Foraminiferal oxygen and carbon isotopes during the last 34 kyr off northern Japan, northwestern Pacific

Oxygen and carbon isotopes of foraminifera were analyzed in core PC4, water depth 1366 m, off northern Japan, near the east side of the Tsugaru Strait (130 m depth) between the open northwestern Pacific Ocean and the Japan Sea. At present, the site is at the confluence of the Tsugaru Warm Current which flows eastwards out of the Sea of Japan through the Tsugaru Strait, the subarctic Oyashio Current and the subtropic Kuroshio Current. During the Last Glacial Maximum (LGM), the Oyashio Current penetrated further to the South and outflow from the Japan Sea was restricted by glacio-eustatic sea level lowering.The isotopic values of the planktic foraminifer Neogloboquadrina pachyderma (sinistral) and the benthic foraminifer Uvigerina akitaensis reflect rapid millennial-scale paleoceanographic changes between 34 and 6 ka. Hydrographic changes during deglaciation were related to events at high northern latitudes, but Holocene hydrographic changes were dominated by local effects, such as the development of the outflow of the Tsugaru Warm Current. High values of planktic δ¹⁸O during the LGM reflect the southward advance of the Oyashio Current. These values decreased by 0.3‰ from 19.4 to 18.9 ka, then increased by 0.5‰ at 18 ka, with highest values between 17.5 and 15 ka. The δ¹⁸O oscillations between 19.4 and 15 ka may reflect millennial-scale warm–cold oscillations during Heinrich event 1. Planktic microfossil data indicate that cold Oyashio waters flowed from the northwestern Pacific into the Japan Sea via the Tsugaru Strait between 17 and 16 ka, consistent with the occurrence of the highest planktic δ¹⁸O values in core PC4. Planktic δ¹⁸O values rapidly decreased by 0.9‰ at 15 ka, possibly reflecting the effects of both a rapid increase in fresh water flux and rising temperatures in the subarctic North Pacific. During the Younger Dryas, cold event planktic δ¹⁸O values increased by 0.5‰, followed by a gradual decrease by 1‰ from the early to middle Holocene, reflecting a gradual increase in eastward outflow via the Tsugaru Strait with sea level rise. Both planktic and benthic foraminiferal δ¹³C values oscillated between 34 and 10 ka, at relatively large amplitudes (about 0.5‰), then remained relatively stable during the last 10 kyr. Several negative planktic and benthic ( − 0.7‰) δ¹³C excursions were present in sediment dated between the precipitation of secondary carbonates during episodic methane release possibly associated with methane release from continental margin sediments.     

Catastrophic mass extinction and assemblage evolution in planktic foraminifera across the Cretaceous/Paleogene (K/Pg) boundary at Bidart (SW France)

A high-resolution biostratigraphic analysis of planktic foraminifers confirms that the Bidart section at the eastern margin of the Atlantic Ocean exhibits a continuous and complete Cretaceous/Paleogene (K/Pg) transition interval. The biozones and subzones recorded in this section are less expanded than their equivalent in Tunisian sections: El Kef (Global Stratotype Section and Point: GSSP for the K/Pg boundary) and Ellès (auxiliary section), but they are sufficiently thick to allow a detailed analysis of the evolution of the planktic foraminiferal assemblages across the K/Pg transition.Throughout the uppermost 4 m Maastrichtian, the planktic foraminiferal assemblages are highly diversified, containing up to 72 species. These Maastrichtian assemblages are rich in cosmopolitan taxa (70%), dominated by small biserial morphotypes which belong mainly to the genus Heterohelix which coexist with less abundant but highly diverse tropical and subtropical species.The extinction pattern at the Bidart section suggests a sudden catastrophic mass extinction at the K/Pg boundary which affected at least 53 out of 72 species. The species becoming extinct include globotruncanids (e.g. Contusotruncana spp., Globotruncana spp., Globotruncanita spp.) and complex heterohelicids (e.g. Racemiguembelina spp., Pseudotextularia spp., Gublerina spp.). At the Bidart section, only Archaeoglobigerina cretacea disappears 2 m below the K/Pg boundary event. Specimens of 18 small and even tiny Maastrichtian species, are found at the lowermost Danian. Only a few of these species belonging to the genera of Guembelitria, Hedbergella and Heterohelix are considered to be real “Cretaceous survivor species”, whereas the specimens belonging to the rest, are most probably reworked, because they differ in their preservation.Throughout lowermost Danian, the planktic foraminiferal assemblages are dominated by “opportunistic” species of the genus Guembelitria. These opportunists are associated to small and poorly diversified pioneer globigerinids (Palaeoglobigerina spp. and Parvularugoglobigerina spp.). These assemblages became progressively more diversified across the early Danian containing species with cancellate walls (Eoglobigerina spp., Parasubbotina spp., Subbotina triloculinoides and Praemurica spp.) and new taxa of biserial heterohelicids (Woodringina spp. and Chiloguembelina spp.) suggesting a paleoenvironmental recovery.     

