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End-Permian (ca. 252 Ma) carbon isotope, paleobiological, and sedimentary data suggest that changes in ocean carbonate chemistry were directly linked to the mass extinction of marine organisms. Calcium isotopes provide a geochemical means to constrain the nature of these changes. The δ 44/40 Ca of carbonate rocks from southern China exhibits a negative excursion across the end-Permian extinction horizon, consistent with either a negative shift in the δ 44/40 Ca of seawater or a change in the calcite/aragonite ratio of carbonate sediments at the time of deposition. To test between these possibilities, we measured the δ 44/40 Ca of hydroxyapatite conodont microfossils from the global stratotype section and point (GSSP) for the Permian-Triassic boundary at Meishan, China. The conodont δ 44/40 Ca record shows a negative excursion similar in stratigraphic position and magnitude to that previously observed in carbonate rocks. Parallel negative excursions in the δ 44/40 Ca of carbonate rocks and conodont microfossils cannot be accounted for by a change in carbonate mineralogy, but are consistent with a negative shift in the δ 44/40 Ca of seawater. Such a shift is best accounted for by an episode of ocean acidifi cation, pointing toward strong similarities between the greatest catastrophe in the history of animal life and anticipated global change during the twenty-fi rst century.

Understanding carbon cycling in continental margin settings is critical for constraining the global carbon cycle. Here we apply a multiproxy geochemical approach to evaluate regional carbon cycle dynamics in six New Zealand fjords. Using carbon and nitrogen concentrations and isotopes, lipid biomarkers, and redoxsensitive element concentrations, we show that the New Zealand fjords have carbon-rich surface sediments in basins that promote long-term storage (i.e., semirestricted basins with sediment accumulation rates of up to 4 mm yr 21 ). Using d 13 C distributions to develop a mixing model, we find that organic carbon in fjord sediments is well-mixed from marine and terrestrial sources in down-fjord gradients. This is driven by high regional precipitation rates of >6 m yr 21 , which promote carbon accumulation in fjord basins through terrestrial runoff. In addition, we have identified at least two euxinic subbasins, based on uranium, molybdenum, iron, and cadmium enrichment, that contain >7% organic carbon. Because the strength and position of the Southern Hemisphere westerly winds control precipitation and fjord circulation, carbon delivery and storage in the region are intimately linked to westerly wind variability. We estimate that the fjord region (759 km 2 ) may be exporting up to 1.4 3 10 7 kgC yr 21 , outpacing other types of continental margins in rates of carbon burial by up to 3 orders of magnitude.

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