Date of Award

Summer 2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean & Earth Sciences

Committee Director

John Klinck

Committee Director

Chet Grosch

Committee Member

Eileen Hofmann

Committee Member

fang Hu

Committee Member

Dennis McGillicuddy

Committee Member

Laurie Padman

Abstract

The Ross Sea is the most biologically productive region in the Southern Ocean. Primary production is controlled by dissolved iron (dFe), a limiting micronutrient. The main focus of this thesis, motivated by the PRISM-RS project, is to investigate how tides and mesoscale eddies affect the pathways of dFe to the surface ocean.

A regional ocean model with four hindcast simulations are used. Tidal forcing is added to simulations and mesoscale eddies are resolved by changing the horizontal grid resolution from 5 to 1.5 km. Simulations cover 1.5 years, ending at the time of the PRISM-RS cruise in early 2012. An extended 20 year simulation provides an estimate of model variability and significance. The model is validated using hydrographic data from the PRISM-RS cruise and climatological values of water mass volumes. Compared to observations, simulations show a salinity offset at depth, that can be attributed to freshening of the Ross Sea in recent years. The model represents water mass volumes well, but has a reduced amount of Ice Shelf Water. Analysis of eddy formation in the model indicates that the weak stratification produces small and short-lived mesoscale eddies in the Ross Sea. The increased resolution approximately doubles the number of eddies seen in one year of simulation and significantly increases the baroclinic eddy kinetic energy.

The effect of tidal forcing on sea ice is investigated using a new method to extract a diurnal signal from satellite swath data. In the northwest corner of the Ross Sea continental shelf, strong tidal divergence causes the sea ice to decrease by 20% in winter. Simulation results show a strong heat flux that generates sea ice during spring tide conditions.

The supply of dFe in simulations is calculated using four passive tracer dyes representing sources of dFe: sea ice, glacial ice, Circumpolar Deep Water, and benthic supply. The simulation without tides at 5 km resolution estimates the total supply of dFe to the surface at 6.63 μmol m-2 yr-1. Tides increase this by 20%, eddies decrease it by 15%, and the net change from both is not significant. Spatially, the pattern of dFe supply varies significantly between all simulations.

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DOI

10.25777/c0en-7b20

ISBN

9780355405378

ORCID

0000-0002-0995-9678

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