Benthic ostracods and deep water-masses in the Atlantic Ocean

Ostracod faunas at six locations are compared, and related to distributions in an Atlantic Ocean-wide data base. Five, widely developed, vertical faunal sequences are recognised at particular levels within deep water-masses: Henryhowella Fauna (lower part of Antarctic Intermediate Water); Krithe Fauna (Upper North Atlantic Deep Water); Poseidonamicus-Bosquetina Fauna (upper part of Lower NADW); Dutoitella Fauna (lower part of Lower NADW); Legitimocythere Fauna (Antarctic Bottom Water). These faunas are correlated with previously established deep water benthic foraminiferal assemblages, and their possible palaeo-oceanographic use is discussed.     

A Late Pleistocene time-series of bottom-current speed in the Vema Channel

A coarsening of the mean particle size of the carbonate-free silt fraction from sea-floor samples below 4000 m in the Vema Channel has been used to separate high-velocity Antarctic Bottom Water (AABW) from the overlying, slower North Atlantic Deep Water (NADW). A time-series of fluctuations in bottom-current speed within the modern AABW/NADW transition zone was examined by determining the particle-size distribution of sediments from eight gravity cores with a high-resolution stratigraphy for the past 250 kyrs. The bottom-current paleospeed was inferred from a correlation of particle size in seafloor samples with mean current speed from nearby current-meters. The mean bottom-current speed at depths comparable to modern AABW was highest (7–10 cm/s) during interglacial to glacial transitions corresponding to the oxygen isotopic stage 6/7 and 4/5 boundaries and at present. The mean bottom-current speed at depths comparable to modern NADW was nearly uniform for most of the past 250 kyrs except during glacial oxygen isotopic stage 2 when the speed dropped to 2 cm/s, or one-half of the present speed. The application of the “calibrated” particle-size method to examine bottom-current paleospeed allows testing of paleoceanographic models which rely on assumptions or inferences of changes in bottom-water production rate during the late Pleistocene paleoclimatic fluctuations.     

A benthic foraminiferal record of middle to late Pliocene (3.15-2.85 Ma) deep water change in the North Atlantic

Records of benthic foraminifera from North Atlantic DSDP Site 607 and Hole 610A indicate changes in deep water conditions through the middle to late Pliocene (3.15 to 2.85 Ma). Quantitative analyses of modern associations in the North Atlantic indicate that seven species, Fontbotia wuellerstorfi, Cibicidoides kullenbergi, Uvigerina peregrina, Nuttallides umboniferus, Melonis pompilioides, Globocassidulina subglobosa and Epistominella exigua are useful for paleoenvironmental interpretation. The western North Atlantic basin (Site 607) was occupied by North Atlantic Deep Water (NADW) until ~2.88 Ma. At that time, N. umboniferus increased, indicating an influx of Southern Ocean Water (SOW). The eastern North Atlantic basin (Hole 610A) was occupied by a relatively warm water mass, possibly Northeastern Atlantic Deep Water (NEADW), through ~2.94 Ma when SOW more strongly influenced the site. These interpretations are consistent with benthic δ¹⁸O and δ¹³C records from 607 and 610A (Raymo et al., 1992). The results presented in this paper suggest that the North Atlantic was strongly influenced by northern component deep water circulation until 2.90–2.95 Ma. After that there was a transition toward a glacially driven North Atlantic circulation more strongly influenced by SOW associated with the onset of Northern Hemisphere glaciation. The circulation change follows the last significant SST and atmospheric warming prior to ~2.6 Ma.     

Benthic foraminiferal extinctions linked to late Pliocene–Pleistocene deep-sea circulation changes in the northern Indian Ocean (ODP Sites 722 and 758)

