin | Observations of Carbon Export by Small Sinking Particles in the Upper Mesopelagic[END_REF] .

Black et al. (2019) reported no significant differences in SSF and LSF pP: 234 Th, pCo: 234 Th and pCd: 234 Th ratios contrasting with the higher pMn: 234 Th ratios in the LSF compared to the SSF, leading to a greater contribution of the LSF to the total pMn flux [START_REF] Black | Insights from the 238U-234Th Method into the Coupling of Biological Export and the Cycling of Cadmium, Cobalt, and Manganese in the Southeast Pacific Ocean. Global Biogeochem[END_REF] .

Vertical export fluxes were determined at the depth where total 234 Th is back to secular equilibrium with 238 U (equilibrium depth or Eq hereafter; Table 3). The 234 Th export at Eq represents the fully-integrated depletion of total 234 Th in the upper waters [START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] . To collect particles, three to four depths were sampled per ISP in the upper 150m while in that same depth range, Niskin casts sampled nine depths. Because of this difference of depth resolution we use an interpolation method to estimate the component: 234 Th ratios for the layer between surface and Eq. The depth-weighted average (DWA) was chosen as this method yields similar TE: 234 Th or mineral: 234 Th ratios than those obtained from sediment traps [START_REF] Lemaitre | Impact of the Natural Fe-Fertilization on the Magnitude, Stoichiometry and Efficiency of Particulate Biogenic Silica, Nitrogen and Iron Export Fluxes[END_REF] (DWA;

element: 234 Th=[Ʃ(element i × Z i ) / Ʃ(Z i )] / [Ʃ( 234 Th i × Z i ) / Ʃ(Z i )]
where Z i are the depth intervals sampled above Eq). Uncertainties of ratios and fluxes were obtained using error propagation law.

Residence times

We also investigated the total residence time (τ) of TEs, which was obtained by dividing the TE inventory within a specific reservoir by the TE flux into or out of this reservoir, thereby assuming steady state with removal rates equalling supply rates (Equation 8). We focused on total (dissolved+particulate) residence time (τtotal) within the surface-Eq layer depth (Table 5)

and we considered the particulate export flux as the main output flux of TE from the upper ocean. Advective and diffusive circulation fluxes are generally slow processes compared to the vertical export processes and were neglected here [START_REF] Hayes | Replacement Times of a Spectrum of Elements in the North Atlantic Based on Thorium Supply[END_REF][START_REF] Black | Ironing out Fe Residence Time in the Dynamic Upper Ocean[END_REF] . However these processes have been shown to have impact, though limited, on measured 234 Th export fluxes along the GEOVIDE transect [START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] , and therefore τtotal of TE might represent a higher end estimation in the present study.

τ =

𝑡𝑜𝑡𝑎𝑙 𝑇𝐸 𝑖𝑛𝑣𝑒𝑛𝑡𝑜𝑟𝑦 𝑝𝑎𝑟𝑡𝑖𝑐𝑢𝑙𝑎𝑡𝑒 𝑇𝐸 𝑒𝑥𝑝𝑜𝑟𝑡 𝑓𝑙𝑢𝑥 (8) with the particulate TE export flux in µg/m 2 /d at Eq (from this study), and the total TE inventory in µg/m 2 obtained by summing the particulate (>0.45 µm) and dissolved (<0.45 µm) TE phases, both being collected using GO-FLO bottles (Planquette et al., personal communication, 2019 and [START_REF] Gourain | Inputs and Processes Affecting the Distribution of Particulate Iron in the North Atlantic along the GEOVIDE (GEOTRACES GA01) Section[END_REF][START_REF] Menzel Barraqueta | Aluminium in the North Atlantic Ocean and the Labrador Sea (GEOTRACES GA01 Section): Roles of Continental Inputs and Biogenic Particle Removal[END_REF][START_REF] Tonnard | Dissolved Iron in the North Atlantic Ocean and Labrador Sea along the GEOVIDE Section (GEOTRACES Section GA01)[END_REF] ). Inventories were calculated using a depth-weighted integration in the surface-Eq layer. Uncertainties in Table 5 represent the highest deviation between the residence time obtained at Eq and those obtained at Eq+20m or Eq-20m (20m being the average error on the determination of the Eq depth).

RESULTS

Activities of p 234

Th and concentrations of TEs, lithogenic, authigenic and biogenic phases in the large size fraction (>53µm)

Distributions of p 234 Th vary along the transect (Fig. S3, Table S1) with the lowest activities being determined in the Iberian basin (as low as 0.006 dpm/L in subsurface of Station #1) and the highest in surface waters of the Irminger basin (up to 0.2 dpm/L in surface of Station #51).

In general, activities are high in surface and decrease with depth but some subsurface maxima also occur, such as at 100m of Station #64 where activities reach 0.16 dpm/L.

As shown in Figure S3 and Table S1, >53µm concentrations vary between elements, with values ranging from 10 -6 to 10 1 nmol/L in the suite of Cd, Co < Cu, Mn, Ni, Ti, Zn < Fe < Al, P. Similarly to p 234 Th activities, concentrations and distributions also vary significantly for each pTE along the transect, like those of the lithogenic, authigenic and biogenic phases.

Concentrations of pAl or lithogenic material, like that of pFe and pTi, which are known to be associated with lithogenic material, generally increase with depth and are highest at proximity Overall, our >53µm pTE concentrations are comparable with those of the world ocean literature [START_REF] Lemaitre | Impact of the Natural Fe-Fertilization on the Magnitude, Stoichiometry and Efficiency of Particulate Biogenic Silica, Nitrogen and Iron Export Fluxes[END_REF][START_REF] Black | Insights from the 238U-234Th Method into the Coupling of Biological Export and the Cycling of Cadmium, Cobalt, and Manganese in the Southeast Pacific Ocean. Global Biogeochem[END_REF][START_REF] Planquette | Origin of Iron and Aluminium in Large Particles (> 53 Μm) in the Crozet Region, Southern Ocean[END_REF] . If we compare more closely to data from the GA03 cruise, which also took place in the North Atlantic (GEOTRACES IDP2017 [START_REF] Schlitzer | The GEOTRACES Intermediate Data Product 2017[END_REF] ), our concentrations of pP are slightly higher, reaching 24 nmol/L during GEOVIDE (4.7 nmol/L during GA03), likely because of the higher productivity observed in the subpolar compared to the subtropical North Atlantic. On the other hand, both cruises have similar order of magnitudes in the whole water column for pCd (up to 7.1 and 1.5 pmol/L for GEOVIDE and GA03, respectively), pCo (up to 1.5 and 8.3 pmol/L for GEOVIDE and GA03, respectively), pCu (up to 36 and 28 pmol/L for GEOVIDE and GA03, respectively), pNi (up to 70 and 158 pmol/L for GEOVIDE and GA03, respectively) pV (up to 92 and 87 pmol/L for GEOVIDE and GA03, respectively) and pZn (up to 0.9 and 0.3 nmol/L for GEOVIDE and GA03, respectively). However, concentrations during GEOVIDE of pAl (0.1-15 nmol/L), pFe (0.02-3.2 nmol/L) and pTi (0.004-0.2 nmol/L) are lower than those observed during GA03 (0.1-98, 0.04-25 and 0.004-3.6 nmol/L, respectively [START_REF] Ohnemus | Cycling of Lithogenic Marine Particulates in the US GEOTRACES North Atlantic Transect[END_REF] ). This might be due to the fact that both cruises took place at different latitudes, with the GA03 transect located in the dust rich region of the Atlantic.