Faunal turnovers in central Pacific benthic foraminifera during the Paleocene-Eocene thermal maximum

Although it is well known that the Paleocene/Eocene thermal maximum (PETM) coincided with a major benthic foraminiferal extinction event, the detailed pattern of the faunal turnover has not yet been clarified. Our high-resolution benthic foraminiferal and carbon isotope analyses at the low latitude Pacific Ocean Shatsky Rise have revealed the following record of major faunal transitions: (1) An initial turnover which involved the benthic foraminiferal extinction event (BFE). The BFE, marked by a sharp transition from Pre-extinction fauna to Disaster fauna represented by small-sized Bolivina gracilis, expresses the onset of the PETM and the abrupt extinction of about 30% of taxa. This faunal transition lasted about 45-74 kyr after the initiation of the PETM and was followed by: (2) the appearance of Opportunistic fauna represented by Quadrimorphina profunda, which existed for about 74-91 kyr after the initiation of the PETM. These two faunas, which appeared after the extinction event, are characterized by low diversity and dwarfism, possibly due to lowered oxygen condition and decreased surface productivity. The second pronounced turnover involved the gradual recovery from Opportunistic Fauna to the establishment of Recovery fauna, which coincided with the recovery about 83-91 kyr after its initiation.     

Food supply to the seafloor in the Pacific Ocean after the Cretaceous/Paleogene boundary event

Deep-sea benthic foraminifera show important but transient assemblage changes at the Cretaceous/Paleogene (K/Pg) boundary, when many biota suffered severe extinction. We quantitatively analyzed benthic foraminiferal assemblages from lower bathyal–upper abyssal (1500–2000 m) northwest Pacific ODP Site 1210 (Shatsky Rise) and compared the results with published data on assemblages at lower bathyal (~ 1500 m) Pacific DSDP Site 465 (Hess Rise) to gain insight in paleoecological and paleoenvironmental changes at that time.At both sites, diversity and heterogeneity rapidly decreased across the K/Pg boundary, then recovered. Species assemblages at both sites show a similar pattern of turnover from the uppermost Maastrichtian into the lowermost Danian: 1) The relative abundance of buliminids (indicative of a generally high food supply) increases towards the uppermost Cretaceous, and peaks rapidly just above the K/Pg boundary, coeval with a peak in benthic foraminiferal accumulation rate (BFAR), a proxy for food supply. 2) A peak in relative abundance of Stensioeina beccariiformis, a cosmopolitan form generally more common at the middle than at the lower bathyal sites, occurs just above the buliminid peak. 3) The relative abundance of Nuttallides truempyi, a more oligotrophic form, decreases at the boundary, then increases above the peak in Stensioeina beccariiformis. The food supply to the deep sea in the Pacific Ocean thus apparently increased rather than decreased in the earliest Danian. The low benthic diversity during a time of high food supply indicates a stressed environment. This stress might have been caused by reorganization of the planktic ecosystem: primary producer niches vacated by the mass extinction of calcifying nannoplankton may have been rapidly (<10 kyr) filled by other, possibly opportunistic, primary producers, leading to delivery of another type of food, and/or irregular food delivery through a succession of opportunistic blooms.The deep-sea benthic foraminiferal data thus are in strong disagreement with the widely accepted hypothesis that the global deep-sea floor became severely food-depleted following the K/Pg extinction due to the mass extinction of primary producers (“Strangelove Ocean Model”) or to the collapse of the biotic pump (“Living Ocean Model”).     

Palaeoenvironmental conditions preceding the Messinian Salinity Crisis: A case study from Gavdos Island

The Messinian pre-evaporitic sedimentary succession of Gavdos Island (Metochia section) is a nearly uninterrupted succession of marine sediments, dominated by finely laminated diatomaceous marls, which are cyclically alternating with clayey diatomites and white diatomites. The qualitative and quantitative analysis of the planktonic foraminiferal fauna allowed the recognition of nine bioevents, which have been astronomically dated for the Mediterranean. The base of the diatomitic succession in Gavdos Island is dated at 6.722 Ma and the top at 6.015 Ma. The studied section contains benthic foraminiferal genera characteristic of an outer shelf to slope environment. The qualitative and quantitative analysis of this microfauna revealed three benthic foraminiferal fossil assemblages and the occurrence of allochthonous species transported into the bathyal environment by current activity. The cyclical pattern of the benthic foraminifera assemblages indicates that the studied sediments have been affected by repeated episodes of basin restriction characterized by low diversity benthic foraminifera populations, and a limited planktonic foraminifer association typified by shallow, surface-dwelling forms. This restriction was partly due to Antarctic cooling, which produced palaeo-Mediterranean sea-level oscillations during the Early Messinian, as a prelude to closure of the Atlantic connections. The relative impact of climatic versus tectonic control on sedimentation patterns within this basin is discussed.     

