Direct and Indirect Contributions of the Cryosphere to Micronutrient Supply to the Open Surface Waters around Antarctica
Abstract
Although difficult to measure, the cryosphere has obvious direct effects on the supply of the limiting micronutrient iron to the surface waters around Antarctica due to the injection of melt water from either sea ice or floating (ice shelves and icebergs) land ice. Satellite estimates of chlorophyll in the coastal polynyas over the Antarctic continental shelf are strongly correlated with the basal melt rate of adjacent ice shelves. This has led to speculation that the high productivity of coastal polynyas may be related to the release of iron from melting ice shelves. However, the interaction of the cryosphere with the ocean also leads to indirect methods of iron supply. The formation of sea ice in coastal polynyas leads to deep vertical mixing over the continental shelf in some locations that can allow iron from benthic water or deep laying intrusions of Circumpolar Deep Water to be mixed up to the surface prior to the growing season. Basal melting of ice shelves can drive a vigorous overturning circulation within ice shelf cavities ("meltwater pump") that can also bring "deep" sources of iron to the surface through a three dimensional pathway.
Here, we use a 5 km resolution ocean/sea ice/ice shelf model of the Southern Ocean to examine these different mechanisms over the Antarctic continental shelf. Four possible sources of dissolved iron are simulated with independent tracers, assumptions about the end member concentrations, and an idealized summer biological uptake. Although some end member concentrations are not well constrained, direct injection of iron from melting ice is shown to be an important contributor to the total dissolved iron supply to the surface waters. However, there is generally an even larger contribution from deep sources of iron on the shelf. The importance of the "meltwater pump" is quite heterogeneous around Antarctica, but in several locations it is the primary mechanism for mixing deep dissolved iron up to the surface.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.C21C1336D
- Keywords:
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- 0720 Glaciers;
- CRYOSPHEREDE: 0726 Ice sheets;
- CRYOSPHEREDE: 0728 Ice shelves;
- CRYOSPHEREDE: 4207 Arctic and Antarctic oceanography;
- OCEANOGRAPHY: GENERAL