Species Of Planktic Foraminifera Research Articles

Quantitative analysis and paleoenvironmental reconstruction of the middle Cenomanian deposits from southern Bellezma-Batna Mountains (northeastern Algeria)

The middle Cenomanian deposits of the southern part of the Bellezma-Batna Mountains, northeastern Algeria, have been investigated to evaluate the response of Foraminifera to variations of paleo-bathymetry, oxygen, and salinity. The Djebel Azeb section, with a thickness of 40 m, is composed of a clay-marl mass interspersed with lumachellic limestone layers. It makes up the middle part of the ‘’Marnes de Smail’’ Formation. The Turrilites acutus Subzone of the upper part of the Acanthoceras rhotomagense Zone corresponds to the Aspidiscus cristatus Total Range Zone, and the Rotalipora cushmani Zone was recognized based on the study of ammonites, scleractinian and planktic foraminifera in this section. The statistical analysis of the foraminifera yielded only one assemblage of planktic foraminifera with globular chambers and trochospiral test belonging to the Cenomanian–Turonian; no association is typically restricted to the middle Cenomanian. The benthic foraminifera are poorly represented, belonging to the orders Textulariina, Lituolina, Trochamminina, Verneuilinina, Loftusiina, Orbitolinina, Miliolina, and Rotaliina. These foraminifera assemblages indicate that the bottom-water conditions during the middle Cenomanian were characterized by periodic changes in the oxygen and salinity. All planktic foraminifera species are opportunists related to poorly oxygenated, eutrophic conditions interspersed by a short interval of well-oxygenated environment with Planolites. The maximum abundance of Whiteinella and Muricohedbergella and the minimum amount of Planoheterohelix species within the Cenomanian of Djebel Azeb reflect dwindling palaeosalinity during this time, except for a slight increase in the middle of the section. Keywords: Foraminifera, corals, biostratigraphy, oxygen, salinity, Cretaceous.

Geochemical Differences Between Alive, Uncrusted and Dead, Crusted Shells of Neogloboquadrina pachyderma: Implications for Paleoreconstruction

AbstractPlanktic foraminiferal‐based trace element‐calcium ratios (TE/Ca) are a cornerstone in paleoceanographic reconstructions. While TE‐environment calibrations are often established through culturing experiments, shell growth in culture is not always consistent with growth in a natural setting. For example, many species of planktic foraminifera thicken their shell at the end of their life cycle, producing a distinct “gametogenic” crust. Crust is common in fossil foraminifers, however, shells grown in culture do not often develop a thick crust. Here, we investigate potential vital effects associated with the crusting process by comparing the trace element (Mg/Ca, Na/Ca, Ba/Ca, Sr/Ca, Mn/Ca, Zn/Ca) and stable isotope (δ13C, δ18O) composition of alive, fully mature, uncrusted shells to recently deceased, crusted shells of Neogloboquadrina pachyderma collected from the same plankton tows off the Oregon (USA) coast. We find that uncrusted (N = 55) shells yield significantly higher Ba/Ca, Na/Ca, Mn/Ca, and Sr/Ca than crusted (N = 66) shells, and crust calcite records significantly lower TE/Ca values for all elements examined. Isotopic mixing models suggest that the crust calcite accounts for ∼40%–70% of crusted shell volume. Comparison of foraminiferal and seawater isotopes indicate that N. pachyderma lives in the upper 90 m of the water column, and that crust formation occurs slightly deeper than their average living depth habitat. Results highlight the necessity to establish calibrations from crusted shells, as application of calibrations from TE‐enriched uncrusted shells may yield attenuated or misleading paleoceanographic reconstructions.

Large-scale culturing of Neogloboquadrina pachyderma, its growth in, and tolerance of, variable environmental conditions.

