Coccolithophore Communities Research Articles

Distribution and diversity of coccolithophore communities living in the tropical and subtropical South Atlantic: Preliminary results from AMT28.

Distribution and diversity of coccolithophore communities living in the tropical and subtropical South Atlantic: Preliminary results from AMT28.

Evolution of coccolithophore communities in the Atlantic Iberian margin during the Common Era.

Evolution of coccolithophore communities in the Atlantic Iberian margin during the Common Era.

Local hydrodynamic in coastal system affects the coccolithophore community at a short spatial scale

Coccolithophores are an ecologically and biogeochemically important group of calcifying marine plankton, contributing globally to both the organic carbon pump and the carbonate counter pump. Understanding their distribution in today's ecosystems is crucial for both paleoenvironmental reconstruction and for predicting their fate under climate change and environmental pollution. Traditionally regarded as open ocean dwellers, more recent studies have highlighted their importance in coastal systems.Here we describe the coccolithophore community in the Catalan Sea (Northwestern Mediterranean), off the Ebro River Delta, based on an oceanographic survey conducted in autumn 2019. We identify three environmentally distinct regimes: mixed (mostly shallow), transition (upper photic layers offshore), and stratified deep waters (below 75 m). Total coccolithophore density is driven by E. huxleyi and peaks in the mixed zone where nutrient concentrations are low, but nitrite concentrations are high. We propose that peak cell densities are partly explained by a switch from nitrate to nitrite usage similarly to diatoms behavior. Species diversity peaks in deeper offshore waters due to vertical stratification. Helicosphaera carteri and Algirosphaera robusta benefit from Emiliania huxleyi decrease both in coastal and offshore environment.

Inferred nutrient forcing on the late middle Eocene to early Oligocene (~40–31 Ma) evolution of the coccolithophore Reticulofenestra (order Isochrysidales)

AbstractThe first size reduction (FSR) in the Reticulofenestra-Gephyrocapsa-Emiliania (RGE) lineage (order Isochrysidales), which occurred in the early Oligocene (~32 Ma), is of great significance for understanding the Lilliput effect that has affected coccolithophore communities from the late Eocene to this day. We conducted a morphologic analysis on the coccoliths of Reticulofenestra species that lived during the late middle Eocene to early Oligocene (~40–31 Ma), using marine sediments from the South Atlantic Ocean. Our data show increasing size and decreasing abundance of the large species during the late Eocene, leading to their disappearance at the FSR, and a concurrent decrease in the size variability of the small- to medium-sized coccoliths whose central opening diameter had become very reduced. Although the cosmopolitan late Paleogene through Neogene size decrease in coccolithophores has been linked to the concomitant long-term decline in global pCO2, we suggest here that the FSR was the result of environmental destabilization caused by the expansion of eutrophic environments following the late Eocene establishment of overturning circulation associated with ice buildup on Antarctica. This study also leads us to propose a hypothetical model that links coccolith morphology of species of the RGE lineage and trophic resources in the upper ocean: the small- to medium-sized, r-selected coccolithophores with smaller coccolith central openings live in nutrient-rich waters where they rely mostly on photosynthesis and little on mixotrophy, whereas the larger, K-selected species with larger coccolith central openings live in oligotrophic waters where they are more dependent on mixotrophy.

Response of coccolithophore communities to oceanographic and atmospheric processes across the North- and Equatorial Atlantic

