Radiocarbon datings of mollusk shells, sedimentation rates and accumulation rates of sediment matter in core PS2718-6

A bottom sediment core about 8 m long sampled in the eastern Kara Sea near the entrance to the Vil'kitsky Strait was studied. An age model was constructed based on four 14C datings obtained from by thy accelerating mass spectrometry method. Results of grain size, chemical, mineralogical, and foraminiferal analyses were adjusted to the model. A paleoceanological interpretation of these data together with paleoclimatic data on the Bol'shevik Island located in the neighborhood was performed.

Geochemistry and sedimentation rates of ODP Leg 199 sites and of surface sediments in the eastern Pacific ocean

We present the first high-resolution organic carbon mass accumulation rate (MAR) data set for the Eocene equatorial Pacific upwelling region, from Sites 1218 and 1219 of the Ocean Drilling Program. A maximum Corg MAR anomaly appears at 41 Ma and corresponds to a high carbonate accumulation event (CAE). Independent evidence suggests that this event (CAE-3) was a time of rapid cooling. Throughout the Eocene, organic carbon burial fluxes were an order of magnitude lower than fluxes recorded for the Holocene. In contrast, the expected organic carbon flux, calculated from the biogenic barium concentrations for these sites, is roughly equal to modern. A sedimentation anomaly appears at 41 Ma, when both the measured and the expected organic carbon MAR increases by a factor of two-three relative to the background Eocene fluxes. The rain of estimated Corg and barium from the euphotic zone to the sediments increased by factors of three and six, respectively. We suggest that the discrepancy between the expected and measured Corg in the sediments is a direct consequence of the increased metabolic rates of all organisms throughout the Eocene oceans and sediments. This hypothesis is supported by recent work in ecology and biochemical kinetics that recognizes the fundamental basis of ecology as following from the laws of thermodynamics. This dependence is now elucidated as the Universal Temperature Dependence (UTD) "law" of metabolism and can be applied to all organisms over their biologically relevant temperature range. The general pattern of organic carbon and barium deposition throughout the Eocene is consistent with the UTD theory. In particular, the anomaly at 41 Ma (CAE-3) is associated with rapid cooling, an event that triggered slower metabolic rates for all organisms, slower recycling of organic carbon in the water and sediment column, and, consequently, higher deposition of organic carbon in the sediments. This "metabolism-based" scenario is consistent with the sedimentation patterns we observe for both Sites 1218 and 1219.

(Table 1, page 168) Iron, manganese, and phosphorus concentrations in Fe-Mn-concretions from the Gulf of Bothnia, northern Baltic Sea

Fe-Mn-concretions of a spheroidal type were found according to electron probe determinations to consist of alternating iron- and manganese-rich layers. This pattern was ascribed to seasonal variations in the physico-chemical conditions governing the precipitation of the hydrous oxides of iron and manganese. Calculations based on the rhythmic growth of the concretions investigated gave a mean accumulation rate of 0.15-0.20 mm/yr. The rather high phosphorus content (average 3.5 % P2O5) of the concretions was found to be concentrated in the iron-rich layers, probably as a result of the scavenging effect of ferric hydroxide.

Geochemistry of Eocene/Oligocene sediments of ODP Site 177-1090

The Agulhas Ridge, off the tip of Africa between the Atlantic and Indian Oceans, is ideally located to capture the evolution of Paleogene-early Neogene circulation patterns associated with global cooling. Multiproxy records of productivity (biogenic barium (Baex), opal, CaCO3 mass accumulation rates (MARs)), nutrient and organic carbon burial (reactive phosphorus (Pr) MARs), and redox state of deep waters (U enrichment) from Ocean Drilling Program (ODP) Site 1090 reflect hydrographic shifts in this region between the middle Eocene and early Oligocene (~9-33 Ma). Several peaks in increased export productivity and burial of organic matter occurred within the late Eocene (~36.5, ~34, and ~33.7 Ma), which along with surface hydrologic conditions favoring opaline organisms over calcareous organisms could have aided in the draw down of pCO2 to a threshold level that facilitated large ice sheet development on Antarctica in the earliest Oligocene. Our multiproxy approach illustrates the importance of vertical as well as spatial hydrographic reorganization in amplifying or driving climatic cooling of the middle Eocene to early Oligocene by facilitating increases in the relative or absolute burial of organic carbon.

Major and trace element composition of clinopyroxenes from an olivine gabbro of ODP Hole 176-735B (Table 1)

Major and trace element profiles of clinopyroxene grains in oceanic gabbros from ODP Hole 735B have been investigated by a combined in situ analytical study with ion probe, and electron microprobe. In contrast to the homogeneous major element compositions, trace elements (REE, Y, Cr, Sr, and Zr) show continuous core to rim zoning profiles. The observed trace element systematics in clinopyroxene cannot be explained by a simple diffusive exchange between melts and gabbros along grain boundaries. A simultaneous modification of the melt composition is required to generate the zoning, although Rayleigh fractional crystallization modelling could mimic the general shape of the profiles. Simultaneous metasomatism between the cumulate crystal and the porous melt during crystal accumulation is the most likely process to explain the zoning. Deformation during solidification of the crystal mush could have caused squeezing out of the incompatible element enriched residual melts (interstitial liquid). Migration of the melt along grain boundaries might carry these melt out of the system. This process named as synkinematic differentiation or differentiation by deformation (Natland and Dick, 2001, doi:10.1016/S0377-0273(01)00211-6) may act as an important magma evolution mechanism in the oceanic crust, at least at slow-spreading ridges.

