White paper: Terminations and seesaws: an ice core contribution to understanding orbital and millennial scale climate change

Records of our planet’s climate history help to reveal the dynamics and processes by which the Earth system operates. Studies of large and rapid climate changes in the past complement recent information from instrumental and satellite records. They provide a benchmark to ensure that all relevant processes are adequately represented in Earth system models, used both to understand past variations and to assess future climate. Glacial terminations offer case studies of a large global climate response to external forcing and involve significant change and interaction among many components of the Earth system, including ice sheets, the carbon cycle, vegetation and dust. Millennial scale Dansgaard-Oeschger (D-O) cycles are case studies of very fast regional redistribution of climate, most likely resulting from rapid reorganizations internal to the climate system, involving ocean and atmospheric circulation. During these cycles, abrupt warming of parts of the northern hemisphere was accompanied by a slower, out of phase cooling in the southern hemisphere – the so-called bipolar seesaw – and vice-versa. For both types of change, ice cores have already provided evidence about spatial patterns, temporal sequences, and some of the feedbacks, for example in the carbon cycle, that have been at play. However, they still offer limited regional information, and a lack of details prior to the last glacial period. Further work is needed to complete a network of synchronized, high-resolution ice cores, from both polar regions, in order to understand the processes involved in abrupt millennial scale change and in glacial terminations. Furthermore, a small number of Antarctic ice cores now allow us to delve into previous glacial cycles in the same detail that has until now been available only for the last glacial cycle.