Shells Of Planktonic Foraminifera Research Articles

ON THE AGE AND CONDITIONS OF THE FORMATION OF THE POLYANYTSKA SUITE ACCORDING TO THE FORAMINIFERA STUDY RESULTS (LOWER MIOCENE, BORYSLAV-POKUTTYA NAPPE, UKRAINIAN CARPATHIANS)

Neogene deposits of the Polyanytska Suite were exposed by the South Boryslav-1 well within the eastern block of the South Boryslav structure of the Boryslav oil and gas condensate field of the Outer Carpathians. The studied sediments of the Polyanytska Suite belong to the complex zone of planktonic foraminifers Globigerina pseudoedita with a characteristic association: Globigerina pseudoedita, Globoquadrina dehiscens, Dentoglobigerina langhiana, Trilobatus trilobus, Tenuitella brevispira, Tenuitella denseconnexa, Globorotalia tetracamerata, Globigerinella evoluta, Globigerinella obesa, Chiloguembelina gracillima. The Globigerina pseudoedita zone of planktonic foraminifera correlates with the zonal interval of nannoplankton NN2-NN3 of the Central Paratethys, which covers the upper part Eggerian, Eggenburgian, and the lowest part Ottnangian of the Central Paratethys and is compared with the upper Aquitan – the lower part of the Burdigal of the lower Miocene of the Neogene of the International Chronostratigraphic Scale. The sediments of the Polyanytska Suite were formed in a normally saline sea basin, with depths from the middle to the inner shelf. The medium shelf conditions (intervals 1812–1805 m; 1684–1645 m and 1546–1485 m in the the South Boryslav-1 well) are indicated by a relatively high percentage content and morphology of the shells of planktonic foraminifera, the taxonomic composition of calcareous benthic foraminifera. The presence of plankton indicates normal water salinity. Analysis of foraminifera in the interval 1395–1365 m indicates the depths of the inner shelf. The identified redeposited foraminifera of the Paleocene-Lower Oligocene testify to the erosion and demolition of clastic material from the uplifted part of the Carpathians.

Development of a Deep‐Water Carbonate Ion Concentration Proxy Based on Preservation of Planktonic Foraminifera Shells Quantified by X‐Ray CT Scanning

AbstractThe quantitative and objective characterization of dissolution intensity in fossil planktonic foraminiferal shells could be used to reconstruct past changes in bottom water carbonate ion concentration. Among proxies measuring the degree of dissolution of planktonic foraminiferal shells, X‐ray micro‐Computed Tomography (CT) based characterization of apparent shell density appears to have good potential to facilitate quantitative reconstruction of carbonate chemistry. However, unlike the well‐established benthic foraminiferal B/Ca ratio‐based proxy, only a regional calibration of the CT‐based proxy exists based on a limited number of data points covering mainly low‐saturation state waters. Here we determined by CT‐based proxy the shell dissolution intensity of planktonic foraminifera Globigerina bulloides, Globorotalia inflata, Globigerinoides ruber, and Trilobatus sacculifer from a collection of core top samples in the Southern Atlantic covering higher saturation states and assessed the reliability of CT‐based proxy. We observed that the CT‐based proxy is generally controlled by deep‐water Δ[] like the B/Ca proxy, but its effective range of Δ[] is between −20 and 10 µmolkg−1. In this range, the CT‐based proxy appears directly and strongly related to deep‐water Δ[], whereas we note that in some settings, there appears to be a secondary influence on B/Ca which we suggest may be due to elevated alkalinity from carbonate dissolution in sediments. On the other hand, the CT‐based proxy is affected by supralysoclinal dissolution in areas with high productivity. Like the B/Ca proxy, the CT‐based proxy requires species‐specific calibration, but the effect of species‐specific shell difference in susceptibility to dissolution on the proxy is small.

