Geochemistry of sediments in the central equatorial Pacific Ocean

In order to quantify changes in export production and carbonate dissolution over the past 1 Myr in the central equatorial Pacific Ocean we analyzed Ba, P, Al Ti, and Ca in 1106 samples from five piston cores gathered from 5°S to 4°N at 140°W. We focused on Ba/Ti, Al/Ti, and P/Ti ratios as export proxies and employed areally integrated time slice as well as time series strategies. Carbonate maxima from 0-560 kyr are characterized by 15-30% greater export than carbonate minima. The increases in export fall on glacial delta18O transitions rather than glacial maxima. From 560-800 kyr, overlapping with the mid-Pleistocene transition, there is a very large increase in total export yet no glacial-interglacial variability. The highest latitudes (5°S and 4°N) record minimal absolute export change from glacials to interglacials and yet record the most extreme minima in percent CaCO3, indicating that carbonate records there are dominated by dissolution, whereas near the equator they are more influenced by changes in export.

Trace element ratios of Globigerina bulloides from the southwest Pacific Ocean

We present Mg/Ca data for Globigerina bulloides from 10 core top sites in the southwest Pacific Ocean analyzed by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Mg/Ca values in G. bulloides correlate with observed ocean temperatures (7°C-19°C), and when combined with previously published data, an integrated Mg/Ca-temperature calibration for 7°C-31°C is derived where Mg/Ca (mmol/mol) = 0.955 * e**(0.068 * T) (r**2 = 0.95). Significant variability of Mg/Ca values (20%-30%) was found for the four visible chambers of G. bulloides, with the final chamber consistently recording the lowest Mg/Ca and is interpreted, in part, to reflect changes in the depth habitat with ontogeny. Incipient and variable dissolution of the thin and fragile final chamber, and outermost layer concomitantly added to all chambers, caused by different cleaning techniques prior to solution-based ICPMS analyses, may explain the minor differences in previously published Mg/Ca-temperature calibrations for this species. If the lower Mg/Ca of the final chamber reflects changes in depth habitat, then LA-ICPMS of the penultimate (or older) chambers will most sensitively record past changes in near-surface ocean temperatures. Mean size-normalized G. bulloides test weights correlate negatively with ocean temperature (T = 31.8 * e**(-30.5*wtN); r**2 = 0.90), suggesting that in the southwest Pacific Ocean, temperature is a prominent control on shell weight in addition to carbonate ion levels.

Abundance and chemical and mineral compositions of nodules from the Pacific Ocean

The monograph highlights extensive materials collected during expeditions of P.P. Shirshov Institute of Oceanology. We consider facial conditions of nodule formation, regularities of their distribution, stratigraphic position, petrography, mineral composition, textures, geochemistry of nodules and hosting sediments. Origin of iron-manganese nodules in the Pacific Ocean is considered as well.

Rare earth and other chemical element contents and partitions in bottom sediments, micronodules, and nodules from the bioproductive zone of the Pacific Ocean

Concentrations and compositions of rare earth elements (REE) in three micronodule fractions (50-250, 250-500, and >500 ?m), coexisting macronodules, and host sediments were studied. Samples were collected at three sites (Guatemala Basin, Peru Basin, and northern equatorial Pacific) located in elevated bioproductivity zones of surface waters. Influence of micronodule size is dominant for REE compositions and subordinate for REE concentrations. For example, Ce concentration inversely correlates with micronodule size and drops to the lowest value in macronodules and host sediments. Decrease of Ce concentration is generally accompanied by Mn/Fe increase in micro- and macronodules. Hence, the role of diagenetic source of material directly correlates with micronodule sizes. Contribution of the diagenetic source is maximal for macronodules. REE composition distinctions for micronodules and macronodules can be attributed to variations of hydrogenic iron oxyhydroxides and diagenetic (hydrothermal) iron hydroxophosphates that are the major REE carriers in ferromanganese ore deposits. Relationship and general trend in chemistry of coexisting macronodules suggest that they can represent products of the initial stage of nodule formation.

