THERMAL STRUCTURE OF DEEP WATER ON GARDAR DRIFT: VARIABILITY IN THE COMPONENTS OF NORTH ATLANTIC DEEP WATER OVER THE PAST 380,000 YEARS

Paleoceanographic studies show a strong link between climate and deep-water variability on orbital as well as millennial time scales. We describe results of stable isotope, carbonate, and trace metal analyses from a core collected on Gardar Drift, 946 km south of Iceland during RV Knorr cruise 166-14. The jumbo piston core (JPC) was collected at 2,700 m water depth in a field of migrating mudwaves. The core was sampled at a down-core spacing of 5 cm, yielding a resolution of ~ 600 yr. We generated a planktonic foraminiferal d18O record and were able to identify marine isotope chronozones (MIC) in the core down to MIC 7. Ages were assigned by correlation to the d18O stack of Lieseki and Raymo (2005). Stable isotope analyses were completed on Globigerina bulloides, a subpolar surface dwelling planktonic foraminifera, and three species of benthic foraminifera: Planulina wuellerstorfi, Cibicidoides kullenbergi, and Hoeglundina elegans. The d18O value in foraminifera reflects the temperature of calcification and the d18O of the water in which the foraminifera grew. Therefore, the difference between benthic and planktonic d18O reveals the intensity of stratification in the water column. The d13C record of benthic foraminifera indicates that Northern Component Water (NCW) usually bathes this site but that Antarctic Bottom Water (AABW) infringes on the site during MIC 2 and is the dominant water mass during MIC 4. Because there can be local variations resulting from water mass switching and precipitation-evaporation changes, the ratio of magnesium to calcium in benthic foraminifera (Planulina wuellerstorfi), a paleotemperature proxy, was also measured. Results from this aspect of research will help to elucidate changes in temperature, salinity and water mass source though this period.