Concentration of C2-C6 hydrocarbon gases in dry sediments of ODP Sites 180-1109 and 180-1115

Low molecular weight hydrocarbon (LMWH) distributions were examined in sediments from Sites 1109 and 1115 in the western Woodlark Basin using purge-trap thermal adsorption/desorption gas analysis. A number of different hydrocarbon components >C1, which were not detected during shipboard gas analysis, were detected at both sites using the purge-trap procedure. Concentrations of ethane, propane, and butane remained relatively low (<100 pmol/g) throughout Site 1109 and had no consistent trend with depth. In contrast, the longer-chain components increased in concentration with depth. Hexane concentrations rose to 716 pmol/g at the base of the site with a concomitant increase in both 2-methyl- and 3-methylpentane. At Site 1115, concentrations of ethane, propane, butane, and isobutylene + 1-butene remained low (<60 pmol/g) throughout the site and again had no consistent trend with depth. 2-Methylpentane, 3-methylpentane, and hexane concentrations had a subsurface maximum that coincided with sediments containing abundant plant-rich material. The LMWH downhole profiles plus low in situ temperatures suggest that the LMWH components were formed in situ by low-temperature biological processes. Purge-trap analysis has indicated the presence of some unexpected deep low-temperature bacterial reactions, which demonstrates that further analysis of LMWH may provide valuable information at future Ocean Drilling Program sites.

(Table 2) Concentration of suspended matter and dissolved Mn in water samples above the Mid-Atlantic Ridge rift zone near 29°N

Data on nephelometry, CTD probing, and dissolved manganese obtained during Cruise 34 of R/V Akademik Mstislav Keldysh showed that a multiplume was found over the Mid-Atlantic Ridge rift zone near 29°N. This multiplume comprises plumes of several hydrothermal vents and is separate from the plume of the Broken Spur hydrothermal field. Approximate coordinates were estimated for three vents.

Opal concentration of ODP Leg 178 holes

Neogene to Quaternary records of biogenic opal contents and opal accumulation rates are presented for Sites 1095, 1096, and 1101, which were drilled during Ocean Drilling Program Leg 178 in the Bellingshausen Sea, a marginal sea in the eastern Pacific sector of the Southern Ocean. The opal records in the drift sediments on the continental rise west of the Antarctic Peninsula provide signals of paleoproductivity, although they are influenced by dissolution in the water column and the sediment column. Opal contents at Sites 1095, 1096, and 1101 show similar long-term trends through the Neogene and Quaternary, whereas the opal accumulation rates exhibit marked discrepancies, which are caused by local differences in opal preservation linked to local variations of bottom current-induced supply of lithogenic detritus. We used a regression describing the relationship between opal preservation and sedimentation rate to extract the signal of primary opal deposition on the seafloor in the Bellingshausen Sea from the opal accumulation in the drift deposits. On long-term timescales, the reconstructed opal depositional rates show patterns similar to those of the opal contents and a much better coherency between the different locations on the Antarctic Peninsula continental rise. Therefore, the estimated opal depositional rates are suggested to represent a suitable proxy for paleoproductivity in the drift setting of the Bellingshausen Sea. Supposing that the sea-ice coverage within the Antarctic Zone was the main factor controlling biological productivity in the Bellingshausen Sea, and thus the estimated opal depositional rates on the continental rise, we reconstructed paleoceanographic long-term changes during the Neogene and Quaternary considering the climatic control on regional and global scales. Slightly enhanced opal depositional rates during the late Miocene are interpreted to indicate warmer climatic conditions in the vicinity of the Antarctic Peninsula than at present. The contribution of heat from the Northern Component Water (NCW) into the Southern Ocean seems only to have played a subordinate role during that time. High opal depositional rates during the early Pliocene document a strong reduction of sea-ice coverage and relatively warm climatic conditions in the Bellingshausen Sea. The early onset of the Pliocene warmth points to a positive feedback of regional Antarctic climate on the global thermohaline circulation. A decrease of opal deposition between 3.1 and 1.8 Ma likely reflects sea-ice expansion in response to reduced NCW flow, caused by the onset and intensification of Northern Hemisphere glaciation. Throughout the Quaternary, a relatively constant level of opal depositional rates in the Bellingshausen Sea indicates stable climatic conditions in the Antarctic Peninsula area.