Preprints
https://doi.org/10.5194/egusphere-2024-1359
https://doi.org/10.5194/egusphere-2024-1359
27 May 2024
 | 27 May 2024
Status: this preprint is open for discussion.

Antarctic Subglacial Trace Metal Mobility Linked to Climate Change Across Termination III

Gavin Piccione, Terrence Blackburn, Paul Northrup, Slawek Tulaczyk, and Troy Rasbury

Abstract. Antarctic meltwater is a significant source of iron that fertilizes present-day Southern Ocean ecosystems and may enhance marine carbon burial on geologic timescales. However, it remains uncertain how this nutrient flux changes through time, particularly in response to climate, due to an absence of geologic records detailing trace metal mobilization beneath ice sheets. In this study, we present a 25 kyr record of aqueous trace metal cycling beneath the East Antarctic Ice Sheet measured in a subglacial chemical precipitate that formed across glacial termination III (TIII). The deposition rate and texture of this sample describe a shift in basal meltwater flow following the termination. Alternating layers of opal and calcite deposited in the 10 kyr prior to TIII record centennial-scale subglacial flushing events, whereas reduced basal flushing resulted in slower deposition of a trace metal-rich (Fe, Mn, Mo, Cu) calcite in the 15 kyr after TIII. This sharp increase in calcite metal concentrations following TIII indicates that diminished subglacial meltwater flow restricted the influx of oxygen from basal ice melt to precipitate-forming waters, causing dissolution of redox-sensitive trace metals from the bedrock substrate. These results are consistent with a possible feedback between orbital climate cycles and Antarctic subglacial iron discharge to the Southern Ocean, whereby heightened basal meltwater flow during terminations supplies oxygen to subglacial waters along the ice sheet periphery, which reduces the solubility of redox sensitive elements. As the climate cools, thinner ice and slower ice flow reduce basal meltwater production rates, limiting oxygen delivery and promoting more efficient mobilization of subglacial trace metals. Using a simple model to calculate the concentration of Fe in Antarctic basal water through time, we show that the rate of Antarctic iron discharge to the Southern Ocean is highly sensitive to this heightened mobility, and may therefore, increase significantly during cold climate periods.

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Gavin Piccione, Terrence Blackburn, Paul Northrup, Slawek Tulaczyk, and Troy Rasbury

Status: open (until 10 Jul 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
Gavin Piccione, Terrence Blackburn, Paul Northrup, Slawek Tulaczyk, and Troy Rasbury

Data sets

U-series Geochronology, Isotope, and Elemental Geochemistry of a Subglacial Precipitate that Formed Across Termination III Gavin Piccione https://doi.org/10.15784/601781

Model code and software

Simplified model of thermal energy balance beneath the Antarctic ice sheet Slawek Tulaczyk https://doi.org/10.5281/zenodo.11126839

Modeled Antarctic subglacial iron discharge across glacial termination III Gavin Piccione https://doi.org/10.5281/zenodo.11126883

Gavin Piccione, Terrence Blackburn, Paul Northrup, Slawek Tulaczyk, and Troy Rasbury

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Short summary
Growth of microorganisms in the Southern Ocean is limited by low iron levels. Iron delivered from beneath the Antarctic Ice Sheet is one agent that fertilizes these ecosystems, but it is unclear how this nutrient source changes through time. Here, we measured the age and chemistry of a rock that records the iron concentration of Antarctic basal water. We show that increased dissolution of iron from rocks below the ice sheet can substantially enhance iron discharge during cold climate periods.