Biogenic carbonate and ice-rafted debris (Heinrich layer) accumulation in deep-sea sediments from a Northeast Atlantic piston core

Biogenic carbonate mass accumulation rates show distinct Quaternary glacial-interglacial changes in a mid-latitude Northeast Atlantic deep-sea core. During the last 208 kyr, these were generally higher during interglacials averaging 2.2 g/cm(2) kyr than during glacial periods with a maximum average of 1.2 g/cm(2) kyr. Intervals containing high ice-rafted debris have very low biogenic carbonate accumulation rates. Paleo-primary productivity estimates based on biogenic carbonate accumulation rates are generally higher during interglacials averaging 80 gC/m(2) yr than during glacials which average 49 gC/m(2) yr (maximum estimate). Short intervals with possibly reduced primary productivity correspond to Heinrich layers which are the result of pulses of massive iceberg production and rapid melting in the North Atlantic. We identified thirteen Heinrich layers in isotopic stages 7 to 2. They have calendar ages of about 201, 189, 182-183, 164-167,146-149, 142, 128-131, 64-67, 52-54, 40-43, 29-31, 21 and 15 kyr. These Heinrich layers contain large amounts of ice-rafted debris, including detrital carbonate, low amounts of coccoliths and planktic foraminifera, mainly Neogloboquadrina pachyderma (sinistral). The upper five Heinrich layers are almost barren of coccoliths and the fourth layer is also free of foraminifera. The virtual absence of coccoliths is interpreted to reflect reduced coccolithophorid productivity in the photic zone due to low salinity of surface waters and to blockage of light by ice and suspended materials shed off by melting icebergs. Considering the limited use of other proxies such as organic carbon, diatom and benthic foraminifera due to their very low content/abundance in the sediments, biogenic carbonate mass accumulation rates offer a workable paleo-primary productivity proxy in open-ocean sediments of the carbonate-dominated Northeast Atlantic.