Reduced Drake Passage through flow during the last glacial and millennial-scale variability

The Antarctic Circumpolar Current (ACC) plays an essential role in the thermohaline circulation and global climate. Today, a large volume of ACC water passes through the Drake Passage, the major geographic constrain for the circumpolar flow. Here we present the first millennial-scale proxy records of Holocene and last glacial variations of the Drake Passage throughflow. Our study reports geochemical, paleomagnetic, and grain-size data from a sediment core retrieved from the upper continental slope off southernmost Chile. The site is located beneath the strong Cape Horn Current that transports northern ACC water towards the Drake Passage. Our data reveal large amplitude changes in current intensity proxy records suggesting pronounced variations in surface and sub-surface flow. We interpret these changes in terms of strongly reduced contributions of northern ACC water to the Drake Passage throughflow during the glacial in general and particularly during millennial-scale cold phases as known from e.g. Antarctic ice-cores. At the same time, advection of northern ACC water into the Humboldt current system was likely enhanced. These results support climate models showing largely reduced volume transport through the Drake Passage during the last glacial maximum and an increasing throughflow during the last deglaciation that affected the strengthening of the Atlantic Meridional Overturning Circulation

Millennial-scale sea surface temperature and Patagonian Ice Sheet changes off southernmost Chile (53 degrees S) over the past similar to 60 kyr

Glacial millennial-scale paleoceanographic changes in the Southeast Pacific and the adjacent Southern Ocean are poorly known due to the scarcity of well-dated and high resolution sediment records. Here we present new surface water records from sediment core MD07-3128 recovered at 53 degrees S off the Pacific entrance of the Strait of Magellan. The alkenone-derived sea surface temperature (SST) record reveals a very strong warming of ca. 8 C over the last Termination and substantial millennial-scale variability in the glacial section largely consistent with our planktonic foraminifera oxygen isotope (delta(18)O) record of Neogloboquadrina pachyderma (sin.). The timing and structure of the Termination and some of the millennial-scale SST fluctuations are very similar to those observed in the well-dated SST record from ODP Site 1233 (41 degrees S) and the temperature record from Drowning Maud Land Antarctic ice core supporting the hemispheric-wide Antarctic timing of SST changes. However, differences in our new SST record are also found including a long-term warming trend over Marine Isotope Stage (MIS) 3 followed by a cooling toward the Last Glacial Maximum (LGM). We suggest that these differences reflect regional cooling related to the proximal location of the southern Patagonian Ice Sheet and related meltwater supply at least during the LGM consistent with the fact that no longer SST cooling trend is observed in ODP Site 1233 or any SST Chilean record. This proximal ice sheet location is documented by generally higher contents of ice rafted debris (IRD) and tetra-unsaturated alkenones, and a slight trend toward lighter planktonic delta(18)O during late MIS 3 and MIS 2