Residence times

Along the GEOVIDE transect, TE inventories and exports, and consequently residence times, vary considerably (Table 5). Trace element residence times in the surface-Eq depth layer range from 2 to 13297 days: Al (4±0.2 -106±3 days), Fe (2±0.1 -147±5 days) < Mn (89±25 -626±80days), Zn (4±0.4 -582±18 days) < Co (64±3 -3427±209 days), Cu (236±11 -3646±698 days) < Ni (339±15 -13297±407 days).

High particulate and dissolved inventories, high export fluxes and short τtotal are observed at Station #1, close to the Iberian margin, for all TEs. There, we observe the shortest residence times for Al (τtotal=4 days), Co (τtotal=64 days), Cu (τtotal=236 days) and Fe (τtotal=2 days).

However, τtotal values for Mn, Zn and Ni at Station #1 are not the shortest ones along the transect.

The Icelandic and western European basins are also characterized by short element residence times. For example, the residence time for Fe is only

DISCUSSION

Since particulate 234 Th was not analysed on filters dedicated to trace metal analyses in the SSF, element: 234 Th ratios could only be determined for the LSF, which is assumed to be representative of sinking particles 89 . To our knowledge, this assumption has been used in all studies dedicated to TE export fluxes and using ISP [START_REF] Lemaitre | Impact of the Natural Fe-Fertilization on the Magnitude, Stoichiometry and Efficiency of Particulate Biogenic Silica, Nitrogen and Iron Export Fluxes[END_REF][START_REF] Planquette | Fluxes of Particulate Iron from the Upper Ocean around the Crozet Islands: A Naturally Iron-Fertilized Environment in the Southern Ocean[END_REF][START_REF] Weinstein | Vertical Flux of Particulate Al, Fe, Pb, and Ba from the Upper Ocean Estimated from 234Th/238U Disequilibria[END_REF][START_REF] Black | Ironing out Fe Residence Time in the Dynamic Upper Ocean[END_REF][START_REF] Black | Insights from the 238U-234Th Method into the Coupling of Biological Export and the Cycling of Cadmium, Cobalt, and Manganese in the Southeast Pacific Ocean. Global Biogeochem[END_REF] . We are aware though, that small particles may contribute to the TE export.

Statistical analyses

In order to gain more insight about the vector phases carrying each elemental flux, we examined the Spearman rank correlation coefficients between TE and mineral exports (XLStat software; Table 4). The analysis was conducted on log-transformed export fluxes to ensure that input variables are more normally distributed and to reduce the influence of extreme values. The influence of lithogenic materials on the pTE export fluxes is highlighted by the significant correlations, especially for pCu, pFe and pZn (p-value < 0.05 and R ≥ 0.9; Table 4). At a lesser extent but still significantly, pCd, pCo, pNi and pTi export fluxes are also correlated to lithogenic fluxes (p-value < 0.05 and R ≥ 0.6; Table 4). Biogenic (opal and CaCO3) and oxide (Fe(OH)3 and MnO2) phases do not show any significant correlations with the pTEs, likely due to the significance of lithogenic particles in controlling TE fluxes in the North Atlantic (Table 4). In order to disentangle the roles of the biogenic and oxide phases on pTE fluxes, we used a principal component analysis (PCA; XLStat software) considering excess pTE exports (ie. pTE export fluxes corrected from the lithogenic fraction; Fig. 3). Recent studies have applied a PCA approach for large datasets of element concentrations, including small and large particle size fractions [START_REF] Ohnemus | Exposing the Distributions and Elemental Associations of Scavenged Particulate Phases in the Ocean Using Basin-Scale Multi-Element Data Sets[END_REF][START_REF] Ohnemus | Cycling of Lithogenic Marine Particulates in the US GEOTRACES North Atlantic Transect[END_REF][START_REF] Gourain | Inputs and Processes Affecting the Distribution of Particulate Iron in the North Atlantic along the GEOVIDE (GEOTRACES GA01) Section[END_REF][START_REF] Shelley | Quantification of Trace Element Atmospheric Deposition Fluxes to the Atlantic Ocean (>40°N; GEOVIDE, GEOTRACES GA01) during Spring 2014[END_REF] , but we only consider here export fluxes at the Eq depth based on the large [START_REF] Ohnemus | Exposing the Distributions and Elemental Associations of Scavenged Particulate Phases in the Ocean Using Basin-Scale Multi-Element Data Sets[END_REF][START_REF] Leinen | An Objective Technique for Determining End-Member Compositions and for Partitioning Sediments According to Their Sources[END_REF] . This analysis is also conducted on log-transformed export fluxes to limit the influence of extreme values and to ensure a more normal distribution of the variables [START_REF] Ohnemus | Exposing the Distributions and Elemental Associations of Scavenged Particulate Phases in the Ocean Using Basin-Scale Multi-Element Data Sets[END_REF][START_REF] Templ | Cluster Analysis Applied to Regional Geochemical Data: Problems and Possibilities[END_REF] . We identified four principal components that together explain 95% of the total dataset variance (Fig. 3).

The first principal component (33 % of the total variance) likely describes the biological influence as it explains 84 and 81% of the excess pCd and pP flux variances, respectively. This component also explains 55% of the excess pCu flux and between 9 and 17% of the excess pCo, pNi and pZn fluxes. In Table 4, pP appears to be correlated with most pTEs (p-value < 0.05 and R > 0.65 for pCd, pCo, pCu and pMn fluxes and R > 0.45 for pAl, pNi and pZn). To investigate the biological influence on pTE fluxes, we also examined their correlations with POC, CaCO3 and opal. No significant correlation was observed.

The second component (30% of the total variance) explains 74% of both excess pCo and pZn fluxes variances and also explains, at a lesser extent, the export fluxes of other pTEs (12-41% of excess pCd, pCu, pNi variances and 6% of excess pP variance). Interestingly, Ohnemus et al. ( 2019) also found a factor strongly driven by pCo abundances, with additional -smaller -contributions for other pTEs. They related this factor to a secondary (heterotrophic) biomass phase [START_REF] Ohnemus | Exposing the Distributions and Elemental Associations of Scavenged Particulate Phases in the Ocean Using Basin-Scale Multi-Element Data Sets[END_REF] .

The third principal component (19% of the total variance) is strongly indicative of authigenic

Fe oxides, as it explains 89% of the variability of excess pFe fluxes. In addition, this third component also explains 21% of the variance of excess pNi flux and between 4 and 9% of the variances of excess pCo, pCu, pMn, pP and pZn fluxes, reflecting the scavenging of these TEs onto this authigenic phase [START_REF] Takematsu | Sorption of Transition Metals on Manganese and Iron Oxides, and Solicate Minerals[END_REF] . Furthermore, the correlation analysis highlights links between authigenic Fe oxide and Mn oxide fluxes (R=0.77), CaCO3 fluxes (R=0.63) and pTEs, especially pNi, pCu and pZn fluxes (R = 0.30 -0.46; Table 4).