During the late Pliocene–middle Pleistocene, 63 species of elongate, bathyal–upper abyssal benthic foraminifera (Extinction Group = Stilostomellidae, Pleurostomellidae, some Nodosariidae) declined in abundance and finally disappeared in the northern Indian Ocean (ODP Sites 722, 758), as part of the global extinction of at least 88 related species at this time. The detailed record of withdrawal of these species differs by depth and geography in the Indian Ocean. In northwest Indian Ocean Site 722 (2045 m), the Extinction Group of 54 species comprised 2–15% of the benthic foraminiferal fauna in the earliest Pleistocene, but declined dramatically during the onset of the mid-Pleistocene Transition (MPT) at 1.2–1.1 Ma, with all but three species disappearing by the end of the MPT (∼0.6 Ma). In northeast Indian Ocean Site 758 (2925 m), the Extinction Group of 44 species comprised 1–5% of the benthic foraminiferal fauna at ∼3.3–2.6 Ma, but declined in abundance and diversity in three steps, at ∼2.5, 1.7, and 1.2 Ma, with all but one species disappearing by the end of the MPT. At both sites there are strong positive correlations between the accumulation rate of the Extinction Group and proxies indicating low-oxygen conditions with a high organic carbon input. In both sites, there was a pulsed decline in Extinction Group abundance and species richness, especially in glacial periods, with some partial recoveries in interglacials. We infer that the glacial declines at the deeper Site 758 were a result of increased production of colder, well-ventilated Antarctic Bottom Water (AABW), particularly in the late Pliocene and during the MPT. The Extinction Group at shallower water depths (Site 722) were not impacted by the deeper water mass changes until the onset of the MPT, when cold, well-ventilated Glacial North Atlantic Intermediate Water (GNAIW) production increased and may have spread into the Indian Ocean. Increased chemical ventilation at various water depths since late Pliocene, particularly in glacial periods, possibly in association with decreased or more fluctuating organic carbon flux, might be responsible for the pulsed global decline and extinction of this rather specialised group of benthic foraminifera.     

Late Quaternary deep and surface water mass evolution in the northeastern Indian Ocean inferred from carbon and oxygen isotopes of benthic and planktonic foraminifera

New planktonic and benthic foraminiferal stable isotope records from core YDY05 (northeastern Indian Ocean) provide new insights into paleoceanographic changes in the northeastern Indian Ocean since the last glacial period. The distinct δ¹⁸O decrease was observed since the beginning of the deglaciation to the mid-Holocene (∼8–6 kyr BP), possibly reflecting a reduction in surface salinity in the central Bay of Bengal (BoB) water, which probably resulted from strengthened precipitation, concurrent enhanced river discharge and rising sea-level, related to the intensification of Indian Summer Monsoon (ISM). Variations in benthic δ¹³C and δ¹³C_{Planktonic-Benthic} in our core site reflect significant variations in source water characteristics over the LGM-Holocene. The large δ¹³C_{Planktonic-Benthic} offset during the glacial period suggests a more sluggish deep water circulation, and lower δ¹³C_{Planktonic-Benthic} from the deglaciation to the Holocene suggests an enhanced deep water circulation in the central BoB. The drastic depletion in benthic δ¹³C during the glacial period suggests a significant reduction of North Atlantic Deep Water (NADW) intrusion and a progressive influx of Antarctic Bottom Water (AABW) and ¹²C-rich Circumpolar Deep Water (CDW) into the central BoB. In contrast, since the deglaciation, the central BoB experienced a drastically increased intrusion of better ventilated and ¹³C-rich NADW. The differences in benthic δ¹⁸O between the LGM section and the Holocene exceeds the ice volume effect by ∼0.5‰, providing further evidence that the deep water mass of the central BoB was influenced by the less dense NADW, instead of the AABW, since the last deglaciation.     

Response of deep-sea benthic foraminifera to Miocene paleoclimatic events, DSDP Site 289

Changes in the Miocene deep-sea benthic foraminifera at DSDP Site 289 closely correlate to the climatically induced variations in deep and bottom waters in the Pacific Ocean. In early Miocene time, oxygen and carbon isotopes indicate that bottom waters were relatively warm and poorly oxygenated. Benthic foraminiferal assemblages are characterized by various species inherited from the Oligocene. Expansion of the Antarctic icecap in the early middle Miocene, 14–16 m.y. ago, increased oxygen isotope values, produced cold, more oxygenated bottom waters and lead to a turnover in the benthic foraminifera. An Oligocene—early Miocene assemblage was replaced by a cibicidoid-dominated assemblage. Some species became extinct and benthic faunas became more bathymetrically restricted with the increased stratification of deep waters in the ocean. In mid-Miocene time, Epistominella exigua and E. umbonifera, indicative of young, oxygenated bottom waters, are relatively common at DSDP Site 289. Further glacial expansion 5–9 m.y. ago lowered sealevel, increased oceanic upwelling and associated biological productivity and intensified the oxygen minima. Abundant hispid and costate uvigerines become a dominant faunal element at shallow depths above 2500 m as E. umbonifera becomes common to abundant below 2500 m. By late Miocene time, benthic faunas similar in species composition and proportion to modern faunas on the Ontong-Java plateau, had become established.     

