Borehole temperatures reveal details of 20th century warming at Bruce Plateau, Antarctic Peninsula

Abstract

Two ice core boreholes of 143.18 m and 447.73 m (bedrock) were drilled during the 2009–2010 austral summer on the Bruce Plateau at a location named LARISSA Site Beta (66°02' S, 64°04' W, 1975.5 m a.s.l.). Both boreholes were logged with thermistors shortly after drilling. The shallow borehole was instrumented for 4 months with a series of resistance thermometers with satellite uplink. Surface temperature proxy data derived from an inversion of the borehole temperature profiles are compared to available multi-decadal records from weather stations and ice cores located along a latitudinal transect of the Antarctic Peninsula to West Antarctica. The LARISSA Site Beta profiles show temperatures decreasing from the surface downward through the upper third of the ice, and warming thereafter to the bed. The average temperature for the most recent year is −14.78°C (measured at 15 m depth, abbreviated <i>T</i><sub>15</sub>). A minimum temperature of −15.8°C is measured at 173 m depth, and basal temperature is estimated to be −10.2°C. Current mean annual temperature and the gradient in the lower part of the measured temperature profile have a best fit with an accumulation rate of 1.9×10<sup>3</sup> kg m<sup>−2</sup> a<sup>−1</sup> and basal heat flux (<i>q</i>) of 88 mW m<sup>−2</sup>, if steady-state conditions are assumed. However, the mid-level temperature variations show that recent temperature has varied significantly. Reconstructed surface temperatures (<i>T</i><sub>s</sub>=<i>T</i><sub>15</sub>) over the last 200 yr are derived by an inversion technique (Tikhonov and Samarskii, 1990). From this, we find that cold temperatures (minimum <i>T</i><sub>s</sub>=−16.2°C) prevailed from ~1920 to ~1940, followed by a gradual rise of temperature to −14.2°C around 1995, then cooling over the following decade and warming in the last few years. The coldest period was preceded by a relatively warm 19th century at <i>T</i><sub>15</sub>≥−15°C. To facilitate regional comparisons of the surface temperature history, we use our <i>T</i><sub>15</sub> data and nearby weather station records to refine estimates of lapse rates (altitudinal, adjusted for latitude: Γ<sub>a(l)</sub>). Good temporal and spatial consistency of Γ<sub>a(l)</sub> over the last 35 yr are observed, implying that the climate trends observed here are regional and consistent over a broad altitude range

Detailed ice loss pattern in the northern Antarctic Peninsula: widespread decline driven by ice front retreats

“…In light of known climate-related changes in the region, such as increasing surface air temperatures and surface melting, regional sea ice decline, and increasing accumulation (e.g., Mulvaney et al, 2012;Zagorodnov et al, 2012;Stammerjohn et al, 2008;Lenaerts et al, 2012;Barrand et al, 2013), our study reveals a pattern of ice mass loss in space and (we infer) in time that may be similar to the characteristics of mass loss in other areas of Antarctica in the coming century.…”

“…Models of precipitation input for the region (Saha et al, 2014;Dee et al, 2011;Lenaerts et al, 2012) also show a strong overall increase for the most recent decades, but some indicate a slight decline in the last decade, covering our dH /dt measurement period (Saha et al, 2010;Lenaerts et al, 2012;Shepherd et al, 2012). The large increase and later reduction in accumulation are associated with multidecadal warming (Barrand et al, 2013) and with reductions in sea ice extent northwest of the nAP (Stammerjohn et al, 2012), recently moderated by a slight cooling trend (Fogt and Scambos, 2013;Zagorodnov et al, 2012).…”

Foehn winds link climate‐driven warming to ice shelf evolution in Antarctica

“…Further examination of temperature and wind data sets reveals a distinct increase between 1962–1972 and the 1999–2002 period, in agreement with concomitant trends in the SAM, followed annually and in all seasons but the winter by a rapid decrease (Figures and ). This apparent cooling trend, paralleled by foehn frequency decreases, is further corroborated by a regional temperature history derived from isotope analysis of an ice core collected on the Bruce Plateau overlooking the Larsen B embayment [ Zagorodnov et al , ], which shows a maximum in temperature between 1995 and the early 2000s followed by a rapid decrease. These observations may indicate a return to more dominant cold, continental conditions characteristics of the early decade, and a switch in synoptic‐scale forcing impacting regional wind patterns.…”

State of the Climate in 2012

“…Four recent borehole temperature studies confirm an accelerated pace of warming in recent decades in the Antarctic Peninsula, West Antarctica, and the Dronning Maud Land in East Antarctica (Barrett et al 2009;Muto et al 2011;Zagorodnov et al 2012;Orsi et al 2012). All find recent warming of order 1°C in the last few decades, confirming time series measurements from Byrd Station (Bromwich et al 2013) and other temporal records (Steig et al 2009;Steig and Orsi 2013).…”