Finally, the fourth component (14% of the total variance) probably describes the influence of authigenic Mn oxides as it explains 90% of the variance of excess pMn fluxes. It is associated at 6-8% with excess pFe and pNi fluxes, and at 1-3% with pCd, pCo, pCu and pP fluxes.

Lithogenic contribution to fluxes

Lithogenic particles play a central role in the North Atlantic (Table 4). They can originate from different sources such as atmospheric deposition, glacial meltwater, advection of sedimentenriched water masses or lateral mixing with shallow coastal waters under continental influence. The importance of lithogenic sources is particularly clear for Station #1, suggesting an input from the Iberian margin (Fig. 2) in agreement with the literature [START_REF] Ohnemus | Cycling of Lithogenic Marine Particulates in the US GEOTRACES North Atlantic Transect[END_REF][START_REF] Lam | Size-Fractionated Major Particle Composition and Concentrations from the US GEOTRACES North Atlantic Zonal Transect[END_REF] . There, we determined the highest fluxes for lithogenic material and some pTEs, which were accompanied by pTE:pAl ratios close to UCC 67 (Fig. 4; Fig. S5). This is especially the case for pFe and pMn for which the respective ratios show only 2 and 20% offset relative to UCC ratios (Fig. 4). For other pTEs, these ratios are slightly greater than for UCC, pointing to the presence of another driver of export fluxes. Such TE enrichments relative to the UCC have also been reported in the estuary of the Tagus river [START_REF] Duarte | Particulate Metal Distribution in Tagus Estuary (Portugal) during a Flood Episode[END_REF] for which the plume has been shown to reach Station #1 [START_REF] Menzel Barraqueta | Aluminium in the North Atlantic Ocean and the Labrador Sea (GEOTRACES GA01 Section): Roles of Continental Inputs and Biogenic Particle Removal[END_REF][START_REF] Tonnard | Dissolved Iron in the North Atlantic Ocean and Labrador Sea along the GEOVIDE Section (GEOTRACES Section GA01)[END_REF] .

This river is known to receive effluents from agricultural, industrial and urban sources and thus represents an important discharge of dissolved and particulate TE concentrations to the estuary [START_REF] Cotté-Krief | Sources of Cd, Cu, Ni and Zn in Portuguese Coastal Waters[END_REF][START_REF] Duarte | Heavy Metal Distribution and Partitioning in the Vicinity of the Discharge Areas of Lisbon Drainage Basins (Tagus Estuary , Portugal)[END_REF][START_REF] Caçador | Accumulation of Zn, Pb, Cu, Cr and Ni in Sediments between Roots of the Tagus Estuary Salt Marshes, Portugal[END_REF][START_REF] Gall | Processes Influencing Distributions and Concentrations of Cd, Cu, Mn and Ni at the North West European Shelf Break[END_REF] . The slightly higher pTE:pAl ratios compared to UCC may indicate that fluxes at Station #1 are under anthropogenic influence via the discharge from the Tagus estuary.

Stations at proximity of the Greenland and Newfoundland margins are also characterized by some higher pTE:pAl ratios (i.e., pCd:pAl or pCu:pAl; Fig. 4), implying additional processes in the export of these pTEs. Although lithogenic particles settle quickly through the water column, they can also adsorb elements onto their surfaces [START_REF] Ohnemus | Cycling of Lithogenic Marine Particulates in the US GEOTRACES North Atlantic Transect[END_REF][START_REF] Ye | On the Role of Dust-Deposited Lithogenic Particles for Iron Cycling in the Tropical and Subtropical Atlantic[END_REF]100 . Such scavenging processes could explain the higher pTE:pAl ratios. Interestingly, the Greenland and Newfoundland margin stations are characterized by much lower lithogenic and pTE flux intensities compared to the Iberian margin (Fig. 2), suggesting that lithogenic material is not similarly released at all margins. Such differences can depend on the morphology of the margin and on the hydrodynamical forcing, providing (or not) significant amounts of lithogenic particles and fluxes. Indeed, Figure 3 shows that Mn oxides could be responsible for 3-8% of the excess export fluxes of pCu, pFe and pNi.

Similarly, Fe-oxide fluxes are high at Stations #32, #38 and #64. As seen in Figures 2 and3, Fe-oxides could represent an important carrier phase for pCo, pCu, pMn, pNi and pZn (from 4 to 21% of the variance explained in the PCA on excess -i.e., non-lithogenic -fluxes, as already discussed in other studies [START_REF] Saito | The Acceleration of Dissolved Cobalt's Ecological Stoichiometry Due to Biological Uptake, Remineralization, and Scavenging in the Atlantic Ocean[END_REF]107,[START_REF] Ohnemus | Exposing the Distributions and Elemental Associations of Scavenged Particulate Phases in the Ocean Using Basin-Scale Multi-Element Data Sets[END_REF] .

Biogenic contribution to fluxes

In addition to Figure 3 and Table 4, the comparison of pTE:POC ratios at each station with those of phytoplankton cells suggests that biogenic particles partly influence pTE exports (Fig. 5). Despite large uncertainties associated with this approach, some pTE:POC ratios are comparable to ratios reported for functional phytoplankton groups (diatoms, autotrophic flagellates and autotrophic picoplankton) collected in the upper 150m of the North Atlantic 71 (Fig. 5; Fig. S5). This suggests that pTE exports, and especially those of pCd, pCo, pCu, pMn, and pZn, can also be driven by biogenic particles. However, higher pTE:POC ratios than cell ratios are also observed. Trace elements are known to be scavenged onto particles with depth [START_REF] Goldberg | Chemical Scavengers of the Sea[END_REF]108 (see previous sections) and it is usual to observe an increase of the bulk ratios compared to cellular ratios [START_REF] Twining | Differential Remineralization of Major and Trace Elements in Sinking Diatoms[END_REF]109,110 . This can be caused by the presence of detrital, authigenic and lithogenic particles on the filters leading to an increase of the pTE:POC, as observed in Figure 5. Moreover, the intracellular TE:C considerably changes between taxa and regions depending on the environmental conditions (e.g. nutrients, sunlight limitations 3 ): Fe:C quota usually range between 10-1700 µg/g for diatoms and coccolithophorids in natural and culture experiments [START_REF] Twining | The Trace Metal Composition of Marine Phytoplankton[END_REF]111,112 but Sunda and Huntsman (1995) have measured a Fe:C ratio equalling 8230 µg/g 113 , highlighting the high variability of the ratio and the difficulty to generalize the intracellular phytoplankton TE:C ratios. Therefore, we searched for indicators of the phytoplankton community structure, such as CaCO3, opal and pigment analyses using CHEMTAX [START_REF] Tonnard | Cycle Biogéochimique Du Fer : Distribution et Spéciation Dans l'océan Atlantique Nord (GA01) et l'océan Austral (GIpr05)[END_REF] . The highest CaCO3 fluxes have been determined within the west European and Icelandic basins (Fig. 2) where coccolithophorids were present [START_REF] Tonnard | Cycle Biogéochimique Du Fer : Distribution et Spéciation Dans l'océan Atlantique Nord (GA01) et l'océan Austral (GIpr05)[END_REF] . The contribution of coccolithophorids to export pZn, pCu, pNi and pMn is indicated by relatively high correlation coefficients (0.3<R<0.5) between these pTEs and CaCO3 exports (Table 4). Opal fluxes are high at Stations #51, #64 and #69 (Irminger and Labrador basins; Fig. 2) where diatoms dominate the phytoplankton community [START_REF] Tonnard | Cycle Biogéochimique Du Fer : Distribution et Spéciation Dans l'océan Atlantique Nord (GA01) et l'océan Austral (GIpr05)[END_REF] . In the Labrador Sea, high POC and opal fluxes are associated with surprisingly low pTE export fluxes (Fig. 2). This basin was sampled during the decline of the bloom (Station #69: 7 weeks after the bloom peak) and was also characterized by an important remineralization event in the mesopelagic layer, evidenced from the excess barium (Baxs) proxy 114 . Both results suggest either a pTE accumulation in surface waters while POC would be preferentially exported, or a limitation of dissolved TEs that would impede a pTE export due to enhanced recycling in surface waters 115 .

