Applicability of the Long Chain Diol Index (LDI) as a Sea Surface Temperature Proxy in the Arabian Sea

The long-chain diol index (LDI) is a relatively new proxy for sea surface temperature (SST) which has been rarely applied in upwelling regions. Here, we evaluated its application by comparison with other SST records obtained by commonly used proxies, that is, the Mg/Ca ratio of the planktonic foraminifera species Globigerinoides ruber and the alkenone paleothermometer U-37(K '). We focused on the last glacial-interglacial transition of four different sedimentary archives from the western and northern Arabian Sea, which are currently under the influence of monsoon-induced upwelling and the associated development of an oxygen minimum zone. The UK ' 37 ${{\mathrm{U}}{\mathrm{K}\prime }}_{37}$ and Mg/Ca-G.ruber SST records revealed an increase of 0.6-3.4 degrees C from the Last Glacial Maximum to the late Holocene with somewhat higher amplitude in the northern part of the Arabian Sea than compared to the western part. In contrast, the LDI SSTs did not reveal major changes during the last glacial-interglacial transition which was followed by a decreasing trend during the Holocene. The LGM versus the Holocene LDI SSTs ranged between -0.2 and -2.7 degrees C. Particularly at one record, offshore Oman, the SST decrease during the Holocene was high in amplitude, suggesting a potential cold bias, possibly related to changes in upwelling intensity. This indicates that care has to be taken when applying the LDI for annual mean SST reconstruction in upwelling regions

Ablagerung und Fruehdiagenese organischen Materials in marinen Hochproduktivitaetsgebieten

Das Ziel der vorliegenden Arbeit war es, das organische Material in Auftriebsedimenten, das im Rahmen des 'Ocean Drilling Programs' waehrend der Legs 112 (Sites 679, 681 und 688) und 117 (Sites 720, 723 und 724) an den Kontinentalhaengen vor Peru und Oman erbohrt wurde, mittels eines interdiziplinaeren Ansatzes geochemisch und mikroskopisch zu charakterisieren. Vergleichend wurden oberflaechennahe Proben aus dem Hochproduktivitaetsgebiet vor der Kueste Pakistans im noerdlichen Arabischen Meer analysiert. Die Untersuchungen sollten dazu beitragen, die Herkunftsgeschichte des sedimentaeren organischen Materials in solchen marinen Hochproduktivitaetszonen zu klaeren und diese in ein Ablagerungsmodell zu integrieren bzw. Ablagerungsmechanismen aufzuzeigen. (orig./SR)This study incorporates a detailed interdisciplinary approach involving geochemistry and microscopy to characterise organic matter in upwelling sediments along the continental margins of Peru and Oman. The sediments were drilled during 'Ocean Drilling Program (ODP)'-Leg 112 (Sites 679, 681 and 688) and Leg 117 (Sites 720, 723 and 724), respectively. In addition samples from a high productivity area off Pakistan in the northern Arabian Sea were included to enable a comparison. The purpose of these investigations were to provide an insight into the origin of sedimentary organic matter in marine high productivity areas and subsequently to integrate these findings into sedimentation models and to demonstrate sedimentation processes. (orig./SR)SIGLEAvailable from TIB Hannover: RA 831(3413) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Holocene erosion of the Lesser Himalaya triggered by intensified summer monsoon

Climate is one of the principal controls setting rates of continental erosion. Here we present the results of a provenance analysis of Holocene sediments from the Indus delta in order to assess climatic controls on erosion over millennial time scales. Bulk sediment Nd isotope analysis reveals a number of changes during the late Pleistocene and early Holocene (at 14–20, 11–12 and 8–9 ka) away from erosion of the Karakoram and toward more sediment flux from the Himalaya. Radiometric Ar-Ar dating of muscovite and U-Pb dating of zircon sand grains indicate that the Lesser Himalaya eroded relatively more strongly than the Greater Himalaya as global climate warmed and the summer monsoon intensified after 14 ka. Monsoon rains appear to be the primary force controlling erosion across the western Himalaya, at least over millennial time scales. This variation is preserved with no apparent lag in sediments from the delta, but not in the deep Arabian Sea, due to sediment buffering on the continental shelf