Planktonic Foraminiferal Species Research Articles

Impact of Seawater Inorganic Carbon Chemistry on Element Incorporation in Foraminiferal Shell Carbonate

AbstractReconstruction of the marine inorganic carbon system relies on proxy signal carriers, such as element/calcium (El/Ca) ratios in foraminiferal shells. Concentrations of boron, lithium, strontium, and sulfur have been shown to vary with carbonate system parameters, but when comparing individual proxy reconstructions based on these elements, they are rarely in complete agreement. This is likely caused by the simultaneous effects of multiple environmental factors on element incorporation. Culture experiments with benthic foraminifera have revealed that the shell's S/Ca reflects the carbon chemistry and can potentially be used as a proxy for seawater []. Aiming to investigate the application potential of sulfur incorporation for carbonate speciation reconstruction, we present S/Ca ratios in five planktonic foraminiferal species, namely Globigerina bulloides, Globigerinoides ruber albus, Globigerinoides ruber ruber, Trilobatus sacculifer, and Neogloboquadrina incompta from core‐top sediments in regions with contrasting [], [], temperature, and salinity. Analyses of B/Ca and Mg/Ca ratios are included here since these elements have been shown to depend to a certain degree on carbon system parameters (e.g., calcite saturation state and pH, respectively) as well. Moreover, foraminiferal Mg/Ca values covary with S/Ca values and thereby might compromise its proxy application. In contrast to previously published results, this new data set shows a positive correlation between the incorporation of sulfur in the foraminifer's shell and seawater []. As the incorporation of sulfur and magnesium are positively correlated, S/Mg values of the same foraminifera may be used to improve inorganic carbon system reconstructions.

Planktonic foraminiferal biostratigraphy in the Surgah Formation (Turonian-Santonian), Zagros sedimentary Basin, SW Iran (Lorestan Zone)

The Surgah Formation was studied in four sections (Kuh-e-Surgah anticline, Zifel, Sarkan, and Mal-e-kuh) from the NW-SE of the Zagros sedimentary basin. Forty-one planktonic foraminiferal species belonging to 20 genera were observed. The recorded species were used to subdivide the Surgah Formation into three biozones: Marginotruncana sigali-Dicarinella primitiva Zone, Dicarinella concavata Zone, and Dicarinella asymetrica Zone. Based on these data, the Surgah Formation was estimated to be of late Turonian to late Santonian age. The Coniacian/Santonian boundary is placed at the Dicarinella asymetrica Zone. The base of the Santonian stage is identified on the FO of Globotruncana linneiana (pill box shaped), the FOs of Dicarinella asymetrica, Globotruncanita elevata and Globotruncana bulloides, and the LOs of Dicarinella primitiva, Dicarinella concavata and Muricohedbergella flandrini.

Equatorial Pacific Sea‐Air CO2 Exchange Modulated by Upper Ocean Circulation During the Last Deglaciation

AbstractThe eastern equatorial Pacific (EEP) is a source of atmospheric CO2 during the last deglaciation, but the associated oceanic dynamics in the broader low‐latitude Pacific is not fully understood. Here, we report 30,000‐year‐long surface and subsurface pCO2 records for the western equatorial Pacific (WEP), based on boron isotopes in two planktonic foraminiferal species from core MD10‐3340. Our results show that the WEP surface became a significant atmospheric CO2 sink despite that its subsurface waters were enriched by CO2 during the last deglaciation to early Holocene. Combined with EEP proxy data and model results, we suggest that a deglacial‐early Holocene zonal seesaw of sea‐air CO2 exchange across the equatorial Pacific led to a net CO2 outgassing much greater than the modern situation. This can be ascribed to strengthened Subtropical‐Tropical Circulation, resulting in stronger upper ocean stratification in the WEP concurrent with enhanced upwelling of CO2‐rich subsurface waters in the EEP.

