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Explaining the Phanerozoic Ca isotope history of seawater

转发Geology文章(doi: 10.1130/G33191.1)“Explaining the Phanerozoic Ca isotope history of seawater” by Blattler, C. L., Henderson, G. M., Jenkyns, H. C.

Abstract: A new geochemical budget for the modern marine carbonate sink helps to explain the major features of the Phanerozoic Ca isotope record. A large compilation of Ca isotope ratios for modern carbonates, incorporating more than 50 new measurements, represents the quantitatively important components of the system. With this data set, distinct Ca isotope ratios are identified for different types of marine carbonate, the balance of which has changed over time with shifts between calcite and aragonite seas and with the development of pelagic calcification during the Mesozoic. It is suggested that large-scale changes in the Ca isotope ratio of seawater, as exemplified by that in the Carboniferous, were no longer possible after Jurassic time because of the generation of a deep-sea calcite sink expressed by deposition of foraminiferal–coccolith ooze across the world ocean. This work demonstrates the close connection between isotopic cycling, carbonate sedimentation, seawater chemistry, and evolutionary trends.

Deoxygenation in warming oceans?

Deoxygenation in warming oceans—Looking back to the future

Timothy W. Lyons and Christopher T. Reinhard

Earth’s climate has varied dramatically over its long history, from snowball glaciations to greenhouse extremes. Ancient warming is one reason we study the past—to get the fullest possible picture of what might lie ahead. No episode of past warming was more dramatic than the Paleocene-Eocene Thermal Maximum (PETM) ∼55 m.y. ago: a rapid temperature increase of ∼5–8 °C unfolded over a mere tens of thousands of years, driving severe perturbations to the marine and terrestrial carbon cycles and concomitant impacts on ecologies in both settings. As we anticipate the impacts possible via modern climate trends, with similar levels of projected carbon release and temperature rise but over only centuries, the PETM has become a conservative poster child for why we look back in time to inform our understanding of the future.

For the more details, see http://geology.gsapubs.org/content/40/7/671.full?rss=1