Ostracoda in five sediment cores from the Laptev and Kara seas

Fossil ostracods were investigated in five AMS14C-dated cores from different parts of the Laptev and Kara seas. Three cores from the Laptev Sea shelf are located in river paleovalleys, and one core originates from the western continental slope. The core from the Kara Sea was obtained in the eastern shelf region. Six fossil assemblages were distinguished: estuarine (1), inner-shelf (2), middle-shelf (3), outer-shelf (4), Pre-Holocene upper continental slope (5), and Holocene upper continental slope (6). They show that during the Postglacial sea-level rise there was a transition from estuarine brackish-water environment to modern marine conditions. Assemblages 1-3 are present in the eastern Laptev Sea with the oldest ostracod-bearing samples aging back to 11.4-11.3 cal.ka. Cores from the western Laptev Sea (12.3 cal.ka, assemblages 1-4) and the Kara Sea (8.1 cal.ka, assemblages 2-4) demonstrate similar pattern in assemblage replacement, but contain a number of relatively deep-water species reflecting stronger influence of open-sea waters. Core from the continental slope, water depth 270 m (~ 17 cal.ka) encompasses assemblages 5 and 6, which are absent in the shelf cores. Assemblage 5 stands out as a specific community dominated by relatively deep-water Arctic and North Atlantic species together with euryhaline ones. The assemblages indicate inflows of Atlantic-derived waters and downslope slides due to the proximity to the paleocoastline. Assemblage (6) is similar to the modern local ostracod assemblage at this site.

Sediment geochemistry, foraminiferal fauna parameter, census counts and Varimax PC-factor loadings and scores of foraminiferal assemblages of sediment core GeoB12615-4

Analogous to West- and North Africa, East Africa experienced more humid conditions between approximately 12 to 5 kyr BP, relative to today. While timing and extension of wet phases in the North and West are well constrained, this is not the case for the East African Humid Period. Here we present a record of benthic foraminiferal assemblages and sediment elemental compositions of a sediment core from the East African continental slope, in order to provide insight into the regional shallow Indian Ocean paleoceanography and East African climate history of the last 40 kyr. During glacial times, the dominance of a benthic foraminiferal assemblage characterized by Bulimina aculeata, suggests enhanced surface productivity and sustained flux of organic carbon to the sea floor. During Heinrich Stadial 1 (H1), the Nuttallides rugosus Assemblage indicates oligotrophic bottom water conditions and therefore implies a stronger flow of southern-sourced AAIW to the study site. During the East African Humid Period, the Saidovina karreriana Assemblage in combination with sedimentary C/N and Fe/Ca ratios suggest higher river runoff to the Indian Ocean, and hence more humid conditions in East Africa. Between 8.5 and 8.1 kyr, contemporaneous to the globally documented 8.2 kyr Event, a severe reduction in river deposits implies more arid conditions on the continent. Comparison of our marine data with terrestrial studies suggests that additional moisture from the Atlantic Ocean, delivered by an eastward migration of the Congo Air Boundary during that time period, could have contributed to East African rainfall. Since approximately 9 kyr, the gaining influence of the Millettiana millettii Assemblage indicates a redevelopment of the East African fringe reefs.

Radiocarbon dating on cold-water corals, grain size, Corg, and benthic foraminfera assemblage of two sediment cores from the Ionian Sea

Continuous sedimentary records from an eastern Mediterranean cold-water coral ecosystem thriving in intermediate water depths (~600 m) reveal a temporary extinction of cold-water corals during the Early to Mid Holocene from 11.4-5.9 cal kyr BP. Benthic foraminiferal assemblage analysis shows low-oxygen conditions of 2 ml l**-1 during the same period, compared to bottom-water oxygen values of 4-5 ml l**-1 before and after the coral-free interval. The timing of the corals' demise coincides with the sapropel S1 event, during which the deep eastern Mediterranean basin turned anoxic. Our results show that during the sapropel S1 event low oxygen conditions extended to the rather shallow depths of our study site in the Ionian Sea and caused the cold-water corals temporary extinction. This first evidence for the sensitivity of cold-water corals to low oceanic oxygen contents suggests that the projected expansion of tropical oxygen minimum zones resulting from global change will threaten cold-water coral ecosystems in low latitudes in the same way that ocean acidification will do in the higher latitudes.

