Age determinations and sedimentology on cores GIK17940 and 184-1144

Sedimentological, geochemical and paleomagnetic records were employed to reconstruct the history of East Asian Monsoon variability in the South China Sea (SCS) on orbital- and millennial-to-sub-decadal time scales. A detailed magnetostratigraphy for the southern central SCS was established as well as a stable isotope stratigraphy for ODP Site 1144 for the last 1.2 million years in the northern South China Sea. Furthermore a volcanic tephra layer from the southern central SCS could be identified as the Youngest Toba Ash, which thus re-presents an important age marker and was used to reconstruct paleo wind directions during the eruption 74 ka. Special attention was paid to the high- and ultrahigh-frequency variability in the last glacial-interglacial cycle and the Holocene, and to a precise age control of climate changes in general.

B, d11B, K and d18O data for altered oceanic crust at DSDP Sites 417/418

Samples of drilled oceanic crust, from DSDP Holes 417A, 417D and 418A and ODP Hole 735B, and oceanic crust from the Oman and Cyprus ophiolites, were analyzed for B contents and d11B. Composite samples from DSDP Holes 417A, 417D and 418A were used to represent the upper 550 m of altered oceanic crustal Layer 2A. Whole-rock samples from the Troodos ophiolite, Cyprus, and the Oman ophiolite were selected to represent crustal Layer 2B dikes. Composite samples from ODP Hole 735B were used to represent crustal Layer 3. The B content of the DSDP composites ranges from 7.2 ppm to 104 ppm and correlates with both d1818O and K, showing that it is a good indicator of the extent of low temperature alteration. The d11B of the DSDP composites varies between -2.5? and 5.4?. The B content of the samples from the Troodos ophiolite ranges from 2.4 ppm to 8.1 ppm; d11B varies from -0.9? to 7.8?. The B content of the Oman ophiolite samples ranges from 5.0 ppm to 11.1 ppm; d11B varies from -1.6? to 16.9?. The B content of the samples from ODP Hole 735B ranges from 1.1 ppm to 7.1 ppm; d11B varies from -4.3? to 24.9?. The general pattern displayed by these samples is one of greatest (and most variable) B enrichment at the top of the crust and least enrichment at the bottom of the section. All of these samples are enriched compared to unaltered MORB, which is believed to have a B content of approximately 0.5 ppm. The d11B values of deeper samples, from Layers 2B and 3, are more variable and generally higher than those from Layer 2A. Boron contents and d11B are not correlated. The data from the DSDP Site 417/418 composites indicate that the d11B of fluid circulating in the upper crust changes only slightly during alteration, increasing by an average of 5.1? with an accompanying decrease in B concentration of 7%. Low temperature alteration appears to be a water-dominated process resulting in minor modification of circulating seawater. A minimum water-rock ratio of 400 is calculated for these samples, implying a minimum low-temperature seawater flux through the upper oceanic crust of 3.4?10**14 l/y. The average B content of altered oceanic crust, as represented by these samples, is 5.2+/-1.7 ppm and the average d11B is 3.4+/-1.1?. This average isotopic composition is measurably different from the apparent average of oceanic sediments, supporting the idea that d11B could be useful for identifying the source(s) of B in island arcs.

Elemental and isotope compositions of lipids, kerogens and asphaltenes from samples of DSDP Hole 41-368

The thermal effects of three (one major and two minor) Miocene diabase intrusions on Cretaceous black shales from DSDP site 41-368 have been analyzed. A concentration gradient was observed, especially for the hydrocarbons, decreasing towards the major intrusion and between the three sills. The thermally-altered samples in the proximity of and between the sills contained elemental sulfur and an excess of thermally-derived pristane over phytane. whereas, the unaltered sediments contained no elemental sulfur, and more phytane than pristane. A maximum yield of the extractable hydrocarbons was observed at a depth of 7 m below the major sill. Two classes of molecular markers were present in this bitumen suite. The first was sesqui-, di- and triterpenoids and steranes. which could be correlated with both terrigenous and autochthonous sources. They were geologically mature and showed no significant changes due to the thermal stress. The second class was found in the altered samples, which contained only polynuclear aromatic hydrocarbons with low alkyl substitution and sulfur and oxygen heterocyclic aromatic compounds. These compounds were derived from pyrolytic reactions during the thermal event. Kerogen was isolated from all of these samples, but only traces of humic substances were present. The H/C, N/C, d13C, d34S and dD all exhibit the expected effects of thermal stress. The kerogen becomes more aromatized and richer in 13C, 34S and D in the proximity of and between the sills. Maturation trends were also measured by the vitrinite reflectance and electron spin resonance, where the thermal stress could be correlated with an elevated country rock temperature and an increased degree of aromaticity. The effects of in situ thermal stress on the organic-rich shales resulted in the generation and expulsion of petroliferous material from the vicinity of the sills.