Changes in coccolithophore productivity in response to climate-driven ocean warming are likely to have cascading biogeochemical effects that feed back to the changing climate. This paper investigates the role (and interplay) of large-scale oceanographic and atmospheric processes across the North- and Equatorial Atlantic, including Saharan dust deposition, on the distribution of coccolithophore communities. The study is based on biological and hydrological data collected across the photic zone of the ocean, and aerosol data collected from the lower atmosphere, across 50°N–1°S during the Atlantic Meridional Transect in boreal Autumn of 2018 (AMT28), in synergy with Earth Observations. Results confirm existing understanding of the distribution of coccolithophore communities which are related to major meridional hydrological gradients across the North Atlantic. Dynamic, oxygenated and microphytoplankton-enriched waters at higher-latitudes were characterized by less diverse coccolithophore populations, dominated by placolith-bearing r-selected coccolithophores. In contrast, the heavily stratified and picoplankton-enriched waters of the subtropical gyre revealed more diverse populations, dominated by umbelliform coccolithophores and holococcolithophores at the surface, and by floriform taxa in the lower photic zone. Mean concentrations of 14.4×103cells/L present in the North Atlantic Tropical Gyre Province (30–12°N), only slightly lower compared to 17.7×103cells/L produced in the North Atlantic Drift province (50–40°N), provide a snapshot perspective on the importance of coccolithophore production in heavily stratified gyre conditions. Higher concentrations of 19’-Hexanoyloxyfucoxanthin (HexFuco) in regions of enhanced production of r-selected placolith-bearing species suggest that this pigment should not be generalized as a proxy for the entire coccolithophore community. Enhanced abundances of fast-bloomingEmiliania huxleyiandGephyrocapsa oceanica, and of cyanobacteria (including both picoplankton and N2-fixingTrichodesmiumspp.) at the surface of the region of more persistent Saharan dust deposition (at ~12-10°N) appeared to result from dust-born nutrient input. Underneath this stratified surface layer, enhanced productivity in the deep chlorophyll maximum (DCM) appeared decoupled from that on the surface, fueled by geostrophic eastward shoaling of the nutricline across the tropical North Atlantic. As this was the region of highest macronutrient concentrations measured along and below the nutricline, our data suggest that the NE tropical Atlantic may act as a permanent dust-born nutrient depocenter as previously hypothesized.

Malformation in coccolithophores in low pH waters: evidences from the eastern Arabian Sea.

Oceanic calcifying plankton such as coccolithophores is expected to exhibit sensitivity to climate change stressors such as warming and acidification. Observational studies on coccolithophore communities along with carbonate chemistry provide important perceptions of possible adaptations of these organisms to ocean acidification. However, this phytoplankton group remains one of the least studied in the northern Indian Ocean. In 2017, the biogeochemistry group at the Council for Scientific and Industrial Research-National Institute of Oceanography (CSIR-NIO) initiated a coccolithophore monitoring study in the eastern Arabian Sea (EAS). Here, we document for the first time a detailed spatial and seasonal distribution of coccolithophores and their controlling factors from the EAS, which is a well-known source of CO2 to the atmosphere. To infer the seasonality, data collected at three transects (Goa, Mangalore, and Kochi) during the Southwest Monsoon (SWM) of 2018 was compared with that of the late SWM of 2017. Apart from this, the abundance of coccolithophores was studied at the Candolim Time Series (CaTS) transect, off Goa during the Northeast Monsoon (NEM). The most abundant coccolithophore species found in the study region was Gephyrocapsa oceanica. A high abundance of G. oceanica (1800 × 103cells L-1) was observed at the Mangalore transect during the late SWM despite experiencing low pH and can be linked to nitrogen availability. The high abundance of G. oceanica at Mangalore was associated with high dimethylsulphide (DMS). Particulate inorganic carbon (PIC) and scattering coefficient retrieved from satellites also indicated a high abundance of coccolithophores off Mangalore during the late SWM of 2017. Interestingly, G. oceanica showed malformation during the late SWM in low pH waters. Malformation in coccolithophores could have a far-reaching impact on the settling fluxes of organic matter and also on the emissions of climatically important gases such as DMS and CO2, thus influencing atmospheric chemistry. The satellite data for PIC in the EAS indicates a high abundance of coccolithophore in recent years, especially during the warm El Nino years (2015 and 2018). This warrants the need for a better assessment of the fate of coccolithophores in high-CO2 and warmer oceans.

Coccolithophore assemblage changes over the past 9 kyrs BP from a climate hotspot in Tasmania, southeast Australia

