664 | Nature | Vol 577 | 30 January 2020
Article
Mallorca and the reversal in the RSL trend at Western Australia and the
Seychelles (Fig. 4 ).
Our results do not account for several other processes that may have
caused LIG global mean sea level and RSL to have been even higher
than modelled here. For example, our atmospheric modelling may
underestimate surface melting around the lower-elevation margins of
the Greenland Ice Sheet. The greater boreal summer insolation forcing
during the LIG relative to the present interglaciation probably caused
even greater mass loss from glaciers, which today account for 0.41 m
GMSLE. Warmer-than-present LIG temperatures would have caused
additional thermosteric sea-level rise^5. Finally, we note that any addi-
tional melt near the start of the LIG would change the preferred Earth
models identified in our analysis (Methods). LIG RSL could also be
influenced by dynamic topography due to mantle convection, intro-
ducing metre-scale displacement on timescales of tens of kiloyears^29.
In summary, several lines of evidence suggest that the greater oceanic
forcing during T-II, as simulated by our climate modelling, contributed
to the more-rapid sea-level rise during that period than T-1. First, forcing
of ice-sheet surface mass balance was similar during the two termina-
tions, indicating that an additional forcing is required to explain the
differences in rates of sea-level rise. Second, our glacio-isostatic adjust-
ment modelling demonstrates that the larger PGM Eurasian ice sheet
caused a substantially larger fraction of the ice-sheet bed to be below
sea level, and thus more vulnerable to oceanic forcing, than during T-I.
Third, our ice-sheet modelling shows that >85% of the volume loss of the
PGM Greenland and Antarctic ice sheets to their present sizes occurs
in response to oceanic forcing during T-II. Although additional model-
ling of the deglaciation of the former Northern Hemisphere ice sheets
during T-II will be required to further support this hypothesis, our ice-
sheet modelling does show that oceanic forcing was the primary driver
of excess ice loss from the Greenland and Antarctic ice sheets during
the LIG. Our sea-level predictions demonstrate that the modelled 4 m
increase in GMSLE from LIG deglaciation of the Greenland and Antarctic
ice sheets may explain much of the LIG RSL at intermediate- and far-field
sites when GIA from T-II deglaciation is included, although additional
melt is required to fully reconcile these data.
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availability are available at https://doi.org/10.1038/s41586-020-1931-7.
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