ПАЛЕОБИОГЕОГРАФИЧЕСКИЕ РЕКОНСТРУКЦИИ ДЛЯ КОНЦА ПОЗДНЕГО КАМПАНА ПО ПЛАНКТОННЫМ ФОРАМИНИФЕРАМ В ТИХОМ ОКЕАНЕ

The paper considers the results of the analysis of the taxonomic composition of planktonic foraminifera (PF) from the end of the Late Campanian in the Pacific Ocean. To identify the latitudinal-zonal faunas of the PF, an assessment was made of the species similarity and differences of the PF complexes of the same age from different wells. Based on the difference in species composition, the fauna of the PF is divided into non-arctic regional and oceanic latitudinal-zonal: subtropical western, tropical central and subtropical central oceanic faunas. To reconstruct the climatic fluctuations that occurred at the end of the Campanian century in the Pacific Ocean, the systematic composition of the shells of planktonic foraminifera was studied from the core samples of eleven deep-sea drilling wells.The identified PF thanatocenoses were assigned to two types (Tethyan, intermediate) and one subtype (thermal-boreal). Based on the spatial distribution of thanatocenoses, the position of climatic zones for two sections of the late Campanian was determined. Within the studied water area, two climatic zones were developed during the studied age interval: intermediate and Tethyan. In the middle of the Late Campanian, the boundary between them passed in the paleoequator region. At the end of the late Campanian, it became sharply colder. The intermediate and Tethyan zones narrowed. In the northern part of the studied water area, a warm-boreal subzone was revealed, in the southern part, the Tethyan subzone was replaced by an intermediate zone. The obtained reconstructions are confirmed by our own and published data of oxygen isotope analysis.

Daily timescale dynamics of planktonic foraminifera shell-size distributions

Planktonic foraminifera (PF) shells comprise a significant fraction of the global oceanic carbonate flux and serve as a primary archive of the history of the oceans. Yet, a limited understanding of their life cycles dynamics and biological rhythms, hampers their application as palaeoceanographic proxies. Here, we present the flux of ten PF species and their shell-size distributions at a daily timescale resolution in the Gulf of Aqaba (GOA), northern Red Sea. We report diameter measurements of ~13,500 shells, associated with ten PF species, retrieved using an automated time-series sediment trap deployed at a water depth of ~410 m (seafloor depth 610 m) throughout more than a full annual cycle between 2015 and 2016. Most of the PF species display a wide intraspecific shell-size distribution among adult PF, while six abundant species (G. ruber, G. rubescens + G. tenellus, G. glutinata, G. calida and G. siphonifera) display significantly smaller shell-sizes compared with corresponding specimens from sediment traps and seafloor sediments across other tropical, subtropical and upwelling regions. The results indicate that PF generation cycles can be classified according to three patterns: (1) Quiescent: minimal shell-size and extended life cycles due to unfavorable conditions and food scarcity when the water column is stratified and oligotrophic, (2) Transient: the gradual increase of Chlorophyll-a (Chl-a) concentrations and food availability enhance shorter life-cycles, although PF do not necessarily reach maximal shell-sizes, (3) Successive: PF fluxes and Chl-a concentrations are maximal, the generation time is extended and individuals might display growth to maximal shell-sizes.

Distribution of recent planktonic foraminifera in surface sediments of the Basque shelf (S Bay of Biscay): Oceanographic implications

In this work we describe for the first time the distribution of planktonic foraminifera assemblages preserved in recent surface sediments that cover the Basque shelf (southern Bay of Biscay), and their relationship with diverse oceanic currents that affect this area. In the 83 studied samples a total of 18 (morpho)species of planktonic foraminifera have been identified, being the most abundant species: Neogloboquadrina pachyderma dex., Globigerinoides ruber, Globigerina bulloides, Globoconella inflata, Orbulina universa and Turborotalita quinqueloba. These species represent the 92.8% of the total hand-picked specimens. The preferential accumulation of planktonic foraminifera shells in fine sediments deposited in the eastern margin of the Basque shelf, and the random distribution of the dominant species in this area, seem to respond to the general surface current that affect the Basque shelf, which flows eastward during most of the year. Moreover, the input of certain currents and deeper water masses in this area has an important impact on assemblage distribution. Thus, the presence of abundant individuals of Globigerinoides ruber indicates the entrance of the warm and salty Iberian Poleward Current (IPC). Likewise, the dominance of subpolar species Globigerina bulloides, Neogloboquadrina pachyderma dex. and Turborotalita quinqueloba, together with the occurrence, as accessories species, of Neogloboquadrina pachyderma sin., Globorotalia scitula, Globorotalia truncatulinoides and Neogloboquadrina dutertrei, suggest the impact of upwelling processes on the Basque shelf. In conclusion, in this work we have evidenced the useful application of planktonic foraminifera assemblages preserved in surface sediments as indicators of oceanic currents and water masses in shallow continental shelves, such as the Basque shelf.

