Speranta-Maria Popescu
email: speranta.popescu@gmail.com

Jean-Pierre Suc
email: jeanpierre.suc@gmail.com

Séverine Fauquette
email: severine.fauquette@umontpellier.fr

Mostefa Bessedik
email: mostefa_bessedik2001@yahoo.fr

Gonzalo Jiménez-Moreno
email: gonzaloj@ugr.es

Cécile Robin
email: cecile.robin@univ-rennes1.fr

Loïc Labrousse
email: loic.labrousse@sorbonne-universite.fr

Mangrove distribution and diversity during three Cenozoic thermal maxima in the Northern Hemisphere (pollen records from the Arctic -North Atlantic -Mediterranean regions) Short running title: Cenozoic North Hemisphere mangrove diversity

Keywords: Avicennia, other mangrove taxa (Rhizophoraceae, Nypa, Xylocarpus, Pelliciera, etc.) Avicennia, Climate change, Eocene-Miocene, Mangrove, Range limit, Thermal optimum

whether they are published or not. The documents may come

INTRODUCTION

Inter-tropical mangrove vegetation comprises major trees such as Avicennia, Rhizophoraceae (Rhizophora, Bruguiera, Ceriops, Kandelia), Nypa, Sonneratia, and other less abundant plants such as Excoecaria, Xylocarpus, Pelliciera, Aegialitis, Heritiera, Scyphiphora and Brownlowia [START_REF] Tomlinson | The botany of mangroves[END_REF]. Mangrove distribution today reveals latitudinal differences between different geographic areas partly due to the influence of marine currents and partly to plant sensitivity to different air and water temperatures (Figure 1; [START_REF] Tomlinson | The botany of mangroves[END_REF]Duke, 1992;Duke et al., 1998;[START_REF] Kao | Sensibility to chiling temperatures and distribution differ in the mangrove species Kandelia candel and Avicennia marina[END_REF][START_REF] Osland | Climatic controls on the global distribution, abundance, and species richness of mangrove forests[END_REF]. If >1,000 mm, annual rainfall is also an important factor affecting the distribution, stature and diversity of mangroves [START_REF] Osland | Climatic controls on the global distribution, abundance, and species richness of mangrove forests[END_REF][START_REF] Bardou | Variability in the fundamental versus realized niches of North American mangroves[END_REF]. Mangrove establishment is closely linked to hydrodynamics and, particularly, to sea-level changes (Woodroffe et al., 2016).

Avicennia occurs in a slightly wider latitudinal range than Rhizophora, but the generally observed latitudinal difference between these genera (median value 1.8°) is 8-9° in northern New Zealand and southern Australia [START_REF] Quisthoudt | Temperature variation among mangrove latitudinal range limits worldwide[END_REF]. Although the lowest temperature limits tolerated by Avicennia, (e.g., 8.1°C minimum air temperature, 12.7°C minimum water temperature) differ significantly from those tolerated by Rhizophora (e.g., 13.1°C minimum air temperature, 16.4°C minimum water temperature), the difference is not enough to explain the observed differences in latitude distribution [START_REF] Quisthoudt | Temperature variation among mangrove latitudinal range limits worldwide[END_REF]. Freezing appears to be a critical factor in limiting mangrove expansion [START_REF] Stuart | The role of freezing in setting the latitudinal limits of mangrove forests[END_REF] while resistance to freezing may drive the northward expansion of North American mangrove in response to current climate warming [START_REF] Cook-Patton | Convergence of three mangrove species towards freeze-tolerant phenotypes at an expanding range edge[END_REF][START_REF] Bardou | Variability in the fundamental versus realized niches of North American mangroves[END_REF].

Avicennia and Rhizophora are emblematic mangrove genera because they occur in both the Atlantic East Pacific (AEP) and Indo-West Pacific (IWP) provinces although they are represented by different species (Figure 1; [START_REF] Tomlinson | The botany of mangroves[END_REF]Duke et al., 1998;Ellison et al., 1999). Some genera only occur in one of the provinces (Pelliciera to the west; Sonneratia, Xylocarpus and Nypa to the east; Figure 1).

The discovery of mangrove vegetation consisting of only Avicennia inhabiting the Mediterranean shorelines during the Miocene (Bessedik, 1981a) advanced our knowledge of mangrove history [START_REF] Plaziat | History and biogeography of the mangrove ecosystem, based on a critical reassessment of the paleontological record[END_REF][START_REF] Srivastava | Evolution and paleobiogeography of mangroves[END_REF]. More recently and surprisingly, Avicennia was recorded up to Arctic latitudes and even near the North Pole during the Early Eocene (Suan et al., 2017;Salpin et al., 2019;Suc et al., 2020). Accordingly, the following question arose: did the poleward limit of Avicennia compared with that of the other mangrove taxa increase or decrease after the Early Eocene? To answer this question, pollen records containing mangrove taxa from three Cenozoic thermal maxima were selected for comparison with present-day mangrove distribution: Palaeocene-Eocene Thermal Maximum (PETM: 56 Ma; [START_REF] Westerhold | Astronomical calibration of the geological timescale: middle Eocene gap[END_REF], Early Eocene Climatic Optimum (EECO: 54-49 Ma; Westerhold et al., 2020), and Mid-Miocene Climatic Optimum (MMCO: 17-14 Ma;Zachos et al., 2001). The Early Eocene pollen records in which Avicennia is the only mangrove tree are limited to the Arctic domain (Suan et al., 2017;Salpin et al., 2019;Suc et al., 2020), and the Mid-Miocene pollen records in which Avicennia is the only mangrove tree are limited to the Mediterranean domain (Bessedik, 1981a[START_REF] Bessedik | Recherches palynologiques sur quelques sites du Burdigalien du midi de la France[END_REF](Bessedik, , 1984;;Jiménez-Moreno & Suc, 2007;Jiménez-Moreno et al., 2008). Hence, we chose to focus on the North Atlantic by analysing new locations and using earlier data (Table S1). The results of this work may inform potential future distribution and diversity of mangroves in response to current climate warming with the need to provide increasing protection against anthropic damage (Giri et al., 2011).

MATERIALS AND METHODS

The pollen records concerned are shown on the palaeogeographic maps in Figure 2 (PETM and EECO) and Figure 3 (MMCO) and listed in Table S1. They were aligned along an Atlantic latitudinal transect (including the Mediterranean region for the MMCO) to enable us to locate the threshold which separates the diversified mangrove from impoverished mangrove containing only Avicennia. The study concerns clayey sediments which are usually excellent deposits for pollen preservation.

The pollen data from each location have been dated independently, most often by micropalaeontology, as specified in Table S1. We selected the pollen spectra that indicated the warmest conditions in the selected records where the expected warming event is diffuse. The duration of each pollen record was appraised by fitting the pollen assemblages and their variations to the reference oxygen isotope curve within the originally defined biostratigraphic interval (see Figure S1 and explanation herein).

Palaeolatitude estimates were deduced from the global Eulerian rotation poles database from [START_REF] Torsvik | Phanerozoic polar wander, palaeogeography and dynamics[END_REF], using the Paleolatitude.org online toolbox [START_REF] Van Hinsbergen | A paleolatitude calculator for paleoclimate studies[END_REF] and then compared to regional maps. Uncertainties vary from ± 2 to ± 3 latitude degrees. For location 1 in the PETM (Figure 2) uncertainty might be higher due to the uncertain position of the Lomonosov Ridge prior to the Eurasian Basin opening but conservative reconstructions place it north of Greenland since 70 Ma (Gion et al., 2017). The 76°N and 78°N palaeolatitudes are probably minimum estimates for PETM and EECO at location 1, respectively (Table S1). The computed position of location 3 (Figure 2) during the EECO is consistent with recent regional palaeogeographical reconstructions (Table S1; Eberle & Greenwood, 2012). For European sites and the Tethyan realm, computed palaeolatitudes are systematically 6° to 7° lower than those mentioned in regional reconstructions [START_REF] Meulenkamp | Tertiary palaeogeography and tectonostratigraphic evolution of the Northern and Southern Peri-Tethys platforms and the intermediate domains of the African-Eurasian convergent plate boundary zone[END_REF]. This discrepancy is mainly explained by the northward rotation of extra-Alpine stable Europe since 50 Ma at least [START_REF] Torsvik | Global plate motion frames: toward a unified model[END_REF]. For the MMCO, as locations 2, 8 and 9 are situated in unconstrained mobile regions, their palaeolatitude was deduced from latitude changes at adjacent locations.

The samples analysed in this work, plus those analysed earlier by our team (Table S1), were processed using a standard protocol: acid digestion (HCl, HF), concentration using ZnCl 2 (at density 2.0), and sieving through a 10-µm nylon mesh. A 40 µl volume of residue was mounted between the coverslip and microscope slide using glycerol.

The major methodological and conceptual contribution of this study is the use of a botanical approach for the Palaeogene samples. This approach was made possible by considering all the morphological characters of the pollen instead of just a few (often secondary). Details on Avicennia and other mangrove taxa are provided in Supporting Information (Figures S1-S10). In addition, we performed pollen counts (at least 100-150 pollen grains per sample excluding over-represented taxa such as Pinus), which is another novelty. Pollen data are shown in synthetic pollen diagrams where the taxa are grouped according to both their present-day ecological significance and to their behaviour during the Cenozoic (Table S2; Suc et al., 2018Suc et al., , 2020)).

Taxa are mainly grouped according to the thermal classification of Nix (1982) with some emphasis on the woody mangrove: Avicennia; other mangrove taxa; other megathermal plants which require a mean annual temperature (MAT) higher than 24°C; mega-mesothermal plants that require a MAT between 24°C and 20°C; mesothermal plants that require a MAT between 20°C and 14°C; Pinus plus indeterminable Pinaceae devoid of thermal significance because of their low level in botanical identification; mesomicrothermal plants that require a MAT between 14°C and 12°C; microthermal plants that require a MAT under 12°C; plants of no significance because of their cosmopolitan status at the family or genus level; Cupressaceae p.p. (Cupressus-Juniperus type); herbaceous plants. A complete list of the identified taxa and additional details on the ecological groups of plants are provided in Table S2.

Some reconstructed terrestrial palaeoclimate parameters taken from pollen records are used to discuss our results. These data come from the Climatic Amplitude Method (Fauquette et al., 1998), which, based on comparison with >6000 present-day pollen records distributed worldwide, relies on the relationship between the relative abundance of each taxon and the climate. To obtain more refined estimates, this method accounts not only for the occurrence/absence criterion but also for pollen grain percentages. The reconstructed climatic values concern the low-elevation vegetation, meso-microthermal and microthermal taxa being excluded from the process. Pinus, which inhabits different vegetation belts, from the lowest to the highest belts, especially in the Mediterranean region, was also excluded from the calculation.

