Planktonic Foraminiferal Assemblages Research Articles

GLOBOROTALIA CRASSAFORMIS OPTIMUM EVENT: A NEW LATE QUATERNARY BIOSTRATIGRAPHIC MARKER FOR THE SOUTHEASTERN BRAZILIAN MARGIN

ABSTRACT The integration of planktonic foraminiferal assemblage, oxygen stable isotope values, and AMS 14C dating allows a more precise chronology of biostratigraphic events recorded in cores GL-74 and GL-75 collected from Campos Basin (southeastern Brazil). This study documents that the third event of disappearance of Pulleniatina plexus (Pulleniatina obliquiloculata biohorizon 3 = YP.3) occurred simultaneously in Campos and Santos Basins around 43 ka. The results also show that the event of higher abundance of Globorotalia crassaformis, the so-called Globorotalia crassaformis Optimum Event (GcOE), occurred between ca. 84 and ca. 71 ka (ca. 13 ka duration), and was also simultaneous in both basins. This study supports the GcOE as an important biostratigraphic marker event in the southeastern Brazilian margin. We propose a revised subdivision of the last glacial Zone Y into subzones Y1, Y2, and Y3. Nevertheless, it is fundamental to establish the true geographic range, as well as building a more robust ...

Sequence stratigraphy of Paleocene–Eocene successions in selected oil wells, Kirkuk area, northern Iraq

The Middle Paleocene-Eocene Megasequence AP10 was deposited during a period of renewed subduction and volcanic arc activity associated with the final closure of the Neo-Tethys . It is subdivided into two sequences according to the regional unconformity at the base of the Middle-Eocene : the Paleocene-Early Eocene, in which the Aaliji and Sinjar Formations were deposited in the studied area and Middle_Late Eocene sequences, in which the Jaddala Formation was deposited in the studied area. The distinguishable facies throughout Aaliji and Jaddala Formations deposits indicated to deep marine environments that lack benthonic foraminifera in contrast with the high percentage of planktonic foraminifera, especially Morozovella and Acarinina reflect the deep marine environment with tropical to subtropical climate condition. The Sinjar Formation characterizes by abundance of the Nummulite and bioclastic-lime wackestone subfacies indicate shallow inner shelf of carbonate shelf margin environments, followed by shoaling upward sequence, with chance to aerial exposure. The systematic investigation of planktonic foraminifera enabled us to identify thirty–four species and subspecies in the studied section, the stratigraphic distribution of these planktonic foraminiferal assemblages permit the recognition of seven biozones, two biozones (P4 and P5) have been established in Aaliji Formation (Late Paleocene) and five biozones (P9-P13 ) in Jaddala Formation (Early-Middle Eocene), where the contact between the two formations is unconformable that represents an interval of about 4 My, recorded by disappearance of three biozones P6, P7 and P8. Sequence stratigraphy analysis, as calibrated by sedimentary facies and biostratigraphy, delineated two sequences in Paleocene deposits that together interpret as 3rd order sequence, and 2nd order sequence in Eocene deposits. The two sequences shows good correlation of the northern Arabian Plate with other part of the platform during Paleocene and Eocene.

Integrated biostratigraphy of the upper Oligocene–middle Miocene successions in west central Sinai, Egypt

