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A leading hypothesis explaining Phanerozoic mass extinctions and associated carbon isotopic anomalies is the emission of greenhouse, other gases, and aerosols caused by eruptions of continental flood basalt provinces. However, the necessary serial relationship between these eruptions, isotopic excursions, and extinctions has never been tested in geological sections preserving all three records. The end-Triassic extinction (ETE) at 201.4 Ma is among the largest of these extinctions and is tied to a large negative carbon isotope excursion, reflecting perturbations of the carbon cycle including a transient increase in CO 2 . The cause of the ETE has been inferred to be the eruption of the giant Central Atlantic magmatic province (CAMP). Here, we show that carbon isotopes of leaf wax derived lipids (n-alkanes), wood, and total organic carbon from two orbitally paced lacustrine sections interbedded with the CAMP in eastern North America show similar excursions to those seen in the mostly marine St. Audrie's Bay section in England. Based on these results, the ETE began synchronously in marine and terrestrial environments slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco, a CO 2 super greenhouse, and marine biocalcification crisis. Because the temporal relationship between CAMP eruptions, mass extinction, and the carbon isotopic excursions are shown in the same place, this is the strongest case for a volcanic cause of a mass extinction to date.astrochronology | CO2 | Jurassic | large igneous provinces | n-alkane P lants record through photosynthetic pathways the atmospheric values of δ 13 C that in turn reflect the exchangeable surface oceanic carbon reservoir (1). One of the most direct known plant proxies is the δ 13 C alk measurements of n-C 25 -n-C 31 n-alkanes derived from leaf wax lipids of plant cuticles (2). We analyzed δ 13 C alk , the carbon isotopic composition of wood (δ 13 C wood ), and total organic carbon (δ 13 C toc ) from sediments from two overlapping lacustrine sections interbedded with the lavas of the Central Atlantic magmatic province (CAMP) (3) in eastern North America to obtain a carbon isotope record unambiguously tied to the eruptions and climate proxies to compare with and calibrate organic carbon and carbonate δ 13 C records from elsewhere (3-7). This allows direct determination of the relationship between one of the largest Phanerozoic mass extinctions, the end-Triassic extinction (ETE) (8), carbon isotopic and CO 2 (9) excursions, the biocalcification crisis (10), and their proposed cause, the CAMP (3, 11-13). Core and outcrop samples were obtained from the Newark (New York, New Jersey, and Pennsylvania) and Hartford (Connecticut and Massachusetts) rift basins at 19-20°N paleolatitude (14) in the tropical humid to arid transition of central Pangea (Fig. 1). A hierarchy of Milankovitchforced lake level cycles permeate the sampled strata in these basins, and in conjunction with a high sediment accumulation rate and ...

We studied the nitrogen biogeochemistry of the ice‐covered eastern Bering Sea shelf using the isotope ratios (15N/14N and 18O/16O) of NO3− and other N species. The 15N/14N of late winter NO3− on the shelf decreases inshore and is inversely correlated with bottom water [NH4+], consistent with an input of low‐15N/14N NO3− from partial nitrification of NH4+ remineralized from the sediments. An inshore 15N/14N increase in total dissolved N (TDN) suggests that (1) the sediment‐derived NH4+ is elevated in 15N due to the same partial nitrification that yields the low‐15N/14N NO3−, and (2) 15N‐deplete NO3− from partial nitrification within the sediments is denitrified to N2. The proportion of newly nitrified NO3− on the shelf, evidenced by an inshore decrease in NO3− 18O/16O, is correlated with the N deficit, further implicating nitrification coupled to denitrification; however, a simple N isotope budget indicates a comparable rate of denitrification supported by diffusion of NO3− into the sediments. The isotopic impact of benthic N loss is further demonstrated by a correlation between the 15N/14N of shelf surface sediment and the N deficit of the overlying water column, both of which increase inshore and northward, as well as by Arctic NO3− isotope data indicating that the fixed N transported through Bering Strait has a 15N/14N higher than is found in the open Bering Sea. The significant net isotope effect of benthic N loss on the Bering shelf, 6–8 ‰, is at odds with previous assumptions regarding the global ocean's N isotope budget.