Residence time of TEs and efficiency of export

Although only few TE residence times within the upper ocean are available in the literature, the τtotal values estimated from the present dataset are comparable with those of other studies.

In the surface global ocean, the majority of τtotal for Fe fall between 10 and 100 days [START_REF] Black | Ironing out Fe Residence Time in the Dynamic Upper Ocean[END_REF] 5). The good consistency between these different studies allows us to rank the turnover rate of TEs in the upper ocean as follows:

Fe < Zn < Mn < Co < Cu.

In the following, our attention is mainly devoted to Fe (Fig. 6). The shortest τtotal (2 days) is observed close to the Iberian margin, indicating an efficient Fe export. Similar short τtotal within the upper ocean (<5 days) have been observed in coastal areas where lithogenic particles probably play an important role in transporting TEs out of the upper ocean [START_REF] Planquette | Fluxes of Particulate Iron from the Upper Ocean around the Crozet Islands: A Naturally Iron-Fertilized Environment in the Southern Ocean[END_REF][START_REF] Black | Ironing out Fe Residence Time in the Dynamic Upper Ocean[END_REF][START_REF] Smith | Comparison of 234Th/238U and Mass Balance Models for Estimating Metal Removal Fluxes in the Gulf of Maine and Scotian Shelf[END_REF] . These lithogenic particles advected from margins may represent a continuous Fe input in surface waters explaining the high inventories and export observed during GEOVIDE at Station #1, even in post-bloom conditions. For example, they contribute for 98% of the total Fe export at Station #1 (Fig. 6). As it consists of dense particles, the sinking rate of lithogenic material is known to be high. Here the particle sinking rate is estimated by dividing the particulate residence time by the surface-Eq depth layer. At Station 1, the sinking rate reaches 63 m/d for pFe, which is in the same order of magnitude as estimated using Stokes law (88 m/d for a particle of 53µm diameter and of density of 1860 kg/m 3 , representing an average density for a mixed aggregate composed of lithogenic, transparent exopolymer particles (TEP), detritus, opal and CaCO3; 116 ). Similarly, high particulate and dissolved inventories, high export fluxes and short τtotal are observed at Station #1 for other TEs, suggesting a fast supply to and removal from the upper ocean by lithogenic particles (Table 5). However, τtotal values for Mn, Zn and Ni at Station #1 are not the shortest observed along the transect, indicating that lithogenic particles are not the only drivers of TE export, even at this coastal station.

The Icelandic and western European basins were sampled during the bloom development and were thus characterized by an important productivity event [START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF][START_REF] Fonseca-Batista | Evidence of High N2 Fixation Rates in the Temperate Northeast Atlantic[END_REF] . In these basins, we observe a (contributing to 62% of total Fe export in these basins; Fig. 6). These mineral phases are presumably denser than lithogenic particles (the density of ferrihydrite is about 3.8 g/cm [START_REF] Twining | The Trace Metal Composition of Marine Phytoplankton[END_REF] compared to a typical clay density of 2.7 g/cm 3 ) but the sinking speed is also controlled by the size of the particle, which might be an important factor in the west European and Icelandic basins. Other TEs also have short τtotal and high sinking rates in these basins, confirming the important contribution of oxides to export pTEs.

Finally, the Labrador and Irminger basins were sampled during the bloom decline and the average pFe export flux is the lowest of the whole transect (182 µg/m 2 /d compared to 441 and 3912 µg/m 2 /d for respectively the west European/Icelandic basins and Iberian margin). Longer residence times are also determined within the Labrador and Irminger basins, suggesting that most of pFe is not exported as efficiently as in the eastern basins. This may be due to the more important fraction of Fe carried by biogenic matter (12% compared to 1 and 3% in the Iberian and west European/Icelandic basins, respectively), leading to a slower export of Fe and/or active recycling processes. The median sinking rate of 3 m/d (Table 5) is similar to the rate estimated by using Stokes law (3.5 m/d) for an organic particle of 53µm diameter and a density of 1060 kg/m 3 . Indeed, Fe removal rate from the upper ocean via biological processes has been shown to be much smaller than via lithogenic and authigenic processes [START_REF] Black | Ironing out Fe Residence Time in the Dynamic Upper Ocean[END_REF] . A greater τtotal is also ) UCC ]; with the UCC ratio from [START_REF] Taylor | The Continental Crust: Its Composition and Evolution[END_REF] ).

FIGURE 4

Figure 4: Ratios of the pTEs over pAl fluxes (in g/g, on y-axis) determined at Eq along the GEOVIDE transect (station numbers on x-axis). The brown horizontal dashed lines represent the ratios for the upper continental crust (UCC) [START_REF] Taylor | The Continental Crust: Its Composition and Evolution[END_REF] .

FIGURE 5

Figure 5: Ratios of the pTEs over particulate organic carbon (POC) fluxes (in µg/g, on y-axis) determined at Eq along the GEOVIDE transect (station numbers on x-axis). The green horizontal dashed lines indicate the average intracellular metal stoichiometries [START_REF] Twining | Metal Contents of Phytoplankton and Labile Particulate Material in the North Atlantic Ocean[END_REF] .

Icelandic

Irminger particulate flux and its standard deviation (sd) obtained by calculating τtot at Eq, Eq+20m or Eq-20m (20m being the average error on the determination of the Eq depth).

  authigenic minerals are obtained after correction of the contribution of lithogenic and biogenic fractions, and therefore show low concentrations along the section, with exceptions at the depths cited just above. At 60m at Station #64, Fe(OH)3 and MnO2 concentrations reach 0.16 and 0.003 µg/L respectively, but are also relatively high at 100m, coinciding with elevated lithogenic contents (0.05 and 0.002 µg/L respectively). High Fe(OH)3 concentrations are also observed in the upper 200m of the Icelandic basin (from 0.01 to 0.03 µg/L at Stations #32 and #38) while high MnO2 concentrations are seen below 100m of Station #26 (up to 0.002 µg/L).