The nannofossil and planktonic foraminiferal biostratigraphy in four upper Oligocene–middle Miocene sections are examined in Nukhul–Sudr area of west central Sinai, Egypt. The integration of calcareous nannofossils and planktonic foraminifera is used to verify the ages and determine the biozones of the upper Oligocene–middle Miocene units in the studied area. This target is important in the light of the great lithofacies changes during the time interval. The detailed examination of the nannofossil and planktonic foraminiferal contents in these sections led to identification of 86 calcareous nannofossil species belonging to 22 genera, 10 families and 3 orders, in addition to 64 planktonic foraminiferal species belonging to 11 genera, 4 families and 2 superfamilies. The identified nannofossil and planktonic foraminiferal assemblages allow to distinguish five calcareous nannofossil biozones and six planktonic foraminiferal biozones. The biostratigraphic integration suggested the Chattian–Aquitanian age for the Nukhul Formation where the Globigerina ciperoensis Zone (P22) and Globigerinoides primordius Zone (M1a) correspond to calcareous nannofossil Sphenolithus ciperoensis Zone (NP25) and Discoaster druggii Zone (NN2), respectively. The Rudeis Formation is assigned to the Burdigalian–Langhian age depending on correspondence of Catpsydrax dissimilis Zone (M2), Globigerinoides bisphericus Zone (M4b) and Praeorbulina sicana Zone (M5) with Discoaster druggii zone (NN2), Sphenolithus belemnos Zone (NN3) and Helicosphaera ampliaperta Zone (NN4). The Somar Formation is found barren ofany microfossils, but it contains index pectens and oysters of Burdigalian age which may be equivalent to the lower part of the Rudeis Formation. The Kareem and Sarbut El-Gamal formations are represented by evaporitic and conglomeratic succession, where no foraminifera or nannofossils are recorded and assigned to the Langhian age according to their stratigraphic position. The Belayim Formation is assigned to the Serravallian age, due to the presence of Globorotalia fohsi Zone (M8) which equivalent to Discoaster exilis Zone (NN6).

Calcareous nannofossil and planktonic foraminifera biostratigraphy through the Middle to Late Eocene transition of Fayum area, Western Desert, Egypt

The Eocene sequence exposed at Gebel Naalun (Fayum-Nile divide), Guta section-I (West of Birket Qarun near Guta Village) and Guta section-II (Northwest of Birket Qarun near Guta Village) is differentiated, from base to top, into two formations; Gehannam Formation (Middle–Late Eocene) and Birket Qarun Formation (Late Eocene), respectively.Two calcareous nannofossil zones were recognized from the Eocene succession at Gebel Naalun; Discoaster saipanensis (NP17) and Chiasmolithus oamaruensis (NP18) zones as well as one planktonic foraminiferal zone; Truncorotaloides (Acaranina) rohri (P14) zone. However, at Guta section-I, two nannofossil zones were defined; Discoaster saipanensis (NP17) and Chiasmolithus oamaruensis (NP18) zones; the preservation of planktonic foraminiferal assemblage is too poor to enable us to recognize marker species as a result of many diagenetic processes. At Guta section-II, two nannofossil zones; Chiasmolitus oamaruensis (NP18) and Isthmolithus recurvus (NP19) and two planktonic foraminiferal zones; T. pseudoampliapertura zone and G. semiinvoluta zone are recorded.Several authors found that the lowest occurrence of Chiasmolithus oamaruensis is a poor criterion for defining the base of NP18 Zone, which is confirmed here. The same criticism has been applied to the lowest occurrence of Isthmolithus recurvus which defines the NP18/NP19 zonal boundary. It is generally agreed that NP19 Zone falls in the Priabonian (Late Eocene).As a result of the occurrence of the nannofossil marker species; Isthmolithus recurvus only in side views below and above the first appearance of Chiasmolithus oamaruensis at both Naalun and Guta section-I, this species is not reliable to define the NP18/NP19 zonal boundary. At Guta section-II, the Middle/Upper Eocene boundary can be delineated by the first appearance of Globigerinatheka semiinvoluta above the first occurrence of Isthmolithus recurvus in both plane and side views.

