27 November, 2013 – Seminar

When: 4pm on Wednesday, November 27th, 2013
Where: DIAS Merrion Square Library

Speaker: Dr. Volker Rath (Complutense University of Madrid)

Title: Past climate change from borehole temperatures: perspectives on the last glacial cycle.

Abstract:It has been known since the 30s of the last century that past changes in ground surface temperature (GST) can be found in recent borehole temperature measurements. Since the 80s, this effect has been used for the reconstruction of past climate using more or less sophisticated inverse methods. However, most studies have used only shallow boreholes of less than 500 m, which allow estimating past temperatures for the last 300 yrs. Studies on deep boreholes (> 1000 m) are comparatively rare, however, they often show a signal originating from the temperature rise of the last glacial-interglacial transition (10-20 kyrs ago, depending on geographic position)

Deep boreholes in Northern America and Europe have not directly recorded the surface air temperature (SAT) but were covered by ice sheets for most of the last glacial cycle. Thus the paleotemperatures estimated form boreholes represent at least partially basal ice sheet temperatures. Conditions at the base of the ice sheet are not well understood, but known to be heterogeneous in space and time for a given ice sheet. I will present a case study on competing physical models for the dynamics of the Laurentide Ice Sheet, demonstrating clearly how recent borehole temperatures can contribute to our understanding of the processes involved in ice sheet related phenomena.

Finally I will present some results concerning the Fennoscandian Ice sheet. Here more than a dozen of very deep boreholes have been collected, which will be complemented by new measurements as part of the COSC ICDP project. For some of these boreholes it was possible to derive climatological consistent GST histories by variational and bayesian methods. However, they also show some of the particular problems of this approach, which are mainly related to the physics of the atmosphere-subsurface coupling, which may be strongly influenced by changes of vegetation and snow cover.