Calcification, Dissolution and Test Properties of Modern Planktonic Foraminifera From the Central Atlantic Ocean

The mass of well-preserved calcite in planktonic foraminifera shells provides an indication of the calcification potential of the surface ocean. Here we report the shell weight of 8 different abundant planktonic foraminifera species from a set of core-top sediments along the Mid-Atlantic Ridge. The analyses showed that near the equator, foraminifera shells of equivalent size weigh on average 1/3 less than those from the middle latitudes. The carbonate preservation state of the samples was assessed by high resolution X-ray microcomputed tomographic analyses of Globigerinoides ruber and Globorotalia truncatulinoides specimens. The specimen preservation was deemed good and does not overall explain the observed shell mass variations. However, G. ruber shell weights might be to some extent compromised by residual fine debris internal contamination. Deep dwelling species possess heavier tests than their surface-dwelling counterparts, suggesting that the weight of the foraminifera shells changes as a function of the depth habitat. Ambient seawater carbonate chemistry of declining carbonate ion concentration with depth cannot account for this interspecies difference. The results suggest a depth regulating function for plankton calcification, which is not dictated by water column acidity.

КЛИМАТИЧЕСКИЕ КОЛЕБАНИЯ В СРЕДНИХ ШИРОТАХ СЕВЕРНОГО ПОЛУШАРИЯ ПО ДАННЫМ ИЗУЧЕНИЯ КАМПАНСКИХ ПЛАНКТОННЫХ ФОРАМИНИФЕР

To reconstruct the climatic fluctuations that occurred in the middle latitudes of the Northern Hemisphere in the Atlantic Ocean in the Campanian Age, the systematic composition of the shells of planktonic foraminifera was studied from core samples from seven deep-water drilling holes. The identified foraminiferal assemblages are assigned to two types (boreal and intermediate) and one subtype (warm boreal) thanatocenosis. On the basis of their spatial distribution, the position of climatic zones for sections of the early, middle, beginning and end of the late Campanian was determined. Different climatic zones were characterized by different types of water masses. Within the studied water area, during most of the studied age interval, two climatic zones were developed: intermediate and boreal. In the Early and Middle Campanian, the boundary between them was in the southern part of the region under consideration. At the beginning of the late Campanian, this border sharply shifted to the north. A short-term Late Campanian warming began. At the end of the late Campanian, the temperature dropped sharply. An intermediate type of thanatocenosis has not been identified. Even in the southernmost part of the water area, the warmboreal subzone prevailed. The obtained reconstructions are confirmed by our own and published data of oxygen isotope analysis.

Formation of Fe-Mn coatings on foraminifera from the ultraslow-spreading southwest Indian Ridge: Implications for hydrothermal and diagenetic overprints in sediments