The advantage of applying this 'Quaternary-Neogene' palynological approach to the Palaeogene samples is that it not only provides reliable information on the palaeoecosystems but also helps to establish robust homogeneous data.

Marine pollen records are reliable indicators of the occurrence of mangrove vegetation along the shoreline whether they are supplied by air or fluvial transport as demonstrated by studies on modern pollen sedimentation [START_REF] Hooghiemstra | Pollen and spore distribution in recent marine sediments: a record of NW-African seasonal wind patterns and vegetation belts[END_REF][START_REF] Caratini | Sédimentation palynologique actuelle sur le plateau continental de Côte d'Ivoire[END_REF][START_REF] Poumot | Palynological evidence for eustatic events in the tropical Neogene[END_REF][START_REF] Somboon | Palynological study of mangrove and marine sediments of the Gulf of Thailand[END_REF][START_REF] Bengo | La sédimentation pollinique dans le Sud-Cameroun et sur la plateforme marine à l'époque actuelle et au Quaternaire récent: étude des paléoenvironnements[END_REF][START_REF] Phuphumirat | Pollen distribution and deposition in mangrove sediments of the Ranong Biosphere Reserve, Thailand[END_REF]. For some of the study areas, the distance travelled by mangrove pollen grains is more than a few kilometres, indeed even after several dozen kilometres percentages can be 5-10% of the pollen sum [START_REF] Hooghiemstra | Pollen and spore distribution in recent marine sediments: a record of NW-African seasonal wind patterns and vegetation belts[END_REF][START_REF] Caratini | Sédimentation palynologique actuelle sur le plateau continental de Côte d'Ivoire[END_REF][START_REF] Bengo | La sédimentation pollinique dans le Sud-Cameroun et sur la plateforme marine à l'époque actuelle et au Quaternaire récent: étude des paléoenvironnements[END_REF]. Such data are of great importance for the reliability of our past mangrove records, all located relatively close to the land (Figures 23). In addition, some modern pollen records show high variability in mangrove pollen percentages with respect to the whole pollen flora: the highest percentages are recorded in front of large mangroves, the lowest percentages in front of weakened mangroves [START_REF] Hooghiemstra | Pollen and spore distribution in recent marine sediments: a record of NW-African seasonal wind patterns and vegetation belts[END_REF][START_REF] Caratini | Sédimentation palynologique actuelle sur le plateau continental de Côte d'Ivoire[END_REF][START_REF] Bengo | La sédimentation pollinique dans le Sud-Cameroun et sur la plateforme marine à l'époque actuelle et au Quaternaire récent: étude des paléoenvironnements[END_REF] or dwarf mangroves (Willard et al., 2001). It will be recalled that in these modern records, Avicennia pollen is usually under-represented in comparison with other mangrove taxa, particularly Rhizophoraceae (e.g., [START_REF] Somboon | Palynological study of mangrove and marine sediments of the Gulf of Thailand[END_REF].

RESULTS

Palaeocene-Eocene Thermal Maximum

Avicennia was the only mangrove taxon we recorded in the Arctic pollen floras (locations 1-2; Figures 2,4). These floras were also very poor in megathermal plants, as they are only represented by two taxa, both at very low percentages (Figure 4; Table S2). In southern Greenland (location 5; Figure 2), larger quantities of Avicennia were recorded than in Arctic samples, along with a small number of other mangrove taxa (Rhizophoraceae, Xylocarpus, Brownlowia) and small percentage of a few megathermal plants (Figure 4; Table S2). At Noirmoutier (location 7; Figure 2), Avicennia was rarely recorded but small percentages documented three other mangrove trees (Rhizophoraceae, Xylocarpus, and Nypa) and megathermal plants (Figure 4; Table S2). In the North Pyrenean Gulf (location 8; Figure 2), Avicennia pollen was found in small quantities with high percentages of Nypa and moderate amounts of a few megathermal plants (Figure 4; Table S2). Offshore northwestern Africa (location 11; Figure 2), Avicennia was found abundantly along with several other mangrove trees (Rhizophoraceae, Excoecaria, Xylocarpus, and possibly Sonneratia-type -see comment in Supporting Information) in equal quantities and with significant percentages of some megathermal plants (Figure 4; Table S2).

Early Eocene Climatic Optimum

As in the PETM, Avicennia was the only mangrove tree recorded in the Arctic pollen floras during the EECO (locations 1 and 3; Figures 2,5). These floras were also very poor in megathermal plants which were only represented by very small percentages of six taxa (Figure 5; Table S2). We found Avicennia pollen in significantly larger quantities with low percentages of other mangrove taxa (Rhizophoraceae, Xylocarpus, Brownlowia, Scyphiphora, Excoecaria, cf. Heritiera, and possibly Sonneratia-type) offshore northwestern Europe and offshore southern Greenland (locations 4 and 5; Figures 2,5). A similar pollen flora characterised the Belgium Basin (location 6; Figure 2) where Avicennia was accompanied by Rhizophoraceae, Nypa and Sonneratia-type and an increasing number of megathermal plants (Figure 5; Table S2). Small to moderate quantities of Avicennia pollen were observed in the North Pyrenean Gulf (locations 9-10; Figure 2), along with a large quantity of Nypa and several other woody mangrove taxa (Rhizophoraceae, Pelliciera, Xylocarpus, Aegialitis and Sonneratia-type); the accompanying megathermal plants were abundant and present at significant percentages (Figure 5; Table S2).

Mid-Miocene Climatic Optimum

The northernmost known pollen flora consisting of only Avicennia indicating mangrove vegetation, occurred together with very few megathermal taxa, was located at 45°N palaeolatitude (location 1; Figures 3,6). Avicennia was commonly recorded south of 41°N (locations 4-7), usually at a low percentage except at locations 4 and 7, and with no other mangrove taxa (Figures 3,6; Tables S1,S2). Megathermal plants were diversified at locations 4 and 7 but at relatively low percentages (Figures 3,6; Table S2). In contrast, location 10 (Figure 3) contained neither Avicennia pollen nor megathermal plants, despite being at an almost similar palaeolatitude to locations 4-6 on the Atlantic side (Figure 6; Table S2).

DISCUSSION

Three thermal optima were chosen as periods during which climatic conditions favoured maximum spreading of Avicennia, and possibly other mangrove taxa accompanied by diverse megathermal taxa, towards high latitudes. In addition, the distribution and diversity of past mangroves during particularly warm periods can be compared to the present-day context characterised by climate warming. The results we obtained from our analyses of pollen floras located along a latitudinal transect in the Northern Hemisphere in both the Atlantic and Mediterranean regions provide new insights into several aspects including [START_REF] Suc | Subtropical mangrove and evergreen forest reveal Paleogene terrestrial climate and physiography at the North Pole[END_REF] the occurrence of latitudinal thresholds leading to successive steps in mangrove development, (2) the spread of the latitudinal limit of Avicennia in relation to other mangrove taxa, (3) the onset of the present mangrove provinces, and (4) location of mangrove refuges during colder periods. But before interpreting our results, we review the representativeness of the occurrence/absence of mangrove pollen grains and the significance of their variations in abundance.

Representativeness of mangrove pollen and implications of its quantitative variations

The three past warm intervals studied correspond to episodes with high global sea level characterised by major elevations (up to 80 m in the PETM and 60 m in the EECO and MMCO;[START_REF] Miller | Cenozoic sea-level and cryospheric evolution from deep-sea geochemical record and continental margin records[END_REF]. During the longer climatic optima such as EECO and MMCO, the global sea level fluctuated somewhat (50 m in the EECO, 40 m in the MMCO) under the direct forcing of global temperature variations [START_REF] Miller | Cenozoic sea-level and cryospheric evolution from deep-sea geochemical record and continental margin records[END_REF]. Variations in mangrove pollen in our long pollen records in the EECO (Site M0004A, Caribou Hills, Kallo 027E148) and MMCO (Göllersdorf, Narbonne V. Hugo College, La Rierussa) may, according to their correlation with the oxygen isotope curve (Figure S1), have been caused by these secondary changes in sea level, which, in any case, resulted from global temperature changes. The same interpretation could be applied to the other locations of shorter duration.

The available reconstructed palaeoclimatic conditions indicate that the annual rainfall was higher than 1,000 mm at many locations: -In the PETM: Faddeevsky (Suan et al., 2017), Site M0004A (Suc et al., 2020), Calavanté 1 (Fauquette, in progress); -In the EECO: Caribou Hills (Salpin et al., 2019), Site M0004A (Suc et al., 2020), Morlaàs 1 and Gan (Fauquette, in progress); -In the MMCO: Göllersdorf (Jiménez-Moreno et al., 2008), Estagel (Fauquette et al., 2007), Narbonne V. Hugo College (Fauquette, in progress).

Only the MMCO records from La Rierussa and Alboran A1 indicate annual precipitation slightly lower and significantly lower than 1,000 mm, respectively (Fauquette et al., 2007). This low precipitation does not seem to have affected the abundance of Avicennia pollen in La Rierussa. This can be compared to the modern distribution of Avicennia in the subdesertic Red Sea region. Conversely, it could be the cause of the small quantity of Avicennia pollen in the Alboran A1 well. Accordingly, annual precipitation does not seem to have played a critical role in the distribution and development of mangroves during the three climatic optima considered here, except at the southernmost location in the Mediterranean in the MMCO.

The reconstructed mean temperature of the coldest month is evidence for the absence of freezing episodes during the PETM and EECO in the Arctic domain (Suan et al., 2017;Salpin et al., 2019;Suc et al., 2020). In this region, the first appearance of ephemeral continental ice seems more recent than 38 Ma (see: Suc et al., 2020). Similarly, the reconstructed mean temperature of the coldest month for the northernmost Avicennia locations during the MMCO suggests a lack of freezing episodes (Fauquette, unpublished data).

We conclude that, at the macroecological (geographical and chronological) scales of our study, sea and land temperatures were the main factors that controlled the development and diversity of the mangrove forests during the Palaeogene and Neogene climatic optima. S1). A first palaeolatitudinal threshold was identified, at about 58-73°N, delimiting the transition from a mangrove ecosystem with only Avicennia (locations 1, 3) to a diversified mangrove ecosystem. A second palaeolatitudinal threshold was identified at about 32-40°N which separated pollen records where the abundance of the other mangrove taxa was less than 5% with little diversity of megathermal plants (locations 4-6) from pollen records where the abundance of the other mangrove taxa was higher than 5% with a relatively high diversity of megathermal flora (locations 9-10) (Figure 5). The value of 5% of other mangrove taxa allowed us to define a scrawny though diversified mangrove between 32°N and 40°N and a well-developed diversified mangrove below 32°N. The same palaeolatitude thresholds were inferred for the PETM, at about 55-76°N and 32-35°N, respectively (Figure 4). The large amount of Avicennia pollen recorded at location 5 may be explained by the existence of a protected area offshore southern Greenland (Figure 2).

