M Biguenet

P. b , Chaumillon, E. a , Chagué, C. c , Arnaud, F. b , Jorissen, F. d , Coulombier, T. a , Geba, E. a , Cordrie, L. e,f , Vacher, P. g , Develle A L Sabatier

E. b , Soufi, F. b , Feuillet N Chalmin

600 year-long sedimentary record of tsunamis and hurricanes in the Lesser Antilles (Scrub Island, Anguilla)

Keywords: Coastal hazards, tsunamis, hurricanes, Lesser Antilles, lagoons sediment, late Holocene

The Lesser Antilles are a densely populated and a very touristic region exposed to many short-term hazards such as hurricanes and tsunamis. However, the historical catalog of these events is too short to allow risk assessment and return period estimations, and it needs to be completed with long-term geological records. Two sediment cores were sampled in March 2018 in a small coastal lagoon on Scrub Island (north eastern Caribbean). Here, we present sedimentological, geochemical, microfaunal and chronological analyses that enabled us to identify 25 sandy layers resulting from high energy marine floods. Two of these layers were interpreted as tsunami deposits based on sedimentological and geochemical evidence. The most recent deposit is associated with the transatlantic tsunami triggered by the 1755 AD Lisbon earthquake. The older is the thickest sandy layer recorded in the lagoon and is dated at 1415 cal. AD (1364-1469 cal. AD). This event was recorded in both the northern and the southern part of the Caribbean, with its large extent supporting a tsunamigenic origin. The 23 remaining sandy This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology 2 layers were interpreted as resulting from hurricanes, with the three most recent layers being associated with historical hurricanes. This new 1600 year-long reconstructed chronicle, has been compared to other published hurricane chronicles from the region. Scrub chronicle is the most eastern site and displays similarities with that of the Bahamas, while it is in antiphase with that of the north eastern US coast. This regional comparison may provide evidence of a latitudinal forcing for the hurricane tracks through time in relation to climate fluctuations.

Introduction

Worldwide, an increasing number of people living along the coasts are threatened by natural hazards (earthquakes, volcanoes, hurricanes, tsunamis and marine floods). To better constrain the risk due to natural hazards in a region, it is crucial to determine the recurrence interval and the intensity of a given hazard. Historical records of these events are of prime importance to this goal but they are often too short. Thus, a geological record establishing time-series extending back thousands of years is the only way to address the long-term recurrence of natural hazards (i.e. [START_REF] Atwater | Evidence for Great Holocene Earthquakes Along the Outer Coast of Washington State[END_REF][START_REF] Nanayama | Unusually large earthquakes inferred from tsunami deposits along the Kuril trench[END_REF][START_REF] Scileppi | Sedimentary evidence of hurricane strikes in western Long Island, New York: hurricane strikes in New York[END_REF][START_REF] Jankaew | Medieval forewarning of the 2004 Indian Ocean tsunami in Thailand[END_REF][START_REF] Woodruff | Exploring typhoon variability over the mid-to-late Holocene: evidence of extreme coastal flooding from Kamikoshiki, Japan[END_REF]. Large overwash related to hurricanes and tsunamis that can occur in a few hours may strongly affect the coastal landscape and ecosystems for millennia.

Large tsunami waves may transport large fragments of rocks or coral ripped off the coasts and reefs over several kilometers, at elevation of several meters [START_REF] Goto | Localized tsunamigenic earthquakes inferred from preferential distribution of coastal boulders on the Ryukyu Islands, Japan[END_REF][START_REF] Atwater | Extreme waves in the British Virgin Islands during the last centuries before 1500 CE[END_REF], they can breach the coastal dunes (e.g. [START_REF] Atwater | Geomorphic and stratigraphic evidence for an unusual tsunami or storm a few centuries ago at Anegada, British Virgin Islands[END_REF], modify the geography and ecosystems of coastal lakes and pond by flooding them with tons of coarse-grained sand, salt marine water, and fauna [START_REF] Chagué-Goff | Chemical signatures of palaeotsunamis: A forgotten proxy?[END_REF][START_REF] Scheucher | Field survey and hydrodynamics of storm-deposited boulders in the southwestern Dominican Republic: Playa Azul[END_REF][START_REF] Chagué-Goff | Applications of geochemistry in tsunami research: A review[END_REF]. The sediment archives in such environment record the traces of past overwash and can be used to reconstruct the intensity and recurrence of these event (e.g., [START_REF] Atwater | Evidence for Great Holocene Earthquakes Along the Outer Coast of Washington State[END_REF]Liu andFearn, 1993, 2000;[START_REF] Donnelly | 700 yr sedimentary record of intense hurricane landfalls in southern New England[END_REF][START_REF] Nanayama | Unusually large earthquakes inferred from tsunami deposits along the Kuril trench[END_REF][START_REF] Scileppi | Sedimentary evidence of hurricane strikes in western Long Island, New York: hurricane strikes in New York[END_REF][START_REF] Sabatier | Reconstruction of paleostorm events in a coastal lagoon (Hérault, South of France)[END_REF][START_REF] Woodruff | Exploring typhoon variability over the mid-to-late Holocene: evidence of extreme coastal flooding from Kamikoshiki, Japan[END_REF] This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology [START_REF] Chaumillon | Storm-induced marine flooding: Lessons from a multidisciplinary approach[END_REF]. It is however still very difficult to distinguish storm and tsunami deposits and this remain a main obstacle against progression in knowledge on hazard related two high energy events in region where they can both occur. [START_REF] Engel | Tsunami deposits of the Caribbean -Towards an improved coastal hazard assessment[END_REF] have already summarized the known criteria to identify tsunami deposits in the Caribbean. Among the most cited arguments, there are: internal mud laminae, intraclasts (rip up clast), truncated flame structures, or backflow induced structures. Storm deposits will tend to have many parallel, cross laminations and climbing ripples (Morton et al., 2007b;[START_REF] Baumann | Signature sédimentaire des submersions de tempête dans le domaine rétrolittoral : application à la Charente Maritime[END_REF]. Moreover, storm deposits will generally tend to be more restricted across the shore than tsunami deposits because of the storm shorter wavelengths (Morton et al., 2007). Added to the sedimentological and morphological criteria, others proxies of a marine source such as geochemical (e.g. [START_REF] Chagué-Goff | Chemical signatures of palaeotsunamis: A forgotten proxy?[END_REF][START_REF] Chagué-Goff | Applications of geochemistry in tsunami research: A review[END_REF][START_REF] Riou | The sediment-fill of Pago Pago Bay (Tutuila Island, American Samoa): New insights on the sediment record of past tsunamis[END_REF] and microfaunal (e.g. [START_REF] Engel | A prehistoric tsunami induced long-lasting ecosystem changes on a semi-arid tropical island-the case of Boka Bartol (Bonaire, Leeward Antilles)[END_REF] markers may also help to characterize tsunami deposits. Most studies have focused on either hurricane or tsunami deposits but rarely on both within the same environment (e.g., [START_REF] Nanayama | Sedimentary differences between the 1993 Hokkaido-nansei-oki tsunami and the 1959 Miyakojima typhoon at Taisei, southwestern Hokkaido, northern Japan[END_REF][START_REF] Goff | Sedimentary differences between the 2002 Easter storm and the 15th-century Okoropunga tsunami, southeastern North Island, New Zealand[END_REF].

Here, we investigate the sedimentary record preserved in a coastal lagoon on a small Caribbean Island of the Lesser Antilles arc (Scrub, Anguilla). Hurricanes represent a major hazard in the Lesser Antilles arc because they occur frequently [START_REF] Oliva | Paleotempestology database for the western North Atlantic basin[END_REF], with recent very destructive events such as Hurricane Irma [START_REF] Baumann | Signature sédimentaire des submersions de tempête dans le domaine rétrolittoral : application à la Charente Maritime[END_REF]AD, Cangialosi, et al., 2018), Donna (1960 AD;[START_REF] Dunn | The Hurricane season of 1960[END_REF] or Luis (1995 AD;[START_REF] Hoggarth | Management Plan for the Marine Parks of Anguilla. Prepared for: Organisation of Eastern Caribbean States Natural Resources Management Unit St Lucia[END_REF]. Furthermore, the densely populated and highly touristic islands of the Lesser Antilles arc are threatened by large earthquakes (Feuillet et al., 2011), volcanic eruptions [START_REF] Boudon | Volcano flank instability in the Lesser Antilles Arc: Diversity of scale, processes, and temporal recurrence[END_REF] and tsunamis [START_REF] Engel | Tsunami deposits of the Caribbean -Towards an improved coastal hazard assessment[END_REF]. However, these natural hazards are still poorly constrained mainly because the historical record is too short. This new sedimentary archive constitutes a unique opportunity to investigate the impact of both hurricanes and tsunamis on coastal lagoons, better understand the sedimentary record of past events on a multi-decadal to centennial timescale and find clues to decipher between past hurricane and tsunami events along the coasts.

We applied a multiproxy approach with sedimentological, geochemical and microfaunal analyses as well as radiocarbon and short-lived radionuclides dating of two one-meter-long sediment cores. We reveal the existence of many sand layers interbedded within the lagoon autochthonous sedimentation. This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology By combining our results with other data available in the literature, we discuss the origin of these sand layers to further establish a chronology for tsunami and hurricane events. We then discussed criteria to distinguish between tsunami and hurricane deposits in this record. On the basis of our catalog of hurricane events we discuss on the modulation of hurricane activity by climate forcing.

