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doi:10.2204/iodp.pr.347.2014

Introduction

The Baltic Sea Basin (BSB) is one of the world’s largest intracontinental basins, occupying 373,000 km² with a drainage area four times this size. Its mean depth is 54 m, although a few relatively deep basins exist (e.g., the Eastern Gotland Basin [248 m] and the Landsort Deep [459 m]) (Fig. F1). The BSB has served as a depositional sink throughout the last several hundred thousand years, and the sediments comprise a unique high-resolution archive of the paleoenvironmental history of the large drainage area, the basin itself, and the neighboring sea areas. The location of the BSB in the heartland of a recurrently waning and waxing ice sheet, the Scandinavian Ice Sheet (SIS), has resulted in a complex development, characteristic of many glaciated regions of the Northern Hemisphere. Repeated glaciations of different magnitudes, sensitive responses to sea level and gateway threshold changes, large shifts in sedimentation patterns, and high sedimentation rates have shaped its development. The geographical location of the BSB also makes it a unique link between the Eurasian and the northwestern European terrestrial records and as such, also serves as a link to North Atlantic marine records and Greenland ice cores. Analyses of terrestrial, marine, and ice archives combined with numerical modeling (e.g., Levine and Bigg, 2008) have shown that North Atlantic Ocean circulation plays an important role in the global climate system, affecting North America and Europe in particular but also closely linked to, for example, the Asian monsoon system (Wang et al., 2001). The position of the BSB roughly halfway between North Atlantic-Greenland and Asia represents a link that preserves the continental response to oceanic forcing. However, long high-resolution marine records showing continental response to this oceanic forcing are scarce. Therefore, the sediments of this largest European intracontinental basin form a unique archive of climate evolution over the last glacial cycle. The high sedimentation rates (100–500 cm/1000 y) of the BSB provide an excellent opportunity to reconstruct climatic variability of global importance at unique resolution from a marine-brackish setting. Some of the sedimentary record can be resolved on interannual timescales, for example, those controlled by changes in Meridional Overturning Circulation (MOC), the North Atlantic Oscillation (NAO), and the Arctic Oscillation (AO). This makes the BSB unique for sampling sediments from the last glacial cycle. Comparable sequences cannot be retrieved anywhere in the surrounding onshore regions. The extreme climatic changes have also had a profound effect on the biota, both in the BSB and in the surrounding terrestrial ecosystems. Shifts between marine, brackish, and fresh water have been accompanied by changes in temperature, oxygen, nutrients, and biological productivity. These large-scale variations in the environment of the BSB have controlled the composition of biotic communities in the past and may be reflected in the buried deposits where the extant deep biosphere controls sediment geochemistry and nutrient cycling.

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