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Author(s): Bernhard Bereiter (corresponding author) [1, 2, 3]; Sarah Shackleton [1]; Daniel Baggenstos [1, 2]; Kenji Kawamura [4, 5, 6]; Jeff Severinghaus [1] Today, the global ocean takes up about [...], Little is known about the ocean temperatures 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 2.570.24 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[sub.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.

Author(s): Vasilii V. Petrenko (corresponding author) [1]; Andrew M. Smith [2]; Hinrich Schaefer [3]; Katja Riedel [3]; Edward Brook [4]; Daniel Baggenstos [5, 6]; Christina Harth [5]; Quan Hua [2]; [...]

Ice-core studies indicate that during the past 800 kyr tropospheric [N.sub.2]O concentrations ranged from about 200 to 300 p.p.b., covarying with climate on glacial-interglacial and millennial timescales (refs 2-8 and [...], Nitrous oxide ([N.sub.2]O) is an important greenhouse gas and ozone-depleting substance that has anthropogenic as well as natural marine and terrestrial sources (1). The tropospheric [N.sub.2]O concentrations have varied substantially in the past in concert with changing climate on glacial-interglacial and millennial timescales (2-8). It is not well understood, however, how [N.sub.2]O emissions from marine and terrestrial sources change in response to varying environmental conditions. The distinct isotopic compositions of marine and terrestrial [N.sub.2]O sources can help disentangle the relative changes in marine and terrestrial [N.sub.2]O emissions during past climate variations (4,9,10). Here we present [N.sub.2]O concentration and isotopic data for the last deglaciation, from 16,000 to 10,000 years before present, retrieved from air bubbles trapped in polar ice at Taylor Glacier, Antarctica. With the help of our data and a box model of the [N.sub.2]O cycle, we find a 30 per cent increase in total [N.sub.2]O emissions from the late glacial to the interglacial, with terrestrial and marine emissions contributing equally to the overall increase and generally evolving in parallel over the last deglaciation, even though there is no a priori connection between the drivers of the two sources. However, we find that terrestrial emissions dominated on centennial timescales, consistent with a state-of-the-art dynamic global vegetation and land surface process model that suggests that during the last deglaciation emission changes were strongly influenced by temperature and precipitation patterns over land surfaces. The results improve our understanding of the drivers of natural [N.sub.2]O emissions and are consistent with the idea that natural [N.sub.2]O emissions will probably increase in response to anthropogenic warming (11).