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Time-series sediment trap experiments were carried out in the western to central equatorial Pacific (Sites MT3, MT4, MT5, and MT7) from 1999 to 2002, over the transitional time period from La Niña to El Niño conditions, in order to evaluate temporal variability in planktic foraminiferal fluxes and their assemblages. The foraminiferal test flux follows a trophic gradient from higher fluxes in the Equatorial Upwelling Region (EUR) and lower fluxes in the Western Pacific Warm Pool (WPWP) region. Globigerinoides ruber commonly dominates in all sites through the experimental period. Trilobatus sacculifer, Globigerinita glutinata, and Neogloboquadrina dutertrei occurred especially in the WPWP. In contrast, Globigerina bulloides and Pulleniatina obliquiloculata characterized the fauna in the EUR. A change in hydrologic conditions from La Niña to El Niño was documented along the sites during the sampled time interval. Simultaneous with an eastward advancement of the WPWP, the EUR retreated to the east. Rapid decreases in the fluxes of G. ruber, G. bulloides, and P. obliquiloculata were recognized immediately after the more oligotrophic WPWP conditions prevailed at Sites MT4, MT5, and MT7. Fluxes of the total planktic foraminifer assemblage increased both in the EUR and in the western side of the WPWP under full El Niño conditions during the second half of 2002. Such increases in test fluxes in the western side of the WPWP were mainly attributed to G. ruber and N. dutertrei, suggesting inputs of eutrophic waters from the northern coastal area of Papua New Guinea. Test fluxes under El Niño conditions in the WPWP were at the same level as those in the EUR, giving rise to strongly increased carbonate fluxes in the western equatorial Pacific.

Shelled pteropods and planktic foraminifers are calcifying zooplankton that contribute to the biological carbon pump via the sinking of their calcareous shells. However, their importance for regional and global plankton biomass and carbon fluxes is not well understood. Here, we modeled global annual patterns of pteropod and foraminifer total carbon (TC) biomass and total inorganic carbon (TIC) export fluxes over the top 200 m using five species distribution models (SDMs). An extended version of the MARine Ecosystem DATa (MAREDAT) of zooplankton abundance observations was used to estimate the biomass of both plankton groups. We found hotspots of mean annual pteropod biomass in the high Northern latitudes and the global upwelling systems, and in the high latitudes of both hemispheres and the tropics for foraminifers. This largely agrees with previously observed distributions. For both groups, temperature is the strongest environmental correlate, followed by chlorophyll-a. We found mean annual standing stocks of 52 Tg TC (48 to 57 Tg TC) and 0.9 Tg TC (0.6 to 1.1 Tg TC) for pteropods and foraminifers, respectively. This translates to mean annual TIC fluxes of 14 Tg TIC yr(-1) (9 to 22 Tg TIC yr(-1)) for pteropod shells and 11 Tg TIC yr(-1) (3 to 27 Tg TIC yr(-1)) for foraminifer tests. These results are similar to previous estimates for foraminifers, but approximately a factor of ten lower for pteropods. Pteropods contribute 0.2%-3.2% and foraminifers 0.1%-3.8% to global surface carbonate fluxes. Including global coccolithophore fluxes, this leaves 40%-60% of the global carbonate fluxes unaccounted for. Our figures are likely lower-bound estimates due to sampling data characteristics and uncertainty associated with organism growth rates., Global Biogeochemical Cycles, 37 (6), ISSN:0886-6236, ISSN:1944-9224