Size Fraction Effects on Planktonic Foraminifera Assemblages: A Compositional Contribution to the Golden Sieve Rush

A comparative study of Last Glacial to Holocene planktonic foraminiferal assemblages obtained from \(>\)150 to \(>\)106 \(\upmu \)m size fractions of a Tyrrhenian sea core was carried out by means of compositional data analysis methods. The results show a major loss of small-sized species in the \(>\)150 \(\upmu \)m size fraction, resulting in underdetection limit values for several Holocene samples. Statistical tests, performed by means of contrast and bootstrap, indicate that the assemblages obtained differ statistically. Nevertheless, despite the drawbacks of the analysis based on the \(>\)150 \(\upmu \)m fraction, these differences do not imply, in the compositional data analysis approach, a significant change in covariance structure. Under compositional data analysis, covariance-based analysis should give similar results regardless of the size fraction adopted, while distance-based ones may give partly different results. The \(>\)106 \(\upmu \)m size fraction, in which both large and small-sized species are sufficiently represented, is proposed for adoption in future studies focussing on palaeoclimatic reconstruction.

Foraminiferal evidence for paleogeographic and paleoenvironmental changes across the Coniacian–Santonian boundary in western Ukraine

Planktonic and benthic foraminiferal assemblages, oxygen stable isotopes, calcium carbonate content and total sulfur and magnetic susceptibility have been studied from the middle Coniacian to middle Santonian interval of the Dubivtsi succession (western Ukraine). At the Coniacian–Santonian boundary significant changes took place in foraminiferal assemblages. Keeled, deep-water forms, which are a common to dominant group in planktonic foraminiferal assemblages in the late Coniacian decline in abundance in the Santonian, where the assemblages are dominated by heterohelicids and Hedbergella. Late Coniacian benthic foraminiferal assemblages dominated by large, calcareous epifaunal (oxic) forms in the early Santonian became dominated by small, thin-walled, infaunal (dysoxic) species with significant increase of agglutinated foraminifers within assemblages. Changes in foraminiferal assemblages correspond with lithological changes from upper Coniacian limestones to lower Santonian marls. An increase in total sulfur in the lower Santonian and increase in magnetic successibility values up the succession are recorded. Changes in foraminiferal assemblages along with decreasing calcium carbonate content and increasing magnetic susceptibility indicate that during the early and middle Santonian the Tethyan connection with the studied part of the south-central European epicontinental sea was partially limited by an area uplifted as a consequence of Subhercynian tectonic movements; thus it constituted a partially restricted basin with sedimentation in an oxygen depleted environment.

Pliocene to Pleistocene vertical movements in the forearc of the Lesser Antilles subduction: insights from chronostratigraphy of shallow-water carbonate platforms (Guadeloupe archipelago)

An integrated stratigraphic study was conducted on the shallow water carbonate platforms of the Guadeloupe archipelago to refine the tectonic evolution of the Lesser Antilles forearc. The carbonate platforms are now dated to the Zanclean–Calabrian interval, and their demise occurred between 1.5 and 1.07 Ma. The precise chronostratigraphy allows dating of the main extensional tectonic events since the late Miocene. An initial episode occurred during the late Miocene, related to the reactivation of inherited N130°E-trending shear zones, and led to the emergence of most parts of the forearc. Subsequently, Zanclean to early Piacenzian carbonate platforms developed in association with a general subsidence of the forearc. During the late Piacenzan, a second extensional episode occurred. At this time La Désirade underwent major uplift and emergence whereas most of the forearc remained submerged. Prior to 1.07 Ma, a third north–south extensional episode occurred and led to the final demise of the carbonate platforms. Thus the forearc was characterized by general subsidence since the early Pliocene interrupted by three main extensional episodes and related differential uplifts. This suggests that the Lesser Antilles subduction is probably erosive north of latitude 15°N since c . 5 Ma, related to aseismic ridge subduction. Supplementary data: Planktonic foraminiferal assemblages, calcareous nannofossil taxa associations, 40 Ar/ 39 Ar geochronological data and palaeomagnetic data are available at www.geolsoc.org.uk/SUP18724 .

