Oxygen and carbon isotope data for benthic foraminifera from DSDP Site 94-608 and ODP Site 208-1264

Small biserial foraminifera were abundant in the early Miocene (ca. 18.9-17.2 Ma) in the eastern Atlantic and western Indian Oceans, but absent in the western equatorial Atlantic Ocean, Weddell Sea, eastern Indian Ocean, and equatorial Pacific Ocean. They have been assigned to the benthic genus Bolivina, but their high abundances in sediments without evidence for dysoxia could not be explained. Apertural morphology, accumulation rates, and isotopic composition show that they were planktic (genus Streptochilus). Living Streptochilus are common in productive waters with intermittent upwelling. The widespread early Miocene high Streptochilus abundances may reflect vigorous but intermittent upwelling, inducing high phytoplankton growth rates. However, export production (estimated from benthic foraminiferal accumulation rates) was low, possibly due to high regeneration rates in a deep thermocline. The upwelled waters may have been an analog to Subantarctic Mode Waters, carrying nutrients into the eastern Atlantic and western Indian Oceans as the result of the initiation of a deep-reaching Antarctic Circumpolar Current, active Agulhas Leakage, and vigorous vertical mixing in the Southern Oceans.

(Table 5) Quaternary paleoproductivity of organic carbon in oceans based on DSDP cores

By analogy with the present-day ocean, primary productivity of paleoceans can be reconstructed using calculations based on content of organic carbon in sediments and their accumulation rates. Results of calculations based on published data show that primary productivity of organic carbon, mass of phosphorus involved in the process, and content of phosphorus in ocean waters were relatively stable during Cenozoic and Late Mesozoic. Prior to precipitation on the seafloor together with biogenic detritus, dissolved phosphorus could repeatedly be involved in the biogeochemical cycle. Therefore, only less than 0.1% of phosphorus is retained in bottom sediments. Bulk phosphorus accumulation rate in ocean sediments is partly consistent with calculated primary productivity. Some epochs of phosphate accumulation also coincide with maxima of primary productivity and minima of the fossilization coefficient of organic carbon. The latter fact can testify to episodes of acceleration of organic matter mineralization and release of phosphorus from sediments leading to increase in the phosphorus reserve in paleoceans and phosphate accumulation in some places.

Siliceous components of Pliocene-Holocene sediments of the South Atlantic

The Pliocene-Holocene sediments recovered on ODP Leg 114 from Holes 699A, 701C, and 704B are the subject of a detailed investigation to interpret changes in the Oceanographic environment of the South Atlantic in the vicinity of the Polar Front Zone (PFZ). The cores sample sediments at shallow (Hole 704B, 2532 m), intermediate (Hole 699A, 3716 m), and basinal (Hole 701C, 4647 m) depths. Sites 699 and 704 come under the influence of the Antarctic Circumpolar Current (ACC) and Circumpolar Deep Water. It is possible that the upper reaches of Antarctic Bottom Water (AABW) may also affect Hole 699A. Site 701 is influenced by AABW. Closely spaced samples were analyzed for grain-size distribution, sand fraction components, biosiliceous microfossils, organic carbon, and water content. PFZ migrations are traced using changes in bulk sedimentaccumulation rates and the abundance of the diatoms Actiniscus ssp. and Genus et species indet. 1 Fenner (1991), as well as changes in sediment grain size and composition. Diatomaceous sediments of Gilbert age in Hole 699A indicate that the PFZ was positioned over this site, but during the Gauss it migrated north, bringing in less productive Antarctic Surface Water. All cores document a very gradual southerly movement of the PFZ throughout the Matuyama (with some sharp fluctuations of the northen PFZ border over Site 704 between 1.45 and 1.83 m.y.). This regressive shift culminated in the late Matuyama. The latest Matuyama to earliest Brunhes record in Hole 699A has been removed by a hiatus lasting from 1.0 to 0.6 m.y., which was probably caused by intensification of the deep-reaching ACC. The corresponding interval in Hole 704B, the shallowest core, contains evidence of winnowing. Sharp fluctuations of large amplitude and high frequency in the lithology of the sediments from Hole 704B in the eastern South Atlantic, starting at about 0.75 m.y. and characterizing the whole Brunhes Epoch, record the rapid movement of the northern border of the PFZ over the site. These reflect strong glacial/interglacial alternations in climate. To a lesser extent, lithologic fluctuations in Hole 701C reflect the same phenomenon, whereas in Hole 699A the lithology does not vary as dramatically.

