Research

Ocean-ice shelf interactions

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Mesoscale eddies on Antarctic shelves

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Eddy tracks from 1 year of simulation in the Ross Sea. Red tracks are anti-cyclonic eddies; blue are cyclonic.
Dominant source of dFe on the Ross Sea continental shelf from simulation

Transport pathways of dissolved iron

Dissolved iron is a limiting micronutrient for the Ross Sea ecosystem - it is only need by phytoplankton in very small amounts (hence "micro"-nutrient), and it is the nutrient that is depleted first, limiting the total productivity.  Potential sources of dissolved iron include atmospheric dust, sea ice, glacial ice, deep nutrient-rich waters such as Circumpolar Deep Water (CDW), and bottom sediments.  To determine how iron gets from these source locations to the surface ocean where it can be used by phytoplankton, I used Lagrangian passive tracer dyes in a regional ocean model of the Ross Sea.  I found that iron supply is dominated by sea ice and near-bottom sources, and the supply is sensitive to tidal forcing and horizontal model resolution.

See Mack et al, 2017

Tidal polynyas

Polynyas are open areas of ocean surrounded by sea ice.  In the Southern Ocean, most polynyas are wind-driven: wind pushes the ice away from the coast, or away from an ice shelf, leaving an area of open water.  The ocean is warmer than the atmosphere in winter, and a wind-driven polynya is often an area of heat loss from the ocean, which can lead to sea ice formation.

In the Ross Sea, there is a region of sea ice near the northwest continental shelf break that is strongly affected by tides.  I developed a new method to examine high frequency satellite observations of sea ice concentration and extract diurnal tidal forcing signatures of the ice concentration.  The sea ice concentration changes with the diurnal tides (~24 hour cycle), and more significantly with the spring-neap tidal cycle (~2 weeks).  The change in sea ice concentration is directly related to tidal divergence: it is the velocity of the tides that pushes the ice apart and then together, not the motion of the sea surface.

This periodic opening of the sea ice has implications for heat fluxes from the ocean to the atmosphere.  The high frequency of the tides means heat is released in short bursts, with the potential for sea ice formation during periods of spring tides.

Tidal polynyas exist elsewhere, both in the Antarctic and the Arctic.  However, if these polynyas are forced by semi-diurnal tides (~12 hour cycle), satellite observations of sea ice concentration are not frequent enough to detect them without aliasing the signal.

See Mack et al, 2013

Probability that sea ice concentration doesn't exceed 95% in austral winter