Distribution, ecology, and oxygen and carbon isotope characteristics of modern planktonic foraminifers in the Makarov Basin of the Arctic Ocean

The Arctic region, with magnificent ice cover on the surface of the Arctic Ocean and adjacent seas, is not only extremely sensitive to but also has strong amplification effects on climate change. Observations during the past decades have documented substantial retreat and thinning of the Arctic sea-ice cover, a process that is accelerating. Its feedback and impact on the global climate has become an important subject of current climate change research. Calcite tests of planktonic foraminifers are major constituents in pelagic sediments, and they provide valuable materials for the reconstruction of past oceanographic conditions. However, research is still sparse in the Arctic sea area because of limited availability of the materials for investigation. Here, we present a study of modern foraminifers from the plankton tow samples taken in the Makarov Basin of the Arctic Ocean during the fourth Arctic expedition of China. We have analyzed ecological information stored in the modern planktonic foraminifers and in their stable isotope signals, and established a relationship between the distribution of the main taxa and the environment. Our main observations are as follows: (1) in the Makarov Basin, the polar species Neogloboquadrina pachyderma (sinistral coiling) dominates the > 150 mu m planktonic foraminiferal assemblages. (2) The planktonic foraminifers live mainly in the upper halocline at a water depth of 50-100 m and less in the depth interval of 100-200 m. (3) Temperature change in the halocline can affect the absolute abundance of planktonic foraminifers and their distribution in the water column. The warmer halocline is more favorable to the development of planktonic foraminifers. (4) A lighter delta O-18 value (2.11 aEuro degrees) of N. pachyderma (sin.) is recorded in the depth interval of 100-200 m, which is likely related to the isotopically light brines separated out during sea ice freezing. The relatively heavy delta O-18 value (1.68 aEuro degrees aEuro"2.68 aEuro degrees, average 2.27 aEuro degrees) in the depth interval of 50-100 m may be influenced by the low salinity water with the relatively heavy delta O-18 value formed during the sea-ice melting in the surface layer.

Paleoceanographic reconstruction of the western equatorial Atlantic during the last 40 kyr

The North Brazil Current in the western equatorial Atlantic is the main route for poleward heat transfer and therefore is a key component of the climate system. To understand the parameters that influence this region, we present a paleoceanographic reconstruction of the last 40kyr based on study of sediment core MC 10/3. This reconstruction is based on: i) the oxygen isotope composition of the planktonic foraminifer Globigerinoides ruber (white); ii) census counts of the planktonic foraminifera assemblage to estimate sea surface temperature (SST) via the Modern Analogue Technique (SSTMAT) and to deduce characteristics of the water column; and iii) values of δ18Oivc-sw (a proxy for sea surface salinity (SSS)). The oxygen isotope composition of G. ruber showed a strong shift of greater than 1‰ after 21calkyrBP. Such a change can be attributed mainly to a salinity reduction of two units, as well as a slight SST increase (~1°C), between 21 and 17.5kyrBP. This change may be related to a southward displacement of the Intertropical Convergence Zone (ITCZ) and its belt of convective activity, which would have increased precipitation over the region and diminished surface salinity. The structure of the planktonic foraminiferal assemblage also indicates such conditions. The productive/thermocline-dwelling Globigerinita glutinata showed higher abundance prior to 21calkyrBP. Other productive/deep-dwellers, i.e., Neogloboquadrina dutertrei, Globorotalia truncatulinoides (left- and right-coiling) and Globorotalia inflata, were slightly more abundant prior to 21calkyrBP and became less frequent with the development of low-salinity surface water that created more stratified and oligotrophic conditions in the water column. However, the warm/oligotrophic surface-dwellers (G. ruber, Globigerinoides sacculifer and Globigerinella siphonifera) became more abundant after 21calkyrBP. The species Globorotalia menardii was nearly absent during the Last Glacial Maximum (LGM), and its growth in abundance, mainly after 17.5calkyrBP, may indicate the resumption of the Agulhas leakage, which would have reached the study area via the South Equatorial Current (SEC). The return of high salinity values synchronous with the G. menardii increase also denotes the influence of Agulhas leakage into the western equatorial Atlantic.

