IODP Expedition 347: Baltic Sea Paleoenvironment

        Integrated Ocean Drilling Program Expedition 347 aimed to retrieve sediments from different settings of the Baltic Sea, encompassing the last interglacial–glacial cycle to address scientific questions along four main research themes:

  1.         Climate and sea level dynamics of marine isotope Stage (MIS) 5, including onsets and terminations;
  2.         Complexities of the last glacial, MIS 4–MIS 2;
  3.         Glacial and Holocene (MIS 2–MIS 1) climate forcing; and
  4.         Deep biosphere in Baltic Sea Basin (BSB) sediments.

        These objectives were accomplished by drilling in six subbasins: (1) the gateway of the Baltic Sea Basin (BSB) (Anholt), where we focused on sediments from MIS 6–5 as well as MIS 2–1; (2) a subbasin in the southwestern BSB (Little Belt) that possibly holds a unique MIS 5 record; (3, 4) two subbasins in the south (Bornholm Basin and Hanö Bay) that may hold long complete records from MIS 4–2; (5) a 450 m deep subbasin in the central Baltic (Landsort Deep) that promised to contain a thick and continuous record of the last ~14,000 y; and (6) a subbasin in the very north (Ångermanälven River estuary) that contains a uniquely varved (annually deposited) sediment record of the last 10,000 y.

These six areas were expected to contain sediment sequences representative of the last ~140,000 y, with paleoenvironmental information relevant on a semicontinental scale due to the Baltic Sea draining an area four times as large as the basin itself.

        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: repeated glaciations of different magnitude, sensitive responses to sea level and gateway threshold changes, large shifts in sedimentation patterns, and high sedimentation rates. Its position also makes it a unique link between Eurasian and northwest European terrestrial records. Therefore, the sediments of this largest European intracontinental basin form a rare archive of climate evolution over the last glacial cycle. High sedimentation rates provide an excellent opportunity to reconstruct climatic variability of global importance at a unique resolution from a marine-brackish setting. Comparable sequences cannot be retrieved anywhere in the surrounding onshore regions. Furthermore, and crucially, the large variability (salinity, climate, sedimentation, and oxygenation) that the BSB has undergone during the last glacial cycle makes it optimal for new research on the deep biosphere and its evolution and biogeochemical processes in a changing environment. The BSB also provides a model for how postglacial diffusive penetration of seawater ions has altered the chemical environment and microbial physiology in the subseafloor biosphere.

        It is envisaged that the transect of drilled sites, from west to east and from south to north, in this repeatedly glaciated and environmentally very dynamic region will add totally new scientific insights into a variety of research fields. These involve, for example, regional and global issues on the timing and forcing of rapid climate and sea level changes, on mechanisms behind hypoxia-driven processes in intracontinental sea basins, and on the glacial history of the SIS and its interaction with the climate system. The drilled sites will also give new insight into the controlling mechanisms for prokaryotic communities and underlying biogeochemical processes in the seabed. New data will show how the highly variable environment has affected the phylogenetic diversity of the microbial communities and which biogeochemical processes predominate today in the deep glacial and interglacial deposits. An extraordinary large set of biological, physical (including a variety of dating and paleomagnetic methods), chemical, and biogeochemical methods, as well as a set of novel approaches, have been applied to the drilled sediments.

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