Circumpolar Deep Water and Shelf Sediments Support Late Summer Microbial Iron Remineralization

• Published in: Global biogeochemical cycles Vol. 35; no. 11
• Main Authors: Smith, Abigail J. R., Ratnarajah, Lavenia, Holmes, Thomas M., Wuttig, Kathrin, Townsend, Ashley T., Westwood, Karen, Cox, Martin, Bell, Elanor, Nicol, Stephen, Lannuzel, Delphine
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-11-2021
• Subjects: biogeochemistry; Biological uptake; Blooms; coastal; Coastal zone; Continental shelves; Deep water; dissolved trace elements; Glaciers; Iron; Manganese; Marine animals; Marine organisms; Microorganisms; Mixed layer; Oceanographic stations; Oceans; Phytoplankton; Polynyas; Primary production; Remineralization; Resuspension; Seasonal variation; Seasonal variations; Sediments; Shelf sedimentation; Summer; Titanium; Trace elements; Antarctica
• ISSN: 0886-6236; 1944-9224
• DOI: 10.1029/2020GB006921

Despite widespread iron (Fe) limitation in the Southern Ocean, intense phytoplankton blooms are observed around productive coastal regions such as the Mertz Polynya (off George V Land and Adelie Land, East Antarctica; 140–155°E). Sources of Fe across coastal East Antarctica vary, with limited data available for late summer months. We investigated the sources of dissolved Fe (dFe; <0.2 μm) at 19 oceanographic stations in the Mertz Glacier Region (64–67°S; 138–154°E), between January and March of 2019. Concentrations of dFe ranged from below detection limit (0.03 nM) at the surface, to 0.34 nM above the base of the mixed layer (35 m), reaching 0.59 nM at depth (520 m). Using oceanographic features and trace element ratios (manganese and titanium), we identified Circumpolar Deep Water (CDW) and shelf sediment resuspension in modified CDW as contributors of dFe to the region over this period. Microbial Fe remineralization was evident where nutrient‐rich water met highly oxygenated waters over the continental shelf. Reduced Fe concentrations in the mixed layer and euphotic zones suggested rapid biological uptake prior to sampling. Despite proposals for pelagic Fe recycling by marine animals, preliminary investigations reveal no significant spatial relationship between animal presence and surface ocean Fe concentrations over the study area. Further research is required to identify seasonal changes to Fe supply in coastal areas which will strengthen our understanding of the Fe cycle and its influence on microbial and primary productivity in this globally significant region.
Key Points
Circumpolar Deep Water and sediment resuspension supply iron to the Mertz Glacier Region during late summer
Significant iron remineralization occurs over the continental shelf as a result of bacterial production
The presence of marine animals show no observable relationship with dissolved iron distributions in surface waters