Predicting phytoplankton responses to a changing climate on Tasmania's east coast is presently based on short-term plankton data sets (∼75 years). However, to better predict future phytoplankton composition, it is crucial to understand longer-term variations from geological records. A particularly important group are the coccolithophores given their vital contribution to the oceanic carbon pump.Here, we expand the archive of coccolithophores in southeast Australian waters by analysing coccolith assemblages in a 268 cm-long marine sediment core collected off Maria Island, Tasmania, using light and scanning electron microscopy in combination with sedimentary ancient DNA (sedaDNA) techniques.Coccoliths underwent a shift from a cold to warm-water adapted assemblage at ∼8.2 kyrs BP expressed by a transition in species dominance from the cold-water species Gephyrocapsa muellerae to the warmer-water species Emiliania huxleyi Type A. A period of coccolithophore community instability characterised by reduced diversity and species richness was also detected spanning ∼900 yrs. between 6 and 5 kyrs BP. The latter may be associated with a Mid-Holocene warm period in the Southern Ocean as well as sea-level rise changing the study site from a shallow coastal to deep water habitat.Emiliania huxleyi coccoliths displayed the highest total relative abundance, but less prevalent larger taxa (Calcidiscus, Coccolithus, Helicosphaera) accounted for >50% of total estimated coccolith CaCO3 sequestration, indicating that relatively scarce, densely calcified species do the ‘heavy-lifting’ of this process. Analysis of sedaDNA revealed coccolithophores contributed ∼44% to the total palaeo eukaryote composition, underlining their importance as part of the marine ecosystem in the study region. The detection of oceanographic shifts and subsequent coccolithophore assemblage composition, including past transitions of species dominance, offer valuable insight into the biological future of southeast Australian waters.

Two-year seasonality (2017, 2018), export and long-term changes in coccolithophore communities in the subtropical ecosystem of the Gulf of Aqaba, Red Sea

A two-year (2017, 2018) study of coccolithophores was undertaken in the Gulf of Aqaba in the northern Red Sea to 1) determine the local diversity and community succession patterns with high temporal and taxonomic resolution, 2) determine the contribution to exported inorganic carbon and 3) evaluate changes in communities relative to those in the mid-1970's reported in Winter et al. (1979). As typical, the oceanographic conditions in the Gulf alternated between stratified, oligotrophic through spring/summer, and mesotrophic during winter due to deep convective mixing. Noticeably, the second summer of 2018 was warmer resulting in a more pronounced thermocline. Overall, the coccolithophore dynamics followed the seasonal changes in oceanographic conditions. During the mixing period, coccolithophores were denser (>25 coccospheres mL−1) and were estimated to account on average for 3.46% of the total Chl-a. The communities were fairly homogeneous through depths and over time with a marked dominance of Emiliania huxleyi and Gephyrocapsa ericsonii. During the stratified season, coccolithophore densities were lower, particularly at the surface, such that coccolithophores were estimated to represent on average 0.72% of the total Chl-a. However, the diversity was higher and a clear vertical zonation developed with well-defined upper, intermediate and deep-dwelling communities. These included Umbellosphaera spp., Rhabdosphaera clavigera, a variety of Syracosphaera spp., holococcolithophores and Florisphaera profunda, respectively, as typical in oligotrophic systems. This further underscores the pelagic nature of the Gulf of Aqaba. Noticeably, however, coccolithophores declined in abundances and diversity during 2018, possibly due to the warmer conditions. The relative export of inorganic carbon by coccolithophores largely correlated with the density of living communities, representing <4% and <10% of total inorganic carbon exports during the stratified and mixing periods, respectively. A marked differentiation between different coccolithophore life phases was also detected. Broadly, holococcolithophores inhabited preferentially shallow, oligotrophic water layers in the stratified season, while heterococcolithophores prevailed in deeper water layers or in winter. Yet, species-specific deviations to this pattern were also detected. Finally, comparisons with the 1970's revealed marked changes compared to current communities. G. ericsonii appeared less prevalent and Umbellosphaera spp. displayed a wider temporal residence through spring/summer. Moreover, F. profunda and other deep dwelling species absent in the past are now common during the peak of summer. These observations are indicative of changes in local microbial communities, possibly linked to the ongoing rise in sea temperatures. This study provides a detailed baseline information on coccolithophores for future reassessments of community changes in the GoA.

Distribution of extant coccolithophores from the northwest continental shelf of India during the summer monsoon

