Sedimentology and geochemistry of core GIK23258-2 in the Barents Sea

At the western continental margin of the Barents Sea, 75°N, hemipelagic sediments provide a record of Holocene climate change with a time resolution of 10-70 years. Planktic foraminifera counts reveal a very early Holocene thermal optimum 10.7-7.7 kyr BP, with summer sea surface temperatures (SST) of 8°C and a much enhanced West Spitsbergen Current. There was a short cooling between 8.8 and 8.2 kyr BP. In the middle and late Holocene summer, SST dropped to 2.5°-5.0°C, indicative of reduced Atlantic heat advection, except for two short warmings near 2.2 and 1.6 kyr BP. Distinct quasi-periodic spikes of coarse sediment fraction (with large portions of lithic grains, benthic and planktic foraminifera) record cascades of cold, dense winter water down the continental slope as a result of enhanced seasonal sea ice formation and storminess on the Barents shelf over the entire Holocene. The spikes primarily cluster near recurrence intervals of 400-650 and 1000-1350 years, when traced over the entire Holocene, but follow significant 885-/840- and 505-/605-year periodicities in the early Holocene. These non-stationary periodicities mimic the Greenland-[Formula: See Text]Be variability, which is a tracer of solar forcing. Further significant Holocene periodicities of 230, (145) and 93 years come close to the deVries and Gleissberg solar cycles.

Sea surface temperature reconstruction for Mediterranean Sea samples

Alkenone unsaturation ratios and planktonic delta18O records from sediment cores of the Alboran, Ionian and Levantine basins in the Mediterranean Sea show pronounced variations in paleo-temperatures and -salinities of surface waters over the last 16,000 years. Average sea surface temperatures (SSTs) are low during the last glacial (averages prior to 13,000 years: 11-15°C), vary rapidly at the beginning of the Holocene, and increase to 17-18°C at all sites during S1 formation (dated between 9500 and 6600 calendar years). The modern temperature gradient (2-3°C) between the Mediterranean sub-basins is maintained during formation of sapropel S1 in the Eastern Mediterranean Sea. After S1, SSTs have remained uniform in the Alboran Sea at 18°C and have fluctuated around 20°C in the Ionian and Levantine Basin sites. The delta18O of planktonic foraminifer calcite decreases by 2 per mil from the late glacial to S1 sediments in the Ionian Basin and by 2.8 per mil in the Levantine Basin. In the Alboran Sea, the decrease is 1.7 per mil. Of the 2.8 per mil decrease in the Levantine Basin, the effect of global ice volume accounts for a maximum of 1.05 per mil and the temperature increase explains only a maximum of 1.3 per mil. The remainder is attributed to salinity changes. We use the temperature and salinity estimates to calculate seawater density changes. They indicate that a reversal of water mass circulation is not a likely explanation for increased carbon burial during S1 time. Instead, it appears that intermediate and deep water formation may have shifted to the Ionian Sea approximately 2000 years before onset of S1 deposition, because surface waters were as cold, but saltier than surface water in the Levantine Basin during the Younger Dryas. Sapropel S1 began to form at the same time, when a significant density decrease also occurred in the Ionian Sea.

Age model, isotope analyses, geochemical measurements and grain size analyses of sediment core GeoB9508-5 from the Senegal River Mouth

The influence of the large-scale ocean circulation on Sahel rainfall is elusive because of the shortness of the observational record. We reconstructed the history of eolian and fluvial sedimentation on the continental slope off Senegal during the past 57,000 years. Our data show that abrupt onsets of arid conditions in the West African Sahel were linked to cold North Atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with Heinrich Stadials. Climate modeling suggests that this drying is induced by a southward shift of the West African monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric African Easterly Jet.