Geochemistry and stable isotopes of peridotites of ODP Hole 103-637A

A ridge of strongly serpentinized, plagioclase-bearing peridotite crops out at the boundary between the Atlantic oceanic crust and the Galicia continental margin (western Spain). These peridotites, cored at Hole 637A (ODP Leg 103) have been mylonitized at high-temperature, low-pressure conditions and under large deviatoric stress during their uplift (Girardeau et al., 1988, doi:10.2973/odp.proc.sr.103.135.1988). After this main ductile deformation event, the peridotite underwent a polyphase metamorphic static episode in the presence of water, with the crystallization of Ti- and Cr-rich pargasites at high-temperature (800°-900°C) interaction with a metasomatic fluid or alkaline magma. Introduction of water produced destabilization of the pyroxenes and the subsequent development of hornblendes and tremolite at temperatures decreasing from 750° to 350°C. The main serpentinization of the peridotite occurred at a temperature below 300°C, and possibly around 50°C, as a consequence of the introduction of a large amount of seawater, which is suggested by stable isotope (d18O and SD) data. Finally, calcite derived from seawater precipitated in late-formed fractures or locally pervasively impregnated the peridotite at low temperature (~10°C).

Stable isotope ratios of foraminifera from sediment cores off northeastern Brazil

The western South Atlantic boundary currents represent a sensitive system within the global thermohaline circulation (THC). We investigated the impact of deglacial THC changes on the western tropical Atlantic studied in six high resolution sediment cores from the upper continental slope of Brazil. The stratigraphy of the cores is mainly based on 14C AMS dating of monospecific foraminiferal samples. Changes in the upper layer tropical ocean during the deglaciation are inferred from stable oxygen isotope measurements on planktic and benthic foraminifera. Variations in the delta18O residuals are assumed to be mainly temperature related. During the Oldest and Younger Dryas cooling periods, two major deglacial THC disturbances are reported from North Atlantic sediment cores. Concomitant to the repeated THC slowdown, we observe an upper layer warming in the tropical ocean. A reduced northward heat export from the tropical areas during these periods (weak North Brazil Current) is additionally reflected by low meridional gradients in the stable oxygen records. This generally agrees with results from coupled ocean atmosphere models.

Isotopic composition of water in fog, rain, throughfall and stemflow in the Monte Verde, Costa Rica

Fog deposition, precipitation, throughfall and stemflow were measured in a windward tropical montane cloud forest near Monteverde, Costa Rica, for a 65-day period during the dry season of 2003. Net fog deposition was measured directly using the eddy covariance (EC) method and it amounted to 1.2 ± 0.1 mm/day (mean ± standard error). Fog water deposition was 5-9% of incident rainfall for the entire period, which is at the low end of previously reported values. Stable isotope concentrations (d18O and d2H) were determined in a large number of samples of each water component. Mass balance-based estimates of fog deposition were 1.0 ± 0.3 and 5.0 ± 2.7 mm/day (mean ± SE) when d18O and d2H were used as tracer, respectively. Comparisons between direct fog deposition measurements and the results of the mass balance model using d18O as a tracer indicated that the latter might be a good tool to estimate fog deposition in the absence of direct measurement under many (but not all) conditions. At 506 mm, measured water inputs over the 65 days (fog plus rain) fell short by 46 mm compared to the canopy output of 552 mm (throughfall, stemflow and interception evaporation). This discrepancy is attributed to the underestimation of rainfall during conditions of high wind.