Holocene North Atlantic Overturning in an atmosphere-ocean-sea ice model compared to proxy-based reconstructions

• Main Authors: Blaschek, M, Renssen, H, Kissel, C, Thornalley, D
• Format: Article in Journal/Newspaper
• Language: English
• Published: AMER GEOPHYSICAL UNION 2015
• Subjects: Science & Technology; Physical Sciences; Life Sciences & Biomedicine; Geosciences; Multidisciplinary; Oceanography; Paleontology; Geology; DEEP-WATER; THERMAL MAXIMUM; NORDIC SEAS; LAST DEGLACIATION; BOTTOM-WATER; CARBON-CYCLE; CLIMATE; CIRCULATION; STRENGTH; FLOW; Greenland; Greenland-Scotland Ridge; Ice Sheet; Iceland; Nordic Seas; North Atlantic; Sea ice
• Online Access: https://discovery.ucl.ac.uk/id/eprint/1499091/1/Thornalley%20-%20Holo%20NATL%20AMOC%20proxy%20model%20comparison.pdf; https://discovery.ucl.ac.uk/id/eprint/1499091/

Climate and ocean circulation in the North Atlantic region changed over the course of the Holocene, partly because of disintegrating ice sheets and partly because of an orbital-induced insolation trend. In the Nordic Seas, this impact was accompanied by a rather small, but significant, amount of Greenland ice sheet melting. We have employed the EMIC LOVECLIM and compared our model simulations with proxy-based reconstructions of δ13C, sortable silt, and magnetic susceptibility (κ) used to infer changes in past ocean circulation over the last 9000 years. The various reconstructions exhibit different long-term evolutions suggesting changes in either the overturning of the Atlantic in total or of subcomponents of the ocean circulation, such as the overflow waters across the Greenland-Scotland ridge. Thus, the question arises whether these reconstructions are consistent with each other or not. A comparison with model results indicates that δ13C, employed as an indicator of overturning, agrees well with the long-term evolution of the modeled Atlantic meridional overturning circulation (AMOC). The model results suggest that different long-term trends in subcomponents of the AMOC, such as Iceland-Scotland overflow water, are consistent with proxy-based reconstructions and allow some of the reconstructions to be reconciled with the modeled and reconstructed (from δ13C) AMOC evolution. We find a weak early Holocene AMOC, which recovers by 7 kyr B.P. and shows a weak increasing trend of 88 ± 1 mSv/kyr toward present, with relatively low variability on centennial to millennial timescales.