Latitudinal thresholds in the

Mangrove expansion depends on air temperatures but chiefly on sea temperatures. Today, Avicennia species are generally limited to coastal areas characterised by a warm climate with sea surface temperatures (SSTs) around 22.6°C [START_REF] Quisthoudt | Temperature variation among mangrove latitudinal range limits worldwide[END_REF] and cannot tolerate extremely cold air temperatures (below -4°C; [START_REF] Cavanaugh | Poleward expansion of mangroves is a threshold response to decreased frequency of extreme cold events[END_REF]. However, thanks to warm marine currents, Avicennia is the only mangrove plant that is not limited to the tropics and can occur at SSTs as low as 15.6°C at its coldest limit in New Zealand and eastern Australia [START_REF] Quisthoudt | Temperature variation among mangrove latitudinal range limits worldwide[END_REF]. Rhizophora requires slightly higher SSTs, even at its coldest limit (SSTs > 20.8°C; [START_REF] Quisthoudt | Temperature variation among mangrove latitudinal range limits worldwide[END_REF]. Model simulations of the sea surface (SSTs) and terrestrial mean annual temperatures (MATs) realised for the PETM and EECO along Earth's latitudinal range give too low temperature estimates and do not provide any evidence for a significantly reduced equator-to-pole temperature gradient (e.g., [START_REF] Huber | The early Eocene equable climate problem revisited[END_REF]Hollis et al., 2012;[START_REF] Lunt | A model-data comparison for a multi-model ensemble of early Eocene atmosphere-ocean simulations: EoMIP[END_REF]Zhu et al., 2020). The only one consistent with the palaeoclimate estimated through tetraether lipids [START_REF] Weijers | Warm arctic continents during the Palaeocene-Eocene thermal maximum[END_REF] and pollen records (Suan et al., 2017;Suc et al., 2020), although SSTs and MATs estimated north of 70° are also too low, reveals a sharp drop in the SST curve between palaeolatitude 65°N and 70°N (Figure 7; [START_REF] Sagoo | The Early Eocene equable climate problem: can perturbations of climate model parameters identify possible solutions[END_REF] that could limit the distribution of the more thermophilous mangrove taxa such as Rhizophoraceae as evidenced in our pollen data (Table 1). Moreover, the inversion of MATs and SSTs curves at ~37°N [START_REF] Sagoo | The Early Eocene equable climate problem: can perturbations of climate model parameters identify possible solutions[END_REF] corresponds in our data to the transition from diversified but scrawny mangrove to diversified and well-developed mangrove at about 35°N (Figure 7, Table 1). These inflexions in the marine and atmospheric temperature curves may record Early Eocene mangrove distribution and diversification in the Northern Hemisphere. Evidence for a similar threshold is shown in the Southern Hemisphere at palaeolatitude 65°S characterised by the occurrence of an Early Eocene scrawny mangrove with only Nypa in Tasmania (Table 1; [START_REF] Pole | Eocene Nypa from Regatta Point, Tasmania[END_REF]. These thresholds should be taken into account to review the so-called Early Eocene 'equable' climate [START_REF] Sloan | Equable" climates during Earth history?[END_REF].

Two challenging-correlating interpretations can be proposed: (1) Are the coupled climate models affected by insufficient performance under greenhouse conditions? It is now generally accepted (e.g., [START_REF] Sagoo | The Early Eocene equable climate problem: can perturbations of climate model parameters identify possible solutions[END_REF]; (2) Are temperature estimates from proxies exaggerated? Do tetraether lipids over-estimate temperatures or are the temperature requirements attributed to Avicennia in estimations based on pollen, too warm? This is possible, but the results based on kaolinite content of sediments in New Siberia (Suan et al., 2017), by MAT estimated in Antarctica [START_REF] Pross | Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch[END_REF] and TEX86-derived SSTs in Tasmania [START_REF] Bijl | Early Palaeogene temperature evolution of the southwest Pacific Ocean[END_REF] are in line with pollen-based estimates. To answer these questions, we need to understand the process and magnitude of Arctic temperature amplification, especially seasonality, which is observed in the present global warming [START_REF] Riboldi | On the linkage between Rossby Wave phase speed, atmospheric blocking, and Arctic Amplification[END_REF] and is believed to have been intense during the PETM and EECO [START_REF] Huber | The early Eocene equable climate problem revisited[END_REF][START_REF] Lunt | A model-data comparison for a multi-model ensemble of early Eocene atmosphere-ocean simulations: EoMIP[END_REF]Frieling et al., 2017).

The inherent forcing of solar radiation should be examined as an outcome. Indeed, studying the Mid-Holocene latitudinal variation of insolation controlling the temperature gradient, [START_REF] Davis | Orbital forcing and role of the latitudinal[END_REF] provide evidence for a threshold at 47°N delimiting increased summer insolation at higher latitudes but reduced insolation at lower latitudes and a threshold between 60 and 70°N of the June insolation. [START_REF] Loutre | Does mean annual insolation have the potential to change the climate?[END_REF] reconstruct global insolation for the Late Quaternary and provide evidence for a phase reversal at 43-44°N with prevalence of obliquity forcing over climate at higher latitudes and eccentricity at lower latitudes, the difference in mean annual irradiance being particularly marked above 70°N. An Early Eocene latitudinal reconstruction of insolation with the respective effect of winter vs. summer irradiance could allow to check if such thresholds forced the progressive diversity of mangrove ecosystems and the distribution of its major components.

MMCO

A threshold at about 40°N seems to have existed during the MMCO in the Mediterranean region, separating the Avicennia mangrove based on the abundance of Avicennia pollen and/or megathermal plants (Figure 6). The difference is particularly well expressed at locations 4 and 7 compared to location 1. Location 4 (Châteauredon) probably benefited from protected environmental conditions at the far end of a narrow gulf.

Our data concern the northern shorelines of the Mediterranean region where no other mangrove taxon was recorded. The lack of coeval pollen data from the southern Mediterranean shorelines does not allow us to hypothesise their occurrence a few latitudinal degrees southward. In this direction (Fig. 3), the first available pollen data are those from La Herradura (location 15: Palacios Chavez & Rzedowski, 1993) and from the coastal area of Senegal (location 11: Médus, 1975). Unfortunately, these pollen floras are not really usable because of their chronological imprecision and unavailable pollen data. However, their abundant pollen illustrations support the occurrence of Nypa and Pelliciera at La Herradura and that of Rhizophora at both locations. In addition, observation of the pollen photographs published convinces us of the occurrence of Avicennia at the two locations (detailed in Supporting Information). Close to the palaeo-equator, location 12 (well M1 from the Niger Delta; [START_REF] Durugbo | Palynological dating and palaeoenvironments of the M1 well, Middle Miocene, Niger Delta, Nigeria[END_REF] shows evidence of abundant Rhizophora and scarce Avicennia pollen grains during a stratigraphic interval attributable to the Mid-Miocene, the redrawing of which is provided in Figure 6 for comparison with the Mediterranean pollen floras. At location 16 (Lower Apaporis River; Fig. 3), Hoorn (2006) documents the occurrence of Rhizophora and Mauritia (Arecaceae). This comparison suggests that the diversity of the AEP mangrove was already significantly impoverished in the Mid-Miocene.

The MMCO has been modelled and sea surface and/or terrestrial temperature simulations are available (e.g.: You et al., 2009;Herold et al., 2011;Goldner et al., 2014). Herold et al. (2011) reconstructed terrestrial MATs that are characterised by strong dip variations between 30 and 35°N with a temperature gradient of 1.5°C per degree in latitude, which is significantly higher than the modern temperature gradient (0.6°C per degree in latitude) and very much higher than the temperature gradient obtained for the MMCO from pollen records in Western Europe (0.48°C per degree in latitude: Fauquette et al., 2007). In addition, the proposed terrestrial MATs for the latitudinal interval 30-42°N are significantly lower (11-17°C) than those estimated from pollen data in the Mediterranean domain (18.2-20.5°C;Fauquette et al., 2007;Jiménez-Moreno et al., 2008). Accordingly, there is a marked discrepancy in the MATs for the MMCO between the model simulation and pollen proxy, as in the SSTs between the model simulation and biomarker proxy [START_REF] Salocchi | Biomarker constraints on Mediterranean climate and ecosystem transitions during the Early-Middle Miocene[END_REF], similarly to previous time periods. As hypothesised above, it is possible that too much weight was attributed to Avicennia and/or the few megathermal plants in the temperature reconstructions based on pollen records. However, it is well known that for the MMCO, like for the previous periods, climate models generally fail to reproduce the polar amplification and lead to over-estimation of the equator to pole temperature gradient (e.g., You et al., 2009;Goldner et al., 2014). It is also possible that, like today, the Mediterranean Basin was a particular climatic region that allowed Avicennia to survive in slightly lower thermal conditions and to develop in some propitious contexts (locations 4 and 7; Figure 6; Table S1). This assumption is supported by some evidence: (1) the unexpected very rare presence of Avicennia pollen in the southernmost pollen flora (location 9: Figures 3,6); (2) the absence of Avicennia and of any megathermal taxon at location 10 on the Atlantic shoreline at a northwestern Mediterranean palaeolatitude (Figures 3,6; Table S1); the absence of Avicennia and of any megathermal taxon at the West Atlantic locations 13 and 14 corresponding to southernmost Mediterranean palaeolatitudes.

Northernmost latitudinal limit of Avicennia distribution with respect to the diversified mangrove

Today, the northernmost distribution of Avicennia is limited to a latitude range of 1.8° of the diversified mangrove (Figure 1; Table 1; [START_REF] Quisthoudt | Temperature variation among mangrove latitudinal range limits worldwide[END_REF]. In the Middle Miocene (MMCO), this interval may have reached latitude range of about 15°, an interval that could be exaggerated considering the lack of data between palaeolatitudes 33°N (location 9) and 15°N (location 15) (Figures 3,67; Table 1). During the Early Eocene (PETM and EECO), this geographical difference in latitude would have been about 10-15° (Figures 2,457; Table 1). Obviously, the size of the gap is linked with warmth, even if the temperature may have been somewhat higher in the Mediterranean Basin, which was probably sheltered from cold air masses. Today, there is a latitudinal difference of about 9° in Avicennia distribution between mangrove consisting only of Avicennia and diversified mangrove in the South Hemisphere, illustrating the high potential thermal flexibility of the genus (Figure 1; Table 1; [START_REF] Quisthoudt | Temperature variation among mangrove latitudinal range limits worldwide[END_REF].

