Element and Sr isotope composition of interstitial waters in sediments of ODP Leg 129

Interstitial water samples from Leg 129, Sites 800, 801, and 802 in the Pigafetta and Mariana basins (central western Pacific), have been analyzed for major elements, B, Li, Mn, Sr, and 87Sr/86Sr. At all sites waters show enrichment in Ca and Sr and are depleted in Mg, K, Na, SO4, B, alkalinity, and 87Sr compared to seawater. These changes are related to alteration of basaltic material into secondary smectite and zeolite and recrystallization of biogenic carbonate. Water concentration depth profiles are characterized by breaks due to the presence of barriers to diffusion such as chert layers at Sites 800 and 801 and highly cemented volcanic ash at Site 802. In Site 800, below a chert layer, concentration depth profiles are vertical and reflect slight alteration of volcanic matter, either in situ or in the upper basaltic crust. Release of interlayer water from clay minerals is likely to induce observed Cl depletions. At Site 801, two units act as diffusion barrier and isolate the volcaniclastic sediments from ocean and basement. Diagenetic alteration of volcanic matter generates a chemical signature similar to that at Site 800. Just above the basaltic crust, interstitial waters are less evolved and reflect low alteration of the crust, probably because of the presence in the sediments of layers with low diffusivities. At Site 802, in Miocene tuffs, the chemical evolution generated by diagenetic alteration is extreme (Ca = 130 mmol, 87Sr/86Sr = 0.7042 at 83 meters below seafloor) and is accompanied by an increase of the Cl content (630 mmol) due to water uptake in secondary hydrous phases. Factors that enhance this evolution are a high sediment accumulation rate, high cementation preventing diffusive exchange and the reactive composition of the sediment (basaltic glass). The chemical variation is estimated to result in the alteration of more than 20% of the volcanic matter in a nearly closed system.

Geochemistry and provenance of basaltic clasts within volcaniclastic debris flows at DSDP Site 89-585

Pebble-sized basaltic and glassy clasts were extracted from seamount-derived volcaniclastic debris flows and analyzed for various trace elements, including the rare earths, to determine their genetic relationships and provenance. All the clasts were originally derived from relatively shallow submarine lava flows prior to sedimentary reworking, and have undergone minor low-grade alteration. They are classified into three petrographic groups (A, B, and C) characterized by different phenocryst assemblages and variable abundances and ratios of incompatible elements. Group A (clast from Hole 585) is a hyaloclastite fragment which is olivine-normative and distinct from the other clasts, with incompatibleelement ratios characteristic of transitional or alkali basalts. Groups B and C (clasts from Hole 585A) are quartz-normative, variably plagioclase-clinopyroxene-olivine phyric tholeiites, all with essentially similar ratios of highly incompatible elements and patterns of enrichment in light rare earth elements (chrondrite-normalized). Variation within Groups B and C was governed by low-pressure fractionation of the observed phenocryst phases, whereas the most primitive compositions of each group may be related by variable partial melting of a common source. The clasts have intraplate chemical characteristics, although relative to oceanic hot-spot-related volcanics (e.g., Hawaiian tholeiites) they are marginally depleted in most incompatible elements. The source region was enriched in all incompatible elements, compared with a depleted mid-ocean-ridge basalt source.

Geochemistry at DSDP Leg 55 Holes

The tops of the Emperor chain guyots, which were drilled during Leg 55, lie above the carbonate compensation depth (CCD), as well as above the foraminiferal dissolution level, i.e., lysocline. They are therefore the sites of accumulation of pelagic foraminiferal nannofossil ooze, such accumulation having taken place here since the moment of the seamounts' subsidence and the termination of shallow-water carbonate accumulation which was formerly developed on their tops. But the existence of strong bottom currents over the tops and slope scarps limits, and at some places reduces to zero, sedimentation of any pelagic particles. At such areas there are formed thick iron-manganese crusts. The seamounts drilled on Leg 55 are within the northern (Boreal) belt of biogenic silica accumulation, which existed in the northern Pacific throughout the Neogene. This circumstance presupposes a possible enrichment of the relatively fine-grained sediments with biogenic silica - diatoms and radiolarians.

