Variability in Sea-Surface Conditions in the North Atlantic-Arctic Gateways during the Last 140,000 Years

Abstract

Three sites from Leg 151 were selected for a study of orbital- and millennial-scale climate variability during the last 140,000 years. This interval, from marine isotope Stage (MIS) 6 to the present, includes the last large climate cycle of the Quaternary. Sites 907, 909, and 910 constitute a transect, roughly north-south, from the Iceland Plateau, through the Fram Strait, to the Yermak Plateau. Sediment cores from these sites were analyzed for the abundance and diversity of planktonic foraminifers and the quantity and composition of ice-rafted debris (IRD). Leg 151 drilling was successful in recovering young sediments. This is best demonstrated in Hole 907A, which has a sedimentation rate of 1.7 cm/k.y., where an 11,000-year-o ld volcanic ash is disseminated at a depth of 0.2 meters below seafloor (mbsf), indicating good recovery of the overlying Holocene section. The last climate cycle in Hole 907A is well defined by faunal assemblages and abundances, which indicate that mild conditions were limited to peak interglacials. Ice-rafted debris is abundant at all other times, although discrete peaks in the ratio of ice-rafted grains to foraminifers, perhaps analogous to the Heinrich events of the North Atlantic, occur only during MIS 2-4 and 6. Site 909 in the Fram Strait has a sedimentation rate of 3.4 cm/k.y., and is characterized by variability in the abundance of ice-rafted debris and clastic rock fragments. Sharp increases in the weight percentage of coarse sediment and the occurrence of detrital coal mark MIS 6, and contrast with the last (MIS 2) glaciation. Site 910 on the Yermak Plateau has a sedimentation rate of 2.7 cm/k.y., and is dominated by detrital sediments. The abundance of coarse sediment remains high with little variation throughout the study interval. Ice-rafted clastic rock fragments are relatively less important on the Yermak Plateau than in the Fram Strait, implying different glacial source areas. The similarity between the last two glacial and interglacial pairs seen on the Iceland Plateau (as in the subpolar North Atlantic) is less evident in our high latitude cores.