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A major puzzle of paleoclimatology is why, after a tong interval of cooling climate, each late Quaternary ice age ended with a relatively short warming leg called a termination. We here offer a comprehensive hypothesis of how Earth emerged from the last global ice age. A prerequisite was the growth of very large Northern Hemisphere ice sheets, whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation. The Southern Hemisphere westerlies shifted poleward during each northern stadial, producing pulses of ocean upwelling and warming that together accounted for much of the termination in the Southern Ocean and Antarctica. Rising atmospheric C[O.sub.2] during southern upwelling pulses augmented warming during the last termination in both polar hemispheres. 10.1126/science.1184119

A decrease in the ratio of [sup.18]O to [sup.16]O ([delta][sup.18]O) of sedimentary carbonate from the Bolivian Altiplano has been interpreted to indicate rapid surface uplift of the late Miocene Andean plateau (AP). Here we report on paleoclimate simulations of Andean surface uplift with an atmospheric general circulation model (GCM) that tracks oxygen isotopes in vapor. The GCM predicts changes in atmospheric circulation and rainfall that influence AP isotopic source and amount effects. On eastern AP slopes, summer convective precipitation increases by up to 6 millimeters per day (>500%) for plateau elevations that are greater than about 2000 meters. High precipitation rates enhance the isotope amount effect, reading to a decrease in precipitation [delta][sup.18]O at high elevations and an increase in [delta][sup.18]O lapse rate. Our results indicate that late Miocene [delta][sup.18]O depletion reflects initiation and intensification of convective rainfall. 10.1126/science.1185078

The mid-latitude atmosphere is dominated by westerly, nearly zonal flow. Occasionally, this flow is deflected poleward by blocking anticyclones that persist for 10 days or longer. Experiments in a rotating annulus used radial pumping to generate a zonal jet under the action of the Coriolis force. In the presence of two symmetric ridges at the bottom of the annulus, the resulting flows were nearly zonal at high forcing or blocked at low forcing. Intermittent switching between blocked and zonal patterns occurs because of the jet's interaction with the topography. These results shed further light on previous atmospheric observations and numerical simulations., On short time scales (1 to 10 days), weather evolution is largely driven by three-dimensional, baroclinic instabilities of the prevailing westerlies (1) that convert the potential energy in the atmosphere's [...]

Atmospheric general circulation models used for climate simulation and weather forecasting require the fluxes of radiation, heat, water vapor, and momentum across the land-atmosphere interface to be specified. These fluxes are calculated by submodels called land surface parameterizations. Over the last 20 years, these parameterizations have evolved from simple, unrealistic schemes into credible representations of the global soil-vegetation-atmosphere transfer system as advances in plant physiological and hydrological research, advances in satellite data interpretation, and the results of large-scale field experiments have been exploited. Some modern schemes incorporate biogeochemical and ecological knowledge and, when coupled with advanced climate and ocean models, will be capable of modeling the biological and physical responses of the Earth system to global change, for example, increasing atmospheric carbon dioxide., Until the early 1980s, global atmospheric general circulation models (AGCMs) incorporated very simple land surface parameterizations (LSPs) to estimate the exchanges of energy, heat, and momentum between the land surface [...]

FUTURE ADVANCES IN RESEARCH ON THE INTERPRETATION of Earth rotation fluctuations will be inseparable from progress toward a better understanding of the structure and dynamics of all parts of the [...]

Annually dated ice cores from Siple Dome, West Antarctica, and central Greenland indicate that meridional atmospheric circulation intensity increased in the polar South Pacific and North Atlantic at the beginning (~1400 A.D.) of the most recent Holocene rapid climate change event, the Little Ice Age (LIA). As deduced from chemical concentrations at these core sites, the LIA was characterized by substantial meridional circulation strength variability, and this variability persists today despite strong evidence for an end to LIA cooling. Thus, increased late 20th century storm variability may be in part a result of the continuation of these climatic fluctuations., The LIA (nominally ~1400 to 1900 A.D.) is recorded in several Northern Hemisphere and equatorial paleoclimatic records; it was a period of cold, dry conditions and increased atmospheric circulation(1-4). It [...]

Inverse Modeling of Atmospheric Carbon Dioxide Fluxes Bousquet et al. (Reports, 17 November 2000, p. 1342) applied an inverse model to 20 years of atmospheric [CO.sub.2] observations to gain insight [...]

Food-web processes are important controls of oceanic biogenic carbon flux and ocean-atmosphere carbon dioxide exchange. Two key controlling parameters are the growth efficiencies of the principal trophic components and the rate of carbon remineralization. We report that bacterial growth efficiency is an inverse function of temperature. This relationship permits bacterial respiration in the euphotic zone to be computed from temperature and bacterial production. Using the temperature-growth efficiency relationship, we show that bacterial respiration generally accounts for most community respiration. This implies that a larger fraction of assimilated carbon is respired at low than at high latitudes, so a greater proportion of production can be exported in polar than in tropical regions. Because bacterial production is also a function of temperature, it should be possible to compute euphotic zone heterotrophic respiration at large scales using remotely sensed information., The net flux of [CO.sub.2] between the atmosphere and ocean is controlled, in large part, by the balance among three key food-web processes: carbon uptake by phytoplankton photosynthesis (PP, net [...]

Although an El Nino-Southern Oscillation (ENSO) event is a coupled ocean-atmosphere phenomenon (1), some stages of ENSO events can be examined usefully if one imposes the behavior of one fluid [...]

Monsoons are the seasonal rainbearing winds best known for their sometimes devastating effect on India and southern Asia. Our ability to forecast their timing and severity depends on understanding the [...]

Validity Tests of the Mixing-Length Theory of Deep Convection THE MIXING-LENGTH THEORY(MLT) of convection (1, 2) is at present the only practical approach for calculating convective fluxes in highly stratified [...]

Since 1976 a glaciological research program (1) has been conducted each summer on the tropical Quelccaya ice cap in the Andes of southern Peru. In 1983 two cores were recovered, [...]

Gas Exchange-Wind Speed Relation Measured with Sulfur Hexafluoride on a Lake Gas exchange across the air-water interface has received much attention (1) because it determines the degree of reaeration and [...]

The Arctic Oscillation is vying to be seen as the prime mover of high-latitude climate shifts, and may even be an agent of greenhouse-induced warming El Nino, the periodic warming [...]