Study area

In the following section the geomorphology, geology and geodynamic characteristics of the study area are described, as well as the main known high energy events from historical data and sedimentary records.

Geomorphologic and geologic settings

The Lesser Antilles form a 850 km-long island arc in the Caribbean Sea (Fig. 1A) [START_REF] Scheffers | Paleo-Tsunami Relics on the Southern and Central Antillean Island Arc[END_REF]. Scrub Island is located in the northern part of the Lesser Antilles arc, southeast of the Anegada Passage. It belongs to a group of islands (including Saint-Martin, Saint-Barthelemy, Anguilla) surrounded by a large 40 m-deep carbonate platform called the Anguilla-Saint-Barthelemy platform (Fig. 1B). Scrub Island and many other small neighboring islets are inhabited. Scrub Island is 3.5 kmlong from east to west and about 1.5 km-wide from north to south (Fig. 1C). It consists of low relief limestones, with the highest point about 25 m above sea level (a.s.l.) close to the center of the island (Fig. 1C). The island displays a karstic limestone landscape, which transfers the rainfall directly into the fractured basement, before it flows into the sea (Bruce, 2000). Therefore, the vegetation, mostly small bushes and cactus species, is sparse. Permanent water bodies are limited on Scrub Island and include three shallow ponds that could have been isolated from the open ocean after the last higher sea level stand, as suggested for the Anguilla ponds (Bruce, 2000). In this study, we focus on the westernmost lagoon, separated from the ocean by a 2 to 5 m-high and 50 m-wide sandy barrier covered by small bushes at the top (Fig. 1D). This salty lagoon is approximately 400 m-long and 130 m-wide and very shallow, with a maximum water depth of 80 cm (as observed in March 2018). Examination of Google Earth aerial photographs from 2003 to 2020 suggests that no barrier breach has occurred over the last 17 years.

Past tsunamis in the Lesser Antilles

The Lesser Antilles arc results from the subduction of the American plate under the Caribbean plate at 2 cm yr -1 (DeMets et al., 2000), with numerous volcanoes and active faults that can generate tsunamis.

Several tsunamis have been reported during the historical period in the Lesser Antilles arc [START_REF] Zahibo | Evaluation of tsunami risk in the Lesser Antilles[END_REF][START_REF] Lander | A brief history of tsunamis in the Caribbean Sea[END_REF][START_REF] Engel | Tsunami deposits of the Caribbean -Towards an improved coastal hazard assessment[END_REF], with their origin including local or more distant earthquakes [START_REF] Reid | The Virgin Islands earthquakes of 1867-1868[END_REF][START_REF] Pelinovsky | Tsunami Generated By the Volcano Eruption On July 12-13, 2003 At Montserrat, Lesser Antilles[END_REF][START_REF] Zahibo | The earthquake and tsunami of November 21, 2004 at Les Saintes, Guadeloupe, Lesser Antilles[END_REF][START_REF] Roger | The Transoceanic 1755 Lisbon Tsunami in Martinique[END_REF][START_REF] Harbitz | Tsunami hazard in the Caribbean: Regional exposure derived from credible worst case scenarios[END_REF][START_REF] Cordrie | Simulation of the 2004 tsunami of Les Saintes in Guadeloupe (Lesser Antilles), in: oceans 2019 -Marseille. Presented at the OCEANS 2019 -Marseille[END_REF], volcanic processes (e.g., [START_REF] Pelinovsky | Tsunami Generated By the Volcano Eruption On July 12-13, 2003 At Montserrat, Lesser Antilles[END_REF][START_REF] Watt | Combinations of volcanic-flank and seafloor-sediment failure offshore Montserrat, and their implications for tsunami generation[END_REF], or transoceanic and associated to far-field sources [START_REF] Roger | The Transoceanic 1755 Lisbon Tsunami in Martinique[END_REF].

The oldest historical tsunami observed in the Lesser Antilles occurred on 6 April 1690 AD in Antigua, Saint Kitts and Nevis. This event was triggered by an earthquake with a magnitude estimated at Ms 8 [START_REF] Dorel | Seismicity and seismic gap in the Lesser Antilles arc and earthquake hazard in Guadeloupe[END_REF].

The most important reported tsunami occurred in 1755 AD. This event is related to the major earthquake (Mw=8-9 class earthquake) that destroyed Lisbon (Portugal) on 1 November 1755 [START_REF] Chester | The 1755 Lisbon earthquake[END_REF], and generated a transoceanic tsunami that hit the coasts of Spain, Portugal, Morocco but also the Caribbean [START_REF] Roger | The Transoceanic 1755 Lisbon Tsunami in Martinique[END_REF]. The tsunami was observed at 17 locations across the north-eastern Caribbean from Dominica to Hispaniola, with a maximum wave height of 6.4 m at Saba Island (Fig. 1A) [START_REF] Fuentes | Sand Scripts of Past Tsunamis in Coastal Ponds of St[END_REF].

On 30 November 1823 AD, the Saint Pierre harbour in Martinique was hit by a strong earthquake (epicenter coordinates: 14.4° N 61.1° W; NOAA/NESDIS data) which was followed by a tsunami 25 minutes later [START_REF] Lander | A brief history of tsunamis in the Caribbean Sea[END_REF].

On 8 February 1843 AD a M8-class earthquake occurred between Antigua and Guadeloupe (e.g., Sainte-Claire [START_REF] Deville | Observations sur le tremblement de terre éprouvé à la Guadeloupe le 8 Février 1843[END_REF][START_REF] Bernard | Subduction and seismic hazard in the northern Lesser Antilles: Revision of the historical seismicity[END_REF]Nathalie Feuillet et al., 2011;[START_REF] Hough | Missing great earthquakes[END_REF]. Despite This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology its magnitude, this event may have triggered only a small tsunami which was observed only in English harbour at Antigua (with a wave amplitude of 1.2 m) and Nevis [START_REF] Shepherd | Comment on "subduction and seismic hazard in the Lesser Antilles[END_REF].

Another historical tsunami occurred in the British Virgin Islands on 18 November 1867 AD [START_REF] Reid | The Virgin Islands earthquakes of 1867-1868[END_REF]. The wave reached 4 to 6-m height according to the observations and exceeded 10m at Guadeloupe, which is the highest reported value of tsunami height in the Caribbean Sea [START_REF] Lander | A brief history of tsunamis in the Caribbean Sea[END_REF]. The tsunami followed a strong earthquake felt in all the British Virgin Islands, but the origin of the event remains poorly constrained [START_REF] Reid | The Virgin Islands earthquakes of 1867-1868[END_REF][START_REF] Zahibo | The 1867 Virgin Island Tsunami[END_REF].

More recently, a tsunami was generated in 2004 by the M 6.3 normal fault earthquake of Les Saintes in the Guadeloupe archipelago [START_REF] Friant | Field survey and numerical simulation of the 21 November 2004 tsunami at Les Saintes (Lesser Antilles): tsunami at Les Saintes[END_REF]N. Feuillet et al., 2011;[START_REF] Cordrie | Simulation of the 2004 tsunami of Les Saintes in Guadeloupe (Lesser Antilles), in: oceans 2019 -Marseille. Presented at the OCEANS 2019 -Marseille[END_REF]. This earthquake generated small waves with 2 m of run-up in several bays of Les Saintes, a group of islands in the South of Guadeloupe [START_REF] Cordrie | Simulation of the 2004 tsunami of Les Saintes in Guadeloupe (Lesser Antilles), in: oceans 2019 -Marseille. Presented at the OCEANS 2019 -Marseille[END_REF].

Other historical tsunamis triggered by volcanic eruptions are reported in this region, such as the Montserrat in 2002 [START_REF] Pelinovsky | Tsunami Generated By the Volcano Eruption On July 12-13, 2003 At Montserrat, Lesser Antilles[END_REF]) but these events are beyond the scope of this study as there are more local and may not hit Scrub Island.

North of the Lesser Antilles arc, beyond the Anegada passage, evidences of extreme overwash have been found in sedimentary records along the coasts and in hypersaline lagoon of Anegada (British Virgin Islands, [START_REF] Atwater | Geomorphic and stratigraphic evidence for an unusual tsunami or storm a few centuries ago at Anegada, British Virgin Islands[END_REF][START_REF] Atwater | Extreme waves in the British Virgin Islands during the last centuries before 1500 CE[END_REF]. 14 C dating of coral boulders, shells and organic remains indicates that these overwash occurred in the Middle age (between 1200 and 1480 cal. AD). This event has been attributed to an extraordinary storm or a tsunami of nearby origin (rupture of the Puerto-Rico megathrust, outer-rise normal faulting). In St Thomas (US Virgin Islands), four coastal ponds and a mangrove site contain a record of a tsunami also dated with radiocarbon from plant remains between 1200 and 1450 cal. AD [START_REF] Fuentes | Sand Scripts of Past Tsunamis in Coastal Ponds of St[END_REF].

