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The study's major goal was to identify the most significant coccoliths based on foraminiferal species and fragment abundances, oxygen isotope ratios, and calculated temperatures. The degree of preservation of coccoliths and foraminifera indicates that the carbonate lysocline is between 3500 and 4000 m. The distribution of forty-four coccolithophore species in one hundred deep-sea core-tops from the southwest Indian Ocean is used. Gephyrocapsa oceanica has the strongest relationship with the foraminiferal fragments and carbonate. Calcidiscus leptoporus has the strongest influence on oxygen isotope and derived temperature. The findings could be useful in advancing paleoceanographic research.

Coccolithophores are potentially affected by ongoing ocean acidification, where rising CO2 lowers seawater pH and calcite saturation state (Ωcal). Southern Patagonian fjords and channels provide natural laboratories for studying these issues due to high variability in physical and chemical conditions. We surveyed coccolithophore assemblages in Patagonian fjords during late spring 2015 and early spring 2017. Surface Ωcal exhibited large variations driven mostly by freshwater inputs. High-Ωcal conditions (max. 3.6) occurred in the Archipelago Madre de Dios. Ωcal ranged from 2.0–2.6 in the western Strait of Magellan and 1.5–2.2 in the inner channel and was subsaturating (0.5) in Skyring Sound. Emiliania huxleyi was the only coccolithophore widely distributed in Patagonian fjords (> 96 % of total coccolithophores), only disappearing in the Skyring Sound, a semi-closed mesohaline system. Correspondence analysis associated higher E. huxleyi biomasses with lower diatom biomasses. The highest E. huxleyi abundances in Patagonia were in the lower range of those reported in Norwegian fjords. Predominant morphotypes were distinct from those previously documented in nearby oceans but similar to those of Norwegian fjords. Moderately calcified forms of E. huxleyi A morphotype were uniformly distributed throughout Patagonia fjords. The exceptional R/hyper-calcified coccoliths, associated with low Ωcal values in Chilean and Peruvian coastal upwellings, were a minor component associated with high Ωcal levels in Patagonia. Outlying mean index (OMI) niche analysis suggested that pH and Ωcal conditions explained most variation in the realized niches of E. huxleyi morphotypes. The moderately calcified A morphotype exhibited the widest niche breadth (generalist), while the R/hyper-calcified morphotype exhibited a more restricted realized niche (specialist). Nevertheless, when considering an expanded sampling domain, including nearby southeast Pacific coastal and offshore waters, even the R/hyper-calcified morphotype exhibited a higher niche breadth than other closely phylogenetically related coccolithophore species. The occurrence of E. huxleyi in naturally low pH–Ωcal environments indicates that its ecological response is plastic and capable of adaptation.

Emiliania huxleyi (Lohmann) evolved from the genus Gephyrocapsa Kamptner (Prymneosiophyceae) of the coccolithophore family Naёlaerhadaceae. Over the past 100 thousand years E. huxleyi has acquired the status of the most ecologically predominant coccolithophore due to its remarkable adaptability to a variety of environmental conditions and interspecific competitiveness. E. huxleyi plays an important role in both the marine carbon system and carbon cycling between the atmosphere and ocean due to its ability to produce organic and inorganic carbon as well as to form massive blooms throughout the world ocean. This study examines both older information and recent findings to shed light on the current tendencies in the two-way interactions between E. huxleyi blooms and the immediate and global environment under conditions of climate change. The assembled knowledge has emerged from laboratory and mesocosm instrumental investigations, retrievals of satellite remote sensing data, machine learning/statistical analyses, and numerical simulations. Special attention is given to both the quantitative data reported over the last two decades on such interactions, and the only very recently appearing mid-term projections of E. huxleyi bloom dynamics across the world ocean. These blooms strongly affect the atmosphere and ocean carbon cycles. They reduce CO2 fluxes from by ~50% to ~150% as is documented for the North Atlantic, and on the global scale release particulate inorganic carbon as calcium calcite in the amounts assessed at 0.4 to 4.8 PgC/yr. At the same time, they are also sensitive to the atmospheric and oceanic state. This results in E. huxleyi blooms having an increased impact on the environment in response to ongoing global warming.

Living coccolithophores (LCs) are regarded as a group of calcifiers and play important roles in global carbon cycle. This study used microscopic observations of LCs in the western Pacific Ocean to investigate their community structure and biodiversity, especially to test whether local physical traits (mesoscale eddies) could explain their biogeographic distributions during autumn of 2017. The coccolithophore calcite inventory based on carbon-volume transformation was estimated in this study. A total of 28 taxa of coccospheres and 19 types of coccoliths were identified from 161 samples. Gephyrocapsa oceanica was the most predominant species in all the coccolithophore community, followed by Florisphaera profunda, Emiliania huxleyi, Umbilicosphaera sibogae, Gladiolithus flabellatus and Umbellosphaera tenuis. The abundance of coccospheres and coccoliths ranged from 0 to 26.8×103 cells/L and from 0 to 138.5×103 coccoliths/L, averaged at 4.2×103 cells/L and 10.9×103 coccoliths/L, respectively. This study indicated that coccolithophore community in the survey area can be clustered into four groups. Three ecological niches of coccolithophores were characterized by their vertical profiles and multivariate statistical analysis. Coccolithophore abundance and species composition were remarkably different among warm-eddy region, G. oceanica dominated warm-eddy region, while F. profunda dominated warm-eddy and none-eddy region. The average values of estimated particulate inorganic carbon, particulate organic carbon were 0.197 μg/L and 0.140 μg/L, respectively. The current field study widened the dataset of coccolithophores in western Pacific Ocean.

The oceanic system has been rapidly changing under human-induced climate change that is taking place at unprecedented rates. The paleoclimate archive of the last two millennia is often adopted to discern the ongoing anthropogenic global warming from the pre-industrial natural climate variability. The Mediterranean Sea is an especially critical system, being particularly affected by climate change. A common group of marine unicellular planktonic calcifiers, coccolithophores, are forming calcite plates, coccoliths. When reaching the sediments, they have been employed as a proxy in many paleoenvironmental reconstructions and are increasingly used in the last centuries. Recent studies indicate a subtle response to historical climate changes, except for primary productivity switches during the Little Ice Age and, most importantly, across the Industrial age. In this work, we use coccolith decadal-scale resolution data from core HER-MC-MR3.3, recovered in the Balearic Sea, exploring their variability over the pre-industrial age, from 700 BCE to 1740 CE. Results are compared to planktonic foraminifera stable isotopes, planktonic foraminiferal assemblages, alkenone-derived SSTs and foraminiferal Mg/Ca-derived SSTs, previously acquired in the same sediment core. Abundance variations in coccolith assemblages, expressed as Shannon-Wiener diversity H-index changes or as trends and fluctuations in ecological groups are associated with historical climate changes, among others the Medieval Climatic Anomaly and the Little Ice Age, indicating repeated modifications in surface water conditions, in response to hydrological and atmospheric changing patterns. A tight relationship between deep nutricline and upper water column stratified conditions, derived from high abundance of Florisphaera profunda, and high solar irradiation levels is established. The solar activity fingerprint in the F. profunda distribution pattern is further assessed by spectral analysis, with the emergence of significant periodicities observed in solar activity proxies, among others the well-known de Vries-Suess cycle. Finally, we notice small but statistically significant abundance fluctuations in holococcoliths (solution susceptible coccolith forms) that may be tied to their enhanced preservation during increased rainfall in western Europe. This implies the advection of westerlies and long-lasting blocking events that may have promoted deep-water formation and seafloor ventilation during this time. The comparison with sedimentological proxies of bottom current strength shows some inconsistencies but still defines variable and intermittent deep-water formation rates in the Gulf of Lions over the pre-industrial period.

The analysis of phytoplankton in the winter-spring period is important for investigating peculiarities of its annual dynamics and the Black Sea ecosystem overall functioning. Phytoplankton state in the winter-spring period in the Black Sea shelf zone is less studied than that of the summer-autumn season; conducting such a research is especially important for solving several problems, related to the productivity of the last links of the food chain, the formation of water hydrochemical regime, and the carbon cycle in the sea. The aim of the work is to assess the effect of seasonal conditions on the development of phytoplankton and its production estimates in the winter-spring period in the coastal waters of Crimea. The article presents the results of studies of hydrophysical (water temperature, density, and relative transparency) and biological indicators (chlorophyll a concentration, its fluorescence, taxonomic composition, and phytoplankton production estimates) in the Black Sea shelf zone in January – April 2016–2019. The studies were carried out at 50 stations, located in the coastal waters of Crimea from the Karkinitsky Bay to the Kerch Strait. Chlorophyll a concentration was measured by the standard fluorometric method, species composition was determined by microscopy, and phytoplankton specific growth rate was calculated according to the previously developed model. In winter (January – February), the values of chlorophyll a content and upper mixed layer depth were the highest (0.42–0.52 mg·m−3 and 44–58 m, respectively); in spring (March – April) they were 2–3 times lower. In January – February, the coccolithophore species Emiliania huxleyi (Lohmann) W. W. Hay & H. P. Mohler, 1967 predominated; in March – April, in different years, either dinoflagellates and diatoms or coccolithophores, dinoflagellates, and diatoms prevailed. In winter, chlorophyll a vertical distribution at most stations was uniform; in spring, unimodal profiles with a depth maximum prevailed, the location of which was not related to temperature and density gradients. Relative changes in chlorophyll a concentration and fluorescence with depth were usually the same. Phytoplankton production and daily production/biomass ratio (P/B) increased from winter to spring. There was no correlation between the values of integral production, biomass, and maximum specific growth rate of algae. Maximum specific growth rate was the least variable indicator. During the winter-spring period, algae in the photosynthetic zone divided on average once every 2–5 days.