The planktic foraminifera Neogloboquadrina pachyderma is a calcifying marine protist and the dominant planktic foraminifera species in the polar oceans, making it a key species in marine polar ecosystems. The calcium carbonate shells of foraminifera are widely used in palaeoclimate studies because their chemical composition reflects the seawater conditions in which they grow. This species provides unique proxy data for past surface ocean hydrography, which can provide valuable insight to future climate scenarios. However, little is known about the response of N. pachyderma to variable and changing environmental conditions. Here, we present observations from large-scale culturing experiments where temperature, salinity and carbonate chemistry were altered independently. We observed overall low mortality, calcification of new chambers and addition of secondary calcite crust in all our treatments. In-culture asexual reproduction events also allowed us to monitor the variable growth of N. pachyderma's offspring. Several specimens had extended periods of dormancy or inactivity after which they recovered. These observations suggest that N. pachyderma can tolerate, adapt to and calcify within a wide range of environmental conditions. This has implications for the species-level response to ocean warming and acidification, for future studies aiming to culture N. pachyderma and use in palaeoenvironmental reconstruction.

Glacial Southern Ocean Expansion Recorded in Foraminifera‐Bound Nitrogen Isotopes From the Agulhas Plateau During the Mid‐Pleistocene Transition

AbstractThe emergence of 100‐Kyr glacial cycles (The Mid‐Pleistocene Transition [MPT]) is attributed in part to slower global overturning circulation and iron stimulation of biological carbon drawdown in the Southern Ocean. We present foraminifera‐bound nitrogen isotope values and polar planktic foraminifera abundances from the Agulhas Plateau that show that increases in biogenic sediment accumulation coincide with northward migrations of the Subtropical Frontal Zone (STFZ) and elevated foraminifera‐bound nitrogen isotope values during MPT glacial episodes. The nitrogen isotope values of two planktic foraminifera species, Globigerina bulloides and Globorotalia inflata show remarkable coherence amongst the sea surface temperature gradient between the STFZ and SAZ, and polar foraminifera abundances, indicating a strong relationship between nitrogen isotope dynamics above the Agulhas Plateau and migrations of the STFZ. Northward migration of the STFZ may have been essential to prolonging glacial intervals by increasing deep ocean carbon storage via a northward shift of the South Westerly Winds and a reduction in upwelling, delivery of fresher surface waters into the upper limb of global overturning circulation, or inhibiting heat and salt delivery to the Atlantic as Agulhas Leakage.

THE OLIGOCENE/MIOCENE BOUNDAR Y IN THE EQUATORIAL ATLANTIC DSDP SITE 354. RESULTS OF STUDIES ON PLANKTIC FORAMINIFERA AND CALCAREOUS NANNOFOSSILS

A first order correlation between planktic foraminiferal and calcareous nannofossil events o( DSDP Site 354 in the Equatorial Atlantic is presented. Within the 323 m thick, discontinuously cored section, 30 sarnples have been studied. In the Oligocene-Miocene sedirnents 57 different species of planktic Foraminifera and 51 species of calcarcous nannofossils have been identified, and 6 foraminiferal zones and 7 nannofossil zones recognized. Besides the generally used biostratigraphic markers, some additional calcareous nannofossil events are considered for a further subdivision of the interval studied.

Calcification response of planktic foraminifera to environmental change in the western Mediterranean Sea during the industrial era

