IODP expedition 347: Baltic Sea basin paleoenvironment and biosphere

Abstract

Abstract. The Integrated Ocean Drilling Program (IODP) expedition 347 cored sediments from different settings of the Baltic Sea covering the last glacial-interglacial cycle. The main aim was to study the geological development of the Baltic Sea in relation to the extreme climate variability of the region with changing ice cover and major shifts in temperature, salinity, and biological communities. Using the Greatship Manisha as a European Consortium for Ocean Research Drilling (ECORD) mission-specific platform, we recovered 1.6 km of core from nine sites of which four were additionally cored for microbiology. The sites covered the gateway to the North Sea and Atlantic Ocean, several sub-basins in the southern Baltic Sea, a deep basin in the central Baltic Sea, and a river estuary in the north.The waxing and waning of the Scandinavian ice sheet has profoundly affected the Baltic Sea sediments. During the Weichselian, progressing glaciers reshaped the submarine landscape and displaced sedimentary deposits from earlier Quaternary time. As the glaciers retreated they left a complex pattern of till, sand, and lacustrine clay, which in the basins has since been covered by a thick deposit of Holocene, organic-rich clay. Due to the stratified water column of the brackish Baltic Sea and the recurrent and widespread anoxia, the deeper basins harbor laminated sediments that provide a unique opportunity for high-resolution chronological studies.The Baltic Sea is a eutrophic intra-continental sea that is strongly impacted by terrestrial runoff and nutrient fluxes. The Holocene deposits are recorded today to be up to 50 m deep and geochemically affected by diagenetic alterations driven by organic matter degradation. Many of the cored sequences were highly supersaturated with respect to methane, which caused strong degassing upon core recovery. The depth distributions of conservative sea water ions still reflected the transition at the end of the last glaciation from fresh-water clays to Holocene brackish mud. High-resolution sampling and analyses of interstitial water chemistry revealed the intensive mineralization and zonation of the predominant biogeochemical processes. Quantification of microbial cells in the sediments yielded some of the highest cell densities yet recorded by scientific drilling.

Reconstructing Holocene temperature and salinity variations in the western Baltic Sea region: a multi-proxy comparison from the Little Belt (IODP Expedition 347, Site M0059)

“…It cannot be excluded that the foraminiferal tests were still contaminated by the presence of authigenic carbonates like rhodochrosite, which can also contain Mg, and which cannot be removed by the current cleaning methodologies. The occurrence of 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 0 5 10 15 20 25 30 35 40 45 (Huckriede and Meischner, 1996;Andrén et al, 2015b;Hardisty et al, 2016;Van Helmond et al, 2017) and likely also affects foraminiferal tests (Groeneveld and Filipsson, 2013). Remaining contamination is also suggested by the significant correlation coefficient between Mg / Ca and Mn / Ca (r 2 = 0.72) after the oxidation-reduction cleaning.…”

“…The change to more marine conditions in EZ2 (∼ 7400 to ∼ 4100 cal yr BP) occurred quickly, as already implied by Andrén et al (2015b), since most proxies show a rapid decrease or disappearance of freshwater indicators (e.g. diatoms, green algae, ostracods).…”

Contamination tracer testing with seabed drills: IODP Expedition 357

“…Similar approaches were also recently used for platform drilling in the relatively shallow waters of the Baltic Sea on IODP Expedition 347, where PFC tracer was added to drilling muds at the platform prior to injection into the borehole (Andrén et al, 2015).…”

Contamination Control for Scientific Drilling Operations

“…As an example for typical cell abundances, a coastal shallow 69 marine or lacustrine sediment contains between 10 6 to 10 8 cells cm -3 . In very organic-70 rich sediments from upwelling areas or other eutrophic systems, cell abundances are in 71 the 10 9 cells cm -3 range but can reach, or in rare cases even exceed, 10 10 cells cm -3 72 (Andrén et al, 2015). At the other end of the spectrum are deep subsurface sediments, 73 which normally only have cell densities around 10 3 to 10 4 cells cm -3 (e.g.…”