M. Klas

Provenance of Heinrich layers in core V28-82, northeastern Atlantic: 40Ar/39Ar ages of ice-rafted hornblende, Pb isotopes in feldspar grains, and Nd–Sr–Pb isotopes in the fine sediment fraction

Abstract Several correlatable layers of sediment, rich in ice rafted grains, have been documented in the North Atlantic. The most notable within the last glacial cycle are the Heinrich layers, layers extremely rich in ice rafted detritus and generally barren of foraminifera within the North Atlantic ice rafted detritus (IRD) belt. The view of these layers is that they represent events where great armadas of icebergs were launched into the North Atlantic. The importance of the Heinrich layers lies in their connection with abrupt climate change in the North Atlantic, and perhaps globally. There is a growing number of published provenance studies of the Heinrich layers in the North Atlantic, based on a variety of methods. However, there is little overlap of methods applied to the same samples. In this contribution, we present a multi-component provenance study of Heinrich layers H1, H2, H4 and H5 from core V28-82 in the eastern North Atlantic. Our results indicate that virtually the entire inventory of terrigenous clastic detritus in Heinrich layers H2, H4 and H5 came from ancient continental sources surrounding the Labrador Sea. Although Heinrich layer H1 is similar in many respects, it appears to have some significant differences relative to the other three.

Provenance change coupled with increased clay flux during deglacial times in the western equatorial Atlantic

Abstract In the western tropical Atlantic, decreases in the percentage of calcium carbonate in marine sediments are concurrent with increases in clay accumulation rates. In cores with records of percent carbonate extending well back into the Pleistocene, a series of low-calcium carbonate events can be seen. Existing 14C geochronology allows the timing of the uppermost low-carbonate event to be constrained to the last deglacial interval and suggests a relatively short duration between about 16 and 14 ka BP (14C), although more dating is needed to confirm the time limits. The bulk compositional changes of the upper low-calcium carbonate zones correspond to changes in clay mineralogy and in Sr isotope composition of the detrital clay fractions. In four cores the kaolinite/chlorite ratio varies systematically along a 1800 km NW–SE transect, starting with low kaolinite/chlorite and low 87Sr/86Sr ratios at the west end of the Vema fracture zone (core RC16-55) and ending with high kaolinite/chlorite and high 87Sr/86Sr ratios at the west end of the Romanche fracture zone (core V26-99). The kaolinite/chlorite ratio and Sr isotopic compositions from several samples in these cores also show a positive co-variation. The changes in composition within the low-carbonate interval correspond to changes in contributions of young, relatively unweathered (Amazon) and old, highly weathered (Rio Sao Francisco) sources. The provenance pattern allows that this pulse of clay deposition is reasonably interpreted to be a climate signal that could represent increased rainfall in tropical South America during the deglaciation, consistent with published oxygen isotope data from the Amazon fan. However, there are published carbonate records from near Africa that appear to show a correlative clay-rich layer. Thus, an alternative hypothesis is that the gray clay layer could reflect a plume of sediment stirred up from the shelf break during sea level rise associated with deglaciation.