Abstract. The Mediterranean Sea sustains a rich and fragile ecosystem currently threatened by multiple anthropogenic impacts that include, among others, warming, pollution, and changes in seawater carbonate speciation associated to increasing uptake of atmospheric CO2. This environmental change represents a major risk for marine calcifiers such as planktonic foraminifera, key components of pelagic Mediterranean ecosystems and major exporters of calcium carbonate to the sea floor, thereby playing a major role in the marine carbon cycle. In this study, we investigate the response of planktic foraminifera calcification in the northwestern Mediterranean Sea on different timescales across the industrial era. This study is based on data from a 12-year-long sediment trap record retrieved in the in the Gulf of Lions and seabed sediment samples from the Gulf of Lions and the promontory of Menorca. Three different planktic foraminifera species were selected based on their different ecology and abundance: Globigerina bulloides, Neogloboquadrina incompta, and Globorotalia truncatulinoides. A total of 273 samples were weighted in both sediment trap and seabed samples. The results of our study suggest substantial different seasonal calcification patterns across species: G. bulloides shows a slight calcification increase during the high productivity period, while both N. incompta and G. truncatulinoides display a higher calcification during the low productivity period. The comparison of these patterns with environmental parameters indicate that controls on seasonal calcification are species-specific. Interannual analysis suggests that both G. bulloides and N. incompta did not significantly reduce their calcification between 1994 and 2005, while G. truncatulinoides exhibited a constant and pronounced increase in its calcification that translated in an increase of 20 % of its shell weight. The comparison of these patterns with environmental data reveals that optimum growth conditions affect positively and negatively G. bulloides and G. truncatulinoides calcification, respectively. Sea surface temperatures (SSTs) have a positive influence on N. incompta and G. truncatulinoides calcification, while carbonate system parameters appear to affect positively the calcification of three species in the Gulf of Lions throughout the 12-year time series. Finally, comparison between sediment trap data and seabed sediments allowed us to assess the changes of planktic foraminifera calcification during the late Holocene, including the pre-industrial era. Several lines of evidence indicate that selective dissolution did not bias the results in any of our data sets. Our results showed a weight reduction between pre-industrial and post-industrial Holocene and recent data, with G. truncatulinoides experiencing the largest weight loss (32 %–40 %) followed by G. bulloides (18 %–24 %) and N. incompta (9 %–18 %). Overall, our results provide evidence of a decrease in planktic foraminifera calcification in the western Mediterranean, most likely associated with ongoing ocean acidification and regional SST trends, a feature consistent with previous observations in other settings of the world's oceans.

Distribution and abundance of early Miocene foraminifera in the Qom Basin of Central Iran

The Oligo-Miocene sediments of Central Iran were deposited in part of the Tethyan Seaway connecting the Mediterranean Sea (western Tethys) to the Indian Ocean (eastern Tethys). The Qom Formation sediments were deposited in the northeastern part of the Tethyan Seaway. For analyzing the depositional environments of the Qom Formation in the Tigheh Reza Abad section (type area of the Qom Formation) samples through 967 m thickness were studied which yielded 64 genera and 106 species of benthic and planktic foraminifera, including index species indicative of Aquitanian to Burdigalian age. Five faunal associations (I-V) are recognized on the basis of foraminiferal diversity and abundance. The faunal associations indicate different paleoenvironments along a gradient from inner to outer shelf in the warm, shallow-marine Qom Basin.

Contrasting vertical distributions of recent planktic foraminifera off Indonesia during the southeast monsoon: implications for paleoceanographic reconstructions

Abstract. Planktic foraminifera are widely used in paleoceanographic and paleoclimatic studies. The accuracy of such reconstructions depends on our understanding of the organisms' ecology. Here we report on field observations of planktic foraminiferal abundances (>150 µm) from five depth intervals between 0–500 m water depth at 37 sites in the eastern tropical Indian Ocean. The total planktic foraminiferal assemblage here comprises 29 morphospecies, with 11 morphospecies accounting for 90 % of the total assemblage. Both species composition and dominance in the net samples are broadly consistent with the published data from the corresponding surface sediments. The abundance and vertical distribution of planktic foraminifera are low offshore western Sumatra and increase towards offshore southern Java and the Lesser Sunda Islands (LSI). Average living depth of Trilobatus trilobus, Globigerinoides ruber, and Globigerina bulloides increases eastward, while that of Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globorotalia menardii remains constant. We interpret the overall zonal and vertical distribution patterns in planktic foraminiferal abundances as a response to the contrasting upper-water-column conditions during the southeast monsoon, i.e., oligotrophic and stratified offshore Sumatra (non-upwelling) vs. eutrophic and well mixed offshore Java–LSI (upwelling). Overall, the inferred habitat depths of selected planktic foraminifera species show a good agreement with those from sediment trap samples and from surface sediments off Sumatra, but not with those from surface sediments off Java–LSI. The discrepancy might stem from the different temporal coverage of these sample types. Our findings highlight the need to consider how foraminiferal assemblages and ecology vary on shorter timescales, i.e., from “snapshots” of the water column captured by a plankton net to seasonal and interannual variability as recorded in sediment traps, and how these changes are transferred and preserved in deep-sea sediments.

