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A new sea-level record for the Neogene/Quaternary boundary reveals transition to a more stable East Antarctic Ice Sheet

Significance We studied the response of global ice volume/sea level to climate forcing from ∼2.75 to 2.4 Ma, when atmospheric CO2 levels last lay in a range similar to the last two centuries. Our data reveal clear cycles in global sea level largely driven by the growth/decay of Northern Hemisphere ice sheets. Peak sea levels suggest melting of East Antarctic land ice prior to ∼2.53 Ma. Thereafter, glacial and interglacial sea levels are distinctly lower than before, suggesting that the growth of larger Northern Hemisphere ice sheets lowered sea level globally and acted to stabilize the East Antarctic Ice Sheet by limiting its exposure to warm ocean waters. Our findings provide a framework to help understand ice-volume variability under warmer-than-preindustrial climates. Sea-level rise resulting from the instability of polar continental ice sheets represents a major socioeconomic hazard arising from anthropogenic warming, but the response of the largest component of Earth’s cryosphere, the East Antarctic Ice Sheet (EAIS), to global warming is poorly understood. Here we present a detailed record of North Atlantic deep-ocean temperature, global sea-level, and ice-volume change for ∼2.75 to 2.4 Ma ago, when atmospheric partial pressure of carbon dioxide (pCO2) ranged from present-day (>400 parts per million volume, ppmv) to preindustrial (<280 ppmv) values. Our data reveal clear glacial–interglacial cycles in global ice volume and sea level largely driven by the growth and decay of ice sheets in the Northern Hemisphere. Yet, sea-level values during Marine Isotope Stage (MIS) 101 (∼2.55 Ma) also signal substantial melting of the EAIS, and peak sea levels during MIS G7 (∼2.75 Ma) and, perhaps, MIS G1 (∼2.63 Ma) are also suggestive of EAIS instability. During the succeeding glacial–interglacial cycles (MIS 100 to 95), sea levels were distinctly lower than before, strongly suggesting a link between greater stability of the EAIS and increased land-ice volumes in the Northern Hemisphere. We propose that lower sea levels driven by ice-sheet growth in the Northern Hemisphere decreased EAIS susceptibility to ocean melting. Our findings have implications for future EAIS vulnerability to a rapidly warming world.