To summarise, the maximum latitudinal gap for Avicennia distribution outside diversified mangrove could have been 15° during the three Cenozoic thermal maxima, which matches the 9° observed today and accounts for uncertainty in palaeolatitude estimates.

The simultaneous occurrence of several (PETM) and many (EECO) megathermal plants including mangrove taxa (represented by abundant pollen grains) (Figures 45; Table S2) marks diversified and well-developed mangrove. Considering the maximum latitudinal expansion of this mangrove, there is no or little latitudinal difference between the Early Eocene and today, which would be feasible in the case of an 'equable' climate during the Early Eocene (Figure 7; Table 1). However, a buffer zone between 35 and 65-70°N, where we recorded a diversified but scrawny mangrove with only few megathermal companions for the Early Eocene (Figures 457; Table 1; Table S2), questions the relative influence of a more 'equable' climate and the ability of some taxa to invade cooler areas in the past. During the Middle Miocene, disregarding the probable peculiar environmental context of the Mediterranean domain (Figure 3), the moderate diversity in megathermal plants expressed by low pollen percentages (Figure 6; Table S2) suggests a transition between the buffer zone and the Avicennia mangrove, as witnessed during the Early Eocene, and signals the gradual withdrawal of the mangrove in Europe.

What is the relationship between the past Avicennia-only and diversified mangroves and the present mangrove provinces?

Avicennia comprises eight modern species (The Plant List, 2013) equally distributed in the AEP province (A. bicolor, A. germinans, A. schaueriana, A. tonduzii) and IWP province (A. balanophora, A. integra, A. marina, A. officinalis) (Dahdouh-Guebas, 2020). Some morphological characters make it possible to distinguish these species by their pollen (Thanikaimoni, 1987), as supported by our own observations (Figures S1-S3).

Precise observation of Early Eocene Avicennia pollen grains from the Arctic indicates the occurrence of several species, some specimens being very close to the modern species A. germinans, A. marina and A. officinalis (Figures S1-S2;Suan et al., 2017;Salpin et al., 2019;Suc et al., 2020). The same variety in Avicennia pollen morphology is observed in the other pollen records from the Early Eocene Atlantic latitudinal transect (Figure 2: locations 4-11: Figures S6-S9), suggesting similar specific diversity to that considered at the higher palaeolatitudes. According to the present geographical distribution of the three above-mentioned Avicennia species, it appears that no mangrove provincialism existed during the Early Eocene, in agreement with evidence at locations 4-11 (Figures 2,45; Tables S1-S2), in addition to the Rhizophoraceae, of Nypa and Xylocarpus, currently restricted to the IWP province (Figure 1; [START_REF] Tomlinson | The botany of mangroves[END_REF]. Pelliciera, now confined to the AEP province (Figure 1; [START_REF] Tomlinson | The botany of mangroves[END_REF], was already present in the Atlantic domain (location 9: Figures 2,5; Tables S1-S2). These data are robust and support a Tethyan origin of mangroves, consequently, the regional taxonomic diversity resulted from the continental drift and not from an Indo-Pacific centre of origin (Ellison et al., 1999;[START_REF] Morley | Origin and evolution of tropical rain forests[END_REF][START_REF] Plaziat | History and biogeography of the mangrove ecosystem, based on a critical reassessment of the paleontological record[END_REF][START_REF] Srivastava | Evolution and paleobiogeography of mangroves[END_REF].

A cluster of probably two Avicennia species inhabited the Mediterranean domain during the Middle Miocene with pollen indicating A. marina and A. officinalis (Figures S3, S10;[START_REF] Bessedik | Recherches palynologiques sur quelques sites du Burdigalien du midi de la France[END_REF]. Today these species belong to the IWP province thereby contributing to the persistence of Avicennia in western Europe, favoured by large marine connections to the east while, at the same time, the eastern Atlantic shoreline is devoid of this taxon at similar palaeolatitudes (Figure 3). This could argue for provincial differentiation almost completely achieved during the Miocene, if not the ultimate occurrence of Nypa along the western Atlantic shoreline (location 15: Figure 3; Palacios Chavez & Rzedowski, 1993). The more restricted distribution of Pelliciera in the AEP province is confirmed by pollen flora found at location 15 (Figure 3; Palacios Chavez & Rzedowski, 1993).

These data lead us to conclude that mangrove provincialism progressively established itself after the Early Eocene warm period, probably forced by plate tectonics, the taxonomic impoverishment of the AEP province probably being caused by successive global colder periods [START_REF] Plaziat | History and biogeography of the mangrove ecosystem, based on a critical reassessment of the paleontological record[END_REF][START_REF] Srivastava | Evolution and paleobiogeography of mangroves[END_REF].

Persistence of mangrove during cooler periods between thermal optima

Our study focuses only on the three warmest episodes of the last 60 Ma but mangrove history obviously continued in the meantime. Here, we only recall or complete some items of this history, which was already summarised by Ellison et al. (1999), [START_REF] Plaziat | History and biogeography of the mangrove ecosystem, based on a critical reassessment of the paleontological record[END_REF] and [START_REF] Srivastava | Evolution and paleobiogeography of mangroves[END_REF].

Considering its high expansion up to the northernmost latitudes during the PETM and EECO, logically Avicennia rarely occurred in the Arctic region up to the Mid-Eocene Climatic Optimum (MECO: 40 Ma; Suc et al., 2020). This late occurrence in the Arctic region also questions the potential ability of Avicennia to persist during cooler periods and/or its possible latitudinal shifts between the EECO and MECO, unless the thermal amplitude suggested by the δ 18 O curves is over-estimated. Its southward retreat is illustrated by one last Early Oligocene occurrence (with no other mangrove taxon) at Site 345 (NW Norway; study in progress). Only Avicennia was present in the northwestern Mediterranean Oligocene (study in progress), where it persisted up to the earliest Serravallian (Bessedik, 1984;Jiménez-Moreno & Suc, 2007). The youngest record of Avicennia at similar palaeolatitude on the European side of the Atlantic belongs to the early Burdigalian. Avicennia persisted in the southern Mediterranean and Atlantic Morocco up to the late Messinian (Suc et al., 2018). The ultimate reliable record of Avicennia concerns the Early Pliocene in the southern Black Sea [START_REF] Biltekin | Anatolia: a long-time plant refuge area documented by pollen records over the last 23 million years[END_REF]. Avicennia expansions and retreats very closely mirror increases and decreases in temperature, respectively, and were driven by the opportune opening or persistence of marine gateways.

The most recent evidence of a diversified and well-developed mangrove in the northwestern Mediterranean Basin was in the Bartonian (ca. 40 Ma) with, in addition to Avicennia, Pelliciera, Bronwlowia, Nypa, Heritiera and Aegiceras [START_REF] Cavagnetto | Une mangrove complexe dans le Bartonien du bassin de l'Ebre (NE de l'Espagne)[END_REF]. A scrawny mangrove was still present during the Oligocene in northern Turkey, including Avicennia, Pelliciera and Nypa (Akgün et al., 2013). These data complete the information on the process of disjunction of the modern mangrove biogeographic provinces, which occurred during the Late Eocene and Oligocene and ended in the earliest Neogene.

CONCLUSION

A set of eleven pollen floras arranged along a North Atlantic latitudinal transect were analysed using a botanical approach and provide information on mangrove distribution and diversity during the warmest Palaeogene phases (PETM and EECO). Evidence is provided for two palaeolatitudinal thresholds, at respectively 65-70°N and 35°N, separating the Avicennia-only mangrove (which reached 80°N) from a diversified but scrawny mangrove, and then from a diversified and well-developed mangrove. These thresholds, which moderate the so-called Early Eocene 'equable' climate hypothesis, were probably due to latitudinal changes in temperature and possibly in solar irradiation. The latitudinal gap between the northward expansion of Avicennia and diversified mangrove during the three Cenozoic thermal maxima (10-15°) could have been almost similar to the southward gap observed today in Australia (9°; Table 1). This mangrove organisation once more reveals significant discrepancies between models and proxies, unless the temperature estimates deduced from Avicennia and some mangrove and other megathermal plants have been somewhat exaggerated when these taxa only are represented by a few pollen grains. A similar expansion event occurred during the MMCO but chiefly concerned Avicennia, which benefited from propitious conditions in the Mediterranean Basin documented by nine pollen records, also suggesting Avicennia's possibly greater adaptive ability in the past.

Our results concerning the Early Eocene North Atlantic and Arctic mangroves provide the missing link to robustly support the Tethyan origin of mangroves, the provincialism of which started in the Late Eocene probably forced by continental drift, and ended in the Early Neogene. The subsequent global colder periods probably played a key role impoverishing the Western mangroves.

Chronology

As indicated above, a relatively rough age model is provided by biostratigraphy (planktonic foraminifera and/or calcareous nannofossils). A recent oxygen isotope curve is used as reference of global climate variations (Fig. S1; Westerhold et al., 2020). This curve comes from a Cenozoic global dataset based on benthic foraminifera with a sampling interval of 2 to 4.4 kyr. The blue curve is a smoothed curve over 20 kyr and the red curve over 1 Myr. They respectively express different rhythms in temperature variability. The variations observed in pollen records are mainly interpreted as variation in temperature for the PETM, EECO and Göllersdorf during the MMCO because the pollen diagrams evidence humid conditions (prevalent thermophilous plants, weakness of herbs). For the other MMCO locations, the variations in pollen records are both interpreted as temperature and precipitation variations (forest humid and warmer phases marked by abundant thermophilous trees opposed to herbaceous drier and less warm phases marked by abundant herbs).

According to the time interval represented by each pollen record and according to the number of samples studied within this interval (i.e., the time resolution of each record), we tentatively correlate the pollen variations observed with either the blue curve either the red curve (Fig. S1), following the principles of climatostratigraphy described by [START_REF] Suc | Origin and evolution of the Mediterranean vegetation and climate in Europe[END_REF], Suc et al. (2018) and Suc et al. (2020). S2. Listing of taxa constituting the ecological groups of plants used for the synthetic pollen diagrams, distributed by locations with respect to PETM, EECO and MMCO, respectively.

