'Interaction between subsurface ocean waters and calving of Jakobshavn Isbrae during the Late Holocene.', The Holocene., 21 (2). pp. 211-224. Further information on publisher's website:http://dx.doi.org/10.1177/0959683610378877Publisher's copyright statement:The nal denitive version of this article has been published in the Journal 'The Holocene' 21/2, 2011 c The Authors by SAGE Publications Ltd at the The Holocene page: http://hol.sagepub.com on SAGE Journals Online: http://online.sagepub.com/ Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. A. IntroductionIt is becoming increasingly clear that the cryosphere is responding quickly to the atmospheric temperature increase observed over recent decades (Box et al., 2006;Fettweis, 2007; Hanna et al. 2 2008;Mernild et al. 2008a). However, prediction of the contribution of the Greenland ice sheet to global sea-level rise is complicated by the lack of detailed knowledge on mechanisms behind ice sheet change. In particular ice streams and their interaction with the atmospheric and oceanic systems needs further investigation in order to make more realistic models of future sea-level rise.In this study the Late Holocene climate history of the Jakobshavn Isbrae region ( also been proposed as a crucial mechanism triggering ice sheet destabilisation and large-scale iceberg surges during glacial periods (Moros et al., 2002). Following these observations we aim at evaluating if intrusion of relatively warmer waters into Disko Bugt occurred on multi-decadal to centennial timescales and if so how these incursions affected the calving of icebergs. This may shed light on whether the modern acceleration of the Jakobshavn Isbrae is one of a kind and whether ocean-ice-sheet interaction is an important component of the climate-cryosphere system that needs to be assessed in details in climate models.Variability of the subsurface and surface water is reconstructed by analysis of the benthic foraminiferal and dinoflagellate assemblage, respectively, and the production of icebergs and sea-ice is reconstructed on the basis of the ice-rafted debris in the sediment core. produced by, among others, the Jacobshavn Isbrae.The modern day climate of the Disko Bugt region is low arctic maritime with a mean annual temperature of -5.2°C, a summer mean of 4.8°C (Fredskild, 1996) and high precipitation.The bay is typically covered by land-fast sea-ice from mid-January to mid-April with a mean thickness of 0.7 m (Buch, 2000). During spring and summer a strong pycnocline is developed ...

Three marine sediment cores distributed along the Norwegian (MD95-2011), Barents Sea (JM09-KA11-GC), and Svalbard (HH11-134-BC) continental margins have been investigated in order to reconstruct changes in the poleward flow of Atlantic waters (AW) and in the nature of upper surface water masses within the eastern Nordic Seas over the last 3000 yr. These reconstructions are based on a limited set of coccolith proxies: the abundance ratio between Emiliania huxleyi and Coccolithus pelagicus, an index of Atlantic vs. Polar/Arctic surface water masses; and Gephyrocapsa muellerae, a drifted coccolith species from the temperate North Atlantic, whose abundance changes are related to variations in the strength of the North Atlantic Current.

The entire investigated area, from 66 to 77° N, was affected by an overall increase in AW flow from 3000 cal yr BP (before present) to the present. The long-term modulation of westerlies' strength and location, which are essentially driven by the dominant mode of the North Atlantic Oscillation (NAO), is thought to explain the observed dynamics of poleward AW flow. The same mechanism also reconciles the recorded opposite zonal shifts in the location of the Arctic front between the area off western Norway and the western Barents Sea–eastern Fram Strait region.

The Little Ice Age (LIA) was governed by deteriorating conditions, with Arctic/Polar waters dominating in the surface off western Svalbard and western Barents Sea, possibly associated with both severe sea ice conditions and a strongly reduced AW strength. A sudden short pulse of resumed high WSC (West Spitsbergen Current) flow interrupted this cold spell in eastern Fram Strait from 330 to 410 cal yr BP. Our dataset not only confirms the high amplitude warming of surface waters at the turn of the 19th century off western Svalbard, it also shows that such a warming was primarily induced by an excess flow of AW which stands as unprecedented over the last 3000 yr

Arctic sea ice affects climate on seasonal to decadal time scales, and models suggest that sea ice is essential for longer anomalies such as the Little Ice Age. However, empirical evidence is fragmentary. Here, we reconstruct sea ice exported from the Arctic Ocean over the past 1400 years, using a spatial network of proxy records. We find robust evidence for extreme export of sea ice commencing abruptly around 1300 CE and terminating in the late 1300s. The exceptional magnitude and duration of this “Great Sea-Ice Anomaly” was previously unknown. The pulse of ice along East Greenland resulted in downstream increases in polar waters and ocean stratification, culminating ~1400 CE and sustained during subsequent centuries. While consistent with external forcing theories, the onset and development are notably similar to modeled spontaneous abrupt cooling enhanced by sea-ice feedbacks. These results provide evidence that marked climate changes may not require an external trigger.