Journal
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
Volume 124, Issue 5, Pages 2943-2968Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2019JC015071
Keywords
polynyas; primary productivity; phytoplankton biomass; ice shelves; sea ice; iron
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Funding
- Australian Antarctic Division research projects [AAS 4131, 4291]
- Australian Government Cooperative Research Centres Programme through the Antarctic Climate & Ecosystems (ACE CRC)
- Australian Research Council's Special Research Initiative for Antarctic Gateway Partnership [SR140300001]
- Edith Cowan University
- Dickhut Fellowship
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In the Southern Ocean, polynyas exhibit enhanced rates of primary productivity and represent large seasonal sinks for atmospheric CO2. Three contrasting east Antarctic polynyas were visited in late December to early January 2017: the Dalton, Mertz, and Ninnis polynyas. In the Mertz and Ninnis polynyas, phytoplankton biomass (average of 322 and 354mg chlorophyll a (Chl a)/m(2), respectively) and net community production (5.3 and 4.6mol C/m(2), respectively) were approximately 3 times those measured in the Dalton polynya (average of 122mg Chl a/m(2) and 1.8mol C/m(2)). Phytoplankton communities also differed between the polynyas. Diatoms were thriving in the Mertz and Ninnis polynyas but not in the Dalton polynya, where Phaeocystis antarctica dominated. These strong regional differences were explored using physiological, biological, and physical parameters. The most likely drivers of the observed higher productivity in the Mertz and Ninnis were the relatively shallow inflow of iron-rich modified Circumpolar Deep Water onto the shelf as well as a very large sea ice meltwater contribution. The productivity contrast between the three polynyas could not be explained by (1) the input of glacial meltwater, (2) the presence of Ice Shelf Water, or (3) stratification of the mixed layer. Our results show that physical drivers regulate the productivity of polynyas, suggesting that the response of biological productivity and carbon export to future change will vary among polynyas.
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