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Abstract Seasonal phytoplankton blooms in Greenland’s coastal waters form the base of marine food webs and contribute to oceanic carbon uptake. In Qeqertarsuup Tunua, West Greenland, a secondary summertime bloom follows the Arctic spring bloom, enhancing annual primary productivity. Emerging evidence links this summer bloom to subglacial discharge from Sermeq Kujalleq, the most active glacier on the Greenland Ice Sheet. This discharge drives localized upwelling that may alleviate nutrient limitation in surface waters, yet this mechanism remains poorly quantified. Here, we employ a high-resolution biogeochemical model nested within a global state estimate to assess how discharge-driven upwelling influences primary productivity and carbon fluxes. We find that upwelling increases summer productivity by 15–40% in Qeqertarsuup Tunua, yet annual carbon dioxide uptake rises by only  ~3% due to reduced solubility in plume-upwelled waters. These findings suggest that intensifying ice sheet melt may alter Greenland’s coastal productivity and carbon cycling under future climate scenarios. 

Abstract Numerous proposed geoengineering schemes to mitigate climate change and its consequences are now widely discussed in the scientific literature. Sea level rise is a clear example of the implications of climate change with a further committed rise of at least 2–3 m embedded within the Earth System from +1.5°C of global warming. A bold suggestion to reduce sea level rise is to install underwater barriers to reduce the inflow of oceanic heat around Antarctica and Greenland. Inflow of warm, saline water masses drives ice melt and the destabilization of tidewater glaciers. Whilst the basic theory that barriers would stem oceanic heat flow is uncontroversial, the extent to which barriers might reduce future ice mass loss is less certain. There are numerous concerns about the viability and side‐effects of this proposed intervention. We use existing field observations and representative fjord‐scale models for the Greenland's largest glacier, Sermeq Kujalleq in the Ilulissat Icefjord, to suggest that there is already sufficient evidence to conclude that artificial barrier installation would have negative regional implications for marine productivity. The effects on fisheries are a concern as negative implications for Greenland's regional fisheries are unlikely to be socially acceptable. Increasing “geoengineeringization” of the Earth Sciences is likely to continue in coming decades as society grapples with the challenges of slowing climate change and mitigating its consequences. To produce beneficial results, the technical and social viabilities of geoengineering concepts need to be considered in parallel, with the latter determined in a complex social, economic and cultural nexus. 

Abstract. Ice calved from the Antarctic and Greenland ice sheets or tidewater glaciers ultimately melts in the ocean, contributing to sea-level rise and potentially affecting marine biogeochemistry. Icebergs have been described as ocean micronutrient fertilizing agents and biological hotspots due to their potential roles as platforms for marine mammals and birds. Icebergs may be especially important fertilizing agents in the Southern Ocean, where low availability of the micronutrients iron and manganese extensively limits marine primary production. Whilst icebergs have long been described as a source of iron to the ocean, their nutrient load is poorly constrained and it is unclear if there are regional differences. Here we show that 589 ice fragments collected from calved ice in contrasting regions spanning the Antarctic Peninsula; Greenland; and smaller tidewater systems in Svalbard, Patagonia, and Iceland have similar (micro)nutrient concentrations with limited or no significant differences between regions. Icebergs are a minor or negligible source of macronutrients to the ocean with low concentrations of NOx- (NO3-+NO2-; median of 0.51 µM), PO43- (median of 0.04 µM), and dissolved Si (dSi; median of 0.02 µM). In contrast, icebergs deliver elevated concentrations of dissolved Fe (dFe; median of 12 nM) and Mn (dMn; median of 2.6 nM). The sediment load for Antarctic ice (median of 9 mg L−1, n=144) was low compared to prior reported values for the Arctic (up to 200 g L−1). Total dissolvable Fe and Mn retained a strong relationship with the sediment load (both R2=0.43, p<0.001), whereas weaker relationships were observed for dFe (R2=0.30, p<0.001), dMn (R2=0.20, p<0.001), and dSi (R2=0.29, p<0.001). A strong correlation between total dissolvable Fe and Mn (R2=0.95, p<0.001) and a total dissolvable Mn:Fe ratio of 0.024 suggested a lithogenic origin for the majority of sediment present in ice. Dissolved Mn was present at higher dMn:dFe ratios, with fluxes from melting ice roughly equivalent to 30 % of the corresponding dFe flux. Our results suggest that NOx- and PO43- concentrations measured in calved icebergs originate from the ice matrix. Conversely, high Fe and Mn, as well as occasionally high dSi concentrations, are associated with englacial sediment, which experiences limited biogeochemical processing prior to release into the ocean. 

Abstract Subglacial discharge emerging from the base of Greenland's marine‐terminating glaciers drives upwelling of nutrient‐rich bottom waters to the euphotic zone, which can fuel nitrate‐limited phytoplankton growth. Here, we use buoyant plume theory to quantify this subglacial discharge‐driven nutrient supply on a pan‐Greenland scale. The modeled nitrate fluxes were concentrated in a few critical systems, with half of the total modeled nitrate flux anomaly occurring at just 14% of marine‐terminating glaciers. Increasing subglacial discharge fluxes results in elevated nitrate fluxes, with the largest flux occurring at Jakobshavn Isbræ in Disko Bay, where subglacial discharge is largest. Subglacial discharge and nitrate flux anomaly also account for significant temporal variability in summer satellite chlorophyll a (Chl) within 50 km of Greenland's coast, particularly in some regions in central west and northwest Greenland.