Investigation of Iron and Carbon in West Greenland Lakes

Expedition Location: Kangerlussuaq, West Greenland

Expedition Dates: 06/30/2024-07/07/2024

Field Team Members: Dr. Jasmine Saros, Dr. Suzanne McGowan, Dr. Robert Northington, Dr. Adam Heathcote, Dr. Vaclava Hazukova, Thomas Grindle, Alex Saros, Misa Saros

Funding Support: Dan and Betty Churchill Exploration Fund, NSF Grant #DGE-2021713 (Systems Approaches to Understanding and Navigating the New Arctic NRT)

Introduction: Lake browning can be caused by a variety of chemical shifts, but the two most important are iron concentration and dissolved organic matter (DOM) (Strock et al., 2017; Björnerås et al., 2017). Determining the fate of these species in lakes is crucial to advancing an understanding of this phenomenon and its potential lasting effects on the system. The lakes of the region around Kangerlussuaq, West Greenland (Fig. 1) are considered relatively closed systems, characterized by low levels of inflow and outflow beyond atmospheric interactions (Yde et al., 2018). Recent shifts in hydrology following a compound extreme heat and precipitation event in the fall of 2022 (Saros et al., 2025) have increased connectivity between lakes and promoted cohesive browning of lakes across the landscape, but outlets from lakes remain limited, allowing for long term observation of the drivers of this phenomenon. Understanding the fate of lake browning in this area requires more information on within-lake chemical cycling.

Iron cycling within lakes is principally mediated by biological components of the system. This is particularly true of anoxic environments, in which anaerobic conditions prevail and bacteria seek alternate physiological routes, including reducing iron species from the very widely accessible Fe(III) to Fe(II), a species less commonly found on the surface due to its high reactivity with oxygen. The presence of Fe(II) in systems could be indicative of iron resuspension into the water column, which could in turn interact with the browning phenomenon.

DOM in lakes is considered in two different categories: autochthonous, in which DOM originates within the lake (e.g. algae), and allochthonous, in which DOM originates outside the lake and is swept in (e.g. thawed permafrost). Both forms of organic matter are present in West Greenlandic lakes, but prior to the 2022 browning event autochthonous regimes dominated (Osburn et al., 2017). The fate of DOM in Arctic lakes is not very well characterized, but some previous experiments have been conducted during the autochthonous regime related to the potential effects of photobleaching on the quality of DOM in closed Arctic lakes (Fowler et al., 2018). Recently, it is likely that the DOM regime has shifted, so prior characterizations are useful insights into the systems prior to cohesive browning, but new characterizations are needed to understand the systems as they now stand. Ultraviolet photobleaching is a prominent potential factor that could impact DOC’s contribution to browning in these lake systems.

Results and significance: To investigate iron speciation in West Greenland lakes, I prepared vials of disodium;4-[3-pyridin-2-yl-6-(4-sulfonatophenyl)-1,2,4-triazin-5-yl]benzenesulfonate, also known as Ferrozine. Ferrozine complexes Fe(II) very effectively and quickly, which is essential given the instability of Fe(II) when coming into contact with molecular oxygen. We sampled lakes that cover a wide range of lake area and volume, watershed area, thermal characteristics, primary productivity, and other factors, and in each lake samples were taken from the epilimnion, metalimnion, and hypolimnion as determined by a temperature probe, and immediately filtered into the ferrozine solution to capture the presence and concentration of Fe(II) in each layer of the lake.

Ferrozine in the presence of Fe(II) flushes purple, allowing for straightforward characterization via UV-Vis Spectrophotometer (Fig. 2). The concentration of Fe(II) was determined in each sample, following which the samples were reduced to convert Fe(III) to Fe(II), then measured again to determine Fe(III). The final form of iron likely to be found in these systems, organically-bound Fe, will be determined by the difference between Fe(II)+Fe(III) and total Fe as determined by ICP-MS.

The impact of ultraviolet radiation on dissolved organic carbon (DOC) complexes was assessed using a similar experiment to one conducted prior to recent hydrologic changes (Fowler et al., 2018), in which water from the epilimnion of lakes was exposed to ultraviolet radiation for approximately one week. Samples of the same water were run as a control, exposed to similar conditions over the same time period but kept wholly in the dark. The samples were transported to Orono for DOC quality analysis.

This work will provide insight into the implications of the new hydrologic regime compared to previous findings on autochthonous carbon, and help characterize the contribution of DOC to the observed browning in the lakes studied, and how constant summertime exposure to UV light may mediate browning moving forward.

Acknowledgements: Thanks to the Dan and Betty Churchill Exploration Fund for their generous support of this field season. Additional thanks to the SAUNNA NRT (NSF Grant #DGE-2021713) for salary support during this work. Thanks to Dr. Jasmine Saros, my advisor, and all the members of the field team for their support in the field. Thanks to the University of Maine for their support, and the government of Greenland for permitting us to conduct research in their sovereign territory.

References:

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Fowler, R.A., Saros, J.E., & Osburn, C.L. (2018). Shifting DOC concentration and quality in the freshwater lakes of the Kangerlussuaq region: An experimental assessment of possible mechanisms. Arctic, Antarctic, and Alpine Research 50(1), e1436815.

Osburn, C.L., Anderson, N.J., Stedmon, C.A., Giles, M.E., Whiteford, E.J., McGenity, T.J., Dumbrell, A.J., & Underwood, G.J.C. (2017). Shifts in the source and composition of dissolved organic matter in Southwest Greenland lakes along a regional hydro-climatic gradient. Journal of Geophysical Research: Biogeosciences 122, 3431-3445.

Saros, J.E., Hazuková, V., Northington, R.M., Huston, G.P., Lamb, A., Birkel, S., Pereira, R., Bourdin, G., Jiang, B., & McGowan, S. (2025). Abrupt transformation of West Greenland lakes following compound climate extremes associated with atmospheric rivers, Proc. Natl. Acad. Sci. U.S.A. 122(4) e2413855122. https://doi.org/10.1073/pnas.2413855122.

Strock, K.E., Theodore, N., Gawley, W.G., Ellsworth, A.C., & Saros, J.E. (2017). Increasing dissolved organic carbon concentrations in northern boreal lakes: Implications for lake water transparency and thermal structure. Journal of Geophysical Research: Biogeosciences 122, 1022-1035.

Yde, J.C., Anderson, N.J., Post, E., Saros, J.E., & Telling, J. (2018). Environmental change and impacts in the Kangerlussuaq area, West Greenland. Arctic, Antarctic, and Alpine Research 50(1). DOI: 10.1080/15230430.2018.1433786.