Publication Date:
2016-06-14
Description:
Glacial environments may provide an important but poorly constrained source of potentially bioavailable iron and manganese
phases to the coastal ocean in high-latitude regions. Little is known about the fate and biogeochemical cycling of glacially
derived iron and manganese in the coastal marine realm. Sediment and porewater samples were collected along transects
from the fjord mouths to the tidewater glaciers at the fjord heads in Smeerenburgfjorden, Kongsfjorden, and Van Keulenfjorden
along Western Svalbard. Solid-phase iron and manganese speciation, determined by sequential chemical extraction,
could be linked to the compositions of the local bedrock and hydrological/weathering conditions below the local glaciers. The
concentration and sulfur isotope composition of chromium reducible sulfur (CRS) in Kongs- and Van Keulenfjorden sediments
largely reflect the delivery rate and isotope composition of detrital pyrite originating from adjacent glaciers. The varying
input of reducible iron and manganese oxide phases and the input of organic matter of varying reactivity control the
pathways of organic carbon mineralization in the sediments of the three fjords. High reducible iron and manganese oxide
concentrations and elevated metal accumulation rates coupled to low input of “fresh” organic matter lead to a strong expression
of dissimilatory metal oxide reduction evidenced in very high porewater iron (up to 800 lM) and manganese (up to
210 lM) concentrations in Kongsfjorden and Van Keulenfjorden. Sediment reworking by the benthic macrofauna and physical
sediment resuspension via iceberg calving may be additional factors that promote extensive benthic iron and manganese
cycling in these fjords. On-going benthic recycling of glacially derived dissolved iron into overlying seawater, where partial reoxidation
and deposition occurs, facilitates the transport of iron across the fjords and potentially into adjacent continental
shelf waters. Such iron-dominated fjord sediments are likely to provide significant fluxes of potentially bioavailable iron to coastal waters and beyond. By contrast, low delivery of reducible iron (oxyhydr)oxide phases and elevated organic carbon
mineralization rates driven by elevated input of “fresh” marine organic matter allow organoclastic sulfate reduction to dominate
carbon remineralization at the outer Smeerenburgfjorden sites, which may limit iron fluxes to the water column.
Type:
Article
,
PeerReviewed
Format:
text
DOI:
10.1016/j.gca.2014.06.007