Detailed fine-scale morphological, mineralogical, and geochemical analyses were conducted on the Si-(Fe) hydroxide formations, planktonic foraminifera (PF) and the Fe-Mn coatings within a typical sediment sample collected from near the newly-discovered active hydrothermal vent field at the ultraslow-spreading Southwest Indian Ridge (SWIR). The analyses were conducted with a combination of different techniques, including Laser Scanning Confocal Microscope (LSCM), Laser Raman, high-resolution XRD, SEM-EDS, C-O isotope measurement, EMPA, and in-situ LA-ICP-MS. The mixed-type hydrothermal-hydrogenetic Si-(Fe) hydroxide formations (commonly occur as cavity-fillings inside the PF chambers) contain a considerable amount of organic matter, and are mainly composed of nontronite, goethite, tridymite, and opal-A with the bulk compositions of 8.13–40.91 wt% SiO2, 6.85–54.50 wt% FeO, and 0.43–23.99 wt% Al2O3. Such high Al content can be mainly attributed to the precipitation and accumulation of hydrothermal-derived Al-rich materials, and the Si-Fe-Al assemblage reveals that it is mainly sourced from plagioclase dissolution/alteration during subseafloor fluid-rock interaction. Meanwhile, the relative enrichments of high field strength elements (HFSEs), heavy rare earth elements (HREE), and Cr-Ni-Sc also imply that these Si-(Fe) hydroxide formations have another source from pyroxene alteration. In addition, their distinct microtextures (filamentous, orbicular, or beaded-like) are indicative of bacterial-related precipitation. The hydrogenetic Fe-Mn coatings have a layered texture and exhibit no apparent fluorescence, and are mainly composed of vernadite and goethite with the bulk compositions of 23.98–30.06 wt% FeO and 8.55– 21.52 wt% MnO. Their average Fe/Mn ratios, growth rates, and Zn-As contents are slightly higher than those of the open-ocean SWIR Fe-Mn deposits, which suggests an additional Fe input from submarine hydrothermal activity. Moreover, the altered PF shell is mainly composed of calcite and have three color types (white/yellowish/yellow). The contents of Si, Al, Fe, Cr, Ni, Cu, Zn, Ba, HFSEs, and REE increase as the yellowish color deepens, which indicates the diagenetic contamination from basalt alteration. Consequently, a new diagenetic Fe-carbonate phase (ankerite) was formed in the inner layer of the altered PF shells, and close correlations were also found between their C-O isotope ratios. Both the δ13C and δ18O values tend to drop from white- to yellow-type PF shells, accompanied with the decreasing contents of Ca, Na, Mg, and Sr. All these parameters and signatures would help to unravel the hydrothermal influence and diagenetic overprinting, which could cause confusion when using foraminifera shell geochemistry (e.g., Sr/Ca and Mg/Ca ratios) as a marine tracer in paleoclimate reconstruction.

Latitudinal Differentiation among Modern Planktonic Foraminiferal Populations of Central Mediterranean: Species–Specific Distribution Patterns and Size Variability

Studies of the spatial distribution and size of modern planktonic foraminifera are still lacking in the Mediterranean Sea. In this study, 17 core-top sediments collected from a north-south transect along the central Mediterranean have been analyzed for planktonic foraminiferal content, in terms of their distributional pattern and intraspecific size variability. Among the analyzed planktonic foraminiferal species, Globigerina bulloides and Globigerinoides ruber (w) were the most abundant, presenting an antagonistic behavior and an overall decreasing trend in their average size values from Adriatic to Ionian sub-basins. Intraspecific differences have been also documented for G. ruber (w), with the dominant sensu stricto morphotype to present generally higher frequencies and more constant shell sizes than sensu lato. The greater size variability of the latter is possibly related to its adaptation in particular hydrographic conditions based on its depth habitat preference and ecological characteristics to reach the (sub)optimum growth conditions. The rest of the species occur in minor percentages and show on average 11% increase with decreasing latitude characterized by distinct species-specific size variations along the transect. Our results show that the relationship between planktonic foraminifera shell size and abundance or sea surface temperature are either absent or weaker than previously reported for other regions and that in central Mediterranean assemblages’ size may be mainly related to nutrient availability. Besides the environmental parameters (sea surface temperature, primary productivity, water depth, stratification), the possible hidden cryptic diversity, still lingers to be consistently determined, could give a better understanding of the geographic and morphological differentiation within the Mediterranean planktonic populations.

Disruption of the Atlantic Meridional Circulation during Deglacial Climates Inferred from Planktonic Foraminiferal Shell Weights

Changes in the density structure of the upper oceanic water masses are an important forcing of changes in the Atlantic Meridional Overturning Circulation (AMOC), which is believed to widely affect Earth’s climate. However, very little is known about past changes in the density structure of the Atlantic Ocean, despite being extensively studied. The physical controls on planktonic foraminifera calcification are explored here, to obtain a first-order approximation of the horizontal density gradient in the eastern Atlantic during the last 200,000 years. Published records of Globigerina bulloides shells from the North and Tropical eastern Atlantic were complemented by the analysis of a South Atlantic core. The masses of the same species shells from three different dissolution assessed sediment cores along the eastern Atlantic Ocean were converted to seawater density values using a calibration equation. Foraminifera, as planktonic organisms, are subject to the physical properties of the seawater and thus their shells are sensitive to buoyancy forcing through surface temperature and salinity perturbations. By using planktonic foraminifera shell weight as an upper ocean density proxy, two intervals of convergence of the shell masses are identified during cold intervals of the last two deglaciations that may be interpreted as weak ocean density gradients, indicating nearly or completely eliminated meridional circulation, while interhemispheric Atlantic density differences appear to alleviate with the onset of the last interglacial. The results confirm the significance of variations in the density of Atlantic surface waters for meridional circulation changes.