Past hurricanes in the Lesser Antilles

Numerous hurricanes have been reported in the Lesser Antilles Arc. They occur mostly between July and November with frequency, magnitude and trajectory changes from one year to another [START_REF] Garnier | The historic reality of the cyclonic variability in French Antilles, 1635-2007[END_REF]. They are influenced by large regional climate oscillations such as the El Niño Southern Oscillation (ENSO) [START_REF] Jury | Subregional precipitation climate of the Caribbean and relationships with ENSO and NAO[END_REF], the Atlantic Multidecadal Oscillation (AMO) [START_REF] Burn | A sediment-based reconstruction of Caribbean effective precipitation during the 'Little Ice Age' from Freshwater Pond, Barbuda[END_REF] or the ITCZ (Van Hengstum et al., 2016), with the latter authors suggesting that the ITCZ position modulates the hurricane activity in the Caribbean. It has been argued that when the ITCZ migrates further north, the vertical shear winds decrease in the Atlantic Hurricane Development Zone, facilitating the formation of intense hurricanes. Furthermore, the ITCZ position may also modulate the hurricane tracks through time. [START_REF] Baldini | Persistent northward North Atlantic tropical cyclone track migration over the past five centuries[END_REF] propose that during cooling periods, the ITCZ southward displacement enables an east-west hurricane track in the south Caribbean. In contrast, during a warming period, the ITCZ moves northward, which would then shift the hurricane track to the northeast of the Caribbean, close to Scrub Island and the Bahamas.

Sedimentary studies along the coasts of various islands and in lagoons have revealed deposits related to past hurricanes [START_REF] Donnelly | Intense hurricane activity over the past 5,000 years controlled by El Niño and the West African monsoon[END_REF][START_REF] Mccloskey | 5000 year sedimentary record of hurricane strikes on the central coast of Belize[END_REF][START_REF] Malaizé | Hurricanes and climate in the Caribbean during the past 3700 years BP[END_REF][START_REF] Donnelly | Climate forcing of unprecedented intense-hurricane activity in the last 2000 years: Donnelly et al[END_REF][START_REF] Denommee | Climatic controls on hurricane patterns: a 1200y near-annual record from Lighthouse Reef[END_REF][START_REF] Wallace | Intense Hurricane Activity Over the Past 1500 Years at South Andros Island, The Bahamas[END_REF], but no paleotempestology studies have been conducted in Anguilla or Scrub Island.

The current observational record in the Lesser Antilles began around 1850 AD and the National Oceanic and Atmospheric Administration (NOAA) documented 13 hurricanes that passed within 30 km of the island of Scrub from 1852 to 2017 (coast.noaa.gov/hurricanes, 2020; Table 1). This region was struck by the extremely strong category 5 Hurricane Irma in September 2017 (Table 1, Fig. 2). This event is unprecedented in the historical record [START_REF] Cangialosi | National Hurricane Center tropical cyclone report: Hurricane Irma[END_REF]. It resulted in major damage, destroying many towns and killing 47 people before continuing its route north-westwards, where it impacted the Virgin Islands and Florida [START_REF] Cangialosi | National Hurricane Center tropical cyclone report: Hurricane Irma[END_REF]. Other category 3 hurricanes, such as Donna (1960 AD [START_REF] Dunn | The Hurricane season of 1960[END_REF] and Dog (1950 AD) (coast.noaa.gov/hurricanes, 2020) with This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology south-west trajectories relative to Scrub Island (Fig. 2), strongly affected this part of the Lesser Antilles (Table 1).

Material and methods

Sampling and core description

Fieldwork took place in March 2018, with the aim of recovering a sedimentary record deposited in Scrub Island westernmost lagoon. Two one-meter-long sediment cores were sampled at 80 cm water depth using an Uwitec gravity corer with a hammer. The location of cores was chosen along a transect perpendicular to the coast. SCR1-18-01 was taken just behind the dune whereas SCR1-18-03 was taken at the opposite side of the lagoon (150 m east of core SCR1-18-01), in distal position relative to potential washovers. The cores were horizontally stored in a walk-in cooler in the laboratory, before being split, photographed, described in detail and subsampled.

Sedimentological and mineralogical analyses

Grain-size analyses were carried out at the EDYTEM laboratory using a Beckman Coulter LS 13 320 XR particle size analyser using sonication, with a range size between 0.010 µm and 3000 µm.

The sampling step was about 5 mm through core SCR1-18-01 respecting facies boundaries. The mean grain size curve and the grain size contour plot were produced using the Matlab software.

Core SCR1-18-01 was scanned at the SYMME laboratory (Annecy, France) using an X-ray tomography system (Easytom XL 150 from RX SOLUTION society) at 150 kV and 200 μA. The core was cut in two sections (110 to 70 cm and 70 to 0 cm), which were scanned one after the other. The acquisition time was about 1 hour per core (for each section, 7 successive scans by translating along the beam were necessary to cover the entire volume of the core). The reconstructed data are sets of 16 bits Tiff image files representing cross-sections of the cores (horizontal slices from top to base). The image resolution (voxel size) is 55 µm for the lower 40 cm and 85 μm for the upper 70 cm of the core. The total number of images available for the core is 12,992 (6,048 + 6,944). For each section, the vertical This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology cross-sections were reconstructed using the Image J software and including the Fiji distribution extension [START_REF] Schindelin | Fiji: an open-source platform for biological-image analysis[END_REF]. X-ray diffraction (XRD) analyses were performed on core SCR1-18-01 with a sampling step of 5 cm to identify the mineralogical species. The diffraction was performed on powder in reflection mode on sample holder of the ASTRE platform of the Université Savoie Mont-Blanc (XRD: INEL; tube CoKα=0,1789 nm X-ray; slit of 1.5 x 0.1; reflection mode; generator INEL XRG3D 30 mA, 30kV; sensitive detector of curve position INEL CPS120 at 0,29° in resolution at FWHM). The mineralogical species were identified using the Match! software. The first 10 cm of the core were not analyzed for mineralogy as they were required for the measurements of short-lived radionuclides ( 210 Pb, 137 Cs and 241 Am).

Geochemical analyses

X-ray fluorescence (XRF) analyses were carried out on both cores at the EDYTEM laboratory using the Avaatech Core Scanner (Avaatech XRF Technology, Alkmaar, The Netherlands) with a rhodium anode and choosing a 1 mm step resolution [START_REF] Richter | The Avaatech XRF Core Scanner: technical description and applications to NE Atlantic sediments[END_REF]. Two runs were used to detect light and heavy weight elements: a run at 10 kV, 0.2 mA for 20 s and a run at 30kV, 0.3 mA for 20 s. A Principal Component Analysis (PCA) was performed on the XRF core scanner data for core SCR1-18-01 using the open-source software R (R Core Team, 2014) to highlight chemical endmembers (e.g., [START_REF] Sabatier | Clay minerals and geochemistry record from northwest Mediterranean coastal lagoon sequence: Implications for paleostorm reconstruction[END_REF] and element correlations.

Loss on ignition (LOI) analyses were performed on core SCR1-18-01 with a sample step of 5 cm to quantify the amount of organic matter (LOI550) and carbonates (LOI950) in the different sedimentary units, according to the protocol described by Heiri et al. (2001). It was noted that for this type of sediment (carbonate-rich), the four hours at 950°C of the protocol were not sufficient to burn all carbonates. Thus, the percentages of carbonates presented are about 20% lower than its real content.

After different heating timing, the relevant percentage of carbonates was reached after a total of eight hours at 950°C. The first 10 cm of the core were not analyzed for LOI as they were required for the measurements of short-lived radionuclides ( 210 Pb, 137 Cs and 241 Am).

Ten slabs were sub-sampled from core SCR1-18-01 and resin-embedded for analysis with a LEO Stereoscan 440 Leica (ASTRE platform of the Université Savoie Mont-Blanc) scanning electron microscope (SEM) with 20 kV tension, in order to qualify small scale sedimentary structures and grains at a 10 mm work distance. Chemical cartographies were performed on the slabs at a 23 mm work distance, using the Quantax EDX probe (Bruker) from the ASTRE platform, to highlight the elementary composition at the grain scale. The images were obtained in high vacuum mode, in secondary electron or backscattering electron modes.

Foraminifera analyses

A total of 35 samples were taken every 10 cm in fine-grained deposits and every 5 to 1 cm in coarse deposits, in core SCR1-18-01. Samples were weighed, dried at 60 °C and were sieved to retain the fractions 125-500 µm and > 500 µm. Foraminifera found in dried residues of the two size fractions were determined and taxa were identified using common taxonomical reference literature, describing the foraminifera in the Gulf of Mexico and the Caribbean Sea. All individuals were identified at least at a generic level, and their abundance was determined semi-quantitatively on the basis of the number of specimens observed in a single 6 x 10 cm picking tray filled with dry residue (Fig. 5): on a scale from 0 to 5: 0: barren sample; 1: 1 to 2 individuals; 2: 3 to 5 individuals; 3: 6 to 15 individuals; 4: 16 to 40 individuals; 5: more than 40 individuals. Only species occurrences with more than 6 individuals were considered as relevant.

