Late Pleistocene and Holocene climate forcing on the Baltic Sea
During autumn 2013 the first ever scientific drilling expedition in the Baltic Sea was carried out within the International Ocean Discovery Program IODP Expedition 347, Baltic Sea Paleoenvironment. The Off- and Onshore Science Party consists of 30 specialist scientists from Europe, USA, Japan, China, Australia and New Zeeland, including the Co-chief Scientist Thomas Andrén and siliceous microfossil specialist Elinor Andrén from Södertörn University. This presented project uses the drilled sediments from Expedition 247 and is designed as two integrated sub-projects.
Sub-project 1, "Late Pleistocene climate forcing"
During the course of deglaciation, varved glacial clay was deposited in front of the retreating ice sheet in the Baltic Sea Basin (BSB). This record has been used to date the ice recession and postglacial events; varves are still being deposited in the Ångermanälven River estuary, providing a link to present time. Because of its geographic location, it is possible to use these unique annually laminated (varved) sediment archives to reconstruct atmospheric (e.g., shifts in North Atlantic Oscillation variability) and oceanic (e.g., effects of changes in the strength of the Atlantic Meridional Overturning Circulation) patterns during the Late Glacial.
- To investigate whether there were substantial ice advances into the southernmost BSB, triggered by rapid North Atlantic warming periods, or whether large parts of the BSB were ice-free during most of Marine Isotope Stage (MIS) 3.
- To detect whether there is a solar forcing signal in the melting record of a shrinking ice sheet as recorded in the glacial varve series.
- To document in detail the response of the Scandinavia Ice Sheet to climate variations during Younger Dryas as recorded in a long glacial varve series from the Landsort Deep.
- To establish the first link to correlate the position of the ice margin across the Baltic Basin during the Younger Dryas.
Traditional varve measurement and counting together with 14C dating, pollen analyses, sedimentological and mineralogical investigations will be performed on the varved sequences fromcentral and southern BSB in cooperation with other members of the science party.
- Varve counting and measurements will be carried out using line-scans, XRF-profiles produced during the Onshore Science Party and CAT-scans done on U-profiles, either manually or automatic by an image analysing software and varve diagrams constructed. Correlations between different varve series will be statically confirmed.
Subproject 2, "Holocene climate forcing"
Ever since the time the Baltic basin was first connected to the world’s oceans the water exchange has been driven by climate, both in terms of the amount of freshwater runoff through precipitation in the drainage area, and the large-scale atmospheric pressure gradient which influences the inflow of marine water first through south-central Sweden and later the Danish straits and Öresund. Which of these two processes are dominant, how they act on different time scales, and whether there are time lags or possible control by different phases of the North Atlantic Oscillation (NAO) are not fully understood. Information on long-term natural climate-driven variability in the Baltic Sea ecosystem provides unique data for refining and validating future climate change models and improve predictions for the area.
- To determine the Holocene Baltic inflow history and implication for changing salinity -- How was the paleoceanographic circulation of the Yoldia Sea? Timing of the first marine inflows over the Danish straits/Öresund. When and how were they recorded in the Bornholm Basin and what is the time-lag before they reached the Landsort Deep?
- To identify triggers for high productivity events -- How are the different high primary production events recorded? What are the most important mechanisms for the onset of hypoxic and return to oxic bottom conditions?
- To understand ongoing climate change -- Historical records of sea-ice -- How has the presently recorded climate change altered the diatom assemblage? Is it possible to separate the relative importance of climate versus nutrientsas unique or interactive predictors of environmental change through time?
Traditional siliceous microfossil stratigraphy (mainly diatoms) will be combined with novel approaches in biostratigraphy:
- Apply in detail study microfabric of laminated sediments in which the annual flux cycle has been preserved it will be possible to present models to propose paleoflux scenarios for laminae formation at different time-slices and where different diatom assemblages reflect changing stratification conditions.
- Perform in depth study of Chaetoceros resting spores using Image analysis, methods to separate taxa to species levels will be performed and increase the understanding of paleoceanography and nutrient flux of the Baltic basin.
- Siliceous microfossil paleoproductivity will be inferred using absolute abundance (microspheres) together with analyses of biogenic silica BSi (performed within the Science Party).
- By identifying the proportion ice-living diatoms the historical record of ice cover will be inferred. Variance partitioning using multivariate analysis, will be used on the diatom stratigraphies to find the proportion of variance in the data that can be explained by climate variability through time.
The PhD-project will focus on sub-project 2 using diatom stratigraphy in two unique high-resolution sediment cores from the Baltic proper; Site M0063 in the Landsort Deep and Site M0065 in the Bornholm Basin. The PhD-project will be carried out as a multiproxy study in cooperation with the Science Party of IODP Baltic Sea Expedition 347. The PhD-student will further collaborate with the ongoing project UPPBASER (funded by the Foundation for Baltic and East European Studies 2014-2016) which will disentangle the influence of changed land-use on coastal waters the last 2000 years.