Dissolved oxygen (O2) is essential for most ocean ecosystems, fuelling organisms’ respiration and facilitating the cycling of carbon and nutrients. Oxygen measurements have been interpreted to indicate that the ocean’s oxygen-deficient zones (ODZs) are expanding under global warming. However, models provide an unclear picture of future ODZ change in both the near term and the long term. The paleoclimate record can help explore the possible range of ODZ changes in warmer-than-modern periods. Here we use foraminifera-bound nitrogen (N) isotopes to show that water-column denitrification in the eastern tropical North Pacific was greatly reduced during the Middle Miocene Climatic Optimum (MMCO) and the Early Eocene Climatic Optimum (EECO). Because denitrification is restricted to oxygen-poor waters, our results indicate that, in these two Cenozoic periods of sustained warmth, ODZs were contracted, not expanded. ODZ contraction may have arisen from a decrease in upwelling-fuelled biological productivity in the tropical Pacific, which would have reduced oxygen demand in the subsurface. Alternatively, invigoration of deep-water ventilation by the Southern Ocean may have weakened the ocean’s ‘biological carbon pump’, which would have increased deep-ocean oxygen. The mechanism at play would have determined whether the ODZ contractions occurred in step with the warming or took centuries or millennia to develop. Thus, although our results from the Cenozoic do not necessarily apply to the near-term future, they might imply that global warming may eventually cause ODZ contraction., Nature, 609 (7925), ISSN:0028-0836, ISSN:1476-4687

Deepwater circulation significantly changed during the last deglaciation from a shallow to a deep-reaching overturning cell. This change went along with a drawdown of isotopically light waters into the abyss and a deep ocean warming that changed deep ocean stratification from a salinity-to a temperature-controlled mode. Yet, the exact mechanisms causing these changes are still unknown. Furthermore, the long-standing idea of a complete shutdown of North Atlantic deepwater formation during Heinrich Stadial 1 (HS1) (17.5–14.6 kyr BP) remains prevalent. Here, we present a new compilation of benthic δ13C and δ18O data from the North Atlantic at high temporal resolution with consistent age models, established as part of the international PAGES working group OC3, to investigate deepwater properties in the North Atlantic. The extensive compilation, which includes 105 sediment cores, reveals different water masses during HS1. A water mass with heavy δ13C and δ18O signature occupies the Iceland Basin, whereas between 20 and 50°N, a distinct tongue of 18O depleted, 13C enriched water reaches down to 4000 m water depths. The heavy δ13C signature indicates active deepwater formation in the North Atlantic during HS1. Differences in its δ18O signature indicate either different sources or an alteration of the deepwater on its southward pathway. Based on these results, we discuss concepts of deepwater formation in the North Atlantic that help to explain the deglacial change from a salinity-driven to a temperature-driven circulation mode. Highlights • Spatial analyses of benthic δ13C and δ18O data from OC3 Atlantic compilation for HS1. • Heavy δ13C, light δ18O waters migrated into deep western North Atlantic basin during HS1. • Active deepwater formation between 30 and 60°N in the North Atlantic during HS1. • New concepts for transport of isotopically light δ18O into deep ocean. • Major contribution of North Atlantic waters to deglacial deep ocean stratification changes.

Analyses of planktic foraminiferal assemblage data, test morphology, and stable oxygen isotopes from the Integrated Ocean Drilling Program (IODP) Site U1304 in the North Atlantic reveal a stepwise regional migration of the oceanic fronts around 0.6 Ma and 0.4 Ma, i.e., during Marine Isotope Stages (MISs) 15 and 11, respectively. Both changes of planktic foraminiferal assemblages and shell carbonate isotopes indicate that the cold Arctic waters in general persisted at IODP Site U1304 from 1.6 to 0.6 Ma (MIS 15), even though the warmer waters originating from the Atlantic waters episodically bathed Site U1304 during the interglacial periods. During the time-interval from ca. 0.6 to 0.4 Ma (MISs 15–11), an alternating dominance of Artic and Atlantic waters at the Site U1304 has been suggested from isotopic evidence. In MIS 11, the dominant planktic foraminiferal species Neogloboquadrina pachyderma experienced a short-term but significant decrease in test size. The test-size change may have been caused by accelerated reproduction in more favorite feeding conditions over the long-lasting interglacial period around the Subarctic Front. This finding is supported by the presence of massive diatoms oozes in the same time-interval. The modern-type glacial/interglacial change of the surface water system established since ca. 0.4 Ma (MIS 11) followed the Mid-Brunhes Event.

