Calcium carbonate contents and carbon and oxygen isotope compositions of bulk carbonate, ODP Leg 165 sediments

Two recently drilled Caribbean sites contain expanded sedimentary records of the late Paleocene thermal maximum, a dramatic global warming event that occurred at ca. 55 Ma. The records document significant environmental changes, including deep-water oxygen deficiency and a mass extinction of deep-sea fauna, intertwined with evidence for a major episode of explosive volcanism. We postulate that this volcanism initiated a reordering of ocean circulation that resulted in rapid global warming and dramatic changes in the Earth's environment.

Chemical and isotopic compositions of groundwaters in the Badain Jaran Desert, Northern China

Despite its extreme aridity the Badain Jaran Desert is rich in groundwater. In the southeastern part of this desert it is characterized by coexistence of high megadunes and a great number of lakes. Deuterium and oxygen 18 isotope compositions as well as hydrochemistry of groundwater, lake water, soil water and river water were investigated in detail to gain an insight into their relationships and the origin of the groundwater. The results show that the groundwater and the lake water are genetically related, but unrelated to local precipitation and the leakage of Heine River at the northern slope of the Qilian mountain. dD and d18O values of deep soil water (deeper than 40 cm) and groundwater plot on the same evaporation line E11, which shows that they have the same recharge source. The point of intersection between E11 and LMWL suggests that the groundwater originates from a water resource, which has a weighted mean value that is lighter by some 6 per mil d18O than local precipitation in Badain Jaran Desert. 3H data of water samples show that the groundwater in the Badain Jaran Desert originates from water recharged after the nuclear test. The deep fault zone underground maybe a water circulation channel based on helium analysis of groundwater. The result has guiding significance to rational exploitation and utilization of the local groundwater.

Mineral and chemical compositions of clay sediments from the Pacific Ocean, DSDP data

Mineral and chemical compositions, as well as conditions of formation of clay sediments in major structural elements of the Pacific Ocean floor with different ages are under consideration in the monograph. Depending on evolution of the region two ways of clay sediment formation are identified: terrigenous and authigenic. It is shown that terrigenous clay sediments predominate in marginal parts of the Pacific Ocean. Authigenic mineral formation occurring in the basal part of the sedimentary cover primarily results from removal of material from underlying basalts. This material is released during secondary alteration of the basalts due to their interaction with sea water, as well as with deep solutions.

Contents and stable carbon isotope compositions of biomarkers indicative for AOM-communities dominated by different ANME groups in two carbonate samples from Hydrate Hole pockmark

Different types of seep carbonates were recovered from the 'Kouilou pockmarks' on the Congo deep-sea fan in approximately 3100 m water depth. The carbonate aggregates are represented by pyritiferous nodules, crusts and slabs, tubes, and filled molds. The latter are interpreted to represent casts of former burrows of bivalves and holothurians. The nodules consisting of high-Mg-calcite apparently formed deeper within the sediments than the predominantly aragonitic crusts and slabs. Nodule formation was caused by anaerobic oxidation of methane dominantly involving archaea of the phylogenetic ANME-1 group, whereas aragonitic crusts resulted from the activity of archaea of the ANME-2 cluster. Evidence for this correlation is based on the distribution of specific biomarkers in the two types of carbonate aggregates, showing higher hydroxyarchaeol to archaeol ratios in the crusts as opposed to nodules. Formation of crusts closer to the seafloor than nodules is indicated by higher carbonate contents of crusts, probably reflecting higher porosities of the host sediment during carbonate formation. This finding is supported by lower d18O values of crusts, agreeing with precipitation from pore waters similar in composition to seawater. The aragonitic mineralogy of the crusts is also in accord with precipitation from sulfate-rich pore waters similar to seawater. Moreover, the interpretation regarding the relative depth of formation of crusts and nodules agrees with the commonly observed pattern that ANME-1 archaea tend to occur deeper in the sediment than members of the ANME-2 group. Methane represents the predominant carbon source of all carbonates (d13C values as low as -58.9 per mil V-PDB) and the encrusted archaeal biomarkers (d13C values as low as -140 per mil V-PDB). Oxygen isotope values of some nodular carbonates, ranging from + 3.9 to + 5.1per mil V-PDB, are too high for precipitation in equilibrium with seawater, probably reflecting the destabilization of gas hydrates, which are particularly abundant at the Kouilou pockmarks.