Anomalous phenomena in the development of phytoplankton in the Black Sea for the period of 2000–2020 have been recorded on the basis of satellite data. Anomalous summer blooms of diatoms were detected in the field of chlorophyll a for the blooming periods of 2001, 2010, and 2015. These blooms were unusual for the summer periods and developed under conditions of a negative anomaly in the surface layer temperature caused by active wind mixing. The highest level of development of summer blooms of coccolithophore was recorded in 2006, 2012, and 2017. These phenomena have been observed after abnormally cold winters. It has been shown that in some years, under conditions of low summer temperatures and active wind mixing, the summer vegetation of coccolithophores is poorly manifested and can be replaced by the development of diatoms. Satellite data over a twenty-year period demonstrated numerous signs of mass development of coccolithophores during the cold season. Winter blooms of coccolithophorids occur in warm winters with low wind activity. It has been noted that after the winter blooms of coccolithophores, their summer vegetation is largely smoothed. The influence of hydrometeorological factors on the seasonal and interannual variability of phytoplankton is discussed.

Mesocosm experiments have been fundamental to investigate the effects of elevated CO2 and ocean acidification (OA) on planktic communities. However, few of these experiments have been conducted using naturally nutrient-limited waters and/or considering the combined effects of OA and ocean warming (OW). Coccolithophores are a group of calcifying phytoplankton that can reach high abundances in the Mediterranean Sea, and whose responses to OA are modulated by temperature and nutrients. We present the results of the first land-based mesocosm experiment testing the effects of combined OA and OW on an oligotrophic Eastern Mediterranean coccolithophore community. Coccolithophore cell abundance drastically decreased under OW and combined OA and OW (greenhouse, GH) conditions. Emiliania huxleyi calcite mass decreased consistently only in the GH treatment; moreover, anomalous calcifications (i.e. coccolith malformations) were particularly common in the perturbed treatments, especially under OA. Overall, these data suggest that the projected increase in sea surface temperatures, including marine heatwaves, will cause rapid changes in Eastern Mediterranean coccolithophore communities, and that these effects will be exacerbated by OA.

[EN]Southern Ocean waters are projected to undergo profound changes in their physical and chemical properties in the coming decades. Coccolithophore blooms in the Southern Ocean are thought to account for a major fraction of the global marine calcium carbonate (CaCO3) production and export to the deep sea. Therefore, changes in the composition and abundance of Southern Ocean coccolithophore populations are likely to alter the marine carbon cycle, with feedbacks to the rate of global climate change. However, the contribution of coccolithophores to CaCO3 export in the Southern Ocean is uncertain, particularly in the circumpolar subantarctic zone that represents about half of the areal extent of the Southern Ocean and where coccolithophores are most abundant. Here, we present measurements of annual CaCO3 flux and quantitatively partition them amongst coccolithophore species and heterotrophic calcifiers at two sites representative of a large portion of the subantarctic zone. We find that coccolithophores account for a major fraction of the annual CaCO3 export, with the highest contributions in waters with low algal biomass accumulations. Notably, our analysis reveals that although Emiliania huxleyi is an important vector for CaCO3 export to the deep sea, less abundant but larger species account for most of the annual coccolithophore CaCO3 flux. This observation contrasts with the generally accepted notion that high particulate inorganic carbon accumulations during the austral summer in the subantarctic Southern Ocean are mainly caused by E. huxleyi blooms. It appears likely that the climate-induced migration of oceanic fronts will initially result in the poleward expansion of large coccolithophore species increasing CaCO3 production. However, subantarctic coccolithophore populations will eventually diminish as acidification overwhelms those changes. Overall, our analysis emphasizes the need for species-centred studies to improve our ability to project future changes in phytoplankton communities and their influence on marine biogeochemical cycles., European Union's Horizon 2020, Marie Skłodowska-Curie Individual fellowship

The Southern Ocean is experiencing rapid and profound changes in its physical and biogeochemical properties that may influence the distribution and composition of pelagic plankton communities. Coccolithophores are the most prolific carbonate-producing phytoplankton group playing an important role in Southern Ocean biogeochemical cycles. However, knowledge is scarce about the record of (sub-)fossil coccolith assemblages in the Southern Ocean, which are constituting invaluable indicators for paleoenvironmental reconstructions. This study investigates coccolith assemblages preserved in surface sediments of southernmost Chile and across the Drake Passage that were retrieved during R/V Polarstern Expedition PS97. We focused on the coccolith response to steep environmental gradients across the frontal system of the Antarctic Circumpolar Current and to hydrodynamic and post-depositional processes occurring in this region. We used statistical analyses to explore which environmental parameters influenced the coccolith assemblages by means of Cluster and Redundancy Analyses. We specifically assessed the morphological diversity of the dominant taxa, i.e. Emiliania huxleyi, emphasizing biogeographical variability of morphotypes, coccolith sizes and calcite carbonate mass estimations. High coccolith abundances and species diversity compared to studies in the same area and in other sectors of the Southern Ocean occur, with a high species richness especially south of the Polar Front. While the surface sediments offshore Chile and north of the Polar Front provide suitable material to reconstruct overlying surface ocean conditions, further factors such as temporary thriving coccolithophore communities in the surface waters or transport of settling coccoliths via surface and bottom currents and eddies are influencing the (sub-)fossil coccolith assemblages south of the Polar Front. Additionally, deeper samples in the southern part of the study area are particularly affected by selective carbonate dissolution. We identified five E. huxleyi morphotypes (A, A overcalcified, R, B/C and O), and estimated coccolith carbonate masses on the basis of scanning electron microscope images. E. huxleyi morphologies reflect diverging biogeographical distributions, trending towards smaller and lighter coccoliths to the south and emphasizing the importance of documenting those morphologies in relation to changing environmental conditions to assess their response to projected environmental change in the SO., Biogeosciences Discussions, ISSN:1810-6277, ISSN:1810-6285

Coccolithophore assemblages were investigated from the Faafu Atoll in November 2018. The surface waters were sampled around the islands of Magoodhoo and Adanga, from the coast to the open water towards both the lagoon and the ocean, as well as waters up to 40 m depth at selected stations. Coccolithophores were scarce close to the coast (0.1–4 × 103 coccospheres/l), increased in abundance towards both the lagoon and the open ocean (20–44 × 103 coccospheres/l) and showed no clear depth trend. The assemblages were dominated by Gephyrocapsa oceanica with a large contribution by species that are typically reported from the mid- to lower-photic zone, i.e., primarily Oolithotus antillarum, followed by Calciosolenia spp., Michaelsarsia adriaticus, Calciopappus rigidus, Ophiaster spp. and Algirosphaera robusta. As for other tropical settings, Emiliania huxleyi made a minor contribution. Taxa that are common in the upper layers of oligotrophic stratified settings like Umbellosphaera spp., Discosphaera tubifera and Rhabdosphaera clavigera were scarce. Overall, such assemblages displayed the characteristics of neritic settings, with high trophic resources and elevated water turbidity, even though the measured chlorophyll-a concentration was low throughout the investigated area.