Diatom biostratigraphy and datum events of ODP Hole 183-1140A

Ocean Drilling Program (ODP) Leg 183 Site 1140 provided a lower Oligocene to middle Miocene record of diatom assemblages from the northern Kerguelen Plateau. Samples were examined to improve the resolution of shipboard diatom biostratigraphy. The material is complementary to that recovered during ODP Legs 119 and 120, and the diatom zonation of Harwood and Maruyama could be readily applied. A standard succession of biostratigraphic zones from the middle Miocene and lower Oligocene was delineated, although some zones were unrecognizable because of poor core recovery. The detailed diatom biostratigraphy presented here agrees well with shipboard calcareous nannofossil biostratigraphy. Sediment accumulation rates based on diatom bioevents average 1.26 cm/k.y.

Geochemistry of frost flowers and snow obtained near Ahlmann summit, Vestfonna ice cap

The chemistry of snow and ice cores from Svalbard is influenced by variations in local sea ice margin and distance to open water. Snow pits sampled at two summits of Vestfonna ice cap (Nordaustlandet, Svalbard), exhibit spatially heterogeneous soluble ions concentrations despite similar accumulation rates, reflecting the importance of small-scale weather patterns on this island ice cap. The snow pack on the western summit shows higher average values of marine ions and a winter snow layer that is relatively depleted in sulphate. One part of the winter snow pack exhibits a [SO4-/Na+] ratio reduced by two thirds compared with its ratio in sea water. This low sulphate content in winter snow is interpreted as the signature of frost flowers, which are formed on young sea ice when offshore winds predominate. Frost flowers have been described as the dominant source of sea salt to aerosol and precipitation in ice cores in coastal Antarctica but this is the first time their chemical signal has been described in the Arctic. The eastern summit does not show any frost flower signature and we interpret the unusually dynamic ice transport and rapid formation of thin ice on the Hinlopen Strait as the source of the frost flowers.

Tab. 1+7: Hydrochemical analyses of firn and meltwater from different "cold" snow patches

In wide areas of Northern Siberia, glaciers have been absent since the Late Pleistocene. Therefore, ground ice and especially ice wedges are used as archives for paleoclimatic studies. In the present study, carried out on the Bykovsky Peninsula, eastern Lena Delta, we were able to distinguish ice wedges of different genetic units by means of oxygen and hydrogen isotopes. The results obtained by this study on the Ice Complex, a peculiar periglacial phenomenon, allowed the reconstruction of the climate history with a subdivision of a period of very cold winters (60-55 ka), followed by a long stable period of cold winter temperatures (50-24 ka), Between 20 ka and 11 ka, climate warming is indicated in stable isotope compositions, most probably after the Late Glacial Maximum. At that time, a change of the marine source of the precipitation from a more humid source to the present North AtIantic source region was assumed. For the Ice Complex, a continuous age-height relationship was established, indicating syngenetic vertical ice wedge growth and sediment accumulation rates of 0.7 m/ky. During the Holocene optimum, ice wedge growth was probably limited due to the extensive formation of lacustrine environments. Holocene ice wedges in thermokarst depressions (alases) and thermoerosional valleys (logs) were formed after climate deterioration from about 4.5 ka until the present. Winter temperatures were warmer at this time as compared to the cooler Pleistocene. Migration of bound water between ice wedges and segregated ice may have altered the isotopic composition of old ice wedges. The presence of ice wedges as diagnostic features for permafrost conditions since 60 ka, implies that a large glacier extending over the Laptev Sea shelf did not exist. For the remote non-glaciated areas of Northern Siberia, ice wedges were established as a powerful climate archive.

Middle Eocene to Miocene calcareous nannofossil of ODP Leg 125

During Ocean Drilling Program Leg 125, a thick sequence of middle Eocene to Pleistocene pelagic sediments, volcanogenic sediments, and predominantly extrusive volcanic rocks was recovered. Calcareous nannofossils were examined from 15 holes at nine sites, but Eocene to Miocene calcareous nannofossils were found only from Holes 782A, 784A, 786A, and 786B. In portions of Holes 786A and 786B, datable nannofossil oozes were found intercalated among volcanic flows. The nannofossil biostratigraphy of these holes indicates the presence of three well-defined hiatuses: within the lower Oligocene, between the upper Oligocene and middle Miocene, and between the middle and upper Miocene. An attempt was made to correlate the magnetochronological data with the first or last occurrences of the following species: Sphenolithus distentus, Reticulofenestra bisecta, Reticulofenestra reticulata, and Cyclicargolithus floridanus abisectus n. comb. The results indicate that the FO of Sphenolithus distentus can extend down to Zone CP16 (34.7 Ma), the LO of Reticulofenestra bisecta best defines the boundary between CP19a and CP19b (23.5 Ma), and the LO of Cyclicargolithus f. abisectus n. comb, can extend up to Subzone CN5a (12.5 Ma). No latest Oligocene Cyclicargolithus f. abisectus n. comb, acme was observed. Cyclicargolithus abisectus is considered a subspecies or variant of Cyclicargolithus floridanus because their LOs coincide. As a consequence of these observations, we have modified the definitions of Bukry's Subzones CP14a, CP14b, and CNla. Analyses of sediment-accumulation rates indicate that the rates increased gradually from the Eocene to Miocene. This is especially evident since the late Miocene in Hole 782A. In different parts of the Izu-Bonin forearc basin, however, the rate is not everywhere the same and appears to vary according to the import of volcanogenic materials.