Seasonal and vertical distribution of living planktonic foraminifera in the western tropical Pacific Ocean

To investigate the seasonal and vertical distributions of planktonic foraminiferal species in the western tropical Pacific Ocean, we collected planktonic foraminifera seasonally and diurnally from eight water depths from 0 to 600 m using the Multiple Opening/Closing Net and Environmental Sensing System. We identified 23 living foraminiferal species (size fraction 212–1000 μm) and examined their abundances at the sites of oligotrophic areas. Seasonal changes were characterized by an increase in the diversity and abundance of planktonic foraminifera in summer. We estimated the habitat depth of planktonic foraminifera based on their vertical distribution. Planktonic foraminifera can be classified into species living in the surface mixed layer, uppermost thermocline, upper thermocline, and lower thermocline in the water column. The uppermost thermocline layer is characterized by the occurrence of subsurface chlorophyll maximum (water depth, 100–150 m). The boundary between the upper and lower thermocline layers (approximately 300 m) is at the depth at which the dissolved oxygen concentration begins to rapidly decrease. The species inhabiting the surface mixed layer were Globigerinoides sacculifer and Globigerinoides ruber white in spring. In summer, G. sacculifer dwelled in the surface mixed layer during night time, whereas they existed in the uppermost thermocline during daytime. Many species were found in the uppermost thermocline layer in summer, including G. ruber white, Globigerinoides conglobatus, Globigerinella siphonifera, Pulleniatina obliquiloculata, Globoquadrina conglomerata, Orbulina universa, Neogloboquadrina dutertrei, Globigerinella calida, and Hastigerina pelagica. The species Globorotalia hirsuta dwelled in the upper thermocline in spring, whereas it occurred in the lower thermocline in summer. Globorotaloides hexagonus inhabited the lower thermocline in all seasons. Our results will provide useful information for reconstructing changes in water column structure using planktonic foraminiferal shells in marine sediments.

Glacial sea level low-stands regulated the upper ocean hydrology in the southern South China Sea over the past ∼ 280 kyr

The southern South China Sea (SCS) is an ideal region for investigating the low-latitude climatic and oceanic dynamics in the context of local and global effects. However, records of upper-water hydrography beyond the last two glacial cycles are still limited from the southern SCS. In this study, we present shell δ18O, Mg/Ca and Nd/Ca records of three planktonic foraminiferal species (Globigerinoides ruber, Globigerinoides sacculifer and Pulleniatina obliquiloculata) from Core TX05 to explore changes in upper-water hydrography in the southern SCS over the past ∼280 kyr. The results show that shell δ18O of the three species exhibit more positive values in glacials than interglacials. The δ18O residual (i.e. δ18Osw-ice) calculated by shell δ18O subtracting the signals of ice volume and temperature suggests fresher upper seawaters (lower salinity) during glacials than interglacials. This may be caused by terrestrial freshwater discharge from the paleo-Sunda continent that exposed during glacial sea level low-stands. The freshwater discharge may further be ascribed to relatively abundant precipitation over the paleo-Sunda continent during glacials, possibly pointing to the collective effects of the southward shift of the Intertropical Convergence Zone and the enhanced Pacific Walker circulation. The vertical thermal gradients (ΔTrub-obl and ΔTsac-obl) at Site TX05 show lower values during glacials than interglacials. The SST differences of the southern SCS from the northern SCS (ΔSSTS-N) and from the western tropical Pacific (ΔSSTSCS-WTP) correlate well with indicators from the Chinese Loess section, indicating relatively strong East Asian winter monsoon during glacials. The good correlation of ΔT, ΔSSTS-N and ΔSSTSCS-WTP to the relative sea-level suggests a remarkable effect of sea level low-stands and the strengthened East Asian winter monsoon during glacials on the upper ocean hydrography in the southern SCS.