Amphistegina are common larger benthic foraminifer in coral reefs, with a nearly circumtropical distribution, and are major contributors to the CaCO3 budget of shallow marine environments. The family Amphisteginidae is dominant in Cenozoic carbonates. However, its potential as a proxy for paleoclimate reconstruction has not been completely explored. The intratest variability in trace elements of Amphistegina lessonii has been investigated using femtosecond‐laser ablation‐inductively coupled plasma‐mass spectrometry (fs‐LA‐ICP‐MS). We collected and analyzed adult specimens of A. lessonii in September 2003, November 2003, January 2004, and March 2004, from ∼2 m water depth in the coral reefs of Akajima, Okinawa, Japan. Tests of A. lessonii from these four collections were analyzed for Mg/Ca of the septa to observe Test Size‐Lifespan relationships. The lifespan of a specimen of A. lessonii of 1,200 µm in diameter is estimated at ∼3 and ∼2 months for specimens 900 µm in size. Over the estimated lifespans, Mg/Ca of individual specimens of A. lessonii is highly variable and displays co‐variation with temperature and tidal heights. Future projects may apply and further test this approach for the reconstruction of the tropical shallow marine paleoenvironments., Geochemistry, Geophysics, Geosystems, 22 (3), ISSN:1525-2027

The increase in anthropogenic induced warming over the last two centuries is impacting marine environments. Marine planktic calcifying organisms interact sensitively to changes in sea surface temperatures (SST), and the food web structure. Here, we study two high resolution multicore records from two western Mediterranean Sea regions (Alboran and Balearic basins), areas highly affected by both natural climate change and anthropogenic warming. Cores cover the time interval from the Medieval Climate Anomaly (MCA) to present. Reconstructed SSTs are in good agreement with other results, tracing temperature changes through the Common Era, and show a clear 20th century warming signal. Both cores show opposite abundance fluctuations of planktic foraminiferal species (Globigerina bulloides, Globorotalia inflata and Globorotalia truncatulinoides) a common group of marine calcifying zooplankton. The abundance ratios between these species show the switch between winter / spring surface productivity and deep winter mixing in the Balearic basin. In the Alboran Sea, Globigerina bulloides and Globorotalia inflata instead respond to local upwelling dynamics. In the pre-industrial era, changes in planktic foraminiferal productivity and species composition can be explained mainly by the natural variability of North Atlantic Oscillation (NAO), and, to lesser extent, by the Atlantic Multidecadal Oscillation (AMO). In the industrial era, starting from about 1800 Common Era (CE), this variability is affected by anthropogenic surface warming, leading to enhanced vertical stratification of the upper water column, and resulting in a decrease of surface productivity at both sites. We found that natural planktic foraminiferal population dynamics in the western Mediterranean is already altered by enhanced anthropogenic impact in the industrial era, suggesting that in this region natural cycles and influences are being overprinted by human influences.

© 2020 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd Rationale: Oxygen (δ18O) and carbon (δ13C) isotope analysis of foraminifera and other CaCO3 samples has been a key technique for paleoceanographical and paleoclimatological research for more than 60 years. There is ongoing demand for the analysis of ever smaller CaCO3 samples, driven, for example, by the desire to analyse single specimen planktic foraminifera, or small samples of tooth enamel. Methods: We present a continuous-flow mass spectrometric technique that uses cryo-focusing of sample CO2 to analyse CaCO3 samples in a weight range between 10 and 3 μg. These are considerably lower sample weights than achievable on most currently available standard instrumentation. The technique is automated, so that sample throughput lies at >60 samples per day. The method involves an on-line vial-flushing routine designed to remove machine drift due to blank CO2 build-up in the sample vials. Results: In a series of experiments the effect of blank CO2 build-up is quantified, and outgassing from the chlorobutyl septa identified as the source. An improved flushing routine together with the use of a cryo-focusing step in the analysis is demonstrated to provide the analytical stability and sensitivity to analyse CaCO3 samples in a weight range between 10 and 3 μg at ≤0.1‰ precision (1σ) for both δ18O and δ13C values. The technique yields similarly precise results for the analysis of the structural carbonate fraction of small tooth enamel samples. Conclusions: This study demonstrates that high-precision oxygen and carbon isotope analysis is possible on CaCO3 samples smaller than 5 μg by use of a continuous-flow isotope technique. Of key importance are (1) the application of a cold trap that drastically reduces sample gas loss, and (2) a modified flushing regime that eliminates increasing background CO2 build-up in sample vials during longer automated sample runs., Rapid Communications in Mass Spectrometry, 34 (19), ISSN:1097-0231, ISSN:0951-4198

