Sediments in sea ice drive the Canada Basin surface Mn maximum: insights
from an Arctic Mn ocean model
Biogeochemical cycles in the Arctic Ocean are sensitive to the transport
of materials from continental shelves into central basins by sea ice.
However, it is difficult to assess the net effect of this supply
mechanism due to the spatial heterogeneity of sea ice content. Manganese
(Mn) is a micronutrient and tracer which integrates source fluctuations
in space and time. The Arctic Ocean surface Mn maximum is attributed to
freshwater, but studies struggle to distinguish sea ice and river
contributions. Informed by observations from 2009 IPY and 2015 Canadian
GEOTRACES cruises, we developed a three-dimensional dissolved Mn model
within a 1/12 degree coupled ocean-ice model centered on the Canada
Basin and the Canadian Arctic Archipelago (CAA). Simulations from
2002-2019 indicate that annually, 87-93% of Mn contributed to the
Canada Basin upper ocean is released by sea ice, while rivers, although
locally significant, contribute only 2.2-8.5%. Downstream, sea ice
provides 34% of Mn transported from Parry Channel into Baffin Bay.
While rivers are often considered the main source of Mn, our findings
suggest that in the Canada Basin they are less important than sea ice.
However, within the shelf-dominated CAA, both rivers and sediment
resuspension are important. Climate induced disruption of the transpolar
drift may reduce the Canada Basin Mn maximum and supply downstream.
Other micronutrients found in sediments, such as Fe, may be similarly
affected. These results highlight the vulnerability of the
biogeochemical supply mechanisms in the Arctic Ocean and the subpolar
seas to climatic changes.