Exploration of an ice-cliff grounding zone in Antarctica reveals frozen-on meltwater and high productivity

Abstract

Ice fluxes across the grounding zone affect global ice-sheet mass loss and sea level rise. Although recent changes in ice fluxes are well constrained by remote sensing, future projections remain uncertain, because key environments affecting ice-sheet dynamics – the ice-sheet bed and grounding zone – are largely unknown. Here, we used a remotely operated vehicle to explore the grounding zone of a Weddell Sea tidewater ice cliff. At 148 m we found a 0.3–0.5 m gap between the ice and the seafloor and a 0.4 m clear facies of debris- and bubble-free basal ice, suggesting freeze-on of meltwater in the distal marine portion of the ice sheet over the last 400 yr. Ploughmarks and low epifauna cover reveal recent grounding line retreat, as corroborated by satellite remote sensing. We found dense algal tufts on the ice cliff and high phytoplankton pigment concentrations, suggesting high productivity fuelled by nutrients from ice melt. As grounded tidewater ice cliffs rim 38% of the Antarctic continent, sinking and downwelling of organic matter along with low benthic turnover may contribute to enhanced carbon sequestration, providing a potentially important feedback to climate.

Animal–Energy Relationships in a Changing Ocean: The Case of Continental Shelf Macrobenthic Communities on the Weddell Sea and the Vicinity of the Antarctic Peninsula

“…Ice also controls sedimentation on the WS; the absence of rivers and the presence of ice shelves restrict sediment inputs mainly to lateral transport along the continental shelf, glacial marine sources from the grounding line of ice shelves, and ice-rafted debris [11,12]. Consequently, lithogenic sediment inputs are comparatively low relative to lower latitude settings.…”

“…Primary production will increase together with space and light availability at the sea surface (e.g., after ice shelf collapses and sea ice extent reduction) and iron fertilization derived from the transit of icebergs [6,71] and ice shelf melting at the surface and grounding lines [12,19,20]. Further, due to warming and iron releases, polynyas may persist longer than usual, hosting vigorous biological production and downward energy fluxes over the continental shelf [19][20][21]66].…”

Polar biocenosis cumulative response to environmental stressors reveals who benefits from marine ice loss

“…Similarly, ice shelf and glacier retreat enables the formation of sea ice in the newly formed glacial bays, increasing the surface area available for sympagic algae and ice-obligate species. Although rapid shifts towards local primary production have been reported due to ice shelf collapse (Ingels et al 2018), little is known about how this may affect benthic sub-ice shelf life that has recently been discovered (Griffiths et al 2021, Owsianowski andRichter 2021). On the one hand, the emergence of highly productive coastal zones can lead to more efficient sinks of anthropogenic carbon and nutrient cycling as well as support higher biodiversity and benefit fish stocks.…”

Direct observations of melting, freezing, and ocean circulation in an ice shelf basal crevasse

“…Throughout the text, we refer to the region spanning from the furthest tidally affected inland GL location to the point of full hydrostatic flotation as the grounding zone (GZ). To date, published oceanographic measurements exist in less than 10 Antarctic GZ ocean cavities (19)(20)(21)(22)(23)(24)(25). This leaves much uncertainty about the hydrographic properties, circulation patterns, and dominant scales of variability that drive ice-ocean interactions in these regions around Antarctica.…”