The iron isotopic composition of subglacial streams draining the Greenland ice sheet

E. I. Stevenson, M. S. Fantle, S. B. Das, H. M. Williams, S. M. Aciego

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

In this study, we present the first measurements of iron (Fe) stable isotopic composition (δ56Fe) of subglacial streams draining the Greenland Ice Sheet (GIS). We measure the δ56Fe values [(δ56Fe, ‰ = (56Fe/54Fe)sample/(56Fe/54Fe)standard − 1) × 103] of both dissolved and suspended sediment Fe in subglacial outflows from five distinct land-terminating glaciers. Suspended sediments have δ56Fe values that lie within the crustal array (δ56Fe ∼ 0‰). In contrast, the δ56Fe values of dissolved Fe in subglacial outflows are consistently less than 0‰, reaching a minimum of −2.1‰ in the outflow from the Russell Glacier. The δ56Fe values of dissolved Fe vary geographically and on daily time scales. Major element chemistry and mineral saturation state modeling suggest that incongruent silicate weathering and sulfide oxidation are the likely drivers of subglacial stream Fe chemistry, and that the extent of chemical weathering influences the δ56Fe of dissolved Fe. The largest difference in δ56Fe between dissolved and suspended load is −2.1‰, and occurs in the subglacial system from the Russell glacier (southwest GIS). Major element chemistry indicates this outflow to be the least chemically weathered, while more mature subglacial systems (i.e., that exhibit greater extents of subglacial weathering) have dissolved loads with δ56Fe that are indistinguishable from suspended sediments (Δ56Fesuspended-dissolved ∼ 0‰). Ultimately, the dissolved Fe generated in some subglacial systems from the GIS is a previously unrecognized source of isotopically light Fe into the hydrosphere. The data illustrate that the dissolved Fe supplied by subglacial weathering can have variable δ56Fe values depending on the degree of chemical weathering. Thus, Fe isotopes have potential as a proxy for subglacial chemical weathering intensity or mode. Finally, based on our regional Fe concentration measurements from each glacial outflow, we estimate a flux weighted continental scale dissolved iron export of 2.1 Gg Fe yr−1 to the coastal ocean, which is within the range of previous estimates.

Original languageEnglish (US)
Pages (from-to)237-254
Number of pages18
JournalGeochimica et Cosmochimica Acta
Volume213
DOIs
StatePublished - Sep 15 2017

Fingerprint

Ice
Weathering
ice sheet
isotopic composition
outflow
Iron
chemical weathering
Glaciers
iron
Suspended sediments
suspended sediment
dissolved load
Chemical analysis
glacier
weathering
Hydrosphere
hydrosphere
suspended load
Silicates
Sulfides

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology

Cite this

Stevenson, E. I. ; Fantle, M. S. ; Das, S. B. ; Williams, H. M. ; Aciego, S. M. / The iron isotopic composition of subglacial streams draining the Greenland ice sheet. In: Geochimica et Cosmochimica Acta. 2017 ; Vol. 213. pp. 237-254.
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abstract = "In this study, we present the first measurements of iron (Fe) stable isotopic composition (δ56Fe) of subglacial streams draining the Greenland Ice Sheet (GIS). We measure the δ56Fe values [(δ56Fe, ‰ = (56Fe/54Fe)sample/(56Fe/54Fe)standard − 1) × 103] of both dissolved and suspended sediment Fe in subglacial outflows from five distinct land-terminating glaciers. Suspended sediments have δ56Fe values that lie within the crustal array (δ56Fe ∼ 0‰). In contrast, the δ56Fe values of dissolved Fe in subglacial outflows are consistently less than 0‰, reaching a minimum of −2.1‰ in the outflow from the Russell Glacier. The δ56Fe values of dissolved Fe vary geographically and on daily time scales. Major element chemistry and mineral saturation state modeling suggest that incongruent silicate weathering and sulfide oxidation are the likely drivers of subglacial stream Fe chemistry, and that the extent of chemical weathering influences the δ56Fe of dissolved Fe. The largest difference in δ56Fe between dissolved and suspended load is −2.1‰, and occurs in the subglacial system from the Russell glacier (southwest GIS). Major element chemistry indicates this outflow to be the least chemically weathered, while more mature subglacial systems (i.e., that exhibit greater extents of subglacial weathering) have dissolved loads with δ56Fe that are indistinguishable from suspended sediments (Δ56Fesuspended-dissolved ∼ 0‰). Ultimately, the dissolved Fe generated in some subglacial systems from the GIS is a previously unrecognized source of isotopically light Fe into the hydrosphere. The data illustrate that the dissolved Fe supplied by subglacial weathering can have variable δ56Fe values depending on the degree of chemical weathering. Thus, Fe isotopes have potential as a proxy for subglacial chemical weathering intensity or mode. Finally, based on our regional Fe concentration measurements from each glacial outflow, we estimate a flux weighted continental scale dissolved iron export of 2.1 Gg Fe yr−1 to the coastal ocean, which is within the range of previous estimates.",
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The iron isotopic composition of subglacial streams draining the Greenland ice sheet. / Stevenson, E. I.; Fantle, M. S.; Das, S. B.; Williams, H. M.; Aciego, S. M.

In: Geochimica et Cosmochimica Acta, Vol. 213, 15.09.2017, p. 237-254.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The iron isotopic composition of subglacial streams draining the Greenland ice sheet

AU - Stevenson, E. I.

AU - Fantle, M. S.

AU - Das, S. B.

AU - Williams, H. M.

AU - Aciego, S. M.

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N2 - In this study, we present the first measurements of iron (Fe) stable isotopic composition (δ56Fe) of subglacial streams draining the Greenland Ice Sheet (GIS). We measure the δ56Fe values [(δ56Fe, ‰ = (56Fe/54Fe)sample/(56Fe/54Fe)standard − 1) × 103] of both dissolved and suspended sediment Fe in subglacial outflows from five distinct land-terminating glaciers. Suspended sediments have δ56Fe values that lie within the crustal array (δ56Fe ∼ 0‰). In contrast, the δ56Fe values of dissolved Fe in subglacial outflows are consistently less than 0‰, reaching a minimum of −2.1‰ in the outflow from the Russell Glacier. The δ56Fe values of dissolved Fe vary geographically and on daily time scales. Major element chemistry and mineral saturation state modeling suggest that incongruent silicate weathering and sulfide oxidation are the likely drivers of subglacial stream Fe chemistry, and that the extent of chemical weathering influences the δ56Fe of dissolved Fe. The largest difference in δ56Fe between dissolved and suspended load is −2.1‰, and occurs in the subglacial system from the Russell glacier (southwest GIS). Major element chemistry indicates this outflow to be the least chemically weathered, while more mature subglacial systems (i.e., that exhibit greater extents of subglacial weathering) have dissolved loads with δ56Fe that are indistinguishable from suspended sediments (Δ56Fesuspended-dissolved ∼ 0‰). Ultimately, the dissolved Fe generated in some subglacial systems from the GIS is a previously unrecognized source of isotopically light Fe into the hydrosphere. The data illustrate that the dissolved Fe supplied by subglacial weathering can have variable δ56Fe values depending on the degree of chemical weathering. Thus, Fe isotopes have potential as a proxy for subglacial chemical weathering intensity or mode. Finally, based on our regional Fe concentration measurements from each glacial outflow, we estimate a flux weighted continental scale dissolved iron export of 2.1 Gg Fe yr−1 to the coastal ocean, which is within the range of previous estimates.

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