Coccolithophores are among the most important calcifying pelagic organisms. To assess how coccolithophore species with different coccolith-carbonate mass and distinct ecological resilience to ocean warming will influence the “rain ratio” and the “biological carbon pump”, 1 yr of species-specific coccolith-carbonate export fluxes were quantified using sediment traps moored at four sites between NW Africa and the Caribbean (i.e., CB-20°N/21°W, at 1214 m; M1-12°N/23°W, at 1150 m; M2-14°N/37°W, at 1235 m; M4-12°N/49°W, at 1130 m). Highest coccolith-CaCO3 fluxes at the westernmost site M4, where the nutricline is deepest along the tropical North Atlantic, were dominated by deep-dwelling small-sized coccolithspecies Florisphaera profunda and Gladiolithus flabellatus. Total coccolith-CaCO3 fluxesof 371 mg m−2 yr−1 at M4 were followed by 165 mg m−2 yr−1 at the north-easternmost CB, 130 mg m−2 yr−1 at M1, and 114 mg m−2 yr −1 at M2 in between. Coccoliths accounted for nearly half of the total carbonate flux at M4 (45%), much higher compared to 23% at M2 and 15% at M1 and CB. At site M4, highest ratios of coccolith-CaCO3 to particulate organic carbon fluxes and weak correlations between the carbonate of deep-dwelling species and particulate organic carbon suggest that increasing productivity in the lower photic zone in response to ocean warming might enhance the rain ratio and reduce the coccolith-ballasting efficiency. The resulting weakened biological carbon pump could, however, be counterbalanced by increasing frequency of Saharan dust outbreaks across the tropical Atlantic, providing mineral ballast as well as nutrients to fuel fast-blooming and ballast-efficient coccolithophore species.

Vertical distributions of biogenic silica (bSi), particulate inorganic carbon (PIC) and key biomineral-forming phytoplankton indicate vertical zoning, or partitioning, during the late summer stratified period in the northeast Atlantic. Coccolithophores were generally more numerous in the surface mixed layer, whilst PIC concentrations were more homogenous with depth throughout the euphotic zone. Diatoms were notably more abundant and more diverse in the lower euphotic zone beneath the mixed layer in association with subsurface maxima in chlorophyll-a, bSi and oxygen concentrations. The four dominant coccolithophore species (Emiliania huxleyi, Gephyrocapsa muellerae, Syracosphera spp., and Rhabdosphaera clavigera) represented 78 ± 20% (range 31–100%) of the observed community across all sampled depths yet simultaneously contributed an average of only 13% to measured PIC pools. The diatom community, which was dominated by Pseudo-nitzschia spp. and by a species tentatively identified as Nanoneis longta, represented only ~1% of the bSi pool on average, with contributions increasing within the chlorophyll maximum. Despite a slow gradual deepening of the surface mixed layer in the period prior to observation, and adequate nutrient availability beneath the mixed layer, biomineral pools at this time consisted largely of detrital rather than cellular material.

Phytoplankton productivity and community structure in the East China Sea (ECS) play an important role in marine ecology and carbon cycle, but both have been changing rapidly in response to recent oceanic and atmospheric circulation changes. However, the lack of long-term records of phytoplankton productivity and community structure variability in the region hinders our understanding of natural forcing mechanisms. Here, we use the phytoplankton biomarker (brassicasterol, dinosterol and alkenones) contents as well as the ratios between these biomarkers in three sediment cores from the ECS shelf to reconstruct the spatiotemporal variations of productivity and community of diatoms, dinoflagellates and coccolithophores during the Holocene, respectively. During 9–7 ka, the ECS shelf was characterized by low phytoplankton productivity with low coccolithophore contribution, caused by the oligotrophic condition mainly owing to the restricted Kuroshio Current (KC) intrusion under low sea-level conditions, thus the lack of nutrient input. Phytoplankton productivity generally increased during 7–4.6 ka, in response to the initial intrusion of the Yellow Sea Warm Current (YSWC, a branch of the KC), bringing nutrient from the subsurface KC to the upper layer of the ECS for phytoplankton growth. Phytoplankton productivity continuously increased during 4.6–1 ka, due to an enhanced circulation system (YSWC and Yellow Sea Coastal Current (YSCC)) driven by strong East Asia Winter Monsoon (EAWM). Significantly, high alkenone contents and coccolithophore contribution in the eastern core F11A was associated with its location closer to the warm and saline YSWC, which was suitable for coccolithophore growth. Beyond diagenetic processes which could partly account for higher biomarker contents near core tops, elevated phytoplankton productivity during the last 1 ka might be induced by more nutrient supply from the intensified circulation system driven by enhanced KC and anthropogenic activities. The latter also resulted in high dinoflagellate proportions in all three cores. These temporal and spatial changes of phytoplankton productivity and community structure in the ECS during the Holocene corresponded to different mechanisms by the air-sea interaction, providing insights into distinguishing natural forcing and anthropogenic influences on marine ecology.

The patterns of the seasonal and inter annual variability in the development of phytoplankton, including coc- colithophores, were studied in the northeastern part of the Black Sea in various seasons. The research was carried out on the base of remote sensed data provided by the Modis Aqua ocean color scanner and long-term ship observations. The results indicate that, in the coastal and open waters of the Black Sea, the development of phytoplankton reaches the highest level in the fall-winter and winter-spring seasons, i.e., in the periods of active winter convection. It was noted that there is a relationship between the level of coccolithophore development in the summer period and the minimal temperature of the sea surface layer in the preceding winter. The most active coccolithophore blooms, were observed after the coldest winters. Unusual winter and early spring coccolithophore blooms taking place in mild hydro meteorological conditions were registered in the Black Sea, on the base of satellite data and were confirmed by in situ measurements.

Anthropogenic CO2 emissions are inundating the upper ocean, acidifying the water, and altering the habitat for marine phytoplankton. These changes are thought to be particularly influential for calcifying phytoplankton, namely, coccolithophores. Coccolithophores are widespread and account for a substantial portion of open ocean calcification; changes in their abundance, distribution, or level of calcification could have far‐reaching ecological and biogeochemical impacts. Here, we isolate the effects of increasing CO2 on coccolithophores using an explicit coccolithophore phytoplankton functional type parameterization in the Community Earth System Model. Coccolithophore growth and calcification are sensitive to changing aqueous CO2. While holding circulation constant, we demonstrate that increasing CO2 concentrations cause coccolithophores in most areas to decrease calcium carbonate production relative to growth. However, several oceanic regions show large increases in calcification, such the North Atlantic, Western Pacific, and parts of the Southern Ocean, due to an alleviation of carbon limitation for coccolithophore growth. Global annual calcification is 6% higher under present‐day CO2 levels relative to preindustrial CO2 (1.5 compared to 1.4 Pg C/year). However, under 900 μatm CO2, global annual calcification is 11% lower than under preindustrial CO2 levels (1.2 Pg C/year). Large portions of the ocean show greatly decreased coccolithophore calcification relative to growth, resulting in significant regional carbon export and air‐sea CO2 exchange feedbacks. Our study implies that coccolithophores become more abundant but less calcified as CO2 increases with a tipping point in global calcification (changing from increasing to decreasing calcification relative to preindustrial) at approximately ∼600 μatm CO2.

The patterns of the seasonal and interannual variability in the development of phytoplankton, including coccolithophores, were studied in the northeastern part of the Black Sea in various seasons. The research was carried out on the basis of long-term observations and data provided by the Modis Aqua ocean color scanner. This paper reports that, in the coastal and open waters of the Black Sea, the development of phytoplankton reaches the highest level in the fall–winter and winter–spring seasons, i.e., in the periods of active winter convection. Coastal waters are also characterized by expressed spring peak of chlorophyll “a” concentrations associated with phytoplankton bloom in March. Winter and spring coccolithophore blooms, which are unusual for the Black Sea, were registered on the basis of satellite data. It was noted that there is a relationship between the level of coccolithophore development in the summer period and the minimal temperature of the sea surface layer in the preceding winter. The most active coccolithophore blooms, which were registered in 2006 and 2012, were observed after the coldest winters.

Coccolithophorids are key player in the marine biological pump and marine carbon cycle, as their production and community-structure are crucial for export and sequestration of carbon from the atmosphere to the deep sea with important implications to climatic trends. Variations in the species composition of coccolithophore communities largely reflect environmental changes and are therefore fundamental for palaeoceanographic reconstructions. The South China Sea (SCS) is an ideal area to study the response of coccolithophores to environmental change because of the remarkable seasonal and interannual variations of the monsoonal climate and the hydrography. However, to date only limited studies on the temporal changes of coccolithophores in the modern SCS have been reported. In the present work, coccolithophores in the northern SCS were investigated using time-series sediment traps during 2009–2010 and 2011–2012. Extinct coccoliths which had their last occurrence in the Miocene (e.g. Triquetrorhabdulus longus, Reticulofenestra floridanus), Pliocene (e.g. Reticulofenestra pseudoumbilica, Discoaster tamilis), and Pleistocene (e.g. Pseudoemiliania locunosa, Discoaster variabilis) were a frequent component of the coccoliths throughout all the seasons and provided, for the first time, a strong micropaleontological evidence for lateral advective transport in the deep SCS. The source of the fossil coccoliths most likely were the reworked Pleistocene sands which cover the outer shelf and upper slope to the west and south of the Dongsha Islands between 20 m and 600 m water depth. These sediments contain limestone fragments with foraminiferal assemblages of Miocene to Pliocene age, and, to the north and south of the islands, Miocene strata are exposed on the sea floor. Mesoscale eddies, both cyclonic and anticyclonic, were probably the main agent for resuspending and transporting the coccoliths as they propagated westwards along-slope from the Dongsha area to the mooring site. Extant coccolithophore were composed of 31 taxa with Florisphaera profunda, Gephyrocapsa oceanica, and Emiliania huxleyi contributing 91.4% and 83.8% of the annual coccolithophore export flux in 2009–2010 and 2011–2012, respectively; F. profunda was the predominant species. Enhanced fluxes of extant coccoliths occurred in the summer of 2009/2010, spring 2010, autumn 2011 and winter 2011/2012, but varied in phase with the extinct species. Therefore, lateral advection of extant taxa may have also taken place but the extent to which this may have masked primary signals from in-situ coccolithophore production remains open. The low fluxes of coccoliths in the winter of 2009/2010 in association with relatively reduced wind strength, higher SST and a shallower mixed layer might compared to those of 2011/2012 have been driven by the weak El Nino event, which affected the northern SCS during that season.