Palaeoceanographical changes recorded by Cenozoic deep-sea ostracod assemblages from the South Atlantic and the Southern Ocean (ODP Sites 1087 and 1088)

Cenozoic palaeoceanography of the SE Atlantic and Southern Oceans has been investigated using Late Eocene/Early Oligocene to Quaternary ostracod assemblages from 49 samples of ODP Sites 1087 and 1088. Although the overall abundance of ostracods is relatively low (means of 17 and 49 specimens per sample at Sites 1087 and 1088, respectively) and there is an apparently high level of endemism (ranging from 50% to 80% at Sites 1087 and 1088), three major changes in the faunal assemblages are identified at Site 1087 (denoted A, B and C) and two at Site 1088 (denoted B' and C'). The assemblage boundaries, detected on the basis of stepwise changes in the abundance, diversity, dominance, endemism, faunal turnover and relative abundance of common taxa, coincide broadly with previously identified, ostracod-based palaeoceanographical 'events' discussed by Benson and co-workers over the last two decades. The data do not extend sufficiently far back to record the initiation of Assemblage A, but the faunal change between Assemblages A and B, marked by a decline in abundance, species diversity and faunal turnover, occurs within the Middle Miocene (NN5-6). It coincides with a previously documented palaeoceanographical 'event' at 16-14 Ma which, we suggest, may be related to the initiation of North Atlantic Deep Water (NADW) production and/or an expansion of the East Antarctic ice sheet. Assemblage B' is subdivided into the two Sub-assemblages B'¹ and B'² mainly on the basis of an increase in diversity, a peak in faunal turnover and a drop in the relative abundance of the genus Krithe in early Late Miocene time (NN9, c. 10.5 Ma). The B'¹/B'² Sub-assemblage boundary cannot be related to any previously documented faunal change in deep-sea ostracods. Changes associated with the boundaries between Assemblages B and C, and B' and C', which we believe to be synchronous, both include a decrease in diversity and abundance. In addition, two strong turnover peaks occur near the B'/C' boundary at Site 1088. The B/C and B'/C' boundaries coincide with a previously documented midPliocene 'event' (3.5 Ma) (NN15-16) which may be linked to putative closure of the Straits of Panama and increased production of NADW, the latter in turn leading to increased production of Antarctic Intermediate Water (AAIW) and Antarctic Bottom Water (AABW). Alternatively, fiuctuations in size of the Antarctic ice sheet during possible Pliocene warm periods could indirectly be responsible for the observed midPliocene faunal changes.     

Deep-sea benthonic foraminiferal faunal turnover near the Eocene/Oligocene boundary

Eocene-Oligocene deep-sea benthonic foraminifera in D.S.D.P. Site 277 in the southwest Pacific have been analyzed to determine the benthonic foraminiferal response to the development of the psychrosphere near the Eocene/Oligocene boundary. Biostratigraphic ranges of 41 taxa show that 23 taxa are found throughout the Late Eocene to Early Oligocene sequence, while 18 taxa exhibit first or last occurrences. Comparison of the faunal changes in Site 277 with a benthonic foraminiferal oxygen isotope record shows that the development of the psychrosphere did not have a profound effect upon the benthonic foraminifera, and the overall faunal change preceding and subsequent to the bottom-water circulation event occurred gradually. The inferred water-mass event affected the relative abundance of one species, Epistominella umbonifera. The lack of major faunal changes at the Eocene/Oligocene boundary in Site 277 probably reflects either wide environmental tolerances of the benthonic foraminifera, or a bottom-water temperature change less than 3°C.Examination of previously published benthonic foraminiferal biostratigraphic data from D.S.D.P. Sites 167, 171, 357, 360, 363, and 400A, and deep-sea ostracode data from D.S.D.P. Leg 3 show faunal changes occurred during discrete intervals in the Middle Eocene-Early Oligocene. The faunal patterns from these data and from Site 277 show that the Eocene/Oligocene cooling event did not cause rapid, catastrophic changes of the benthonic faunas of the open ocean, although significant faunal changes are associated with the water mass event in Sites 167, 171 and 400A.The benthonic faunal changes in Middle Eocene-Early Oligocene time are consistent with the gradual decrease of inferred bottom-water temperatures, based on previously published oxygen isotopic data. The δ ¹⁸O Eocene/Oligocene enrichment of 0.76‰ is a major event in the Southern Ocean oxygen isotopic record, but is considerably less in magnitude than the 1.75-2.00‰ change that occurred gradually from mid-Early Eocene to the Eocene/Oligocene boundary. The benthonic foraminiferal and isotopic data indicate that bottom-water circulation may have developed during the Middle Eocene to Early Oligocene interval, with the 3°C bottom-water cooling near the Eocene/Oligocene boundary representing part of this development.     