The daily resolved temperature dependence and structure of planktonic foraminifera blooms

Planktonic foraminifera (PF) life cycles are highly sensitive to marine conditions, which are evolving rapidly due to anthropogenic climate change. Even though PF shells in the sedimentary record serve as prominent proxies of past ocean conditions, very little is still known about their life cycles, particularly in oligotrophic environments. Here, we present a full annual record of PF fluxes (> 63 µm) from the oligotrophic Gulf of Aqaba, northern Red Sea, sampled at daily timescales during 2015–2016 using an automated time-series sediment trap. These results are coupled with daily surface chlorophyll-a concentrations, sea surface temperatures (SSTs), particulate organic carbon and bulk fluxes, together with monthly resolved vertical profiles of chlorophyll-a, temperatures and nutrient concentrations. The annual cycle of PF fluxes is controlled by SST changes that drive water column mixing and changes in food availability. PF species flux patterns and succession dynamics vary throughout the year, displaying large variability on previously undocumented daily-weekly timescales, and are not synchronized with lunar periodicity. On daily timescales, spring blooms show a complex structure and interplay between SSTs, chlorophyll-a surface concentrations and PF fluxes. These events deliver about a third of the total annual PF flux over a period of several weeks.

X-ray tomographic data of planktonic foraminifera species Globigerina bulloides from the Eastern Tropical Atlantic across Termination II.

Increased planktonic foraminifera shell weights were recorded during the course of Termination II at a tropical site off the shore of the Mauritanian coast. In order to investigate these increased shell mass values, a series of physicochemical analyses were performed, including X-ray computed tomography (CT). The data are given here. Furthermore, the relevant CT setup, scanning, reconstruction, and visualization methods are explained and the acquired datasets are given, together with 3D volumes and models of the scanned specimens.

Recent planktonic foraminifera population and size response to Eastern Mediterranean hydrography

The eastern Mediterranean Sea is a partially isolated sea where excess evaporation over precipitation or riverine discharge results in large north to south gradients in temperature and salinity. Eastern Mediterranean Sea surface sediment samples from 28 locations spanning from the North Aegean to the Levantine Sea have been examined for recent planktonic foraminiferal distribution. In addition to determining the relative abundance of 12 species that have been identified, the average intraspecific size along with the size of the overall faunal pattern was also examined. The quantitative analysis performed on >125μm fraction reveals pronounced and complex changes in planktonic foraminiferal assemblages that do not parallel the intraspecific size variation and sea surface temperature (SST). On the contrary, foraminifera most of the times are slightly larger in the colder and fresher North Aegean and become progressively smaller toward the warmer Levantine Sea. We conclude that the relationship between planktonic foraminifera shell size and abundance or SST are either absent or weaker than previously reported for other regions and that in E. Mediterranean assemblages size may be mainly related to nutrient availability.

The effect of an experimental decrease in salinity on the viability of the Subarctic planktonic foraminifera Neogloboquadrina incompta

Chemical signatures in the calcite of shells of polar and subpolar planktonic foraminifera have been frequently used to trace and quantify past meltwater discharge events. This approach assumes that the foraminifera can tolerate low salinity under extended periods. To obtain a first experimental constraint on salinity tolerance of Subarctic foraminifera, we carried out a culturing experiment with specimens of the subpolar species Neogloboquadrina incompta collected in the northern Norwegian Sea off Tromsø in October 2018. The foraminifera were exposed to a gradient of salinities between 35 and 25 PSU. Survival was monitored over 26 days by measuring the extent of the rhizopodial network. Although chamber growth only occurred in one of the observed specimens, likely due to the largely unknown dietary preference of the species, we observed a strong differential rhizopodial activity pattern along the gradient. The highest rhizopodial activity occurred at salinity between 35 and 31 PSU. The species is clearly able to survive long-term exposure to salinities as low as 28, but no rhizopodial activity and signs of cytoplasm degradation were observed in all specimens exposed to 25 PSU. These preliminary observations provide the first direct evidence for the salinity tolerance of N. incompta, indicating a range of salinity that could be plausibly expected to be recorded in the chemistry of fossil shells of the species.