Oxygen (δWe present a continuous-flow mass spectrometric technique that uses cryo-focusing of sample COIn a series of experiments the effect of blank COThis study demonstrates that high-precision oxygen and carbon isotope analysis is possible on CaCO

Most paleoceanographic studies using planktic foraminifera focus on annual means, but seasonal signals buried by the analyses of lumped specimens could be very valuable. Surface ocean feedbacks on climate change may be more significant in the seasonal realm than annual mean in the northern South China Sea, a region being strongly affected by Asian monsoons and tropical cyclones. Here we use oxygen isotope measurements on individual specimens of surface and subsurface planktic foraminiferal species to reconstruct surface seasonality and seasonal upper ocean stratification in this region. Many studies have shown that the thermocline was deeper in the tropical Pacific during the Pliocene than the Pleistocene, but the mechanism remains unclear. Several processes could lead to changes in the upper ocean stratification, such as changes in sea surface temperature and upper ocean mixing by tropical cyclones. Our results show that the upper ocean stratification was weaker during the Late Pliocene than the Early Pleistocene, with the change more significant in summer than winter, while no systematic offset is observed in the surface seasonality. The observations suggest that enhanced mixing by tropical cyclones might be the major cause of the deeper thermocline during the Pliocene.

We present the first nitrogen isotope (δ15N) measurements of planktic foraminifera, paleoceanographically important zooplankton, from the nutrient‐rich waters of the modern Southern Ocean. Foraminifera were collected from net tows in the Subantarctic and Polar Frontal Zones (SAZ and PFZ, respectively) south of Africa during winter 2015 and late summer 2016. In late summer, consistent with preferential uptake of 14N‐nitrate and the progressive, northward depletion of nitrate by phytoplankton across the Southern Ocean, foraminifer tissue and shell‐bound δ15N rise equatorward along with nitrate δ15N. However, foraminifer δ15N is ~3‰ lower than expected for heterotrophs relying on photosynthetic biomass generated directly from nitrate. This discrepancy appears to originate with the particulate organic N (PON) in late‐summer surface waters, the δ15N of which is lowered by ammonium recycling. In winter, when overall productivity and foraminifer production are reduced, foraminifer δ15N is higher (by 4.6 ± 0.8‰ for tissue and by 4.0 ± 1.5‰ for shell‐bound N compared to late summer) and exhibits no clear north‐south trend. These characteristics can also be explained by the feeding‐driven connection of foraminifera to PON, which is elevated in δ15N by net degradation in winter. Therefore, foraminifer δ15N is more closely tied to PON δ15N than to nitrate δ15N in the Southern Ocean mixed layer. Combining our isotope data with previously reported sediment trap fluxes from the western Pacific SAZ/PFZ suggests that, under modern conditions, the late‐summer ammonium recycling signal outweighs that of wintertime decomposition on the annually integrated δ15N of sinking foraminifera. ISSN:1525-2027