Chronology

Short-lived radionuclides ( 210 Pb, 137 Cs and 241 Am) measurements were performed using the well-type germanium detectors at the Laboratoire Souterrain de Modane following methods outlined in [START_REF] Reyss | Large, low background well-type detectors for measurements of environmental radioactivity[END_REF]. A total of 14 and nine samples were collected from cores SCR1-18-01 and SCR1-18-03, respectively, in the upper 12 cm and 10 cm, according to sedimentary facies boundaries. Excess 210 Pb was calculated as the difference between total 210 Pb and 226 Ra activities [START_REF] Goldberg | Geochronology with 210Pb. Radioactive Dating[END_REF]. Data were computed with the package 'serac' in R software [START_REF] Bruel | Serac: a R package for ShortlivEd RAdionuclide Chronology of recent sediment cores[END_REF]. This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology A total of 13 organic macro-remains (wood and leaves) were collected in the muddy layers. 14 C measurements were performed by accelerator mass spectrometry (AMS) at the Poznan Radiocarbon Laboratory and at the Laboratoire de Mesure 14C (LMC14) ARTEMIS at the CEA (Atomic Energy Commission) Institute at Saclay. The 14 C ages were converted to 'calendar' years at two sigma using the Intcal13 calibration curve [START_REF] Reimer | IntCal13 and Marine13 Radiocarbon Age Calibration Curves 0-50,000 Years cal BP[END_REF]. An age-depth model was constructed using the R code package 'clam' in R software [START_REF] Blaauw | Methods and code for 'classical' age-modelling of radiocarbon sequences[END_REF], based on 14 C ages and on a historical hurricane occurrence, following [START_REF] Sabatier | 7000 years of paleostorm activity in the NW Mediterranean Sea in response to Holocene climate events[END_REF].

Results and interpretations

Facies description

For both cores SCR1-18-01 and SCR1-18-03, the sediment is composed of alternating coarse and fine units, with three main sedimentary facies identified. In the following, we mainly focus on core SCR1-18-01 and compare with samples of core SCR1-18-03.

Facies 1 (F1) consists of an organic-rich matrix with plant macro-remains such as wood and leaf fragments. The color of Facies 1 varies from dark brown to light yellowish brown, reflecting variations in the amount of organic matter. Some sediment layers show a green (olive) color due to the presence of algal mats (at 16 cm depth for example, Fig. 3). Mean organic matter (LOI550) content is 24% (+/-8%) and mean carbonate (LOI950) content is 35% (+/-2%) (Fig. 3). The carbonated fraction is composed of small calcitic shells and some patches of magnesian calcite (confirmed by the XRD data).

These shells are about 0.5 to 1 mm-long and mainly consist of bivalves and benthic foraminifera, such as miliolids (Fig. 3), which are typical of tropical lagoon environments [START_REF] Hallock | Larger Foraminifera: A Tool for Paleoenvironmental Analysis of Cenozoic Carbonate Depositional Facies[END_REF].

Layers of facies 1 display varying amounts of Miliolinella sp. tests (0 to 5 on the semi-quantitative scale) that are thin, transparent and show only minimal amount of wear (Fig. 5). Facies 1 also contains very small (less than 5 µm in diameter) angular quartz grains (Fig. 3). Some rare thin horizontal beds of NaCl deposits (halite) are also visible (Fig. 3).

Facies 2 (F2) is a very pale brown unique deposit in the cores, between 46 and 40 cm depth in core SCR1-18-01, and from 31 to 23 cm depth in Core SCR1-18-03. It is composed of 8% (+/-3%) organic matter (LOI550) and 42% (+/-1%) carbonates (LOI950). It displays many whole and intact shells of variable sizes (0.5 mm to 1 cm) and some larger sandy grains (about 1 mm), the latter consisting of calcite and magnesian calcite (Fig. 3). Small bivalves (Fig. 3) and larger gastropod shells (around 1 cm long) are found. The gastropods were identified as Cerithideopsis costata (da Coasta, 1778), which are known to live in tropical brackish environments such as coastal lagoons [START_REF] Reguero | Molluscs (Mollusca: Gastropoda, Bivalvia, Polyplacophora) of Laguna Madre, Tamaulipas, Mexico: Spatial and Temporal Distribution[END_REF]. The layer of facies 2 displays abundant individuals of Miliolinella sp. (2 to 5 on the semiquantitative scale, Fig. 5), indicative of a tropical lagoon environment. Tests of Miliolinella sp. are thin, transparent and intact. Like facies F1, F2 contains very small quartz grains (Fig. 3). Halite (also evidenced by the XRD data) forms a coating around shells and sediment grains, and exhibits a typical cubic shape (Fig. 3).

Facies 3 (F3) displays a light gray or light yellowish brown color and consists of 40% (+/-2%) carbonates (LOI950) and 9 (+/-5) % organic matter (LOI550) (Fig. 3). The thickness of the F3 layers varies from less than 5 mm (65-64.5 cm depth) to 15 cm (61-46 cm depth) in core SCR1-18-01.

However, in core SCR1-18-03 there are fewer and thinner layers of facies F3. Facies F3 is mainly composed of carbonated sand, largely derived from eroded fragments of marine skeletal material, including bivalves, molluscs and corals. Shell fragments are of variable size (100 to 1000 µm). Most F3 layers display a sharp contact with the underlying units and some layers present interbedded muddy layers or intraclasts. Both sand grains and shells consist of calcite and magnesium calcite (Fig. 3), but also of aragonite (based on XRD data). Layers of facies F3 display rare to abundant individuals of Miliolinella sp. (1 to 5 on the semi-quantitative scale, Fig. 5). Tests of Miliolinella sp. are thin, transparent and intact. However, all F3 samples contained some individuals (1 on the semi-quantitative scale, Fig. 5) of the larger, symbiont-bearing taxa Amphistegina gibbosa and Archais angulatus (Fig. 3). Some Elphidium discoidale (4 on the semi-quantitative scale) were also found between 92 and 93 cm depth in core SCR1-18-01 (Fig. 5). Unlike the specimens of Miliolinella sp., the tests of Amphistegina gibbosa and Archais angulatus are thick, heavily calcified, opaque and strongly abraded. These large This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology foraminifera represent larger symbiont-bearing species with a very robust shell, typical of high-energy reef environments [START_REF] Hallock | Larger Foraminifera: A Tool for Paleoenvironmental Analysis of Cenozoic Carbonate Depositional Facies[END_REF].

In rare F3 layers, very few Cerithideopsis costata shells have been found. Based on the presence or absence of salt coating (halite) on grains, three sub facies are distinguished within F3: Subfacies 3.1 is characterized by salt coating around all grains; subfacies 3.2 is characterized by an absence of salt coating; subfacies 3.3 is characterized by both salt-coated and non-salt-coated grains (Fig. 3).

Geochemistry

The main results obtained from XRF analyses of core SCR1-18-01 are presented in Fig. 4. Linear regression tests on the Br and LOI550 results show a significant relationship with a R of 0.53 and pvalue < 0.05 (0.01342). This suggests that Br XRF peak areas can probably be used as a proxy for organic matter content, since Br is known to have a strong affinity for organic matter (e.g., [START_REF] Chagué-Goff | Geochemical and petrographical characteristics of a domed bog, Nova Scotia: a modern analogue for temperate coal deposits[END_REF][START_REF] Guevara | Bromine as indicator of source of lacustrine sedimentary organic matter in paleolimnological studies[END_REF]. A strong relation between S and Br, in association with organic matter, has been previously reported using PCA, explaining 61% of the variance [START_REF] Chagué | Geological evidence and sediment transport modelling for the 1946 and 1960 tsunamis in Shinmachi, Hilo, Hawaii[END_REF]. However, Br and S also occur in higher concentrations in seawater than freshwater [START_REF] Wedepohl | Environmental influences on the chemical composition of shales and clays[END_REF], and this could also explain their strong relationship in the Scrub lagoon, although it appears that their affinity with organic matter mostly explains their distribution.

The two first dimensions (Dim1 and Dim2) of the PCA (Fig. 4B) represent 67% of the total variance. Br, S, Fe and Si have a positive loading on Dim1 while Sr presents a negative correlation. Dim2 allows to distinguish Na and Cl (positive loading) from Ca with a negative correlation. From this PCA representation, four different endmembers can be identified: 1/ "salt" represented by Na and Cl, 2/ "organic matter" (OM) represented by Br and S, 3/ "silicate" represented by the Si and Fe and allochthonous inputs and 4/ "carbonates" endmembers represented by Ca and Sr. Ca and Sr do not exhibit a strong correlation and this can be explained by the presence of other minerals such as magnesian calcite.

By labelling samples with the facies information in the PCA, it was possible to establish a map of the geochemical data distribution (Fig. 4C). Facies F1 is dominated by the "organic matter", "silicate" endmembers and more or less influenced by the "salt" endmember. Facies F2 seems to be correlated with the "carbonates" endmember, due to the presence of Sr-rich shell fragments (e.g., [START_REF] Sabatier | Clay minerals and geochemistry record from northwest Mediterranean coastal lagoon sequence: Implications for paleostorm reconstruction[END_REF]Chagué-Goff et al., 2017 and references therein). Facies F3 is also linked to the "carbonates" endmembers (represented by Ca and Sr) and more or less influenced by the "salt" endmember.

Moreover, facies F3 is hardly linked to the "organic matter" endmember represented mainly by the Br.