ABSTRACT Coccolithophores contribute substantially to marine primary production as well as to particulate inorganic carbon (PIC) flux to the deep sea; however, there is no literature available so far from the Indian continental shelf on this functional group. We present here the first study describing the spatial variability and species composition of living coccolithophore communities from the north-western continental shelf waters (northeastern Arabian Sea) of India (SW monsoon; August 2018). We found a total of 18 species from 11 genera with Gephyrocapsa oceanica as the dominant coccolithophore. Florisphaera profunda, Calcidiscus leptoporus, Helicosphaera carteri and Umbilicosphaera sibogae were also observed in significant quantities in most of the stations. Cell abundances ranged from 0.3 to 85.6 × 103 l–1 with the maximum occurrence at the northernmost station. Coccolithophore diversity was comparatively higher in the southernmost region, while high dominance was noticed in the north. Redundancy analysis (RDA) revealed that nutrient availability was an important factor to modulate the distribution and abundance of coccolithophores. Gephyrocapsa oceanica was recorded in each station and showed a positive association with NO2 – + NO3 – levels, whereas F. profunda and U. sibogae were confined mostly to deepwater. Our study shows that a substantial number of coccolithophores are present in the shelf water and could be important as primary producers as well as for the carbon export flux. Further research attention to broaden our knowledge of the role of this functional group is warranted.

Distribution of coccoliths in surface sediments across the Drake Passage and calcification of &amp;lt;i&amp;gt;Emiliania huxleyi&amp;lt;/i&amp;gt; morphotypes

Abstract. 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 constitute invaluable indicators for palaeoenvironmental 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 influence 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 Southern Ocean.

Vertical Biogeography and Realized Niche Traits of Living Coccolithophore Community in the Eastern Indian Ocean

AbstractCoccolithophores are crucial components of marine calcifying microalgae and found to be important indicators of ecological changes. The interannual scale and vertical biogeography of springtime living coccolithophore communities were determined in the chronically under‐sampled eastern Indian Ocean (EIO) during seven consecutive years (spring 2011–2018). In addition, we quantified the realized ecological niches of dominant coccolithophore species in the region based on the ecological modeling method (MaxEnt statistics). Results indicated the interannual mean coccolithophore abundance ranged 4,306–11,140 cells L−1. The ecologically important species such as Gephyrocapsa oceanica, Emiliania huxleyi, Algirosphaera robusta, Florisphaera profunda, Umbilicosphaera sibogae, and Umbellosphaera irregularis were identified as dominant species in the coccolithophore community. Based on the ratios of coccoliths and plated coccolithophores, we observed coccolith detachment rates showed a valley near deep chlorophyll maximum layer and peaked in the surface or bottom of euphotic layer which was potentially relevant to near‐surface circulations, nutrients and light availability. From applying the ecological modeling method, we quantified three types of realized niches in coccolithophore species based on mean niche (μ) and breadth of niche (σ) which were consistent with their conventionally vertical biogeography. Our data set could be further incorporated into climatic ecological models.

Living coccolithophore communities in the central Mediterranean Sea (Summer 2016): Relations between ecology and oceanography

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.

Paleoecology of Late Cretaceous Coccolithophores: Insights From the Shallow‐Marine Record

AbstractCoccolithophores, common primary producers in Mesozoic, Cenozoic, and present oceans, are significant components of the earth’s biogeochemical cycles. Being the most productive calcifying organism on earth, their carbonate oozes play a major role in fixing CO2, thereby forming the most important long‐term CO2 sink throughout the last 100 Ma. Our understanding of their fossil ancestors is mainly based on data from chalk sequences. Generally, the Cretaceous chalks were deposited at water depths of ≥200 m under stable, pelagic conditions. Here we report on remarkably diverse fossil coccolithophore assemblages from Cenomanian‐Campanian (100‐72 Ma) nearshore deposits, with estimated water depths of ≤40 m. For interpreting the findings in a broader paleoenvironmental context, we additionally analyzed contemporaneous chalk material from the Santonian‐Campanian (86‐72 Ma) interval. Highly diverse coccolithophore associations (50–81 species/sample) characterize the nearshore setting, while the contemporaneous chalk samples are less diverse (43–54 species/sample). The absolute abundances of coccoliths from the nearshore setting are by a factor 2–10 lower than those from the chalk, diversity indices are by 20%–30% higher (Shannon Index = 2.94–3.46) in the nearshore sediments. The presence of highly diverse coccolithophore communities in nearshore settings provides new insights into their paleoecology and evolution and the paleoceanography of the Late Cretaceous. Our data revise the traditional view of coccolithophores being typical open ocean dwellers. Extreme nearshore settings of the Late Cretaceous greenhouse world were characterized by environmental conditions equating those of the hemipelagic realm but supplying a larger variety of ecological niches.