Paleoenvironmental changes across the Cenomanian/Turonian Boundary Event (Oceanic Anoxic Event 2) as indicated by benthic foraminifera from the Demerara Rise (ODP Leg 207)

This study is based on Cenomanian to lower Turonian sediments of Ocean Drilling Program (ODP) Sites 1258, 1259, 1260, and 1261 from the Demerara Rise (Leg 207, western tropical Atlantic, off Suriname) that are oriented along a paleodepth transect. Studied sediments include the Cenomanian/Turonian Boundary Event (CTBE) or Oceanic Anoxic Event 2 (OAE 2) and consist of laminated black shales with TOC values between 5% and 10% below and above OAE 2 and up to 29% within the OAE 2 interval. Benthic foraminiferal assemblages in this eutrophic environment are generally characterized by low diversities and strong fluctuations of abundances, indicating oxygen depletion and high organic matter fluxes. Dominant taxa at all sites are Bolivina anambra, Gavelinella dakotensis, Tappanina sp., Praebulimina prolixa, and Neobulimina albertensis. Based on the positive stable carbon isotope excursion characteristics of OAE 2 we subdivided the studied successions into three intervals: (1) the interval below OAE 2; (2) the carbon isotope excursion reflecting OAE 2; and (3) the interval above OAE 2. In the bathymetrically shallower Sites 1260 and 1261 benthic foraminiferal assemblages indicate anoxic to sometimes slightly dysoxic bottom-water conditions below the OAE 2 interval. The bathymetrically deepest Site 1258, in contrast, reflects more oxygenated bottom waters with an almost continuous occurrence of benthic foraminifera. It is therefore suggested that the shallower sites were located within the oxygen minimum zone (OMZ), whereas Site 1258 was below the OMZ. During OAE 2 anoxic conditions prevailed at the shallower sites. At Site 1258 benthic foraminifera indicate severe dysoxic but not anoxic conditions. This pattern is proposed to reflect a strengthening of the OMZ possibly related to increased primary production during OAE 2. A short-term repopulation event of benthic foraminifera in the lower third of the OAE 2 interval was observed at all sites, reflecting a brief bottom-water oxygenation event. This short-lived event parallels a surface-water cooling and is probably equivalent to the “Plenus Cool Event” in Europe and the “benthonic zone” in the U.S. Western Interior. The benthic foraminifera of a ~0.5 Ma interval following OAE 2 still indicate oxygen depletion of bottom waters. Subsequently, however, a strong increase in benthic foraminiferal abundance and diversity reflects better oxygenation of the bottom-water masses, probably related to a weakening of the OMZ due to decreasing organic matter flux.     