3. 3 .

 3 Export fluxesExport fluxes at Eq (between40 and 110m) significantly vary between elements and between basins (Table3, Fig.2). The most striking results are the maximal flux of pAl or lithogenic material (9207 µg/m 2 /d and 115 mg/m 2 /d, respectively) and of some pTEs in vicinity of the Iberian margin (Station #1), with extreme values for pCo, pFe, pMn, pP and pTi (3.6, 3912, 55, 8141 and 340 µg/m 2 /d, respectively). Such high fluxes evidence particulate inputs from the Iberian margin, leading to the export of pTE out of the surface layer.The highest CaCO3 export fluxes occur within the west European and Icelandic basins, where blooms of coccolithophorids were observed during GEOVIDE[START_REF] Tonnard | Cycle Biogéochimique Du Fer : Distribution et Spéciation Dans l'océan Atlantique Nord (GA01) et l'océan Austral (GIpr05)[END_REF] . There, we also observe high fluxes of pCd, pCu, pNi or pP, which at Station #21 reach values of 11, 18, 84 and 4648 µg/m 2 /d, respectively. Opal fluxes are the highest in the Irminger and Labrador basins, where diatom blooms were declining during GEOVIDE 60 (568 mg/m 2 /d at Station #64). Surprisingly, the settling of diatoms in these basins is characterized by low pTE export fluxes. High Fe(OH)3 export flux is observed in the Icelandic basin (Station 32) and in the western Labrador basin (Station #64). At Station #32, the high Fe(OH)3 flux (1.3 mg/m 2 /d) goes with high fluxes of pAl, pCd, pCo, pCu, pFe, pMn, pNi, pP, pV and pZn (469, 5.1, 2.7, 10, 931, 13, 33, 4145, 1.7 and 396 µg/m 2 /d, respectively). Export fluxes of MnO2 are small compared to other mineral fluxes (0.007 mg/m 2 /d compared to 0.36 mg/m 2 /d for Fe(OH)3 on average). In general, high fluxes of MnO2 and Fe(OH)3 coincide but MnO2 fluxes are particularly high in the west European (Station #26) and Irminger (Station #44) basins where we can observe a slight increase of pCo, pMn and pV fluxes (reaching 0.4, 9.3 and 0.4 µg/m 2 /d, respectively, at Station #26). Particulate TE export fluxes determined using the 234 Th approach are still scarce in the literature. Comparing different biogeochemical areas is difficult because of differences in sampling periods (and different productivities), export depths (surface versus deep or Eq depth versus fixed depth) or locations (shelf versus open-ocean). However, the overall ranges of pTE export fluxes between GEOVIDE and the literature are comparable. The pFe export flux at proximity of the Iberian margin (3912 µg/m 2 /d) is by far the highest observed along the GEOVIDE transect but is still lower than fluxes determined on the Scotian shelf (7874 µg/m 2 /d 88 ), or close to the Crozet island (8098 µg/m 2 /d 32 ), where lithogenic inputs are even higher. Conversely, the lower pAl export fluxes in the Labrador Sea (67-281 µg/m 2 /d at GEOVIDE Stations #64, #69 and #77 and 432-594 µg/m 2 /d in 2005 34 ) indicate lower lithogenic inputs, which seem to drive lower pFe export fluxes (41-501 µg/m 2 /d at GEOVIDE Stations #64, #69 and #77 and 480-614 µg/m 2 /d in 2005 34 ). Even though GEOVIDE took place during the spring bloom, export of pP (266-8141 µg/m 2 /d) is lower than observed along the GP16 transect, from the Peruvian shelf to the subtropical Pacific gyre (254-27876 µg/m 2 /d 36 ) likely due to high productivities and high biogenic exports induced by the coastal upwelling there. Similarly, particulate organic carbon (POC) export reaches 960 mg/m 2 /d during GP16 compared to 139 mg/m 2 /d during GEOVIDE 83 . For that same Pacific ocean area, Black et al. (2019) 36 reports similar pCo fluxes (0.1-4 µg/m 2 /d) but much higher pCd (0.2-112 µg/m 2 /d) and pMn export fluxes (6-549 µg/m 2 /d) compared to fluxes in the North Atlantic reaching up to 4 µg pCo/m 2 /d, 11 µg pCd/m 2 /d, 55 µg pMn/m 2 /d for the present GEOVIDE section and 3 µg pCd/m 2 /d for the Scotian shelf area 88 . Finally, Smith et al. (2014) 88 reports similar pCu export fluxes for the Scotian shelf (1-22 µg/m 2 /d) compared to those observed for the GEOVIDE transect (1-16 µg/m 2 /d).

4 . 3 .

 43 leading (or not) to the formation of nepheloid layers101 . Indeed, relatively high lithogenic export fluxes are also observed at open-ocean stations beyond the Iberian margin (up to Station#32). The Iberian margin is known to be an efficient exporter of particulate matter to the open and deep sea 102,103 and during GEOVIDE, high proportions of lithogenic particulate rare earth elements 101 and pFe[START_REF] Gourain | Inputs and Processes Affecting the Distribution of Particulate Iron in the North Atlantic along the GEOVIDE (GEOTRACES GA01) Section[END_REF] were observed up to 1700 km far from the Iberian margin. These enrichments were attributed to the presence of intermediate nepheloid layers transported along the isopycnals, which then likely drive pTEs fluxes to the deep ocean. To a lesser extent, lithogenic particles were also transported to the west of the Greenland margin[START_REF] Gourain | Inputs and Processes Affecting the Distribution of Particulate Iron in the North Atlantic along the GEOVIDE (GEOTRACES GA01) Section[END_REF] , in line with the moderate lithogenic export fluxes observed at Station #64, in the eastern Labrador basin.Conversely, lithogenic particles do not seem to spread off the Newfoundland margin, thereby explaining the lower lithogenic export fluxes at Station #77. Authigenic contribution to fluxes High fluxes of Mn-and Fe-oxides were determined at some stations close to margins, also under lithogenic influence (i.e. Station #64), and at open-ocean stations, which are not necessarily characterized by high particulate lithogenic exports. For example, Station #26 presents one of the lowest lithogenic and Fe(OH)3 fluxes, while MnO2 fluxes are among the highest at this station. This decoupling between high pMn and low pAl fluxes has already been observed and was attributed to a distant shelf source of lithogenic particles[START_REF] Lamborg | Sinking Fluxes of Minor and Trace Elements in the North Pacific Ocean Measured during the VERTIGO Program[END_REF] . Indeed, nepheloid layers sourced at the shelves lose particles by gravitational settling during lateral advection, but in the case of Mn, it has been shown that dissolved Mn, remobilized from the shelf, oxidizes very slowly, enriching the particulate phase during transport 104 . Long distance transport inducing a subsurface pMn maximum was observed off the Kuril/Kamchatka margin, in the western subarctic Pacific[START_REF] Lam | The Continental Margin Is a Key Source of Iron to the HNLC North Pacific Ocean[END_REF] . High pMn concentrations and fluxes at Station #26 could thus have originated from authigenically precipitated Mn during its transport from the American coasts, via the North Atlantic Current (NAC, Fig.1). The distance between Station #26 and North Carolina coasts (USA) is around 4500km, which roughly corresponds to the distance of 4220km calculated by multiplying a NAC velocity of 0.4 m/s 105 by the inverse of the oxidation rate constant of Mn (kox=0.341×10 -3 h -1 106 ). Interestingly, the high Mn-oxide fluxes determined at Stations #26, #32, #44 and #64 and to a lesser extent at Stations #13 and #38 drive other pTE

, which corresponds to the 2 - 60 days 25 .

