Distribution of Fe isotopes in particles and colloids in the salinity gradient along the Lena River plume, Laptev Sea

Sarah Conrad, Johan Ingri, Johan Gelting, Fredrik Nordblad, Emma Engström, Ilia Rodushkin, Per S. Andersson, Don Porcelli, Örjan Gustafsson, Igor Semiletov, Björn Öhlander

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Abstract

Riverine Fe input is the primary Fe source for the ocean. This study is focused on the distribution of Fe along the Lena River freshwater plume in the Laptev Sea using samples from a 600&thinsp;km long transect in front of the Lena River mouth. Separation of the particulate (<span classCombining double low line"inline-formula">&gt;0.22</span>&thinsp;<span classCombining double low line"inline-formula">μ</span>m), colloidal (0.22&thinsp;<span classCombining double low line"inline-formula">μ</span>m-1&thinsp;kDa), and truly dissolved (<span classCombining double low line"inline-formula">&lt;1</span>&thinsp;kDa) fractions of Fe was carried out. The total Fe concentrations ranged from 0.2 to 57&thinsp;<span classCombining double low line"inline-formula">μ</span>M with Fe dominantly as particulate Fe. The loss of <span classCombining double low line"inline-formula">&gt;99</span>&thinsp;% of particulate Fe and about 90&thinsp;% of the colloidal Fe was observed across the shelf, while the truly dissolved phase was almost constant across the Laptev Sea. Thus, the truly dissolved Fe could be an important source of bioavailable Fe for plankton in the central Arctic Ocean, together with the colloidal Fe. Fe-isotope analysis showed that the particulate phase and the sediment below the Lena River freshwater plume had negative <span classCombining double low line"inline-formula">d56Fe</span> values (relative to IRMM-14). The colloidal Fe phase showed negative <span classCombining double low line"inline-formula">d56Fe</span> values close to the river mouth (about <span classCombining double low line"inline-formula">ĝ'0.20</span>&thinsp;‰) and positive <span classCombining double low line"inline-formula">d56Fe</span> values in the outermost stations (about <span classCombining double low line"inline-formula">+0.10</span>&thinsp;‰).

We suggest that the shelf zone acts as a sink for Fe particles and colloids with negative <span classCombining double low line"inline-formula">d56Fe</span> values, representing chemically reactive ferrihydrites. The positive <span classCombining double low line"inline-formula">d56Fe</span> values of the colloidal phase within the outer Lena River freshwater plume might represent Fe oxyhydroxides, which remain in the water column, and will be the predominant <span classCombining double low line"inline-formula">d56Fe</span> composition in the Arctic Ocean.

Original languageEnglish
Pages (from-to)1305-1319
Number of pages15
JournalBiogeosciences
Volume16
Issue number6
DOIs
Publication statusPublished - 28 Mar 2019

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Earth-Surface Processes

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    Conrad, S., Ingri, J., Gelting, J., Nordblad, F., Engström, E., Rodushkin, I., Andersson, P. S., Porcelli, D., Gustafsson, Ö., Semiletov, I., & Öhlander, B. (2019). Distribution of Fe isotopes in particles and colloids in the salinity gradient along the Lena River plume, Laptev Sea. Biogeosciences, 16(6), 1305-1319. https://doi.org/10.5194/bg-16-1305-2019