Biochronology and paleoclimatic implications of Middle Eocene to Oligocene planktic foraminiferal faunas

Planktic foraminiferal assemblages have been analyzed quantitatively in six DSDP sites in the Atlantic (Site 363), Pacific (Sites 292, 77B, 277), and Indian Ocean (Sites 219, 253) in order to determine the nature of the faunal turnover during Middle Eocene to Oligocene time. Biostratigraphic ranges of taxa and abundance distributions of dominant species are presented and illustrate striking similarities in faunal assemblages of low latitude regions in the Atlantic, Pacific and Indian oceans. A high resolution biochronology, based on dominant faunal characteristics and 55 datum events, permits correlation between all three oceans with a high degree of precision. Population studies provide a view of the global impact of the paleoclimatic and paleoceanographic changes occurring during Middle Eocene to Oligocene time.Planktic foraminiferal assemblage changes indicate a general cooling trend between Middle Eocene to Oligocene time, consistent with previously published oxygen isotope data. Major faunal changes, indicating cooling episodes, occur, however, at discrete intervals: in the Middle Eocene 44-43 Ma (P13), the Middle/Late Eocene boundary 41-40 Ma ( ), the Late Eocene 39-38 Ma ( ), the Eocene/Oligocene boundary 37-36 Ma (P18), and the Late Oligocene 31-29 Ma ( ). With the exception of the boundary, faunal changes occur abruptly during short stratigraphic intervals, and are characterized by major species extinctions and first appearances. The Eocene/Oligocene boundary cooling is marked primarily by increasing abundances of cool water species. This suggests that the boundary cooling, which marks a major event in the oxygen isotope record affected planktic faunas less than during other cooling episodes. Planktic foraminiferal faunas indicate that the boundary event is part of a continued cooling trend which began during the Middle Eocene.Two hiatus intervals are recognized in low and high latitude sections at the Middle/Late Eocene boundary and in the Late Eocene ( ). These hiatuses suggest that vigorous bottom water circulation began developing in the Middle Eocene, consistent with the onset of the faunal cooling trend, and well before the development of the psychrosphere at the boundary.     

Late Quaternary paleoproductivity and deep water circulation in the eastern South Atlantic Ocean: Evidence from benthic foraminifera

Two late Quaternary sediment cores from the northern Cape Basin in the eastern South Atlantic Ocean were analyzed for their benthic foraminiferal content and benthic stable carbon isotope composition. The locations of the cores were selected such that both of them presently are bathed by North Atlantic Deep Water (NADW) and past changes in deep water circulation should be recorded simultaneously at both locations. However, the areas are different in terms of primary production. One core was recovered from the nutrient-depleted Walvis Ridge area, whereas the other one is from the continental slope just below the coastal upwelling mixing area where present day organic matter fluxes are shown to be moderately high. Recent data served as the basis for the interpretation of the late Quaternary faunal fluctuations and the paleoceanographic reconstruction.

During the last 450,000 years, NADW flux into the eastern South Atlantic Ocean has been restricted to interglacial periods, with the strongest dominance of a NADW-driven deep water circulation during interglacial stages 1, 9 and 11. At the continental margin, high productivity faunas and very low epibenthic δ¹³C values indicate enhanced fluxes of organic matter during glacial periods. This can be attributed to a glacial increase and lateral extension of coastal upwelling. The long term glacial-interglacial paleoproductivity cycles are superimposed by high-frequency variations with a period of about 23,000 yr. Enhanced productivity in surface waters above the Walvis Ridge, far from the coast, is indicated during glacial stages 8, 10 and 12. During these periods, cold, nutrient-rich filaments from the mixing area were probably driven as far as to the southeastern flank of the Walvis Ridge.     

Deep-sea ecosystem variability of the Aegean Sea during the past 22 kyr as revealed by Benthic Foraminifera

Specific responses of the regional deep-sea ecosystems to climatic and oceanographic processes during the last 22 kyr are revealed by benthic foraminiferal faunas from two cores in the northern and southern Aegean Sea. Under glacial boundary conditions, high-diversity benthic foraminiferal faunas and elevated benthic foraminiferal numbers indicate enhanced organic matter availability and well-ventilated deep-water masses in the whole Aegean Sea. The glacial termination is accompanied by significant fluctuations in productivity and deep-water ventilation. In the northern Aegean Sea, meltwater inflow from mountain glaciers during the Bølling/Allerød warm period resulted in a restriction of local deep-water formation, as mirrored by a dominance of bolivinids. During the deposition of sapropel S1, drops in benthic foraminiferal number and diversity are more significant in the southern Aegean Sea when compared to the north. This suggests the persistence of local deep-water formation in the northern Aegean Sea during S1 deposition. In addition, faunal fluctuations within S1 at both sites suggest the repeated influence of short-term cooling events on the re-ventilation and re-colonization of Aegean deep-sea ecosystems. During the middle and late Holocene, benthic foraminiferal faunas document the establishment of oligotrophic and well-ventilated conditions in the southern Aegean Sea. The corresponding faunas from the northern Aegean Sea reflect generally mesotrophic conditions and variable deep-water oxygenation. During the entire Holocene, the deep-sea ecosystems of this region responded very sensitively to short-term changes in humidity and temperature. These abrupt climate changes controlled the inflow of nutrients from rivers and the Black Sea and the formation of local deep-water masses.     

