Richard Bintanja

Marine records of sediment oxygen isotope compositions show that the Earth's climate has gone through a succession of glacial and interglacial periods during the past million years. But the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep-water temperature affect the recorded isotopic composition^1,2,3,4,5. Separating these two effects would require long records of either sea level or deep-ocean temperature, which are currently not available. Here we use a coupled model of the Northern Hemisphere ice sheets⁶ and ocean temperatures, forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores, to quantify both contributions simultaneously. We find that the ice-sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima, suggesting that strong ocean cooling preceded slow ice-sheet build-up. The model yields mutually consistent time series of continental mean surface temperatures between 40 and 80° N, ice volume and global sea level. We find that during extreme glacial stages, air temperatures were 17 ± 1.8 °C lower than present, with a 120 ± 10 m sea level equivalent of continental ice present.

This paper presents snowdrift sublimation rates evaluated from meteorological and snowdrift data observed over Antarctic snow surfaces during austral summer. Snowdrift sublimation is found to be the major contributor to the total surface–atmosphere moisture flux in strong winds (equivalent latent heat fluxes up to 250 W m−2), during which surface sublimation becomes negligible because of formation of a near-surface saturated layer. Both surface and snowdrift sublimation interact strongly with the surface moisture budget of the near-surface atmospheric layer. The sum of surface and snowdrift sublimation rates compares reasonably well with the directly measured latent heat fluxes. On average, surface and snowdrift sublimation contributed about equally to the total latent heat flux of 13.1 W m−2 at one site, whereas snowdrift sublimation was estimated to contribute two-thirds of the total sublimation at three other sites. Spatial variations in snowdrift sublimation depend on differences in wind spee... Abstract This paper presents snowdrift sublimation rates evaluated from meteorological and snowdrift data observed over Antarctic snow surfaces during austral summer. Snowdrift sublimation is found to be the major contributor to the total surface–atmosphere moisture flux in strong winds (equivalent latent heat fluxes up to 250 W m−2), during which surface sublimation becomes negligible because of formation of a near-surface saturated layer. Both surface and snowdrift sublimation interact strongly with the surface moisture budget of the near-surface atmospheric layer. The sum of surface and snowdrift sublimation rates compares reasonably well with the directly measured latent heat fluxes. On average, surface and snowdrift sublimation contributed about equally to the total latent heat flux of 13.1 W m−2 at one site, whereas snowdrift sublimation was estimated to contribute two-thirds of the total sublimation at three other sites. Spatial variations in snowdrift sublimation depend on differences in wind spee...

Detailed concurrent summer observations of surface meteorological variables, high-resolution boundary layer profiles, and upper-air profiles were carried in the intermediate region between the high plateau and the coast in Dronning Maud Land, Antarctica, a region that includes several blue ice areas. The main goal is to find out to what extent the flow is influenced by 1) slope-inversion pressure gradients (katabatic force), 2) synoptic pressure gradients (geostrophic wind), and 3) thermal gradients (thermal wind), and how this compares with the situation near the coast. Both synoptic and katabatic forcings generally induce easterly winds in the boundary layer, with a clear diurnal cycle in their relative importance. Westerly surface winds occur less often than at nearby coastal stations Halley and Neumayer, indicating that the influence of synoptic and thermal effects decreases toward the interior of Antarctica. Hence, katabatic forcing dominates, in particular during clear-sky conditions. Under weak synoptic forcing, the boundary layer over the main blue ice area is susceptible to local-scale circulations, which produces noneasterly winds at the surface. This result is caused mainly by reduced cooling over blue ice, which renders the katabatic force weak or absent, and by the typical topographic setting.