Biostratigraphie, paléoécologie et zones d’acmé des foraminifères planctoniques au passage Crétacé-Paléogène dans la Téthys (Tunisie et Espagne) et l’Atlantique (France)

Biostratigraphical high-resolution analyses and quantitative data confirm that deposition is continuous across the K-Pg transition in several sections in Tunisia (El Kef, stratotype section) and Spain (Agost and Caravaca sections) located in the Tethyan realm and the Bidart sections in the Atlantic realm, without any relevant hiatus. The Upper Maastrichtian assemblages of planktic foraminifera from these sections are largely dominated by small biserial heterohelicids. They are associated to common species having planispiral test (i.e. globigerinelloids), trochospiral test (i.e. hedbergellids, rugoglobigerinids globotruncanids), to rare triserial heterohelicids (i.e. guembelitriids) and trochospiral species showing tubulospines (i.e. schackoinids). Stratigraphical ranges of these diverse taxa through the late Maastrichtian in the Tethyan and Atlantic realms show very few changes in the planktonic foraminiferal assemblages and most of the species are present in the Abathomphalus mayaroensis biozone. By our high-resolution sampling and the intensive research for the A. mayaroensis index species in the uppermost Maastrichtian samples, we confirm that this species is omnipresent up to the top of the Maastrichtian. Therefore, A. mayaroensis is present in almost all samples which are late Maastrichtian in age, but this species became very scarce in the uppermost Maastrichtian samples. This scarceness could be due to a climate cooling. A sharp decrease in relative abundance of the deep dwellers species, like as Abathomphalus intermedius and A. mayaroensis as well as in other keeled globotruncanids is observed at the studied sections from the Tethyan realm (indicative of low latitude) across the latest Maastrichtian. At the K/Pg boundary, all the globotruncanids disappeared. They are considered specialists living in tropical-subtropical deep seawater habitat. At this boundary, large and ornate heterohelicids also disappeared. Therefore, all the studied sections show that about 90 % of the Maastrichtian species became extinct according to a catastrophic mass extinction pattern. Only about 10 % crossed the K/Pg boundary and survived during the earliest Danian. The minor difference in the number of disappeared taxa is related to their latitude location or environment paleodepth. The changes in the species relative abundance, observed in the successive planktic foraminiferal assemblages, make it possible to recognize the Acme-stage 0 typical of the upper Maastrichtian interval. It is characterized by the highest species richness of Globotruncanids and heterohelicids specialists of tropical to subtropical marine conditions, the Acme-stage 1 typical of the Guembelitria cretacea Zone, and in particular of the Hedbergella holmdelensis Subzone dominated by “opportunists” species belonging to Guembelitria, the Acme-stage 2 which corresponds to the Pv. eugubina Zone dominated mainly by specimens belonging to Palaeoglobigerina and Parvularugoglobigerina and the Acme-stage 3 which characterizes mainly the Ps. pseudobulloides Zone dominated by biserial species belonging to Chiloguembelina and Woodringina.

Reflection of changes in sea surface circulation over the northeastern Iceland Basin in planktonic foraminiferal assemblages during the late Pleistocene-Holocene

Paleotemperature reconstructions based on foraminiferal analysis and estimates of the iceberg-rafted debris (IRD) obtained from sediment core AMK-4438 are provided. The sediments are dated 300 ka. It was shown that, during this period, sea surface conditions in the northeastern Iceland Basin varied considerably because of both glacial-interglacial alternation and short-term fluctuations of sea surface temperature due to ice melting during the Heinrich events.

Deepwater circulation in the northeastern Iceland Basin in the Late Pleistocene

Based on changes in planktonic foraminifer assemblages and carbonate content of deposits in the sedimentation column from the northeastern Iceland Basin, nine isotope stages are recognized, covering 300 ka. The study of benthic foraminifer assemblages in the section has shown that, most of this time, it contained “old” water, isolated for a long time from the surface, with a low content of oxygen. At transitions from glacial conditions to interglacials, it was displaced by North East Atlantic Deep Water.

