Seasonal Dynamics of Dissolved Iron on the Antarctic Continental Shelf: Late-Fall Observations From the Terra Nova Bay and Ross Ice Shelf Polynyas

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Sedwick, P. N., Sohst, B. M., O'Hara, C., Stammerjohn, S. E., Loose, B., Dinniman, M. S., Buck, N. J., Resing, J. A., Ackley, S. F.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: ODU Digital Commons 2022
• Subjects: Aluminium; Aluminum; Antarctic shelf; Bays; Benthos; Continental shelves; Convective mixing; Deep water; Heavy metals; Hydrographic data; Ice formation; Ice shelves; Iron; Katabatic winds; Land ice; Local winds; Manganese; Mixed layer; Mixed layer depth; Ocean floor; Offshore; Overturn; Polar environments; Polynya; Polynyas; Primary production; Remineralization; Ross Sea; Sea ice; Sea ice formation; Sea surface; Seasonal variations; Seawater; Shelf dynamics; Shelf water; Summer; Surface mixed layer; surface water; Trace metals; Vertical mixing; Water circulation; Water column; Wind; Wind speed; Winter; Zinc; Glaciology; Hydrology; Oceanography; Antarctic; The Antarctic; Austral; Terra Nova Bay; Ross Ice Shelf; Antarc*; Ice Shelf; Ice Shelves
• Online Access: https://digitalcommons.odu.edu/oeas_fac_pubs/465; https://doi.org/10.1029/2022JC018999; https://digitalcommons.odu.edu/context/oeas_fac_pubs/article/1476/viewcontent/Sedwick_2022_SeasonalDynamicsofDissolvedIronOCR.pdf

Over the Ross Sea shelf, annual primary production is limited by dissolved iron (DFe) supply. Here, a major source of DFe to surface waters is thought to be vertical resupply from the benthos, which is assumed most prevalent during winter months when katabatic winds drive sea ice formation and convective overturn in coastal polynyas, although the impact of these processes on water-column DFe distributions has not been previously documented. We collected hydrographic data and water-column samples for trace metals analysis in the Terra Nova Bay and Ross Ice Shelf polynyas during April-May 2017 (late austral fall). In the Terra Nova Bay polynya, we observed intense katabatic wind events, and surface mixed layer depths varied from similar to 250 to similar to 600 m over lateral distances <10 km; there vertical mixing was just starting to excavate the dense, iron-rich Shelf Waters, and there was also evidence of DFe inputs at shallower depths in the water column. In the Ross Ice Shelf polynya, wind speeds were lower, mixed layers were <300 m deep, and DFe distributions were similar to previous, late-summer observations, with concentrations elevated near the seafloor. Corresponding measurements of dissolved manganese and zinc, and particulate iron, manganese, and aluminum, suggest that deep DFe maxima and some mid-depth DFe maxima primarily reflect sedimentary inputs, rather than remineralization. Our data and model simulations imply that vertical resupply of DFe in the Ross Sea occurs mainly during mid-late winter, and may be particularly sensitive to changes in the timing and extent of sea ice production.