# Thinning Antarctic glaciers expose high-altitude nunataks delivering more bioavailable iron to the Southern Ocean

## TL;DR

As Antarctic glaciers thin, they expose more iron-rich rocks, which could boost ocean life and help absorb more CO2.

## Contribution

The study quantifies labile iron in Antarctic sediments and links glacial thinning to increased bioavailable iron delivery to the Southern Ocean.

## Key findings

- Antarctic sediments contain significant amounts of ascorbate extractable iron (FeA).
- Subaerially exposed sediments show enhanced dithionite extractable iron (FeD) concentrations.
- Glacial retreat may increase bioavailable iron supply to the Southern Ocean, potentially enhancing CO2 drawdown.

## Abstract

Glacial systems entrain and transfer sediment, rich in essential nutrients, from continental sources to the ocean, where they are released by meltwater. In the Southern Ocean, primary producers are limited by the availability of micronutrients, like iron (Fe), so any increase in continental sediment supply could enhance primary productivity and subsequent drawdown of atmospheric CO2. Here we provide a systematic account of labile Fe concentrations in Antarctic continental sediments. Ferrihydrite and crystalline Fe (oxyhydr)oxides were extracted from 27 Antarctic samples collected from nunataks, lateral moraines and blue ice areas in the Sør Rondane Mountains, East Antarctica. We report ascorbate extractable Fe (FeA) in all samples and enhanced precipitation of dithionite extractable Fe (FeD) in subaerially exposed mountain sediments. Our results suggest that as temperatures rise and Antarctic glaciers thin, newly exposed rock surfaces could supply more bioavailable iron to glacier systems, and subsequently the Southern Ocean.

Iron-rich sediments are transferred from Antarctic mountains to the coast by glacial systems. Sediments that reach ice shelf fronts provide iron to ocean phytoplankton, increasing CO2 uptake; this could increase with climate warming.