 26025 147 days range estimated in this study. Hayes et al. (2018) examined the dissolved TE residence times in the upper 1000m of the North Atlantic (note the wider depth layer) and found that Fe had the shortest residence time relative to other TEs, of about 30-The authors estimated dissolved residence times of less than 6 years for Zn, Co and Mn (0.01 to 6 years in our study, except at Station #64 where τtotal for Co reaches 14 years) and of 80-90 years for Cu (0.65-15 years in this study; Table

τtotal averaging 3

 3 days for Fe, suggesting an efficient transport to the deep ocean. As seen previously, Stations #21, #32 and #38 are characterized by high export fluxes of Fe-and Mnoxides, carrying other TEs to the deep ocean. At these stations, pFe sinks faster compared to the Iberian margin (up to 135 m/d at Station #32), likely because of the presence of Fe-oxides

  estimated for other TEs. The slower removal of biogenic TEs can also be reflected by the longer residence times of less detrital TEs, such as Ni, Co or Cu (from 65 days to >35 years) compared to more detrital TEs (Al, Fe with τtotal <150 days).CONCLUSIONUsing the 234 Th approach and the elemental composition of large, sinking particles, this study investigated the pTE export fluxes, sinking rates and residence times in the North Atlantic.Lithogenic material is present everywhere along the section, but mainly controls the fluxes near the Iberian margin, where the highest pTE fluxes are observed. As a result, TE residence time in the upper ocean is short in vicinity of the Iberian Margin. In the open ocean, and especially within the Icelandic basin, Mn-and Fe-oxides are likely the main TE carriers to the deep ocean.Zinc and Ni, for example, have shorter residence times there compared to the Iberian basin which is under lithogenic influence. Biogenic particles also contribute to export pTEs, as reflected by the similarity of pTE:POC export ratios and TE:C cell ratios. Particulate TE export fluxes especially those of pZn, pCu, pNi and pMn might be enhanced by sinking coccolithophorid cells within the west European and Icelandic basins, where CaCO3 exports are the highest. Diatoms are dominating the phytoplankton community within the Irminger and Labrador basins, in agreement with the highest opal fluxes. However there, pTE fluxes are low, possibly suggesting TE recycling due to dissolved TE limitations in surface waters, in line with the decline of the bloom. The inefficient pTE export in this area is also illustrated by the longer residence times, which may be due to greater biogenic contribution.

FIGURE 1 715Figure 1 :

 11 FIGURE 1

FIGURE 2 Figure 2 :

 22 FIGURE 2

FIGURE 3 Figure 3 :

 33 FIGURE 3

Figure 6 :

 6 Figure 6: Biogeochemical iron budget in the upper ocean for the Labrador and Irminger basins

  Irminger and Labrador basins or pCd, pCu, pFe pNi and pZn in the west European and Icelandic basins. These coincide with elevated concentrations of both opal and CaCO3 in the upper 100m, where they are produced: highest CaCO3 concentrations mainly occur within the west European

	and Icelandic basins (up to 14 µg/L) whereas highest opal concentrations occur within the west
	European, Irminger and Labrador basins (up to 95 µg/L). In general, both biogenic phases
	display nutrient-like profiles with highest concentrations in surface waters, but deeper CaCO3
	maxima occur at Station #32 at 100m, Station #38 at 60m and Station #64 at 100m while deeper
	opal maxima occur at Stations #38 and #64 at 100m.
	pNi and pV (7.1 pmol/L, 0.04, 0.02 and 0.05 nmol/L, respectively; Table S1). Lithogenic
	material is also strongly enriched at 100m at Station #64 and 200m at Station #77 (> 0.8 µg/L).
	Except for these stations located closer to margins, concentrations of lithogenic material are
	low, averaging 0.2 µg/L.

of the Iberian margin (Station #1) reaching up to 15 nmol/L, 5.2 µg/L, 3.2 nmol/L and 0.2 nmol/L at 550m respectively. Similarly, pMn and pZn show maximal concentrations over the transect at 550m at Station #1 (0.05 and 0.9 nmol/L, respectively) though high concentrations are also observed at 100m at Station #64 (0.03 and 0.07 nmol/L, respectively) like pCd, pCu, Particulate Cd, Co and P are characterized by biogenic distributions, with higher concentrations in surface waters, especially in the productive west European basin (Stations #21 and #26). Other pTEs are characterized by high surface concentrations such as pV and pZn in the Slight increase of pFe, pMn, pCd, pCo, pCu, pNi and pZn concentrations are observed in subsurface, such as at 60m and 100m at Station #64, in the upper 200m at Stations #32 and #38 and below 100m at Station #26. Iron and manganese oxide contents follow similar trends. Both

  3.2. Particulate TE:234 Th and mineral:234 Th ratios in the large size fraction (>53µm) Magnitudes of ratios differ among elements (pCd:234 Th, pCo: 234 Th < pCu: 234 Th, pNi: 234 Th, pV: 234 Th < pMn: 234 Th, pTi: 234 Th, pZn: 234 Th < pFe: 234 Th < pAl: 234 Th, pP: 234 Th) and vary between basins as described below. Profiles of pTE: 234 Th and mineral:234 Th ratios in the >53 µm fraction generally follow those observed for the concentrations (Fig.S4). Lithogenic: 234 Th ratios generally increase with depth but also show elevated values at the surface (15-30m) of Stations #1, #21 and #32.High pP:234 Th and pV: 234 Th ratios are observed in the upper 100m of the Irminger and Labrador basins (reaching 121 and 0.9 nmol/dpm, respectively), like high opal:234 Th ratios (750 µg/dpm at 30m of Station #69). In the west European and Icelandic basins, ratios of pCd:234 Th, pCo: 234 Th, pCu: 234 Th, pFe: 234 Th, pNi: 234 Th, pP: 234 Th and pZn: 234 Th increase towards the surface, similarly to CaCO3: 234 Th (reaching 271 µg/dpm at 109m at Station #38). Some exceptions are observed at 60m at Station #64 and in the Icelandic basin, especially at 200m at Station #32, where we determined high ratios of pCo: 234 Th (0.01 and 0.04 nmol/dpm at Stations #64 and #32, respectively), pCu: 234 Th (0.17 nmol/dpm at Station #32), pNi: 234 Th (0.14 and 1.04 nmol/dpm at Stations #64 and #32, respectively) and pZn: 234 Th (from 1.5 to 5.2 nmol/dpm in the upper 60m of the Icelandic basin). These high values correspond to the highest Fe(OH)3: 234 Th ratios (6.5 µg/dpm at 60m at Station #64, and 1.04-2.25 µg/dpm in the upper 200m at Station #32). The highest MnO2: 234 Th ratios are also observed at 60m at Station #64, and at 153m at Station #26, coinciding with a slight increase of the pZn: 234 Th ratio (1.2 nmol/dpm).