Stable isotope analysis of biogenic carbonates has remained one of the most important tools in paleoceanography since Emiliani (1955) first described the fluctuation of oxygen isotopes in planktic foraminifers over the Pleistocene. Many laboratories now possess equipment with the capability to analyse foraminifer specimens singularly, at least for larger planktic forms.Being able to run single specimens of planktic foraminifers is significant, because it yields entirely different information than when one would analyse multiple specimens from the same species. Planktic foraminifers have an average life span of about one month, so analysing single specimens, makes paleoceanographic data at seasonal resolution available (e.g. Ganssen et al., 2011; Metcalfe et al 2019, and references therein).Most modern equipment for stable isotope analysis of CaCO3 samples yields good precision down to 10 microgram sample size. The smallest samples are generally measured with a dual inlet technique, because that quantitatively collects the CO2 gas sample in a cold trap before analysis, leading to a more efficient use of the sample gas. Modern dual inlet equipment has a sample size limit somewhere between 10 and 6 microgram CaCO3 sample weight, and in that range usually operates at increased analytical uncertainty when compared to larger samples (e.g. Ganssen et al., 2011). Smaller samples are problematic, because at small amounts of sample gas, the dual inlet system is not able to maintain viscous flow conditions required for precise isotope analysis. To circumvent that barrier, one can use continuous-flow (CF) mass spectrometry because in CF systems the carrier gas ensures proper flow conditions even if there is (virtually) no sample gas produced. Doing so has previously allowed for the isotope analysis of CaCO3 samples in the 10 – 6 microgram range at an external precision (1SD) of ~0.12‰ for both δ18O and δ13C (e.g. Metcalfe et al 2019).To further improve the performance of CF mass spectrometry for small CaCO3 samples, we ran experiments on a Thermo GASBENCH system, equipped with a cold trap (cf. Fiebig et al 2005) and interfaced with a Delta-V mass spectrometer. The experiments consisted of replicate analysis of CaCO3 standards between 10 and 3 micrograms in weight, which is the weight range of many of the smaller specimens of planktic foraminifers.Several hardware modifications were implemented to improve system stability and remove observed effects of contribution of blank CO2 building up in the sample vials. With these modifications, external reproducibility of the set-up for carbonate standard aliquots between 10 and 4 microgram reached a precision of ~0.10 ‰ for both δ18O and δ13C (1SD). This is similar to precisions typically attained for routine analysis of much larger samples in standard operation on the same equipment, and demonstrates that precise stable isotope analysis of smaller single-specimen planktic foraminifers than we could achieve so far is within reach of CF mass spectrometry.References:Emiliani, C. 1955, DOI: 10.1086/626295Fiebig, J., et al. 2005, DOI: 10.1002/rcm.2060Ganssen, G.M., et al., 2011, DOI:10.5194/cp-7-1337-2011Metcalfe, B., et al., 2019, DOI: 10.1029/2018PA003475

We report the nitrogen (N) isotope ratios (δ15N) of planktic foraminifera collected from upper-ocean net tows (surface to 200 m), moored sediment traps, and core-top sediments at the Bermuda Time-series Site in the northern Sargasso Sea between 2009 and 2013. Consistent with previous measurements from low-latitude core-top sediments, the annually-averaged δ15N of organic matter bound within the shells of euphotic zone-dwelling, dinoflagellate symbiont-bearing foraminifera collected in net tows (2.3‰ on average) approximates that of shallow thermocline (∼200 m) nitrate (2.6‰), the dominant source of new N to Sargasso Sea surface waters. Deeper-dwelling foraminifer species without dinoflagellate symbionts tend to have a higher δ15N (3.6‰ on average). We observe no systematic difference between the bulk tissue and shell-bound δ15N in net tow-collected foraminifera. A decline in shell N content is observed from net tows (6.8 nmol/mg) to sediment traps (5.4 nmol/mg) and surface sediment (3.0 nmol/mg). On average, shell-bound δ15N rises from net tows (3.1‰) to sediment traps (3.7‰) but does not change further upon incorporation into the sediments (3.7‰). Together, these observations are consistent with preferential loss of shells or shell portions with lower δ15N and higher N content during sinking through the upper 500 m, followed by a non-isotope fractionating decrease in N content between sinking and burial. Time-series data from sediment traps (and to a lesser extent, surface net tows) exhibit seasonal δ15N variations, with a minimum in early spring, a maximum in late spring and a decline from summer to fall. These variations appear to arise from seasonal changes in the δ15N of total upper-ocean biomass, which are, in turn, driven by early springtime nitrate supply, subsequent nitrate drawdown, and an increase in the relative importance of ammonium recycling into the late summer and early fall. The δ15N connection between total upper ocean biomass and foraminifera indicates that foraminifer-bound δ15N records the δ15N of the annual nitrate supply in oligotrophic (e.g., subtropical) environments but will also be sensitive to the degree of nitrate consumption in high-nutrient regions and possibly to changes in upper-ocean ammonium recycling under some conditions.

