Abstract
Arctic Ocean sea ice proxies generally suggest a reduction in sea ice during parts of the early and middle Holocene (∼6000–10,000 years BP) compared to present day conditions. This sea ice minimum has been attributed to the northern hemisphere Early Holocene Insolation Maximum (EHIM) associated with Earth's orbital cycles. Here we investigate the transient effect of insolation variations during the final part of the last glaciation and the Holocene by means of continuous climate simulations with the coupled atmosphere–sea ice–ocean column model CCAM. We show that the increased insolation during EHIM has the potential to push the Arctic Ocean sea ice cover into a regime dominated by seasonal ice, i.e. ice free summers. The strong sea ice thickness response is caused by the positive sea ice albedo feedback. Studies of the GRIP ice cores and high latitude North Atlantic sediment cores show that the Bølling–Allerød period (c. 12,700–14,700 years BP) was a climatically unstable period in the northern high latitudes and we speculate that this instability may be linked to dual stability modes of the Arctic sea ice cover characterized by e.g. transitions between periods with and without perennial sea ice cover.
Highlights
Numerous palaeoclimate archives and numerical simulations suggest that the Arctic was warmer than present day during early and middle Holocene with peak air temperatures occurring at slightly different times in different regions (Kaufman et al, 2004; Renssen et al, 2012)
Since the Arctic sea ice cover is subject to a hysteresis when transitioning between seasonal and perennial ice, a third reversed simulation was carried out where the model was run from present day conditions and backwards in time in terms of short wave (SW) forcing
The present idealized model study focuses on the isolated effect of variations in the SW forcing during Holocene by means of transient simulations performed with a coupled oceanesea icee atmosphere column model
Summary
Numerous palaeoclimate archives and numerical simulations suggest that the Arctic was warmer than present day during early and middle Holocene with peak air temperatures occurring at slightly different times in different regions (Kaufman et al, 2004; Renssen et al, 2012). Vare et al, 2009; Hanslik et al, 2010; Funder et al, 2011; Müller et al, 2012) The cause of this sea-ice minimum, occurring between about 6000 and 10,000 years BP, is often attributed to the northern hemisphere Early Holocene Insolation Maximum (EHIM) associated with Earth’s orbital cycles (Jakobsson et al, 2010; Polyak et al, 2010; Müller et al, 2012). The radiative forcing from a doubling of the pre-industrial atmospheric CO2 concentration has been estimated to w3.5 WmÀ2 (Gettelman et al, 2012) This is on the same order of magnitude as the increased SW forcing in the Arctic during the EHIM, only a fraction of the insolation is available for melting ice due to the cloud and surface albedos
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