Calcareous plankton response to orbital and millennial-scale climate changes across the Middle Pleistocene in the western Mediterranean

The paleoenvironmental conditions through MIS 15-9 at the Mediterranean Ocean Drilling Program (ODP) Site 975 were interpreted by high resolution study of calcareous plankton assemblages compared with available δ18O and δ13C records and high resolution paleoclimate proxies from the Atlantic Ocean. Sea Surface Temperatures (SSTs) have been estimated from planktonic foraminiferal assemblages using the artificial neural networks method. Calcareous plankton varied dominantly on a glacial–interglacial scale as testified by the SST record, foraminiferal diversity, total coccolith abundance and changes in warm-water calcareous nannofossil taxa. A general increase in foraminiferal diversity and of total coccolith abundance is observed during interglacials. Warmest SSTs are reached during MIS 11, while MIS 12 and MIS 10 represent the coldest intervals of the studied record. During MIS 12, one of the most extreme glacials of the last million years, occurrence of Globorotalia inflata and of neogloboquadrinids indicates a shoaling of the interface between Atlantic inflowing and Mediterranean outflowing waters. Among calcareous nannofossils the distribution of Gephyrocapsa margereli–Gephyrocapsa muellerae>4μm also supports a reduced Atlantic–Mediterranean exchange during MIS 12. Superimposed on glacial–interglacial variability, six short-term coolings are recognized during MIS 12 and 10, which appear comparable in their distribution and amplitude to the Heinrich-type events documented in the Atlantic Ocean in the same interval. During these H-type events, Neogloboquadrina pachyderma (s) and G. margereli–G. muellerae>4μm increase as a response to the enhanced inflow of cold Atlantic water into the Mediterranean via the Strait of Gibraltar. Mediterranean surface water hydrography appears to have been most severely affected at Termination V during the H-type event Ht4, possibly as a response to a large volume of Atlantic meltwater inflow via the Strait of Gibraltar and/or to freshwater/terrigenous input deriving from local mountain glaciers. Three additional SST coolings are recorded through MIS 14–16, but these are not well correlated with Heinrich-type events documented in the Atlantic Ocean in the same interval; during these cooling episodes only the subpolar Turborotalita quinqueloba increases. These results highlight the sensitive response of the Mediterranean basin to millennial-scale climate variations related to Northern Hemisphere ice-sheet instability and support the hypothesis that the tight connection between high latitude climate dynamics and Mediterranean sea surface water features can be traced through the Middle Pleistocene.

Santonian–Campanian planktonic foraminifera from Tanzania, Shatsky Rise and Exmouth Plateau: Species depth ecology and paleoceanographic inferences

Abstract The Santonian–Campanian interval is of particular interest as it encompasses a cooling trend after the Late Cretaceous greenhouse maximum warmth of the Turonian as well as a possibly related major faunal turnover among planktonic foraminifera. The recovery of pristinely preserved planktonic foraminifera from Santonian–Campanian sequences in southeastern Tanzania allows examination of faunal changes and documentation of species-specific stable isotope (δ 13 C and δ 18 O) signatures. These isotopic data are ideal for inferring species paleoecological preferences and for tracing major paleoceanographic changes. This study reports the first δ 18 O and δ 13 C data generated on “glassy” specimens of Marginotruncana coronata , M. undulata , M. marginata , and M. pseudolinneiana and Sigalia carpatica . Additional results from Shatsky Rise (Ocean Drilling Program Leg 198, Hole 1210B) and Exmouth Plateau (ODP Leg 122, Hole 762C) provide geographic control on species habitat preferences and paleoceanographic context. Isotopic analyses suggest that double-keeled species, including Globotruncana bulloides , Contusotruncana fornicata , C. plummerae and probably marginotruncanids, inhabited the surface mixed layer, whereas the biserial Gublerina rajagopalani was a permanent thermocline dweller. Thus, our study confirms recent suggestions that the depth-distribution models based on shell morphology and analogies with modern taxa are not applicable. At all the examined localities, changes in planktonic foraminiferal assemblages are used to define several ecological intervals, each one characterized by a distinctive taxonomic composition and/or increasing/decreasing species diversity. Combined geochemical and paleontological observations suggest that, by the middle–late Campanian, a stratified upper water column developed in Tanzania while less stratified and/or mesotrophic conditions prevailed at Shatsky Rise and Exmouth Plateau.

