Distribution of planktonic foraminifera and paleotemperature reconstruction for the Subantarctic Zone of the South Atlantic

Pleistocene summer sea-surface temperatures (SSST) have been reconstructed on a composite core section recovered in the Subantarctic Zone of the Southern Ocean from planktonic foraminifers applying the Modern Analog Technique. The composite consists of Core PS2489-2 and the sections recovered at ODP Site 1090, and documents the last 1.83 Ma. Three distinct climatic periods can be identified that mirror the Pleistocene development of the Southern Ocean hydrography. Cold climatic conditions prevailed at 43°S during glacial as well as during interglacial periods during the early Pleistocene (1.83-0.87 Ma), indicating a northward shift of isotherms that characterize the present-day Polar Front Zone by about 7° of latitude. Evidence shows a strong linkage between Southern Ocean and low latitude climate during that interval time. Between the Mid-Pleistocene Revolution (ca. 0.9 Ma) and the Mid-Brunhes Event (ca. 0.4 Ma), we observe higher amplitude fluctuations in the SSST between glacial and interglacial periods, corresponding to the temperature range between the present Polar Front and Subantarctic Front. These climatic variations have been related to changes in the northern hemisphere ice sheets. The past 0.4 Ma are characterized by strong SSST variations, of up to 8°C, between glacials and interglacials. Only during the climatic optima (stages 11.3, 9.3, 7.5, 7.1, 5.5, and the early Holocene), SSST exceeded present SSST at the core locality (10.2°C). Although the carbonate dissolution record exhibits high variability during the Pleistocene, it can be shown that SSST estimates were not significantly biased. The Mid-Brunhes dissolution cycle as well as the Mid-Pleistocene enhanced carbonate preservation appear to belong to a global long-term variability in carbonate preservation.

Benthic foraminiferal assemblages and epifaunal isotope record of the Agulhas Plateau

Benthic foraminiferal assemblages and the carbon isotope composition of the epifaunal benthic foraminifera Epistominella exigua and Fontbotia wuellerstorfi have been investigated along core MD02-2589 located at the southern Agulhas Plateau (41°26.03'S, 25°15.30'E, 2660 m water depth). This study aims to evaluate changes in the benthic paleoenvironment and its influence on benthic d13C with a notable focus on E. exigua, a species associated with phytodetritus deposits and poorly studied in isotope paleoceanographic reconstructions. The benthic foraminiferal assemblages (>63 µm) show large fluctuations in species composition suggesting significant changes in the pattern of ocean surface productivity conceivably related to migrations of the Subtropical Convergence (STC) and Subantarctic Front (SAF). Low to moderate seasonality and relatively higher food supply to the seafloor are indicated during glacial marine isotope stages (MIS) 6, 4, and 2 and during MIS 3, probably associated with the northward migration of the SAF and confluence with the more stationary STC above the southern flank of the Agulhas Plateau. The lowest organic carbon supply to the seafloor is indicated from late MIS 5b to MIS 4 as a consequence of increased influence of the Agulhas Front (AF) and/or weakening of the influence of the STC over the region. Episodic delivery of fresh organic matter, similar to modern conditions at the core location, is indicated during MIS 5c-MIS 5e and at Termination I. Comparison of this paleoenvironmental information with the paired d13C records of E. exigua and F. wuellerstorfi suggests that organic carbon offsets d13C of E. exigua from ambient bottom water d13CDIC, while its d13C amplitude, on glacial-interglacial timescales, does not seem affected by changes of organic carbon supply to the seafloor. This suggests that this species calcifies preferentially during the short time span of the year when productivity peaks and phytodetritus is delivered to the seafloor. Therefore E. exigua, while offset from d13CDIC, potentially more faithfully records the amplitude of ambient bottom water d13CDIC changes than F. wuellerstorfi, notably in settings such as the Southern Ocean that experienced substantial changes through time in the organic carbon supply to the seafloor.