First occurrence of planktonic foraminiferal species Boliella adamsii as a marker for the Pleistocene-Holocene Boundary in the sea around Sumba Island

The expensive cost of Accelerator Mass Spectrometry radiocarbon dating (AMS 14C), the main tool for geochronology in Late Pleistocene-Holocene paleoclimate and paleoceanography study using marine sediment cores, hinders Indonesian researchers to produce competing research outputs. The first occurrences of planktonic foraminiferal species which have been applied as Pleistocene-Holocene Boundary markers in previous Quarternary marine sediment studies in the Indonesian region need to be confirmed as these species might actually occur since the Late Pleistocene. Quantitative foraminifera determination and oxygen isotope (δ18O) analysis of planktonic foraminiferal species Globigerinoides (Gs.) ruber have been carried out in marine sediment cores ST10 (off south Sumba) and ST14 (Sumba strait). δ18O of Gs. ruber was correlated to North Greenland Ice Core Project (NGRIP) Greenland Ice Core Chronology 2005 (GICC05) δ18O to determine the depth of the Pleistocene-Holocene Boundary (11653 BP) in core ST10 and ST14. Pleistocene-Holocene Boundary depth in core ST10 (31 cm) and ST14 (28 cm) are nearly coeval with the First occurrence (FO) of planktonic foraminifera Boliella adamsii, which at 34-35 cm depth interval in core ST10 and at 26-27 cm depth interval in core ST14. This indicated the practicality of Boliella adamsii FO as a Pleistocene-Holocene Boundary marker in the sea around Sumba Island, in case radiocarbon ages and proper planktonic foraminiferal δ18O data are not available. Future studies using a similar method in other Indonesian regions are needed to confirm the practicality of Boliella adamsii FO as a Pleistocene-Holocene Boundary marker in the Indonesian region.

Dynamics of the subpolar gyre and transition zone of the North Atlantic during the last glacial cycle

Past studies of marine sediments of the North Atlantic documented millennial-scale sea-surface cooling related to the Dansgaard-Oeschger events that influenced the oceanic fronts and surface hydrology during the last glacial cycle. Most studies have focused on using ice-rafting, single or multiple species of planktonic foraminifers' abundances, and geochemistry to assess environmental changes. However, detailed planktonic foraminiferal assemblage data in the North Atlantic Transition Zone (NATZ) and subpolar gyre (SPG) for the full last glacial cycle are scarce. Here we report planktonic foraminiferal abundances, oxygen isotopes, and ice-rafted detritus (IRD) counts from two sediment cores, Hu9007-08 and Hu71022-377, collected from the Milne seamount of southwestern SPG (SW SPG) and NATZ, respectively. Further, we have used the published planktonic foraminiferal assemblage, IRD, and isotopic data from the eastern and western SPG to provide an integrated reconstruction of changes in the surface water masses and dynamics of the Polar, Arctic, and subarctic fronts (PF, AF, and SAF, respectively). Despite the overall warmth of the SW SPG (near the Newfoundland Basin) compared to the eastern SPG during marine isotope stage (MIS) 5, the North Atlantic-wide cooling events C24 and C21 were still identified in the SW SPG. Further, the planktonic foraminiferal abundances in cores EW9303-37JPC (i.e., scarce Neogloboquadrina pachyderma and abundant Globigerinoides inflata) and Hu9007-08 reveal a relatively warm MIS 5e compared to the Holocene. However, the decrease in the abundance of G. inflata suggests that the SW SPG was influenced by the seasonal presence of subpolar waters and possibly a southward shift in the oceanic frontal systems between ∼126 and ∼120 ka. During the Heinrich ice-rafting events, when meltwater flooded the surface North Atlantic, the PF, AF, and SAF shifted southward, and the polar/subpolar water masses briefly invaded the western and eastern SPG and NATZ. In the early part of MIS 3 (60–40 ka), the oceanic frontal system shifted northward from its position during MIS 4. The SPG and NATZ gradually warmed, and the subpolar species Globigerina bulloides in cores Hu9007-08, Hu71022-377, and CH69-K09 increased in the middle of MIS 3 (i.e., 38–30 ka), suggesting continuous sea surface warming while the oceanic frontal systems continued to move northward. This hydrological environment rapidly cooled in the late MIS 3-MIS 2 (30–19 ka), with the PF shifted southward to the mid-latitude (∼45°N) during the Last Glacial Maximum. During the last deglaciation-Holocene, the regions of cores Hu9007-08 and Hu71022-377 were mainly influenced by the warm North Atlantic Current, and the SAF was located north of both cores. This study presents the first large-scale water mass movements and frontal changes in the SPG and NATZ to better understand the dynamics of the surface circulation in the North Atlantic during the last glacial cycle.

