Sea surface temperature reconstruction of sediment core GeoB6518-1

Past hydrological changes in Africa have been linked to various climatic processes, depending on region and timescale. Long-term precipitation changes in the regions of northern and southern Africa influenced by the monsoons are thought to have been governed by precessional variations in summer insolation (Kutzbach and Liu, 1997, doi:10.1126/science.278.5337.440; Partridge et al., 1997, doi:10.1016/S0277-3791(97)00005-X). Conversely, short-term precipitation changes in the northern African tropics have been linked to North Atlantic sea surface temperature anomalies, affecting the northward extension of the Intertropical Convergence Zone and its associated rainbelt (Hastenrath, 1990, doi:10.1002/joc.3370100504, Street-Perrott and Perrott, 1990, doi:10.1038/343607a0). Our knowledge of large-scale hydrological changes in equatorial Africa and their forcing factors is, however, limited (Gasse, 2000, doi:10.1016/S0277-3791(99)00061-X). Here we analyse the isotopic composition of terrigenous plant lipids, extracted from a marine sediment core close to the Congo River mouth, in order to reconstruct past central African rainfall variations and compare this record to sea surface temperature changes in the South Atlantic Ocean. We find that central African precipitation during the past 20,000 years was mainly controlled by the difference in sea surface temperatures between the tropics and subtropics of the South Atlantic Ocean, whereas we find no evidence that changes in the position of the Intertropical Convergence Zone had a significant influence on the overall moisture availability in central Africa. We conclude that changes in ocean circulation, and hence sea surface temperature patterns, were important in modulating atmospheric moisture transport onto the central African continent.

Sea-surface temperature reconstruction of ODP Hole 175-1078C

A prominent feature in the Southeast Atlantic is the Angola-Benguela Front (ABF), the convergence between warm tropical and cold subtropical upwelled waters. At present, the sea-surface temperature (SST) gradient across the ABF and its position are influenced by the strength of southeasterly (SE) trade winds. Here, we present a record of changes in the ABF SST gradient over the last 25 kyr. Variations in this SST contrast indicate that periods of strengthened SE trade-wind intensity occurred during the Last Glacial Maximum, the Younger Dryas, and the Mid to Late Holocene, while Heinrich Event 1, the early part of the Bølling-Allerød, and the Early Holocene were periods of weakened SE trade-winds.

Sulfur compounds in bottom sediments and interstitial waters of the Pacific Ocean to the east of Japan

In near-shore Pacific bottom sediments to the east of Japan unusually high content of free H2S ocurs. H2S resulting from bacterial reduction of sulfates from interstitial waters has a number of derivatives; pyrite dominates among them. Contents of other derivatives of H2S: sulfide sulfur and organic sulfur do not exceed 0,01%, content of organic sulfur does not exceed 0.1%. Due to reduction content of sulfates can reduce to 0,03% S. Capacity of the process of sulfate reduction, estimated by sum of all reduced forms of S - derivatives of H2S, is a function of organic matter content in sediments. Ability of bottom sediments to accumulate free H2S depends on content of reactive forms of Fe. Spatial distribution of reduced forms of S in the studied sediments is considered.

Tab. 1: Mass changes and balances 1982/83 for stakes on the Inland Ice at Päkitsup ilordlia north-east of Jakobshavn

In connection with hydropower investigations in West Greenland mass balance measurements have been carried out 1982/83 on the Inland lce at Päkitsup ilordlia north-east of Jakobshavn. The mass balance was measured at seven stakes drilled into the ice at altitudinal intervals of 200 metres from 300 m to 1500 m a.s.l. The measurements show that mass balance conditions in the Jakobshavn area must have been abnormally positive for the 1982/83 hydrological year.