Thus, facies F3 can be highlighted by the Sr/Br ratio, which increases in facies F3. (Fig. 5).

Grain size

Grain size results for core SCR1-18-01 are presented in Fig. 5. Denser layers highlighted by X-ray tomography data are characterized by a coarser grain size, and correspond to carbonated sand. The grain size contour plot shows that all these coarser layers have a similar grain size distribution with a mode around 800 µm (Fig. 5). Moreover, the Sr/Br ratio increases simultaneously with the grain size in F3 but presents a higher resolution than the grain size samples. This enable us to use Sr/Br as a high-resolution grain size proxy, which is useful to precisely identify the coarse deposits boundaries in the study area.

Based on grain-size and Sr/Br ratio, 25 coarse layers (F3) were identified in core SCR1-18-01 and labelled L1 to L25.

Chronology

Short-lived radionuclides

Unfortunately, short-lived radionuclide results obtained from core SCR1-18-01 did not provide any interpretable information. For core SCR1-18-03, no sedimentation rate could be calculated on the basis of the 210 Pbex data. Nevertheless, the 210 Pbex profile shows that there is still some excess 210 Pb at 85 mm (Fig. 6), suggesting that sediment at this depth was deposited during the 20 th century. Moreover, a clear peak in the 137 Cs profile at 17 mm depth (highest activity > 15 mBq/g) can be attributed to the maximum nuclear weapon tests in 1963 AD [START_REF] Pennington | Observations on Lake Sediments using Fallout 137Cs as a Tracer[END_REF]. This suggests that F3 layer 25 (L#25 at 22 mm depth, Fig. 6) is probably older than 1963 AD. The deepest significant presence of 137 Cs activity, at 40 mm depth (5 mBq/g), could correspond to the first fallouts of nuclear weapon tests in 1955 AD [START_REF] Pennington | Observations on Lake Sediments using Fallout 137Cs as a Tracer[END_REF]. Thus, the youngest F3 layer (Layer 25, Fig. 5) in both cores was probably deposited between 1955 and 1963 AD (Fig. 6). Deeper L#24 and L#23 (Fig. 5) were probably deposited before 1955 AD but during the 20 th century.

14 C ages and age-depth model

The oldest age in core SCR1-18-01 is 464 +/-74 cal AD at 105 cm depth (Table 2; Fig. 7). In Core SCR1-18-03, the oldest age is 1132 +/-96 cal BC at 98.5 cm depth showing that the eastern part of the lagoon preserves a longer sediment record (Table 2; Fig. 7). A correlation between Core SCR1-18-01 and Core SCR1-18-03 was performed, based on F3 layers and using Sr/Br ratio and 14 C ages (Fig. 7).

An age-depth model was constructed for core SCR1-18-01 using the 10 14 C ages (Table 2) and the information provided by the radionuclides ( 137 Cs peaks at 1963 AD and 1955 AD) (Fig. 6) for the topmost part of the core. First, the sediment depth of core SCR1-18-01 was corrected by subtracting the 25 F3 layers, which were interpreted as "instantaneous" events, in order to build an event-free sedimentary record (Fig. 8A) [START_REF] Sabatier | 6-kyr record of flood frequency and intensity in the western Mediterranean Alps -Interplay of solar and temperature forcing[END_REF]. Then, an age-depth model was calculated by a smooth spline function using the R package Clam [START_REF] Blaauw | Methods and code for 'classical' age-modelling of radiocarbon sequences[END_REF]. The vertical blue bars (Fig. 8B) represent the ages of the 25 "instantaneous" deposits with uncertainties (2s) resulting from the age model. The mean sedimentation rate (without "instantaneous" deposits) is 0.47 +/-0.24 mm yr -1 .

Discussion

Sedimentary facies interpretation

Sedimentary facies F1 consists of mostly silty brown deposits, which contain only one single taxon of Miliolinella sp.. Miliolids are known to be particularly tolerant for increased salinity [START_REF] Murray | Ecology and Applications of Benthic Foraminifera[END_REF] and assemblages strongly dominated by miliolids are typically found in hypersaline lagoons. Thus they most likely represent the autochthonous fauna of the lagoon. This facies is also rich in organic matter, Br and S ("Organic Matter" endmember, Fig. 4B). This high organic matter content is probably related This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology to autochthonous algal productivity as terrestrial organic matter inputs through run-off reaching the lagoon from the inner part of this small karstic island is very limited.

The very small angular quartz grains found in the organic matrix are unlikely to originate from Scrub Island, which only comprises carbonates. Both the grain size and morphology can be interpreted as the result of fragmentation of larger quartz grains. Moreover, the angular quartz grains suggest that they have been transported in suspension, without an erosive rolling/saltation phase (Coude-Gaussen, 1991).

Furthermore, the very small mean grain size (< 5 µm) may indicate an aeolian transport, far away from the source, as reported by [START_REF] Van Der Does | Particle size traces modern Saharan dust transport and deposition across the equatorial North Atlantic[END_REF]. Therefore, we interpret these grains as long-rangetransported (LRT) aeolian particles, transported from the Saharan desert to this island. African dust is already known to be transported to the Caribbean, at least as far as Florida [START_REF] Prospero | African Droughts and Dust Transport to the Caribbean: Climate Change Implications[END_REF][START_REF] Muhs | Geochemical evidence for African dust inputs to soils of western Atlantic islands: Barbados, the Bahamas, and Florida[END_REF][START_REF] Muhs | Geochemical evidence for African dust and volcanic ash inputs to terra rossa soils on carbonate reef terraces, northern Jamaica, West Indies[END_REF][START_REF] Muhs | Soil genesis on the island of Bermuda in the Quaternary: The importance of African dust transport and deposition: African dust in Bermuda soils[END_REF]. The Saharan dust includes other particles such as clays and iron oxides [START_REF] Coude-Gaussen | Les poussières sahariennes. Cycle sédimentaire et place dans les environnements et paléoenvironnements désertiques[END_REF][START_REF] Muhs | Soil genesis on the island of Bermuda in the Quaternary: The importance of African dust transport and deposition: African dust in Bermuda soils[END_REF]. The strong positive correlation between Fe and Si on the PCA (Fig. 4B) suggests that Fe in F1 most probably had the same aeolian origin ("silicates" endmember, Fig. 4B). These two poles are the major components of facies F1 (Fig. 4C).

Based on these data, sedimentary facies F1 is interpreted as recording both the autochthonous lagoon sedimentation and probably aeolian sediment inputs.

Sedimentary facies F3 consists of 25 layers of carbonated sand with mostly aragonitic shell fragments.

These layers are plotting close to the "carbonates" endmembers (Fig. 4B) with high Ca and Sr contents found in primary marine carbonate minerals, including aragonite and high-Mg calcite. Since Br is associated with autochthonous organic matter in this lagoon, the synchronous variations of Sr/Br ratio and grain-size increase are used to identify these 25 layers (Fig. 5). Eleven intervals of facies 3 (Fig. 5) display large symbiont-bearing foraminifera A. gibbosa and A. angulatus, which are typical of open marine subtropical to tropical environments with a normal salinity. Based on their living environment and their abraded tests, it is likely that these taxa are allochthonous and that they were transported in the lagoon during marine incursions (e.g., [START_REF] Pilarczyk | Micropaleontology of the 2013 Typhoon Haiyan overwash sediments from the Leyte Gulf, Philippines[END_REF]. Most F3 layers exhibit a sharp basal contact and thin inland, with the number of these units also decreasing landward as attested from core correlation (Fig. 7). Consequently, F3 layers are interpreted as high-energy deposits resulting from overwash of the sandy barrier related to either hurricanes or tsunamis.

Sedimentary facies F2 (46 to 40 cm depth) is the only one showing large accumulations of intact Cerithideopsis costata shells associated with small bivalve shells. The large amount of shells explains the high counts of Sr for the "carbonates" endmember. This shell accumulation is found at the same period (1450-1635 AD) in both cores (Fig. 7), suggesting that it probably extended in the entire lagoon.

It could record a change in physical or chemical parameters inside the lagoon. The thickest F3 sandy layer (L#14, 61 to 47 cm depth in core SCR1-18-01) occurs just below facies F2, and was identified in core SCR1-18-03 (41 to 38 cm depth). Two hypotheses may explain such accumulation of Cerithideopsis costata shells in the lagoon. First, we assume that the massive sand accumulation revealed bay L#14 led to drastic changes in quantity and quality of sedimentary organic matter, sulfide contents, and sediment redox condition, compared to normal organic rich sediment (facies F1) as also reported in a shallow eutrophic lagoon from Sendai Bay in Japan [START_REF] Kanaya | Tsunami-induced Changes in a Shallow Brackish Lagoon Ecosystem (Gamo Lagoon) in Sendai Bay[END_REF]. Such changes in the habitat quality may explain the development of Cerithideopsis costata. According to the radiocarbon ages (Table 2), this change in macrozoobenthic assemblage lasted 200 years after the massive sand input and before the deposition of the next facies F1 layer. The second hypothesis is that the F3 deposit (Layer 14) could correspond to a high-energy event that may have breached the sand barrier causing the level of the lagoon to drop. A low water level would have resulted in a salinity increase in the lagoon. Indeed, Facies 2 displays high concentration of halite around the shells (Facies 2) (Fig. 3). Following this hypothesis, salinity would have become too high for Cerithideopsis costata, that develop in brackish water, leading to the death of the individuals and accumulation of their shells in the lagoon during this period.