The crucial boundaries in the development of the late cretaceous biota of plankton foraminifers in the southern part of the Indian ocean

The article analyzes own data on the species composition of shells of planktonic foraminifera from the Upper Cretaceous sediments of the Indian Oceans, as well as from the sections of the offshore seas of Australia. The species of planktonic foraminifera are grouped and arranged in a climatic series. An analysis of the change in the systematic composition of foraminifers made it possible to distinguish periods of extreme and intermediate climatic states in the Late Cretaceous.

КЛИМАТИЧЕСКАЯ ЗОНАЛЬНОСТЬ ЮЖНОГО ПОЛУШАРИЯ В КАМПАНСКОЕ ВРЕМЯ ПО ДАННЫМ ИЗУЧЕНИЯ ПЛАНКТОННЫХ ФОРАМИНИФЕР

In the Campanian cores of deep water drilling in the Indian Ocean, on the Falklands Plateau, in the central part of the Atlantic Ocean and in the Australian shelf seas, the systematic composition of shells of planktonic foraminifera was studied. The revealed complexes of foraminifera are attributed to one or another type of than at ocenosis. On the basis of the spatial distribution of types of tanatocenoses, maps of climatic zonality for sections of the early, middle beginning, and end of the late campaign have been constructed. Different climatic zones correspond to different types of water masses. In the southern hemisphere, there were three climatic zones, but their sizes and the outline of the boundaries changed during the Campanian period. In the early and middle campaigns, the climate was smooth and mild. The beginning of the late campaign is marked by short-term warming which was replaced by a sharp late Campan cooling. The obtained reconstructions are confirmed by our own and literary data of oxygen isotope analysis.

Logarithmic expression of Globigerina bulloides shell evolution through the biometric analysis: Paleoceanographic implications for the late Quaternary

Fossil foraminifera are a treasure trove of information in applications ranging from microevolution to paleoclimatology. The architecture of their tests is of the key importance in systematic and phylogenetic studies and can reveal micro-evolutionary traits through the biometric analyses. In the present paper, we analyze the laws of growth that control planktonic foraminifera shell morphology. We report the results of a biometric study of the temporal variation in the shell shape and chamber size of the cosmopolitan, subpolar to temperate species Globigerina bulloides d’Orbigny from core top sediments in the eastern tropical Atlantic Ocean. Morphological variation in terms of test shape and adult chamber size in G. bulloides, has been measured in 116 down core sediment samples from the tropical waters (19°N) of the northern Antarctic Ocean and has resulted in a model that simulates the basic morphology (chamber size and spatial arrangement) of planktonic foraminiferal shells of that species. The investigated samples comprise a continuous record that spans the last 200 kyrs. The specimens for this morphometric study were picked from a restricted sieve fraction and were mounted for Scanning Electron Microscopy (SEM) analysis. The restricted size of the specimens constrained the analysis to adult specimens and minimized ontogenic effects while allowing the documentation of very small overall changes in the parameters under investigation in time. The dimensions that were measured for each test were its height, width and the diameters of the last seven chambers. This allowed the determination of chamber centers and their analogies resulting in a mathematical model based on a logarithmic spiral equation that describes the evolution of the test with the growth during their adult phases. The model presented herein belongs to a family of so-called “fixed-axis” coiling models.

Oxygen isotope composition of the final chamber of planktic foraminifera provides evidence of vertical migration and depth-integrated growth