Geochemistry of volcaniclastites of the western Pacific Ocean

Samples collected from the coarse basal portions of mid-Cretaceous volcaniclastic turbidites from the Mariana and Pigafetta basins are remarkably similar in terms of the petrographic and chemical features of their igneous clasts and bulk rock composition. Clasts of magmatic origin are dominated by glassy vesicular shards, variably phyric, holocrystalline basalts, and crystal fragments (olivine, clinopyroxene, plagioclase, amphibole, and biotite). The composition of the pyroxenes and amphiboles are typical of those found in differentiated hydrous alkali basalts. The bulk chemical composition of the volcaniclastites (based on stable incompatible elements and their ratios in highly vitric samples) is characteristic of alkali basalts found in within-plate oceanic eruptive environments. Miocene volcaniclastites from Site 802 are broadly similar to the Cretaceous samples in terms of clast type and bulk composition, and have also been derived from an oceanic alkali basalt source. The chemistry of the Miocene volcaniclastites differ, however, in having distinctive Zr/Y and Zr/Nb ratios and a more restricted chemical composition. The magmatic products of nearly emergent seamounts within the western Pacific basins appears to have been dominated by alkali basalt volcanism during the mid-Cretaceous and also the Miocene. The highly vitric nature of the Cretaceous and Miocene volcaniclastites, together with the morphology and vesicularity of their shards, suggests that they are the reworked (via mass flow) products of hyaloclastite accumulations produced in a shallow-water eruptive environment, such as that adjacent to nearly emergent seamounts or ocean islands. The association of ooids, reefal debris, and, in rare cases, woody material with the volcaniclastites supports their shallow-water derivation.

(Table 1) Redox potential and chemical element contents in CaCO3 and amorphous silica free matter in surface layer bottom sediments of the Pacific Ocean from Hawaiian Islands to Mexico coast

Distribution of Fe, Mn, P, Ti, Cu, Ni, Co, V, Cr, W, Mo, and As in the surface sediment layer on the section from the Hawaiian Islands to the coast of Mexico (Mexico section) is studied. Contents of all studied elements increase from biogenic-terrigenous sediments off the coast of Mexico to pelagic red clays of the Northeast Basin, and more sharply for mobile elements - Mn, Mo, Cu, Ni, Co, and As. In near Hawaii sediments rich in coarsely fragmented volcanic-terrigenous and pyroclastic material of basaltic composition with high contents of Ti, Fe, V, Cr, W, and P, contents of these elements increase sharply, and contents of Mn, Mo, Ni, Co, and Cu for the same reason decrease sharply in comparison with red clay. Abnormally high contents of Mn, Mo, Cu, Ni, Co, and As in the upper layer of hemipelagic and transition sediments of the Mexico section result from diagenetic redistribution and their accumulation on the surface. Processes of diagenetic redistribution in hemipelagic and transition sediment mass of the Mexico section are more rapid than in similar sediments of the Japan section due lower sedimentation rates and higher initial concentrations of Mn. Basic similarity of element distribution regularities in sediments of Japan and Mexico sections is shown.

Results of a Finite-Element Sea-Ice Ocean Model (FESOM) set-up to study the interannual to decadal variability in the deep-water formation rates

The characteristics of a global set-up of the Finite-Element Sea-Ice Ocean Model under forcing of the period 1958-2004 are presented. The model set-up is designed to study the variability in the deep-water mass formation areas and was therefore regionally better resolved in the deep-water formation areas in the Labrador Sea, Greenland Sea, Weddell Sea and Ross Sea. The sea-ice model reproduces realistic sea-ice distributions and variabilities in the sea-ice extent of both hemispheres as well as sea-ice transport that compares well with observational data. Based on a comparison between model and ocean weather ship data in the North Atlantic, we observe that the vertical structure is well captured in areas with a high resolution. In our model set-up, we are able to simulate decadal ocean variability including several salinity anomaly events and corresponding fingerprint in the vertical hydrography. The ocean state of the model set-up features pronounced variability in the Atlantic Meridional Overturning Circulation as well as the associated mixed layer depth pattern in the North Atlantic deep-water formation areas.