Planktic foraminifera were collected with 150 µm BONGO nets from the upper 200 m water depth at 20 stations across the Mediterranean Sea between 2 May and 2 June 2013. The main aim is to characterize the species distribution and test the covariance between foraminiferal area density (ρA) and seawater carbonate chemistry in a biogeochemical gradient including ultraoligotrophic conditions. Average foraminifera abundances are 1.42 ± 1.43 ind. 10 m−3 (ranging from 0.11 to 5.20 ind. 10 m−3), including 12 morphospecies. Large differences in species assemblages and total abundances are observed between the different Mediterranean sub-basins, with an overall dominance of spinose, symbiont-bearing species indicating oligotrophic conditions. The highest values in absolute abundance are found in the Strait of Gibraltar and the Alboran Sea. The western basin is dominated by Globorotalia inflata and Globigerina bulloides at slightly lower standing stocks than in the eastern basin. In contrast, the planktic foraminiferal assemblage in the warmer, saltier, and more nutrient-limited eastern basin is dominated by Globigerinoides ruber (white). These new results, when combined with previous findings, suggest that temperature-induced surface water stratification and food availability are the main factors controlling foraminiferal distribution. In the oligotrophic and highly alkaline and supersaturated with respect to calcite and aragonite Mediterranean surface water, standing stocks and ρA of G. ruber (white) and G. bulloides are affected by both food availability and seawater carbonate chemistry. Rapid warming increased surface ocean stratification impacting food availability and changes in trophic conditions could be the causes of reduced foraminiferal abundance, diversity, and species-specific changes in planktic foraminiferal calcification.

The shoaling of the Central American Seaway (CAS) around 4.6 Ma (million years ago) is thought to have enhanced the Gulf Stream, strengthening the Atlantic Meridional Overturning Circulation and potentially influencing the evolution of Pliocene climate. Paleoclimate records indicate a buildup of heat and salt in the Caribbean and changes in the formation of North Atlantic Deep Water (NADW) associated with a major step in the shoaling of the CAS at 4.6 Ma. However, so far, direct evidence supporting an intensification of the Gulf Stream is scarce. Here we report new North Atlantic early Pliocene (5.3–3.9 Ma) records of sea surface temperature (SST) reconstructed using the U 37 K ' and TEX86 paleotemperature indices. Based on new sediment trap measurements near the study site, we suggest that in this particular region, the two paleothermometers record SST during different seasons: spring for U K 37 ' and summer for TEX86. At 4.6 and 4.2 Ma, our results indicate substantial increases in SST and salinity during summer but not spring, pointing to a significant intensification of the Gulf Stream and its extension, the North Atlantic Current, after the shoaling of the CAS. The divergence of the U 37 K ' and TEX86 temperature trends in those intervals suggests that the Gulf Stream intensification contributed to the strong North Atlantic seasonality that is observed today.

