Effect of increased glacier melt on diagenetic Fe cycling in marine sediments at King George Island (Antarctica)

• Published in: Mineralogical Magazine
• Main Authors: Henkel, Susann, Kasten, Sabine, Sala, Hernan, Busso, Adrian S., Staubwasser, Michael
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: MINERALOGICAL SOC 2013
• Subjects: Antarctic; Southern Ocean; Antarctic Peninsula; King George Island; South Shetland Islands; Potter Cove; Marian; Maxwell Bay; Marian Cove; Antarc*; Antarctica; Iceberg*
• Online Access: https://epic.awi.de/id/eprint/34693/; https://hdl.handle.net/10013/epic.42888

The glacier melt of the Western Antarctic Peninsula and its surrounding islands influences biogeochemical processes in the water column and the marine sediment by changing the flux of mineral particles and nutrients (e.g. Fe) into the ocean. Sediment and pore water samples were collected at King George Island (South Shetland Islands) to unravel how the vicinity of ice-covered and -uncovered terrestrial environment affects redox zonation and diagenetic processes in the coastal sediments. The post-depositional dissolution of Fe-minerals and the stable Fe isotope signatures of pore water and specific Fe minerals were of special interest since changing Fe supplies - as reactive particles via melting icebergs or meltwater streams or dissolved via diffusion from the sediment into the bottom water - might not only impact local biogeochemical cycles but most likely also impact productivity in the Southern Ocean. Sediment cores of up to 45 cm length were retrieved in Potter Cove, Marian Cove, and Maxwell Bay. In vicinity to the glaciers the sediments showed an extended redox zonation. The post-oxic zone with Fe2+ concentrations of up to 300 μM ranged from 1 to 25 cm depth. Most probably, microbial activity in sediments close to the glaciers is sluggish due to low input of organic matter (OM). More condensed redox zones prevailed in troughs where OM from terrestrial or marine sources accumulates and in vicinity to research stations. The upward directed diffusive Fe2+ fluxes as inferred from pore water profiles range between 0 and ~1050 μM m-2 d-1. However, the correlation to the intensity of diagenesis is not straightforward. Fe isotopes of specific minerals were used to assess the intensity of Fe cycling. With ongoing Fe-oxide dissolution, the residual Fe pool becomes enriched in 56Fe, whereas dissolved Fe and secondary Fe-oxides become enriched in 54Fe. Thus, easily reducible Fe oxides show lowest !56Fe values at the top of the sediment column. We suggest that the retreat of the glaciers indirectly results in higher OM fluxes to shelf areas fueling diagenetic processes/nutrient recycling.