The Baltic Sea Basin: its suitability, results, and promise

The Baltic Sea Basin (BSB) proposal addresses four overarching themes:

  1. Climate and sea level dynamics of marine oxygen isotope Stage (MIS) 5, including onsets and terminations,

  2. The complexities of the last glacial (MIS 4–MIS 2),

  3. Glacial and Holocene climate forcing (MIS 2–MIS 1), and

  4. Deep biosphere responses to glacial–interglacial cycles.

These themes will be addressed by the sedimentary records contained within the BSB.

The BSB is one of the world’s largest intracontinental basins, occupying 373,000 km2 and with a drainage area four times its size (Fig. F1). 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]). The BSB has served as depositional sink throughout at least the last several hundred thousand years, and its sediments comprise a unique high-resolution archive of the paleoenvironmental history of the huge drainage area, the basin itself, and 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 developmental history, characteristic for 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.

The BSB’s position also makes it a unique link between the Eurasian and the northwest European terrestrial records and as such also serves as a link to North Atlantic marine records and Greenland ice cores. Analysis 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 seems closely linked to the Asian monsoon system (Wang et al., 2001), for example. The position of the BSB roughly halfway between North Atlantic-Greenland and Asia represents a link that preserves the continental response to these oceanic forcings. These unique factors help explain why 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 resolutions from a marine-brackish setting—some of the sediments can be resolved on interannual timescales—controlled by, for example, 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 and the sole location to achieve these scientific targets, as comparable sequences cannot be retrieved anywhere in the surrounding onshore regions.

Decades of marine geological and geophysical research in the BSB have given us a good understanding of the thickness and distribution of the Quaternary deposits, but no (deep) drilling for scientific purposes has been performed. Our knowledge of the development of the BSB is currently based on short cores as long as 20 m, the majority of which are only half that length or shorter, and regional interpretations mainly based on terrestrial records. Marine geophysical data show, however, that much thicker and apparently undisturbed sediment sequences exist from the last glacial cycle, and until now we have merely scraped the surface of the Baltic’s paleoenvironmental records.

The proposal outlined here addresses many of the main themes in the IODP science plan, particularly “Environmental changes, processes and effects,” such as “External forcing of environmental change,” “Environmental change induced by internal and external processes,” and the initiative on “Rapid climate change.” We will focus on fundamental scientific questions related to the global, hemispheric, and regional paleoenvironmental evolution of the last glacial cycle, especially the climate, glacial, and sea level history.