Contourite systems in the region of the southern São Paulo Plateau escarpment, South Atlantic

Seismoacoustic investigations with a high-resolution parametric echo-sounder “SES 2000 deep” carried out on cruises 33, 35, and 37 of the R/V Akademik Ioffe revealed several erosional-depositional contourite systems on the Sao Paulo Plateau escarpment and its toe in the South Atlantic. Two contourite terraces related to interfaces between different water masses are observable on the escarpment. These terraces presumably reflect the activity of internal waves and turbulent eddies. The Sao Paulo contourite channel and genetically related drift are traceable along the escarpment toe. Changes in planktonic foraminiferal assemblages in Core AI-2563 retrieved from the summit of the Sao Paulo contourite drift suggest a shallowing of the Weddell Sea Deep Water mass during glacial times. It is established that the contour current of the Weddell Sea Deep Water and Lower Circumpolar Water considerably affect the formation of contourite depositional systems on the escarpment and its toe.

Millennial‐scale variability to 735 ka: High‐resolution climate records from Santa Barbara Basin, CA

Determining the ultimate cause and effect of millennial‐scale climate variability remains an outstanding problem in paleoceanography, partly due to the lack of high‐resolution records predating the last glaciation. Recent cores from Santa Barbara Basin provide ~2500–5700 year “windows” of climate with ~10–50 year resolution. Ages for three cores, determined by seismic stratigraphic correlation, oxygen isotope stratigraphy, and biostratigraphy, date to ~293 ka (MIS 8), ~450 ka (MIS 12), and ~735 ka (MIS 18). These records sample the Late Pleistocene, during which the 100 kyr cycle strengthened and the magnitude of glacial‐interglacial cyclicity increased. Thus, these records provide a test of the dependence of millennial‐scale behavior on variations in glacial‐interglacial cyclicity. The stable isotopic (δ18O) composition of planktonic foraminifera shows millennial‐scale variability in all three intervals, with similar characteristics (duration, cyclicity) to those previously documented during MIS 3 at this site. Stadial G. bulloides δ18O values are 2.75–1.75‰ (average 2.25‰) and interstadial values are 1.75–0.5‰ (average 1‰), with rapid (decadal‐scale) interstadial and stadial initiations of 1‐2‰, as in MIS 3. Interstadials lasted ~250–1600 years and occurred every ~650–1900 years. Stadial paleotemperatures were 3.5–9.5°C and interstadial paleotemperatures were 7.5–13°C. Upwelling, evidenced by planktonic foraminiferal assemblages and δ13C, increased during interstadials, similar to MIS 3; high productivity during some stadials was reminiscent of the Last Glacial Maximum. This study builds upon previous records in showing that millennial‐scale shifts were an inherent feature of Northern Hemisphere glacial climates since 735 ka, and they remained remarkably constant in the details of their amplitude, cyclicity, and temperature variability.

Foraminiferal records of bottom-water oxygenation and surface-water productivity in the southern Japan Sea during 160–15ka: Associations with insolation changes