Paleotemperature reconstruction for the past 0.55 Ma of the Subantarctic zone

Estimates of summer sea surface temperatures (SSSTs) derived from planktic foraminiferal associations using the Modern Analog Technique and combined with isotopic analyses and determination of ice-rafted debris, mirror the Pleistocene evolution of the planktic Subantarctic surface waters in the Atlantic Ocean. The SSSTs indicate that the isotherms that define the modern polar front zone and Subantarctic front, were located at more northerly latitudes (up to 7°) during most of the investigated period, which covers the past 550 kyr. Exceptions are during climatic optima in the early Holocene, at marine isotope stages (MIS) 5.5, 7.1, 7.5, 9.3, and presumably during MIS 11.3 when SSSTs exceeded modern values by 1 -5°C. The close similarity between the SSST and the Vostok temperature indicates strong regional temperature correlation. Both records show that MIS 9.3 was the warmest period during the last 420 kyr whereas SSSTs obtained for MIS 11.3 are overestimated due to strong carbonate dissolution. Spectral analysis corroborates that the initiation of warming in southern high latitudes heralds the start of deglaciation on the Northern Hemisphere.

Late Quaternary radiolarian assemblages of ODP Site 181-1124

Abundant and diverse polycystine radiolarian faunas from ODP Leg 181, Site 1123 (0-1.2 Ma at ~21 kyr resolution) and Site 1124 (0-0.6 Ma, ~5 kyr resolution, with a disconformity between 0.42-0.22 Ma) have been used to infer Pleistocene-Holocene paleoceanographic changes north of the Subtropical Front (STF), offshore eastern New Zealand, southwest Pacific. The abundance of warm-water taxa relative to cool-water taxa was used to determine a radiolarian paleotemperature index, the Subtropical (ST) Index. ST Index variations show strong covariance with benthic foraminifera oxygen isotope records from Site 1123 and exhibit similar patterns through Glacial-Interglacial (G-I) cycles of marine isotope stages (MIS) 15-1. At Site 1123, warm-water taxa peak in abundance during Interglacials (reaching ~8% of the total fauna). Within Glacials cool-water taxa increase to ~15% (MIS2) of the fauna. Changes in radiolarian assemblages at Site 1124 indicate similar but much better resolved trends through MIS15-12 and 7-1. Pronounced increases in warm-water taxa occur at the onset of Interglacials (reaching ~15% of the fauna), whereas the abundance of cool-water taxa increases in Glacials peaking in MIS2 (~17% of the fauna). Overall warmer conditions at Site 1124 during the last 600 kyrs indicate sustained influence of the subtropical, warm East Cape Current (ECC). During Interglacials radiolarian assemblages suggest an increase in marine productivity at both sites which might be due to predominance of micronutrient-rich Subtropical Water. At Site 1123, an increased abundance of deep-dwelling taxa in MIS 13 and 9 suggests enhanced vertical mixing. During Glacials, reduced vigour of ECC flow combined with northward expansion of cool, micronutrient-poor Subantarctic Water occurs. Only at Site 1123 there is evidence of a longitudinal shift of the STF, reaching as far north as 41°S.

Sedimentological and paleomagnetic investigations on two gravity cores and ODP sites 113-690 and 693 off Kapp Norvegia, Antarctic continental margin

Oligocene to Quaternary sediments were recovered from the Antarctic continental margin in the eastern Weddell Sea during ODP Leg 113 and Polarstern expedition ANT-VI. Clay mineral composition and grain size distribution patterns are useful for distinguishing sediments that have been transported by ocean currents from those that were ice-rafted. This, in turn, has assisted in providing insights about the changing late Paleogene to Neogene sedimentary environment as the cryosphere developed in Antarctica. During the middle Oligocene, increasing glacial conditions on the continent are indicated by the presence of glauconite sands, that are interpreted to have formed on the shelf and then transported down the continental slope by advancing glaciers or as a result of sea-level lowering. The dominance of illite and a relatively high content of chlorite suggest predominantly physical weathering conditions on the continent. The high content of biogenic opal from the late Miocene to the late Pliocene resulted from increased upwelling processes at the continental margin due to increased wind strength related to global cooling. Partial melting of the ice-sheet occurred during an early Pliocene climate optimum as is shown by an increasing supply of predominantly current-derived sediment with a low mean grain size and peak values of smectite. Primary productivity decreased at ~ 3 Ma due to the development of a permanent sea-ice cover close to the continent. Late Pleistocene sediments are characterized by planktonic foraminifers and biogenic opal, concentrated in distinct horizons reflecting climatic cycles. Isotopic analysis of AT. pachyderma produced a stratigraphy which resulted in a calculated sedimentation rate of 1 cm/k.y. during the Pleistocene. Primary productivity was highest during the last three interglacial maxima and decreased during glacial episodes as a result of increasing sea-ice coverage.