DISTRIBUCION DE LOS FORAMINIFEROS PLANCTONICOS DEL PLIOCENO EN LA PLATAFORMA CONTINENTAL DEL SW DE ESPANA

Planktonic Foraminifera assemblages from cores of a borehole are studied. Depth interval is from 380 m to 2300 m. The drill site is located in the continental shelf of "Golfo de Cadiz" (SW Spain). The distribution of planktonic foraminiferal species is in agreement with Blow's zonation (1969) extending in age from the Messinian to the Pleistocene.

Planktonic Foraminiferal Biostratigraphy of the Kometan Formation from Kurdistan Region, NE Iraq

The Kometan Formation is widely spread in northeastern Iraq and is mostly composed of deep marine carbonates, with a predominance of planktonic foraminiferal assemblages throughout its sequences. Two outcrop sections, Smaquli and Tabin, were chosen to study the biostratigraphy of the Kometan Formation. The study identified 32 planktonic foraminiferal species belonging to 12 genera. According to stratigraphic distribution and the relative distribution of planktonic foraminifera assemblages, the study demonstrated the possibility of subdividing the sequence of the Kometan Formation into five foraminiferal biozones, including: Marginotruncana schneegansi Partial Range Zone, Dicarinella primitiva Interval Zone, Dicarinella concavata Interval Zone, Dicarinella asymetrica Total Range Zone, Globotruncanita elevata Partial Range Zone. The Planktonic zones were correlated with other zonal schemes inside and outside Iraq. They are considered to be extending from Late Turonian to Early Campanian.

Abrupt warming of the equatorial intermediate Pacific during Heinrich Stadial 1

The Pacific intermediate water is essential for global ocean heat storage and transfer and connected to the higher latitude sea areas. Its thermohaline evolution and relationship to high latitudes on millennium scales, however, are both poorly understood. In this study, we used sediment core KX22–4 in the western equatorial Pacific to reconstruct the thermohaline and δ13C variations in the intermediate water over the past 28,000 years based on Mg/Ca, δ18O and δ13C measurements of deep dwelling planktonic foraminiferal species. The results show that during Heinrich Stadial 1, the temperature of intermediate water rapidly increased by roughly 6 °C and was simultaneous with the Southern Ocean surface water, carrying a typical Antarctic signature along with the salter and reduced δ13C signals. The Southern Hemisphere climatic development and the advection of the thermal anomaly into the tropical intermediate Pacific via the Southern Ocean intermediate water are thought to be closely coupled.

Environmental Controls of Size Distribution of Modern Planktonic Foraminifera in the Tropical Indian Ocean

AbstractPaleoceanographic studies often rely on abundance changes in microfossil species, with little consideration for characteristics such as organism size, which may also be related to environmental changes. Using a tropical Indian Ocean (TIO) core‐top data set, we test the Optimum size‐hypothesis (OSH), investigating whether relative abundance or environmental variables are better descriptors of planktonic foraminifera species' optimum conditions. We also investigate the environmental drivers of whole‐assemblage planktonic foraminiferal test size variation in the TIO. We use an automated imaging and sorting system (MiSo) to identify planktonic foraminiferal species, analyze their morphology, and quantify fragmentation rate using machine learning techniques. Machine model accuracy is confirmed by comparison with human classifiers (97% accuracy). Data for 33 environmental parameters were extracted from modern databases and, through exploratory factor analysis and regression models, we explore relationships between planktonic foraminiferal size and oceanographic parameters in the TIO. Results show that the size frequency distribution of most planktonic foraminifera species is unimodal, with some larger species showing multimodal distributions. Assemblage size95/5 (95th percentile size) increases with increasing species diversity, and this is attributed to vertical niche separation induced by thermal stratification. Our test for the OSH reveals that relative abundance is not a good predictor of species' optima and within‐species size95/5 response to environmental parameters is species‐specific, with parameters related to carbonate ion concentration, temperature, and salinity being primary drivers. At the species and assemblage levels, our analyses indicate that carbonate ion concentration and temperature play important roles in determining size trends in TIO planktonic foraminifera.

