Retreat of large marine-terminating glaciers may increase iron supply to surface waters

The availability of the micronutrient iron (Fe) limits primary production in large parts of the high latitude oceans. There, glacial discharge enriched in dissolved Fe may stimulate phytoplankton growth and carbon sequestration. Previous research conducted in pro-glacial environments with samples collected on land suggested that glacial dissolved Fe supply to shelf waters may scale with freshwater discharge volume. Yet, data to support this conclusion is lacking for marine-terminating glaciers where glacial freshwater is injected subsurface into subglacial cavity waters residing beneath floating ice-tongues. GEOTRACES expedition GN05 on RV Polarstern sampled immediately adjacent to Greenland’s largest floating ice-tongue. Results reveal that subglacial dissolved Fe discharge from glacier Nioghalvfjerdsbrae at 79°N is decoupled from freshwater Fe inputs, but has important benthic dissolved Fe sources. Krisch et al (2021, see reference below) show that the long residence time of waters inside the subglacial cavity results in equilibration between dissolved Fe, and sedimentary and freshwater Fe sources. As a consequence, dissolved Fe fluxes to the shelf are currently unaffected by increasing freshwater discharge, and may instead scale with the seawater circulation beneath the large floating ice-tongue. The findings demonstrate that glacial retreat and loss of ice-shelves may potentially result in increases in dissolved Fe supply to surface waters downstream of large marine terminating glaciers in future.

Figure: Iron cycling in subglacial cavity underneath the 79oN floating ice tongue. Sediment supply, particle-dissolved Fe exchange and Fe ligand binding in combination with a prolonged water residence in the cavity (~162 days) resulted in enhanced dissolved Fe concentrations in the waters exiting the cavity.

Reference:

Krisch, S., Hopwood, M. J., Schaffer, J., Al-Hashem, A., Höfer, J., Rutgers van der Loeff, M. M., Conway, T. M., Summers, B. A., Lodeiro, P., Ardiningsih, I., Steffens, T., Achterberg, E. P. (2021). The 79°N Glacier cavity modulates subglacial iron export to the NE Greenland Shelf. Nature Communications, 12(1), 3030. Access the paper: https://doi.org/10.1038/s41467-021-23093-0

Latest highlights

Science Highlights

Controls of cadmium-phosphate systematic unraveled by Neural Networks and Ocean Circulation Inverse Model

Roshan and DeVries explore the similarities and contrasts between oceanic cadmium and phosphate cycles using an Artificial Neural Network mapping technique and Ocean Circulation Inverse Model.

23.06.2021

Science Highlights

A new and more quantitative atlas of the deep-sea burial fluxes of major and trace elements

Among other findings, authors find that the new opal flux is roughly a factor of two increase over previous estimates having important implications for the global silicon cycle.

21.05.2021

Science Highlights

Updated compilation of the global continental and marine lithogenic neodymium isotopic measurements

This new compilation and gridded datasets offer a concrete way forward to improve the application of neodymium isotopes as a useful tracer of ocean circulation.

05.05.2021

Science Highlights

Neodymium concentrations and isotopes help disentangling Siberian river influences on the Arctic Ocean

Paffrath and co-autors followed the relative contributions of the main Siberian rivers to the waters of the Transpolar Drift using neodymium parameters.

Rechercher