A 19-year (1998–2016) continuous dataset is presented of coccolithophore Emiliania huxleyi distributions and activity, i.e. the release of CaCO3 in water and the decrease of uptake of dissolved CO2 by Emiliania huxleyi cells (e.g. Kondrik et al., 2018a), in Arctic and sub-Arctic seas. The dataset is based on optical remote-sensing data (mostly OC CCI data) with assimilation of different relevant in situ observations, preprocessed with authorial algorithms. Alongside bloom locations, we provide both detailed information on E. huxleyi impacts on carbon balance and the sub-datasets of quantified coccolith concentrations, particulate inorganic carbon content and CO2 partial pressure in water driven by coccolithophores. All data are presented on a regular 4×4 km grid at a temporal resolution of 8 days. The paper describes the theoretical and methodological basis for all processing and modelling steps. The data are available on Zenodo: https://doi.org/10.5281/zenodo.1402033.

Coccolithophores are an important group of ∼200 marine phytoplankton species which cover themselves with a calcium carbonate shell called “coccosphere.” Coccolithophores are ecologically and biogeochemically important but the reason why they calcify remains elusive. One key function may be that the coccosphere offers protection against microzooplankton predation, which is one of the main causes of phytoplankton death in the ocean. Here, we investigated the effect of the coccosphere on ingestion and growth of the heterotrophic dinoflagellate Oxyrrhis marina. Calcified and decalcified cells of the coccolithophore species Emiliania huxleyi, Pleurochrysis carterae, and Gephyrocapsa oceanica were offered separately to the predator as well as in an initial ∼1:1 mixture. The decrease of the prey concentrations and predator abundances were monitored over a period of 48–72 h. We found that O. marina did not actively select against calcified cells, but rather showed a size selective feeding behavior. Thus, the coccosphere does not provide a direct protection against grazing by O. marina. However, O. marina showed slower growth when calcified coccolithophores were fed. This could be due to reduced digestion rates of calcified cells and/or increased swimming efforts when ballasted with heavy calcium carbonate. Furthermore, we show that the coccosphere reduces the ingestion capacity simply by occupying much of the intracellular space of the predator. We speculate that the slower growth of the grazer when feeding on calcified cells is of limited benefit to the coccolithophore population because other co-occurring phytoplankton species within the community that do not invest energy in the formation of a calcite shell could also benefit from the reduced growth of the predators. Altogether, these new insights constitute a step forward in our understanding of the ecological relevance of calcification in coccolithophores.

Through a combination of selective extractions and molecular characterization techniques including Isoelectric Focusing Chromatography and Electrospray Ionization Fourier-Transform Ion Cyclotron Resonance Mass spectrometry, molecular structures of diatom (Phaeodactylum tricornutum) and coccolithophore (Emiliania huxleyi)-associated biopolymers that are responsible for the distinct partitioning behavior between 210Pb and 210Po were determined. Our results show that diatom-derived biopolymers have distinctive elemental grouping distributions as compared to those excreted by the coccolithophore, with the former consisting of more heterogeneous elements (i.e., nitrogen, sulfur and phosphorus-containing organic compounds). For the coccolithophore culture, two 210Pb-enriched biopolymers (non-attached exopolymeric substances and coccosphere shell-associated biopolymers) have a higher abundance of CHO-type compounds, suggesting CHO-only-type compounds as the main binding moieties for 210Pb. In contrast, such association was not evident in the diatom culture. Different with 210Pb, 210Po enrichment in coccolithophore-derived attached exopolymeric substances and Fe-Mn-associated metabolites coincided with the higher abundance of nitrogen/sulfur-containing organic compounds in these two biopolymer fractions, suggesting the strong parallel of Po with the production of nitrogen-rich organic matter as well as sulfur-containing amino acids. These different associations between 210Pb/210Po and organic functional groups were further explored by separating 210Pb or 210Po-labeled coccolithophore-derived biopolymers via isoelectric focusing. This technique suggests that phosphate group-containing molecules but not the other molecules that contain heterogeneous elements (e.g., CHONS, CHON, and CHOS) as the strongest binding agents for 210Pb, while the more hydrophobic (high protein to carbohydrate ratio) nitrogen/sulfur-enriched organic moieties acted as the main 210Po-binding ligands. It is concluded that the deficiency of 210Po with respect to 210Pb can be influenced by the relative abundance of nitrogen/sulfur-enriched organic moieties to the nitrogen/sulfur-depleted organic compounds in the water column. This behavior constrains the application of 210Po-210Pb approach to quantify the particulate organic carbon (POC) export flux in the ocean. It also explains that differences in chemical binding of the 210Po as compared to those of other radionuclides (e.g., thorium-234) as the main factor. That suggests that differences in decay half-lives or physical factors are less important when these nuclides are applied to estimate the POC flux in the ocean.

International audience; Heterococcoliths are calcite platelets produced inside diploid coccolithophore cells and extruded to form a covering on the cell surface called a coccosphere. The size of coccoliths is an important parameter sometimes used to identify species, and it is observed to be influenced in extant species by abiotic parameters (e.g., CO2, light). However, the variable distribution of coccolith sizes occurring within a single coccosphere questions the mechanisms controlling coccolith size. A relationship between cell/coccosphere size and mean coccolith size was previously identified, called the “coccolithophore size rules”. In this study, we query the mechanisms controlling the size of a coccolith during coccolithogenesis. A culture experiment on Gephyrocapsa huxleyi strain RCC1216 shows that coccolithogenesis occurs during the cell growth G1 interphase and newly produced coccoliths get bigger as the cell grows. These observations provide parameters for the development of two numerical models used to simulate the coccolith size distribution within a coccolithophore population. Neither model can accurately reproduce an empirical monoclonal coccolith size distribution, indicating that additional factors influence coccolith size. According to our results, coccolith size is only clearly related to cell size at the time of its formation. We confirm that application of the coccolithophore size rules model should be limited to inferring average cell dimensions from (fossil) coccolith biometry, and that comparisons are valid only in multipopulational studies. The coccolith size rule model – the constraining effect of coccolith production during G1 interphase cell growth on coccolith size – proposed here is applicable only for some placolith-forming species.

Wind-driven upwelling followed by relaxation results in cycles of cold nutrient-rich water fueling intense phytoplankton blooms followed by nutrient depletion, bloom decline, and sinking of cells. Surviving cells at depth can then be vertically transported back to the surface with upwelled waters to seed another bloom. As a result of these cycles, phytoplankton communities in upwelling regions are transported through a wide range of light and nutrient conditions. Diatoms appear to be well suited for these cycles, but their responses to them remain understudied. To investigate the bases for diatoms’ ecological success in upwelling environments, we employed laboratory simulations of a complete upwelling cycle with a common diatom, Chaetoceros decipiens, and coccolithophore, Emiliania huxleyi. We show that while both organisms exhibited physiological and transcriptomic plasticity, the diatom displayed a distinct response enabling it to rapidly shift-up growth rates and nitrate assimilation when returned to light and available nutrients following dark nutrient-deplete conditions. As observed in natural diatom communities, C. decipiens highly expresses before upwelling, or frontloads, key transcriptional and nitrate assimilation genes, coordinating its rapid response to upwelling conditions. Low-iron simulations showed that C. decipiens is capable of maintaining this response when iron is limiting to growth, whereas E. huxleyi is not. Differential expression between iron treatments further revealed specific genes used by each organism under low iron availability. Overall, these results highlight the responses of two dominant phytoplankton groups to upwelling cycles, providing insight into the mechanisms fueling diatom blooms during upwelling events. IMPORTANCE Coastal upwelling regions are among the most biologically productive ecosystems. During upwelling events, nutrient-rich water is delivered from depth resulting in intense phytoplankton blooms typically dominated by diatoms. Along with nutrients, phytoplankton may also be transported from depth to seed these blooms then return to depth as upwelling subsides creating a cycle with varied conditions. To investigate diatoms’ success in upwelling regions, we compare the responses of a common diatom and coccolithophore throughout simulated upwelling cycles under iron-replete and iron-limiting conditions. The diatom exhibited a distinct rapid response to upwelling irrespective of iron status, whereas the coccolithophore’s response was either delayed or suppressed depending on iron availability. Concurrently, the diatom highly expresses, or frontloads, nitrate assimilation genes prior to upwelling, potentially enabling this rapid response. These results provide insight into the molecular mechanisms underlying diatom blooms and ecological success in upwelling regions.

