Reconstructing Baltic Sea hypoxia from sediment cores

Abstract

The establishment of hypoxia (oxygen concentrations of <2 ml L−1) and associated dead zones in coastal marine systems is receiving increasing attention. The Baltic Sea may be a good target for extensive research into present-day hypoxia as well as hypoxia throughout the Holocene. While several hypoxic periods in the Baltic Sea have been identified (such as the Holocene Thermal Maximum (HTM) and the Medieval Climate Anomaly (MCA) ), most of these studies use low-resolution records. In this study, hypoxia at F80 in the Baltic Sea and SR5 in the Bothnian Sea has been reconstructed on a high, sub- annual resolution using Laser Ablation-Inductively Coupled Plasma- Mass Spectrometry. Onset of hypoxia in the Baltic Sea requires a complex interplay of several different forcings such as precipitation, internal and external nutrient loading and inflow through the Danish Straits to influence nutrient availability and stratification. Hypoxia during the MCA may have been forced – in part – by anthropogenic influences. Anthropogenic influences on modern hypoxia are virtually certain. Correlations with climatic records throughout Europe show the important role of large-scale multi-decadal climatic variability such as the North Atlantic Oscillation.