Average compositions and analyses range for clinopyroxene, olivines, orthopyroxene, and spinel from the MARK area at DSDP Site 45-395A, and ODP Site 153-920

Mineral compositions of residual peridotites collected at various locations in the Mid-Atlantic Ridge south of the Kane transform (MARK area) are consistent with generally smaller degrees of melting in the mantle near the large offset Kane transform than near the other, small offset, axial discontinuities in the area. We propose that this transform fault effect is due to along-axis variations in the final depth of melting in the subaxial mantle, reflecting the colder thermal regime of the ridge near the Kane transform. Calculations made with a passive mantle flow regime suggest that these along-axis variations in the final depth of melting would not produce the full range of crustal thickness variations observed in the MARK area seismic record. It is therefore likely that the transform fault effect in the MARK area is combined with other mechanisms capable of producing crustal thickness variations, such as along-axis melt migration, the trapping of part of the magma in a cold mantle root beneath the ridge, or active mantle upwelling.

Stable carbon isotope compositions and concentrations of biphytanes from IODP Hole 311-U1327C and 311-U1328B

We have investigated the distributions and carbon isotopic compositions of archaeal membrane lipids in gas-hydrate-bearing sediments collected from the northern Cascadia Margin offshore from Vancouver Island (Sites U1327 and U1328) by the R/V JOIDES Resolution during IODP Expedition 311. Archaeal lipid biomarkers, including glycerol dialkyl glycerol tetraethers (GDGTs), tend to become abundant below 100 mbsf (meters below sea floor). Tricyclic biphytane (BP[3]; which is a robust biomarker derived from GDGT), crenarchaeol, and other BPs exhibit d13C values of ca. -20 per mil, and become abundant between 130 and 230 mbsf at Site U1328. In this depth range, concentrations of ammonium and phosphate in interstitial waters also increase, suggesting that a larger population and higher activity of heterotrophic community consisting of crenarchaeota and other archaea decompose the sedimentary organic matter, thereby liberating ammonium and phosphate. Such crenarchaeotic activity can produce other metabolic products such as molecular hydrogen by fermentation of organic matter during diagenesis. Furthermore, near the organic matter decomposition zone (130 to 230 mbsf), a probable methanogen biomarker (13C-depleted BP[1] with d13C values as low as -48.8 per mil) becomes abundant, indicating that methanogens utilize these diagenetic products. The molecular and isotopic distributions of archaeal lipid biomarkers indicate that the archaeal community plays an important role in the biogeochemical cycles of deep-sea sediments, including both methanogenesis and nutrient recycling.

Seawater carbonate chemistry and phytoplankton and eubacterial community compositions in the northwest subarctic Pacific

On-deck CO2-Fe-manipulated incubation experiments were conducted using surface seawater collected from the Western Subarctic Gyre of the NW Pacific in the summer of 2008 to elucidate the impacts of ocean acidification and Fe enrichment on the abundance and community composition of phytoplankton and eubacteria in the study area. During the incubation, excluding the initial period, the mean partial pressures of CO2 in non-Fe-added bottles were 230, 419, 843, and 1124 µatm, whereas those in Fe-added treatments were 152, 394, 791, and 1008 µatm. Changes in the abundance and community composition of phytoplankton were estimated using HPLC pigment signatures with the program CHEMTAX and flow cytometry. A DGGE fingerprint technique targeting 16S rRNA gene fragments was also used to estimate changes in eubacterial phylotypes during incubation. The Fe addition induced diatom blooms, and subsequently stimulated the growth of heterotrophic bacteria such as Roseobacter, Phaeobacter, and Alteromonas in the post-bloom phase. In both the Fe-limited and Fe-replete treatments, concentrations of 19'-hexanoyloxyfucoxanthin, a haptophyte marker, and the cell abundance of coccolithophores decreased at higher CO2 levels (750 and 1000 ppm), whereas diatoms exhibited little response to the changes in CO2 availability. The abundances of Synechococcus and small eukaryotic phytoplankton (<10 µm) increased at the higher CO2 levels. DGGE band positions revealed that Methylobacterium of Alphaproteobacteria occurred solely at lower CO2 levels (180 and 380 ppm) during the post-bloom phase. These results suggest that increases in CO2 level could affect not only the community composition of phytoplankton but also that of eubacteria. As these microorganisms play critical roles in the biological carbon pump and microbial loop, our results indicate that the progression of ocean acidification can alter the biogeochemical processes in the study area.