Palaeoenvironments of deposition of Neogene laminated diatom mat deposits from the eastern equatorial Pacific from studies of benthic foraminifera (sites 844, 849, 851)

Massive sedimentation of mats of the diatom Thalassiothrix longissima forming laminated diatom mat deposits (LDM) occurred intermittently in the equatorial Pacific throughout the Neogene from at least 15 to 4.8 m.y. ago. The background deposition was otherwise calcareous nannofossil diatom ooze (NO). Benthic foraminifera have been used to reconstruct the benthic environment of deposition and the role of both surface waters (as a source of food) and bottom waters (including their corrosivity) during LDM deposition. Three LDM events were studied: Site 844 (11.4 Ma, early Tortonian), Site 849 (4.8 Ma, early Zanclian and 6.6–6.8 Ma, early Messinian). A control section of NO spanning the 4.8 Ma event was studied from Site 851. In addition, the carbonate high NO immediately preceding the 4.8 Ma event was examined in Site 849. From the foraminiferal evidence it can be shown that the LDM was deposited under conditions of normal oxygenation because infaunal taxa are present throughout and there was an increase in epifaunal taxa such as Cibicides spp. However, there was a reduction in test size probably because only those smaller than 250 μm were able to move through the restricted sediment pore spaces caused by the diatom mat meshwork. The rate of accumulation of tests is highest in LDM interval and may reflect reduced predation from macrofaunal endobenthos. Among the epifaunal taxa, Nuttallides spp. show a decrease in abundance in the LDM and even immediately preceding it. This may be linked to a greater influence of corrosive AABW. Species known to feed opportunistically on phytodetritus (Epistominella exigua and Alabaminella weddellensis) are common in both NO and LDM. The increased relative abundance of A. weddellensis in the LDM may be due to this species being smaller than E. exigua and better able to exploit the food resource within the restrictive mat meshwork. The foraminiferal results corroborate the previous interpretation that preservation of lamination in the LDM is due to the physical exclusion of macro endobenthos rather than oxygen depletion of the bottom waters.     

Equatorial Pacific sea surface temperatures, faunal patterns, and carbonate burial during the Pliocene

A high-resolution record of radiolarian faunal abundances from the eastern equatorial Pacific is compared to records of carbonate and noncarbonate burial to examine the evolution of eastern tropical Pacific climate processes during the Pliocene. These data provide a means to evaluate the sensitivity of the equatorial Pacific to the onset of Northern Hemisphere glaciation around 2.8−2.5 Ma, to the closure of the Isthmus of Panama around 4.4−3.2 Ma, and to orogeny-related weathering changes before 4.0 Ma. Radiolarian faunal assemblages and sea surface temperature (SST) estimates indicate a gradual cooling from early to late Pliocene, but no significant changes occur near the onset of northern hemisphere glaciation. Records of carbonate and noncarbonate mass accumulation show a long term decrease from the Miocene/Pliocene boundary to the upper Pliocene. Greater carbonate burial in the early Pliocene relative to the late Pliocene parallels a gradual cooling from early to late Pliocene, and may reflect changes related to Isthmus closure or widespread orogeny. No significant time domain changes are seen in the eastern equatorial Pacific that could be related to the onset of Northern Hemisphere glaciation.Evolutive spectral analyses of these equatorial Pacific climate parameters indicate that variance in SST and seasonality commonly concentrate at frequencies not linearly related to orbital variations. Furthermore, cross spectral comparisons with a high resolution benthic δ¹⁸O record indicate that the surface ocean and carbonate flux share little coherent variance with high latitude climate processes during the Pliocene. Given the high degree of chronostratigraphic control in these records, these results suggest that Milankovitch-band surface ocean processes as well as carbonate burial in the equatorial Pacific are decoupled from high latitude climate processes during the Pliocene.     

