Results of the sorting of the mikronekton and zooplankton material sampled by the German Antarctic Expedition 1975/1976

A description is given of the taxa sorted out of the zooplanktion and mikronekton material of the 1st German Antarctic Expedition 1975/76 by the Kiel sorting center. The methods employed in the sorting center are describined in detail. Notes for further use of the material are also given.

Chemical and isotopic compositions of deep-sea carbonate sediments and interstitial waters from DSDP Sites 30-288 and 30-289

Interstitial waters and sediments from DSDP sites 288 and 289 contain information on the chemistry and diagenesis of carbonate in deep-sea sediments and on the role of volcanic matter alteration processes. Sr/Ca ratios are species dependent in unaltered foraminifera from site 289 and atom ratios (0.0012-0.0016) exceed those predicted by distribution coefficent data (~0.0004). During diagenesis Sr/Ca ratios of carbonates decrease and reach the theoretical distribution at a depth which is identical to the depth of Sr isotopic equilibration, where 87Sr/86Sr ratios of interstitial waters and carbonates converge. Mg/Ca ratios in the carbonates do not increase with depth as found in some other DSDP sites, possibly because of diagenetic re-equilibration with interstitial waters showing decreasing Mg(2+)/Ca(2+) ratios with depth due to Ca input and Mg removal by alteration of volcanic matter. Interstitial 18O/16O ratios increase with depth at site 289 to d18O = 0.67? (SMOW), reflecting carbonate recrystallization at elevated temperatures (>/= 20°C), the first recorded evidence of this effect in interstitial waters. Interstitial Sr2+ concentrations reach high levels, up to 1 mM, chiefly because of carbonate recrystallization. However, 87Sr/86Sr ratios decrease from 0.7092 to less than 0.7078, lower than for contemporaneous sea water, showing that there is a volcanic input of strontium at depth. This volcanic component is recorded in the Sr isotopic composition of recrystallized calcites. Isotopic compositions of the unrecrystallized calcites suggests that the rate of increase of the 87Sr/86Sr ratio of sea water with time has been faster since 3 my ago than in the preceding 13 my.

Miocene strontium isotope record of DSDP Hole 30-289

A composite strontium isotopic seawater curve was constructed for the Miocene between 24 and 6 Ma by combining 87Sr/86Sr measurements of planktonic foraminifera from Deep Sea Drilling Project sites 289 and 588. Site 289, with its virtually continuous sedimentary record and high sedimentation rates (26 m/m.y.), was used for constructing the Oligocene to mid-Miocene part of the record, which included the calibration of 63 biostratigraphic datums to the Sr seawater curve using the timescale of Cande and Kent (1992 doi:10.1029/92JB01202). Across the Oligocene/Miocene boundary, a brief plateau occurred in the Sr seawater curve (87Sr/86Sr values averaged 0.70824) which is coincident with a carbon isotopic maximum (CM-O/M) from 24.3 to 22.6 Ma. During the early Miocene, the strontium isotopic curve was marked by a steep rise in 87Sr/86Sr that included a break in slope near 19 Ma. The rate of growth was about 60 ppm/m.y. between 22.5 and 19.0 Ma and increased to over 80 ppm/m.y. between 19.0 and 16 Ma. Beginning at ~16 Ma (between carbon isotopic maxima CM3 and CM4 of Woodruff and Savin (1991 doi:10.1029/91PA02561)), the rate of 87Sr/86Sr growth slowed and 87Sr/86Sr values were near constant from 15 to 13 Ma. After 13 Ma, growth in 87Sr/86Sr resumed and continued until ~9 Ma, when the rate of 87Sr/86Sr growth decreased to zero once again. The entire Miocene seawater curve can be described by a high-order function, and the first derivative (d87Sr/86Sr/dt) of this function reveals two periods of increased slope. The greatest rate of 87Sr/86Sr change occurred during the early Miocene between ~20 and 16 Ma, and a smaller, but distinct, period of increased slope also occurred during the late Miocene between ~12 and 9 Ma. These periods of steepened slope coincide with major phases of uplift and denudation of the Himalayan-Tibetan Plateau region, supporting previous interpretations that the primary control on seawater 87Sr/86Sr during the Miocene was related to the collision of India and Asia. The rapid increase in 87Sr/86Sr values during the early Miocene from 20 to 16 Ma imply high rates of chemical weathering and dissolved riverine fluxes to the oceans. In the absence of another source of CO2, these high rates of chemical weathering should have quickly resulted in a drawdown of atmospheric CO2 and climatic cooling through a reversed greenhouse effect. The paleoclimatic record, however, indicates a warming trend during the early Miocene, culminating in a climatic optimum between 17 and 14.5 Ma. We suggest that the high rates of chemical erosion and warm temperatures during the climatic optimum were caused by an increase in the contribution of volcanic CO2 from the eruption of the Columbia River Flood Basalts (CRFB) between 17 and 15 Ma. The decrease in the rate of CRFB eruptions at 15 Ma and the removal of atmospheric carbon dioxide by increased organic carbon burial in Monterey deposits eventually led to cooling and increased glaciation between ~14.5 and 13 Ma. The CRFB hypothesis helps to explain the significant time lag between the onset of increased rates of organic carbon burial in the Monterey at 17.5 Ma (as marked by increased delta13C values) and the climatic cooling and glaciation during the middle Miocene (as marked by the increase in delta18O values), which did not begin until ~14.5 Ma.