Determining the habitat depth of the planktic foraminifera Dentoglobigerina altispira in the eastern Arabian Sea during the middle Miocene

Tests of planktic foraminifera are important tracers for reconstructing past oceanic environments. It is essential to have accurate information of the habitat depth of the planktic foraminiferal species whose isotopic and elemental signatures are being used to infer past climatic and oceanographic conditions. The planktic foraminifera species Dentoglobigerina altispira is a very common component of Miocene and Pliocene tropical to warm subtropical planktic foraminiferal assemblages but different findings exist about the habitat depth of this species from shallow to deep water. For that reason, comparative stable carbon and oxygen isotope analyses of four coexisting planktic foraminifera species from National Gas Hydrate Program Expedition Site 01 (Site NGHP-01-01A) were performed in order to reconstruct the habitat depth of D. altispira in the eastern Arabian Sea for the middle Miocene (~16–12.5 Ma). The D. altispira oxygen isotope values are on average higher than those of the shallow water reference species Trilobatus sacculifer and Globigerinoides obliquus, but still significantly lower than those for the deeper dwelling species Dentoglobigerina venezuelana. This suggests that D. altispira inhabited a deeper habitat depth than the estimated habitat depth for modern T. sacculifer in the eastern Indian Ocean (~50 m). Paired D. altispira and T. sacculifer Mg/Ca data reveal lower Mg/Ca and thus colder temperatures for D. altispira than for T. sacculifer, also suggesting that D. altispira calcified at a greater water depth than T. sacculifer. The data of this study suggest that D. altispira inhabited the lower mixed layer and/or upper thermocline in the eastern Arabian Sea during the middle Miocene.

Biostratigraphy, Paleoecology, Microfacies and Depositional environment of the Asmari formation (Oligocene-Early Miocene) in Karanj oil field, SW Iran

Core data analysis of one well from the Karanj oil field, southwestern Iran, allowed us to precise the biostratigraphy, microfacies and paleoecology of the Asmari Formation. Analysis of thin section from this cored well permitted identification of 28 genera and 20 species of benthic and planktic foraminifera respectively. Subsequently four benthic foraminiferal assemblage biozones were identified, as follows: (1) Lepidocyclina-Operculina-Ditrupa Assemblage zone, (2) Archaias asmaricus-Archaias hensoni-Miogypsinoides complanatus Assemblage zone, (3) Miogypsina-Peneroplis farsensis–Elphidium sp. 14 Assemblage zone and (4) Borelis melo curdica-Borelis melo melo Assemblage zone; indicating an Oligocene (Rupelian-Chattian) to early Miocene (Aquitanian to Early Burdigalian) age for the Asmari Formation. Microfacial study of depositional textures led to characterizing 12 microfacies types, indicating environments in five different settings: restricted lagoon, open lagoon, shoal, slope, and basin mostly in the upper Asmari Formation. These sediments had been deposited under 3 different salinity levels (from 34 to more than 50 psu) in an environment ranging from aphotic to oligophotic and to euphotic zones, and under oligotrophic to eutrophic conditions from the Chattian to the Burdigalian on a carbonate platform (homoclinal ramp). In the studied well, the Asmari Formation had been deposited in a marine environment with normal salinity during the Rupelian-Chattian interval and in a marine environment with high salinity during the Aquitanian to the Burdigalian times.

Vertical distribution of planktic foraminifera through an oxygen minimum zone: how assemblages and test morphology reflect oxygen concentrations

Abstract. Oxygen-depleted regions of the global ocean are rapidly expanding, with important implications for global biogeochemical cycles. However, our ability to make projections about the future of oxygen in the ocean is limited by a lack of empirical data with which to test and constrain the behavior of global climatic and oceanographic models. We use depth-stratified plankton tows to demonstrate that some species of planktic foraminifera are adapted to life in the heart of the pelagic oxygen minimum zone (OMZ). In particular, we identify two species, Globorotaloides hexagonus and Hastigerina parapelagica, living within the eastern tropical North Pacific OMZ. The tests of the former are preserved in marine sediments and could be used to trace the extent and intensity of low-oxygen pelagic habitats in the fossil record. Additional morphometric analyses of G. hexagonus show that tests found in the lowest oxygen environments are larger, more porous, less dense, and have more chambers in the final whorl. The association of this species with the OMZ and the apparent plasticity of its test in response to ambient oxygenation invites the use of G. hexagonus tests in sediment cores as potential proxies for both the presence and intensity of overlying OMZs.

