Persistent influence of ice sheet melting on high northern latitude climate during the early Last Interglacial

Abstract

Abstract. Although the Last Interglacial (LIG) is often considered as a possible analogue for future climate in high latitudes, its precise climate evolution and associated causes remain uncertain. Here we compile high-resolution marine sediment records from the North Atlantic, Labrador Sea, Norwegian Sea and the Southern Ocean. We document a delay in the establishment of peak interglacial conditions in the North Atlantic, Labrador and Norwegian Seas as compared to the Southern Ocean. In particular, we observe a persistent iceberg melting at high northern latitudes at the beginning of the LIG. It is associated with (1) colder and fresher surfacewater conditions in the North Atlantic, Labrador and Norwegian Seas, and (2) a weaker ventilation of North Atlantic deep waters during the early LIG (129-125 ka) compared to the late LIG. Results from an ocean-atmosphere coupled model with insolation as a sole forcing for three key periods of the LIG show warmer North Atlantic surface waters and stronger Atlantic overturning during the early LIG (126 ka) than the late LIG (122 ka). Hence, insolation variations alone do not explain the delay in peak interglacial conditions observed at high northern latitudes. Additionally, we consider an idealized meltwater scenario at 126 ka where the freshwater input is interactively computed in response to the high boreal summer insolation. The model simulates colder, fresher North Atlantic surface waters and weaker Atlantic overturning during the early LIG (126 ka) compared to the late LIG (122 ka). This result suggests that both insolation and ice sheet melting have to be considered to reproduce the climatic pattern that we identify during the early LIG. Our modeldata comparison also reveals a number of limitations and reinforces the need for further detailed investigations using coupled climate-ice sheet models and transient simulations.

The last interglacial climate: comparing direct and indirect impacts of insolation changes

“…The maximum annual mean overturning strength increases by 37 % from 15.8 Sv in PI to 21.6 Sv in LIG (with standard deviations 1.03 and 1.27 Sv, respectively). This increase is in line with the increase of approximately 30 % found in previous, similar GCM simulations of 125 ka (Govin et al 2012;Langebroek and Nisancioglu 2014).…”

“…In GCM simulations of the LIG (126 ka), Govin et al (2012) show that the addition of meltwater from Greenland could even weaken the AMOC below the pre-industrial state. As the authors discuss, this finding is, however, an estimate of the highest potential effect of the GIS meltwater, as the flux of 0.17 Sv is very high compared to the expected GIS melt at 126 ka; a recent estimate suggests a meltwater flux of approximately 12.7 mSv at 125 ka (Blaschek et al 2014).…”

“…The dataset consists of several time slices; including 125 ka employed here. While being based on a smaller number of records, it benefits from having a coherent temporal (Govin et al 2012;Bakker et al 2013), and as highlighted by Bakker and Renssen (2014) the 'synchronous warming' assumption behind the previous data compilations contributes to model-data mismatch. Thus, we have preferred the Capron et al (2014) dataset for model-data comparison due to the consistent dating; despite the more limited spatial coverage.…”

“…along the Greenland east coast, in Baffin Bay and in the Labrador Sea. Sea ice export through the Fram Strait constitutes a substantial freshwater export southward from the Arctic Ocean (Serreze et al 2006), and previous studies have illustrated that the sea ice export affects the salinity in the North Atlantic, the Labrador Sea convection and AMOC strength (Born et al 2010;Govin et al 2012).…”

“…Transient simulations usually rely on earth system models of intermediate complexity , while general circulation models (GCMs) primarily are employed for equilibrium, snapshot simulations (Fischer and Jungclaus 2010;Govin et al 2012;Lunt et al 2013;Nikolova et al 2013;Otto-Bliesner et al 2013;Langebroek and Nisancioglu 2014). Recent model assessments find very low global annual mean warming during LIG, contrasting the proxy reconstruction estimate of 1-2 K warming (Masson-Delmotte et al 2013;Otto-Bliesner et al 2013).…”