Planktonic foraminiferal biostratigraphy of the upper Turonian-lower Santonian succession in the Lorestan Zone of the Zagros sedimentary Basin, SW Iran

The Surgah Formation was studied in four sections (Tang-e-Shirin Ab, Kuh-e-Surgah Holostem Valley, and Sarkan) from the NW-SE of the Zagros sedimentary Basin. Forty-one planktonic foraminiferal species belonging to eighteen genera were recognized. These species were used to identify three zones across the Surgah Formation from the bottom to the top: Dicarinella primitiva – Marginotruncana sigali Zone, Dicarinella concavata Zone, and Dicarinella asymetrica Zone. Based on these data, the Surgah Formation was assigned to the Late Turonian-Santonian age. The base of the Coniacian Stage projects within the lower part of the Dicarinella concavata Zone and is traced at the first occurrence (FO) of Pseudotextularia nuttalli. Owing to the absence of Pseudotextularia nuttalli at the Sarkan well, we utilized the extinction of Whiteinella aprica to estimate the base of the Coniacian Stage. The Coniacian/Santonian (C/S) boundary is placed within the basal part of the Dicarinella asymetrica Zone based on the FO of Globotruncana linneiana. The base of the Santonian Stage denotes marked radiation in the globotruncanids among the planktonic foraminiferal assemblage. Great lithofacies and thickness variations have been observed within the D. concavata Zone. These variations likely indicate that the shoreline was located northwest of the Lorestan province during the Coniacian. In contrast, the southwest extreme of the Lorestan province was characterized by deep-water settings.

Middle Eocene–early Miocene planktonic foraminiferal biostratigraphy, chronostratigraphy, sea‐level reconstruction and sequence biostratigraphy at N. ElFaras‐1Xwell, Qattara Depression, Western Desert, Egypt

The planktonic foraminiferal assemblages are tracked in the middle Eocene–early Miocene succession within N. El Faras‐1X Well, Qattara Depression, Egypt. This succession is composed mainly of three lithostratigraphic units the upper part of the Apollonia Formation (middle to late Eocene), Dabaa Formation (late Eocene and Oligocene) and the lower part of the Moghra Formation (early Miocene). Biostratigraphically, the recorded 77 planktonic foraminiferal species enabled the recognition of 12 planktonic foraminiferal biozones; 4 biozones belong to middle to late Eocene, 7 biozones belong to the Oligocene and 1 belongs to the early Miocene. The proposed biozones were compared with their equivalents in other Egyptian regions and other schemes. Eleven Lowest Occurrence and two Highest Occurrence planktonic foraminiferal bioevents were also recognized and correlated all over the world. The chronostratigraphy and the stage boundaries were mainly delineated according to the diagnostic planktonic foraminifera. The middle–late Eocene boundary (Bartonian–Priabonian boundary), The Eocene–Oligocene boundary (Priabonian–Rupelian boundary), the early Oligocene–late Oligocene boundary (Rupelian–Chattian boundary) and the Oligocene–Miocene boundary (Chattian–Aquitanian boundary) were accurately determined. Based on the % P, the palaeobathymetry was estimated and hence the sea‐level fluctuation. The reconstructed sea‐level curve revealed two major transgressive–regressive cycles with minor oscillation within them. These events were globally correlated and match in most parts with that of the worldwide sea‐level curves. The sequence stratigraphy framework consists mainly of two transgressive–regressive (T–R) depositional sequences (DS1 and DS2). The DS1 includes the TST1 below which is capped by mfs1 and the HST1 above. The DS2 involves the TST2 below that was capped by mfs2 and the HST2 above.