Early Neogene biochemostratigraphy of Pohang Basin: a paleoceanographic response to the early opening of the Sea of Japan (East Sea)

The location of the Pohang Basin near the Korea Strait in the southwest of the Sea of Japan (East Sea) makes this area appropriate for providing a record of paleoenvironmental/biotic changes associated with the early Neogene (16.5 Ma) opening of this gateway to the Pacific Ocean. Stable isotopic and planktonic foraminiferal records are presented that assist with the understanding of paleoenvironmental changes in the Sea of Japan resulting from the opening of the Korea Strait. The oldest sediments of early Neogene age of the Pohang Basin overlie Cretaceous basement and are Early Miocene (>16.5 Ma) shallow, estuarine facies containing a benthic foraminiferal assemblage dominated by Ammonia beccarii (L.). The oldest early Neogene planktonic foraminiferal assemblages in the basin are 16.5 Ma in age (latest Early Miocene foraminiferal zone N8). The migration of these planktonic assemblages to the Sea of Japan at that time appears to have resulted from the initial opening of the Korea Strait. The overlying early Neogene marine sequence of the Pohang Basin extends from 16.5 Ma (Zone N8) through 14 Ma (Zone N10). Change in the oxygen isotopic record of the Pohang Basin sequence suggests strong local paleoenvironmental control related to the early opening of the Korea Strait. Early Middle Miocene isotopic temperatures of planktonic foraminifera are relatively cool at 15 Ma at a time when global temperatures were high in the middle/low latitude regions. It was not until 14.8 Ma that isotopic temperatures of planktonic foraminifera increased markedly. This distinct warming is inferred to reflect the major intrusion of the Kuroshio Current into the Sea of Japan probably as a result of further critical opening and deepening of the Korea Strait. At this time planktonic foraminifera increased in abundance reflecting expanding oceanic influence. A cooling that followed at 14.5 Ma, when the strait was well open is unlikely to reflect local tectonic control on the paleoceanography, but global cooling during the early Middle Miocene associated with the expansion of the East Antarctic ice sheet.     

Albian calcareous nannofossils from ODP Site 1258, Demerara Rise

Site 1258, drilled during Ocean Drilling Program (ODP) Leg 207 on Demerara Rise off the northern coast of South America, recovered organic-rich Albian sediments that yield abundant, moderately to well preserved calcareous nannofossils. Biostratigraphic analysis shows the section primarily spans Roth’s (Initial Reports DSDP 44. US Government Printing Office, Washington (1978) 731) middle to late Albian Zone NC9. A disconformity separates these sediments from overlying uppermost Albian laminated shales from Zone NC10. The presence of Seribiscutum primitivum within the Albian section represents the first known occurrences of this species at such low latitudes, as Demerara Rise was located within 15° of the equator during the mid-Cretaceous. This species exhibits a bipolar distribution and is considered a cool-water, high-latitude species. Its presence on Demerara Rise indicates cooler water incursions either through changes in surface circulation or upwelling conditions during the opening of the Equatorial Atlantic.     

The Holocene Pulleniatina Minimum Event revisited: Geochemical and faunal evidence from the Okinawa Trough and upper reaches of the Kuroshio current

The Holocene Pulleniatina Minimum Event (PME) is characterized by a very low abundance of the planktonic foraminifer Pulleniatina obliquiloculata between  4.5 and 3 ka. The PME occurs widely in the Okinawa Trough and the South China Sea, and can be correlated throughout this area; it has been related to variability in the Kuroshio current. To further explore the nature of the PME, we studied cores obtained from the southern Okinawa Trough and the upper reaches of the Kuroshio current. Faunal census data indicate that all cores record the PME between  4.5 and  3 ka. The relative abundance of Neogloboquadrina dutertrei is negatively correlated to that of P. obliquiloculata in the southern Okinawa Trough, but not in the sites at the upper reaches. Mg/Ca and δ¹⁸O measurements on Globigerinoides ruber shells from the southern Okinawa Trough indicate that there was no change in sea surface temperature or sea surface salinity during the PME. The vertical structure of the water column as reconstructed by multispecies δ¹⁸O and δ¹³C profiles shows no consistent anomalies in the southern Okinawa Trough and western Philippine Sea during the PME. These observations suggest that: (1) the PME was not restricted to marginal seas, but widespread in the western North Pacific. (2) The high abundance of N. dutertrei during the PME in the Okinawa Trough may be a result of higher food-availability in the absence of P. obliquiloculata. (3) No distinctive, consistent anomalies in the paleoceanographic proxies are associated with the PME, implying there were no changes in hydrography and productivity. The absence of a linkage between faunal variation and paleoceanographic proxies indicates that we do not yet understand what causes changes in planktonic foraminiferal assemblages. This lack of understanding implies that we cannot always trust fauna-based paleothermometry at millennial timescales.     