Geochemical composition of surface snow, ice and debris from glaciers in Norway, Nepal and New Zealand

Alpine glacier samples were collected in four contrasting regions to measure supraglacial dust and debris geochemical composition. A total of 70 surface glacier ice, snow and debris samples were collected in 2009 and 2010 in Svalbard, Norway, Nepal and New Zealand. Trace elemental abundances in snow and ice samples were measured via inductively coupled plasma mass spectrometry (ICP-MS). Supraglacial debris mineral, bulk oxide and trace element composition were determined via X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF). A total of 45 elements and 10 oxide compound abundances are reported. The uniform data collection procedure, analytical measurement methods and geochemical comparison techniques are used to evaluate supraglacial dust and debris composition variability in the contrasting glacier study regions. Elemental abundances revealed sea salt aerosol and metal enrichment in Svalbard, low levels of crustal dust and marine influences to southern Norway, high crustal dust and anthropogenic enrichment in the Khumbu Himalayas, and sulfur and metals attributed to quiescent degassing and volcanic activity in northern New Zealand. Rare earth element and Al/Ti elemental ratios demonstrated distinct provenance of particulates in each study region. Ca/S elemental ratio data showed seasonal denudation in Svalbard and Norway. Ablation season atmospheric particulate transport trajectories were mapped in each of the study regions and suggest provenance pathways. The in situ data presented provides first order glacier surface geochemical variability as measured from four diverse alpine glacier regions. This geochemical surface glacier data is relevant to glaciologic ablation rate understanding as well as satellite atmospheric and land-surface mapping techniques currently in development.

Phosphorus components, CaCO3 and biogenic opal in sediments from ODP Leg 167 sites

The ocean history of reactive phosphorus (P) (i.e., dissolved P available to fuel oceanic primary productivity) is of interest because of the role of P as a biolimiting nutrient, and knowledge of P burial in marine sediments is key to testing hypotheses about temporal changes in P input or output fluxes. Our understanding of the history of the P cycle over the Cenozoic has increased substantially with temporal records of reactive P mass accumulation rates from open-ocean Pacific and Atlantic equatorial sites. However, questions about the relative importance of nutrient burial in ocean-margin sediments relative to burial in open-ocean sediments and about the extent of P remobilization in organic-rich, reducing environments characteristic of margin sediments remain unresolved. Nutrient burial in oceanic boundary current systems has been suggested to have a controlling role in oceanic nutrient budgets in certain time intervals (Vincent and Berger, 1985, doi:10.1029/GM032p0455), with higher sediment accumulation rates balancing the limited spatial extent of these sediments. Some investigators suggest that remobilization of P from reducing sediments in margin settings is a significant positive feedback to primary productivity (e.g., Van Cappellan and Ingall, 1994, doi:10.1029/94PA01455), whereas other results indicate that both P uptake and P release may occur in these settings depending on the balance of organic carbon and iron supply to the sediments and on the oxygenation of bottom waters (McManus et al., 1997, doi:10.1016/S0016-7037(97)00138-5). It is important to quantitatively understand the geochemistry of reactive P in margin sediments, where productivity and delivery of organic-rich material to the sediments in relatively shallow-water settings is often sufficient to promote anoxia in interstitial waters. To address these questions, we determined the P concentrations and geochemistry in sediment samples from eight sites drilled during Ocean Drilling Program (ODP) Leg 167, California margin (Sites 1010-1012, 1014, 1016-1017, and 1021-1022). These results are the first records of reactive P concentrations on long time scales-required for the calculation of P accumulation rates-for sediments from a highly productive eastern boundary current setting. In addition, we determined calcium carbonate contents and biogenic silica concentrations to define the environments of sedimentary production, burial, and diagenesis.