| Title | Testing the limits in a greenhouse ocean: did low nitrogen availability limit marine productivity during the end-Triassic mass extinction? |
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| Author | Schoepfer, S D; Algeo, T J ; Ward, P D; Williford, K H; Haggart, J W |
| Source | Earth and Planetary Science Letters vol. 451, 2016 p. 138-148, https://doi.org/10.1016/j.epsl.2016.06.050  Open Access |
| Image |  |
| Year | 2016 |
| Alt Series | Earth Sciences Sector, Contribution Series 20160084 |
| Publisher | Elsevier BV |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Subjects | tectonics; paleontology; marine geology; extinctions, biotic; oceanography; nitrogen; isotopes; paleoenvironment; paleogeography; Wrangellia; Panthalassic Ocean; Panthalassa; Mesozoic; Jurassic;
Triassic |
| Illustrations | location maps; stratigraphic columns; plots; models |
| Program | GSC Pacific Division |
| Released | 2016 10 01 |
| Abstract | The end-Triassic mass extinction has been characterized as a 'greenhouse extinction', related to rapid atmospheric warming and associated changes in ocean circulation and oxygenation. The response of
the marine nitrogen cycle to these oceanographic changes, and the extent to which mass extinction intervals represent a deviation in nitrogen cycling from other ice-free 'greenhouse' periods of Earth history, remain poorly understood. The
well-studied Kennecott Point section in Haida Gwaii, British Columbia, Canada, was deposited in the open Panthalassic Ocean, and is used here as a test case to better understand changes in the nitrogen cycle and marine productivity from the
pre-crisis greenhouse of the Rhaetian to the latest-Rhaetian crisis interval. We estimated marine productivity from the late Norian to the early Hettangian using TOC-and P-based paleoproductivity transform equations, and then compared these estimates
to records of sedimentary nitrogen isotopes, redox-sensitive trace elements, and biomarker data. Major negative excursions in d15N (to -<0perthousand) correspond to periods of depressed marine productivity. During these episodes, the development of a
stable pycnocline below the base of the photic zone suppressed vertical mixing and limited N availability in surface waters, leading to low productivity and increased nitrogen fixation, as well as ecological stresses in the photic zone. The
subsequent shoaling of euxinic waters into the ocean surface layer was fatal for most Triassic marine fauna, although the introduction of regenerated NH+4into the photic zone may have allowed phytoplankton productivity to recover. These results
indicate that the open-ocean nitrogen cycle was influenced by climatic changes during the latest Triassic, despite having existed in a greenhouse state for over 50 million years previously, and that low N availability limited marine productivity for
hundreds of thousands of years during the end-Triassic crisis. |
| Summary | (Plain Language Summary, not published)
The authors have studied ecological processes that may have contributed to the mass extinction of life at the end of the Triassic Period of Earth
history, about 200 million years ago. To do this, they studied geochemical signatures reflecting the composition of the oceans and atmosphere during Triassic time, preserved in rocks deposited at that time and preserved on the archipelago of Haida
Gwaii in western Canada. Haida Gwaii is so far the only place in the world where rocks of appropriate age and of sufficient quality to be studied in this manner are known to exist. Based on their analyses, the authors conclude that low levels of
oxygen and high levels of nitrogen in the world's oceans in latest Triassic time changed the biological composition of the oceans significantly, and were likely strong contributing factors of the mass-extinction event recognized at the end of the
Triassic Period. |
| GEOSCAN ID | 298846 |
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