Thursday, October 21, 2010, 4:30PM - 5:30PM
Full title: "Holocene subpolar gyre evolution and implications for paleonutrient transport to high latitudes."
Pronounced changes in the water mass properties of the northern North Atlantic have taken place over the last decades and substantial evidence is being provided over the past five years that the observed changes are caused by exchanges between polar water masses and subtropical water masses in the North Atlantic subpolar gyre (SPG). However, mechanisms and implications of SPG are not well understood. By looking at Holocene SPG evolution we can add to our understanding of ongoing and future changes in SPG dynamics.
We present the results of Mg/Ca and Cd/Ca ratios measured on Globigerina bulloides, a planktic foraminifer, from core NEAP4K from Björn Drift in the northern Iceland Basin south of Iceland (61° 29.91 N, 24° 10.33 W, 1627 m water depth), which lies in a critical position to monitor fluctuations in the density and nutrient structure at the eastern SPG boundary. We calculate the temperature from the Mg/Ca ratios in G. bulloides and combine it with δ18Ocalcite to extract the δ18Osw contribution, which covaries with salinity in the upper oceans. Dissolved Cd has a similar distribution as the nutrient phosphate and therefore the Cd/Ca ratios are used as paleonutrient tracers.
We document regime shifts in the water mass characteristics at our study site at ~9.7, 7.7, 6.0, 3.8, 2.6. 1.9, and 0.9 kyr BP. The SPG went generally from more extended modes in the early Holocene to more contracted modes towards the present, except between 7.7 and 6.0, 2.6 and 1.9 and after 0.9 kyr BP when the SPG was extended again. During the extended modes the water masses showed more polar water characteristics and during the contracted modes more subtropical Atlantic water characteristics. Higher nutrient levels at the study site were present during extended SPG modes.