Distribution of benthic foraminifers in surface layer of bottom sediments from the littoral zone of the Kunashir Island, South Kuriles

Composition and abundance of modern benthic foraminifers in the littoral zone of the Kunashir Island (South Kuriles) were studied. This littoral zone was examined on the sides of the Sea of Okhotsk, the Pacific Ocean, and the Izmena Bay. In the littoral zone of the Izmena Bay benthic foraminifers were not found. The highest biodiversity and maximal density of foraminifers were observed at a bench among rocks and blocks, in depressions of various size and depth (baths), at places where algae and water plants were attached, on silty sands, and on sands with admixture of broken shells, silt, and clastic matter composing the coast. The lowest density and biodiversity were found in mouths of creeks and rivers, on rock plates free from sediments and attached algae and water plants, as well as in places not protected from wind and wave activity. It was established that on both sides of the Sea of Okhotsk and of the Pacific Ocean foraminiferal complexes vary both in biodiversity and in density of their distribution in the littoral zone.

Benthic foraminifera of the central Indian Ocean

Late Oligocene to late Pliocene vertical water-mass stratification along depth traverses in the northern Indian Ocean is depicted in this paper by benthic foraminifer index faunas. During most of this time, benthic faunas indicate well-oxygenated, bottom-water conditions at all depths except under the southern Indian upwelling and in the Pliocene in the southern Arabian Sea. Faunas suggest the initiation of lower oxygen conditions at intermediate depths in the northern Indian Ocean beginning in Oligocene Zone P21a. Lower oxygen conditions intensified during primary productivity pulses, possibly related to increased upwelling vigor, in the latest Oligocene and throughout most of the late middle through late Miocene. During times of elevated primary production, there may be more oxygen flux into sedimentary pore waters and the shallow infaunal habitat may become more oxygenated. One criterion for locating the source of "new" water masses is vertical homogeneity of benthic foraminifer indexes for well-oxygenated water masses from intermediate through abyssal depths. In the northern Mascarene Basin, this type of faunal homogeneity with depth corroborates the proposal that the northern Indian Ocean was an area of sinking well-oxygenated waters through most of the Miocene before Zone N17. Oxygenated, possibly "new" intermediate-water masses in the low- to middle-latitude Mascarene and Central Indian basins first developed in the late Oligocene. These well-oxygenated waters were probably more fertile than the Antarctic Intermediate Waters (AAIW) that cover intermediate depths in these areas today. Production of intermediate waters more similar to modern AAIW is indicated by the sparse benthic population of epifaunal rotaloid species in the northern Mascarene Basin during middle Miocene Zone N9 and from early through late Pliocene time. Deep-water characteristics are more difficult to interpret because of the extensive redeposition at the deeper sites. Redeposited intermediate, rather than shallow, water fossils and erosion from north to south in the Mascarene Basin are incompatible with the sluggish circulation from south to north through the western Indian Ocean basins today. Such erosion could result from the vigorous sinking of an intermediate-depth water mass of northern origin. Before late Oligocene Zone P22, benthic faunas indicate a twofold subdivision of the troposphere, with the boundary between upper and lower well-oxygenated water masses located from 2500-3000 mbsl. No characteristic bottom-water fauna developed before the end of late Oligocene Zone P22. Deep and abyssal benthic indexes suggest the development of water masses similar to those of the present day in the latest Miocene. Faunas containing deep-water benthic indexes, including the uvigerinids, suggestive of a water mass similar to modern Indian Deep Water (IDW), appeared during the late Miocene in the northern Mascarene and Central Indian basins. In the early Pliocene, this deep-water fauna was found only in the Central Indian Basin, whereas a fauna typical of modern Antarctic Bottom Water (AABW) spread through deep waters at 2800 mbsl in the Mascarene Basin. By late Pliocene Zone N21, however, deep-water faunas similar to their modern analogs were developed in both the eastern and western basins. Abyssal faunas, studied only in the Mascarene Basin, show more or less similarity to those under modern AABW. Bottom-water faunas containing Nuttallides umbonifera or Epistominella exiguua were first differentiated at the end of Zone P22, then appeared episodically during the early Miocene. These AABW-type faunas reappeared and migrated updepth into deep waters during the glacial episodes at the end of the Miocene and at the beginning of the Pliocene. By late Pliocene Zone N21, however, a bottom-water fauna similar to that under eastern Indian Bottom Water (IBW) developed in the Mascarene Basin. Modern bottom-water characteristics of the Mascarene Basin must have developed after ZoneN21.