Perturbation at the sea floor during the Paleocene–Eocene Thermal Maximum: Evidence from benthic foraminifera at Contessa Road, Italy

Detailed analyses of the benthic foraminiferal assemblages extracted with the cold acetolyse method together with high resolution geochemical and mineralogical investigations across the Paleocene/Eocene (P/E) boundary of the classical succession at Contessa Road (western Tethys), allowed to recognize and document the Paleocene–Eocene Thermal Maximum (PETM) interval, the position of the Benthic Extinction Event (BEE) and the early recovery of benthic faunas in the aftermath of benthic foraminiferal extinction. The stratigraphical interval spanning the P/E boundary consists of dominantly pelagic limestones and two prominent marly beds. Benthic foraminifera indicate that these sediments were deposited at lower bathyal depth, not deeper than 1000–1500 m. The Carbon Isotope Excursion (CIE) interval is characterized by high barite abundance with a peak at the base of the same stratigraphic interval, indicating a complete, although condensed record of the early CIE. A succession of events and changes in the taxonomic structure of benthic foraminifera has been recognized that may be of use for supra-regional stratigraphic correlation across the P/E boundary interval. The composition of the benthic foraminiferal assemblages, dominated by infaunal taxa, indicates mesotrophic and changing conditions on the sea floor during the last  45 kyr of the Paleocene. The BEE occurs at the base of the CIE within the lower marly bed and it is recorded by the extinction of several deep-water cosmopolitan taxa. Then, the lysocline/CCD rose and severe carbonate dissolution occurred. Preservation deteriorated, the faunal density and simple diversity dropped to minimum values and a peak of Glomospira spp. has been observed. Stress-tolerant and opportunistic groups, represented mainly by bi-and triserial taxa, dominate the low-diversity post-extinction assemblages, indicating a benthic foraminiferal recovery under environmental unstable conditions, probably within a context of sustained food transfer to the bottom. A three-phase pattern of faunal recovery is recognizable. At first the lysocline/CCD started to descend and then recovered. Small-sized “Bulimina”, Oridorsalis umbonatus, and Tappanina selmensis rapidly repopulated the severely stressed environment. Later on, Siphogenerinoides brevispinosa massively returns, dominating the assemblage together with other buliminids, Nuttallides truempyi, and Anomalinoides sp.1. Finally, a marked drop in abundance of S. brevispinosa is followed by a bloom of the opportunistic and recolonizer agglutinated Pseudobolivina that, for the first time, is recorded within the main CIE. A second interval of dissolution, but less severe than the previous one, has been recognized within the upper marly bed (uppermost part of the main CIE interval) and it is interpreted as a renewed, less pronounced shoaling of the lysocline/CCD that interrupted the recovery of benthic faunas. This further rise likely represents a response to persistent instability of ocean geochemistry in this sector of the Tethys before the end of the CIE. In the CIE recovery and post CIE intervals, the composition of the benthic foraminiferal assemblages suggests mesotrophic and unstable conditions at the sea floor. According to the geochemical proxy for redox conditions, the deposition of the PETM sediments at Contessa Road occurred in well-oxygenated waters, leading out a widespread oxygen depletion as major cause of the BEE. Changing oceanic productivity, carbonate corrosivity and global warming appear to have played a much more important role in the major benthic foraminiferal extinction at the P/E boundary.     

Centennial-scale climate variability in the Timor Sea during Marine Isotope Stage 3

We present a high-resolution ( 60–110 yr) multi-proxy record spanning Marine Isotope Stage 3 from IMAGES Core MD01-2378 (13°04.95′ S and 121°47.27′ E, 1783 m water depth), located in the Timor Sea, off NW Australia. Today, this area is influenced by the Intertropical Convergence Zone, which drives monsoonal winds during austral summer and by the main outflow of the Indonesian Throughflow, which represents a key component of the global thermohaline circulation system. Thus, this core is ideally situated to monitor the linkages between tropical and high latitude climate variability. Benthic δ¹⁸O data (Planulina wuellerstorfi) clearly reflect Antarctic warm events (A1–A4) as recorded by the EPICA Byrd and Dronning Maud Land ice cores. This southern high latitude signal is transferred by deep and intermediate water masses flowing northward from the Southern Ocean into the Indian Ocean. Planktonic δ¹⁸O shows closer affinity to northern high latitudes planktonic and ice core records, although only the longer-lasting Dansgaard–Oeschger warm events, 8, 12, 14, and 16–17 are clearly expressed in our record. This northern high latitude signal in the surface water is probably transmitted through atmospheric teleconnections and coupling of the Asian–Australian monsoon systems. Benthic foraminiferal census counts suggest a coupling of Antarctic cooling with carbon flux patterns in the Timor Sea. We relate increasing abundances of carbon-flux sensitive species at 38–45 ka to the northeastward migration of the West Australian Current frontal area. This water mass reorganization is also supported by concurrent decreases in Mg/Ca and planktonic δ¹⁸O values (Globigerinoides ruber white).     

