Composition of sediments from the Arabian Sea

Thirty seven deep-sea sediment cores from the Arabian Sea were studied geochemically (49 major and trace elements) for four time slices during the Holocene and the last glacial, and in one high sedimentation rate core (century scale resolution) to detect tracers of past variations in the intensity of the atmospheric monsoon circulation and its hydrographic expression in the ocean surface. This geochemical multi-tracer approach, coupled with additional information on the grain size composition of the clastic fraction, the bulk carbonate and biogenic opal contents makes it possible to characterize the sedimentological regime in detail. Sediments characterized by a specific elemental composition (enrichment) originated from the following sources: river suspensions from the Tapti and Narbada, draining the Indian Deccan traps (Ti, Sr); Indus sediments and dust from Rajasthan and Pakistan (Rb, Cs); dust from Iran and the Persian Gulf (Al, Cr); dust from central Arabia (Mg); dust from East Africa and the Red Sea (Zr/Hf, Ti/Al). Corg, Cd, Zn, Ba, Pb, U, and the HREE are associated with the intensity of upwelling in the western Arabian Sea, but only those patterns that are consistently reproduced by all of these elements can be directly linked with the intensity of the southwest monsoon. Relying on information from a single element can be misleading, as each element is affected by various other processes than upwelling intensity and nutrient content of surface water alone. The application of the geochemical multi-tracer approach indicates that the intensity of the southwest monsoon was low during the LGM, declined to a minimum from 15,000-13,000 14C year BP, intensified slightly at the end of this interval, was almost stable during the Bölling, Alleröd and the Younger Dryas, but then intensified in two abrupt successions at the end of the Younger Dryas (9900 14C year BP) and especially in a second event during the early Holocene (8800 14C year BP). Dust discharge by northwesterly winds from Arabia exhibited a similar evolution, but followed an opposite course: high during the LGM with two primary sources-the central Arabian desert and the dry Persian Gulf region. Dust discharge from both regions reached a pronounced maximum at 15,000-13,000 14C year. At the end of this interval, however, the dust plumes from the Persian Gulf area ceased dramatically, whereas dust discharge from central Arabia decreased only slightly. Dust discharge from East Africa and the Red Sea increased synchronously with the two major events of southwest monsoon intensification as recorded in the nutrient content of surface waters. In addition to the tracers of past dust flux and surface water nutrient content, the geochemical multi-tracer approach provides information on the history of deep sea ventilation (Mo, S), which was much lower during the last glacial maximum than during the Holocene. The multi-tracer approach-i.e. a few sedimentological parameters plus a set of geochemical tracers widely available from various multi-element analysis techniques-is a highly applicable technique for studying the complex sedimentation patterns of an ocean basin, and, specifically in the case of the Arabian Sea, can even reveal the seasonal structure of climate change.

Physical oceanography, sea-bed photographs and videos of benthos from the Weddell Sea taken with remote operated vehicle CHEROKEE during POLARSTERN cruise ANT-XXIII/8

The marine ecosystem on the eastern shelf of the Antarctic Peninsula was surveyed 5 and 12 years after the climate-induced collapse of the Larsen A and B ice shelves. An impoverished benthic fauna was discovered, that included deep-sea species presumed to be remnants from ice-covered conditions. The current structure of various ecosystem components appears to result from extremely different response rates to the change from an oligotrophic sub-ice-shelf ecosystem to a productive shelf ecosystem. Meiobenthic communities remained impoverished only inside the embayments. On local scales, macro- and mega-epibenthic diversity was generally low, with pioneer species and typical Antarctic megabenthic shelf species interspersed. Antarctic Minke whales and seals utilised the Larsen A/B area to feed on presumably newly established krill and pelagic fish biomass. Ecosystem impacts also extended well beyond the zone of ice-shelf collapse, with areas of high benthic disturbance resulting from scour by icebergs discharged from the Larsen embayments.

Chemical and mineral composition of rocks from the Philippine Sea

The book is devoted to geology of the Philippine Sea floor. This region is studied most extensively among other marginal seas of the Pacific Ocean. Rocks of the sedimentary and basalt layers within this sea have been studied during five legs of D/S Glomar Challenger. International geological expedition on board R/V Dmitry Mendeleev carried out according to the Project ''Ophiolites of Continents and Comparable Rocks of the Ocean Floor''obtained unique collection of rocks from the second and third layers of the ocean crust in the Philippine Sea. The book provides detailed petrographic and geochemical description of igneous and sedimentary formations from the Philippine Sea and compares them with rocks of the continental ophiolite association. An analysis of structure and history of the ocean crust formation in the region is based on all known geological information. The main periods of tectonic movement activation and nature of their manifestations within the sea are shown.

Chemical composition of tephra from the Greenland-Iceland-Norwegian-Sea

Explosive ocean island volcanism in the Greenland-Iceland-Norwegian Sea (GIN Sea) is indicated by marine tephra layers at 10-300 ka. Peaks of explosive volcanism occurred in oxygen isotope stages 8, 7, 5 and 1. The depositional age of the tephra was estimated using the oxygen isotope stratigraphy and dating of marine records. Geochemical analyses of the tephra layers show that all originate from Iceland. Here we report the characteristics of tephra from these major Icelandic events in 30 deep-sea cores from the GIN Sea. Our findings provide constraints on the distribution of tephra from the eruption source. For the Vedde Ash (oxygen isotope stage 1) we estimate a minimum fallout area of 2*10**5 km**2, stretching from central Greenland in the west and southern Sweden in the east, to 71°N in the GIN Sea. The magnitude of the eruption and the regional wind conditions controlled the extent and concentrations of these ash fallout events. Oceanic circulation and differential settling may have affected the distribution and final deposition of ash particles such as bubble wall shards.

