The Baltic Sea inflow regime at the termination of the Medieval Climate Anomaly linked to North Atlantic circulation

Abstract

Baltic Sea water exchange is primarily governed by atmospheric forcing of the inflow of saline waters by strong westerly winds prevailing over the central North Atlantic and north-western Europe. Our sediment core study uses geochemical element records indicative of phytoplankton and cyanobacterial blooming as well as continent-derived mineral input for reconstructing hydrographic changes in the deeper Baltic Sea basins around AD 1200. An alkenone-based Sea Surface Temperature (SST) reconstruction for the relevant time span, AD 500-1500, is presented for another sediment core obtained from the shallow Isefjord located at the southern coast of the Kattegat at the entrance of the Baltic. At the termination of the Medieval Climate Anomaly at approximately AD 1200, the basin sediment facies and the geochemical records reveal an environmental change indicative of a marked decrease of inflow activity and marine productivity. This change coincides with a SST decrease and recently reported general fall in Kattegat sea level. A comparison with palaeo-climate data from the wider North Atlantic region demonstrates that this regime shift in Baltic Sea water exchange is linked to a large-scale change in ocean and atmosphere circulation from a dominating, positive North Atlantic Oscillation (NAO+) mode to more negative NAO conditions.

Echoes from the Past: A Healthy Baltic Sea Requires More Effort

“…Around a thousand years ago, during the MCA, the SST of the Baltic Sea was approximately the same as today (Kabel et al 2012 ). This is supported by temperature reconstructions in the shallow water coastal environment of the Kattegat (Kuijpers et al 2012 ). Sediment studies reveal that the Medieval Baltic Sea was severely affected by oxygen depletion.…”

Eugen Seibold – a promoter of European marine geology

“…Westman and Sohlenius (1999) and Sohlenius et al (2001) did use diatom analyses and oxygen isotope measurements, to show that the changes from homogeneous to laminated layers coincide with variations in salinity. Recently, findings of Kabel et al (2012) and Kuijpers et al (2012) confirm Seibold's (1965) assumptions about driving forces of salt-water inflow to the Baltic Sea and its variability in time.…”

Sealing economy: Exploring seals as resources in the Åland islands ca. 1100-1700 CE through zooarchaeology and account books

“…One possible reason for the increase of saline water is the Medieval Climate Anomaly, which lasted until ca. 1400 CE (Kuijpers et al, 2012). Saline water can also enter the Baltic Sea if sufficiently long periods of low air pressure and strong westerly winds blow towards the area (Carlsson, 1997: 13).…”