Evidence for rapid trace element alteration of planktic foraminiferal shells from the Panama Basin: Manganese adsorption during vertical transport

Abstract The trace elemental composition of planktic foraminifera shells serves as a proxy for understanding the physical environment in which foraminifera lived, but may also reflect chemical alterations that occur after death. Understanding how foraminiferal geochemistry varies across time, species, and after death is therefore essential for deconvolving ecological from diagenetic information and decoding the environmental signals contained within foraminiferal shells. We analyzed the trace elemental composition (Mg/Ca, Sr/Ca, Ba/Ca, Mn/Ca, and U/Ca) of four species of planktic foraminifera (Globigerina ruber, Neogloboquadrina dutertrei, Globorotalia menardii, and Globorotaloides hexagonus) from moored sediment traps (890, 2590, and 3560 m deep) in the Panama Basin collected over one calendar year (1979–1980). Shells recovered from the shallowest trap demonstrate moderate variability in trace elemental composition, both throughout the time series and between species. Most elemental ratios are not significantly influenced by depth, with the exception of Mn/Ca. Ratios of Mn/Ca are substantially higher in the 3560 m trap versus the 890 m trap, with increases with depth greater in the thin walled species G. ruber and G. hexagonus. Elevated Mn/Ca ratios are frequently noted in fossil foraminifera shells as the result of diagenesis within the sediment. Our results demonstrate the potential for Mn-enrichment of foraminiferal calcite, via Mn adsorption onto the surface of foraminiferal shells, within the water column during sinking and prior to deposition in the sediment.

Investigating ENSO‐Related Temperature Variability in Equatorial Pacific Core‐Tops Using Mg/Ca in Individual Planktic Foraminifera

AbstractEl Niño Southern Oscillation (ENSO) is the largest source of interannual climate variability on Earth today; however, future ENSO remains difficult to predict. Evaluation of paleo‐ENSO may help improve our basic understanding of the phenomenon and help resolve discrepancies among models tasked with simulating future climate. Individual foraminifera analysis allows continuous down‐core records of ENSO‐related temperature variability through the construction and comparison of paleotemperature distributions; however, there has been little focus on calibrating this technique to modern conditions. Here, we present data from individual measurements of Mg/Ca in two species of planktic foraminifera, surface dwelling Globigerinoides ruber and thermocline dwelling Neogloboquadrina dutertrei, from nine core tops across the equatorial Pacific (n ≈ 70 per core for each species). Population variance, kernel probability density functions, and quantile‐quantile analyses are used to evaluate the shape of each Mg/Ca‐temperature distribution and to compare them to modern conditions using monthly temperatures from the Simple Ocean Data Assimilation. We show that populations of individual Mg/Ca measurements in both G. ruber and N. dutertrei reflect site‐specific temperature distribution shapes and variances across the equatorial Pacific when accounting for regional differences in depth habitats. Individual measurements of both taxa capture zonal increases in population variance from the western equatorial Pacific to the central equatorial Pacific and a spatially heterogeneous eastern equatorial Pacific, consistent with modern conditions. Lastly, we show that populations of individual Mg/Ca measurements are able to recover meaningful differences in temperature variability between sites within the eastern equatorial Pacific, lending support to this tool's application for paleo‐ENSO reconstructions.

Deciphering the Variability in Mg/Ca and Stable Oxygen Isotopes of Individual Foraminifera.