The Paleocene–Eocene Thermal Maximum as recorded by Tethyan planktonic foraminifera in the Forada section (northern Italy)

The Forada section in the Venetian Pre-Alps of northern Italy represents an expanded record of the Paleocene–Eocene Thermal Maximum (PETM) at a depositional paleodepth of about 1 km ± 0.5 km. High-resolution planktonic foraminiferal analysis of this section, in a time interval of approximately 1.3 Myr across the Paleocene/Eocene boundary, reveals striking faunal changes that allow the identification of eight phases (a–h). The late Paleocene was represented by stable, warm and oligotrophic surface water conditions (phase a). Unstable environmental conditions start well before the onset of PETM (ca. 150 kyr, phase b) and involved a change towards eutrophy, as marked by the increase of Subbotina and the concomitant decrease of Morozovella. This step is also characterized by enhanced fragmentation and dissolution.The interval corresponding to the main body of the carbon isotope excursion (CIE) is characterized by a marked increase of Acarinina, though with some differences in the species composition and relative abundance, both in high-and low-latitudes, particularly in the Tethyan area. Forada is no exception to this pattern. However, at Forada, two prominent peaks in abundance of acarininids are recorded ca. 30 kyr prior to the onset of the CIE, thus suggesting an increase in temperature heralding the onset of the PETM (phase c). Interestingly, the lower peak in abundance of Acarinina just precedes the 1‰ carbon isotope negative shift occurring below the onset of the main CIE. The basalmost Eocene, corresponding to the lower part of CIE curve, is represented by intense planktonic foraminiferal dissolution, implying an extraordinary rise of the CCD. This interval has an estimated duration of about 16 kyr (phase d).The dominance of acarininids in the lower part of the CIE (phase e, f; ca. 14 and 22.5 kyr) is interpreted as a consequence of the extreme warmth coupled with eutrophic conditions characterizing the Forada depositional environment at that time. These acarininids include at Forada also the temporally constrained Acarinina sibaiyaensis and A. africana. The morphological similarity between these peculiar species with the radially elongated chambered forms characterizing the Cretaceous anoxic events, suggests the hypothesis that depletion of oxygen in the upper water column might have been one of the factors causing their conspicuous occurrence at the PETM.The recovery in abundance of the specialized morozovellids and of other planktonic foraminiferal groups (e.g., biserials, globanomalinids, igorinids, planorotalids and pseudohastigerinids), occurring in the middle part of the CIE (ca. 30 kyr after the onset of the PETM), indicates an initial environmental recovery (phase g). A new stable state is definitely reached in the upper part of the Forada section where the relative proportions of the main component of planktonic foraminiferal assemblages move towards values similar to those of the late Paleocene conditions (phase h). However, the perturbation during the PETM produced significant changes in the ocean geochemistry that endured after the PETM event, as testified by the prominent high carbonate dissolution characterizing the marly levels, and the large variability in relative abundance among different components of the planktonic foraminiferal assemblages. These striking oscillations were not present in the latest Paleocene.     

Upper Albian planktic foraminifera and radiolarian biostratigraphy (Nebeur – northern Tunisia)

Preliminary lithostratigraphic and biostratigraphic data recovered from Upper Albian pelagic successions of the Jebel Srassif area (Tunisian trough) reveal the presence of a moderately well preserved radiolarian fauna. This fauna is fossilized in blackshale beds of Rotalipora subticinensis, R. ticinensis and the lower part of the R. appenninica foraminifer zones. Thirty-five radiolarian morphotypes were identified. A correlation established with foraminifer planktic biochronology allows us to distinguish three radiolarian assemblages. The close association between organic-rich deposits and the radiolarian bloom can be interpreted as productivity proxy triggered by semi-enclosed basin configuration and an intensified upwelling currents provided by a possibly halokinetic-induced hydrothermalism.     

Abyssal NE Atlantic benthic foraminifera during the last 15 kyr: Relation to variations in seasonality of productivity

Benthic foraminiferal faunas (> 63 μm) and stable isotopes from the last 15 kyr were studied in BENGAL programme (high-resolution temporal and spatial study of the BENthic biology and Geochemistry of a north-eastern Atlantic abyssal Locality) kasten core 13078#16 from the Porcupine Abyssal Plain, NE Atlantic (48°49.91 N, 16°29.94 W, water depth 4844 m). Changes occurred in the accumulation rates, species composition, diversity, and stable isotopes during the last 15 kyr. Today, the area is strongly influenced by seasonal inputs of phytodetritus following the spring blooms in surface water primary productivity. Variations in the relative abundance of the two most abundant species, Epistominella exigua and Alabaminella weddellensis, which today show significant increases in abundance with the presence of phytodetritus on the sea-floor, are interpreted as resulting from changes in the seasonality of productivity. Seasonal productivity was higher during the Holocene than during the last deglaciation and Younger Dryas, probably coinciding with the retreat of the polar front to higher latitudes. This hypothesis is consistent with simultaneous decreases in the percentage of the polar planktic foraminifera Neogloboquadrina pachyderma (s), and increases in the percentage of Globigerina bulloides, a warmer water planktic foraminifera indicative of phytoplankton blooms and enhanced productivity. The relative abundance of the ‘phytodetritus species’ (E. exigua and A. weddellensis) covary between 14.7 and 8.1 kyr, but not between 7.8 and 1.2 kyr. Major decreases in the numbers per gram and accumulation rates of planktic and benthic foraminifera occurred at ∼ 12–8.5 kyr and at ∼ 4 kyr which correspond to decreases in the % sediment coarse fraction and published data on inorganic carbon contents suggesting that dissolution may have increased at these times. Relationships between benthic foraminiferal faunas and benthic stable isotope records suggest no simple relationship between faunal abundances and test isotope chemistry. For example, the abundances of phytodetritus species do not show strong correlations with either the δ¹³C values of E. exigua or the Δδ¹³C _{E. exigua − P. wuellerstorfi} record, which have previously been suggested as indicative of seasonality of productivity.     