Ratios of pAl: 234 Th (1204 nmol/dpm) or lithogenic: 234 Th (404 µg/dpm) reach highest values at 250m at Station #1. Similarly, highest pCo: 234 Th (0.08 nmol/dpm), pCu: 234 Th (0.4 nmol/dpm), pFe: 234 Th (245 nmol/dpm), pMn: 234 Th (4 nmol/dpm) and pTi: 234 Th (18 nmol/dpm) occur at 250m at Station #1.

  a year or even only a few days, within the west European/Icelandic and Iberian basins. For example, Fe residence times average 47 days within the Labrador and Irminger basins compared to an average of 10 days for the west European/Icelandic basins and 2 days for Station #1 at the Iberian margin. For all TEs, except Co, τtotal is maximal at Station #77 in the Labrador Sea. For Co, the maximum τtotal is reached at Station #64, also in the Labrador Sea.

	3 days (at Stations #32 and #38) and Ni
	and Zn residence times are shorter there (Ni: τtotal=339 days at Station #21; Zn: τtotal=4 days at
	Station #32) than near the Iberian margin. A major difference with the Iberian margin is the
	generally lower surface water particulate and dissolved inventories for most TEs in the
	Icelandic and west European basins (Table 5).

Finally, τtotal for all TEs are much longer, generally of the order of years (5, 9, 7, 36 and 2 years for Co, Cu, Mn, Ni and Zn respectively) within the Labrador and Irminger basins, while they are less than

  particle size fraction (with GEOVIDE particulate concentrations being reported and discussed elsewhere; Planquette et al., personal communication, 2019 and Gourain et al., 2019 65 ). To only comment on the distribution of the pTEs, neither mineral exports nor chemical variables are included in the PCA. The PCA has been conducted after a Varimax rotation which appeared to clarify the relationship among variables by better capturing known dynamics of the water column

TABLE 1 Table 1 :

 11 Station characteristics with the number of weeks between the sampling time and beginning of the spring bloom (obtained from satellite data products[START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] ), primary production (obtained from incubations[START_REF] Fonseca-Batista | Evidence of High N2 Fixation Rates in the Temperate Northeast Atlantic[END_REF] ), POC export fluxes (obtained with the 234 Th approach[START_REF] Lemaitre | High Variability of Export Fluxes along the North Atlantic GEOTRACES Section GA01: Particulate Organic Carbon Export Deduced from the 234Th Method[END_REF] ), and phytoplankton classes (from HPLC pigment analysis and CHEMTAX analysis[START_REF] Tonnard | Cycle Biogéochimique Du Fer : Distribution et Spéciation Dans l'océan Atlantique Nord (GA01) et l'océan Austral (GIpr05)[END_REF] ).

		Station	Number of weeks since beginning of spring bloom	In-situ primary production (mmol/m 2 /d)	Phytoplankton class	POC export (mmol/m 2 /d)
	Iberian	1	10	33	diatoms & coccolith.	12
	basin	13	11	79	pelagophytes & cyano.	2.2
	west Europ.	21	9	135	diatoms	4.8
	Basin	26	8	174	diatoms	7.9
	Icelandic	32	5	105	coccolith.	8.3
	basin	38	4	68	coccolith.	4.8
	Irminger	44	5	137	diatoms	1.4
	basin	51	4	166	diatoms	2.7
	Labrador basin	64 69 77	5 4 5	54 27 80	diatoms diatoms diatoms	7.8 10 6.1

TABLE 2 Table 2 :

 22 Blanks

		Al +	Ca	+	Cd	Co*	Cu	Fe*	Mn	Na ^Ni	P	+	Ti +	V	Zn
	Blank (ppm)	1.6E-03	1.4	1.2E-06 3.2E-06 1.3E-05 1.5E-03 1.4E-04	936	3.4E-04 2.5E-03 1.0E-04 7.3E-06 2.6E-04
	BCR-414 (n=5; ppm)	3112	51133	0.385	1.44	29.7	1860	301	6601	17.8	15541	95	9	112.4
	RSD (%)	15	2.1	5.2	15	13	12	14	0.2	16	24	8	1	17
	Recovery CRM (%)	118	80	101	101	101	101	101	/	95	113	75	111	101

, average concentrations of the certified reference material (CRM; BCR-414), relative standard deviation (RSD) of the 5 analyses of the CRM and recoveries. Elements without any superscript sign have certified concentrations (Cd, Cu, Mn, Ni, V and Zn); elements marked with (*) have indicative concentrations reported on the official certificate (Co and Fe); elements marked with ( + ) have indicative concentrations reported on the GEOREM website (Al, Ca, P, and Ti) and Na has no reported concentration. The official certificate can be found at https://crm.jrc.ec.europa.eu/p/40455/40461/By-material-matrix/Animal-materials/BCR-414-PLANKTON-trace-elements/BCR-414 .

TABLE 3 Table 3 :

 33 Particulate export fluxes in µg/m 2 /d for aluminum (pAl), cadmium (pCd), cobalt (pCo), copper (pCu), iron (pFe), manganese (pMn), CaCO3), opal and in dpm/m 2 /d for 234 Th. Standard deviations (sd) were calculated by considering the standard deviations of the 234 Th fluxes and pTE: 234 Th ratios at Eq, with all concentration and activity uncertainties estimated using error propagation law.

	nickel (pNi), phosphorus (pP), titanium (pTi), vanadium (pV) and zinc (pZn); in mg/m 2 /d for lithogenic material, iron oxides (Fe(OH)3), manganese
	oxides (MnO2), calcium carbonate (

TABLE 4

 4

Table 4 :

 4 Spearman rank correlation coefficients between trace element and mineral export fluxes for the large size fraction at the Eq depth. The analysis was conducted on log-transformed export fluxes to ensure that input variables were more normally distributed and to reduce the influence of extreme values. Correlations with R < 0.1 are not shown. Values in bold are correlation coefficients with p-value ≤ 0.05 (t-test; XLStat software).