(Table 1) Grain size, sedimentation rates and accumulation rates of ODP Hole 152-919A coarse-sand ice-rafted debris

At mid- to high-latitude marine sites, ice-rafted debris (IRD) is commonly recognized as anomalously coarse-grained terrigenous material contained within a fine-grained hemipelagic or pelagic matrix (e.g., Conolly and Ewing, 1970; Ruddiman, 1977, doi:10.1130/0016-7606(1977)88<1813:LQDOIS>2.0.CO;2; Krissek, 1989, doi:10.2973/odp.proc.sr.104.114.1989; Jansen et al., 1990; Bond et al., doi:10.1038/360245a0, 1992; Krissek, 1995, doi:10.2973/odp.proc.sr.145.118.1995). The presence of such ice-rafted material is a valuable indicator of the presence of glacial ice at sea level on an adjacent continent, whereas the composition of the IRD can often be used to identify the location of the source area (e.g., Goldschmidt, 1995, doi:10.1016/0025-3227(95)00098-J). Because the amount of core recovered during Leg 163 was very limited, this shore-based, postcruise study focuses on materials recovered at a nearby site during Leg 152. In particular, this study examines sediments recovered at Site 919; these sediments were described as containing a significant ice-rafted component in the Leg 152 Initial Reports volume (Larsen, Saunders, Clift, et al., 1994, doi:10.2973/odp.proc.ir.152.1994). In this study, the sedimentary section from Site 919 has been examined with the goal of providing a detailed history of glaciations on Greenland and other landmasses adjacent to the Norwegian-Greenland Sea; this history ultimately will be calibrated using an oxygen isotope stratigraphy (Flower, 1998, doi:10.2973/odp.proc.sr.152.219.1998), although that calibration has not been completed at this time. Because ice-core studies of the Greenland Ice Sheet (GIS) have shown that the GIS changed dramatically, and in some cases extremely rapidly, during at least the last interglacial stage (GRIP Members, 1993, doi:10.1038/364203a0), a detailed IRD record from the Southeast Greenland margin should provide insight into the longer term behavior of this sensitive component of the Northern Hemisphere climate system.

Age determinations, biomarker analyses, and accumulation rates of three sediment cores from the Fram Strait

A reconstruction of Holocene sea ice conditions in the Fram Strait provides insight into the palaeoenvironmental and palaeoceanographic development of this climate sensitive area during the past 8,500 years BP. Organic geochemical analyses of sediment cores from eastern and western Fram Strait enable the identification of variations in the ice coverage that can be linked to changes in the oceanic (and atmospheric) circulation system. By means of the sea ice proxy IP25, phytoplankton derived biomarkers and ice rafted detritus (IRD) increasing sea ice occurrences are traced along the western continental margin of Spitsbergen throughout the Holocene, which supports previous palaeoenvironmental reconstructions that document a general cooling. A further significant ice advance during the Neoglacial is accompanied by distinct sea ice fluctuations, which point to short-term perturbations in either the Atlantic Water advection or Arctic Water outflow at this site. At the continental shelf of East Greenland, the general Holocene cooling, however, seems to be less pronounced and sea ice conditions remained rather stable. Here, a major Neoglacial increase in sea ice coverage did not occur before 1,000 years BP. Phytoplankton-IP25 indices ("PIP25-Index") are used for more explicit sea ice estimates and display a Mid Holocene shift from a minor sea ice coverage to stable ice margin conditions in eastern Fram Strait, while the inner East Greenland shelf experienced less severe to marginal sea ice occurrences throughout the entire Holocene.

Geochemistry, grain sizes and radiocarbon age of sediment core Lz1005 from Amery Oasis, East Antarctica

The clay mineralogical composition of a 552 cm long sediment core from Lake Terrasovoje in Amery Oasis, East Antarctica, was analysed and compared with that in surface sediments from other locations in the vicinity. The lower part of the sediment core is formed by sub- and proglacial sediments with a dominance of smectite and illite, and lower amounts of kaolinite and chlorite. The upper part of the core is deposited after 12 500 cal yr bp and mainly composed of illite and kaolinite, with low amounts of smectite and chlorite, such as found in samples from rock outcrops and covering sediments throughout Amery Oasis. The clay composition in the lower section of core Lz1005 suggest that the basin of Lake Terrasovoje was filled by a 150-200 m thickened Nemesis Glacier prior to 12 500 cal yr bp rather than by local ice caps.