Imprinting solar and orbital signals on Greenland and Antarctic ice cores

An accurate understanding of the record of solar and orbital variations, from 0.1 to 100 ky time scales, in polar ice cores is crucial to our grasp of past variations in climate. At long time scales, the resemblance of key Antarctic ice core isotopic records to the northern hemisphere summer duration and intensity suggests that ice sheet changes in the Northern Hemisphere drive global temperature changes. At short time scales, centennial and sub-centennial modulations of solar activity are clearly recorded in Greenland ice cores during the last glacial period. These variations have been tentatively ascribed to regional shifts in the dominant modes of atmospheric circulation regimes (e.g. Adolphi et al., 2014). However, despite the crucial importance of ice core records to our understanding of climate, we don’t yet understand how these solar signals are actually integrated in Antarctic and Greenland cores.

Antarctic and Greenland ice core records, alongside sets of isotopically enabled climate model simulations will enable the PhD student to tackle fundamental solar and orbital related palaeoclimate and ice core problems. The student will discriminate between competing hypothesis which attempt to explain ice-core long- and short-term external forcing signals. The key hypothesises that will be tested are: 1. Whether isotopic imprints of changes in solar activity are transmitted synchronously via the atmosphere system throughout the globe. 2. Whether the (in)stability of Antarctic accumulation seasonality impacts on key core interpretations (e.g. Sime and Wolff, 2011). 3. Whether there is a local linear temperature-isotope relationship and the local-versus-distal explanation of the orbital (21 to 100 ky) isotope signal in Antarctic ice cores (e.g. Jouzel et al., 2007).

Assumptions and hypotheses governing ice core interpretations will be tested by conducting and analyzing a set of numerical simulations. Climate model output will be compared to a comprehensive compilation of published and unpublished isotope records from Greenland and Antarctic ice cores, alongside other absolutely dated climate archives. Simulations to be carried out will include: (1) Changing the solar constant to constrain the effects of short-term changes in solar activity on the isotopic signatures in ice cores. (2) “Snapshot” simulations with the Hadley Centre climate model (HadCM3) over the last 130,000 years which will enable to isolate the impacts of CO2 and solar/orbital changes on ice core records.