Planktonic foraminiferal biostratigraphy of the Farrokhi Formation and determination of the Campanian/Maastrichtian boundary in Central Iran

The Cretaceous Farrokhi Formation is located in the Khur area of central Iran and yielded a reasonably well-preserved rich planktonic foraminiferal assemblage. This formation consists of 154 m of fossiliferous marl and limestone. The lower and upper bounding surfaces of the Farrokhi Formation are unconformable with the underlying Haftoman Formation and the overlying Chupanan Formation. In this research, 46 planktonic foraminiferal species belonging to 19 genera were identified and resulted in recognition of the following three biozones (from base to top); the Globotruncana aegyptiaca Interval Zone (IZ), the Gansserina gansseri IZ, and the Contusotruncana contusa IZ. This biozonal framework places deposition of the Farrokhi Formation during the late Campanian to early Maastrichtian. Biostratigraphic comparison between the samples for this research and data from three other studied sections within the Farrokhi Formation indicates that the basal and upper boundaries of the formation are time-transgressive and migrate chronologically from north to southeast. Since the first occurrences of Pseudoguembelina palpebra and Rugoglobigerina pennyi mark the latest Campanian worldwide, we approximate the Campanian/Maastrichtian boundary based on the FOs of Trinitella scotti and Rugoglobigerina hexacamerata, and identify the basal Maastrichtian by the last occurrence of Laeviella bollii.

Globorotalia truncatulinoides in the Mediterranean Basin during the Middle–Late Holocene: Bio-Chronological and Oceanographic Indicator

The planktonic foraminiferal species Globorotalia truncatulinoides is widely used as a biostratigraphic proxy for the Quaternary in the Mediterranean region. High-resolution quantitative studies performed on sediment cores collected in the central and western Mediterranean Sea evidence a significant abundance of G. truncatulinoides during the Middle Holocene. The robust chronological frame allows us to date this bio-event to 4.8–4.4 ka Before Present (BP), very close to the base of the Meghalayan stage (4.2 ka BP). As a consequence, we propose that G. truncatulinoides can be considered a potential marker for the Middle–Late Holocene chronological subdivision. G. truncatulinoides is a deep-dwelling planktonic foraminifer and their distributional pattern in the central and western Mediterranean Sea provides a tool to monitor the onset of the regional deep vertical mixing of the water column. During the Holocene, the significant increase in the abundance of this species is in phase with the end of African Humid Period, which marks the transition from a more humid climate to the present-day semi-arid climate.

The influence of seasonal calcification depth change on the planktonic foraminiferal stable oxygen isotope signal

Seasonal changes in temperature and habitat migration both leave large imprints on the stable oxygen isotope composition (δ18O) of planktonic foraminiferal tests, but little is known about how much the depth habitat change affects the calcite δ18O on seasonal timescales, potentially introducing numerous errors to the study of seasonality applied individual foraminifera. In this study, two time series sediment trap moorings deployed in the northern South China Sea (SCS) from July 2012 to April 2013 and southern SCS (upwelling area) from April to October 2014 were used to infer seasonal calcification depth variations for four commonly used planktonic foraminiferal species, Globigerinoides ruber, Trilobatus sacculifer, without a sac-like final chamber, Pulleniatina obliquiloculata and Neogloboquadrina dutertrei by analyzing their test δ18O values. The findings demonstrate that planktonic foraminifera deposit their tests shallower in the winter and during cold water upwelling activity, and deeper in the summer, with a changing seasonal depth habitat for all species that tends to follow the isothermals. More importantly, we devised a new approach for quantifying the effect of seasonal calcification depth changes on the δ18O signature of planktonic foraminiferal tests. After applying this method to our trap site and nine other published global sediment trap sites, the results show that foraminiferal seasonal δ18O signal is strongly distorted (amplified or damped) by seasonal variations in their habitat depth, particularly for the species living in low latitude, attributed to the strong vertical temperature gradient relative to the seasonal temperature change at a given water depth. Surface water species that live in the homogeneous mixed layer may be able to provide the most comprehensive seasonality information.