The global ocean acts as a climate regulator through the uptake of Earth’s excess heat and the absorption of about 30% of anthropogenic CO2 emissions since 1750. Southern Ocean waters are warming faster than the global ocean average and their low temperatures and moderate alkalinity make this region especially vulnerable to ocean acidification. Coccolithophores are a major group of calcifying phytoplankton and an important component of the Southern Ocean carbon cycle. Controlled laboratory experiments on Emiliania huxleyi (the most abundant coccolithophore) over a broad range of carbonate chemistry scenarios suggest that this taxon may be susceptible to ongoing environmental change. However, it remains uncertain whether Southern Ocean coccolithophore populations have been modified by environmental change during the industrial era. The main reason for this knowledge gap is the lack of observational data since the onset of the Industrial Revolution. In particular, continuous monitoring of key Southern Ocean ecosystems only started a few decades ago, a period insufficiently long to permit assessments of whether anthropogenic impacts on the environment have affected coccolithophore populations beyond their natural state. In order to overcome this limitation, here we take advantage of the preservation capacity of coccolithophores in the sedimentary record to provide a benchmark of their pre-industrial state. We compare the morphotype assemblage composition and morphometric parameters in coccoliths of E. huxleyi from a suite of Holocene-aged sediments south of Tasmania with annual sediment trap records retrieved at the Southern Ocean Time Series observatory in the Australian sector of the Subantarctic Zone. Our results suggest that carbonate dissolution in the sediments reduced the coccolith mass and length of the coccoliths but, coccolith thickness appeared to be decoupled from dissolution. The biogeographical distribution of coccolith thickness in subtropical and subantarctic sediments mirrored the distribution of E. huxleyi morphotypes, highlighting the important role of E. huxleyi assemblage composition on the control of coccolith morphometrics. Moreover, comparison of coccolith assemblages from the sedimentary record with those collected from subantarctic sediment traps indicates that modern E. huxleyi coccoliths are about 2% thinner than those from the pre-industrial Holocene. The subtle change in coccolith thickness is in stark contrast with previous work that documented a dramatic reduction in shell calcification in the planktonic foraminifera Globigerina bulloides that resulted in a shell-weight decrease of 30-35%, most likely induced by ocean acidification. Overall, our results underscore the variable sensitivity of different marine calcifying plankton groups to ongoing environmental change in the Southern Ocean.

High nutrient loading discharge into the oceans is an evolving threat to the marine biota at large, including the Bay of Bengal (BoB) which receives one of the highest inflows of nutrient fluxes from rivers like the Ganga and the Brahmaputra. Further, the complex riverine and deltaic formations are difficult to be quantified, hence satellite-based observation of chlorophyll and phytoplankton species can add more insight in the nutrient aggregation process. We evaluated the spatial sensitive zones in the BoB in terms of anthropogenic nutrients. Our study shows that coccolithophore population and chlorophyll a concentration can be an active indicator of flood mediated nutrient inflow into the oceans. SST illustrated weaker correlation with phytoplankton species during the monsoon owing to prevalence of cyclonic conditions and high nutrient concentration, however, the relationship is relatively stronger during the pre-monsoon when more stable oligotrophic conditions exist. Higher concentration of diatoms, cyanobacteria and chlorophytes in BOB compared to the Pacific Ocean indicates the ecological sensitivity and the resilience of the Bay of Bengal in terms of nutrient cycling.

In this paper, we provide the first evidence of a bloom formation of coccolithophore Syracosphaera halldalii in a salt‐wedge estuary of Krka River (Mediterranean Sea), during stratified conditions. The increase of coccolithophore abundance was firstly noticed in August 2017 and occurred again in October 2017. The increased abundance appeared over wide salinity (16.9–35.3) and temperature ranges (16.4–23.3ºC). On these two occasions, the highest abundance of S. halldalii confirmed by SEM counts reached 2.51 × 106 cells L−1 at halocline in October. The contribution of S. halldalii to total coccolithophore assemblage was more than 97%. Vertical distribution of total coccolithophores abundance varied over time and followed the temperature curve, with the highest abundances co‐occurring with maximum temperature in the water column. A positive association of coccolithophore abundances with nitrates was found, but pulses of both organic nitrogen and nitrites seem to be important for sustaining the bloom after the initial proliferation. During the entire study period, S. halldalii was found only in the heterococcolith‐bearing phase, and the absence of the holococcolith‐bearing phase could be related to increased turbulence in the estuary. SEM analysis of cell morphology was in concordance with earlier descriptions, with apical coccoliths and body coccoliths of approximately equal size and both having distinct protruding teeth along the inner rim. A single exothecal coccolith was found in association with two S. halldalii cells indicating possible dithecatism of this species.

Two ocean colour features in the western Iberian margin (western Europe) were described in present work. They were identified in 10 years (2002–2012) of MODIS-AQUA normalized water-leaving radiance (nLw) at 555 nm and their causes were investigated using complementary satellite, in-situ and model data. One feature was a band of high nLw555 (>0.8 mW cm−2 μm−1 sr−1) with exceptionally large widths (>20 km) along the coast. Over the 10-year period, this wide coastal band of high nLw555 only occurred during winter, following better the increases in wave height, than the increases in precipitation and river discharge. The band seemed particularly associated with episodes of large wave heights (>6 m), under weak thermal stratification and northerly winds. Findings suggest that the band is the signature of exceptional offshore extensions of the more reflective turbid coastal waters, as a result of wave-induced sediment resuspension along the coast. The other feature consisted in areas of equally high nLw555, but separated from the coast by more than 40 km. These offshore areas of high nLw555 shared spectral signatures of phytoplankton, namely coccolithophores, typically formed during spring following water column re-stratification and reached larger areas after winters with deeper oceanic mixed layers. Less commonly, they also occurred from summer to autumn. Results indicate they are mainly the signature of enhanced coccolithophore abundances that also create turbid reflective waters due to their calcite plates. The used methodology separated the two features in time and therefore seems to allow for satellite monitoring of sediment resuspension and coccolithophore blooms off west Iberia and similar coastal environments, which is particularly relevant for detecting events of sediment transport, potentially linked to water quality problems, and long-term changes in phytoplankton composition.

Coccolithophores represent a major component of the marine phytoplankton and contribute to the bulk of biogenic calcite formation on Earth. These unicellular protists produce minute calcite scales (coccoliths) within the cell, which are secreted to the cell surface. Individual coccoliths and their arrangements on the cell surface display a wide range of morphological variations. This review explores some of the recent evidence that points to similarities and differences in the mechanisms of calcification, focussing on the transport mechanisms that bring substrates to, and remove products from the site of calcification, together with new findings on factors that regulate coccolith morphology. We argue that better knowledge of these mechanisms and their variations is needed to inform more generally how different species of coccolithophore are likely to respond to changes in ocean chemistry. STATEMENT OF SIGNIFICANCE: Coccolithophores, minute single celled phytoplankton are the major producers of biogenic carbonate on Earth. They also represent an important component of the ocean's biota and contribute significantly to global carbon fluxes. Coccolithophores produce intricate calcite scales (coccoliths) internally that they secrete onto their external surface. This review presents some recent key findings on the mechanisms underlying the production of coccoliths. It also considers the factors that regulate the rate of production as well as the variety of shapes of individual coccoliths and their arrangements at the cell surface. Understanding these processes is needed to allow better predictions of how coccolithophores may respond to changing ocean chemistry associated with climate change.

Coccolithophores were collected at 21 stations during summer 2016, from coastal and offshore areas of the Central Mediterranean Sea, to describe the ecology of the coccolithophore community integrating information on their abundance, environmental parameters (salinity, temperature, dissolved oxygen, and fluorescence) and oceanographic data. Emiliania huxleyi dominated the assemblage from surface to intermediate layers, while Florisphaera profunda was more abundant in the deep photic zone. Principal Component Analysis revealed that the distribution of coccolithophore taxa was influenced by environmental parameters: K-strategist taxa were related to warm surface waters, whereas lower photic zone taxa were influenced by the development of a Deep Chlorophyll Maximum and high salinity values, well below the thermocline. These results confirmed that a vertical species zonation, as a typical feature of low-middle latitude, characterizes the Central Mediterranean during summer. The distribution of F. profunda once again confirmed its use as a proxy of Deep Chlorophyll Maximum development and paleoproductivity estimates. Gephyrocapsa spp. (=total Gephyrocapsa), and in particular G. oceanica, were more abundant along the Atlantic Water pathway. Finally, the high concentration value of Helicosphaera carteri, recorded in the Ligurian Sea at an offshore station, suggested an expansion of the opportunist nature of this taxon from coastal environments to the offshore areas characterized by high turbidity and high productivity.

