Little Ice Age cold interval in West Antarctica: Evidence from borehole temperature at the West Antarctic Ice Sheet (WAIS) Divide

Abstract

The largest climate anomaly of the last 1000 years in the Northern Hemisphere was the Little Ice Age (LIA) from 1400–1850 C.E., but little is known about the signature of this event in the Southern Hemisphere, especially in Antarctica. We present temperature data from a 300 m borehole at the West Antarctic Ice Sheet (WAIS) Divide. Results show that WAIS Divide was colder than the last 1000‐year average from 1300 to 1800 C.E. The temperature in the time period 1400–1800 C.E. was on average 0.52 ± 0.28°C colder than the last 100‐year average. This amplitude is about half of that seen at Greenland Summit (GRIP). This result is consistent with the idea that the LIA was a global event, probably caused by a change in solar and volcanic forcing, and was not simply a seesaw‐type redistribution of heat between the hemispheres as would be predicted by some ocean‐circulation hypotheses. The difference in the magnitude of the LIA between Greenland and West Antarctica suggests that the feedbacks amplifying the radiative forcing may not operate in the same way in both regions.

Borehole temperatures reveal a changed energy budget at Mill Island, East Antarctica, over recent decades

“…Dahl-Jensen et al, 1998Barrett et al, 2009); and (iii) generalised least-squares solution of a linearised version of the problem (e.g. MacAyeal et al, 1991;Muto et al, 2011;Orsi et al, 2012). The methods used herein most closely resemble the latter two methods for the PSO and LSQR methods respectively.…”

“…Such an approach of using both a forward model and a method of optimising surface temperature histories has been used previously (see, for example Johnsen, 1977;MacAyeal et al, 1991;Johnsen et al, 1995;Cuffey et al, 1995;Cuffey and Clow, 1997;Dahl-Jensen et al, 1998Barrett et al, 2009;Muto et al, 2011;Orsi et al, 2012). The forward models used in these studies all included the heating associated with firn densification with the exceptions of MacAyeal et al (1991);Johnsen et al (1995); Barrett et al (2009) and Muto et al (2011).…”

“…These studies all select which possible surface temperature history reconstructions to accept based on minimising the mismatch between the simulated and observed borehole temperature profiles. However, the methods of generating possible surface temperature histories (to select from) differ and fall into three broad categories (Orsi et al, 2012): (i) optimisations based on relationships between surface temperature and stable water isotope ratios (e.g. Johnsen, 1977;Cuffey et al, 1995;Cuffey and Clow, 1997;Johnsen et al, 1995); (ii) Monte Carlo based approaches (e.g.…”

“…3). Further, these results can be set in the context of wider Antarctic warming, with comparable Antarctic Peninsula warming (Mulvancy et al, 2012), a reconstructed recent temperature trend of up to 0.8 K decade −1 for the West Antarctic Ice Sheet divide (Orsi et al, 2012) and large but spatially variable temperature trends in inland Dronning Maud Land, East Antarctica (Muto et al, 2011).…”

Acceleration of snow melt in an Antarctic Peninsula ice core during the twentieth century

“…2c) 35 , although with the length constraints of the current ice-core records it is not possible to determine whether the strong multi-decadal variability in PC1 masks an earlier inception of the warming trend over the West Antarctic Ice Sheet. Recently, borehole temperature estimates from the West Antarctic Ice Sheet have provided evidence for a rapid acceleration of West Antarctic warming over the past two decades 36 . Antarctic Peninsula warming is captured by PC2 of the icecore array (Fig.…”