Microbial Fe(III) reduction as a potential iron source from Holocene sediments beneath Larsen Ice Shelf

Jaewoo Jung,Tim M Conway,Chung Yeon Hwang,Jinwook Kim,Jae Il Lee,Kiho Yang,Kyu-Cheul Yoo,Brad E Rosenheim,Christina Subt,Ho Il Yoon

doi:10.1038/s41467-019-13741-x

Abstract

Recent recession of the Larsen Ice Shelf C has revealed microbial alterations of illite in marine sediments, a process typically thought to occur during low-grade metamorphism. In situ breakdown of illite provides a previously-unobserved pathway for the release of dissolved Fe2+ to porewaters, thus enhancing clay-rich Antarctic sub-ice shelf sediments as an important source of Fe to Fe-limited surface Southern Ocean waters during ice shelf retreat after the Last Glacial Maximum. When sediments are underneath the ice shelf, Fe2+ from microbial reductive dissolution of illite/Fe-oxides may be exported to the water column. However, the initiation of an oxygenated, bioturbated sediment under receding ice shelves may oxidize Fe within surface porewaters, decreasing dissolved Fe2+ export to the ocean. Thus, we identify another ice-sheet feedback intimately tied to iron biogeochemistry during climate transitions. Further constraints on the geographical extent of this process will impact our understanding of iron-carbon feedbacks during major deglaciations.

Highlights

Recent recession of the Larsen Ice Shelf C has revealed microbial alterations of illite in marine sediments, a process typically thought to occur during low-grade metamorphism
Induced geochemical reactions can modify both mineral structure and chemistry[13], properties that are sensitive to redox conditions[12], and microbes are present in cold but diverse glacio-marine environments[19] associated with ice sheets[20], introducing the possibility that microbes may play a role in biogeochemical weathering and mineral alteration, even at very low temperatures[21]
The sedimentary sequence unveiled adjacent to LIS-C preserved a depositional record through the Holocene at shallow core depths (

Summary

Introduction

Recent recession of the Larsen Ice Shelf C has revealed microbial alterations of illite in marine sediments, a process typically thought to occur during low-grade metamorphism. We present a broadly applicable alternative pathway for dissolved Fe2+ production in sediment porewaters through microbial alteration of clay minerals, in addition to Fe(III) oxides, the strength of which will change corresponding to the depositional conditions during the expansion and retreat of ice shelves.

Results

Conclusion