Silt content of two lake records from the Eifel

A comparison of a last interglacial annually laminated and varve counted maar lake record from the Eifel/Germany, with a laminated lake sediment record from Northern Germany shows, that high resolution cores can be correlated across central Europe by dust/loess content, if the resolution of grain size data is on the order of decades/centuries. Phases of widespread dust dispersal are the same as the cold events in the Greenland ice and North Atlantic sea surface temperature patterns. The first occurrence of dust in Northern Germany and in the Eifel is during the Late Eemian Aridity Pulse (LEAP, Sirocko et al. 2005) which is called C26 in ocean records (McManus, same vol.). This cold and arid event occurred exactly at the time of the last glacial inception at 118 kyr. Vegetation change in Northern Germany and the Eifel is out of phase after the LEAP. A taiga/tundra vegetation charcterizes Northern Germany between the LEAP and C24, whereas at the same time a Carpinus dominated temperate forest spread in the Eifel region, comparable to the Carpinus dominated forests in France (Sánchez Goñi et al., 2005). A drastic cooling, associated with widespread aridity, came with the C24 cold event, when the vegetation of central Europe changed to a tundra or shrub tundra.

Silt grain-size analysis of ODP holes from the western equatorial Atlantic

Grain-size records of the terrigenous and calcareous silt fraction, preservation of planktic foraminifera, and benthic foraminiferal stable-isotope data (delta13C, delta18O values of C. wuellerstorfi) at ODP Site 927 on the Ceará Rise (5°27.7'N, 44°28.8'W), are used to reconstruct variations in the history of bottom current strength, ventilation, and carbonate corrosiveness of deep waters during the time interval from 0.8 to 0.3 Ma. Glacial periods are characterized by generally smaller mean sizes of the terrigenous sortable silt fraction (mean(SS)), lower delta13C values, and poorer preservation of planktic foraminifera compared to interglacials. This indicates lower bottom current speeds, larger nutrient contents and more corrosive deep water. By contrast, larger mean(SS) sizes, higher delta13C values, and well preserved planktic foraminifera indicate strong circulation and a well ventilated deep-water mass during interglacials. The observed changes are most likely related to the weakening and strengthening of circulation of Lower North Atlantic Deep Water (LNADW). Cross-spectral analysis between the mean(SS) and benthic delta18O records reveals that minima in mean(SS) occur about 7.6 k.y. after the maximum in ice volume. This indicates a considerable lag time between ice-shield induced changes in LNADW production and subsequent changes in the velocity of LNADW flow in the western equatorial Atlantic. Striking changes in bottom current speed occur regularly during glacial to interglacial transitions. Extremely fine mean(SS) minima point to an almost complete shutdown of bottom current vigor in response to a cessation of LNADW production caused by an enhanced melt water release during the initial phases of deglaciation. However, each of the fine minima extremes is followed by a rapid shift to very high mean(SS) values that indicate strong bottom currents, and hence, vigorous LNADW flow during the early interglacials. After the onset of glacial Stage 12, generally poorer carbonate preservation and higher variability is registered. This coincides with a global decrease in carbonate preservation during the mid-Brunhes (mid-Brunhes dissolution event). Detailed grain-size analysis of the calcareous fine fraction (<63 µm) revealed a considerable reduction of particles in the fraction from 7 to 63 µm during periods of enhanced dissolution. This indicates a preferential dissolution of larger planktic foraminiferal fragments which leads to an enrichment of coccoliths in the calcareous fine fraction.