Holocene multidecadal- to millennial-scale variations in Iceland-Scotland overflow and their relationship to climate

The Nordic Seas overflows are an important part of the Atlantic thermohaline circulation. While there is growing evidence that the overflow of dense water changed on orbital time scales during the Holocene, less is known about the variability on shorter time scales beyond the instrumental record. He...

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Bibliographic Details
Published in:Paleoceanography 2015-05, Vol.30 (5), p.558-569
Main Authors: Mjell, Tor Lien, Ninnemann, Ulysses S., Eldevik, Tor, Kleiven, Helga Kikki F.
Format: Article
Language:English
Subjects:
Climate change
ISOW
Nordic Seas overflows
Oceanography
Paleoclimate science
THC
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Summary:The Nordic Seas overflows are an important part of the Atlantic thermohaline circulation. While there is growing evidence that the overflow of dense water changed on orbital time scales during the Holocene, less is known about the variability on shorter time scales beyond the instrumental record. Here we reconstruct the relative changes in flow strength of Iceland‐Scotland Overflow Water (ISOW), the eastern branch of the overflows, on multidecadal‐millennial time scales. The reconstruction is based on mean sortable silt ( SS¯) from a sediment core on the Gardar Drift (60°19′N, 23°58′W, 2081 m). Our SS¯ record reveals that the main variance in ISOW vigor occurred on millennial time scales (1–2 kyr) with particularly prominent fluctuations after 8 kyr. Superimposed on the millennial variability, there were multidecadal‐centennial flow speed fluctuations during the early Holocene (10–9 kyr) and one prominent minimum at 0.9 kyr. We find a broad agreement between reconstructed ISOW and regional North Atlantic climate, where a strong (weak) ISOW is generally associated with warm (cold) climate. We further identify the possible contribution of anomalous heat and freshwater forcing, respectively, related to reconstructed overflow variability. We infer that ocean poleward heat transport can explain the relationship between regional climate and ISOW during the middle to late Holocene, whereas freshwater input provides a possible explanation for the reduced overflow during early Holocene (8–10 kyr). Key Points The main variance in ISOW vigor occurs on millennial time scales A strong (weak) ISOW is associated with warm (cold) climate during the past 8 kyr The thermal versus haline buoyancy forcing of the Arctic determines the ISOW vigor
ISSN:0883-8305
2572-4517
1944-9186
2572-4525
DOI:10.1002/2014PA002737