Climate-modulated nutrient conditions along the Labrador Shelf: Evidence
from nitrogen isotopes in a six-hundred-year-old crustose coralline alga
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]
Author ProfileEsme 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
Author ProfileAbstract
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.