Abstract. The translation of the original seawater signal (i.e. ambient temperature and δ18Osw) into distinct chambers of a single shell of a foraminifer during calcification can influence our interpretation of surface ocean conditions of the past, when based upon oxygen and carbon stable isotope geochemistry. In this study three different hypotheses were tested to gain more insight into biological and ecological processes that influence the resultant composition of stable isotopes of oxygen (δ18O) in the shells of planktonic foraminifera. These hypotheses were related to the shell size; the differences in isotopic composition between the final chamber and the remaining shell; and the differences between different species. Shells of Trilobatus sacculifer, Globigerinoides ruber white and Neogloboquadrina dutertrei were picked from the top of multi-core GS07-150-24, of modern age, offshore of north-eastern Brazil (3∘46.474′ S, 37∘03.849′ W) and analysed for single-shell and single-chamber stable isotope analysis. We show that the mean value of δ18O of the final chambers (δ18OF) is 0.2 ‰ ± 0.4 ‰ (1σ) higher than the mean value δ18O of the test minus the final chamber (δ18O<F) of T. sacculifer. The formation of the final chamber happens at temperatures that are approximately 1 ∘C cooler than the chambers formed prior, suggesting both ontogenetic depth migration to deeper water and a potential offset from the surface signal. Furthermore, we show that there is no statistical difference in the δ18Osacculifer values of shells of three different size classes of T. sacculifer, although the pattern between the different size classes indicates depth migration during the life and growth of T. sacculifer. Comparison of vital effect corrected δ18Oshell between T. sacculifer, G. ruber white and N. dutertrei suggests that G. ruber has a slightly shallower depth habitat (∼90–120 m) compared to the other two species (∼100–130 m). Disentangling depth vs. seasonal habitat is complicated given the commonality between isotope values from similar depths but different seasons; for instance, the same average isotope value will have a shallower depth habitat in May than September. Calculation of seasonal-depth habitat was therefore tested. Our results highlight the complicated nature of interpreting oxygen isotopes even for the modern record.

Influence of surface ocean density on planktonic foraminifera calcification

This study provides evidence that ambient seawater density influences calcification and may account for the observed planktonic foraminifera shell mass increase during glacial times. Volumes of weighed fossil Globigerina bulloides shells were accurately determined using X-ray Computer Tomography and were combined with water density reconstructions from Mg/Ca and δ18O measurements to estimate the buoyancy force exerted on each shell. After assessment of dissolution effects, the resulting relationship between shell mass and buoyancy suggests that heavier shells would need to be precipitated in glacial climates in order for these organisms to remain at their optimum living depth, and counterbalance the increased buoyant force of a denser, glacial ocean. Furthermore, the reanalysis of bibliographic data allowed the determination of a relationship between G. bulloides shell mass and ocean density, which introduces implications of a negative feedback mechanism for the uptake of atmospheric CO2 by the oceans.

Latitudinal Variation of Planktonic Foraminifera Shell Masses During Termination I

The oceans’ surface layer holds large amounts of dissolved inorganic carbon that is exchanged rapidly with the atmosphere. Carbon enters the ocean mainly through the dissolution of atmospheric carbon dioxide (CO2), and a part of it is converted into carbonate by marine organisms. Calcifying marine organisms include planktonic foraminifers that contribute to the marine carbon turnover by generating inorganic carbon production (CaCO3 shells). Anthropogenic CO2 acidifies the surface ocean, changes the carbonate chemistry and decreases the saturation state of carbonate minerals in sea water, thus affecting the biological precipitation of carbonate shells. Relative changes in average foraminiferal shell mass can be interpreted as variations in test thickness and the extent of calcification that subsequently impacts the global carbonate budgets. The response of calcifying marine organisms to elevated atmospheric pCO2 is diverse and complex with studies reporting from reduced rates of net calcification to neutral receptivity or even increased calcification intensities. This diverse behavior implies that the concentration of dissolved inorganic carbon may not be the dominant factor controlling the amount of carbonate shell masses. Here we provide further evidence that glacial/interglacial variations of planktonic foraminifera shell masses are invariant to atmospheric pCO2. We identify that differences in shell weights of several planktonic foraminiferal species from narrow size intervals, over the most recent deglaciation (Termination I) vary systematically as a function of latitude. Past intervals of abruptly changing pCO2 and temperatures, such as the terminations, can offer a glimpse into the response of marine calcifying plankton to changes in surface oceans. We have compiled all the available bibliographic data of planktonic foraminifera shell weights from restricted sieve fractions of different species from the Atlantic, Pacific and Indian Oceans and we find that for the same pCO2 conditions planktonic foraminifera from equatorial regions may alter their shell mass only as little as 8.2%, while towards higher latitudes changes in shell mass reach up to 54% during the transition from the last glacial to interglacial conditions. We attribute this low variability in the shell mass of planktonic foraminifera from the equator to the stability of the physical oceanographic conditions that characterize the equatorial zone.