The suffix '-type' is used to indicate that the concerned pollen morphology exists in several taxa (species or genera). The prefix 'cf.' means that the selected taxon has the nearest morphology with the fossil pollen after comparison with pollen of modern species or genera. 1 2 5 7 8 11 1 3 4 5 6 9 10 1 4 5 6 7 9 x x Cupressaceae (former Taxodiaceae type) x x x x x x x x x x x x x x x x x x x x Cyrillaceae-Clethraceae

x x x x x x x Dacrydium x Decodon x x x x Dicoryphe x x Diplodiscus x Distylium x x x x x x x x x x x x x x x x x Embolanthera x x x x x Engelhardia x x x x x x x x x x x x x x x x x x x x Eustigma x x x Hamamelidaceae x x x x x x Hamamelis x x x Ilex floribunda type x x x x x Ipomoea x Itea x Lauraceae x Leea x x x x x x x Liriodendron x Loranthaceae x x Loropetalum x x x x x Ligustrum x x x x cf. Lysidice x Magnolia x Matudaea x x Menispermaceae x x x x x x x Microtropis fallax x x x x Mussaenda type x x x x x Myrica x x x x x x x x x x x x x x x x Nolina x Nyssa x x x x x x x x x x x x x Nyssa cf. sinensis x x x x x x Olea x x x x x x x x Phillyrea x x x x Pistacia x Platycarya x x x x x x x x x x x x Rhamnus x Rhodoleia x x x x x x x x x x Rhoiptelea x x x Rhus cf. cotinus x x cf. Ricinus x x x x x x x Rubiaceae x x x x x x x x x x x Sapotaceae x x x x x x x x x x x x x Sciadopitys x x x x x x x x x Sequoia type x x x Styracaceae x Symplocos x x x x x x x x x Taxodium type x x x x x x x x x x x x x x x x x cf. Trichocladus x Uncaria type x x x x x x
Ecological groups of plants

Mega-mesothermal plants

Taxa PETM EECO locations MMCO locations 1 2 5 7 8 11 1 3 4 5 6 9 10 1 4 5 6 7 9 10

Acer x x x x x x x x x x x x x x x x Aesculus x Alnus x x x x x x x x x x x x x x x x Anacardiaceae x x x x Araliaceae x Betula x x x x x x x Buxus sempervirens type x x x x x x x Caprifoliaceae x Carpinus x x x x x x x x x x x Carya x x x x x x x x x x x x x x x x x x x Celtis x x x x x x x x x x Corylus x Ericaceae x x x x x x x x x x x x x Erica cf. terminalis x Eucommia x x x x x x x x x Fraxinus x x Hedera x x x x x Ilex x x x x Juglans x x x x x x Liquidambar x x x x x x x x x x x Lonicera x Nothapodytes x Oleaceae x x x x x Ostrya x x x x x Parrotia cf. persica x x x x x x x x x Parrotiopsis cf. jacquemontiana x x x Parthenocissus x x x x x x Parthenocissus cf. henryana x x x x Phelline x Platanus x x Populus x x x x x x x x x Pterocarya x x x x x x x x x x x x x x Quercus x x x x x x x x x x x x x x x x x x x Quercus ilex type x x x x x Rhamnaceae x x x x x x x Rhus x x x x x x x x x Salix x x x x x x x x x x x x x x x Sambucus x Tamarix x x x x Tilia x x x x x x x x x x Ulmus x x x x x x x x x x x x x x x x Ulmus-Zelkova x Viburnum x x Vitis x x x Zelkova x x x x x x x x x x x x x diplostellate type x x x x x x x x x x x x x x x x x x haplostellate type x x x haploxylon type x Cathaya x x x x x x x x x x x x x x x x x Cedrus x x x x x x x Fagus x x x x x x x Podocarpus x x x x x x x x x Tsuga x x x x x x Abies x x x x x x Picea x x x x x x x x x x x

Meso-microthermal plants

Microthermal plants PETM locations EECO locations MMCO locations

Mesothermal plants

Pinus + indeterminable Pinaceae

Ecological groups of plants Taxa

Herbaceous plants

The pollen data used for the PETM and EECO result from recent analyses because of a noteworthy evolution in Paleogene palynology. The pollen records used for MMCO are relatively recent and homogenous enough in terms of botanical identifications.

Botanical identification of pollen grains

The rarely used technique of mounting the residue in glycerol allows some mobility of the pollen grains so their different sides can be examined, thus facilitating their botanical identification. Analyses were made using a light microscope at 200x magnification, and each pollen grain was identified at 1,000x magnification. Aiming to optimize reliability of pollen analysis, we perform appropriate techniques (see the chapter 'Material and methods' of the main text and we follow an accurate nomenclature in pollen morphology [START_REF] Punt | Glossary of pollen and spore terminology[END_REF] for understanding shape, structure, aperture(s) and ornamentation, according to the LO-analysis (Lux = light vs. Obscuritas = darkness) technique of observation at the transmitted light microscope (TLM) [START_REF] Erdtman | Pollen morphology and plant taxonomy. Angiosperms[END_REF]. Scanning electronic microscope (SEM) has also been used to check some of the pollen characters, particularly those perceptible in surface, such as shape and ornamentation. Information on the present-day accepted botanical taxa and synonymies comes from The Plant List (2013). Most of the pollen photographs come from specimens from the ISEM collection (website: data.oreme.org), some others come from the GeoBioStratData private collection.

Below, we provide an accurate description, illustrated by photographs, of some critical pollen grains benefiting from a botanical identification, which belong to plants of the mangrove ecosystem. This approach challenges for elevating pollen floras at the same step of botanical relevance than macrofloras, at least at the genus level. In this context, the genus appears to be the most relevant taxonomic entity because (1) most of genera existed from the earliest Paleogene, and (2) its bioclimatic significance is generally well delimited [START_REF] Harris | The effects of taxonomic rank on climatic calibrations: a test using extant floras of United States counties[END_REF]. The limited identification at the genus level replaces the so-called species, we believe imagined, in most of the previous Paleogene studies.

1 2 5 7 8 11 1 3 4 5 6 9 10 1 4 5 6 7 9 10 Myriophyllum

x x x Nitraria x x Nympheaceae x Oenotheraceae x x x x Papaveraceae x x x x x x x Plantago x x x x x x x Plumbaginaceae x x x Poaceae x x x x x x x x x x x x Polygonaceae x x x Polygonum x Polygonum aviculare type x x Potamogeton x x x x x x Primulaceae x Resedaceae x x x x x x x Restionaceae x x x x x x x x x Restio x x x x x Rumex x x x x x x x x Saxifragaceae x Sparganium x x x x x x x Thalictrum x x x Typha x x x x Urticaceae x x x x x x x x x x x x Valerianaceae x x x

Herbaceous plants

Ecological groups of plants Taxa PETM locations EECO locations MMCO locations Avicennia (Acanthaceae) Because the Early Eocene and Mid-Miocene recorded pollen grains ascribed to Avicennia show some morphological variety, we present hereafter three figures with photographs from pollen grains of six modern species (among the eight accepted species by The Plant List, 2013), four from the Western province (A. bicolor,A. germinans,A. schaueriana,A. tonduzii;, two from the Eastern province (A. marina, A. officinalis; Fig. S4). Comparisons can be done with ten photographs of Avicennia pollen from PETM (Figure S7), thirty-one photographs of Avicennia pollen from EECO (Figures S8-S10), sixteen photographs of Avicennia pollen from MMCO (Figure S11).

Avicennia shows prolate to spheroidal tricolpate or tricolporate pollen grains characterised by long and largely opened colpi (with or without costae) that makes the polar area (apocolpium) very small and the pollen close to be syncolp(or)ate. Tricolporate pollen grains show a slightly elongated endoaperture along the polar axis, which does not pass the edges of colpus at the pollen equator. A homobrochate semitectate reticulum constitutes the exine sculpture with dense muri, larger than luminae, which are characterised by a polygonal and slightly elongated outline. Thickness of muri somewhat increases toward the poles that reduces the size of luminae. Colpi are bordered by a thin margo where reticulum is smaller. The structure of the semi-tectate ectexine shows dense columellae with large head constituting the tectum overlying a thinner endexine. At SEM, general shape and exine sculpture can be observed in finer detail showing, in particular, the smooth surface of the tectum somewhat prominent above the columellae. These characters, whatever the pollen is colpate or colporate, are those of the modern Avicennia pollen (also supported by an almost similar size), which unique morphology has been extensively described and documented by many photographs at TLM and SEM (Thanikaimoni, 1987;[START_REF] Mao | Key to mangrove pollen and spores of southern China: an aid to palynological interpretation of Quaternary deposits in the South China Sea[END_REF].

Three modern Avicennia species display pollen morphologies (with a colpate or colporate apertural system) very close to the Avicennia pollen grains of the Early Eocene Arctic-Atlantic: A. germinans (L.) L., A. marina (Forssl.) Vierh., and A. officinalis L. Two of these species (A. marina and A. officinalis) have pollen grains very close to those recorded in the Mid-Miocene sediments from the Mediterranean region. S5, A1-A2). The great-sized spheroidal pollen of this species is tricolporate with thin and relatively short colpi as ectoapertures that confers a large apocolpial field in polar view. The endoapertures are perpendicular to the ectoapertures delimited by slightly marked costae discontinuous at the equator. The pollen is tectate with relatively thick endexine and ectexine, which shows a foveolate-fossulate to verrucate-rugulate ornamentation. This pollen morphology is described and illustrated by Thanikaimoni (1887).

Rhizophoraceae (Figure S5, B1-E2).

The mangrove genera of Rhizophoraceae show an almost similar pollen morphology. Slightly prolate to spheroidal, the pollen is tricolporate, sometimes tetracolporate, with long ectoapertures and perpendicular long endoapertures bordered by prominent costae. Rounded triangular polar view shows vestibula. Ectexine, thicker than endexine, shows a variable ornamentation, scabrate to microreticulate or foveolate. In addition to variability in pollen size, such a homogenous morphology makes very difficult the identification of genera according to pollen. A, Avicennia. A1-A2, La Rierussa (location 7), sample 1, equatorial view (aperture facing): A1, reticulate ornamentation; A2, optical section. A3, Saint-Geniès (location 6), equatorial view (intercolpium), overview. A4-A13, Estagel (location 5), sample 8. A4-A5, equatorial view (intercolpium): A4, reticulate ornamentation; A5, focus at base of columellae and optical section. A6-A7, polar view: A6, reticulate ornamentation; A7, optical section. A8-A10, polar view: A8, reticulate ornamentation; A9, focus at base of columellae; A10, optical section. A11-A13, equatorial view (aperture facing): A11, reticulate ornamentation; A12, focus at base of columellae; A13, optical section. A14-A16, Göllersdorf (location 1), sample 22, equatorial view (intercolpium): A14, reticulate ornamentation; A15, optical section; A16, apertures.