Linkages between surface and deep circulations in the southern Japan Sea during the last 27,000 years: Evidence from planktic foraminiferal assemblages and stable isotope records

We analyzed planktic foraminiferal assemblages, oxygen and carbon isotope records, and the presence or absence of laminations to reconstruct the paleoenvironments of the southern Japan Sea since the last glacial period. Data were collected from two well-dated cores. One core (water depth 999 m) included thinly laminated mud layers, the other (water depth 283 m) contained nonlaminated sediments. Tephrochronology and accelerator mass spectrometry ¹⁴C dating of 14 horizons revealed that the two cores contained continuous records of the last 27 cal kyr. A total of 13 planktic foraminiferal species belonging to six genera were identified in down-core samples. The typical indicators of the Tsushima Current water, Globigerinoides ruber, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, Globigerinoides tenellus, and Globigerinita glutinata occurred since 9.3 cal kyr BP. Neogloboquadrina incompta, which was the dominant species in the Tsushima Current region of the modern Japan Sea, first occurred at 8.2 cal kyr BP and dominated the assemblage since 7.3 cal kyr BP. These results clearly indicate that the warm Tsushima Current started to inflow into the Japan Sea at 9.3 cal kyr BP, and the modern surface conditions in the southern Japan Sea were essentially established at 7.3 cal kyr BP. Our data and comparison of the presence or absence of laminated sediments in three locations from the southern Japan Sea suggest that deep circulation during the deglacial period was weaker than that at present. In addition, deep circulation in the modern Japan Sea, which supplies oxygen-rich water to the entire basin, started probably in association with the first inflow of the Tsushima Current beginning at 9.3 cal kyr BP.     

Western equatorial Pacific planktic foraminiferal fluxes and assemblages during a La Niña year (1999)

A correlation between foraminiferal community dynamics and environmental conditions may provide a basis for establishing paleoclimatic proxies. We studied planktic foraminiferal shell fluxes and assemblages in samples collected in three time-series sediment trap deployments in the western equatorial Pacific under La Niña conditions from January to November 1999. Eleven species contributed about 90% of the total flux in all traps. Two sites (MT1, MT3) in the Western Pacific Warm Pool region (WPWP) were characterized by common occurrences of the species Globigerinoides ruber, Globigerinoides sacculifer, Globigerinoides tenellus, and Neogloboquadrina dutertrei. Site MT5 farther to the east in the equatorial upwelling region had common occurrences of Globigerina bulloides, Globigerinita glutinata, and Pulleniatina obliquiloculata. Very high abundances of G. bulloides and G. glutinata at MT5 indicate that equatorial upwelling (EU) occurred during the 1999 La Niña. The two western sites have similar assemblage compositions, but MT1 ( 135°E) has the highest fluxes (up to  3800 tests m^− 2 day^− 1), whereas MT3 ( 145° E) has fluxes below  2200 tests m^− 2 day^− 1. Relatively high fluxes (up to  3000 tests m^− 2 day^− 1) occur at site MT5 ( 176° E), where upwelling occurred.The differences in faunal composition in the WPWP and EU might be attributable to differences in the way in which nutrients are supplied to the phytoplankton: large amounts of suspended material are supplied to the WPWP by advection of waters passing through the coastal region of an archipelago, whereas upwelling of nutrient-rich waters enhances primary production in the EU. At the westernmost site in the WPWP, a peak in the G. bulloides flux coincided with southward flow of the New Guinea Coastal Current (NGCC) in late February, but the highest G. ruber flux coincided with northward flow of this current in late May. Thus, the differences in species dominance at this location may be caused by monsoon-driven variability in the flow direction of the NGGC.     

