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 in 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 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 to 2019
indicate that annually, 82% of Mn contributed to the Canada Basin upper
ocean is released by sea ice, while rivers, although locally
significant, contribute only 4%. Downstream, sea ice provides 18% of
Mn transported from Parry Channel into Baffin Bay and rivers supply 4%.
While rivers are often considered the main source of Mn, our findings
suggest that in the Canada Basin they are much 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 nutrients 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.