Trophic niche separation of two non-spinose planktonic foraminifers Neogloboquadrina dutertrei and Pulleniatina obliquiloculata

Based on laboratory observations, planktonic foraminifers are omnivorous, feeding zooplankton and phytoplankton. Spinose species tend toward greater dependence on zooplankton prey than on phytoplankton prey, while non-spinose species are more adapted to herbivorous diets. However, the trophic activity of planktonic foraminifers in the natural environment and their trophic positions in the marine food web have not yet been fully understood. The trophic position (TP) of two non-spinose species, Neogloboquadrina dutertrei and Pulleniatina obliquiloculata, was determined by differences in the nitrogen isotopic composition between two amino acids (glutamic acid and phenylalanine). Results show that TP values of N. dutertrei were ~ 2.4, indicating dependence on omnivorous (mixed herbivorous and carnivorous) diets, while those of P. obliquiloculata were ~ 2.1, indicating dependence on herbivorous diets. Together with previous laboratory observations, these TP values suggest that N. dutertrei is a detritivore or scavenger, while P. obliquiloculata is generally a herbivore. This trophic niche separation likely allows these two planktonic foraminiferal species to live within a similar depth zone in the open water column and provides a clue for understanding causes of spatial and temporal changes in their relative abundances in living and sediment assemblages.

Taxonomy and phylogeny of Albian-Maastrichtian planispiral planktonic foraminifera traditionally assigned to Globigerinelloides

We propose a considerably revised taxonomy and phylogeny for Albian-Maastrichtian planispiral planktonic foraminiferal species that have traditionally been included in Globigerinelloides. The revised taxonomy is necessary because of a ~6 m.y. gap between the extinction of planispiral species during the late Aptian and the next younger occurrence of planispiral species in the middle Albian. Our stratophenetic taxonomic groupings utilize ontogenetic morphometric data, shell wall ultrastructure, and general morphologic features observed from Scanning Electron Microscope and X-radiograph images of primary type specimens and globally distributed hypotype specimens. The planispiral lineage Laeviella n. gen., whose type species is La. bentonensis (Morrow), first appeared in the middle Albian and is postulated to have evolved from the evolutionary series Ticinella primula Luterbacher-Laviella primuloides n. sp. Laeviella is characterized as having a smooth to finely pustulose wall texture and a moderate chamber size increase rate. Two additional species, La. tururensis (Bronnimann) and La. bollii (Pessagno), are included in Laeviella with the youngest species of the genus, La. bollii, becoming extinct during the late Campanian. Planohedbergella, with Plh. aspera (Ehrenberg) as its type species, is revised to include 10 species that show a wide variation in chamber arrangement, wall microstructure and test morphology, but all have a moderately to coarsely pustulose wall texture on some or most final whorl chambers. Its stratigraphic range is from the late Albian-Cretaceous/Paleogene boundary. The oldest species is Plh. ultramicra (Subbotina), which evolved from Planomalina pulchella Todd and Low during the late Albian. Planohedbergella circularis n. sp. is described as a new late Campanian-Maastrichtian species representing forms with evolute coiling, a large number of final whorl chambers, and a slow chamber size increase rate. Polycamerella n. gen. is described as a monospecific genus, with Po. tardata n. sp. as the type species. It is a small, biapertural form with a very slow chamber expansion rate and a stratigraphic range from the late Campanian-Maastrichtian. The ancestor of Po. tardata, is tentatively identified as Plh. ultramicra.