			.706	1
	Opal flux	0.164	0.028 0.073	1
	POC flux	0.391			0.473	1
	Al flux	1.000	0.083	0.200 0.164 0.391	1
	Cd flux	0.618	0.018 0.037 0.100 0.364 0.273 0.618	1
	Co flux	0.745		0.200		0.282 0.745 0.591	1
	Cu flux	0.845	0.330 0.156 0.255 0.064 0.191 0.845 0.791 0.609	1
	Fe flux	0.855	0.395 0.220 0.273 0.145 0.455 0.855 0.591 0.527 0.900	1
	Mn flux	0.527	0.183 0.440 0.364 0.136 0.473 0.527 0.636 0.527 0.718 0.736	1
	Ni flux	0.764	0.440 0.138 0.491			0.764 0.573 0.673 0.791 0.636 0.345	1
	P flux	0.491		0.073 0.209 0.236 0.491 0.891 0.718 0.627 0.400 0.655 0.473	1
	Ti flux	0.691	0.312	0.018 0.000 0.564 0.691 0.300 0.400 0.627 0.845 0.427 0.409 0.100	1
	V flux		0.119		0.009 0.336		0.200 0.127	0.327	0.445	1
	Zn flux	0.909	0.303 0.000 0.318 0.018 0.245 0.909 0.527 0.764 0.791 0.818 0.464 0.855 0.464 0.718	1

TABLE 5 Table 5 :

 55 Dissolved inventories (diss. invent. from[START_REF] Menzel Barraqueta | Aluminium in the North Atlantic Ocean and the Labrador Sea (GEOTRACES GA01 Section): Roles of Continental Inputs and Biogenic Particle Removal[END_REF][START_REF] Tonnard | Dissolved Iron in the North Atlantic Ocean and Labrador Sea along the GEOVIDE Section (GEOTRACES Section GA01)[END_REF] and from Planquette et al., personal communication, 2019), particulate inventories (part. invent. from 65 and from Planquette et al., personal communication, 2019), sinking rates calculated as the inverse of particle residence time multiplied by the Eq depth layer; total residence time (τtot, in days) calculated by dividing the total inventory (dissolved+particulate) by the Station diss. invent. part. invent. sinking rate diss. invent. part. invent. sinking rate diss. invent. part. invent. sinking rate diss. invent. part. invent. sinking rate

				Al					Co					Cu					Fe
	Basin					τ tot					τ tot					τ tot					τ tot
			µg/m 2	µg/m 2	m/d	d	sd	µg/m 2	µg/m 2	m/d	d	sd	µg/m 2	µg/m 2	m/d	d	sd	µg/m 2	µg/m 2	m/d	d	sd
	Iberian	1 13	20847 7720	12741 6672	65 5	4 0.2 51 5	219 124	13 32	25 2	64 269	3 29	3718 5002	28 129	52 4	236 11 1033 110	2392 1564	5553 1139	63 13	2 20	0.1 2
	west	21	13038	3628	15	33	1	151	37	5	125	5	6224	186	9	422 19	861	599	66	4	0.2
	Europ.	26	6181	1741	7	62 12	195	20	2	598 114	6100	133	1	3646 698	691	741	6	31	6
	Icelandic	32 38	12630 6007	1465 716	42 32	30 23	4 1	224 111	22 9	16 3	92 380	11 19	5539 2859	202 113	7 2	534 66 944 47	1471 786	898 539	135 64	3 3	0.3 0.2
	Irminger	44 51	443 9983	1831 4558	3 4	15 76	4 5	49 312	7 2	1 7	401 111 2125 145	1281 8128	147 200	1 1	512 142 3191 218	809 1983	996 3275	5 3	14 52	4 4
		64	3525	3049	6	30	2	203	4	1	3427 209	5812	160	3	966 59	2086	1976	20	8	0.5
	Labrador	69	969	3314	3	15 11	31	9	1	245 175	2150	129	1	996 713	294	1915	3	16	12
		77	2621	4465	1	106 3	122	44	0.1	1873 57	3588	237	0.3	3442 105	864	5128	0.5	147	5
				Mn					Ni					Zn
	Basin	Station diss. invent. part. invent. sinking rate	τ tot		diss. invent. part. invent. sinking rate	τ tot		diss. invent. part. invent. sinking rate	τ tot
			µg/m 2	µg/m 2	m/d	d	sd	µg/m 2	µg/m 2	m/d	d	sd	µg/m 2	µg/m 2	m/d	d	sd
	Iberian	1 13	6726 2606	408 332	12 1	130 6 664 70	8236 11488	23 167	37 10	854 789	39 84	5769 1355	1174 951	16 4	32 67	1 7
	west	21	2134	272	3	280 12	27694	816	11	339	15	2736	536	15	44	2
	Europ.	26	2868	204	5	330 63	20682	194	1	12374 2369	1647	552	1	271 52
		32	2505	175	9	212 26	19375	193	22	597	74	709	679	76	4	0.4
		38	1018	98	6	151 8	8152	88	11	674	33	790	400	22	11 0.1
		44	361	312	1	89 25	3611	118	2	544 151	658	757	1	99	27
		51	2317	102	2	1080 74	9212	181	4	1240 85	3668	855	3	171 12
		64	1833	113	8	162 3	15196	97	3	3987 243	4112	536	3	256 16
	Labrador	69	152	152	1	129 92	4705	202	1	1902 1361	464	345	3	33	24
		77	1353	461	0.1	2626 80	9488	1006	0.05	13297 407	3177	638	1	582 18

ACKNOWLEDGEMENTS

We are grateful to the helpful captain and crew of the R/V Pourquoi Pas?, as well as to Fabien Perault and Emmanuel De Saint Léger from the CNRS DT-INSU who assisted during in situ pump deployments. Special thanks to Yi Tang (Queens College, USA), Virginie Sanial (WHOI, USA), Raphaëlle Sauzède (LOV, France) and Lorna Foliot (LSCE, France) for their help at sea and for the pump coordination and collaboration. We would also like to thank Phoebe Lam for providing two modified McLane ISP. Claire Bollinger from the Pôle Spectrométrie Océan (PSO, Brest, France) greatly helped during the element analysis by ICP-MS. We acknowledge Yoan Germain and Emmanuel Ponzevera for the use of the clean lab at IFREMER. Finally, we would like to thank the co-chief scientist Pascale Lherminier. This work was funded by the French ANR Blanc GEOVIDE (ANR-13-BS06-0014), ANR RPDOC BITMAP (ANR-12-PDOC-0025-01), IFREMER, CNRS-INSU (programme LEFE), INSU OPTIMISP and Labex-Mer (ANR-10-LABX-19) and the Flanders Research Foundation (project G071512N) and Vrije Universiteit Brussel (Strategic Research Program, project SRP-2). Satellite chlorophyll a data and visualisations used in this study were produced with the Ocean Color (Ocean Biology Processing Group; OBPG) online data system, developed and maintained by NASA.

ASSOCIATED CONTENT Supporting Information

Figure S1: Summary of the different sampling and analytical steps for the >53µm particle size fraction, collected on in-situ pump (ISP) filters and for total 234 Th activities, collected via standard CTD rosette. In this figure, each filter is defined by a nominal porosity (in µm) and a diameter (corresponding to the symbol Ø, in mm). Table S1: Trace element concentrations (in nmol/L), mineral concentrations (in µg/L) and 234 Th activities (in dpm/L) for the large size fraction (>53µm) along the GEOVIDE transect.

The (*) indicate depths where POC was collected using a separate ISP unit, 10 to 50 m apart from the ISP dedicated to TEs. Table S2: Particulate TE: 234 Th (in nmol/dpm) and mineral: 234 Th (in µg/dpm or ng/dpm) ratios in the large size fraction (>53µm), estimated at the Eq depth, along the GEOVIDE transect.

AUTHOR INFORMATION Corresponding Author

* Nolwenn Lemaitre (nolwenn.lemaitre@erdw.ethz.ch)

Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Notes

The authors declare no competing financial interest.