The modern Eastern Equatorial Pacific (EEP) Ocean is a high nutrient low chlorophyll (HNLC) upwelling region and a large oceanic source of carbon to the atmosphere. During the last deglaciation, the EEP played a major role in the outgassing of carbon dioxide into the atmosphere from the upwelling surface water system of CO2-enriched deep-water masses originating from the Southern Ocean. The EEP upwelling system is also fertilizing the surface waters and enhancing the biological pump. Here we present data on the mass and calcification dynamics of the coccolithophore species Emiliania huxleyi spanning the last 30 ky at Site ODP 1238 (1°52.310′S, 82°46.934′W; 2203 m) in the EEP. Our results show an increased coccolith calcification degree during times of high pCO2 and low surface water pH conditions; this unexpected result is tentatively explained as related to changes in homeostasis equilibrium at the site of calcification and between the cell and the seawater environment. We estimated the E. huxleyi particulate inorganic to organic carbon ratio (PIC:POC) in order to detect changes in the carbonate counter-pump to carbon pump activity, which can act as either a positive or negative feedback to atmospheric CO2 modulating air-sea gas exchange. Our study indicates an enhanced coccolithophore biological pump during the last glacial that could have buffered, at least partially, the excess of pCO2atm via absorption into the ocean. Finally, during the last deglaciation, the enhanced carbonate counter pump was a major source of high pCO2sw in the EEP surface ocean.

Calcification and silicification are two major kinds of biomineralization on the Earth. Coccolithophore and diatom are major calcifier and silicifier in the oceans, respectively. Thus, these marine phytoplankton play important roles in global cycle of carbon, silicon, and calcium. In this section, the standard measurement methods for calcification and silicification, such as measuring principles, sampling and measuring procedures, and calculation, were introduced using coccolithophore and diatom as examples, respectively.

Culture experiments with coccolithophore algae—the dominant group of marine calcifying phytoplankton—imply a strong sensitivity in growth rate, degree of cellular calcification, and cell size to changes in the carbon chemistry of their growth environment. These results underpin recent studies that have explored how these physiological parameters have varied on geological time scales, in response to changing surface ocean habitats and the concentrations of carbon in the ocean-atmosphere system. Here, we add to this work with a study of reticulofenestrid coccolith size—the dominant coccolithophore family of the Cenozoic—over the Oligocene to Early Miocene time interval. We examine sediments from contrasting latitudes and regional environmental settings, comparing sites using coherent, updated age models to distinguish globally synchronous trends in cell size from regional trends. Our results confirm several changes in coccolith size—which is strongly correlated to cell size—that are globally reproducible within the ~1 Myr age uncertainty, including a reduction in mean size by >2 μm from 30.2 to 27 and 24.5 to 23 Ma, and then increase in mean size after 20 Ma. The main difference among regions is the presence/absence of coccoliths larger than 8 μm. We evaluate which scenarios of change in carbon dioxide, temperature, and nutrient availability could have exerted selective pressure on cell size for different size classes to produce the observed size trends at each studied site. These million-year scale adaptations of ancient coccolithophores contribute to the understanding of phytoplankton physiology in the transition to the modern “icehouse” world. ©2020. American Geophysical Union. All Rights Reserved. ISSN:2572-4525 ISSN:2572-4517

The effect of global climate cycles driven by Earth’s orbital variations on evolution is poorly understood because of difficulties achieving sufficiently-resolved records of past evolution. The fossil remains of coccolithophores, a key calcifying phytoplankton group, enable an exceptional assessment of the impact of cyclic orbital-scale climate change on evolution because of their abundance in marine sediments, and because coccolithophores demonstrate extreme morphological plasticity in response to the changing environment1,2. Recently, evolutionary genetic analyses linked broad changes in Pleistocene fossil coccolith morphology to species radiation events3. Here, using high-resolution coccolith data, we show that during the last 2.8 million years coccolithophore evolution was forced by Earth’s orbital eccentricity with rhythms of ~100,000 years and 405,000 years - a distinct spectral signature to that of coeval global climate cycles4. Simulations with an Earth System Model5 including the marine carbon cycle6 demonstrate that eccentricity directly impacts the diversity of ecological niches occurring over the annual cycle in the tropical ocean. Reduced seasonality favours species with mid-size coccoliths that bloom year-round, increasing coccolith carbonate export and burial. We posit that eccentricity pacing of phytoplankton evolution contributed to the strong 405,000-year pacing seen in records of the global carbon cycle. ; The effect of global climate cycles driven by Earth's orbital variations on evolution is poorly understood because of difficulties achieving 14 sufficiently-resolved records of past evolution. The fossil remains of coccolithophores, a key calcifying phytoplankton group, enable an 15 exceptional assessment of the impact of cyclic orbital-scale climate change on evolution because of their abundance in marine sediments, 16 and because coccolithophores demonstrate extreme morphological plasticity in response to the changing environment 1,2. Recently, 17 evolutionary genetic analyses linked broad changes in Pleistocene fossil coccolith morphology to species radiation events 3. Here, using 18 high-resolution coccolith data, we show that during the last 2.8 million years coccolithophore evolution was forced by Earth's orbital 19 eccentricity with rhythms of ~100,000 years and 405,000 years-a distinct spectral signature to that of coeval global climate cycles 4. 20 Simulations with an Earth System Model 5 including the marine carbon cycle 6 demonstrate that eccentricity directly impacts the diversity 21 of ecological niches occurring over the annual cycle in the tropical ocean. Reduced seasonality favours species with mid-size coccoliths 22 that bloom year-round, increasing coccolith carbonate export and burial. We posit that eccentricity pacing of phytoplankton evolution 23 contributed to the strong 405,000-year pacing seen in records of the global carbon cycle. 24 25 Coccolithophores are important producers of CaCO3 in the ocean and their fossil remains (calcite platelets called coccoliths) first appeared in 26 sediments during the late Triassic (~210 million years ago, Ma). Coccolithophores rose to dominance in the open ocean during the early 27 Cretaceous 7 and thereafter become a key biological modulator of the global carbon cycle, via both photosynthesis and calcification 8. In the 28 dominant Noëlaerhabdaceae family (including the cosmopolitan genera Emiliania, Gephyrocapsa and Reticulofenestra), species are defined by 29 the morphological characteristics of their coccoliths, with size being a key criterion 9. For Gephyrocapsa and Emiliania, phylogenies 30 reconstructed from gene sequence data indicate that morphology-based definitions correspond to biological species 3,10. Yet, within a given 31 Noëlaerhabdaceae population, interspecific and intraspecific changes in coccolith length and mass (the latter encoding degree of calcification as 32 well as size) occur in response to environmental parameters such as carbonate chemistry 1 and temperature 2. Existing studies of coccolithophore 33 evolution have focused on geological-timescale changes in species richness and turnover 11 , coccolith carbonate accumulation 7,12 , or calcification 34 potentially driven by carbon cycle changes 13. However, to date a lack of records that are both long-term and high-resolution has precluded an 35 understanding of the impact of orbital cycles (on timescales of tens to hundreds of thousands of years) on coccolithophore evolution and 36 carbonate production. 37 38

Coccolithophores are unique primary producers in the ocean with the ability to calcify. They are known to produce calcareous scales, which form the significant part of calcite oozes or chalk deposits on the seafloor. Coccolithophores are very noteworthy and they are explored to a great extent as nannofossils to reconstruct the past climate. Calcite plates in coccolithophores make them a vital tool in global climate change studies specifically with ocean acidification. These microscopic plants are the major contributor of the carbonate rain that controls the inorganic carbon pump in the ocean, which in turn influences both carbon and carbonate cycles. The emergence of advanced techniques enables us to study the biological aspects of this pelagic calcifier with improved precision. But still, they are understudied world over compared to any other phytoplankton groups. The northern Indian Ocean, being landlocked in three sides and vulnerable to climate change and ocean acidification, severely lacks focused studies on coccolithophores, though the US JGOFS in the 1990s have outlined the ecological significance of coccolithophores in the Arabian Sea. This paper reviews and outlines our understanding of coccolithophores as well as the nix in the northern Indian Ocean.