Establishment of the western Pacific warm pool during the Pliocene: Evidence from planktic foraminifera, oxygen isotopes, and Mg/Ca ratios

This study presents new evidence of when and how the Western Pacific Warm Pool (WPWP) was established in its present form. We analyzed planktic foraminifera, oxygen isotopes, and Mg/Ca ratios in upper Miocene through Pleistocene sediments collected at Deep Sea Drilling Program (DSDP) Site 292. These data were then compared with those reported from Ocean Drilling Program (ODP) Site 806. Both drilling sites are located in the western Pacific Ocean. DSDP Site 292 is located in the northern margin of the modern WPWP and ODP Site 806 near the center of the WPWP. Three stages of development in surface-water conditions are identified in the region using planktic foraminferal data. During the initial stage, from 8.5 to 4.4 Ma, Site 806 was overlain by warm surface water but Site 292 was not, as indicated by the differences in faunal compositions and sea-surface temperature (SST) between the two sites. In addition, the vertical thermal gradient at Site 292 was weak during this period, as indicated by the small differences in the δ¹⁸O values between Globigerinoides sacculifer and Pulleniatina spp. During stage two, from 4.4 to 3.6 Ma, the SST at Site 292 rapidly increased to 27 °C, but the vertical thermal gradient had not yet be strengthened, as shown by Mg/Ca ratios and the presence of both mixed-layer dwellers and thermocline dwellers. Finally, a warm mixed layer with a high SST ca. 28 °C and a strong vertical thermal gradient were established at Site 292 by 3.6 Ma. This event is marked by the dominance of mixed-layer dwellers, a high and stable SST, and a larger differences in the δ¹⁸O values between G. sacculifer and Pulleniatina spp. Thus, evidence of surface-water evolution in the western Pacific suggests that Site 292 came under the influence of the WPWP at 3.6 Ma. The northward expansion of the WPWP from 4.4 to 3.6 Ma and the establishment of the modern WPWP by 3.6 Ma appear to be closely related to the closure of the Indonesian and Central American seaways.     

Middle Eocene–Early Pliocene Subantarctic planktic foraminiferal biostratigraphy of Site 1090, Agulhas Ridge

The analysis of planktic foraminiferal assemblages from Site 1090 (ODP Leg 177), located in the central part of the Subantarctic Zone south of South Africa, provided a geochronology of a 330-m-thick sequence spanning the Middle Eocene to Early Pliocene. A sequence of discrete bioevents enables the calibration of the Antarctic Paleogene (AP) Zonation with lower latitude biozonal schemes for the Middle–Late Eocene interval. In spite of the poor recovery of planktic foraminiferal assemblages, a correlation with the lower latitude standard planktic foraminiferal zonations has been attempted for the whole surveyed interval. Identified bioevents have been tentatively calibrated to the geomagnetic polarity time scale following the biochronology of Berggren et al. (1995). Besides planktic foraminiferal bioevents, the disappearance of the benthic foraminifera Nuttallides truempyi has been used to approximate the Middle/Late Eocene boundary. A hiatus of at least 11.7 Myr occurs between 78 and 71 m composite depth extending from the Early Miocene to the latest Miocene–Early Pliocene. Middle Eocene assemblages exhibit a temperate affinity, while the loss of several planktic foraminiferal species by late Middle to early Late Eocene time reflects cooling. During the Late Eocene–Oligocene intense dissolution caused impoverishment of planktic foraminiferal assemblages possibly following the emplacement of cold, corrosive bottom waters. Two warming peaks are, however, observed: the late Middle Eocene is marked by the invasion of the warmer water Acarinina spinuloinflata and Hantkenina alabamensis at 40.5 Ma, while the middle Late Eocene experienced the immigration of some globigerinathekids including Globigerinatheka luterbacheri and Globigerinatheka cf. semiinvoluta at 34.3 Ma. A more continuous record is observed for the Early Miocene and the Late Miocene–Early Pliocene where planktic foraminiferal assemblages show a distinct affinity with southern mid- to high-latitude faunas.     

