Heinz Lange

Atmospheric and Oceanic Circulation Patterns off Northwest Africa During the Past 25 Million Years

The sediments of the eastern Atlantic contain excellent historical records of the patterns of oceanic and atmospheric circulation in the subtropics. This is particularly the case at the low relief northwest African continental margin which favors unrestrained interaction of the land- sea climatic system and which forms a schematic, vertical cross section through the ocean from the equator to Mediterranean latitudes. Our synthesis of the Neogene and Quaternary evolution of paleoenvironments along this margin tries to show that oceans and land respond in a complementary way to global climatic events and mechanisms.

Atmospheric summer circulation and coastal upwelling in the Arabian Sea during the Holocene and the last glaciation

Accumulation rates of biogenic and lithogenic components were studied in 39 turbidite-free, well-dated sediment cores from the northern Indian Ocean to define the proportions of fluvial and eolian input and to reconstruct Quaternary patterns of coastal upwelling. The majority of dust deposited in the western Arabian Sea during the Holocene (about 100 × 106 t yr−1) is advected from Arabia by northwesterly winds, which overlie the low-level southwest monsoon. The glacial increase in dust flux to 160 × 106 t yr−1 culminated in the northern Arabian Sea, most probably due to (i) entrainment of dust, rich in chlorite, dolomite, and lithogenic carbonate in the then-dry Persian Gulf, and (ii) a southward shift of the mean position of the southwest monsoon during glacial summer. This shift is recorded in reduced accumulation rates of biogenic opal and increased rates of marine carbonate off Somalia and Oman. Both the terrigenous and biogenic sediment records show that the northwesterly winds and the southwest monsoon persisted over the last 27,000 yr, as well as the Asian continental summer heat low. However, the glacial seasonal time span of the southwest monsoon season was much reduced, most likely because of a delay in the seasonal onset of the southwest monsoon.

Clay-mineral accumulation rates in the Arabian sea during the late Quaternary

Abstract The regional variations in clay-mineral concentrations in 39 turbidite-free and undisturbed deep-sea sediment cores from the Arabian Sea are compared with distribution patterns of clay-mineral accumulation rates during the Holocene and the last glaciation. Dust plumes from the Red Sea area, Arabia, Mesopotamia, Iran and Pakistan can be traced by accumulation rates of mineral-specific dust loads. During the late Quaternary, the major proportions of aeolo-marine sediments in the western Arabian Sea were derived from Arabia during the summer season. The clay-mineral assemblage in these dust plumes consists of illite, smectite, kaolinite, chlorite and palygorskite, in decreasing order of abundance. The distribution pattern of palygorskite in particular reveals that dust transport from southern Arabia occurs mainly with northwesterly to westerly winds in the mid-troposphere. Dust plumes from Iran and Pakistan, which are characterized by high chlorite content, are dispersed by northwesterly winds over the northwestern Arabian Sea. Dust contributions from the Red Sea area, which are rich in smectite and characterized by the occurrence of amphiboles, are transported to the Gulf of Aden. The amount of dust related to northeast monsoon winds during the winter season appears to be negligible when compared to the proportions borne on other dust-bearing winds. In addition to aeolian contributions we distinguish two fluvial contributions: a chlorite-, illite-, kaolinite- and quartz-rich assemblage from Oman and Pakistan into the Gulf of Oman, and a smectite-rich assemblage which is dominant off southern India, originating from rivers that drain the Indian subcontinent. The significant difference between the Holocene and glacial accumulation rates of wind-transported clay minerals consist in the higher abundance of quartz, illite and chlorite in the northwestern Arabian Sea during the last glaciation. This pattern indicates intensified dust contributions by northwesterly winds from the Persian Gulf area, which was dry during glacial times.

Implications of a connection between clay mineral variations and coarse grained debris and lithology in the central Norwegian-Greenland Sea

Abstract A sediment core from the central Norwegian-Greenland Sea has been studied for sedimentary features and clay mineral composition. During numerous events within isotope stage 6 relatively high contents of kaolinite as well as a distinctive dropstone association, originating from the Barents Shelf, were rafted to the southwest by rapidly melting ice, causing the formation of dark diamictons. The strong variations in the smectite content in glacial periods were controlled mainly by ice transport rather than by current transport; the main source area is the shelf of the Faeroe Islands.

Clay mineral distribution in surface sediments of the Laptev Sea : indication for sediment provinces, dynamics and sources

Forty-eight surface sediment samples from the Laptev Sea taken during the Russian - German expedition Transdrift I in summer 1993 were analysed for their clay mineral composition (illite, smectite, chlorite, and kaolinite). Different clay mineral provinces, the role of fluvial sediment-supply, transport mechanisms, and possible source areas are discussed.