Foraminifera are commonly used in paleoclimate reconstructions as they occur throughout the world's oceans and are often abundantly preserved in the sediments. Traditionally, foraminifera‐based proxies like δ18O and Mg/Ca are analyzed on pooled specimens of a single species. Analysis of single specimens of foraminifera allows reconstructing climate variability on timescales related to El Niño–Southern Oscillation or seasonality. However, quantitative calibrations between the statistics of individual foraminifera analyses (IFA) and climate variability are still missing. We performed Mg/Ca and δ18O measurements on single specimens from core top sediments from different settings to better understand the signal recorded by individual foraminifera. We used three species of planktic foraminifera (Globigerinoidesruber (s.s.), T. sacculifer, and N. dutertrei) from the Indo‐Pacific Warm Pool and one species (G. ruber (pink)) from the Gulf of Mexico. Mean values for the different species of Mg/Ca versus calculated δ18O temperatures agree with published calibration equations. IFA statistics (both mean and standard deviation) of Mg/Ca and δ18O between the different sites show a strong relationship indicating that both proxies are influenced by a common factor, most likely temperature variations during calcification. This strongly supports the use of IFA to reconstruct climate variability. However, our combined IFA data for the different species only show a weak relationship to seasonal and interannual temperature changes, especially when seasonal variability increases at a location. This suggests that the season and depth habitat of the foraminifera strongly affect IFA variability, such that ecology needs to be considered when reconstructing past climate variability.

Stratigraphic Occurrences of Sub-Polar Planktic Foraminifera in Pleistocene Sediments on the Lomonosov Ridge, Arctic Ocean

Turborotalita quinqueloba is a species of planktic foraminifera commonly found in the sub-polar North Atlantic along the pathway of Atlantic waters in the Nordic seas and sometimes even in the Arct ...

Paleoceanographic changes across the Latest Danian Event in the South Atlantic Ocean and planktic foraminiferal response

A number of short warming events occurred during Paleocene and Eocene, of which the “Paleocene-Eocene Thermal Maximum” (PETM, 56 Ma) is the most severe and most investigated event. The less known “Latest Danian Event” (LDE) at 62.2 Ma represents a 200 ky-lasting warming phase, superimposed on a long-term cooling trend after the Early Paleocene. South Atlantic ODP Site 1262 data, covering ~1 myr, indicate a warming of the entire water column by 1.5–2.6 °C, accompanying a prominent negative carbon isotope excursion (~0.9–1.1‰) and a long-term re-organization of the planktic foraminiferal fauna associated with the LDE. This study unravels a different paleoceanographic evolution of the upper ocean structure compared to results from Pacific ODP Site 1210. Unlike the Pacific, the Atlantic site lacks an apparent change of stratification as well as an overall dominance of thermocline dwelling planktic foraminifera species and a low abundance of surface dwelling photosymbiotic foraminifera. Within the LDE, indications for a slightly enhanced stratification of the upper water column and transient warming were indicated when surface dwelling planktic foraminifera became temporarily more abundant. The long-term evolution in planktic foraminifera with the disappearance of Praemurica at the LDE onset and a contemporaneous rise in Morozovella is similar to the trends reported from Shatsky Rise ODP Site 1210.

Automated species-level identification of planktic foraminifera using convolutional neural networks, with comparison to human performance

Abstract Picking foraminifera from sediment samples is an essential, but repetitive and low-reward task that is well-suited for automation. The first step toward building a picking robot is the development of an automated identification system. We use machine learning techniques to train convolutional neural networks (CNNs) to identify six species of extant planktic foraminifera that are widely used by paleoceanographers, and to distinguish the six species from other taxa. We employ CNNs that were previously built and trained for image classification. Foraminiferal training and identification use reflected light microscope digital images taken at 16 different illumination angles using a light-emitting diode (LED) ring. Overall machine accuracy, as a combination of precision and recall, is better than 80% even with limited training. We compare machine performance to that of human pickers (six experts and five novices) by tasking each with the identification of 540 specimens based on images. Experts achieved comparable precision but poorer recall relative to the machine, with an average accuracy of 63%. Novices scored lower than experts on both precision and recall, for an overall accuracy of 53%. The machine achieved fairly uniform performance across the six species, while participants' scores were strongly species-dependent, commensurate with their past experience and expertise. The machine was also less sensitive to specimen orientation (umbilical versus spiral views) than the humans. These results demonstrate that our approach can provide a versatile ‘brain’ for an eventual automated robotic picking system.