Benthic foraminifera, stable isotope record and sedimentology of Holocene sediments in the Skagerrak

A high-resolution multi-proxy study of core MD99-2286 reveals a highly variable hydrographic environment in the Skagerrak from 9300 cal. yr BP to the present. The study includes foraminiferal faunas, stable isotopes and sedimentary parameters, as well as temperature and salinity reconstructions of a ca. 29 m long radiocarbon-dated core record. The multivariate technique fuzzy c-means was applied to the foraminiferal counts, and it was extremely valuable in defining subtle heterogeneities in the foraminiferal fauna data corresponding to hydrographic changes. The major mid-Holocene (Littorina) transgression, led to flooding of large former land areas in the North Sea, the opening of the English Channel and Danish straits and initiation of the modern circulation system. This is reflected by fluctuating C/N values and an explosive bloom of Hyalinea balthica. A slight indication of ameliorated conditions between 8000-5750 cal. yr BP is related to the Holocene Thermal Maximum. A subsequent increase in fresh water/Baltic water influence between 5750-4350 cal. yr BP is reflected by dominance of Bulimina marginata and depleted d18O-values. The Neoglacial cooling (after 4350 cal. yr BP) is seen in the Skagerrak as enhanced turbidity, increasing TOC-values and short-term changes in an overall Cassidulina laevigata dominated fauna suggesting a prevailing influence of Atlantic waters. This is in agreement with increased strength of westerly winds, as recorded for this period. The last 2000 years were also dominated by Atlantic Water conditions with generally abundant nutrient supply. However, during warm periods, particularly the Medieval Warm Period and the modern warming, the area was subject to a restriction in the supply of nutrients and/or the nutrient supply had a more refractory character.

Benthic foraminifera in sapropels of the eastern Mediterranean Sea

High-resolution benthic foraminiferal and geochemical investigations were carried out across sapropels S5 and S6 from two sediment cores in the Levantine Sea to evaluate the impact of climatic and environmental changes on benthic ecosystems during times of sapropel formation. The faunal successions indicate that eutrophication and/or oxygen reduction started several thousand years prior to the onset of sapropel formation, suggesting an early response of the bathyal ecosystems to climatic changes. Severest oxygen depletions appear in the early phases of sapropel formation. The initial reduction of deep-water ventilation is caused by a warming and fresh water-induced stratification of Eastern Mediterranean surface waters. During the late phase of S5 formation improved oxygenation is restricted to middle bathyal ecosystems, indicating that at least some formation of subsurface water took place. During S6 formation oxygen depletions and eutrophication were less severe and more variable than during S5 formation. Estimated oxygen contents were low dysoxic at middle bathyal to anoxic at lower bathyal depths during the early phase of S6 formation but never dropped to anoxic values in its late phase. The high benthic ecosystem variability during S6 formation suggests that water column stratification at deep-water formation sites was in a very unstable mode and susceptible to minor temperature fluctuations at a millennial time-scale.