Characterization of the coccolithophore community off Cabo Verde archipelago, including the Senghor Seamount (Eastern North Atlantic)

A systematic investigation of the extant coccolithophore community around Cabo Verde archipelago was performed during the cruise MSM49 of RV Maria S. Merian, which took place in the late fall of 2015. The description of the spatial and vertical distributions of coccolithophores was based on a survey performed to the north, east and south of Cabo Verde archipelago, between the surface and 150 m water depth. The total cell densities obtained for the studied region were relatively low, reaching to a maximum of 30 × 103 cell L−1 in the upper 50 m over the southeastern slope of the Senghor seamount. Emiliania huxleyi and Gephyrocapsa oceanica were the dominant species, followed by Florisphaera profunda. The coccolithophore distribution off Cabo Verde was essentially explained by relatively warm and nutrient-depleted waters in the region during the surveyed interval, in result of the weaker NE trade winds and the northward migration of the Intertropical Convergence Zone. In these conditions, a notable zonation of coccolithophores along depth was depicted, in consequence of the inferred general well-stratified water column. Four typical depth-related groups were identified: (i) a Shallow oligotrophic (10–30 m), represented by Discosphaera tubifera and Umbellosphaera spp.; (ii) an Intermediate (40–50 m), formed by the three placolith-bearing species E. huxleyi, G. ericsonii and G. oceanica, and by Algirosphaera robusta, Helicosphaera spp., Michaelsarsia spp., Syracosphaera spp. and Umbilicosphaera spp.; (iii) a Deep (60–75 m) with F. profunda, Ophiaster spp., Oolithotus spp. and Reticulofenestra sessilis as typical members; (iv) and The Deepest (>80 m), composed by Gladiolithus flabellatus and Syracosphaera lamina. In addition, high abundances of G. oceanica related with the Eddy station were attributed to the transport and thriving of the coastal coccolithophore community, dominated by this species, from the African coast towards Cabo Verde.

Shifts in Phytoplankton Composition and Stepwise Climate Change During the Middle Miocene

AbstractThe abundance and composition of modern phytoplankton are primarily related to equator‐to‐pole temperature gradients and global ocean circulation, which in turn determine the availability of nutrients in the photic zone. The nutricline is found at greater depths in warm, tropical waters, whereas more vigorous surface mixing in higher latitudes (seasonally) enhances nutrient availability and primary productivity. Ocean temperatures were ~7°C higher during the middle Miocene Climatic Optimum (MCO; ~16.9–14.7 million years ago, Ma), which was followed by Antarctic glaciation and global cooling during the middle Miocene Climate transition (MMCT; 14.7–13.8 Ma). Four decades ago, Haq (1980, https://doi.org.10.2307/1485353) already related migration patterns of low‐latitude versus high‐latitude calcareous nannoplankton in the Atlantic Ocean to major climatic fluctuations during the Miocene. Here, we detail and discuss the macroevolutionary patterns and processes across the middle Miocene (~16.5–11 Ma) at five deep sea sites on a north‐south transect in the Atlantic Ocean (57°N to 28°S). We show that the major cooling step toward the modern “icehouse” world impacted coccolithophore communities at all latitudes. Contrary to previous observations suggesting that tropical sites showed little change and that midlatitudes were the most sensitive recorders of climate change across the MMCT, we show that all sites recorded a marked diversification and increase in abundance of reticulofenestrids. Global cooling and related increased meridional overturning circulation are implicated as likely forcings for this macroevolutionary step toward establishing modern coccolithophore communities that are dominated by eurythermal and eurytrophic species such as Emiliania huxleyi.

Coccolithophore community response to ocean acidification and warming in the Eastern Mediterranean Sea: results from a mesocosm experiment

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.

The effect of a transient frontal zone on the spatial distribution of extant coccolithophores around the Madeira archipelago (Northeast Atlantic)