The tropical rainbelt and productivity changes off northwest Africa: A 31,000-year high-resolution record

Benthic foraminiferal assemblage compositions and sedimentary geochemical parameters were analyzed in two radiocarbon dated sediment cores from the upwelling area off NW Africa at 12°N, to reconstruct productivity changes during the last 31 kyr. High-latitude cold events and variations in low-latitude summer insolation influenced humidity, wind systems, and the position of the tropical rain belt over this time period. This in turn caused changes in intensity and seasonality of primary productivity off the southern Northwest African continental margin.High accumulation rates of benthic foraminifera, carbonate, and organic carbon during times of north Atlantic melt water events Heinrich 2 (25.4 to 24.3 kyr BP) and 1 (16.8 to 15.8 kyr BP) indicate high productivity. Dominance of infaunal benthic foraminiferal species and high numbers of deep infaunal specimens during that time indicate a strong and sustained supply of refractory organic matter reworked from the upper slope and shelf. A more southerly position of the tropical rainbelt and the Northeast trade wind belt during Heinrich 2 and 1 may have enhanced wind intensity and almost permanent upwelling, driving this scenario.A phytodetritus-related benthic fauna indicates seasonally pulsed input of labile organic matter but generally low year-round productivity during the Last Glacial Maximum (23 to 18 kyr BP). The tropical rainbelt is more expanded to the North than during Heinrich events, and relatively weak NE trade winds resulted in seasonal and weak upwelling, thus lower productivity.High productivity characterized by a seasonally high input of labile organic matter, is indicated for times of orbital forced warming, such as the African Humid Period (9.8 to 7 kyr BP). An intensified African monsoon during boreal summer and the northernmost position of the tropical rainbelt within the last 31 kyr resulted in enhanced river discharge from the northward-extended drainage area initiating intense phytoplankton blooms. In the late Holocene (4 to 0 kyr BP) strong carbonate dissolution may have been caused by even more enhanced organic matter fluxes to the sea floor. Increasing aridity on the continent and stronger NE trade winds induced intensive, seasonal coastal upwelling.     

Late Neogene planktonic foraminifera of the Cibao Valley (northern Dominican Republic): Biostratigraphy and paleoceanography

An assemblage of planktonic foraminifera is described from 125 samples taken from the Cercado, Gurabo, and Mao Formations in the Cibao Valley, northern Dominican Republic. The primary objectives of this study are to establish a biochronologic model for the late Neogene of the Dominican Republic and to examine sea surface conditions within the Cibao Basin during this interval. The Cercado Formation is loosely confined to Zones N17 and N18 ( 7.0–5.9 Ma). The Gurabo Formation spans Zones N18 and N19 ( 5.9–4.5 Ma). The Mao Formation is placed in Zone N19 ( 4.5–3.6 Ma). Changes in the relative abundances of indicator species are used to reconstruct sea surface conditions within the basin. Increasing relative abundances of Globigerinoides sacculifer and Globigerinoides ruber, in conjunction with a decreasing relative abundance of Globigerina bulloides, suggests the onset of increasing sea surface temperature and salinity in conjunction with diminishing primary productivity at 6.0 Ma. Abrupt increases in the relative abundances of G. sacculifer and G. ruber at 4.8 Ma suggest a major increase in sea surface temperature and salinity in the early Pliocene. The most likely mechanism for these changes is isolation of the Caribbean Ocean through progressive restriction of Pacific–Caribbean transfer via the Central American Seaway. Periods of high productivity associated with upwelling events are recorded in the upper Cercado Formation ( 6.1 Ma) and in the middle Mao Formation ( 4.2 Ma) by spikes in G. bulloides and Neogloboquadrina spp. respectively. The timing of major increases in sea surface salinity and temperature as well as decreasing productivity ( 4.8 Ma) and periods of upwelling ( 6.1and 4.2 Ma) in the Cibao Basin generally corroborate previously suggested Caribbean oceanographic changes related to the uplift of Panama. Changes in sea surface conditions depicted by paleobiogeographic distributions in the Cibao Basin suggest that shoaling along the Isthmus of Panama had implications in a shallow Caribbean basin as early as 6.0 Ma. Major paleobiologic changes between 4.8 and 4.2 Ma likely represent the period of final closure of the CAS and a nearly complete disconnection between Pacific and Caribbean water masses. This study illustrates the use of planktonic foraminifera in establishing some paleoceanographic conditions (salinity, temperature, productivity, and upwelling) within a shallow water basin, outlining the connection between regional and localized oceanographic changes.     

The Pandinus imperator haemolymph lipoprotein, an unusual phosphatidylserine carrying lipoprotein

The haemolymph lipoprotein of the scorpion, Pandinus imperator was isolated and characterised. Contrary to the lipoproteins of insects and the discoidal HDL-lipoproteins of a crayfish and polychaete, the Pandinus lipoprotein consists of three instead of two apoproteins (apoPiLp I = 230 kDa, apoPiLp II = 130 kDa and apoPiLp III = 120 kDa). The apolipoproteins are arranged in varying stoichiometries as judged by cross-linking experiments. In lipoprotein samples from individual animals, the two smaller subunits occurred in a 1:1 stoichiometry, while the relative amount of the 230 kDa peptide varied. The lipoprotein is a slightly heart-shaped HDL with a diameter of 15 nm. It is present in two densities of 1100 and 1190 kg/m³, of which the latter is by far more abundant. The native molecular mass was estimated to be 500 kDa. The lipid content was determined as 33.5% and consists of 70% neutral lipids and 30% phospholipids. Strikingly, 42.5% of the phospholipids is phosphatidylserine while phosphatidylcholine and phosphatidylethanolamine account for 55.1% and 2.3%, respectively. Carbohydrate analysis suggests the presence of only high-mannose-type N-glycans. N-glycan profiling shows glycans corresponding to a size of 8.0–11.5 hexose units.     

