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Changes in the inflow of saline water into the Bornholm Basin (SW Baltic Sea) over the past 7 100 years: evidence from benthic foraminifera record.

Journal article
Authors Anna Binczewska
Matthias Moros
Irina Polovodova Asteman
Małgorzata Bąk
Published in Boreas
Volume in press
ISSN 0300-9483
Publication year 2017
Published at
Language en
Links onlinelibrary.wiley.com/doi/10.1111...
Keywords Elphidium spp., benthic foraminifera, inflow, salinity, Littorina Sea, Baltic Sea
Subject categories Climate Research, Oceanography, Hydrology, Water Resources, Geosciences, Multidisciplinary, Environmental Sciences, Earth and Related Environmental Sciences

Abstract

The Baltic Sea (~393 000 km2) is the largest brackish sea in the world and its hydrographic and environmental conditions are strongly dependent on the frequency of saline water inflows from the North Sea. To improve our understanding of the natural variability of the Baltic Sea ecosystem detailed reconstructions of past saline water inflow changes based on palaeoecological archives are needed. Here we present a high-resolution study of benthic foraminiferal assemblages accompanied by sediment geochemistry (loss on ignition, total organic carbon) and other microfossil data (ostracods and cladocera) from a well-dated 8-m long gravity core taken in the Bornholm Basin. The foraminiferal diversity in the core is low and dominated by species of Elphidium. The benthic foraminiferal faunas in the central Baltic require oxic bottom water conditions and salinities >11–12 PSU. Consequently, shell abundance peaks in the record reflect frequent saline water inflow phases. The first appearance of foraminiferal tests and ostracods in the investigated sediment core is dated to ~6.9 cal. ka BP and attributed to the first inflows of saline and oxygenated bottom waters into the Bornholm Basin during the Littorina Sea transgression. The transgression terminated the Ancylus Lake phase, reflected in the studied record by abundant cladocera. High absolute foraminiferal abundances are found within two time intervals: i) ~5.5–4.0 cal. ka BP (Holocene Thermal Maximum) and ii) ~1.3–0.75 cal. ka BP (Medieval Climate Anomaly). Our data also show three intervals of absent or low saline water inflows: i) ~6.5–6.0 cal. ka BP, ii) ~3.0–2.3 cal. ka BP and iii) ~0.5–0.1 cal. ka BP (Little Ice Age). Our study demonstrates a strong effect of saline and well-oxygenated water inflows from the Atlantic Ocean on the Baltic Sea ecosystem over millennial timescales, which is linked to the major climate transitions over the last 7 ka

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