Browsing by Subject "GREENLAND"

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  • Jackson, Rebecca; Kvorning, Anna Bang; Limoges, Audrey; Georgiadis, Eleanor; Olsen, Steffen M.; Tallberg, Petra; Andersen, Thorbjorn J.; Mikkelsen, Naja; Giraudeau, Jacques; Masse, Guillaume; Wacker, Lukas; Ribeiro, Sofia (2021)
    Baffin Bay hosts the largest and most productive of the Arctic polynyas: the North Water (NOW). Despite its significance and active role in water mass formation, the history of the NOW beyond the observational era remains poorly known. We reconcile the previously unassessed relationship between long-term NOW dynamics and ocean conditions by applying a multiproxy approach to two marine sediment cores from the region that, together, span the Holocene. Declining influence of Atlantic Water in the NOW is coeval with regional records that indicate the inception of a strong and recurrent polynya from similar to 4400 yrs BP, in line with Neoglacial cooling. During warmer Holocene intervals such as the Roman Warm Period, a weaker NOW is evident, and its reduced capacity to influence bottom ocean conditions facilitated northward penetration of Atlantic Water. Future warming in the Arctic may have negative consequences for this vital biological oasis, with the potential knock-on effect of warm water penetration further north and intensified melt of the marine-terminating glaciers that flank the coast of northwest Greenland.
  • Gong, Yongmei; Zwinger, Thomas; Åström, Jan; Altena, Bas; Schellenberger, Thomas; Gladstone, Rupert; Moore, John (2018)
    The marine-terminating outlet in Basin 3, Austfonna ice cap, has been accelerating since the mid-1990s. Stepwise multi-annual acceleration associated with seasonal summer speed-up events was observed before the outlet entered the basin-wide surge in autumn 2012. We used multiple numerical models to explore hydrologic activation mechanisms for the surge behaviour. A continuum ice dynamic model was used to invert basal friction coefficient distributions using the control method and observed surface velocity data between April 2012 and July 2014. This has provided input to a discrete element model capable of simulating individual crevasses, with the aim of finding locations where meltwater entered the glacier during the summer and reached the bed. The possible flow paths of surface meltwater reaching the glacier bed as well as those of meltwater produced at the bed were calculated according to the gradient of the hydraulic potential. The inverted friction coefficients show the "unplugging" of the stagnant ice front and expansion of low-friction regions before the surge reached its peak velocity in January 2013. Crevasse distribution reflects the basal friction pattern to a high degree. The meltwater reaches the bed through the crevasses located above the margins of the subglacial valley and the basal melt that is generated mainly by frictional heating flows either to the fast-flowing units or potentially accumulates in an overdeepened region. Based on these results, the mechanisms facilitated by basal meltwater production, crevasse opening and the routing of meltwater to the bed are discussed for the surge in Basin 3.
  • Hellén, Heidi; Leck, Caroline; Paatero, Jussi; Virkkula, Aki; Hakola, Hannele (2012)
  • Ribeiro, Sofia; Limoges, Audrey; Masse, Guillaume; Johansen, Kasper L.; Colgan, William; Weckstrom, Kaarina; Jackson, Rebecca; Georgiadis, Eleanor; Mikkelsen, Naja; Kuijpers, Antoon; Olsen, Jesper; Olsen, Steffen M.; Nissen, Martin; Andersen, Thorbjorn J.; Strunk, Astrid; Wetterich, Sebastian; Syvaranta, Jari; Henderson, Andrew C. G.; Mackay, Helen; Taipale, Sami; Jeppesen, Erik; Larsen, Nicolaj K.; Crosta, Xavier; Giraudeau, Jacques; Wengrat, Simone; Nuttall, Mark; Gronnow, Bjarne; Mosbech, Anders; Davidson, Thomas A. (2021)
    High Arctic ecosystems and Indigenous livelihoods are tightly linked and exposed to climate change, yet assessing their sensitivity requires a long-term perspective. Here, we assess the vulnerability of the North Water polynya, a unique seaice ecosystem that sustains the world's northernmost Inuit communities and several keystone Arctic species. We reconstruct mid-to-late Holocene changes in sea ice, marine primary production, and little auk colony dynamics through multi-proxy analysis of marine and lake sediment cores. Our results suggest a productive ecosystem by 4400-4200 cal yrs b2k coincident with the arrival of the first humans in Greenland. Climate forcing during the late Holocene, leading to periods of polynya instability and marine productivity decline, is strikingly coeval with the human abandonment of Greenland from c. 2200-1200 cal yrs b2k. Our long-term perspective highlights the future decline of the North Water ecosystem, due to climate warming and changing sea-ice conditions, as an important climate change risk. The North Water polynya is a unique but vulnerable ecosystem, home to Indigenous people and Arctic keystone species. New palaeoecological records from Greenland suggest human abandonment c. 2200-1200 cal yrs BP occurred during climate-forced polynya instability, foreshadowing future ecosystem declines.
  • Schenk, Frederik; Väliranta, Minna; Muschitiello, Francesco; Tarasov, Lev; Heikkilä, Maija; Björck, Svante; Brandefelt, Jenny; Johansson, Arne V.; Näslund, Jens-Ove; Wohlfarth, Barbara (2018)
    The Younger Dryas (YD) cold reversal interrupts the warming climate of the deglaciation with global climatic impacts. The sudden cooling is typically linked to an abrupt slowdown of the Atlantic Meridional Overturning Circulation (AMOC) in response to meltwater discharges from ice sheets. However, inconsistencies regarding the YD-response of European summer temperatures have cast doubt whether the concept provides a sufficient explanation. Here we present results from a high-resolution global climate simulation together with a new July temperature compilation based on plant indicator species and show that European summers remain warm during the YD. Our climate simulation provides robust physical evidence that atmospheric blocking of cold westerly winds over Fennoscandia is a key mechanism counteracting the cooling impact of an AMOC-slowdown during summer. Despite the persistence of short warm summers, the YD is dominated by a shift to a continental climate with extreme winter to spring cooling and short growing seasons.