Two recent studies confirming two previous conclusions:



Two massive, rapid releases of carbon during the onset of the Palaeocene-Eocene thermal maximum
Gabriel J. Bowen, Bianca J. Maibauer et alNature Geoscience (2014) doi:10.1038/ngeo2316Published online 15 December 2014Abstracthttp://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2316.htmlThe Earth's climateabruptly warmed by 5-8 °C during the Palaeocene-Eocene thermal maximum (PETM),about 55.5 million years ago (1, 2). This warming was associated with amassive addition of carbon to the ocean-atmosphere system, but estimates ofthe Earth system response to this perturbation are complicated by widelyvarying estimates of the duration of carbon release, which range from less thana year to tens of thousands of years. In addition the source of the carbon, andwhether it was released as a single injection or in several pulses, remains thesubject of debate (2, 3, 4). Here we present a new high-resolution carbonisotope record from terrestrial deposits in the Bighorn Basin (Wyoming, USA)spanning the PETM, and interpret the record using a carbon-cycle box model ofthe ocean-atmosphere-biosphere system. Our record shows that the beginning ofthe PETM is characterized by not one but two distinct carbon release events,separated by a recovery to background values. To reproduce this pattern, ourmodel requires two discrete pulses of carbon released directly to theatmosphere, at average rates exceeding 0.9 Pg C yr?1, with the first pulselasting fewer than 2,000 years. We thusconclude that the PETM involved one or more reservoirs capable of repeated,catastrophic carbon release, and that rates of carbon release during the PETMwere more similar to those associated with modern anthropogenic emissions (5)than previously suggested (3, 4).

Nature Climate Change (2014)doi:10.1038/nclimate2479Published online 15 December 2014Saturation-statesensitivity of marine bivalve larvae to ocean acidification
George G. Waldbusser, Burke Haleset alAbstract:http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2479.htmlOcean acidification results in co-varying inorganic carbonsystem variables. Of these, an explicit focus on pH and organismal acid-baseregulation has failed to distinguish the mechanism of failure in highly sensitivebivalve larvae. With unique chemical manipulations of seawater we showdefinitively that larval shell development and growth are dependent on seawatersaturation state, and not on carbon dioxide partial pressure or pH. Althoughother physiological processes are affected by pH, mineral saturation state thresholds will be crossed decades to centuries ahead of pH thresholdsowing to nonlinear changes in the carbonate system variables as carbon dioxideis added. Our findings were repeatable for two species of bivalve larvaecould resolve discrepancies in experimental results, are consistent with aprevious model of ocean acidification impacts due to rapid calcification inbivalve larvae, and suggest a fundamental ocean acidification bottleneck atearly life-history for some marine keystone species.