n-fatty acids of shale partings in the Franciscan bedded cherts

Normal saturated fatty acid (n-fatty acid) in marine sediments from coastal and pelagic environments were analyzed. The coastal sediments contain both short-chained n-fatty acids with carbon numbers from 12 to 18 and long-chained acids from 22 to 32, whereas the pelagic sediments contain predominantly short-chained acids. The relative abundance of short-chained to long-chained n-fatty acids, expressed by the molar ratio C16/C26, can be an indicator to assess the depositional environment of sedimentary rocks. The ratio of long-chained n-fatty acids (C22-C32) to the total n-fatty acids also has the potential to discriminate sedimentary environments. The indicators based on the n-fatty acids were applied to the Franciscan bedded cherts. The result shows that the bedded cherts had deposited in continuous environments from the pelagic to the coastal. This is in harmony with the same inference based on major, trace and rare earth elements and normal paraffins.

Age determination and stable isotope record of foraminifera of sediment core SO82_5-2

Surface and deepwater paleoclimate records in Irminger Sea core SO82-5 (59°N, 31°W) and Icelandic Sea core PS2644 (68°N, 22°W) exhibit large fluctuations in thermohaline circulation (THC) from 60 to 18 calendar kyr B.P., with a dominant periodicity of 1460 years from 46 to 22 calendar kyr B.P., matching the Dansgaard-Oeschger (D-O) cycles in the Greenland Ice Sheet Project 2 (GISP2) temperature record [Grootes and Stuiver, 1997, doi:10.1029/97JC00880]. During interstadials, summer sea surface temperatures (SSTsu) in the Irminger Sea averaged to 8°C, and sea surface salinities (SSS) averaged to ~36.5, recording a strong Irminger Current and Atlantic THC. During stadials, SSTsu dropped to 2°-4°C, in phase with SSS drops by ~1-2. They reveal major meltwater injections along with the East Greenland Current, which turned off the North Atlantic deepwater convection and hence the heat advection to the north, in harmony with various ocean circulation and ice models. On the basis of the IRD composition, icebergs came from Iceland, east Greenland, and perhaps Svalbard and other northern ice sheets. However, the southward drifting icebergs were initially jammed in the Denmark Strait, reaching the Irminger Sea only with a lag of 155-195 years. We also conclude that the abrupt stadial terminations, the D-O warming events, were tied to iceberg melt via abundant seasonal sea ice and brine water formation in the meltwater-covered northwestern North Atlantic. In the 1/1460-year frequency band, benthic ?18O brine water spikes led the temperature maxima above Greenland and in the Irminger Sea by as little as 95 years. Thus abundant brine formation, which was induced by seasonal freezing of large parts of the northwestern Atlantic, may have finally entrained a current of warm surface water from the subtropics and thereby triggered the sudden reactivation of the THC. In summary, the internal dynamics of the east Greenland ice sheet may have formed the ultimate pacemaker of D-O cycles.