Upper Maestrichtian to Eocene benthic foraminifera in ODP Leg 121 holes

Late Maestrichtian to late Eocene bathyal benthic foraminiferal faunas at Sites 752,753, and 754 on Broken Ridge in the eastern Indian Ocean were analyzed as to their stratigraphic distribution of species to clarify the relation between faunal turnovers and paleoceanographic changes. Based on Q-mode factor analysis, eight varimax assemblages were distinguished: the Stensioina beccariiformis assemblage in the upper Maestrichtian to upper Paleocene; the Cibicidoides hyphalus assemblage in the upper Maestrichtian; the Cibicidoides cf. pseudoperlucidus assemblage in the upper Paleocene; the Anomalinoides capitatusldanicus assemblage in the uppermost Paleocene to lower Eocene; the Cibicidoides subspiratus assemblage in the lower Eocene; the Nuttallides truempyi assemblage in the lower and middle Eocene; the Osangularia sp. 1 - Hanzawaia ammophila assemblage in the upper Eocene; and the Lenticulina spp. assemblage in the uppermost Eocene, Oligocene, and lower Miocene. The presence of the Osangularia sp. 1 - Hanzawaia ammophila assemblage is related to the shallowing episode on Broken Ridge (upper bathyal), as a result of the rifting event that occurred in the middle Eocene. The most distinct faunal change (the disappearance of about 37% of the species) occurred between the S. beccariiformis assemblage and the A. capitatusldanicus assemblage, at the end of the upper Paleocene. A. capitatusldanicus, Lenticulina spp., and varied forms of Cibicidoides replaced the Velasco-type fauna at this time. The timing of this event is well correlated with the known age at South Atlantic sites (Thomas, 1990 doi:10.2973/odp.proc.sr.113.123.1990; Kennett and Stott, 1990 doi:10.2973/odp.proc.sr.113.188.1990; Katz and Miller, 1990 doi:10.2973/odp.proc.sr.114.147.1991). The primary cause of the extinction of the Stensioina beccariiformis assemblage is elusive, but may have resulted from the cessation of deep-water formation in the Antarctic (Katz and Miller, 1990), and subsequent arrival of warm saline deep water (Thomas, 1990; Kennett and Stott, 1990). Another possibility may be a weakened influence of high-salinity water formed at the low latitudes such as the Tethys Sea. The extinction event corresponds to the change from higher delta13C values in benthic foraminifers to lower ones. An interpretation of delta13C values is that the eastern Indian deep water, characterized by young and nutrient-depleted water, became old water which was devoid of a supply of new water during the latest Paleocene to early Eocene. Prior to this benthic event, signals of related faunal change were detected in the following short periods: early and late Paleocene, near the boundary of nannofossil Zone CP4, and Zone CP5 of the late Paleocene at Site 752. Among common taxa in the upper Maestrichtian, only seven species disappeared or became extinct at the Cretaceous/ Tertiary boundary at Site 752. The benthic foraminiferal population did not change for up to 2 m above the boundary, in contrast to the rapid decrease of the plankt onic foraminiferal population at the boundary. A decrease in the number of benthic foraminifers occurs after that level, corresponding to an interval of decreased numbers of planktonic foraminifers and higher abundance of volcanic ash. Reduced species diversity (H') suggests a secondary effect attributable to the dissolution of foraminiferal tests. The different responses of planktonic and benthic foraminifers to the event just above the boundary suggest that the Cretaceous/Tertiary event was a surface event as also suggested by Thomas (1990). In addition, a positive shift of delta13C in benthic foraminifers after the event indicates nutrient-depleted bottom water at Site 752.

Neogene benthic foraminifers from the Kerguelen Plateau

Benthic foraminifers were studied quantitatively in 120 lower Miocene through upper Pleistocene samples from Ocean Drilling Program Site 747 (Central Kerguelen Plateau) and Sites 748 and 751 (Southern Kerguelen Plateau). These sites are situated on an 450-km-long, north-south transect between 54°49'S and 58°26'S at present water depths between 1696 and 1288 m. Principal component analysis on the census data of the most abundant 92 taxa helped to identify 8 benthic foraminifer assemblages. These benthic foraminifer assemblages were compared with Holocene faunas from southern high latitudes to reconstruct paleoenvironmental conditions. Middle lower Miocene sediments are characterized by a Uvigerina hispidocostata assemblage, indicating high paleoproductivity and/or not well-ventilated bottom water. From late early to late middle Miocene time, the Southern Kerguelen Plateau was bathed by a young, well-oxygenated, and carbonate-aggressive water mass, as indicated by a Nuttallides umbonifer-dominated benthic foraminifer assemblage. During late middle Miocene time, an Astrononion pusillum assemblage took over for only about 1 m.y., probably indicating the first injection of an aged water mass, similar to the North Atlantic Deep Water (NADW), into a developing circumpolar current system. Around the middle to late Miocene boundary, the fauna again became dominated by N. umbonifer. After the last appearance of N. umbonifer, reestablishment of the A. pusillum assemblage from the early late through at least the late late Miocene, indicated the established influence of a NADW-like water mass. The latest Miocene through middle late Pliocene benthic foraminifer assemblage was characterized by Epistominella exigua and strong carbonate dissolution, indicating very high biosiliceous production, and this in turn may indicate the formation and paleoposition of an Antarctic Polar Frontal Zone. From the late late Pliocene, a Trifarina angulosa assemblage (indicative today of sandy substrate and vigorous bottom currents) strongly dominated the fauna up to the late Pleistocene, when Bulimina aculeata (indicative today of calm sedimentation with high organic matter fluxes) became an important and partly dominating constituent of the fauna. This is interpreted as the faunal response to the decreased winnowing force (bottom current velocities) of the Antarctic Circumpolar Current during periods of global climatic amelioration and raised sea level.