A1 A2 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15 A16
A3

  Mangrove distribution and diversity during three Cenozoic thermal maxima in the Northern hemisphere (pollen records from the Arctic -North Atlantic -Mediterranean regions) Speranta-Maria Popescu, Jean-Pierre Suc, Séverine Fauquette, Mostefa Bessedik, Gonzalo Jiménez-Moreno, Cécile Robin, Loic Labrousse To cite this version: Speranta-Maria Popescu, Jean-Pierre Suc, Séverine Fauquette, Mostefa Bessedik, Gonzalo Jiménez-Moreno, et al.. Mangrove distribution and diversity during three Cenozoic thermal maxima in the Northern hemisphere (pollen records from the Arctic -North Atlantic -Mediterranean regions). Journal of Biogeography, 2021, 48, pp.2771-2784. hal-03618080

  Northern Hemisphere separated diversified mangroves from Avicennia-only mangroves 4.2.1. PETM and EECO The abundance of pollen records in the EECO allowed us to reconstruct an almost continuous latitudinal gradient of mangrove distribution in the North Atlantic region (Figures 2, 5; Table

Figure 1 .

 1 Figure1. Present-day geographic distribution of mangroves with respect to their two provinces with information on occurrence of some taxa according to[START_REF] Tomlinson | The botany of mangroves[END_REF] and latitudinal limits of Avicennia and Rhizophora according to[START_REF] Quisthoudt | Temperature variation among mangrove latitudinal range limits worldwide[END_REF]. The used geographic map is from Strebe, D. R. -CC BY-SA 3.0 (Mollweide projection equalarea), https://commons.wikimedia.org/w/index.php?curid=16115320.

Figure 2 .Figure 3 .

 23 Figure 2. Palaeocene-Eocene (PETM) and early Eocene (EECO) mangrove pollen records (with information on the occurrence of some taxa) along a North-South transect. Palaeogeographical map with estimated palaeolatitudes (Polar orthographic Projection) is from Backman et al. (2006) and Eberle & Greenwood (2012), modified by Suc et al. (2020). Locations: 1, Site M0004A; 2, Faddeevsky Island; 3, Caribou Hills; 4, Site 343; 5, Site 918; 6, Kallo 027E148; 7, Noirmoutier; 8, Calavanté 1; 9, Morlaàs 1; 10, Gan; 11, Site 547.

Figure 4 .Figure 5 .Figure 6 .

 456 Figure 4. Synthetic diagrams of PETM pollen records arranged according to their estimated palaeolatitude with listing of their mangrove woody taxa. Site Number (No) refers to Figure 2. Detail of taxa constituting the ecological groups of plants is given in TableS2.For locations made of several samples, the thickness scale is indicated to the left of the diagram.

Figure 7 .

 7 Figure 7. Sea surface temperature (SST) vs. land (air) mean annual temperature (MAT) and mangrove distribution and diversification in the North Hemisphere during the Early Eocene (simulation E17 from: Sagoo et al., 2013).

Figure S1 .

 S1 Figure S1. Climatostratigraphic correlations of the studied pollen records with the reference oxygen isotope curve: a, during the PETM and EECO; b, during the MMCO. Explanations are given above.

Figure S2 .

 S2 Figure S2. Photographs at TLM and SEM of pollen grains of the modern species Avicennia bicolor Standl. (slide n° 10887 from the ISEM collection, plant specimen collected in Panama), A. africana P.Beauv. = A. germinans (L.)L. (slide 875 of the GeoBioStratData collection, plant specimen 14273 from the Herbarium of the University C. Bernard Lyon, France, plant specimen collected in Africa), and A. tomentosa Jacq. = A. germinans (L.)L. (slide 874 of the GeoBioStratData collection, plant specimen 5 from the Herbarium of the University C. Bernard Lyon, France, plant specimen collected in India) (shots by J.-P. Suc & S.-M. Popescu). Scale bar = 5 µm.

Figure S10 .Figure S11 .

 S10S11 Figure S10. Photographs at TLM and SEM of fossil pollen grains from EECO sedimentslocation numbers refer to Figure 2 (shots by J.-P. Suc & S.-M. Popescu). Scale bar = 5 µm.

Table 1 .

 1 Latitudinal distribution and diversification of mangroves during three noteworthy thermal maxima compared to Present.

	PETM and EECO	MMCO		Present	Hemisphere
	Palaeolatitude	Mangrove type	Palaeolatitude	Mangrove type	Latitude	Mangrove type
	70-80°N	Avicennia-only mangrove
	60-70°N	No data
	35-60°N	Diversified but scrawny mangrove					N O
	<35°N	Diversified and well-developed mangrove	33-45°N 15-33°N ?<20°N	Avicennia-only mangrove No data Diversified and well-developed mangrove	30-31.8°N <30°N	Avicennia-only mangrove Diversified and well-developed mangrove	R T H
						Diversified and
					<30°S	well-developed	S
						mangrove	O
					30-39°S	Avicennia-only mangrove	U T
	65°S	Nypa					H

Table S1 .

 S1

	45°N
			N
	30°N
	+
	5°N
	0°1
	No mangrove taxon	Avicennia only as mangrove taxon	Diversified mangrove (Rhizophoraceae, Nypa, Pelliciera) +

Locations: 1, Göllersdorf; 2, Herend 46; 3, Balgarevo C136A; 4, Les Mées 1, Châteauredon; 5, Estagel, Bayanne; 6, Narbonne V. Hugo College, Lespignan II, Montady, Saint-Géniès, Montagnac, Mèze, Loupian, Issanka, Poussan, Montbazin; 7, La Rierussa, Sant Pau d'Ordal; 8 Kultak; 9, Alboran A1; 10, Laborde 1D; 11, Bignona well; 12, Niger Delta well M1; 13, Site M00027; 14, Alum Bluff; 15, La Herradura; 16, Apaporis River.

Table S1 .

 S1 ). Pollen assemblages as palaeoenvironmental proxies in the Florida Everglades. Review ofPalaeobotany and Palynology, 113, 213-235. Woodroffe, C. D., Rogers, K., McKee, K. L., Lovelock, C. E., Mendelssohn, I. A., & Saintilan, N. (2016). Mangrove sedimentation and response to relative sea-level rise. Compiled mangrove pollen records at three thermal maxima (PETM, EECO, MMCO), referring to locations (exposed sections and boreholes) in Figures2 and 3, with sources on bio-and chronostratigraphy and palaeolatitude estimates.

	Annual Review of Marine Science, 8, 243-266.
	doi: 10.1146/annurev-marine-122414-034025
	You, Y., Hubern M., Müller, R. D., Poulsen, C. J., & Ribbe, J. (2009). Simulation of the
	Middle Miocene Climate Optimum. Geophysical Research Letters, 36, L04702.
	doi:10.1029/2008GL036571
	Zachos, J., Pagani, M., Sloan, L., Thomas, E., & Billups, K. (2001). Trends, rhythms, and
	aberrations in global climate 65 Ma to present. Science, 292, 686-693.
	Zhu, J., Poulsen, C. J., Otto-Bliesner, B. L., Liu, Z., Brady, E. C., & Noone, D. C. (2020).
	Simulation of early Eocene water isotopes using an Earth system model and its
	implication for past climate reconstruction. Earth and Planetary Science Letters, 537,
	116164.
	https://doi.org/10.1016/j.epsl.2020.116164

BIOSKETCH

Speranta-Maria Popescu is a palynologist involved in Cenozoic environmental reconstructions using pollen grains and dinoflagellate cysts, particularly in relation with climatic and geographical-geodynamic changes. After her Ph.D. and Accreditation to supervise research, which she received from the Lyon 1 University, in 2001 and 2008, respectively, and postdoc at Woods Hole Oceanographic Institution, she started the GeoBioStratData.Consulting company (www.geobiostratdata.com), which mainly specialises in biostratigraphic and palaeoenvironmental research projects with academic institutes and industrial companies.

56 Ma Paleocene-Eocene thermal maximum (PETM): late Thanetian -early Ypresian.

	17-
	Site No	Location (studied interval for holes)	Present latitude -longitude	Estimated N palaeolatitude	Mangrove pollen identified by	Mangrove taxa	References Bio-chronostratigraphy	Pollen data
	1	Site M0004A (382.44 mbsf)	1		87°51'59.76"N 136°10'38.64"E	>76°	S.-M. Popescu J.-P. Suc	Avicennia	Suc et al. (2020)
	2	Faddeevsky Island Samples GS124-127	2	76°06'23.30"N 141°49'01.70"E	80°	S.-M. Popescu J.-P. Suc	Avicennia	Suan et al. (2017)
	5	Site 918 hole D (1180.71-1180.49 mbsf)	63° 5'10.82"N 38°39'35.30"W	55°	S.-M. Popescu J.-P. Suc	Avicennia Rhizophoraceae Brownlowia Xylocarpus	Wei (1998) Jolley (1998) Larsen et al. (1994)	This work
								Avicennia
	7	Noirmoutier Samples 1-3			47° 0'39.99"N 2°13'11.04"W	35°	S.-M. Popescu J.-P. Suc	Nypa Rhizophoraceae Xylocarpus	Ters (1978) Ollivier-Pierre (1980)	This work
	8	Calavanté 1 (3350 m)			43°12'31.00"N 0°10'59.00"E	32°	S.-M. Popescu J.-P. Suc	Avicennia Nypa	Sztràkos et al. (1998)	This work
								Avicennia
	11	Site 547 hole A (279.53-279.31 mbsf)	33°46'50.40"N 9°20'58.80"W	19°	S.-M. Popescu J.-P. Suc	Rhizophoraceae Excoecaria Sonneratia-type	Hinz et al. (1984)	This work
								Xylocarpus
	Site No	Location (studied interval for holes)	Present latitude -longitude	Estimated N palaeolatitude	Mangrove pollen identified by	Mangrove taxa	References Bio-chronostratigraphy	Pollen data
	1	Site M0004A (318.86-282.05 mbsf)	87°51'59.76"N 136°10'38.64"E	>78°	S.-M. Popescu J.-P. Suc	Avicennia	Backman et al. (2006)	Suc et al. (2020)
	3	Caribou Hills Samples 12-18		68°45'0.07"N 134°14'0.00"W	73°	S.-M. Popescu J.-P. Suc	Avicennia	Salpin et al. (2019)
								Avicennia
	4	Site 343 (214.30-213.99 mbsf)	68°43'13.07"N 5°46'21.54"E	58°	S.-M. Popescu J.-P. Suc	Rhizophoraceae Xylocarpus Scyphiphora	Müller (2007) Schrader et al. (2007)	This work
								Excoecaria
								Avicennia
	5	Site 918 hole D (1158.21-1156.71 mbsf)	63° 5'10.82"N 38°39'35.30"W	55°	S.-M. Popescu J.-P. Suc	Rhizophoraceae Sonneratia-type Brownlowia	Larsen et al. (1994) Wei (1998)	This work
								cf. Heritiera
								Avicennia
	6	Kallo 027E148 (286.50-239 m)		4°17'38.21"E 51°15'8.25"N	40°	J.-P. Suc S.-M. Popescu	Nypa Sonneratia-type Rhizophoraceae	Steurbaut (2006) Roche (1973)	This work
								Avicennia
								Rhizophoraceae
	9	Morlaàs 1 (1462-1083 m)		43°19'42.00"N 0°14'17.00"W	32°	S.-M. Popescu J.-P. Suc	Pelliciera Sonneratia-type Nypa	Sztràkos et al. (1998)	This work
								Xylocarpus
								Avicennia
	10	Gan Samples 1-2			43°13'54.20"N 0°23'45.80"W	33°	S.-M. Popescu J.-P. Suc	Nypa Rhizophoraceae Aegialitis Sonneratia-type	Alimen et al. (1963)	This work
	Site Number (No) refers to Figure 2.

