Source: Geophysical Research Letters
Much of Earth’s heat uptake is passed to the ocean, making ocean heat content key for understanding long-term climate patterns. Ocean heat content is typically lower during ice ages and rises during warmer periods of glacier retreat. Over the past 1.2 million years, ice ages and interglacials have occurred in cycles lasting about 100,000 years, and we are currently in an interglacial period after the Last Glacial Maximum occurred about 20,000 years ago.
Recent climate modeling studies have suggested that ocean heat content also changes on shorter timescales of just a few thousand years as a result of intermittent changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC)—a pattern of Atlantic Ocean currents that carries warm water north and cold water south. The models suggest that a weaker AMOC leads to increased ocean heat content. However, real-world evidence to support or refute AMOC’s potential influence on ocean heat content has been limited.
Grimmer et al. present the first record of ocean heat content during the ends of the last four ice ages and the subsequent warm periods, enabling the team to test modeling predictions against paleoclimate data.
To generate the new record, the researchers analyzed the ratios of specific noble gases trapped within 59 new samples from a 3,260-meter-long ice core drilled in East Antarctica as part of the European Project for Ice Coring in Antarctica (EPICA). The noble gas ratios in different ice layers serve as fingerprints of ocean heat content at various times in Earth’s past.
Analysis of the new record showed that at the end of each of the last four ice ages, ocean heat content generally increased alongside a weaker AMOC, as predicted by the models. These transitions to warmer interglacial periods, known as deglaciations, last several thousand years. The record also showed evidence of millennial-scale changes in ocean heat content that occurred alongside changes in ocean circulation. When the AMOC strengthened, ocean heat content either increased at a slower pace or decreased.
These findings align with the prior modeling predictions, supporting the idea that on millennial timescales, the AMOC plays a key role in controlling heat uptake by Earth’s oceans. In turn, this interaction likely influences subsequent sea levels, climate conditions, and atmospheric carbon dioxide levels. (Geophysical Research Letters, https://doi.org/10.1029/2024GL114415, 2025)
—Sarah Stanley, Science Writer
