Abstract
Abstract. The last glacial period (LGP; ca. 110–10 kyr BP) was marked by the existence of two types of abrupt climatic changes, Dansgaard–Oeschger (DO) and Heinrich (H) events. Although the mechanisms behind these are not fully understood, it is generally accepted that the presence of ice sheets played an important role in their occurrence. While an important effort has been made to investigate the dynamics and evolution of the Laurentide ice sheet (LIS) during this period, the Eurasian ice sheet (EIS) has not received much attention, in particular from a modeling perspective. However, meltwater discharge from this and other ice sheets surrounding the Nordic seas is often implied as a potential cause of ocean instabilities that lead to glacial abrupt climate changes. Thus, a better comprehension of the evolution of the EIS during the LGP is important to understand its role in glacial abrupt climate changes. Here we investigate the response of the EIS to millennial-scale climate variability during the LGP. We use a hybrid, three-dimensional, thermomechanical ice-sheet model that includes ice shelves and ice streams. The model is forced off-line via a novel perturbative approach that, as opposed to conventional methods, clearly differentiates between the spatial patterns of millennial-scale and orbital-scale climate variability. Thus, it provides a more realistic treatment of the forcing at millennial timescales. The effect of both atmospheric and oceanic variations are included. Our results show that the EIS responds with enhanced ice discharge in phase with interstadial warming in the North Atlantic when forced with surface ocean temperatures. Conversely, when subsurface ocean temperatures are used, enhanced ice discharge occurs both during stadials and at the beginning of the interstadials. Separating the atmospheric and oceanic effects demonstrates the major role of the ocean in controlling the dynamics of the EIS on millennial timescales. While the atmospheric forcing alone is only able to produce modest iceberg discharges, warming of the ocean leads to higher rates of iceberg discharges as a result of relatively strong basal melting at the margins of the ice sheet. Our results clearly show the capability of the EIS to react to glacial abrupt climate changes, and highlight the need for stronger constraints on the ice sheet's glacial dynamics and climate–ocean interactions.
Highlights
The last glacial period (LGP; ca. 110–10 kyr before present, BP) was marked by the existence of two types of abrupt climatic changes: Dansgaard–Oeschger (DO) and Heinrich (H) events (e.g., Alley et al, 1999)
Under constant forcing, the CTRL run shows negligible millennial-scale sea-level equivalent (SLE) variations, a lower frequency SLE fluctuation is found as a result of internal ice-sheet variability (Fig. 4) through a thermomechanical feedback
Our results indicate that the timing of the response with respect to changes registered in Greenland depends, on whether the surface or the subsurface of the ocean is considered as the relevant forcing of the ice sheet
Summary
The last glacial period (LGP; ca. 110–10 kyr before present, BP) was marked by the existence of two types of abrupt climatic changes: Dansgaard–Oeschger (DO) and Heinrich (H) events (e.g., Alley et al, 1999). 110–10 kyr before present, BP) was marked by the existence of two types of abrupt climatic changes: Dansgaard–Oeschger (DO) and Heinrich (H) events (e.g., Alley et al, 1999). DO-events are identified in Greenland ice-core records as regional abrupt warmings by up to 16 ◦C (Huber et al, 2006; Kindler et al, 2014) from cold (stadial) to relatively warm (interstadial) conditions within decades (Dansgaard et al, 1993) followed by a gradual cooling interval lasting from centuries to millennia and an ultimate phase of rapid cooling back to stadial conditions (Steffensen et al, 2008). Superimposed on the millennialscale variability associated with DO-events, an additional lower-frequency climatic cycle is identified. -called “Bond cycles” are flanked by prolonged stadials ending with prominent DO-events within about 7–10 kyr (Bond et al, 1993). Alvarez-Solas et al.: Eurasian ice-sheet response to oceanic forcing
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