A Deep Eastern Equatorial Pacific Thermocline During the Last Glacial Maximum

AbstractThe mean state and variability of the tropical Pacific is influenced by the depth of the thermocline. During the Last Glacial Maximum (~21,000 years ago), the zonal sea surface temperature gradient across the equatorial Pacific was reduced and productivity was generally lower than modern. To understand the thermocline depth's role in determining the Last Glacial Maximum tropical mean state, we reconstruct the upper ocean δ18O profile from multiple species of planktic foraminifera. We synthesize existing records of surface and subsurface dwelling foraminifera to reconstruct the vertical δ18O gradient throughout the eastern equatorial Pacific. We find the thermocline was deeper during the Last Glacial Maximum than the Holocene throughout the eastern equatorial Pacific region. The thermocline depth's role in the dynamic forcing of the cold tongue contributed to the reduced zonal SST gradient across the equatorial Pacific, decreased productivity, and presumably impacted El Niño‐Southern Oscillation variability relative to the Holocene.

Distribution and ecology of planktic foraminifera in the North Pacific: Implications for paleo-reconstructions

Planktic foraminifera census data have been used to reconstruct past temperatures through transfer functions, as well as changes in ocean ecosystems, chemistry and circulation. Here we present new multinet, plankton net and core-top census data from 20 sites in the Subpolar North Pacific. We combine these with previous data to provide an up to date compilation of North Pacific planktic foraminifera assemblage data. Our compilation is used to define 6 faunal zones: the subpolar zone; transitional zone; upwelling zone; subtropical zone; east equatorial zone; west equatorial zone; based on the distribution of 10 major species of planktic foraminifera. Two species of planktic foraminifera Neogloboquadrina pachyderma and Globigerina bulloides provide the basis for many subpolar paleo-reconstructions. Through the analysis of new multinet and CTD data we find that G. bulloides and N. pachyderma are predominantly found within 0–50 m of the water column and coincide with high food availability. N. pachyderma also shows a strong temperature control and can thrive in food poor waters where temperatures are low. Both species bloom seasonally, particularly during the spring bloom of March to June, with G. bulloides exhibiting greater seasonal variation. We suggest that percentage abundance of N. pachyderma in paleo-assemblages can be used to assess relative changes in past temperature, with G. bulloides abundance more likely to reflect changes in food availability. By comparing our core-top and multinet data, we also find a dissolution bias of G. bulloides over N. pachyderma in the North Pacific, which may enrich assemblages in the latter species.

Assimilation, translocation, and utilization of carbon between photosynthetic symbiotic dinoflagellates and their planktic foraminifera host

Some species of planktic foraminifera inhabiting oligotrophic surface water environments are in an obligate symbiotic relationship with dinoflagellate microalgae, which can assimilate carbon (C) through photosynthesis. However, the mechanism and dynamics of C photosynthate translocation to the foraminiferal host, and related benefits for the dinoflagellates in this symbiotic association, are poorly constrained. As a consequence, the role of planktic foraminifera as autotroph organisms in ocean surface ecosystems is not well understood. Here, we performed pulse-chase experiments with 13C-enriched dissolved inorganic carbon, followed by TEM and quantitative NanoSIMS isotopic imaging to visualize photosynthetic C assimilation by individual symbiotic dinoflagellates and subsequent translocation to their Orbulina universa host. Although most of the dinoflagellate population migrates out of the host endoplasm onto external spines during the day, our observations show that a small fraction remains inside the host cell during daytime. All symbionts, whether outside or inside the foraminifera cell, effectively assimilate C into starch nodules during daytime photosynthesis. At the onset of night, all dinoflagellates from the exterior spine–ectoplasm region migrate back into the foraminiferal cell. During the night, respiration by dinoflagellates and carbon translocation to the host, likely in the form of lipids, greatly reduces the abundance of starch in dinoflagellates. Dinoflagellate mitosis is only observed at night, with a substantial contribution of carbon fixed during the previous day contributing to the production of new biomass.