Controls on summer phytoplankton blooms in a highly productive Antarctic coastal polynya
Abstract
Coastal polynyas, areas of seasonally open waters surrounded by sea ice, account for of all Antarctic continental shelf primary production. Of the Antarctic polynyas, the Amundsen Sea Polynya (ASP) is the most productive per unit area, and is important for understanding the role of polynyas in the global carbon cycle. The flux of both light and the micronutrient iron (Fe) to the surface mixed layer are important controls on productivity in the ASP, and both are likely to be altered rapidly with ongoing global climate change. By understanding the dynamic mechanisms controlling the full seasonal bloom in the ASP, we will enable more accurate projections of future changes in highly productive Antarctic coastal polynyas. To examine these controlling factors, we used a 1-D, ASP-specific physical-biogeochemical model to simulate the bloom at twelve Amundsen Sea Polynya International Research Expedition (ASPIRE) stations where the bloom was observed in austral summer 2010-2011. Surface forcing matched the time period of the simulations and included wind speed, sea ice concentration, incoming shortwave radiation, surface air temperature, net surface longwave radiation, and sea ice melt at the location of each station. We determined model parameters by Bayesian optimization and data assimilation of ASPIRE observations. The 1-D model captured the basic elements of ASPIRE observations, despite some differences between modeled and observed dissolved iron distributions. With this model, we explored the way iron limitation, paired with self-shading, controlled the rise, peak, and decline of the bloom at twelve polynya stations, and the role of the mixed layer depth in determining light vs. iron controls on the bloom. Modeled light limitation by self-shading was very high, but iron was drawn down as the bloom rose, becoming similarly limiting as light before the bloom went into decline. We also demonstrated that the depth of the mixed layer was influential for the development of the bloom. When mixed layers were deep, iron limitation took longer to intensify, so the bloom took longer to reach its maximum Chl a concentration with lower stratification. We also examined the bloom's climate sensitivity by testing the model response to imposed changes in light and nutrient conditions anticipated under a future climate change scenario.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMOS34B..06O
- Keywords:
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- 4207 Arctic and Antarctic oceanography;
- OCEANOGRAPHY: GENERALDE: 4255 Numerical modeling;
- OCEANOGRAPHY: GENERALDE: 4260 Ocean data assimilation and reanalysis;
- OCEANOGRAPHY: GENERALDE: 4262 Ocean observing systems;
- OCEANOGRAPHY: GENERAL