Determination of Mg/Ca in foraminifer shells as a proxy of seawater temperature is of particular interest in paleoclimate reconstruction. Here we show that femtosecond–200 nm–laser ablation–inductively coupled plasma–mass spectrometry is a suitable technique to precisely and accurately determine Mg/Ca in the micrometer‐sized calcareous chambers of foraminifers. At low fluence (0.3–0.6 J/cm2) the double‐charged 44Ca++ and the single‐charged 25Mg+ ions are measured nearly simultaneously. Integrated single‐shot measurements using a pulse repetition rate of 1 Hz enable precise analyses at a depth resolution of about 50–100 nm/pulse corresponding to an ablated material of 0.3–0.6 ng calcite/pulse for a spot size of 55 μm. High‐resolution analyses can be performed until a depth of 10–20 μm and thus particularly suitable for thin‐shelled foraminifers. Reproducibility (relative standard deviation) is about 5% as approved by homogeneous reference materials. Calibration is performed with the microanalytical synthetic reference material MACS‐3. Magnesium and Ca data of different carbonate and silicate reference materials agree within uncertainties with reference values. The procedure has been successfully applied for detailed analyses of single chambers and shell‐depth profiles of live individuals and empty planktic and benthic foraminifer tests from different ocean basins. Plain Language Summary The ratio of magnesium and calcium (Mg/Ca) of the calcareous shells of singled‐celled marine microorganisms called foraminifers is used for temperature reconstruction of the past ocean and climate. We have been using very short laser pulses of 10−13 s to sample small amounts of calcite and Mg/Ca from very thin layers to analyze temperature at high accuracy and precision. Using low energy densities of 0.3–0.6 J/cm2, Mg/Ca has been determined by mass spectrometry by applying a new single‐shot analysis. Reproducibility of the analyses is about 5% as approved by homogeneous reference materials. The procedure has been successfully applied for detailed analyses of single chambers and shell‐depth profiles of live individuals and empty planktic and benthic foraminifer shells from different ocean basins. The new method allows analyses of fossil shells to determine physiological processes and temperatures of ocean waters dating back several millions of years.

The literature on the relative contributions of pelagic calcifying taxa to the global ocean export of CaCO3 is divided. Studies based on deep sediment trap data tend to argue that either foraminifers or coccolithophores, both calcite producers, dominate export. However, the compilations of biomass observations for pteropods, coccolithophores, and foraminifers instead show that pteropods dominate the global ocean calcifier biomass and therefore likely also carbonate export. Here we present a new global ocean biogeochemical model that explicitly represents these three groups of pelagic calcifiers. We synthesize databases of the physiology of the three groups to parameterize the model and then tune the unconstrained parameters to reproduce the observations of calcifier biomass and CaCO3 export. The model can reproduce both these observational databases; however, substantial dissolution of aragonite above the aragonite saturation horizon is required to do so. We estimate a contribution of pteropods to shallow (100 m) export of CaCO3 of at least 33% and to pelagic calcification of up to 89%. The high production‐high dissolution configuration that shows closest agreement with all the observations has a CaCO3 production of 4.7 Pg C/year but CaCO3 export at 100 m of only 0.6 Pg C/year.

The dawn of animals remains one of the most mysterious milestones in the evolution of life. The fossil lipids 24-isopropylcholestane and 26-methylstigmastane are considered diagnostic for demosponges—arguably the oldest group of living animals. The widespread occurrence and high relative abundance of these biomarkers in Ediacaran sediments from 635–541 million years (Myr) ago have been viewed as evidence for the rise of animals to ecological importance approximately 100 Myr before their rapid Cambrian radiation. Here we show that the biosynthesis of 24-isopropylcholestane and 26-methylstigmastane precursors is common among early-branching unicellular Rhizaria—heterotrophic protists that play an important role in trophic cycling and carbon export in the modern ocean. Negating these hydrocarbons as sponge biomarkers, our study places the oldest evidence for animals closer to the Cambrian Explosion. Cambrian silica hexactine spicules that are approximately 535 Myr old now represent the oldest diagnostic sponge remains, whereas approximately 558-Myr-old Dickinsonia and Kimberella (Ediacara biota) provide the most reliable evidence for the emergence of animals. The proliferation of predatory protists may have been responsible for much of the ecological changes during the late Neoproterozoic, including the rise of algae, the establishment of complex trophic relationships and the oxygenation of shallow-water habitats required for the subsequent ascent of macroscopic animals. Fossil lipid biomarkers previously thought to be diagnostic of sponges (and thus indicative of animal life) are found to be preserved in unicellular Rhizarian protists, questioning a pre-Cambrian origin of sponges.

