Zhuravleva, Anastasia (2011) Paleoceanographic Reconstruction of Surface Water Characteristics in the Northern North Atlantic During the Holocene and MIS 5 Using Planktic Foraminifera. (Master thesis), State University of St. Petersburg, Russia ; University of Hamburg, St. Petersburg, Russia ; Hamburg, 71 pp.

Text 2011_Zhuravleva-Anastasia_MSc-Thesis.pdf - Accepted Version Restricted to Registered users only Available under License Creative Commons: Attribution-Noncommercial 3.0. Download (2MB) | Contact

Abstract

Paleoceanographic changes of surface water characteristics have been studied in the Nordic Seas during the Holocene and the Eemian warm periods as well as during late phases of preceding glacial periods based on a sediment core from the Iceland Sea. The age model is constrained for the Holocene by three accelerator mass spectrometry (AMS) 14C dates, correlation of some distinct and easily defined age points, obtained from the visual comparison of studied records with NPGRIP core and some tephra markers. The age model for MIS 5e is based on correlation of δ18O record to SPECMAP alongside with tephrochronolgy. Planktic foraminiferal assemblages were analyzed using the >150μm size fraction, foraminiferal δ13C and δ18O stable isotopes were measured on the polar planktic foraminifera N. pachyderma (s) for the Eemian period.
According to high proportions of subpolar planktic forminifera (T. quinqueloba, G. bulloides, B. megastoma) during the late MIS 6, the presence of huge meltwater lids on the shelf of the Norwegian Sea was assumed resulting in deflecting of warm Atlantic water masses from its present circulation pattern towards the Iceland Sea. The proximity of the core to the Arctic and Polar fronts give possibility for their migration reconstruction. Hence, proxy records bear witness to the influence of cold fresh Polar water at the 6/5e boundary. The concomitant T. quinqueloba and B. megastoma (species that have different salinity tolerance) appearance alongside with low δ13C values evidence for subduction of warm and saline Atlantic water under fresh and cold surface water during the early part of the Last Interglacial. The same pattern is observed for the Holocene at about 10 ka cal. BP, corroborated by later T. quinqueloba appearance than G. bulloides, species that reflect Atlantic water masses. Cooling events during the periods of high solar insolation were noted and described in the current study for both interglacials. The observed reservoir ages for 8.2 – cold event is higher, by up to 200 years, than the standard model ocean. This could deflect incursions of Arctic water masses derived from the East Greenland Current to the Iceland Sea. The warmest part of the Holocene occurred in the early part (5.5-8 ka cal. BP) of the interglacial, when the insolation values were still high. In comparison the Last Interglacial 5e – ss warm period occurred with 8 ka delay only towards the end of interglacial when the isolation was low (118-122 ka cal. BP). This time lag could be explained by the huge Saalian ice sheets, inducing meltwater plumes that change the salinity gradients and resulted in easily sea ice formation. The Sea Surface Temperature (SST) reconstructions show similar values for the warmest intervals of the current and last interglacials (5oC and 2.5oC for summer and winter respectively).

Actions (login required)

View Item