If you can't explain the 'pause', you can't explain the cause...
Tuesday, May 1, 2012
Widespread rapid melting of the Greenland ice sheet!
...started 8,600 years ago and over the next thousand years resulted in a rapid retreat of the ice sheet margin to become mainly land-based, according to a paper published last week inPalaeogeography, Palaeoclimatology, Palaeoecology. Around 800-1200 years ago during the Medieval Warming Period, the Vikings settled and farmed Greenland, but perished during the Little Ice Age, their farms still covered by permafrost today.
Records of foraminiferal assemblages combined with lithological properties (grain size, magnetic parameters and XRF data) of marine sediment cores from West Greenland coastal waters and the adjacent Labrador Sea document widespread early Holocene meltwater discharge. This discharge is concluded to originate from large-scale melting of the Greenland Ice Sheet (GIS) having started prior to 8,600 calendar years BP [before the present] and ended at about 7,700-7,500 calendar years BP, when the Greenland Ice Sheet margin had withdrawn from the fjords and become mainly land-based. The benthic foraminiferal record from one of the coastal sites mainly reflects West Greenland Current (WGC) subsurface water properties and to a minor degree surface productivity. The most significant feature in this record is an abrupt shift to a higher-productivity regime around ~ 7,700 cal. yr BP. We suggest that the cessation of a widespread GIS meltwater discharge at that time favoured an increased influence of (sub)surface water of Atlantic origin and initiation of modern subpolar gyre circulation enabling Labrador Sea deep convection. Further offshore, a record of planktonic foraminiferal assemblages shows an oceanographic change at ca. 9,500 cal. yr BP, while a gradual but marked change in the planktonic foraminiferal assemblage between 8,800-7,000 cal. yr BP may be related to a narrowing of the WGC low-salinity surface water belt. The oceanic regime off West Greenland prior to ~ 7,800 cal. yr BP was thus characterised by the presence of a permanent and widespread meltwater surface layer, presumably preventing deep convection in this region. Apart from indications of a slight decrease in meltwater discharge by the benthic foraminiferal fauna data, neither of the records shows any clear signal of a regionally important 8.2 ka event.
► Large-scale melt water plumes from Greenland Ice Sheet in Early Holocene ► Rapid glacial retreat of West Greenland ice sheet in early Holocene ► A strong West Greenland Current existed already in early Holocene ► Modern oceanographic conditions established ~ 7,700-7,500 cal yrs BP ► No or very little indication of 8.2 ka event off West Greenland