Limitations of the study site for paleo tsunami and paleo hurricane chronicles

Since F3 layers are probably sediment records of high-energy marine flooding, the studied lagoon seems to represent an ideal site for recording past tsunamis or hurricanes. Today the sandy barrier separating the lagoon from the open ocean is 2 to 5 m-high from north to south. Therefore, a maximum wave height over 2 to 5 m is needed to overwash or overtop the dune crest. Such a runup may result from exceptionally high sea levels (e.g., [START_REF] Atwater | Effects of 2010 Hurricane Earl amidst geologic evidence for greater overwash at Anegada, British Virgin Islands[END_REF] reached during hurricanes, due to the combined effects of storm surge (resulting from low pressure effect and wind stress), wave setup, swash and infra gravity waves (e.g., [START_REF] Chaumillon | Storm-induced marine flooding: Lessons from a multidisciplinary approach[END_REF]. Alternatively, runups higher than 2 to 5 m may also occur during tsunamis (e.g., [START_REF] Atwater | Geomorphic and stratigraphic evidence for an unusual tsunami or storm a few centuries ago at Anegada, British Virgin Islands[END_REF]. The sensitivity of a given barrier to overwash may vary through time because of many factors that can be grouped as allogenic and autogenic [START_REF] Scileppi | Sedimentary evidence of hurricane strikes in western Long Island, New York: hurricane strikes in New York[END_REF]. One major allogenic parameter corresponds to sea level variations, since sea level rise increases the vulnerability of barriers to overwash. However, no major sea level changes have been reported over the last 1600 years in the Antilles [START_REF] Khan | Drivers of Holocene sea-level change in the Caribbean[END_REF]. Autogenic parameters, including the presence or absence of an inlet or a breach also control the barrier sensitivity to overwash [START_REF] Donnelly | 700 yr sedimentary record of intense hurricane landfalls in southern New England[END_REF][START_REF] Sabatier | 7000 years of paleostorm activity in the NW Mediterranean Sea in response to Holocene climate events[END_REF]. The sensitivity of a lagoon system to record a hurricane and/or a tsunami increases when the barrier is breached or cut by an inlet. After an overwash, barrier breach and/or lowering of the barrier may occur for a limited period of time and lead to a greater vulnerability to future overwash. It is very likely that the barrier morphology has evolved during the past 1600 years (e.g., [START_REF] Atwater | Geomorphic and stratigraphic evidence for an unusual tsunami or storm a few centuries ago at Anegada, British Virgin Islands[END_REF]. However, we do not have any constraints about such evolution, thus reconstruction of paleo intensities from the sediment records in the studied lagoon remains difficult. Indeed, estimating the frequency of marine-flooding sediment records from coarse sediment layers (F3 layers) must be done with caution. In fact, every F3 layer does not necessary correspond to a single short-term event. For example, if two such events occurred in a short period of time, this may lead to the deposition of two amalgamated sandy layers that cannot be differentiated. On the other hand, very high energy events may erode lagoon sediments, including previously deposited event layers, as reported on the Sendai Plain during the 2011 Tohoku-oki tsunami [START_REF] Shinozaki | Erosion of a paleo-tsunami record by the 2011 Tohoku-oki tsunami along the southern Sendai Plain[END_REF]. Thus, this cannot be completely discounted, although it is also possible that the frequency of high energy events is close to the frequency of sand layers recorded on Scrub Island.

Processes involved in high energy events

F3 high-energy deposits may either record hurricane or tsunami events. Hurricane and tsunami deposits mostly result from onshore transport of near-shore sediment and exhibit a number of similar characteristics (e.g., Morton et al., 2007). Many criteria have already been defined to distinguish tsunami from storm deposits (e.g., [START_REF] Goff | Sedimentary differences between the 2002 Easter storm and the 15th-century Okoropunga tsunami, southeastern North Island, New Zealand[END_REF]Morton et al., 2007 ;[START_REF] Engel | Tsunami deposits of the Caribbean -Towards an improved coastal hazard assessment[END_REF][START_REF] Kusumoto | Geological evidence of tsunamis in the past 3800 years at a coastal lowland in the Central Fukushima Prefecture, Japan[END_REF], however, these criteria are most of the time site-dependent. Among the 25 F3 deposits, two deposits display specific criteria which may contribute to their identification as tsunami records.

Tsunami deposits

The upper layer displaying specific criteria corresponds to layer 17 (L#17, Fig. 5). It is 4 cm thick in core SCR1-18-01. L#17 is also recorded in Core SCR1-18-03 (Fig. 7). L#17 is composed of a sandy layer with a mud layer at the top. The sandy part displays an upward small grain size decrease (530 to 470 µm), which most likely indicates that the sediment fell out of suspension (e.g., Morton et al., 2007). An intraclast, which is a rip up clast of the underlying cohesive substrate (facies F1), is visible in the sand layer (Fig. 3). Such feature occurs when the underlying deposit is eroded by the high energy flow and suspended in the water before being deposed, when the flow speed decreases (e.g., Morton et al., 2007). These characteristics are commonly used to identify tsunami deposits and thus have led us to interpret L#17 as a tsunami deposit.

Moreover, L#17 does not display salt-coated grains. Considering tsunami waves have longer wavelengths than hurricanes waves, tsunami deposits often contain records of deeper reworked sediment [START_REF] Uchida | Sources and depositional processes of tsunami deposits: Analysis using foraminiferal tests and hydrodynamic verification: Sources of tsunami deposits[END_REF].Variations of salt coating around grains (subfacies 3.1, 3.2 and 3.3, Fig. 3) could be a potential marker of the origin of sediment reworked by marine flooding. Salt coatings may result from halite precipitation on sand grains exposed to both sea spray /sea water and strong evaporation.

Such conditions are commonly found on beach barriers (e.g., [START_REF] Ward (nee Milne | Studies in ecology on a shell barrier beach section III chemical factors of the environment[END_REF] but also on land following tsunami inundation (e.g., [START_REF] Chagué-Goff | Environmental impact assessment of the 2011 Tohoku-oki tsunami on the Sendai Plain[END_REF], even one year after the event despite dilution by rainfall [START_REF] Chagué-Goff | Impact of Tsunami Inundation on Soil Salinisation: Up to One Year After the 2011 Tohoku-Oki Tsunami[END_REF], due to capillary action. Thus, abundance of salt coating could be an indicator of beach barrier sands. On the contrary, the absence of salt coatings can be related to an absence of strong evaporation, a situation which can be found in submarine sand, or sand from the lower shoreface (e.g., [START_REF] Ward (nee Milne | Studies in ecology on a shell barrier beach section III chemical factors of the environment[END_REF]. Thus, the absence of salt coating on grains in L#17 might indicate a deeper sediment source, farther away from the shoreline. Even though post-depositional processes should also be considered, the covering of sandy deposits by the fine grained facies 1 allows the preservation of halite coatings on the sandy grains.

Finally, the 2 cm thick mud layer above the sand deposit contains a large amount of wood and vascular plant remains. This concentration of plant remains shows an important terrestrial input in the lagoon that can be interpreted as resulting from the backwash during the L#17 event. Alternatively, this concentration in plants remains could also be due to the incorporation of vegetation eroded from the sand barrier by the tsunami wave. As organic matter is less dense, it is deposited on top of the tsunamis deposit out of suspension, as previously reported (e.g., [START_REF] Chagué-Goff | Expanding the proxy toolkit to help identify past events -Lessons from the 2004 Indian Ocean Tsunami and the 2009 South Pacific Tsunami[END_REF].

According to the age model (Fig. 8), this event is dated at 1720 cal. AD (1652-1810 cal. AD), which could correspond to the 1755 AD Lisbon tsunami [START_REF] Chester | The 1755 Lisbon earthquake[END_REF]. Although originating in the Eastern Atlantic, this tsunami was able to reach Scrub Island lagoon, which is oriented towards the west. This could be explained by local tsunami amplification due to the shallow bathymetry of the area and the interconnected channel between Anguilla and Scrub, with for example a resonant amplification of the tsunami waves between Anguilla and Scrub (e.g., [START_REF] Munger | Resonance in Hawaii waters from the 2006 Kuril Islands Tsunami: the 2006 Kuril Islands tsunami[END_REF]. Layer L14 (L#14, Fig. 5) is the older layer displaying specific criteria. First, it is the thickest (14 cm thick in SCR1-18-01) among all the F3 layers in both cores (Fig. 7), possibly indicating the occurrence of an exceptional marine incursion. It is composed of a massive single sandy bed. The absence of grain size variations is indicative of an extremely rapid deposition such as would occur when flow decelerates between the uprush and backwash phases during a tsunami (Morton et al., 2007).