Cenozoic benthic foraminifers from ODP Leg 134 holes

This paper discusses the Paleobathymetric and paleoenvironmental history of the New Hebrides Island Arc and North d'Entrecasteaux Ridge during Cenozoic time based on benthic foraminiferal and sedimentological data. Oligocene and Pliocene to Pleistocene benthic foraminiferal assemblages from Sites 827, 828, 829, and 832 of Ocean Drilling Program (ODP) Leg 134 (Vanuatu) are examined by means of Q-mode factor analysis. The results of this analysis recognize the following bathymetrically significant benthic foraminiferal biofacies: (1) Globocassidulina subglobosa biofacies and Bulimina aculeata-Bolivinita quadrilatera biofacies representing the upper bathyal zone (600-1500 m); (2) Gavelinopsis praegeri-Cibicides wuellerstorfi biofacies, indicating the Pacific Intermediate Water (water depth between 1500 and 2400 m); (3) Tosaia hanzawai-Globocassidulina muloccensis biofacies, Valvulineria gunjii biofacies, and the Melonis barleeanus-Melonis sphaeroides biofacies, which characterize the lower bathyal zone; (4) the Nuttallides umbonifera biofacies, which characterizes the interval between the lysocline (approximately 3500 m) and the carbonate compensation depth (approximately 4500 m); and (5) the Rhabdammina abyssorum biofacies representing the abyssal zone below the carbonate compensation depth. Benthic foraminiferal patterns are used to construct Paleobathymetric and paleogeographic profiles of the New Hebrides Island Arc and North d'Entrecasteaux Ridge for the following age boundaries: late Miocene/Pliocene, early/late Pliocene, Pliocene/Pleistocene, and Pleistocene/Holocene.

Foraminifer faunas in the Tagus Prodelta

Pluri-annual proxy records of marine sediment cores from the Tagus Prodelta off Lisbon, Portugal, have been generated to gain insight into the climatic and hydrographic changes in the area during the twentieth century. The study includes benthic and planktonic foraminiferal faunas and the stable isotopic composition of one benthic (Uvigerina celtica) and two planktonic (Globigerina bulloides and Globorotalia inflata) foraminiferal species. Sea bottom and surface water temperatures were estimated based on the d18O values of these species and compared with instrumental data. The foraminiferal fauna and the isotope-based temperature record indicate increasing temperatures throughout the last century. The immigration of a new species, Saidovina karreriana, to the area around 100 years ago indicates changes in the trophic conditions and water mass properties, which are probably at least partly due to anthropogenic pollution.

Neogene benthic foraminiferal community and organic carbon at DSDP Holes 95-612 and 95-613

Quantitative study of benthic foraminifers from the upper Miocene to lower Pliocene section at Site 612 (1404 m present water depth) and the Pliocene section at Site 613 (2323 m present water depth) shows no evidence of widespread downslope transport of shallow-water biofacies or reworking of older material in the greater than 150 µm size fraction. In contrast, upper Miocene sediments from Site 604 (2364 m present water depth) show extensive reworking and downslope transport. At Site 612, benthic foraminifers show a succession from an upper Miocene Bolivina alata-Nonionella sp. biofacies, to an uppermost Miocene Bulimina alazanensis biofacies, to a lower Pliocene Cassidulina reflexa biofacies, to an upper Pliocene Melonis barleeanum-Islandiella laevigata biofacies. Evidence suggests that the Pliocene biofacies are in situ, although they could have been transported downslope from the upper-middle bathyal zone. At Site 613, Uvigerina peregrina dominated the "middle" Pliocene, while Globocassidulina subglobosa was dominant in the early and late Pliocene. High abundances of U. peregrina at Site 613 are associated with high values of sedimentary organic carbon.