Analyses of the benthic and planktonic foraminiferal record were conducted to understand temporal variations in sea-floor oxygenation and surface productivity during periods of dark-layer deposition between 160 and 15 ka, based on data from sediment core IMAGES MD01-2407 (water depth, 932 m) from the southern Japan Sea. The dark layers in the core were classified into six types on the basis of benthic foraminiferal assemblages, which reflect the nature and amount of organic material on the sea floor, as well as the degree of oxygenation of bottom waters. Three of the dark layer types were deposited in conditions strongly associated with increased surface productivity, which correlates with positive or negative peaks of summer insolation in the Northern Hemisphere. During periods of insolation maxima, summertime surface productivity was enhanced because of the inflow of nutrient-rich surface waters associated with high precipitation in eastern Asia, caused by intensification of the East Asian summer monsoon. In contrast, relatively sustained organic matter fluxes to the sea floor occurred during insolation minima, possibly affected by active vertical mixing. When the East Asian summer and winter monsoons were both intensified in a given period well oxygenated bottom-water environments combined with high surface productivity may have resulted in dark-layer deposition, because of a combination of strong wintertime water convection and increased summertime surface productivity. It is likely that the organic carbon content of sediments underestimates surface productivity during depositional conditions favoring the sedimentary decomposition of organic matter. • Benthic and planktonic foraminiferal assemblages in the Japan Sea during 160–15 ka. • Dark layers are classified into six types based on benthic foraminiferal assemblages. • Stratigraphic distribution of the dark-layer types is related to insolation changes.

Late quaternary oceanographic conditions in the Western Bering Sea

The benthic and planktonic foraminiferal assemblages and the distribution of coarse grain-size factions were studied in the upper 4.5 m of the Core SO201-2-85KL (57°30.30′ N, 170°24.79′ E, water depth 968 m) retrieved from the Shirshov Ridge. This part of the core covers 7.5 to 50 kyr BP. The glacial period is established to be characterized by low surface water productivity, the wide distribution of sea ice and/or icebergs in this area, and a high oxygen concentration in the bottom layer. Enhanced productivity is inferred from the maximum abundance of planktonic foraminifers at the very beginning of the deglaciation. The late Bølling-Allerød interstadial and the early Holocene were marked by the further two-phase increase in the surface productivity and the weakened ventilation of the bottom water.

Paleoproductivity evolution in the West Philippine Sea during the last 700 ka

In order to reconstruct the paleoproductivity evolution history of the West Philippine Sea during the last 700 ka, the vertical gradient of Delta delta C-13 in dissolved inorganic carbon (Delta delta C-13 between those of foraminifera Pulleniatina obliquiloculata and Cibicidoides wuellerstorfi) and planktonic foraminiferal assemblages were analysed in piston Core MD06-3047 retrieved from the Benham Rise (east of the Luzon Island). Paleoproductivity evolution in the West Philippine Sea during the last 700 ka is closely related to glacial-interglacial cycles and precession-controlled insolation. Controlling factors of paleoproductivity could have been both thermocline fluctuations related with ENSO-like processes and eolian input associated with East Asian winter monsoon, and the former could have been the primary factor. A higher productivity and a shallower thermocline coeval with the occurrence of low CO2 concentrations in the EPICA Dome C ice core might indicate that biological export production in the low-latitude could act as a significant sink in the global carbon cycle, and modify atmospheric CO2 concentrations. Spectral analysis further reveals that the paleoproductivity is mainly controlled by thermocline fluctuations subjected to ENSO processes responding to processional variability of insolation. High coherences in eccentricity, obliquity and precession periods further revealing the close link between thermocline fluctuations, paleoproductivity and atmospheric CO2 levels.

Changes of planktonic and benthic foraminiferal assemblages in upper quaternary sediments of the Deryugin Basin, Sea of Okhotsk

The analysis of foraminiferal assemblages in sediments that were deposited during the last 30 kyr revealed similar patterns in their distribution in the central and marginal parts of the Deryugin Basin. The similar composition of foraminifers through the entire basin implies similarity in natural environments within its limits. The absence of benthic foraminifers or extreme impoverishment of the assemblages during the maximum of the last glaciation could result from a combination of several factors: drastic decrease in bioproductivity due to general cooling, development of bottom anoxia, and presumably unfavorable influence of seeps on geochemical parameters of bottom waters. The weak activity of barite-methane seeps in the central part of the basin during the Holocene is evident from some variations in the structure of benthic foraminiferal assemblages against the background of their similar taxonomic compositions.