However, the CT image (Fig. 5) displays some internal mud laminae at 57.5 and 59 cm depth. These layers are related to the suspension load during the waning stage between waves, with sufficient time for mud to settle between successive waves [START_REF] Jaffe | Identification and interpretation of tsunami deposits from the June 23[END_REF][START_REF] Naruse | Features and formation processes of multiple deposition layers from the 2004 Indian Ocean Tsunami at Ban Nam Kem, southern Thailand: Multiple deposition layers from tsunami[END_REF]. L#14 shows a mix of salt coated and non-salt coated grains, probably indicating sediment reworked from both the barrier This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology and the shoreface. Thus, these criteria have led us to interpret this deposit as the result of a major tsunami event. Finally, the presence of the single facies F2 deposit just above L#14 suggests that this event was the only one able to have a long-term environmental impact (changes in nutrient inputs and/or salinity for 200 years) inside the lagoon over the last 1600 years BP, reinforcing the hypothesis of an exceptional event.

L#14 is dated at 1415 cal. AD (1364-1469 cal. AD). By comparison with others studies in the Caribbean region, this age corresponds to the late Middle Age event identified in St Thomas (US Virgin Islands) dated between 1200 and 1450 cal. AD [START_REF] Fuentes | Sand Scripts of Past Tsunamis in Coastal Ponds of St[END_REF] but also in Anegada (British Virgin Islands), where it was dated between 1200 and 1480 cal. AD [START_REF] Atwater | Extreme waves in the British Virgin Islands during the last centuries before 1500 CE[END_REF]. These two islands are located between 150 and 200 km northwest from Scrub Island, close to the seismically active Puerto Rico Trench (Fig. 1B), which is a possible source for a tsunami in the Caribbean [START_REF] Atwater | Extreme waves in the British Virgin Islands during the last centuries before 1500 CE[END_REF].

In Bonaire (south Caribbean) sublittoral sediments interrupting onshore sedimentary sequences on the eastern shore (Boka Washikemba), provided evidence for a major wave impact shortly before 500 cal. BP (1450 cal. AD), which most likely corresponds to a tsunami [START_REF] Engel | Coastal stratigraphies of eastern Bonaire (Netherlands Antilles): New insights into the palaeo-tsunami history of the southern Caribbean[END_REF]. In the same region, the study of a sediment core from a saline lagoon on Cayo Sal Island, (western Venezuela) showed probably tsunami-laid reworked peat [START_REF] Weiss | A Saline Lagoon on Cayo Sal, Western Venezuela[END_REF]. This event is dated between 1180 and 1450 AD [START_REF] Weiss | A Saline Lagoon on Cayo Sal, Western Venezuela[END_REF], which correspond to an age between 1046 and 1481 cal AD [START_REF] Reimer | IntCal13 and Marine13 Radiocarbon Age Calibration Curves 0-50,000 Years cal BP[END_REF]. These two islands are more than 800 km south from the Puerto Rico Trench, indicating that if all the study sites cited above recorded the same tsunami, it most probably hit the whole Caribbean area.

It is also possible that coarse layers dated to the expected age of this tsunami in other study sites have been misinterpreted as hurricane or storm events, such as in St-Martin 25 km from Scrub Island, within a lagoon with the same orientation [START_REF] Malaizé | Hurricanes and climate in the Caribbean during the past 3700 years BP[END_REF] or in Vieques, Puerto Rico with a single high energy event during a period with fewer intense hurricane strikes [START_REF] Donnelly | Intense hurricane activity over the past 5,000 years controlled by El Niño and the West African monsoon[END_REF] or in Belize where the event was described as "much stronger than all other storms in the record" [START_REF] Mccloskey | 5000 year sedimentary record of hurricane strikes on the central coast of Belize[END_REF]. If all the above-cited sediment records are related to the same event, their wide geographical extent would exclude the hypothesis of a hurricane record, as one hurricane generally cannot cross both the north and south of the Caribbean. Finally, while most of these studies This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology proposed an age for this event with a more than a 200-year uncertainty, the new age constrain provided by our age model gives a much more accurate age with only a 100-year uncertainty. The identification of new sedimentary records of this event would therefore provide an opportunity to further refine its chronology and source. A record of this event might be preserved in others islands in the northern or southern Caribbean and it should be investigated.

Hurricane chronicle and climate forcing

If layers L#14 and L#17 are related to tsunami events, the 23 remaining sandy layers (F3 deposits) deposited in the studied lagoon over the last 1600 years, can probably be interpreted as resulting from storms/hurricanes (Fig. 8). Among those 23 layers, the three most recent F3 deposits occurred since the mid-19th century and can be associated with historical hurricanes. Intriguingly only three high-energy events are recorded in the lagoon as sandy layers, while 13 hurricane trajectories (Table 1) passed less than 30 km from Scrub Island since 1852 AD (coast.noaa.gov/hurricanes, 2020). Thus, we assume that Scrub lagoon has only recorded the closest and most intense hurricanes.

According to 137 Cs activities, L#25 was deposited between 1955 (first 137 Cs fallouts) and 1963 AD (maximum nuclear weapon test in the Northern Hemisphere, Fig. 6). This layer can be tentatively related to the only hurricane that passed within 30 km from Scrub between 1955 and 1963, the Category 3 Hurricane Donna, which took place in 1960 AD (Table 1, coast.noaa.gov/hurricanes, 2020). According to the short-lived radionuclide measurements, L#24 occurred before 1955 AD but during the 20 th century, as the sediment still presents 210 Pbex activities (Fig. 6), and based on our age model, it is dated between 1935 and 1959 AD (Fig. 8). There were two hurricanes in the region during this period: Category 3 Hurricane Dog (1950) and Category 1 Hurricane Alice (1955) (Table 1). As Dog seems to be both closer and stronger than Alice, it may be recorded by L#24. L#23 is dated between 1903 and 1957 AD with the best age being 1930 AD according to the age model (Fig. 8). L#23 can be attributed to the unnamed category 3 hurricane that occurred in 1922 AD (Table 1).

Based on the instrumental data available, it appears that three conditions must be fulfilled for a given hurricane to leave a sedimentary record in the studied lagoon, assuming enough sediment This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology availability: (1) at least category 3 on the Saffir-Simpson scale, (2) a hurricane track less than 30 km from Scrub Island and (3) a hurricane heading southward of Scrub and northwest of Anguilla (Fig. 2).

It is likely that the hurricane path must face the barrier to be recorded in the lagoon and thus must reach northwest Anguilla, as Anguilla Island appears to act as a barrier for hurricanes passing south of the island. This could explain why Category 5 Hurricane Irma and Category 3 Hurricane Lenny were not recorded in the studied lagoon, as their path bypassed Anguilla from the south (Fig. 2). Moreover, hurricanes passing north of the lagoon cannot be recorded.

The studied lagoon provides an opportunity to estimate long term hurricane activity in the region over the last 1600 years. A 101-year window event frequency was made for Scrub Lagoon (Fig. 9D) based on the chronology of the hurricane deposits in the sediment record. Six time periods are characterized by more frequent hurricane sediment records (at least two per century): 445-525, 720-835, 1080-1230, 1625-1695, 1745-1890 and 1920-1970 cal AD (Fig. 9D). The longest period with a relative high frequency of hurricanes (1080-1230 AD) occurred during the Medieval Warm Period (800-1300 AD).

It is known that during this period, the sea surface temperatures (SSTs) were high in the Atlantic Main Development Region of hurricanes (MDR), which extends in the east from Cape Verde to Guinea in Africa, to the Caribbean Sea in the west [START_REF] Wallace | Intense Hurricane Activity Over the Past 1500 Years at South Andros Island, The Bahamas[END_REF]. [START_REF] Murakami | Dominant effect of relative tropical Atlantic warming on major hurricane occurrence[END_REF] showed that high frequency hurricanes periods seems to be linked to warm SSTs in the tropical North Atlantic, as hurricanes obtain more energy from warmer oceans during their westward propagation from the MDR.

On the other hand, five time periods are characterized by an absence of hurricane in the sediment record: ~560, ~670, 965-1020, 1400-1600, ~1740 cal AD (Fig. 9D). The longest period without hurricane (1400-1600 AD) occurred during the first part of the Little Ice Age (1450-1900 AD), when the SSTs where low in the Atlantic Ocean [START_REF] Wallace | Intense Hurricane Activity Over the Past 1500 Years at South Andros Island, The Bahamas[END_REF]. However, the period with the highest frequency also occurred from 1740 to 1890 cal AD, when SSTs are supposed to be low in the Atlantic Ocean. [START_REF] Burn | A sediment-based reconstruction of Caribbean effective precipitation during the 'Little Ice Age' from Freshwater Pond, Barbuda[END_REF] showed that in Barbuda Island (Fig. 1), El Niño Southern Oscillation (ENSO) combined with the Atlantic Multidecadal Oscillation (AMO) appear to have exerted some additional influence on the rainfall activity from 1720 to 1860 cal AD, which could indicate the influence of these parameters in the Lesser Antilles and may explain the singularity of the increase in the hurricane frequency in Scrub Island during this period.