XRF iron (Fe) counts of ODP Hole 171-1050A and 171-1051A

Upper Paleocene to lower Eocene sediments drilled at Ocean Drilling Program (ODP) Site 1051 (Blake Nose, off Florida) display well-defined orbital cycles, a detailed magnetic stratigraphy, and a suite of planktonic foraminiferal datums. We derived a cyclostratigraphy by using spectral analysis of high-resolution records of elemental concentrations obtained by an X-ray fluorescence (XRF) Core Scanner. XRF counts of iron serve as a proxy for the relative amount of terrestrial material. Sliding-window spectral analysis, bandpass filtering, and direct counting of precession and obliquity cycles yield minimum durations for magnetic polarity chrons C22 to C26 (~49 to ~61 Ma), calculations of sediment accumulation rates, as well as constraints on the timing of biostratigraphic and climatological events in the vicinity of the Initial Eocene Thermal Maximum (IETM). Durations of polarity chrons as represented in sediments drilled at Site 1051 were estimated using a conservative assignment of 41 k.y. for obliquity cycles and 21 k.y. for precession cycles. Combined polarity chrons C26r and C26n span 3.61 m.y., and chron C25r spans 1.07 m.y. Polarity chron C24r is estimated as 2.877 m.y. The interpretation of polarity chron C24n is ambiguous, but its duration is probably <1.23 m.y. Polarity chron C23r spans 0.53 m.y., chron C23n is 0.74 m.y., and chron C22r is 0.9 m.y. Spectral analysis through this interval indicates that spectral peaks shift through time and are related to changes in sedimentation rate in Site 1051. The sedimentation rates dramatically increased ~200 k.y. after the IETM and remained high for most of chron C24r.

Lipid biomarkers in urface sediments of the Southeast Atlantic

Surface sediments from the eastern South Atlantic were investigated for their lipid biomarker contents and bulk organic geochemical characteristics to identify sources, transport pathways and preservation processes of organic components. The sediments cover a wide range of depositional settings with large differences in mass accumulation rates. The highest marine organic carbon (OC) contributions are detected along the coast, especially underlying the Benguela upwelling system. Terrigenous OC contributions are highest in the Congo deep-sea fan. Lipid biomarker fluxes are significantly correlated to the extent of oxygen exposure in the sediment. Normalization to total organic carbon (TOC) contents enabled the characterization of regional lipid biomarker production and transport mechanisms. Principal component analyses revealed five distinct groups of characteristic molecular and bulk organic geochemical parameters. Combined with information on lipid sources, the main controlling mechanisms of the spatial lipid distributions in the surface sediments are defined, indicating marine productivity related to river-induced mixing and oceanic upwelling, wind-driven deep upwelling, river-supply of terrigenous organic material, shallow coastal upwelling and eolian supply of plant-waxes.

Hydrogen and oxygen isotopes in ground lce of Bykovsky Peninsula, North Siberia

In wide areas of Northern Siberia, glaciers have been absent since the Late Pleistocene. Therefore, ground ice and especially ice wedges are used as archives for paleoclimatic studies. In the present study, carried out on the Bykovsky Peninsula, eastern Lena Delta, we were able to distinguish ice wedges of different genetic units by means of oxygen and hydrogen isotopes. The results obtained by this study on the Ice Complex, a peculiar periglacial phenomenon, allowed the reconstruction of the climate history with a subdivision of a period of very cold winters (60-55 ka), followed by a long stable period of cold winter temperatures (50-24 ka), Between 20 ka and I I ka, climate warming is indicated in stable isotope compositions, most probably after the Late Glacial Maximum. At that time, a change of the marine source of the precipitation from a more humid source to the present North Atlantic source region was assumed. For the Ice Complex, a continuous age-height relationship was established, indicating syngenetic vertical ice wedge growth and sediment accumulation rates of 0.7 m/ky. During the Holocene optimum, ice wedge growth was probably limited due to the extensive formation of lacustrine environments. Holocene ice wedges in thermokarst depressions (alases) and thermoerosional valleys (logs) were formed after climate deterioration from about 4.5 ka until the present. Winter temperatures were warmer at this time as compared to the cooler Pleistocene. Migration of bound water between ice wedges and segregated ice may have altered the isotopic composition of old ice wedges. The presence of ice wedges as diagnostic features for permafrost conditions since 60 ka, implies that a large glacier extending over the Laptev Sea shelf did not exist. For the remote non-glaciated areas of Northern Siberia, ice wedges were established as a powerful climate archive.