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”).     

Middle to Upper Miocene benthonic foraminiferal palaeoecology of the Tap Marls (Alicante Province,SE Spain) and its palaeoceanographic implications

The benthonic foraminiferal faunas of twenty sections have been analysed statistically (cluster analysis) and interpreted palaeoecologically. The analysis shows that oxygenation was the most important factor for the distribution of the faunas in the investigated area. The lifting and lowering of the sill to the Atlantic Ocean (Gibraltar sill), in conjunction with climatic changes and sea level fluctuations, led to changes in the current system and to two faunal turnovers at the transition from Langhian to Serravallian (∼15.2–15.0 Ma) and at the end of the Serravallian, respectively (∼11.7–11.4 Ma). The faunas indicate well oxygenated (Langhian), reduced oxygenated (Serravallian) and again well oxygenated (Tortonian) conditions. A simplified circulation model for the western Mediterranean, based on the author's interpretation and additional sources, suggests: (a) an estuarine circulation during the Langhian; (b) a `restricted' anti-estuarine pattern with sluggish circulation until the end of the Serravallian; and (c) an anti-estuarine circulation similar to today's situation during the Tortonian.     

Oxygen minimum expansion in the Sulu Sea,western equatorial Pacific,during the last glacial low stand of sea level

The Sulu Sea in the western equatorial Pacific is presently a shallowly-silled, dysaerobic, deep-marine basin. Deep waters in the Sulu Sea are ventilated through a single sill at 420 m depth which connects it to the China Sea. Benthic and planktonic foraminiferal oxygen and carbon isotope records, benthic and planktonic foraminiferal census data and total organic carbon measurements have been used to evaluate changes in water mass conditions in the Sulu Sea between the last glacial maximum (18,000 yrs. B.P.) and the present day.An increase in the abundance of the planktonic foraminiferaNeogloboquadrina dutertrei and relatively light planktonic foraminiferal δ¹⁸O values suggest that during the last glacial maximum surface water salinities were reduced in the Sulu Sea. Enhanced isolation of the basin due to glacio-eustatic lowering of sea level and reduced surface salinities resulted in stagnation of deep water and an expansion of the mid-water oxygen minimum layer. Increased organic carbon preservation at mid-water depths occurs at this time. Benthic carbon isotope data and an increase in the abundance of benthic foraminiferal species considered to prefer low oxygen environments support the conclusion of an oxygen-minimum expansion at mid-water depths during the last glacial maximum. At water depths greater than 4000 m, bottom waters appear to have maintained some degree of oxygenation during the last glacial maximum. Stronger Pacific Ocean trade winds at this time may have caused the influx of denser Celebes Sea surface water into the southern part of the Sulu Sea. The slow sinking of this water would have then ventilated bottom waters in this part of the basin.At the transition from glacial to interglacial conditions, rising sea level caused denser water to flow over the deepest sill into the Sulu Sea. Vertical circulation increased, resulting in a greater downward flux of oxygen and a dissipation of the oxygen minimum. Continued post-glacial sea level rise caused periodic ventilation of deep water until the present dysaerobic conditions were established.     

Regional differences in pelagic productivity in the late Eocene to early Oligocene—a comparison of southern high latitudes and lower latitudes

Paleoproductivity patterns at the Eocene-Oligocene boundary in southern high latitudes and in the equatorial oceans were synthesized from the literature. Three ODP/DSDP sites from the Southern Ocean (Sites 689, 748 and 511) were compared with three DSDP/ODP sites from the equatorial oceans (Sites 574, 462 and 959). Paleoproductivity was estimated by multiple sedimentological, biological and geochemical proxies. Changes in paleoproductivity at the Eocene-Oligocene boundary mainly took place in the southern high latitudes. At Site 689, the benthic foraminiferal fauna also indicates an increase in seasonality. In equatorial oceans, there are no indications for a shift to higher paleoproductivity at the Eocene-Oligocene boundary. On the contrary at Site 959, sedimentology documents decreasing paleoproductivity in the Oligocene. Major changes in temperature and ocean circulation in southern high latitudes versus only minor changes in the lower latitudes were probably responsible for the geographically different changes in paleoproductivity.