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A high-resolution diatom-based Middle and Late Holocene environmental history of the Little Belt region, Baltic Sea

journal contribution
posted on 25.10.2019 by Jonathan Warnock, Elinor Andren, Stephen Juggins, Jonathan Lewis, David Ryves, Thomas Andren, Kaarina Weckstrom

The large-scale shifts in the salinity of the Baltic Sea over the Holocene are well understood and have been comprehensively documented using sedimentary proxy records. More recent work has focused on understanding how past salinity fluctuations have affected other ecological parameters (e.g. primary productivity, nutrient content) of the Baltic basin, and salinity changes over key events and over short timescales are still not well understood. The International Ocean Drilling Program Expedition 347 cored the Baltic basin in order to collect basin-wide environmental records through a glacial-interglacial cycle. Site M0059 is located in the Little Belt between the Baltic Sea and the Atlantic Ocean. A composite splice section from Site M0059 was analysed at a decadal resolution to study changes in salinity, nutrient conditions and other surface water column parameters based on changes in diatom assemblages and on quantitative diatom-based salinity inferences. A mesotrophic slightly brackish assemblage is seen in the lowermost analysed depths, corresponding to 7, 00 - 7 00 cal. a BP. An increase in salinity and nutrient content of the water column leads into a meso-eutrophic brackish phase. The observed salinity increase is rapid, lasting from 7 f OO to 7 150 cal. a BP. Subsequently, the Little Belt becomes oligotrophic and is dominated by tychopelagic diatoms from c 7f-100 to ·9\ 3/ 00 cal. a BP. This interval contains some of the highest salinities observed followed by diatom assemblages similar to that of the Northern Atlantic Ocean, composed primarily of cosmopolitan open ocean marine diatoms. A return to tychopelagic productivity is seen from 3,_850 to 980 cal. a BP. Anthropogenic eutrophication is detected in the last 300 years of the record which intensifies in the uppermost sediments. These results represent the first decadally-resolved record in the region and provide new insight into the transition to a brackish basin and subsequent ecological development. The large-scale shifts in the salinity of the Baltic Sea over the Holocene are well understood and have been comprehensively documented using sedimentary proxy records. More recent work has focused on understanding how past salinity fluctuations have affected other ecological parameters (e.g. primary productivity, nutrient content) of the Baltic basin, and salinity changes over key events and over short timescales are still not well understood. The International Ocean Drilling Program Expedition 347 cored the Baltic basin in order to collect basin-wide environmental records through a glacial-interglacial cycle. Site M0059 is located in the Little Belt between the Baltic Sea and the Atlantic Ocean. A composite splice section from Site M0059 was analysed at a decadal resolution to study changes in salinity, nutrient conditions and other surface water column parameters based on changes in diatom assemblages and on quantitative diatom-based salinity inferences. A mesotrophic slightly brackish assemblage is seen in the lowermost analysed depths, corresponding to 7, 00 - 7 00 content of the water column leads into a meso-eutrophic brackish phase. The observed salinity increase is rapid, lasting from 7 f OO to 7 150 cal. a BP. Subsequently, the Little Belt becomes oligotrophic and is dominated by tychopelagic diatoms from c 7f-100 to ·9\ 3/ 0 cal. a BP. This interval contains some of the highest salinities observed followed by diatom assemblages similar to that of the Northern Atlantic Ocean, composed primarily of cosmopolitan open ocean marine diatoms. A return to tychopelagic productivity is seen from 3,_850 to 980 cal. a BP. Anthropogenic eutrophication is detected in the last 300 years of the record which intensifies in the uppermost sediments. These results represent the first decadally-resolved record in the region and provide new insight into the transition to a brackish basin and subsequent ecological development

Funding

The Foundation for Baltic and East European Studies (grant 2207/3.1.1/2014)

History

School

  • Social Sciences

Department

  • Geography and Environment

Published in

Boreas: an international journal of quaternary research

Volume

49

Issue

1

Pages

1-16

Publisher

Wiley

Version

AM (Accepted Manuscript)

Rights holder

© Collegium Boreas

Publisher statement

This is the peer reviewed version of the following article: Warnock, Jonathan; Andren, Elinor; Juggins, Stephen; Lewis, Jonathan; Ryves, David; Andren, Thomas; et al. (2019): A high-resolution diatom-based Middle and Late Holocene environmental history of the Little Belt region, Baltic Sea. Boreas, 49(10, pp. 1-16., which has been published in final form at https://doi.org/10.1111/bor.12419. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions

Acceptance date

29/09/2019

Publication date

2019-10-31

Copyright date

2019

ISSN

0300-9483

eISSN

1502-3885

Language

en

Depositor

Dr Dave Ryves Deposit date: 23 October 2019

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