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Climate-modulated nutrient conditions along the Labrador Shelf: Evidence from nitrogen isotopes in a six-hundred-year-old crustose coralline alga
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  • John Doherty,
  • Branwen Williams,
  • Esme Kline,
  • Walter Adey,
  • Benoit Thibodeau
John Doherty
The University of Hong Kong, The University of Hong Kong, The University of Hong Kong, The University of Hong Kong
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Branwen Williams
Claremont McKenna College, Pitzer College, Scripps College, Claremont McKenna College, Pitzer College, Scripps College, Claremont McKenna College, Pitzer College, Scripps College, Claremont McKenna College, Pitzer College, Scripps College

Corresponding Author:[email protected]

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Esme Kline
Claremont McKenna College, Pitzer College, Scripps College, Claremont McKenna College, Pitzer College, Scripps College, Claremont McKenna College, Pitzer College, Scripps College, Claremont McKenna College, Pitzer College, Scripps College
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Walter Adey
Department of Botany, Smithsonian Institution, Department of Botany, Smithsonian Institution, Department of Botany, Smithsonian Institution, Department of Botany, Smithsonian Institution
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Benoit Thibodeau
University of Hong Kong, University of Hong Kong, University of Hong Kong, University of Hong Kong
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Abstract

The impacts of climate change on north Atlantic nutrient chemistry remain poorly understood, as there exist a multitude of rapidly changing biological and physical drivers of nutrient conditions throughout the region. Here, we present nitrogen isotope measurements derived from a six-hundred-year-old crustose coralline alga (δ15Nalgal) to elucidate historical and contemporary trends in nitrate utilization and circulation patterns along the Labrador Shelf. Prior to the early 1900s, we argue that intervals during which utilization approached completion were controlled by reduced nitrate advection linked to an increased proportion of nitrate-poor polar waters and subdued Atlantic influence, as expected from concurrent negative modes of the Atlantic multidecadal oscillation. While nitrate conditions should have recovered in recent years, our record suggests that high utilization persisted since ~1870, which we also attribute to reduced Atlantic advection, likely associated with the twentieth-century anthropogenic weakening of the Atlantic meridional overturning circulation. These results highlight the role of ongoing climate-induced circulation changes in modulating nutrient distributions throughout the subpolar north Atlantic, which may have implications for other environmental phenomena such as fisheries and oceanic carbon storage.
May 2021Published in Paleoceanography and Paleoclimatology volume 36 issue 5. 10.1029/2020PA004149