# Tidewater cycle drives alpine glacial sediment plume geochemistry

## TL;DR

Glacier retreat in Alaska reduces the availability of iron and manganese in fjords, affecting coastal ecosystems and preserving glacier history in sediment.

## Contribution

The study reveals how tidewater glacier retreat alters trace-metal lability in sediment plumes, impacting ocean fertilization.

## Key findings

- Recent glacier retreat is linked to lower lability of iron and manganese in fjord surface plumes.
- Particle size does not influence chemical lability in transported sediment.
- Results suggest implications for future ecosystem fertilization and interpreting sediment archives.

## Abstract

Sediments transported by glacial meltwaters are important sources of trace-metal micronutrients for coastal microbial communities, linking cryospheric processes with ocean fertilization and biogeochemical cycles. Tidewater glacier advance-retreat cycles drive sediment fluxes and influence fjord geochemistry. Here, we used a chemical extraction method to determine the iron and manganese fertilization potential of suspended sediment-plume and iceberg-laden particulate matter from two adjacent, yet geomorphologically distinct, fjords in Southcentral Alaska. We found that the glacier retreat status underpinned the fraction of labile trace-metals within fjord surface plumes, with distinctly lower lability of metals associated with recent and rapid retreat coincident with enhanced erosion and chemical weathering. Particle size did not affect chemical lability, resulting in a well-mixed particle assemblage transported to the coastal ocean. With global tidewater glacier retreat, these results provide implications for future ecosystem fertilization via cryospheric processes and the interpretation of fjord sediment archives.

Glaciers grind rock into nutrient-rich sediments that fertilize fjords. A study of tidewater glaciers in Alaska found that retreat reduces iron and manganese availability, altering coastal ecosystems and recording glacier change over time.