This paper presents and discusses the results of optical and biological measurements performed during the coccolithophore blooms. This study uses data of measurements from a stationary oceanographic platform (near the Southern coast of Crimea, 44°23' N, 33°59' E) in July 2012 (7–16 July) and in May 2017 (24–31 May), and data obtained during the R/V “Professor Vodyanitsky” expedition to the northern part of the Black Sea in June 2017 (14–30 June). Observation periods coincided with intensive blooms of coccolithophore. The measurements of the Secchi disk depth, light beam attenuation coefficient and reflectance coefficient, as well as biological determinations of the coccolithophore cells number in water samples, are considered and analyzed. In addition to field data, satellite information on the sea reflectance and backscattering are used. The beam attenuation coefficient, reflectance coefficient, backscattering coefficient and coccolithophore concentrations were increased as compared with no bloom period. The Secchi disk depth was abnormally low. The number of coccolithophore cells, according to biological data, varied from 150 thousand cells/L to 1.7 million cells/L and averaged 0.6 ± 0.4 million cells/L. According to these data, the estimated concentration of shed coccoliths was (1.46 ± 0.42) 1011 m-3 . The average coccolith concentrations calculated from satellite data were (1.29 ± 0.23) 1011 m-3 in July 2012, (1.32 ± 0.12) 1011 m-3 in May 2017, and (2.37 ± 0.69) 1011 m-3 in June 2017. During blooms, high variability was observed not only in optical properties, but also in biological properties, and the relationship between their spatial distribution was weak. From the optical point of view, the indicator of bloom is the number of coccoliths, not cells, which can lead to an incorrect description of the biological situation.

While seawater acidification induced by elevated CO2 is known to impact coccolithophores, the effects in combination with decreased salinity caused by sea ice melting and/or hydrological events have not been documented. Here we show the combined effects of seawater acidification and reduced salinity on growth, photosynthesis and calcification of Emiliania huxleyi grown at 2 CO2 concentrations (low CO2 LC:400 μatm; high CO2 HC:1000 μatm) and 3 levels of salinity (25, 30, and 35‰). A decrease of salinity from 35 to 25‰ increased growth rate, cell size and photosynthetic performance under both LC and HC. Calcification rates were relatively insensitive to salinity though they were higher in the LC-grown compared to the HC-grown cells at 25‰ salinity, with insignificant differences under 30 and 35‰. Since salinity and OA treatments did not show interactive effects on calcification, changes in calcification:photosynthesis ratios are attributed to the elevated photosynthetic rates at lower salinities, with higher ratios of calcification to photosynthesis in the cells grown under 35‰ compared with those grown at 25‰. In contrast, photosynthetic carbon fixation increased almost linearly with decreasing salinity, regardless of the pCO2 treatments. When subjected to short-term exposure to high light, the low-salinity-grown cells showed the highest photochemical effective quantum yield with the highest repair rate, though the HC treatment enhanced the PSII damage rate. Our results suggest that, irrespective of pCO2, at low salinity Emiliania huxleyi up-regulates its photosynthetic performance which, despite a relatively insensitive calcification response, may help it better adapt to future ocean global environmental changes, including ocean acidification, especially in the coastal areas of high latitudes.

A quasi-tropical cyclone (QTC) observed over the Black Sea on 25–29 September 2005 caused an exceptionally strong anomalous autumn coccolithophore bloom that lasted for more than 1.5 months. The QTC induced intense upwelling, causing a decrease in sea surface temperature of 15 ∘C and an acceleration of the cyclonic Rim Current up to extreme values of 0.75 m s−1. The Rim Current transported nutrient-rich Danube plume waters from the northwestern shelf to the zone of the cyclone action. Baroclinic instabilities of the plume boundary caused intense submesoscale processes, accompanied by mixing of the shelf and upwelling of the waters. These processes triggered the initial growth of remote sensing reflectance (Rrs) on the offshore front of the plume, indicating the beginning of the coccolithophore bloom. Furthermore, the bloom shifted to the zone of the strongest upwelling in the western cyclonic gyre. Intense vertical entrainment of nutrients in this area caused the increase in chlorophyll a concentration (Chl), which was then followed by a strong bloom of coccolithophores. Advection by the Rim Current spread the bloom over the entire southern part of the Black Sea, more than 1000 km from its initial source. A month after the QTC action, Rrs in these areas reached a value of 0.018 sr−1, corresponding to an estimate of a coccolithophore concentration of 107 cells per liter.

Time series of particulate nitrogen isotope delta (PN-δ 15N) and flux of trapped particles at 200 m were determined in the northwestern North Pacific subtropical gyre between 2010 and 2014 in order to examine temporal variations in mixed layer nitrate availability and downward particle export. Lower PN-δ 15N (50%), implying that new nitrogen supply stimulated predominantly coccolithophore growth and downward transport of coccoliths. Even in the stratified summer of 2011, a δ 15N drop associated with a spike in particulate flux was found and was attributed to the uplift of nitrate-rich deep waters due to a mesoscale cyclonic eddy passing the mooring station. Total nitrate input sustains 86–93% of annual new production in this region while nitrogen fixation accounts for the rest. Trapped particles also showed that the winter δ 15N decrease appeared earlier in the 2011–2012 blooms than those in 2013–2014, coinciding with 8% higher CaCO 3 concentrations and a 40% lower particulate organic carbon to inorganic carbon export ratio, R(POC:PIC). This reflected stronger convective mixing and hence larger nutrient supply in 2011–2012, caused by larger ocean heat loss related to winter monsoon intensity. Such interannual change of winter R(POC:PIC) can affect CO 2 uptake rate in the northwestern North Pacific subtropical gyre where anthropogenic CO 2 accumulates in subtropical mode waters.

Coccolithophores are a key functional phytoplankton group and produce minute calcite plates (coccoliths) in the sunlit layer of the pelagic ocean. Coccoliths significantly contribute to the sediment record since the Triassic and their geometry have been subject to palaeoceanographic and biological studies to retrieve information on past environmental conditions. Here, we present a comprehensive analysis of coccolith, coccosphere and cell volume data of the Southern Ocean Emiliania huxleyi ecotype A, subject to gradients of temperature, irradiance, carbonate chemistry and macronutrient limitation. All tested environmental drivers significantly affect coccosphere, coccolith and cell volume with driver-specific sensitivities. However, a highly significant correlation emerged between cell and coccolith volume with Vcoccolith = 0.012 ± 0.001 * Vcell + 0.234 ± 0.066 (n = 23, r2 = .85, p

A high-resolution study (centennial scale) has been performed on the calcareous plankton assemblage of the Holocene portion of the Ocean Drilling Program Site 976 (Alboran Sea) with the aim to identify the main changes in the surface water dynamic. The dataset also provided a seasonal foraminiferal sea surface water temperatures (SSTs), estimated using the modern analog technique SIMMAX 28, and it was compared with available geochemical and pollen data at the site. Three main climate shifts were identified as (1) the increase in abundance of Syracosphaera spp. and Turborotalita quinqueloba marks the early Holocene humid phase, during maximum summer insolation and enhanced river runoff. It is concomitant with the expansion of Quercus, supporting high humidity on land. It ends at 8.2 ka, registering a sudden temperature and humidity reduction; (2) the rise in the abundances of Florisphaera profunda and Globorotalia inflata, at ca. 8 ka, indicates the development of the modern geostrophic front, gyre circulation, and of a deep nutricline following the sea-level rise; and (3) the increase of small Gephyrocapsa and Globigerina bulloides at 5.3 ka suggests enhanced nutrient availability in surface waters, related to more persistent wind-induced upwelling conditions. Relatively higher winter SST in the last 3.5 ka favored the increase of Trilobatus sacculifer, likely connected to more stable surface water conditions. Over the main trends, a short-term cyclicity is registered in coccolithophore productivity during the last 8 ka. Short periods of increased productivity are in phase with Atlantic waters inflow, and more arid intervals on land. This cyclicity has been related with periods of positive North Atlantic Oscillation (NAO) circulations. Spectral analysis on coccolithophore productivity confirms the occurrence of millennial-scale cyclicity, suggesting an external (i.e. solar) and an internal (i.e. atmospheric/oceanic) forcing. Geoscience PhD scholarship, Universita degli Studi di Bari Potenziamento Strutturale dell'Universita degli Studi di Bari, Laboratorio per lo Sviluppo Integrato delle Scienze e delle Tecnologie dei Materiali Avanzati e per dispositivi innovativi (SISTEMA) [PONa3_00369] Fundacao para a Ciencia e a Tecnologia (FCT)Portuguese Foundation for Science and TechnologyEuropean Commission [SFRH/BPD/111433/2015] info:eu-repo/semantics/submittedVersion