Sedimentological investigations of a sediment core profile from the continental slope of the South Orkney Islands

Sediment patterns such as texture, composition, and facies from three selected areas of the Antarctic continental margin of the Weddell Sea are discussed in relation to environmental variations of the Quaternary hydrosphere and kryosphere. Advance and retreat of ice shelves as well as oscillations in sea ice coverage are reflected by particular sediment facies. The distribution of ice-rafted detritus tracks the Antarctic Coastal Current, and the Weddell Sea Bottom water contour current can be recognized by its distinctive winnowing and erosion pattern. Distribution and abundance of biogenic sediment components are mainly controlled by duration of sea ice coverage reflecting the long-term climatic evolution.

Diversity of benthic foraminiferal faunas in Tertiary and Quaternary sediments of DSDP Hole 33-317_Site from the Manihiki Plateau, Pacific Ocean (Table 1)

A study is made of the benthic foraminifers (size fraction > 63 µm) recovered from 59 upper Eocene through Quaternary sediment samples at DSDP Site 317 (Leg 33), located at a depth of 2598 m in the central part of the Manihiki Plateau (South Pacific). The sediments cored are disturbed in only two samples. The stratigraphic assignements used are based on previous studies of planktic foraminifers and other microfossils. In total, 216 taxa are identified. A cluster analysis based on the 77 species which comprised 5% or more of the entire foraminiferal assemblage in at least one sample suggests the presence of 3 major biostratigraphic zones corresponding approximately to the following ages, zone A: middle Miocene-Quaternary; zones B-C: early Miocene-Oligocene; and zone D: Eocene. The most important faunal turnover occurred between the Eocene and the Oligocene; a less pronounced break took place between the early and the middle Miocene, and an additional minor turnover between the Oligocene and the early Miocene. Eighteen taxa are long-ranging, being recorded from the middle Eocene through the Pliocene-Quaternary. It is concluded that, in general, benthic foraminifers of the bathyal zone are poor worldwide stratigraphic guide fossils; the following taxa are conditionally considered as the most suitable in the Eocene-Quaternary sequence: Aragonia aragonensis, Quadrimorphina profunda, Nuttallides truempyi, Abyssamina poagi, Buliminella grata, Bulimina jarvisi, B. macilenta, Turrilina alsatica, Cibicides notocenicus, C. wuellerstorfi, Pyrgo murrhina. However, most of these species are relatively rare.

Benthic foraminifera in surface sediments of the Persian Gulf

During "Meteor"cruise 1965 the author collected 134 samples of surface sediments from the Iranian part of the Persian Gulf. Benthic Foraminifera populations have been analysed for determining their depth zonation. These data are supposed to allow detailed depth interpretation of Pleistocene sediments found in cores. In addition, the ecological information might be usefull to reconstruct the depositional environment of fossil sediments in similar shallow epicontinental seas. The investigation is published in two parts: the present part 1 contains the catalogue of species with short discussions of taxonomic problems, notes on the distribution within the Persian Gulf and 11 plates, partly with scanning electron micrographs. The results of the statistical analysis are given in data tables which include number of species, percentages of 2 (and 5) ranked species, standing crop and foraminiferal numbers. The author used "species groups" to avoid ambiguities with species requiring additional taxonomic studies. However, species numbers within these units are estimated to yield applicable diversity information. - A total of 52 species and 7 "species groups" were separated, 2 new species were described.