Site Number (No) refers to Figure

2

.

1

Depth is indicated in mbsf (metres below sea level) for offshore boreholes. 2 Samples are listed from base to top.

54-49 Ma Early Eocene climatic optimum (EECO): Ypresian.

14 Ma Mid-Miocene climatic optimum (MMCO): late Burdigalian -Langhian.

	Site Number (No) refers to Figure 3.

mesothermal plants Other mangrove trees and shrubs Other megathermal plants PETM locations EECO locations MMCO locations Taxa Ecological groups of plants 1 2 5 7 8 11 1 3 4 5 6 9 10 1 4 5 6 7 9 10

	Avicennia Mega-Castanopsis-Lithocarpus Avicennia cf. Aegialitis Brownlowia Excoecaria cf. Heritiera Nypa Pelliciera Rhizophoraceae Scyphiphora Sonneratia type Xylocarpus Acanthaceae Alchornea Amanoa Bombax type cf. Bridelia Buxus bahamensis type Canthium type cf. Corypha Croton Dodonaea cf. Drypetes Euphorbiaceae Fothergilla cf. Gordonia Grewia-Corchorus Icacinaceae cf. Lasianthus Leguminosae Caesalpinoideae Leguminosae Mimosoideae Malpighiaceae Mappianthus Melastomataceae Meliaceae Morinda-Randia type cf. Parsonsia Passifloraceae Phyllostylon Prosopis Sapindaceae cf. Sapium Simaroubaceae Sindora Theaceae Tiliaceae cf. Acanthopanax Agavaceae Alangium cf. Alfaroa Casuarina Celastraceae Ceratonia Chloranthaceae Cissus Cordyline Cornaceae cf. Corylopsis Craigia	x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x	10 x
	Arecaceae	x x x x	x x x x x x x x x x x x x x
	cf. Beaumontia	x

  Photographs at TLM of pollen grains of the modern species Avicennia schaueriana Stapf & Leechm. ex Moldenke (slide 10886 from the ISEM collection, plant specimen collected in the West Indies) and A. tonduzii Moldenke (slide 10885 from the ISEM collection, plant specimen collected at Costa Rica) (shots by J.-P. Suc & S.-M. Popescu). Photographs at TLM and SEM of pollen grains of the modern species Avicennia alba Blume = A. marina (Forssk.) Vierh. and A. officinalis L. (shots by J.-P. Suc & S.-M. Photographs at TLM of pollen grains of the modern species Pelliciera rhizophorae Planch. & Triana (Tetrameristaceae) (slide 38826 from the ISEM collection) and Rhizophoraceae: Rhizophora candelaria DC. = R. apiculata Blume (slide 34256 from the ISEM collection, plant specimen collected in India), R. mucronata Lam. (slide 10833 from the ISEM collection), Bruguiera parviflora (Roxb.) Wright & Arn. ex Griff. (slide 40409 from the ISEM collection), Ceriops roxburghiana Arn. = C. decandra (Griff.) W.Theob. (slide 15072 from the ISEM collection, plant specimen collected in India) (shots by J.-P. Suc & S.-M. Popescu).

	Figure S5. Scale bar = 5 µm.	A1		A2	A3	A4
	A, Pelliciera rhizophorae.	A1	A2		A3
	A1, Equatorial view (aperture facing), optical section.
	A1 A2, Polar view, optical section.	A2	A3	A4
	B, Rhizophora candelaria = R. apiculata.
	B1-B2, LO-analysis of equatorial view (aperture facing): B1, microreticulate ornamentation;
	A. Avicennia bicolor. A1-A4, LO-analysis of equatorial view (aperture facing): A1, reticulate ornamentation; A2, A5 A6 A7 B2, optical section. A8 B3-B4, LO-analysis of equatorial view (intercolpium): B3, microreticulate ornamentation; B4, optical section. Figure S4. Popescu). Scale bar = 5 µm. B5-B6, LO-analysis of polar view: B5, microreticulate ornamentation; B6, optical section. C, Rhizophora mucronata. C1-C2, LO-analysis of equatorial view (aperture facing): C1, scabrate ornamentation; C2, Figure S3. Scale bar = 5 µm. A4 A6 A, Avicennia alba = A. marina. A5 A6 A7 A8 optical section. A5 A1-A4, LO-analysis of equatorial view (intercolpium): A1, reticulate ornamentation; A2, C3-C4, LO-analysis of polar view: C3, scabrate ornamentation; C4, optical section.
	focus at base of columellae; A3, ecto-and endo-apertures; A4, optical section. focus at base of columellae; A3, colpori; A3, optical section. D, Bruguiera parviflora.
	A5-A8, LO-analysis of polar view: A5, reticulate ornamentation; A6, focus at base of columellae; A7, apocolpium; A8, optical section. B1 B3 B4 A. Avicennia schaueriana. A5-A6, LO-analysis of polar view: A5, reticulate ornamentation and focus at base of D1-D2, LO-analysis of equatorial view (aperture facing): D1, scabrate ornamentation; D2, B2 A1-A3, LO-analysis of equatorial view (aperture facing): A1, reticulate ornamentation; A2, columellae; A6, optical section. optical section.
	B, Avicennia africana = A. germinans. focus at base of columellae; A3, optical section. A7, Equatorial overview (aperture facing). D3-D4, LO-analysis of polar view: D3, scabrate ornamentation; D4, optical section.
	B1-B4, LO-analysis of equatorial view (intercolpium): B1, reticulate ornamentation; B2, A4-A6, LO-analysis of polar view: A4, reticulate ornamentation; A5, focus at base of A8, Polar overview. E, Ceriops roxburghiana = C. decandra.
	focus at base of columellae; B3, colpi; B4, optical section. columellae; A6, optical section. B, Avicennia officinalis. E1-E2, LO-analysis of equatorial view (aperture facing): E1, scabrate ornamentation; E2,
	B5-B6, LO-analysis of polar view: B5, reticulate ornamentation; B6, optical section. B7, Equatorial overview (aperture facing). B. Avicennia tonduzii. B1-B3, LO-analysis of equatorial view (aperture facing): B1, reticulate ornamentation; B2, B1-B4, LO-analysis of equatorial view (intercolpium): B1, reticulate ornamentation; B2, focus at base of columellae; B3, colpi; B4, optical section. B1 B2 B4 optical section. B3 E3, Polar view, optical section.
	B8, Polar overview. focus at base of columellae; B3, optical section. B5-B7, LO-analysis of equatorial view (aperture facing): B5, reticulate ornamentation; B6,
	C, Avicennia tomentosa = A. germinans. C1-C4, LO-analysis of equatorial view (aperture facing): C1, reticulate ornamentation; C2, B5 B6 B7 B4-B6, LO-analysis of polar view: B4, reticulate ornamentation; B5, focus at base of focus at base of columellae; B7, optical section. B8 columellae; B6, optical section. B1 B2 B3 B8-B11, LO-analysis of polar view: B8, reticulate ornamentation; B9, focus at base of
	focus at base of heads of columellae, ectoaperture; C3, focus at base of columellae; C4, columellae; B10, apocolpium; B11, optical section.
	optical section. B12, Equatorial overview (intercolpium).
	C5-C6, LO-analysis of polar view: C5, reticulate ornamentation and focus at base of
	columellae; C6, optical section.
	C7, equatorial overview (intercolpium). C8, polar overview. B5	B6	B7	B12
		C1		C2	C3	C4
			B4	B5		B6
		B8		B9	B10	B11
		C5		C6	C7	C8