A high-resolution study of the MIS 12/MIS 11 transition and the MIS 11 (430–376 kyr) coccolithophore assemblages at Ocean Drilling Program Site 977 was conducted to reconstruct the palaeoceanographic and climatic changes in the Alboran Sea from the variability in surface water conditions. The nannofossil record was integrated with the planktonic oxygen and carbon stable isotopes, as well as the Uk'37 Sea Surface Temperature (SST) at the studied site during the investigated interval. The coccolithophore primary productivity, reconstructed from the PPP (primary productivity proxy = absolute values of Gephyrocapsa caribbeanica + small Gephyrocapsa group) revealed pronounced fluctuations, that were strongly associated with variations in the intensity of the regional Alboran Upwelling System. The comparison of the nannoplankton record with opal phytolith content for the studied site and the already available pollen record at the nearby Integrated Ocean Drilling Program Site U1385, suggests an association of the upwelling dynamics with the variability of the North Atlantic Oscillation-like (NAO-like) phase. High PPP during positive (+) NAO-like phases is the result of intensified upwelling, owing to the complete development of the surface hydrological structures at the Alboran Sea. This scenario was identified during the MIS 12/MIS 11 transition (428-422 kyr), the late MIS 11c (405-397 kyr), and MIS11 b to MIS 11a (397-376 kyr). Two short-term minima in the PPP and SST were observed during MIS 11 b and were coeval with the North Atlantic Heinrich-type (Ht) events Ht3 (∼390 kyr) and Ht2 (∼384 kyr). Increased abundance of the subpolar Coccolithus pelagicus subsp. pelagicus and Gephyrocapsa muellerae was consistent with the inflow of cold surface waters into the Mediterranean Sea during the Ht events. Lowered PPP during negative (−) NAO-like phases is the result of moderate upwelling by the incomplete development of surface hydrological structures at the Alboran Sea. This scenario is expressed during the early MIS 11c (422-405 kyr). Overall, the results of our study provide evidence of the important role of atmospheric circulation patterns in the North Atlantic region for controlling phytoplankton primary production and oceanographic circulation dynamics in the Western Mediterranean during MIS 11., This work was supported by the FPU contract of the Ministry of Education and Professional Formation of the Spanish government [FPU17/03349] awarded to A. González-Lanchas and by the financing infrastructure provided by the programs of the Ministry of Economy and Competitiveness [CGL 2015-68459-P] and the Ministry of Science, Innovation and Universities [RTI 2018-099489-B-100] granted to the GGO (Grupo de Geociencias Oceánicas) of the University of Salamanca. DO acknowledges funding from Portuguese Foundation for Science and Technology (FCT) through the CCMAR Research Unit - project UIDB/04326/2020 and contract (CEECIND/02208/2017). The authors thank Editor Antje Voelker and the two anonymous reviewers for their valuable comments and suggestions.

Coccolithophores (calcifying phytoplankton) form extensive blooms in temperate and subpolar oceans as evidenced from ocean‐color satellites. This study examines the potential to detect coccolithophore blooms with BioGeoChemical‐Argo (BGC‐Argo) floats, autonomous ocean profilers equipped with bio‐optical and physicochemical sensors. We first matched float data to ocean‐color satellite data of calcite concentration to select floats that sampled coccolithophore blooms. We identified two floats in the Southern Ocean, which measured the particulate beam attenuation coefficient (c p) in addition to two core BGC‐Argo variables, Chlorophyll‐a concentration ([Chl‐a]) and the particle backscattering coefficient (b bp). We show that coccolithophore blooms can be identified from floats by distinctively high values of (1) the b bp/c p ratio, a proxy for the refractive index of suspended particles, and (2) the b bp/[Chl‐a] ratio, measurable by any BGC‐Argo float. The latter thus paves the way to global investigations of environmental control of coccolithophore blooms and their role in carbon export., Key Points We matched profiling float trajectories with ocean‐color satellite observations of coccolithophore bloomsTwo simple bio‐optical indices permitted successful identification of coccolithophore blooms from floats in the Southern OceanA method for identifying coccolithophore blooms at the global scale is proposed using regional thresholds of bio‐optical float measurements

Current study is investigated chlorophyll-a (Chl-a) pigment concentration and its relationship with Sea Surface Temperature (SST) using cloud-free high resolution 59 Landsat-The Operational Land Imager (OLI) images from May 2013 to September 2018 covering Lake Van of Turkey. In addition, the concentrations of coccolithophore which is a kind of phytoplankton was also studied using the same method. The fact that Van Lake is extremely rich in terms of aquatic life has led to the investigation of the factors affecting the marine habitat. Therefore, SST, Chl-a concentrations, as well as the relationship between them and coccolithophore concentrations were investigated to evaluate marine life and ecosystem in the Lake. Satellite-generated data can provide information about the marine life in a particular area worldwide. Coccolithophore, SST and Chl-a were obtained from high resolution 59 Landsat OLI using SeaDAS software. Aforementioned parameters were extracted from images using SeaDAS's OCSSW L2GEN module and then output processed by QGIS (Open Source Geographic Information System) to conduct statistical calculation. Negative correlation coefficients of 74% and 73.7% were found for 2014 and 2017, respectively, and these were not statistically significant. Although the information does not give meaningful results, it may be useful in future studies about the effects of global temperature changes and the marine life for particular region Bu çalışmada, Van Gölü'nü Mayıs 2013ve Eylül 2018 tarihleri arasını kapsayan bulutsuz 59 Landsat-The Operational Land Imager (OLI) görüntüleri kullanılarak klorofil-a (Chl-a) pigment konsantrasyonu,ve Su Yüzey Sıcaklığı (SST) ile ilişkisi araştırılmıştır ayrınca fitoplankton türü olan kokolit miktarı incelenmiştir. Türkiye'nin en büyük gölü olarak kabul edilen ve dünyanın en büyük soda gölü olan Van Gölü'nün tuzlu ve soda suları biyoçeşitliliği artıran faktörler arasındadır. Van Gölü'nün su canlılığı açısından son derece zengin olması, deniz yaşam alanını etkileyen faktörlerin araştırılmasına yol açmıştır. Bu nedenle Van Gölü'nde deniz yaşamı ve ekosistemi değerlendirmek için SST ve Chl-a konsantrasyonları ve ayrıca aralarındaki ilişki araştırılmıştır. Uydudan üretilen veriler, dünya çapında belirli bir alanda bulunan akuatik yaşam hakkında bilgi sağlayabilir. Van Gölü'nün klorofil-a pigment konsantrasyonlarını incelemek için yüksek çözünürlüklü 59 Landsat-OLI imager görüntüleri kullanıldı. SST ve Chl-a, SeaDAS yazılımı kullanılarak Landsat OLI'den elde edildi. SST, Chl-a ve Kokolit SeaDAS’ın OCSSW L2GEN modülü kullanılarak görüntülerden elde edildi ve daha sonra istatistiksel hesaplama yapmak için QGIS’de ((QGIS), 2009) (Open Source Geographic Information System) işlendi. 2014 ve 2017 yılları için istatistiksel olarak anlamlı olmayan %74 % 73,7 gibi korelasyon katsayıları bulundu. Bilgiler anlamlı sonuçlar vermese de, gelecekteki çalışmalarda küresel ısınma değişikliklerinin etkileri ve belirli bir bölge için akuatik yaşam hakkında faydalı olabilir.

Different morphotypes of the abundant marine calcifying algal species Emiliania huxleyi are commonly linked to various degrees of E. huxleyi calcification, but few studies have been done to validate this assumption. This study investigated therefore whether E. huxleyi morphotypes can be related to coccolithophore calcification and coccolith mass. Samples from January (high productivity) and September (low productivity) 1997 at an open ocean and a coastal site near the Canary Islands were analysed using a combination of thickness measurements (Circular Polarizer Retardation estimates (CPR) method), Scanning Electron Microscope imaging, and Markov Chain Monte Carlo (MCMC) models. Mean E. huxleyi coccolith mass varied from a maximum of 2.9pg at the open ocean station in January to a minimum of 1.7pg in September at both stations. In contrast, overall calcite produced by E. huxleyi (assuming 23 coccoliths/cell) varied from a maximum of 2.6 μgL-1 at the coastal station in January to a minimum of 0.5 μgL-1 in September at the open ocean site. The relative abundance of “Overcalcified” Type A, Type A, Group B and malformed coccoliths was determined from SEM images. The mean coccolith mass of “Overcalcified” Type A was 2.0pg using the CPR-method, while mean mass of Type A and Group B coccoliths was determined using coccolith length measurements from SEM images and MCMC models relating thickness measurements to morphotype relative abundance. Type A cocccolith mass varied from a 1.6pg to 2.6pg and Group B coccolith mass varied from 1.5pg to 2.0pg. These results demonstrate that the coccolith mass of Type A, “Overcalcified” Type A, and Group B do not differ systematically and there is no systematic relationship between relative abundance of a morphotype and the overall calcite production of E. huxleyi. Therefore, morphotype appearance and relative abundance can not be uniformly used as reliable indicators of E. huxleyi calcification or calcite production.