Remote forcing of winter cooling in the Arabian Sea: Implications for the NE monsoon

The regional climate in the Asian subcontinent is highly influenced by the Southwest Monsoon (SWM) and Northeast Monsoon (NEM) during boreal summer and winter, respectively. Although the response of the SWM to the abrupt climatic changes recorded in the Greenland ice core records is well documented, the response of the NEM to the high latitude climate shifts is less well-understood due to the lack of winter monsoon records in the region. Here for the first time, we report the variability of winter cooling in the Arabian Sea and the associated NEM strength over the last ~37 kyr BP using seasonal sea surface temperatures (SST) derived by artificial neural network technique (ANN), based on planktonic foraminiferal species abundance data. Low winter SST anomalies in the northeastern Arabian Sea, a proxy for NEM strength, coincide with cold stadials (YD, H1, H2, H3) in the Greenland record and weakened SWM, implying that the cold conditions in Greenland strengthen the NEM and weaken the SWM on the Asian Subcontinent. Asynchrony between the NEM and SWM variability between ~37 and 9 kyr BP was driven by the southward shift of the Intertropical Convergence Zone (ITCZ) during colder phases of the Greenland stadials strengthening the NEM and weakening the SWM. This study implies that the migration of the ITCZ in the tropical Indian Ocean is controlled by the meridional atmospheric temperature gradient resulting from Atlantic Meridional Overturning Circulation (AMOC) changes. • Close link between NEM and winter cooling in the Arabian Sea was documented. • Strong coupling between AMOC and ITCZ migration • Distinct asynchrony between strengths of NEM & SWM during YD, H1, H2, H3 • NEM variability shows a clear contrast between MIS 2 and MIS 1.

The marine environmental evolution in the northern Norwegian Sea revealed by foraminifera during the last 60 ka

Both planktonic and benthic foraminifera were identified in a sediment core collected from the northern Norwegian Sea to reconstruct the paleoceanographic evolution since the last glaciation. The assemblages and distribution patterns of dominant foraminiferal species with special habitat preferences indicated that three marine environments occurred in the northern Norwegian Sea since 62 ka BP: (1) an environment controlled by the circulation of the North Atlantic Current (NAC); (2) by polynya-related sinking of brines and upwelling of intermediate water surrounding the polynya; (3) by melt-water from Barents Sea Ice Sheet (BSIS). At 62–52.5 ka BP, a period with the highest summer insolation during the last glaciatial period, intensification of the NAC led to higher absolute abundances and higher diversity of foraminiferal faunas. The higher abundance of benthic species Cibicidoides wuellerstorfi indicates bottom water conditions that were well-ventilated with an adequate food supply; however, higher abundances of polar planktonic foraminiferal species Neogloboquadrina pachyderma (sin.) indicate that the near-surface temperatures were still low. During mid-late MIS 3 (52.5–29 ka BP), the marine environment of the northern Norwegian Sea alternately changed among the above mentioned three environments. At 29–17 ka BP during the last glacial maximum, the dominant benthic species Bolivina arctica from the Arctic Ocean indicates an extreme cold bottom environment. The BSIS expanded to its maximum extent during this period, and vast polynya formed at the edge of the ice sheet. The sinking of brines from the formation of sea ice in the polynyas caused upwelling, indicated by the upwelling adapted planktonic species Globigerinita glutinata. At 17–10 ka BP, the northern Norwegian Sea was controlled by melt-water. With the ablation of BSIS, massive amounts of melt water discharged into the Norwegian Sea, resulting in strong water column stratification, poor ventilation, and an oligotrophic bottom condition, which led to a drastic decline in the abundance and diversity of foraminifera. At 10–0 ka BP, the marine environment was transformed again by the control of the NAC, which continues to modern day. The abrupt decrease in relative abundance of Neogloboquadrina pachyderma (sin.) indicates a rise in near-surface temperature with the strengthening of the NAC and without the influence of the BSIS. Citation : Wang W G, Zhao M W, Yang J C, et al. The marine environmental evolution in the northern Norwegian Sea revealed by foraminifera during the last 60 ka. Adv Polar Sci, 2021, 32(3): 210-220, doi: 10.13679/j.advps.2021.0020