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- Title
Sensitivity of the Relationship Between Antarctic Ice Shelves and Iron Supply to Projected Changes in the Atmospheric Forcing.
- Authors
Dinniman, Michael S.; St‐Laurent, Pierre; Arrigo, Kevin R.; Hofmann, Eileen E.; van Dijken, Gert L.
- Abstract
Upward advection or mixing of iron‐rich deep waters due to circulation changes driven by the rate of basal ice shelf melt was shown to be a primary control on chlorophyll a production in coastal polynyas over the Antarctic continental shelf. Here, the effects of atmospheric changes projected in 2100 on this relationship were examined with a 5‐km resolution ocean/sea ice/ice shelf model of the Southern Ocean with different simulated dissolved iron sources and idealized biological uptake. The atmospheric changes are added as idealized increments to the forcing. Inclusion of a poleward shift and strengthening of the winds, increased precipitation, and warmer atmospheric temperatures resulted in doubling of the heat advected onto the continental shelf and an 83% increase in the total Antarctic ice shelf basal melt. The total dissolved iron supply to the surface waters over the continental shelf increased by 62%, while the surface iron supply due just to basal melt driven overturning increased by 48%. However, even though the ice shelf driven contribution becomes less important to the total iron supply on average (29% of total), the ice shelf involvement becomes relatively even more important in some locations, such as the Amundsen and Bellingshausen Seas. The modified atmospheric conditions also produced a reduction in summer sea ice extent and a shoaling of the summer mixed layers. These simulated responses to projected changes suggest relief of light and nutrient limitation for phytoplankton blooms over the Antarctic continental shelf and perhaps an increase in annual production in years to come. Plain Language Summary: The growth of phytoplankton in Antarctic coastal waters is limited by the availability of light for photosynthesis and the supply of the trace nutrient dissolved iron. When the bottom of the floating margins of the Antarctic ice sheet (the ice shelves) melts, the melt water is less dense and rises along the base of the ice shelf, which causes deeper waters with high iron concentrations to rise toward the surface. An earlier study showed that this overturning circulation driven by the melting ice shelves is an important source of dissolved iron to the well‐lit surface waters in many locations around Antarctica. In this study, a computer model of the ocean and ice shelves is forced with projected future changes in different atmospheric conditions. These changes in the atmosphere lead to an increase in the ice shelf melt, the dissolved iron supplied to the ocean surface due to overturning driven by the ice shelf melt, and the total dissolved iron supplied to the surface. The atmospheric changes also reduce the summer sea ice cover, making more light available to the ocean surface. All these changes suggest that in the future, phytoplankton growth around Antarctica will increase. Key Points: Projected atmospheric changes increased ice shelf basal melt in a circum‐Antarctic ocean/sea ice/ice shelf circulation modelSurface dissolved iron supply, including from sediments, increased but the ice shelf melt effect on the supply was spatially heterogeneousSummer sea ice decreased and summer mixed layers shoal suggesting a possible reduction in nutrient and light limitation
- Subjects
ANTARCTICA; ICE shelves; ANTARCTIC ice; IRON; SEA ice; TERRITORIAL waters; CONTINENTAL shelf
- Publication
Journal of Geophysical Research. Oceans, 2023, Vol 128, Issue 2, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2022JC019210