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Falkje van Wirdum

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Falkje van Wirdum
Doctoral Student
Alfred Nobels allé 7
Södertörns Högskola
Flemingsberg
Phone: +46 8 608 4748
MD 473 Moas Båge

Holocene climate forcing on the open Baltic Sea

A high-resolution reconstruction from Landsort Deep sediments

Ever since the connection to the worlds oceans was established through the Öresund and the Danish straits, around 10 000 years ago, the water exchange in the Baltic Sea basin has been driven by climate, both in terms of freshwater runoff through precipitation and the large-scale atmospheric pressure gradient which influences the inflow of marine water. Which of these processes are dominant, how they act on different timescales and whether there are time lags or possible control by different phases of the North Atlantic Oscillation are not fully understood.

During the Holocene epoch, three major periods of hypoxia have been determined in the open Baltic Sea basin. During ca. 8500 – 4000 yr BP, overlapping the Holocene Thermal Maximum, during ca. 2000 – 800 yr BP, overlapping the Medieval Warm Period, and from 1900 AD to the present.

Changes in the long-term nutrient record of the Baltic Sea basin are directly linked to changes in marine water inflow, stratification, oxygenation, freshwater runoff, and the magnitude and extension of cyanobacterial blooms. The role of climate change versus human impact in driving the utrophication and hypoxia in the present Baltic Sea is not fully understood.

This project aims to investigate the role of climate-driven processes on the open Baltic Sea during the Holocene. The objectives are to determine the history and timing of Holocene Baltic inflows and its implications for changing salinity; to reconstruct the Holocene historical record of ice cover in the open Baltic Sea; to identify triggers and timing of high primary productivity events and return to low productivity throughout the Holocene; and to assess the relative importance of natural climate forcing versus anthropogenic forcing on environmental change of the Baltic Sea.

During IODP Expedition 347 ‘Baltic Sea Paleoenvironment’, sediment cores with extremely expanded laminated Holocene sequences from Landsort Deep, the deepest sub basin in the Baltic Sea basin, have been retrieved.

Diatom analysis will be used to reconstruct changes in salinity, sea-ice, productivity, and to investigate mechanisms behind changes in productivity and Baltic inflows.

Micro fabric analyses of sediments will be carried out to determine the laminas composition and formation in order to assess implications for paleoproductivity, hypoxia, and oceanic nutrient cycling.

In collaboration with the UPPBASER project any synchronicity between the coastal and open Baltic Sea of environmental change will be investigated.

In collaboration with IODP Expedition 347 Science Party Members other sites and proxies will be included, in order to get a comprehensive high-resolution reconstruction of Holocene climate-driven processes in the Baltic Sea.