Planktonic foraminifera grow by adding chambers onto their tests, modifying their surface area, volume, porosity, and ornamentation with each addition. This process results in a wide variety of adult morphologies and preserves a record of the early morphology. With high-resolution three-dimensional imaging techniques, precise measurements can be made on previously inaccessible parameters like surface area and volume of the test interior. Here, we used three-dimensional images (microCT scans) of extant planktonic foraminifera from plankton tows and sediment traps to measure and compare the variation in chamber and whole test volume within and between seven morphospecies. By incorporating data from Caromel et al., (2015), we were able to explore the extent of interspecific variation in growth (i.e., total volume) with each chamber addition from a total of 12 extant species. All species measured approximately adhered to log-linear growth trajectories through the majority of their ontogeny. Species exhibited characteristic deviations from the log-linear growth trajectory and were grouped into three categories on the basis thereon. The volume of the first chamber—the proloculus—varied by more than two orders of magnitude. However, subtle differences in relative growth rates could make up for the initial variation proloculus size, such that the correlation between proloculus size and biovolume decreased through ontogeny. Intraspecific variation in proloculus size, cavity volume at the final five chamber stages, and terminal calcite volume was pronounced in the seven morphospecies investigated and attributed environmental and ontogenetic differences among individuals. Finally, we generated linear models for estimating cell volume and calcium carbonate test volume from linear measurements (major and minor axis) that are more accurate than the spherical equivalents used previously.

International audience; Planktonic foraminifer tests are major archives of environmental change and provide a multitude of proxies in paleoceanography and paleoclimatology. The application of such proxies is contingent upon a collaborative effort to better understand how the living organisms record the properties of their environment and how the resulting signals are recorded in marine sediments. In this contribution, we provide a review of the rapidly developing sub-fields of research, where new advances have been made possibleby technological developments, and by cross-disciplinary work of the scientific community. Following brief historical overviews of the sub-fields, we discuss the latest advances in planktonic foraminifer research and highlight the resulting new perspectives in ocean and climate research. Natural classification based on consistent species concepts forms the basis for analysis of any foraminifer-derived proxy. New approaches in taxonomy and phylogeny of Cenozoic planktonic foraminifers (Section 2) are presented, highlighting new perspectives on sensitivity and response of planktonic foraminifers to the changing climate and environment (Section 4). Calibration of foraminifer-specific data and environmental parameters is improving along with the technical development of probes and the access to samples from the natural environment (Section 3), enhancing our understanding of the ever-changing climate and ocean system. Comprehension of sedimentation and flux dynamics facilitates maximum gain of information from fossil assemblages (Section 5). Subtle changes in the physical (e.g., temperature), chemical (e.g., pH), and biological (e.g., food) conditions of ambient seawater affect the abundance of species and composition of assemblages as well as the chemical composition of the foraminifer shell and provide increasingly-detailed proxy data on paleoenvironments (Section 6).

International audience; Eight SSU rDNA genetic types have been described in the planktonic foraminifera Neogloboquadrina pachyderma, but the level of correlation between genetic diversity and morphological variation remains unknown in this morphospecies. In this study, we combine molecular and morphometric analyses of specimens of N. pachyderma sampled during two consecutive years across a latitudinal gradient in the Indian sector of the Southern Ocean. We observe that three genetic types of N. pachyderma inhabit the (sub-)polar waters of the southern Indian Ocean where they have equivalent regional distributions to those previously observed in the South Atlantic. The geographic ranges of these genetic types are largely overlapping. Our morphometric data show that contrary to other planktonic foraminiferal morphospecies, there is no relationship between genetic diversity and morpho- logical di␣erentiation in at least two of the austral representatives of N. pachyderma (Type III and Type IV) despite a high morphological variability and large genetic distance between these types. These genetic types of N. pachyderma in the southern Indian Ocean thus constitute true cryptic species of planktonic foraminifera.