A low climate threshold for south Greenland Ice Sheet demise during the Late Pleistocene

Abstract

The Greenland Ice Sheet (GIS) has been losing mass at an accelerating rate over the recent decades. Models suggest a possible temperature threshold between 0.8 and 3.2 °C, beyond which GIS decline becomes irreversible. The duration of warmth above a given threshold is also a critical determinant for GIS survival, underlining the role of ocean warming, as its inertia prolongs warmth and triggers longer-term feedbacks. The exact point at which these feedbacks are triggered remains equivocal. Late Pleistocene interglacials provide potential case examples for constraining the past response of the GIS to a range of climate states, including conditions warmer than present. However, little is known about the magnitude and duration of warming near Greenland during these periods. Using high-resolution multiproxy surface ocean climate records off southern Greenland, we show that the previous 4 interglacials over the last ∼450 ka all reached warmer than present climate conditions and exceeded the modeled temperature threshold for GIS collapse but by different magnitudes and durations. Complete deglaciation of the southern GIS in Marine Isotope Stage 11c (MIS 11c; 394.7 to 424.2 ka) occurred under climates only slightly warmer than present (∼0.5 ± 1.6 °C), placing the temperature threshold for major GIS retreat in the lower end of model estimates and within projections for this century.

Reorganization of Atlantic waters at sub-polar latitudes linked to deep water overflow in both glacial and interglacial climate states

“…Preceding the glacial inception, MIS 11 was a particularly long interglacial period and while the northern high-latitude insolation maximum was weaker overall than that of our current interglacial period (MIS 1), due to precession and obliquity being out of phase, the warmest interval of this interglacial (e.g., MIS 11c, defined as in Railsback et al (2015)) had very similar eccentricity/precession parameters to MIS 1 (Yin and Berger, 2015). In terms of temperature, MIS 11c was generally warmer than MIS 1, but variable depending on the location within the North Atlantic (Irvalı et al, 2020). In addition, greenhouse gas concentrations, specifically carbon dioxide (pCO2), were similar to pre-industrial values (e.g., 285 ppmv at 407.5 kilo annum (ka) vs. 280 ppmv at 1850 CE) (EPICA, 2004), leading to one of the warmest and longest interglacial periods in the past 800 ka (Irvalı et al, 2020).…”

“…In terms of temperature, MIS 11c was generally warmer than MIS 1, but variable depending on the location within the North Atlantic (Irvalı et al, 2020). In addition, greenhouse gas concentrations, specifically carbon dioxide (pCO2), were similar to pre-industrial values (e.g., 285 ppmv at 407.5 kilo annum (ka) vs. 280 ppmv at 1850 CE) (EPICA, 2004), leading to one of the warmest and longest interglacial periods in the past 800 ka (Irvalı et al, 2020). The unusual strength/warmth and long duration of MIS11c when considering the weak insolation parameters has led to a series of publications discussing potential mechanisms that could have positively amplified the warmth of MIS11c (Droxler et al, 2003 and chapters therein) A negative feedback involving a stronger Nordic heat pump supported by stronger cross-equatorial heat exchange from the South into the North Atlantic has been proposed as one of the main mechanism explaining this apparent paradox (Berger and Wefer, 2003).…”

Sea ice feedbacks influence the isotopic signature of Greenland ice sheet elevation changes: last interglacial HadCM3 simulations

“…We ascribe these changes in summer sea ice to variations in ocean salinity caused by anomalous downwelling or upwelling, induced by anomalously low or high sea level pressure over the Arctic (Jackson and Vellinga, 2012). In HadCM3, the geostrophic balance of the Beaufort gyre can be altered ageostrophically by wind stresses linked to lowfrequency sea level pressure variability (Jackson and Vellinga, 2012).…”

A tephra‐based correlation of marine and terrestrial records of MIS 11c from Britain and the North Atlantic

“…That this interval of MIS 11c was a period of climatic instability in the North Atlantic is supported by lower resolution records from higher latitudes (i.e. Irvali et al ., 2020).…”

“…Consequently, it is not possible to directly correlate the high‐resolution record of abrupt change that they contain with the history of ice‐sheet dynamics and palaeoceanographic change preserved in the marine realm. Whilst North Atlantic marine sediment cores preserve proxy records of oceanographic processes and ice‐sheet history (Reyes et al ., 2014; Kandiano et al ., 2017; Irvali et al ., 2020, etc. ), set on the absolute timescale of the LR04 stack (Lisiecki and Raymo, 2005), the low resolution of these records means that abrupt climate events are frequently recorded in only a small number of data points (Kandiano et al ., 2017).…”