Pelliciera rhizophorae Planch. & Triana (Tetrameristaceae) (Figure

  Photographs at TLM of pollen grains of the modern species Nypa fruticans Wurmb (Arecaceae) (slide 34258 from the ISEM collection, plant specimen collected in India), Tarrietia perakensis King = Heritiera sumatrana (Miq.) Kosterm. (Malvaceae) (slide 17929 from the ISEM collection, plant specimen collected in Malaysia), Scyphiphora hydrophylacea C.F.Gaertn. (Rubiaceae) (slide 21266 from the ISEM collection, plant specimen collected at Singapore), Brownlowia argentata Kurz (Malvaceae) (slide 20764 from the ISEM collection, plant specimen collected in Indonesia), Brownlowia elata Roxb. Brownlowia argentata Kurz and Brownlowia elata Roxb. (Malvaceae) (FigureS6, D1-D4). Oblate pollen, tricolporate, interaperturate with marked costae along the short ectoapertures, reticulate ornamentation of the thick ectexine. Xylocarpus mekongensis Pierre (Meliaceae) (FigureS6, E1-E2). Oblate pollen, tricolporate to tetracolporate, scabrate. Ectoapertures (colpi) are very short, endoapertures (pori) are bordered by a thick discontinuous annulus. Sonneratia caseolaris (L.)Engl. (Lythraceae) (Figure S6, F1-F2). Large prolate pollen, triporate, granulate to verrucate ornamentation. Apertures (pori) are circular, prominently protruding and bordered by a thin annulus. Excoecaria agallocha L. (Euphorbiaceae) (Figure S6, G1-G5). Prolate to oblate pollen, tricolporate, finely reticulate ornamentation. Ectoapertures are long, endoapertures narrowly elliptic. Figures S6-S10 display photographs of fossil pollen grains ascribed to mangrove taxa from PETM, EECO and MMCO samples. To complete our iconography of Avicennia fossil pollen grains, it is to be specified that the pollen grains published as Gunnera by Palacios Chavez & Rzedowski (1993: Plate XXIV, Fig. 479) and as Retitricolpites sp. by Médus (1975: Plate XIV, Figs. 27-28) probably belong to Avicennia. Comment about the Sonneratia-type pollen. Only seven pollen grains (from Gan, Kallo, Morlaàs 1, Site 547 and Site 918) have been recorded showing a morphology evoking that of Sonneratia. The best preserved pollen of this group is shown in Figure S9 (C1-C2). These pollen grains, similar to that published by Gruas-Cavagnetto et al. (1988) from Thanetian of Southern France, are characterised by mesocolpal ridges, a verrucate equatorial belt, and no distinctive polar caps: according to Mao and Foong (2013), they are possibly assignable to the fossil genus Florschuetzia, a potential precursor of the extant Sonneratia genus. Waiting for more records of such pollen grains, we chose to group them within the term Sonneratiatype. Photographs at TLM of fossil pollen grains from PETM sediments -location number refer to Figure 2 (shots by J.-P. Suc & S.-M. Popescu). Site 918 (location 5), 1180,49 mbsf, equatorial view (aperture facing). C2, Site 547 (location 11), 279.31 mbsf, equatorial view (aperture facing). C3-C4, Site 547 (location 11), 279.53 mbsf, equatorial view (aperture facing). Site 547 (location 11), 279.53 mbsf, LO-analysis of equatorial view (intercolpium): F1, reticulate ornamentation; F2, optical section. Photographs at TLM and SEM of fossil pollen grains from EECO sedimentslocation numbers refer to Figure 2 (shots by J.-P. Suc & S.-M. Popescu). Scale bar = 5 µm. A, Avicennia. A1-A2, Site M0004A (location 1), 318.86 mbsf, LO-analysis of equatorial view (aperture facing): A1, reticulate ornamentation; A2, aperture. A3, Site M0004A (location 1), 313.41 mbsf, equatorial view (aperture facing). A4-A5, Site M0004A (location 1), 297.72 mbsf, equatorial view: A4, intercolpium; A5, aperture facing. A6, M0004A (location 1, 301.53 mbsf, equatorial view (intercolpium). Caribou Hills (location 3), sample 12, polar view, reticulate ornamentation. A14, Caribou Hills (location 3), sample 18, equatorial view (aperture facing), optical section. A15-A16, Caribou Hills (location 3), sample 18, equatorial overview (intercolpium). Photographs at TLM of fossil pollen grains from EECO sediments -location numbers refer to Figure 2 (shots by J.-P. Suc & S.-M. Popescu). Site 918 (location 5). A7, 1157.21 mbsf: polar view, reticulate ornamentation. A8-A9, 1156.71 mbsf, LO-analysis of polar view: A8, reticulate ornamentation; A9, optical section. A10, 1157.71 mbsf: polar view, optical section. A11-A12, 1158.21 mbsf: A11, polar view, optical section; A12, equatorial view (aperture facing), reticulate ornamentation. B, Excoecaria. B1-B3, Site 343 (location 4), 213.995 mbsf, LO-analysis of equatorial view (intercolpium): B1, microreticulate ornamentation; B2, optical section; B3, aperture.

	Fossil pollen flora Figure S6. (Malvaceae) (slide 19839 from the ISEM collection, plant specimen collected in Burma), Xylocarpus mekongensis Pierre (Meliaceae) (slide 11310 from the ISEM collection, plant specimen collected in India), Sonneratia caseolaris (L.)Engl. (Lythraceae) (slide 653 of the Figure S9. Scale bar = 5 µm.
	GeoBioStratData collection), Excoecaria agallocha L. (Euphorbiaceae) (slide 11306 from the
	ISEM collection, plant specimen collected in Vietnam) (shots by J.-P. Suc & S.-M. Popescu). Scale bar = 5 µm. A, Avicennia. A1-A6, Site 343 (location 4). A4 A2 A5 A3 A1
	A, Nypa fruticans. A1-A3, 213.995 mbsf, equatorial view: A1, intercolpium, reticulate ornamentation; A2-A3,
	A1, Equatorial view (aperture facing), optical section. aperture facing, reticulate ornamentation.
	B, Tarrietia perakensis = Heritiera sumatrana. A4-A6, 214.30 mbsf, equatorial view (intercolpium): A4-A5, reticulate ornamentation; A6, A2 A3 A4
	A1 B3 C2 B1-B2, LO-analysis of equatorial view (aperture facing): B1, reticulate ornamentation; B2, A2 B1 B2 B4 B5 B6 C1 C3 C4 optical section. C, Scyphiphora hydrophylacea. C1-C2, LO-analysis of equatorial view (aperture facing): C1, reticulate ornamentation; C2, focus at base of columellae and colporus. C3-C4, LO-analysis of polar view: C3, reticulate ornamentation; C4, optical section. D, Brownlowia. D1-D2, Brownlowia argentata, LO-analysis of polar view: D1, reticulate ornamentation; D2, optical section. D3-D4, Brownlowia elata, LO-analysis of polar view: D3, reticulate ornamentation; D4, optical section. E, Xylocarpus mekongensis. E1, Polar view of a tetracolporate pollen, optical section. E2, Polar view of a tricolporate pollen, optical section. F, Sonneratia caseolaris. F1-F2, LO-analysis of equatorial view (aperture facing): F1, verrucate ornamentation; F2, optical section. D4 E1 E2 F1 F2 C4 D1 D2 C3 D3 B1 A1 C2 B2 C1 Figure S7. Scale bar = 5 µm. A, Avicennia. A1-A2, Site M0004A (location 1), 382.44 mbsf: A1, cluster of pollen grains; A2, polar view. A3, Faddeevsky Island (location 2), sample GS127, polar view. A4-A6, Site 918 (location 5), 1180.49 mbsf: A4-A5, equatorial view (aperture facing); A6, polar view. A7, Site 918 (location 5), 1180.71 m, equatorial view (aperture facing). A8-A10, Site 547 (location 11), equatorial views (aperture facing): A8, 279.31 mbsf; A9-A10, 279.53 mbsf. A9 A10 A8 B1 B2 A1 A5 A6 A7 Figure S8. A7, M0004A (location 1), 318.86 mbsf, equatorial view (intercolpium). A8-A9, M0004A (location 1), 287.395 mbsf, equatorial view (intercolpium), reticulate ornamentation. A10-A12, Caribou Hills (location 3), sample 18, polar view: A10, optical section; A11, reticulate ornamentation; A12, reticulate ornamentation. C1-C2, Site 343 (location 4), 214.3 mbsf, equatorial view (aperture facing): C1, ornamentation; C2, aperture. C3-C5, Site 343 (location 4), 213.995 mbsf, LO-analysis of equatorial view (aperture facing): C3, ornamentation, aperture; C4, aperture; C5, optical section. C6-C7, Site 918, 1158.21 mbsf, LO-analysis of equatorial view (aperture facing): C6, C1 C2 C3 C4 C5 A13, A1 A2 A3 optical section. A4 A5 A6 A7 A8 B1 B3 B2 A12 A11 A7-A12, C, Rhizophoraceae. A6 A7 A8 A9 A10
	G, Excoecaria agallocha. B, Brownlowia. ornamentation and aperture; C7, optical section.
	G1-G4, LO-analysis of equatorial view (aperture facing): G1, finely reticulate B1-B2, Site 918 (location 5), 1180.49 mbsf, LO-analysis polar view: B1, reticulate A9 A10 A11 A12 D, Xylocarpus.
	D1 ornamentation; G2, focus at base of columellae; G3, colporus; G4, optical section. D3 D2 G5, polar view, optical section. Nypa fruticans Wurmb (Aceraceae) (Figure S6, A1). Large spheroidal to elliptical pollen, monocolpate, with long spines, finely reticulate in D4 between spines. Tarrietia perakensis King = Heritiera sumatrana (Miq.) Kosterm. (Malvaceae) (Figure S6, B1-B2). Small prolate spheroidal pollen, tricolporate, finely reticulate. Ectoapertures (colpi) are long with thin costae, endoapertures (pori) are small and weakly annulate. Scyphiphora hydrophylacea C.F.Gaertn. (Rubiaceae) (Figure S6, C1-C4). Large spheroidal pollen, tricolporate, with reticulate ornamentation. Endoapertures (pori) are G1 G2 G4 G3 G5 ornamentation; B2, optical section. C, Rhizophoraceae. C1, D, Xylocarpus. D1, Noirmoutier (location 7), sample 2, equatorial view (intercolpium). D2, Site 547 (location 11), 279.31 mbsf, polar view. E, Nypa. E1, Noirmoutier (location 7), sample 2, optical section. E2, Calavanté 1 (location 8), 3402 m, optical section. F, Excoecaria. D1 C3 C2 C4 E1 E2 D2 F1 F2 A13 A14 A15 A16 D1-D3, Site 343 (location 4), 214.3 mbsf, LO-analysis of polar view: D1, finely reticulate ornamentation; D2, aperture; D3, optical section. E, Scyphiphora. E1-E2, Site 343 (location 4), 213.995 mbsf, LO-analysis of polar view: E1, ornamentation F1-F2, Site 918 (location 5), 1158.21 mbsf, polar view: F1, ornamentation; F2, optical section. G, Heritiera. G1, Site 918 (location 5), 1158.21 mbsf, polar view. E1 E2 F1 F2 G1 F1-F2, C1 and apertures; E2, optical section. F, Brownlowia. D3 C6 C7 D1 D2
	bordered by a thick annulus.
	E1	E2	E3

Jiménez-Moreno & Suc (2007) Jiménez-[START_REF] Jiménez-Moreno | Miocene to Pliocene vegetation reconstruction and climate estimates in the Iberian Peninsula from pollen data[END_REF]

Bernier, Peter Stassen, Noël Vandenberghe and Nadia Barhoun provided samples. This work benefited from very fruitful discussions with Jean-Claude Plaziat.

The PYRAMID project (ANR, studies of the Early Eocene in the Arctic domain benefited from grants by Sorbonne University, Rennes 1 University, Total S.A. and IODP-France. O.

sampling field trips, obtaining sediment core samples, sample analyses). The successive

DATA AVAILABILITY STATEMENT

The detailed pollen data are stored in the Dryad repository (URL for the Miocene pollen records: https://doi.org/10.5061/dryad.n02v6wwxn; URL for the Eocene pollen records: https://doi.org/10.5061/dryad.4j0zpc8bt.

CONFLICT OF INTEREST STATEMENT

The authors declare that they have no conflict of interest. Authors' Contribution: S.-M.P. & J.-P.S conceived the research, performed the Early Eocene pollen analyses, contributed to the Mid-Miocene pollen analyses, and wrote the first draft of the paper; S.F. contributed by specifying the thermal requirements of the mangrove plant ecosystems and performed the climatic data-model comparison; M.B. and G.J.-M. provided several unpublished Mid-Miocene pollen analyses; C.R. helped conceive the research; L.L. contributed by estimating the palaeolatitude of the study locations. All the authors contributed to improve the manuscript. Editor: Mark Bush.