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General Session 3: Biological oceanography & global change |
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Natural forcing of the north Atlantic N cycle in the anthropocene
Monday 9th @ 1525-1545
Multi-function Hall
Xingchen T. Wang* , Princeton University
Daniel M. Sigman, Princeton University
Anne L. Cohen, Woods Hole Oceanographic Institution
Presenter Email: xingchen@princeton.edu
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| Human alteration of the global nitrogen cycle accelerated with the invention of the Haber-Bosch process (i.e. ammonia synthesis) in the 1910s. As of today, the rate of N fixation by humans (~200 Tg/yr) is similar to the global rate of natural N fixation (200-250 Tg/yr), with a substantial fraction of the human-fixed N entering the broader environment and altering terrestrial and coastal ocean ecosystems. Model results suggest that the open ocean might also be affected by the anthropogenic N through atmospheric transport and deposition. However, it remains challenging to assess the impacts of atmospheric anthropogenic N on the open ocean N cycle due to a lack of continuous atmospheric and oceanographic measurements. Here, we investigate the possibility of changes in the North Atlantic open ocean N cycle since 1880 AD using the nitrogen isotopes of the organic matter bound in the skeletal carbonate of corals from offshore Bermuda. The coral skeletal d15N record shows <1.0‰ variation since the 1880s, with no significant decreasing trend associated with increasing anthropogenic N fixation. In addition, the d15N record shows significant correlation with the coral growth record on decadal timescales, with the latter suggested to be controlled by ocean dynamics linked to the North Atlantic Oscillation. Thus, our data indicate that the North Atlantic N cycle in the Anthropocene has been minimally affected by anthropogenic N, in contrast to the recent suggestions that the North Pacific N cycle has already been significantly altered by human activities. Given that anthropogenic N emissions (NOx and ammonia) have been decreasing in North America since 1990s, we postulate that in the coming decades North Atlantic will remain largely unaffected by anthropogenic N, even as other drivers of environmental change intensify. |
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