Most glaciers worldwide are undergoing climate-forced recession, but the impact of glacier changes on biogeochemical cycles is unclear. This study examines the influence of proglacial sediment weathering on meltwater chemistry at the early stages of glacier recession in the High Arctic of Svalbard. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) in combination with a wide range of geochemical analyses were used in this study. The SEM-EDS analyses of sediments collected in front of Werenskioldbreen show general degradation of pyrite and carbonate grains with age. The outer parts of pyrite grains have a gradual decrease in sulphur and gradual increase in iron oxides due to pyrite oxidation. This process was less advanced in the proglacial zone younger than 100 years compared to older sites such as the terminal moraine from the Little Ice Age. In both the proglacial zone and the terminal moraine, physical weathering of mineral grains, including formation of microcracks and microfractures, clearly enhanced pyrite oxidation. A consequence of proglacial sediment weathering is that the river chemistry is strongly affected by carbonate dissolution driven by sulphuric acid from sulphide oxidation. Also, reactive iron oxides, a product of sulphide oxidation, are mobilized in the proglacial zone. The results of this study show that proglacial weathering in the High Arctic of Svalbard is strongly coupled to river geochemistry, especially during the early stages of proglacial exposure after glacier recession.

Retreating glaciers are altering sediment and micronutrient fluxes to coastal waters, yet the magnitude and environmental impacts of change remain unclear. Here we examine how contrasting glacier systems in an Arctic fjord control the export and speciation of dissolved and particulate iron (Fe) and manganese (Mn) by comparing locations influenced by marine-terminating and land-terminating glaciers. Data was collected from two glacierized bays in Hornsund, a southern Svalbard fjord, during research cruises conducted in 2022 and 2023. Highly reactive ascorbate‑extractable particulate Fe was a major component of the Fe pool in both systems, exceeding dissolved Fe even beyond the inner coastal zone, indicating that reactive particulate Fe is transported farther offshore than previously assumed. The marine-terminating glacier influenced bay exhibited substantially higher concentrations of reactive particulate Fe and Mn, elevated dissolved Mn, and sedimentation rates one to two orders of magnitude greater than in the bay with a land‑terminating glacier. These differences might be a result of higher subglacial discharge, a larger glacier cover with enhanced chemical weathering, and a higher abundance of freshly weathered mineral surfaces in the marine-terminating glacier influenced bay. In contrast, the input of suspended particulate matter and reactive micronutrient phases from the land‑terminating system was lower, as advanced glacial retreat has led to stabilisation of proglacial sediments and the glacier is smaller. Based on this dataset, coastal micronutrient inputs are likely to decline as glaciers continue to retreat, due to falling glacier discharge and supply of reactive sediment enriched in reactive micronutrients.

Retreating glaciers are altering sediment and micronutrient fluxes to coastal waters, yet the magnitude and environmental impacts of change remain unclear. Here we examine how contrasting glacier systems in an Arctic fjord control the export and speciation of dissolved and particulate iron (Fe) and manganese (Mn) by comparing locations influenced by marine-terminating and land-terminating glaciers. Data was collected from two glacierized bays in Hornsund, a southern Svalbard fjord, during research cruises conducted in 2022 and 2023. Highly reactive ascorbate‑extractable particulate Fe was a major component of the Fe pool in both systems, exceeding dissolved Fe even beyond the inner coastal zone, indicating that reactive particulate Fe is transported farther offshore than previously assumed. The marine-terminating glacier influenced bay exhibited substantially higher concentrations of reactive particulate Fe and Mn, elevated dissolved Mn, and sedimentation rates one to two orders of magnitude greater than in the bay with a land‑terminating glacier. These differences might be a result of higher subglacial discharge, a larger glacier cover with enhanced chemical weathering, and a higher abundance of freshly weathered mineral surfaces in the marine-terminating glacier influenced bay. In contrast, the input of suspended particulate matter and reactive micronutrient phases from the land‑terminating system was lower, as advanced glacial retreat has led to stabilisation of proglacial sediments and the glacier is smaller. Based on this dataset, coastal micronutrient inputs are likely to decline as glaciers continue to retreat, due to falling glacier discharge and supply of reactive sediment enriched in reactive micronutrients.

Retreating glaciers are altering sediment and micronutrient fluxes to coastal waters, yet the magnitude and environmental impacts of change remain unclear. Here we examine how contrasting glacier systems in an Arctic fjord control the export and speciation of dissolved and particulate iron (Fe) and manganese (Mn) by comparing locations influenced by marine-terminating and land-terminating glaciers. Data was collected from two glacierized bays in Hornsund, a southern Svalbard fjord, during research cruises conducted in 2022 and 2023. Highly reactive ascorbate‑extractable particulate Fe was a major component of the Fe pool in both systems, exceeding dissolved Fe even beyond the inner coastal zone, indicating that reactive particulate Fe is transported farther offshore than previously assumed. The marine-terminating glacier influenced bay exhibited substantially higher concentrations of reactive particulate Fe and Mn, elevated dissolved Mn, and sedimentation rates one to two orders of magnitude greater than in the bay with a land‑terminating glacier. These differences might be a result of higher subglacial discharge, a larger glacier cover with enhanced chemical weathering, and a higher abundance of freshly weathered mineral surfaces in the marine-terminating glacier influenced bay. In contrast, the input of suspended particulate matter and reactive micronutrient phases from the land‑terminating system was lower, as advanced glacial retreat has led to stabilisation of proglacial sediments and the glacier is smaller. Based on this dataset, coastal micronutrient inputs are likely to decline as glaciers continue to retreat, due to falling glacier discharge and supply of reactive sediment enriched in reactive micronutrients.