Scrub Island sediment record brings new knowledge about variations in past hurricane activity in the Caribbean. Thus we compared this new chronicle to other sites where hurricane sediment records are available: A/ Salt Pond, Massachusetts [START_REF] Donnelly | Climate forcing of unprecedented intense-hurricane activity in the last 2000 years: Donnelly et al[END_REF], B/ South Andros, Bahamas [START_REF] Wallace | Intense Hurricane Activity Over the Past 1500 Years at South Andros Island, The Bahamas[END_REF], C/ Lighthouse Reef blue hole, Belize [START_REF] Denommee | Climatic controls on hurricane patterns: a 1200y near-annual record from Lighthouse Reef[END_REF] (Fig. 9A,B,C). From this comparison (Fig. 9), it appears that Scrub and South Andros (Bahamas) records are in phase, except from a short period between 900 and 1050 cal AD and at lesser extend between 1230 to 1500 cal AD with an increase in the Bahamas hurricane chronicle. On the other hand, the Long Pond (Massachusetts, USA) signal is in antiphase with Scrub Island, except from 445 to 525 cal AD, where storm frequency increases in both sites, but with a larger increase for Long Pond. The signal in the Lighthouse Reef blue hole (Belize) is mostly not in phase with the Scrub Island signal, except for the periods 1400-1600 and 1920-1970 cal AD.

Differences in hurricane sediment records between Scrub Island and the others sites can be partially explained by the position of Scrub Island with respect to hurricane tracks. Compared to the three other sites, Scrub Island is the most eastern one, located at the forefront of many hurricane trajectories heading westward to the northern part of Gulf of Mexico/Caribbean. Among the 13 historical hurricanes that passed within 30 km from Scrub, two also hit the Bahamas, two headed towards Belize but did not reach this area and most of them have made their way close to the American East coast but never reached the Massachusetts region (Fig. 9). Nevertheless, even if this regional comparison provides a relative coherent pattern, small differences of hurricane activity between each site could be also explained by the hurricane intensity changes between Scrub Island and the other sites and by the long term sensitivity variations of the different sedimentary systems for recording hurricanes.

However, the antiphase signal of the Massachusetts with respect to the three other sites may provide evidence of a latitudinal forcing for the hurricane tracks. Thus, [START_REF] Wallace | Intense Hurricane Activity Over the Past 1500 Years at South Andros Island, The Bahamas[END_REF] showed that periods of intense hurricane activity in the Bahamas correspond to a position further north of the ITCZ (Haug This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology et al., 2001) (Fig. 9B,E), except for the 640-815 cal AD period. For the Scrub Island signal, some periods (445-525 and 1745-1840 cal AD) with numerous hurricane sediment records, correspond to a northern position of the ITCZ (Fig. 9D,E), which is consistent with the Bahamas signal. However, other periods high hurricane record in Scrub Island correspond to a more southern ITCZ position (720-835, 1080-1230 and 1625-1695 cal AD, Fig. 9,D,E) showing that for the Scrub Island signal, the correspondence between the ITCZ position and the hurricane activity intensification is not obvious. Thus, other climatic forcing parameters are expected to influence hurricane tracks. Therefore, it is necessary to investigate other sites in the Caribbean in order to better understand climatic parameters modulating the trajectory of hurricanes.

Conclusion

Using sedimentological, geochemical, microfaunal and chronological analyses of two cores from a small coastal lagoon on Scrub Island in the north eastern Caribbean region, we identified 25 marine-sourced sand layers alternating with lagoon deposits. These sand layers most probably result from high-energy marine flooding related to tsunami or hurricane events.

Based on sedimentological criteria and correlations with already published data, two of these 25 sand layers were interpreted as tsunami deposits. The most recent presenting intraclasts and a mud drape is associated with the transatlantic tsunami that was generated by the 1755 AD Lisbon earthquake already recorded in many Caribbean islands. The oldest is the thickest homogenous sandy layer recorded in the lagoon and dated at 1415 cal. AD (1364-1469 cal. AD). It displays two internal mud laminae, related to the suspension load of the waning stage between waves. Published studies in the Caribbean region suggest that this event has left a sedimentary record in other islands, although sometime interpreted as a hurricane. As this event was recorded in both the northern and the southern part of the Caribbean, its large extent supports a tsunamigenic source. The presence or absence of salt coating on sand grains, indicating a barrier or lower shoreface origin for sand grains, respectively, could be used as a new criterion to distinguish tsunami (reworking both barrier and shoreface sediments) from hurricane (mostly reworking barrier sediments) deposits. This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology The 23 remaining sandy layers were interpreted as resulting from hurricanes. The chronology established with short lived radionuclides suggests that the three most recent deposits were associated with historical hurricanes and it appears that three conditions must be fulfilled for a given hurricane to leave a record in the studied lagoon: (1) at least category 3 on the Saffir-Simpson scale, (2) a storm track at less than 30 km from Scrub Island and (3) a storm track located southwestward with respect to the studied lagoon.

The studied sedimentary sequence provides an opportunity to explore the past hurricane activity in the region over the last 1600 years. Six periods of increase in hurricane frequency and five periods without hurricane events are suggested. Those variations in hurricane frequency are similar to the variations recorded in the Bahamas and are in antiphase with the Massachusetts (USA) hurricane chronicle, which could provide evidence of a latitudinal forcing for the hurricane tracks through time.

The position of the ITCZ has already been proposed as a forcing parameter modulating the hurricane tracks but as its relation with the Scrub Island chronicle is not obvious, other climatic forcing parameters are probably involved.

Finally, the position of Scrub lagoon sediment-fill in the north eastern part of the Caribbean area provides a new and unique sedimentary record of both tsunamis and hurricanes, and this study helps gain a better understanding of the long-term climate and geodynamic history of this region particularly vulnerable to those destructive events. This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology

Figure 1 .

 1 Figures and Tables

Figure 2 .

 2 Figure 2. Historical hurricane tracks (1852-2017) passing within 30 km of the westernmost Scrub Island

Figure 4 .

 4 Figure 4. Geochemical data for core SCR1-18-01. A: From left to right, picture, sedimentary log, XRF

Figure 5 .

 5 Figure 5. Data for core SCR1-18-01. From left to right: F3 Layers (in red) associated to the orange

Figure 7 .Figure 8 .

 78 Figure 7. Sedimentary logs for cores SCR1-18-01 and SCR1-18-03 with the depth of the 14C ages in

Figure 9 .

 9 Figure 9. 101-year moving window event frequency on (A) Salt Pond, MA[START_REF] Donnelly | Climate forcing of unprecedented intense-hurricane activity in the last 2000 years: Donnelly et al[END_REF]

Table 1 .

 1 Hurricanes that passed within 30 km from Scrub Island (Anguilla) from 1852 to 2017 (coast.noaa.gov/hurricanes, 2020). SSHWS: Saffir-Simpson hurricane wind scale. Kt = knot, mb = millibar.

	Year	Name	Month	Hurricane category (SSHWS) within 30 km around Scrub	Distance hurricane-Scrub (km)	Hurricane path with respect to Anguilla Island	Wind speed (kt)	Pressure (mb)
	2017	Irma	September	H5	25	SW	155	914
	2014	Gonzalo	October	H1	18	NW	74	984
	2010	Earl	September	H2	18	NE	95	967
	1999	Lenny	November	H2	26	SW	85	975
	1995	Luis	September	H4	8	NE	115	942
	1960	Donna	September	H3	21	NW	110	952
	1955	Alice	January	H1	26	SE	65	991
	1950	Dog	September	H3	17	NW	105	NA
	1922 Unnamed	September	H3	15	NW	100	NA
	1906 Unnamed	September	H2	13	NE	90	NA
	1899 Unnamed	September	H3	29	NE	100	NA
	1871 Unnamed	September	H1	23	NE	75	NA
	1852 Unnamed	September	H1	26	NW	70	NA

C analyses were acquired thanks to the CNRS-INSU ARTEMIS national radiocarbon AMS measurement programme at Laboratoire de Mesure 14C (LMC14) in the CEA Institute at Saclay (French Atomic Energy Commission). The authors thank the Laboratoire Souterrain de Modane (LSM) facilities for the gamma spectrometry measurements and Environnement, Dynamique et Territoires de Montagne for the X-ray fluorescence analyses. The Lidar DEM of Anguilla is a courtesy of the Government of Anguilla (Department of Disaster Management) for academic research projects dedicated to seismic and tsunami hazard in Anguilla.

Acknowledgements

This work is part of the CARQUAKES project (ANR-17-CE03-0006). The objective of the CARQUAKES project is to improve the catalog of large earthquakes and tsunamis in the Lesser Antilles and characterize the related hazards by applying an innovative and novel multidisciplinary approach combining several state-of-the-art methods of offshore and onshore paleoseismology and tsunami modelling.

We thank the skipper Nicolas Jammes, who was involved in the March 2018 field survey. This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology

Figure 6. SCR1-18-03 short-lived radionuclide data with the excess 210Pb in logarithmic scale associated with the 137Cs (NWT: Nuclear Weapon Tests; FF: First Fallout recorded) and 241Am profiles and Sr/Br XRF ratio.

This is a non-peer reviewed preprint submitted to EarthArXiv The manuscript is under review at Sedimentary Geology

Figure 3. Facies of core SCR1-18-01. On the left of the figure: Facies, photo and sedimentary log. On the right of the image: the three main facies of the core. For every facies there is: a picture of a thin slide on the left, SEM images, geochemical cartographies (with Ca in green, Mg in red, Si in yellow, Na in blue and Cl in purple). On the top right corner of Facies 3, there is a photograph of a foraminifera (Amphistegina gibbosa) taken from an optical microscope.