Planktic foraminifera isotopes, temperature and d18O of seawater at the central Walvis Ridge for Termination II (MIS 6 to 5), sediment core 64PE-174P13

Salty and warm Indian Ocean waters enter the South Atlantic via the Agulhas leakage, south of Africa. Model simulations and proxy evidence of Agulhas leakage strengthening during glacial terminations led to the hypothesis that it was an important modulator of the Atlantic Ocean circulation. Yet, the fate of the leakage salinity and temperature anomalies remains undocumented beyond the southern tip of Africa. Downstream of the leakage, new paleoceanographic evidence from the central Walvis Ridge (southeast Atlantic) shows that salinity increased at the thermocline, and less so at the surface, during glacial termination II. Thermocline salinity change coincided with higher frequency of Agulhas rings passage at the core location and with salinity maxima in the Agulhas leakage area, suggesting that leakage waters were incorporated in the Atlantic circulation through the thermocline. Hydrographic changes at the Walvis Ridge and in the leakage area display a distinct two-step structure, with a reversal at ca. 134 ka. This matched a wet interlude within the East Asia weak monsoon interval of termination II, and a short-lived North Atlantic warming. Such concurrence points to a Bølling-Allerød-like recovery of the Atlantic circulation amidst termination II, with a northward shift of the Intertropical Convergence Zone and Southern Hemisphere westerlies, and attendant curtailment of the interocean connection south of Africa.

Geochemistry of basalts from the Caribbean Large Igneous Province

Oceanic flood basalts are poorly understood, short-term expressions of highly increased heat flux and mass flow within the convecting mantle. The uniqueness of the Caribbean Large Igneous Province (CLIP, 92-74 Ma) with respect to other Cretaceous oceanic plateaus is its extensive sub-aerial exposures, providing an excellent basis to investigate the temporal and compositional relationships within a starting plume head. We present major element, trace element and initial Sr-Nd-Pb isotope composition of 40 extrusive rocks from the Caribbean Plateau, including onland sections in Costa Rica, Colombia and Curaçao as well as DSDP Sites in the Central Caribbean. Even though the lavas were erupted over an area of ~3*10**6 km**2, the majority have strikingly uniform incompatible element patterns (La/Yb=0.96+/-0.16, n=64 out of 79 samples, 2sigma) and initial Nd-Pb isotopic compositions (e.g. 143Nd/144Ndin=0.51291+/-3, epsilon-Nd i=7.3+/-0.6, 206Pb/204Pbin=18.86+/-0.12, n=54 out of 66, 2sigma). Lavas with endmember compositions have only been sampled at the DSDP Sites, Gorgona Island (Colombia) and the 65-60 Ma accreted Quepos and Osa igneous complexes (Costa Rica) of the subsequent hotspot track. Despite the relatively uniform composition of most lavas, linear correlations exist between isotope ratios and between isotope and highly incompatible trace element ratios. The Sr-Nd-Pb isotope and trace element signatures of the chemically enriched lavas are compatible with derivation from recycled oceanic crust, while the depleted lavas are derived from a highly residual source. This source could represent either oceanic lithospheric mantle left after ocean crust formation or gabbros with interlayered ultramafic cumulates of the lower oceanic crust. High 3He/4He in olivines of enriched picrites at Quepos are ~12 times higher than the atmospheric ratio suggesting that the enriched component may have once resided in the lower mantle. Evaluation of the Sm-Nd and U-Pb isotope systematics on isochron diagrams suggests that the age of separation of enriched and depleted components from the depleted MORB source mantle could have been <=500 Ma before CLIP formation and interpreted to reflect the recycling time of the CLIP source. Mantle plume heads may provide a mechanism for transporting large volumes of possibly young recycled oceanic lithosphere residing in the lower mantle back into the shallow MORB source mantle.

Geochemistry, and Nd- and Pb-isotopic composition of basalts from the upper oceanic crust of the Costa Rica Rift

The DSDP/ODP Hole 504B, drilled in the 5.9 Ma southern flank of the Costa Rica Rift, represents the deepest section through modern ocean floor basaltic basement. The hole penetrates a 570 m thick volcanic zone, a 210 m thick transition zone of volcanic rocks and dykes, and 1056 m of dykes. A representative selection of these basalt types has been investigated with respect to Nd and Pb isotopes. The epsilonNd of the basalts varies from 7.62 to 11.16. This range in the Nd-isotope composition represents about 67% of the total range reported for Pacific MORB. The Pb-isotope composition also shows significant variation, with 206Pb/204Pb varying from 17.90 to 18.82. The isotopic data show that a small volume of enriched mantle existed in the source. The large ranges in isotopic composition in a single drill hole demonstrate the importance of small-scale mantle heterogeneities in the petrogenesis of MORB. Fractional melting and extraction of small magma batches by channelled flow, and small, short-lived crustal magma reservoirs, with limited potential for mixing of the mantle derived magmas, are favored by these isotopic data.