Petrology and isotope characteristics of basalts from ODP Hole 111-504B

Petrography and isotope geochemical characteristics of H, O, S, Sr, and Nd have been described for basalts recovered from Hole 504B during Leg 111 of the Ocean Drilling Program. The petrographic and chemical features of the recovered basalts are similar to those obtained previously (DSDP Legs 69, 70, and 83); they can be divided into phyric (plagioclase-rich) and aphyric (Plagioclase- and clinopyroxene-rich) basalts and show low abundances of TiO2, Na2O, K2O, and Sr. This indicates that the basalts belong to Group D, comprising the majority of the upper section of the Hole 504B. The diopside-rich nature of the clinopyroxene phenocrysts and Ca-rich nature of the Plagioclase phenocrysts are also consistent with the preceding statement. The Sr and Nd isotope systematics (average 87Sr/86Sr = 0.70267 ± 0.00007 and average 143Nd/144Nd = 0.513157 ± 0.000041) indicate that the magma sources are isotopically heterogeneous, although the analyzed samples represent only the lowermost 200-m section of Hole 504B. The rocks were subjected to moderate hydrothermal alteration throughout the section recovered during Leg 111. Alteration is limited to interstices, microfractures, and grain boundaries of the primary minerals, forming chlorite, actinolite, talc, smectite, quartz, sphene, and pyrite. In harmony with the moderate alteration, the following alteration-sensitive parameters show rather limited ranges of variation: H2O = 1.1 ±0.2 wt%, dD = - 38 per mil ± 4 per mil, d180 = 5.4 per mil ± 0.3 per mil, total S = 562 ± 181 ppm, and d34S = 0.8 per mil ± 0.3 per mil. Based on these data, it was estimated that the hydrothermal fluids had dD and d180 values only slightly higher than those of seawater, the water/rock ratios were as low as 0.02-0.2, and the temperature of alteration was 300°-400°C. Sulfur exists predominantly as pyrite and in minor quantities as chalcopyrite. No primary monosulfide was detected. This and the d34S values of pyrite (d34S = 0.8 per mil) suggest that primary pyrrhotite was almost completely oxidized to pyrite by reaction with hydrothermal fluids containing very little sulfate.

Stable isotope ratios and paleoceanaographic reconstructions from sediment cores 80-548 and 161-978A

Largely continuous millennial-scale records of benthic d18O, Mg/Ca-based temperature, and salinity variations in bottom waters were obtained from Deep Sea Drilling Project Site 548 (eastern Atlantic continental margin south of Ireland, 1250 m water depth) for the period between 3.7 and 3.0 million years ago. This site monitored mid-Pliocene changes in Mediterranean Outflow Water (MOW) documented by continuously high Nd values between -10.7 and -9. Site 978 (Alboran Sea, 1930 m water depth) provides a complementary record of bottom water variability in the westernmost Mediterranean Sea, which is taken to represent MOW composition at its source. Both sites are marked by a singular and persistent rise in bottom water salinities by 0.7-1.4 psu and in densities by ~1 kg m-3 from 3.5 to 3.3 Ma, which is matched by an average 3 °C increase in bottom water temperatures at Site 548. This event suggests the onset of strongly enhanced deep-water convection in the Mediterranean Sea and a related strengthened MOW flow, which implies a major aridification of the Mediterranean source region. In harmony with model suggestions, the enhanced MOW flow has possibly intensified Upper North Atlantic Deep Water formation.

Stable isotope, UK'37, SST, chlorin, alkenone and TOC data of sediment cores GIK17927-2 and GIK17928-3

Upwelling intensity in the South China Sea has changed over glacial-interglacial cycles in response to orbital-scale changes in the East Asian Monsoon. Here, we evaluate new multi-proxy records of two sediment cores from the north-eastern South China Sea to uncover millennial-scale changes in winter monsoondriven upwelling over glacial Terminations I and II. On the basis of U/Th-based speleothem chronology, we compare these changes with sediment records of summer monsoondriven upwelling east of South Vietnam. Ocean upwelling is traced by reduced (UK'37-based) temperature and increased nutrient and productivity estimates of sea surface water (d13C on planktic foraminifera, accumulation rates of alkenones, chlorins, and total organic carbon). Accordingly, strong winter upwelling occurred north-west of Luzon (Philippines) during late Marine Isotope Stage 6.2, Heinrich (HS) and Greenland stadials (GS) HS-11, GS-26, GS-25, HS-1, and the Younger Dryas. During these stadials, summer upwelling decreased off South Vietnam and sea surface salinity reached a maximum suggesting a drop in monsoon rains, concurrent with speleothem records of aridity in China. In harmony with a stadial-to-interstadial see-saw pattern, winter upwelling off Luzon in turn was weak during interstadials, in particular those of glacial Terminations I and II, when summer upwelling culminated east of South Vietnam. Most likely, this upwelling terminated widespread deep-water stratification, coeval with the deglacial rise in atmospheric CO2. Yet, a synchronous maximum in precipitation fostered estuarine overturning circulation in the South China Sea, in particular as long as the Borneo Strait was closed when sea level dropped below -40 m.