(Table T3) Granulometry of sediments from ODP Leg 190 sites

We present the results of grain-size analysis performed on hemipelagic sediment from Sites 1173, 1174, 1175, and 1177 at the Nankai Trough. Analyses of the <63-µm fraction were performed with a laser particle counter, and results were converted to equivalent settling diameters by means of an empirical regression with data from pipette analysis. The relations among grain size, porosity, bulk density, void ratio, and moisture content are influenced by the increasing compaction of sediment with depth as well as facies changes. Thus, departures of bulk density and porosity from normal compaction trends cannot be attributed to grain size on the basis of our laboratory results.

Distribution of foraminiferal fauna from ODP Hole 122-762C (Table 1)

Planktonic foraminiferal diversity, equitability and biostratigraphic analysis of samples from Ocean Drilling Program (ODP) Leg 122, Hole 762C show that in general, cool water conditions prevailed during the latest Campanian-Maastrichtian in the eastern Indian Ocean. This is indicated by planktonic foraminiferal assemblages characterized by low species diversity and equitability with abundant rugoglobigerinids and heterohelicids. Archaeoglobigerinids, globigerinelloids, hedbergellids, and long-ranging double-keeled globotruncanids are also present in varying abundance but single-keeled forms occur rarely and sporadically. Identification of the stage and zonal boundaries for the studied geologic interval have been achieved through biostratigraphic analyses of closely spaced samples. Three planktonic foraminiferal biozones were identified, namely; in stratigraphic order, the Heterohelix rajagopalani, Contusotruncana contusa and Abathomphalus mayaroensis Zones. In Hole 762C, a Transitional Realm with Austral influences is defined for the latest Campanian to Maastrichtian, as shown by the high relative abundance of fauna characteristic of Transitional and Austral Realms. Austral endemic species such as Archaeoglobigerina australis Huber and Hedbergella sliteri Huber were found in the samples studied but Globigerinelloides impensus Sliter andA rchaeoglobigerina mateola Huber are conspicuously absent. From the latest Campanian to middle Maastrichtian, cooler parts of the Transitional Realm prevailed. A slight warming trend is assumed towards the end of the middle Maastrichtian because the faunas contain more species indicative of warm water conditions. The late Maastrichtian also appears to have been warmer than the latest Campanian-middle Maastrichtian. This conclusion is based on the high diversity and equitability values and recognition of some thermophilic taxa. A Tethyan influence is inferred for the latest Maastrichtian on the basis of an increase of planktonic foraminiferal species diversity and occurrences of several keeled taxa.

(Table 1) Distribution of Cretaceous-Tertiary benthic foraminifers in ODP Hole 129-802A

Reworked shallow-water larger and deep-water calcareous benthic foraminifers were recovered from foraminiferal packstones and nannofossil chalks in Hole 802A. The autochthonous zeolitic pelagic claystone is characterized by late Campanian abyssal agglutinated foraminifers that allow correlation with the North Atlantic and the adjacent Pigafetta Basin. Assemblages of DendrophryalRhizammina in graded beds within the zeolitic claystone indicate reworking through entrainment in the flocculent E layer of turbidites, rather than recolonization following a biosiliceous event. Background sedimentation of the claystone took place below the carbonate compensation depth. The nannofossil chalk contains reworked lower bathyal to abyssal calcareous foraminifers of late Paleocene to early Miocene age. The topmost bed of the nannofossil chalk unit commences with an algal foraminiferal packstone containing Lepidocyclina sumatrensis, Heterostegina borneensis, Amphistegina hauerina, Asterigerina marshallana, and A. tentoria, which indicate that the source area was a shallow-water reef and allow the bed to be dated as early Miocene. The absence of obviously younger planktonic microfossils in the graded bed indicates that the resedimentation event was generally contemporaneous with original deposition and took place during an early Miocene global sea-level highstand. An early Miocene shallow-water assemblage is also seen in the graded beds at the base of a volcaniclastic turbidite sequence overlying the nannofossil chalks. Resedimentation of this unit was associated with volcanic activity some distance away.