Processes Controlling Trace Metal Distributions Within the Sub-surface Waters of a Mesoscale Anti-cyclonic Eddy
Abstract
In 2000 and 2001, a series of cruises were undertaken to study the physical, chemical and biological processes occurring within large eddies that form off the coast of British Columbia and travel westward into the Gulf of Alaska. This project allowed for the study of processes affecting trace metal distributions as coastal water ages. A simple physical mixing box-model for the sub-surface waters of an eddy was developed based on the change in the average salinity within the core of the eddy over time. This physical mixing model was found to produce results, such as initial salinity, lifetime prediction, and volume exchanged, similar to the observations and published estimates from other studies. With the use of the physical mixing model, the major controls on trace metals in the eddy core were studied. The average dissolved aluminum and manganese concentrations decreased within the eddy core as it aged. For aluminum it was found that 51% of the average dissolved decrease within core waters could be attributed to physical mixing with surrounding waters, whereas 49% was a result of particle scavenging. For manganese, 61% of the overall decrease in dissolved manganese concentration could be explained by the mixing of the eddy with the waters surrounding the eddy while 39% is presumably due to oxidative scavenging. From the model predictions the removal rates for aluminum and manganese were determined to be 4.0 ± 0.2pM/day and 0.68 ± 0.03pM/day respectively. Also, residence times of 3.2 ± 0.2 years for aluminum and 6.5 ± 0.3 years for manganese were calculated. The average dissolved cadmium and copper concentrations within the core of the eddy increased as the eddy traveled offshore into HNLC waters. For both cadmium and copper, the amount of the dissolved metal concentration increase within the core of the eddy at 16 months was not significantly different from the amount predicted from the physical mixing model. This suggested that between the depths of 40 to 400m within the eddy any recycling occurring from biological uptake in surface waters was minimal.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMOS11B1120C
- Keywords:
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- 4273 Physical and biogeochemical interactions;
- 4805 Biogeochemical cycles;
- processes;
- and modeling (0412;
- 0414;
- 0793;
- 1615;
- 4912);
- 4875 Trace elements (0489);
- 4899 General or miscellaneous