Large flux of iron from the Amery Ice Shelf marine ice to Prydz Bay, East Antarctica

Abstract

The Antarctic continental shelf supports a high level of marine primary productivity and is a globally important carbon dioxide (CO2) sink through the photosynthetic fixation of CO2 via the biological pump. Sustaining such high productivity requires a large supply of the essential micronutrient iron (Fe); however, the pathways for Fe delivery to these zones vary spatially and temporally. Our study is the first to report a previously unquantified source of concentrated bioavailable Fe to Antarctic surface waters. We hypothesize that Fe derived from subglacial processes is delivered to euphotic waters through the accretion (Fe storage) and subsequent melting (Fe release) of a marine‐accreted layer of ice at the base of the Amery Ice Shelf (AIS). Using satellite‐derived Chlorophyll‐a data, we show that the soluble Fe supplied by the melting of the marine ice layer is an order of magnitude larger than the required Fe necessary to sustain the large annual phytoplankton bloom in Prydz Bay. Our finding of high concentrations of Fe in AIS marine ice and recent data on increasing rates of ice shelf basal melt in many of Antarctica's ice shelves should encourage further research into glacial and marine sediment transport beneath ice shelves and their sensitivity to current changes in basal melt. Currently, the distribution, volume, and Fe concentration of Antarctic marine ice is poorly constrained. This uncertainty, combined with variable forecasts of increased rates of ice shelf basal melt, limits our ability to predict future Fe supply to Antarctic coastal waters.

Sea Ice Meltwater and Circumpolar Deep Water Drive Contrasting Productivity in Three Antarctic Polynyas

“…While low‐latitude environments of the Southern Ocean may receive atmospheric inputs of iron, coastal Antarctica generally does not (Heywood et al, ), except for places such as McMurdo Sound which is in close proximity to the dry valleys and Mount Erebus volcano (de Jong et al, ). The main sources of iron to coastal Antarctica are (1) melting ice shelves, glaciers, and icebergs, particularly if marine ice is present (Herraiz‐Borreguero et al, ; Lin et al, ); (2) upwelled iron‐rich mCDW interacting with Fe‐rich sediments (de Jong et al, ; Measures et al, ; Sherrell et al, ); and (3) sea ice (Lannuzel, Vancoppenolle, et al, ). We examine each of these sources in this and the following two sections.…”

Summer Carbonate Chemistry in the Dalton Polynya, East Antarctica

“…Seasonal deficits in mixed‐layer TCO 2 were attributed to a combination of sea ice melt and biological production (Roden et al, ), similar to the drivers of TCO 2 depletion in the Dalton Polynya, resulting in low surface water f CO 2 and an air‐to‐sea flux of CO 2 . Recent studies in Prydz Bay propose that glacial meltwater from the nearby Amery Ice Shelf may bring a large, bioavailable source of dissolved iron from marine‐accredited ice beneath the ice shelf, locally enhancing primary productivity (Herraiz‐Borreguero et al, ). In contrast to the glacial meltwaters introduced by the intrusions of mCDW beneath the TIS and MUIS (warm‐regime) to Dalton Polynya, the glacial meltwaters introduced into Prydz Bay are the result of intrusions of cold Dense Shelf Water beneath the Amery Ice Shelf (cold regime; Silvano et al, ).…”

“…In contrast to the glacial meltwaters introduced by the intrusions of mCDW beneath the TIS and MUIS (warm‐regime) to Dalton Polynya, the glacial meltwaters introduced into Prydz Bay are the result of intrusions of cold Dense Shelf Water beneath the Amery Ice Shelf (cold regime; Silvano et al, ). The resulting outflow of supercooled ISW can entrain subglacial dissolved iron into the marine ice layer beneath the ice shelf and, upon basal melting, can deliver dissolved iron onto the continental shelf in concentrations up to 4 orders of magnitude higher than typical Southern Ocean waters (Herraiz‐Borreguero et al, ). In the analysis by Arrigo et al (), the input of basal meltwater by nearby ice shelves can explain almost 60% of the variance in mean Chl a concentrations in Antarctic polynyas.…”

Distributions, sources, and transformations of dissolved and particulate iron on the Ross Sea continental shelf during summer

“…These dFe sources are thought to include seafloor sediments and benthic detritus [ Hatta et al ., ; Marsay et al ., ], melting sea ice [ Lannuzel et al ., ; Schallenberg et al ., ; Sedwick and DiTullio , ], melting glacial ice and icebergs [ Gerringa et al ., ; Lin et al ., ; Raiswell et al ., ], subglacial meltwaters [ Death et al ., ; Herraiz‐Borreguero et al ., ], upwelling Circumpolar Deep Water [ McGillicuddy et al ., ; Prézelin et al ., ; Sedwick et al ., ], and deposition of iron‐bearing aerosols [ Cassar et al ., ; Edwards and Sedwick , ; Winton et al ., ]. In addition, relatively high concentrations of particulate iron (pFe) have been measured in surface waters over the Antarctic continental shelves [ Coale et al ., ; Fitzwater et al ., ; Planquette et al ., ], although the potential availability of this iron pool to phytoplankton, either directly or via conversion to dFe, remains to be established.…”