Sea-floor hydrothermal activity links climate to tectonics: the Eocene carbon dioxide greenhouse.

Two important findings of recent ocean floor drilling in the southeast Pacific (Deep Sea Drilling Project Leg 92) are (i) that sea-floor hydrothermal activity may fluctuate through time by as much as an order of magnitude and (ii) that episodes of greatest hydrothermal flux correspond to times when ridge-transform plate boundaries are undergoing major changes in their configuration rather than to known times of increased spreading rate or volcanism. Evidence is presented here in support of the hypothesis that heightened hydrothermal activity induced by the Eocene tectonic activity caused a global greenhouse effect, which may represent the long-sought-after historical analog to the carbon dioxide-induced global warming expected to occur by the middle of the next century.

Geologic approach to the long-term history of atmospheric circulation.

Eolian dust preserved in deep-sea pelagic sediments can be used as a proxy indicator of paleoclimate. Analyses of the particle size, composition, and mass accumulation rate of dust grains provide independent evidence of the intensity of atmospheric circulation and the availability of material in the eolian source region. These data provide information on atmospheric circulation and on the climate of the source area at time scales ranging from 103 to 108 years and have the potential to test computer-generated global circulation models.

The advanced group practice model.

This professional paper reviews the market and medical economic forces at work which favor the group practice model, and investigate alternative structures in the group practice model that would appeal to the solo practitioner and two-man association.

Possible methane-induced polar warming in the early Eocene.

Reconstructions of early Eocene climate depict a world in which the polar environments support mammals and reptiles, deciduous forests, warm oceans and rare frost conditions. At the same time, tropical sea surface temperatures are interpreted to have been the same as or slightly cooler than present values. The question of how to warm polar regions of Earth without noticeably warming the tropics remains unresolved; increased amounts of greenhouse gases would be expected to warm all latitudes equally. Oceanic heat transport has been postulated as a mechanism for heating high latitudes, but it is difficult to explain the dynamics that would achieve this. Here we consider estimates of Eocene wetland areas and suggest that the flux of methane, an important greenhouse gas, may have been substantially greater during the Eocene than at present. Elevated methane concentrations would have enhanced early Eocene global warming, and also might specifically have prevented severe winter cooling of polar regions because of the potential of atmospheric methane to promote the formation of optically thick, polar stratospheric ice clouds.