Solid-phase Mn speciation in suspended particles along meltwater-influenced fjords of West Greenland

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C. M. van Genuchten
M. J. Hopwood
T. Liu
J. Krause
E. P. Achterberg
Rosing, Minik Thorleif
L. Meire

Manganese (Mn) is an essential micro-nutrient that can limit or, along with iron (Fe), co-limit phytoplankton growth in the ocean. Glacier meltwater is thought to be a key source of trace metals to high latitude coastal systems, but little is known about the nature of Mn delivered to glacially-influenced fjords and adjacent coastal waters. In this work, we combine in-situ dissolved Mn (dMn) measurements of surface waters with Mn K-edge X-ray absorption spectroscopy (XAS) data of suspended particles in four fjords of West Greenland. Data were collected from transects of up to 100 km in fjords with different underlying bedrock geology from 64 to 70°N. We found that dMn concentrations generally decreased conservatively with increasing salinity (from 80 to 120 nM at salinity < 8 to < 40 nM at salinities > 25). Dissolved Fe (dFe) trends in these fjords similarly declined with increasing distance from glacier outflows (declining from > 20 nM to < 8 nM). However, the dMn/dFe ratio increased rapidly likely due to the greater stability of dMn at intermediate salinities (i.e. 10–20) compared to rapid precipitation of dFe across the salinity gradient. The XAS data indicated a widespread presence of Mn(II)-rich suspended particles near fjord surfaces, with structures akin to Mn(II)-bearing phyllosilicates. However, a distinct increase in Mn oxidation state with depth and the predominance of birnessite-like Mn(IV) oxides was observed for suspended particles in a fjord with tertiary basalt geology. The similar dMn behaviour in fjords with different suspended particle Mn speciation (i.e., Mn(II)-bearing phyllosilicates and Mn(IV)-rich birnessite) is consistent with the decoupling of dissolved and particulate Mn and suggests that dMn concentrations on the scale of these fjords are controlled primarily by dilution of a freshwater dMn source rather than exchange between dissolved and particle phases. This work provides new insights into the Mn cycle in high latitude coastal waters, where small changes in the relative availabilities of dMn, dFe and macronutrients may affect the identity of the nutrient(s) proximally limiting primary production.

Originalsprog	Engelsk
Tidsskrift	Geochimica et Cosmochimica Acta
Vol/bind	326
Sider (fra-til)	180-198
Antal sider	19
ISSN	0016-7037
DOI	https://doi.org/10.1016/j.gca.2022.04.003
Status	Udgivet - 2022

Bibliografisk note

Funding Information:
We gratefully thank Ryan Davis at SSRL who facilitated collection of the Mn K-edge XAS data during virtual experiments imposed by COVID-19 travel restrictions. We acknowledge Alain Manceau for providing Mn reference spectra via an online database and Jasquelin Peña and her research group for useful discussions that improved the Mn K-edge XAS data interpretation. We also thank the three anonymous reviewers of this work who provided highly detailed and constructive reviews that improved the quality of our study. Use of SSRL, SLAC National Accelerator Laboratory, was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences , under Contract No. DE-AC02- 607 76SF00515 . This study formed part of project MarineGreen; Novo Nordic Foundation grant NNF17SH0028142. Mark Hopwood was financed by the DFG (award number HO 6321/1-1) and by the GLACE project, organised by the Swiss Polar Institute and supported by the Swiss Polar Foundation. T.L. was funded by the China Scholarship Council, and T.L. and J.K. were funded by GEOMAR. L.M. was funded by research programme VENI with project number 016.Veni.192.150, which is financed by the Dutch Research Council (NWO). We gratefully acknowledge the contributions from the Danish Centre for Marine Research (DCH), Greenland Institute of Natural Resources and the crew of RV Sanna for excellent field assistance. Thomas Juul-Pedersen (GINR) is thanked for assistance with fieldwork in Nuuk.

Funding Information:
We gratefully thank Ryan Davis at SSRL who facilitated collection of the Mn K-edge XAS data during virtual experiments imposed by COVID-19 travel restrictions. We acknowledge Alain Manceau for providing Mn reference spectra via an online database and Jasquelin Pe?a and her research group for useful discussions that improved the Mn K-edge XAS data interpretation. We also thank the three anonymous reviewers of this work who provided highly detailed and constructive reviews that improved the quality of our study. Use of SSRL, SLAC National Accelerator Laboratory, was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Contract No. DE-AC02- 607 76SF00515. This study formed part of project MarineGreen; Novo Nordic Foundation grant NNF17SH0028142. Mark Hopwood was financed by the DFG (award number HO 6321/1-1) and by the GLACE project, organised by the Swiss Polar Institute and supported by the Swiss Polar Foundation. T.L. was funded by the China Scholarship Council, and T.L. and J.K. were funded by GEOMAR. L.M. was funded by research programme VENI with project number 016.Veni.192.150, which is financed by the Dutch Research Council (NWO). We gratefully acknowledge the contributions from the Danish Centre for Marine Research (DCH), Greenland Institute of Natural Resources and the crew of RV Sanna for excellent field assistance. Thomas Juul-Pedersen (GINR) is thanked for assistance with fieldwork in Nuuk. In the Supplementary Materials (SM), we provide the tabulated dMn, TdMn and salinity measurements used to produce Fig. 2 in Excel format and the dFe used to produce several figures. We also include in the Supplementary Materials the tabulated XANES, EXAFS and modelling fits in Excel format.

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© 2022 Elsevier Ltd

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