In order to characterize the coccolithophore community around the Madeira archipelago and to understand the effect of a transient frontal zone on its distribution, 149 seawater samples from the first 150 m were collected in 37 stations, during the research cruise POS466 of RV Poseidon. The present study revealed the occurrence of two biogeographic domains, NE and SW, during the late winter of 2014, with distinct physical-chemical and calcareous nannoplankton characteristics. The NE sector was characterized by higher coccolithophore cell densities (mean of 56 × 103 cell L−1) and a slightly lower diversity (Margalef diversity index of 1.80) when compared with the SW sector (mean of 47 × 103 cell L−1; Md index of 1.86). The more productive sector, NE, was associated with colder, less saline and higher nutrient content water masses, linked to the injection of a westerly flow with origin in the Azores frontal system.Total cell densities ranged between 12 × 103 and 112 × 103 cell L−1, being Emiliana huxleyi the dominant species followed by small Gephyrocapsa. The most common and subordinate taxa, in order of decreasing abundance, were: Gephyrocapsa oceanica, Michaelsarsia spp., Syracosphaera spp., Umbilicosphaera spp. and Algirosphaera robusta. Relationships between environmental conditions and spatial and vertical variability in coccosphere abundance, associated E. huxleyi and small Gephyrocapsa with the more productive water mass conditions, linked to the thermohaline transient front. G. oceanica distribution indicated its preference for warmer and less turbulent coastal waters, when compared to E. huxleyi and small Gephyrocapsa. Michaelsarsia spp. and A. robusta revealed preference for the northwest coast of Madeira, associated with mesotrophic conditions of the water column. Syracosphaera spp. and Umbilicosphaera spp. were well distributed throughout the archipelago and along the sampled depths, from the coast to open ocean conditions, as well as from lower to higher productive zones, displaying affinities for the meso to oligotrophic conditions, typical of these subtropical waters. The broad depth range of several taxa and the nonexistence of the coccolithophore vertical succession were the result of homogeneous and generalized well-mixed surface layer during the present survey.

A comparison of species specific sensitivities to changing light and carbonate chemistry in calcifying marine phytoplankton

Coccolithophores are unicellular marine phytoplankton and important contributors to global carbon cycling. Most work on coccolithophore sensitivity to climate change has been on the small, abundant bloom-forming species Emiliania huxleyi and Gephyrocapsa oceanica. However, large coccolithophore species can be major contributors to coccolithophore community production even in low abundances. Here we fit an analytical equation, accounting for simultaneous changes in CO2 and light intensity, to rates of photosynthesis, calcification and growth in Scyphosphaera apsteinii. Comparison of responses to G. oceanica and E. huxleyi revealed S. apsteinii is a low-light adapted species and, in contrast, becomes more sensitive to changing environmental conditions when exposed to unfavourable CO2 or light. Additionally, all three species decreased their light requirement for optimal growth as CO2 levels increased. Our analysis suggests that this is driven by a drop in maximum rates and, in G. oceanica, increased substrate uptake efficiency. Increasing light intensity resulted in a higher proportion of muroliths (plate-shaped) to lopadoliths (vase shaped) and liths became richer in calcium carbonate as calcification rates increased. Light and CO2 driven changes in response sensitivity and maximum rates are likely to considerably alter coccolithophore community structure and productivity under future climate conditions.

Seasonal and interannual variability of coccolithophore flux in the northern South China Sea

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 Niño event, which affected the northern SCS during that season.

Distribution of living coccolithophores in eastern Indian Ocean during spring intermonsoon

We studied the biodiversity of autotrophic calcareous coccolithophore assemblages at 30 locations in the Eastern Equatorial Indian Ocean (EEIO) (80°–94°E, 6°N–5°S) and evaluated the importance of regional hydrology. We documented 26 species based on the identification of coccospheres and coccoliths, respectively. The coccolithophore community was dominated by Gephyrocapsa oceanica, Emiliania huxleyi, Florisphaera profunda, Umbilicosphaera sibogae, and Helicosphaera carteri. The abundance of coccoliths and coccospheres ranged from 0.2 × 103 to 160 × 103 coccoliths l−1 and 0.2 × 103 to 68 × 103 cells l−1, averaged 23 × 103 coccoliths l−1 and 9.4 × 103 cells l−1, respectively. Biogenic PIC, POC, and rain ratio mean values were 0.50 μgC l−1, 1.047 μgC l−1, and 0.10 respectively. High abundances of both coccoliths and coccospheres in the surface ocean layer occurred on the north of the equator. Vertically, the great majority of coccoliths and coccospheres were concentrated in water taken from depths of <75 m. The ratios between the number of coccospheres and free coccoliths indicated that coccoliths experience different levels of dissolution when transported to deep water. Abundant coccolithophores mainly occurred at the west of 90°E, which is in accordance with the presence of Wyrtki jets. Patterns of coccolithosphores and of coccoliths have been reflected in hydrological processes.