Warm climate isotopic simulations: what do we learn about interglacial signals in Greenland ice cores?
Measurements of Last Interglacial stable water isotopes in ice cores show that central Greenland d18O
increased by at least 3& compared to present day. Attempting to quantify the Greenland interglacial
temperature change from these ice core measurements rests on our ability to interpret the stable water
isotope content of Greenland snow. Current orbitally driven interglacial simulations do not show d18O or
temperature rises of the correct magnitude, leading to difficulty in using only these experiments to
inform our understanding of higher interglacial d18O. Here, analysis of greenhouse gas warmed simulations
from two isotope-enabled general circulation models, in conjunction with a set of Last Interglacial
sea surface observations, indicates a possible explanation for the interglacial d18O rise. A reduction in the
winter time sea ice concentration around the northern half of Greenland, together with an increase in sea
surface temperatures over the same region, is found to be sufficient to drive a >3& interglacial
enrichment in central Greenland snow. Warm climate d18O and dD in precipitation falling on Greenland
are shown to be strongly influenced by local sea surface condition changes: local sea surface warming
and a shrunken sea ice extent increase the proportion of water vapour from local (isotopically enriched)
sources, compared to that from distal (isotopically depleted) sources. Precipitation intermittency
changes, under warmer conditions, leads to geographical variability in the d18O against temperature
gradients across Greenland. Little sea surface warming around the northern areas of Greenland leads to
low d18O against temperature gradients (0.1e0.3& per �C), whilst large sea surface warmings in these
regions leads to higher gradients (0.3e0.7& per �C). These gradients imply a wide possible range of
present day to interglacial temperature increases (4 to >10 �C). Thus, we find that uncertainty about local
interglacial sea surface conditions, rather than precipitation intermittency changes, may lead to the
largest uncertainties in interpreting temperature from Greenland ice cores. We find that interglacial sea
surface change observational records are currently insufficient to enable discrimination between these
different d18O against temperature gradients. In conclusion, further information on interglacial sea surface
temperatures and sea ice changes around northern Greenland should indicate whether þ5 �C during
the Last Interglacial is sufficient to drive the observed ice core d18O increase, or whether a larger temperature
increases or ice sheet changes are also required to explain the ice core observations.
Authors: Sime, Louise C. ORCID record for Louise C. Sime, Risi, Camille, Tindall, Julia C., Sjolte, Jesper, Wolff, Eric W., Masson-Delmotte, Valérie, Capron, Emilie ORCID record for Emilie Capron
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