Mean global ocean temperatures during the last glacial transition

Little is known about the ocean temperature’s long-term response to climate perturbations owing to limited observations and a lack of robust reconstructions. Although most of the anthropogenic heat added to the climate system has been taken up by the ocean up until now, its role in a century and beyond is uncertain. Here, using noble gases trapped in ice cores, we show that the mean global ocean temperature increased by 2.57 ± 0.24 degrees Celsius over the last glacial transition (20,000 to 10,000 years ago). Our reconstruction provides unprecedented precision and temporal resolution for the integrated global ocean, in contrast to the depth-, region-, organism- and season-specific estimates provided by other methods. We find that the mean global ocean temperature is closely correlated with Antarctic temperature and has no lead or lag with atmospheric CO 2 , thereby confirming the important role of Southern Hemisphere climate in global climate trends. We also reveal an enigmatic 700-year warming during the early Younger Dryas period (about 12,000 years ago) that surpasses estimates of modern ocean heat uptake. Noble gases trapped in ice cores are used to show that the mean global ocean temperature increased by 2.6 degrees Celsius over the last glacial transition and is closely correlated with Antarctic temperature. Reconstructing past ocean temperatures Many techniques exist to reconstruct past ocean temperatures. The majority of these approaches, however, can be used to study only specific depths or seasons, or are based on complicated and poorly understood biological processes. Bernhard Bereiter and colleagues use noble gases in ice cores to build a high-resolution reconstruction of mean ocean temperature from the Last Glacial Maximum to the early Holocene. They find an overall ocean warming of about 2.5 ℃ over this period, which is closely correlated with variations in Antarctic ocean temperature. A dramatic ocean warming exceeding that of the modern era occurred during the Younger Dryas period—a time of sharp cooling over much of the high-latitude Northern Hemisphere land mass.