Glacial Holocene environment of the southeastern Okhotsk Sea: evidence from geochemical and palaeontological data

Environmental conditions and productivity changes in the southeastern Okhotsk Sea have been reconstructed for the last 20 ka using planktonic and benthic foraminiferal oxygen isotope records and calcium carbonate, organic carbon and opal content data from two sediment cores. Species variability in benthic foraminiferal and diatom assemblages provides additional palaeoceanographic evidence. AMS radiocarbon dating of the sediments and oxygen isotope stratigraphy serve as the basis for the age models of the cores for the last 20 ¹⁴C kyr and for correlation between environmental variations in the Okhotsk Sea, and regional and global climate changes. Benthic foraminiferal assemblages in the two cores (depth 1590 and 1175 m) varied with time, so that we could recognise seven zones with different species composition. Changes in the benthic foraminiferal assemblages parallel major environmental and productivity variations. During the last glaciation, fluxes of organic matter to the sea floor showed strong seasonal variations, indicated by the presence of abundant A. weddellensis and infaunal Uvigerina spp. Benthic foraminiferal assemblages changed with warming at 12.5–11 and 10–8 ¹⁴C kyr BP, when productivity blooms and high organic fluxes were coeval with global meltwater pulses 1A and 1B. Younger Dryas cooling caused a decline in productivity (11–10 kyr BP) affecting the benthic faunal community. Subsequent warming triggered intensive diatom production, opal accumulation and a strong oxygen deficiency, causing significant changes in benthic fauna assemblages from 5.26–4.4 kyr BP to present time.     

The Middle Miocene climatic transition in the Southern Ocean: Evidence of paleoclimatic and hydrographic changes at Kerguelen plateau from planktonic foraminifers and stable isotopes

Middle Miocene (14.8–11.9 Ma) deep-sea sediments from ODP Hole 747A (Kerguelen Plateau, southern Indian Ocean) contain abundant, well-preserved and diverse planktonic foraminiferal assemblages. A detailed study of the climatic and hydrographic changes that occurred in this region during the Middle Miocene Climatic Transition led to the identification of an intense cooling phase (the Middle Miocene Shift). Abundance fluctuations of planktonic foraminiferal species with different paleoclimatic affinities, and oxygen and carbon stable isotopes have been integrated in a multi-proxy approach. Reconstruction of changes in foraminiferal faunal composition and diversity through time were the basis for identification of three foraminiferal biofacies. The most prominent faunal change took place at 13.8 Ma, when a fauna with warm-water affinity (marked by high abundance of Globorotalia miozea group and Globoturborotalita woodi plexus) was replaced by an oligotypic, opportunistic fauna with typical polar characters and dominated by neogloboquadrinids. This faunal change is interpreted as the result of foraminiferal migration from adjacent bioprovinces, caused by modifications in climate and hydrography. A positive 2.0‰ shift in δ¹⁸O (interpreted as the Mi3 event) and a related positive 1.0‰ shift in δ¹³C (corresponding to the CM6 event) accompanied this faunal turnover. These are interpreted to reflect substantial reorganization of Southern Ocean waters, the northward migration of the Polar Front and a strong increase in primary productivity. The second faunal change took place at 12.9 Ma and was characterized by the gradual decrease in abundance of the neogloboquadrinids and the recovery of Globorotalia praescitula/scitula group and Globigerinita glutinata. A positive 1.5‰ shift in δ¹⁸O (interpreted as the Mi4 event) and a concurrent gradual negative shift in δ¹³C accompanied this faunal change, witnessing further modifications of the climate/ocean system. Variations in sea surface temperature, considered as the main factor causing changes of surface hydrography at the Kerguelen Plateau, seem to have been driven by obliquity and long-term eccentricity, thus suggesting a key role played by the astronomical forcing on the evolution of Southern Ocean dynamics during the Middle Miocene. Also an evident 1.2 Myr modulation of the δ¹³C record suggests a main control of the long-term obliquity cycles on the carbon cycle dynamics. Particularly, the Mi3/CM6 events exactly fit with a node of the 1.2 Myr modulation cycles. This confirms the key role played by orbital parameters on high-latitude temperatures and Antarctic ice volume, and indirectly on global carbon burial and/or productivity. This climatic transition was marked also by changes in surface hydrography. From 14.8 to 13.8 Ma an intermediate-strength thermocline controlled by seasonality developed just below the photic zone. Weaker seasonality characterized the interval from 13.8 to 12.9 Ma, when the thermocline became shallower and sharper and favored intermediate-water foraminifers. From 12.9 Ma, seasonality increased again and an intermediate-strength thermocline re-developed.