Abstract
Expansion of fresh and sea-ice loaded surface waters from the Arctic Ocean into the sub-polar North Atlantic is suggested to modulate the northward heat transport within the North Atlantic Current (NAC). The Reykjanes Ridge south of Iceland is a suitable area to reconstruct changes in the mid- to late Holocene fresh and sea-ice loaded surface water expansion, which is marked by the Subarctic Front (SAF). Here, shifts in the location of the SAF result from the interaction of freshwater expansion and inflow of warmer and saline (NAC) waters to the Ridge. Using planktic foraminiferal assemblage and concentration data from a marine sediment core on the eastern Reykjanes Ridge elucidates SAF location changes and thus, changes in the water-mass composition (upper ˜200 m) during the last c. 5.8 ka BP. Our foraminifer data highlight a late Holocene shift (at c. 3.0 ka BP) in water-mass composition at the Reykjanes Ridge, which reflects the occurrence of cooler and fresher surface waters when compared to the mid-Holocene. We document two phases of SAF presence at the study site: from (i) c. 5.5 to 5.0 ka BP and (ii) c. 2.7 to 1.5 ka BP. Both phases are characterized by marked increases in the planktic foraminiferal concentration, which coincides with freshwater expansions and warm subsurface water conditions within the sub-polar North Atlantic. We link the SAF changes, from c. 2.7 to 1.5 ka BP, to a strengthening of the East Greenland Current and a warming in the NAC, as identified by various studies underlying these two currents. From c. 1.5 ka BP onwards, we record a prominent subsurface cooling and continued occurrence of fresh and sea-ice loaded surface waters at the study site. This implies that the SAF migrated to the southeast of our core site during the last millennium.
Original language | English |
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Pages (from-to) | 175-188 |
Number of pages | 14 |
Journal | Boreas |
Volume | 47 |
Issue number | 1 |
Early online date | 29 May 2017 |
DOIs | |
Publication status | Published - Jan 2018 |
Funding
Acknowledgements. – We thank the Deutsche Forschungsgemein-schaft for funding the project ‘GreenClime’ (PE2071/2-1) and K. Perner. Furthermore, we thank the EU-ERC project ‘ice2ice’ (grant No 610055) for financial support. Two anonymous reviewers are thanked for their thorough and critical comments, which helped to improve our manuscript. The authors also sincerely thank the captains and crews of the RV ‘Prof. Logachev’ and ‘G.O. Sars’ for their help and assistance during collection of the sediment cores at sea. Trond Dokken and Ulysses Ninnemann are thanked for collecting core GS06-144-04. Furthermore, we wish to acknowledge the support of Rúne Soras during stable isotope measurements.
Funders | Funder number |
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EU-ERC | 610055 |
Deutsche Forschungsgemeinschaft | PE2071/2-1 |