The discharge of nutrient-rich meltwater from the Greenland Ice Sheet has emerged as a potentially important contributor to regional marine primary production and nutrient cycling. While significant, this direct nutrient input by the ice sheet may be secondary to the upwelling of deep-ocean-sourced nutrients driven by the release of meltwater at depth in glacial fjords. Here, we present a comprehensive suite of micro- and macronutrient observations collected in Sermilik Fjord at the margin of Helheim, one of Greenland’s largest glaciers, and quantitatively decompose glacial and ocean contributions to fjord dissolved nutrient inventories. We show that the substantial enrichment in nitrate, phosphate and silicate observed in the upper 250 m of the glacial fjord is the result of upwelling of warm subtropical waters present at depth throughout the fjord. These nutrient-enriched fjord waters are subsequently exported subsurface to the continental shelf. The upwelled nutrient transport within Sermilik rivals exports by the largest Arctic rivers and the ice sheet as a whole, suggesting that glacier-induced pumping of deep nutrients may constitute a major source of macronutrients to the surrounding coastal ocean. The importance of this mechanism is likely to grow given projected increases in surface melt of the ice sheet.
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Continuous hydrographic (CTD) profiles are available from the National Oceanographic Data Center (http://accession.nodc.noaa.gov/0171277), while discrete nutrient measurements and CTD bottle data (https://doi.org/10.1594/PANGAEA.887304), as well as discrete iron data (https://doi.org/10.1594/PANGAEA.887324), are available from the PANGEA information system77,78. Ocean current data for Sermilik Fjord are publicly available from Data.gov(NODC accession number 0126772 and NCEI accession number 0127325). Downscaled RACMO2.3.2 data were provided by M. van den Broeke and B. Noël and are available from them upon request. Hydrographic data for the West Greenland continental shelf (Supplementary Table 2 and Supplementary Fig. 12) are available from K. Azetsu-Scott upon request. Other data supporting the findings of this study are available as described in the Methods, and otherwise from the corresponding author upon request.
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This work was supported by: an internal grant from the Woods Hole Oceanographic Institution (WHOI) Ocean and Climate Change Institute (to M.R.C., F.S. and M.A.C.), grants from the National Science Foundation to M.A.C. (OCE-1458305), N.B. (OCE-1536856) and F.S. (OCE-1657601), and Woods Hole Oceanographic Institution Postdoctoral Fellowships to M.R.C. and R.M.B. We are grateful to J. Hawkings for sharing Leverett Glacier nutrient data, to K. Azetsu-Scott and B. Curry for sharing the Davis Strait and West Greenland continental shelf hydrographic data, to P. Henderson and the WHOI Nutrient Analytical Facility for assistance with macronutrient sample collection and analysis, to R. Jackson for helpful conversations concerning data analysis, to A. Ramsey for logistical support, to S. Laney for loan of and technical assistance with oceanographic instrumentation, to M. Swartz for CTD assembly and testing, and to the captain and crew of the RV Adolf Jensen for support in the field.
The authors declare no competing interests.
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Cape, M.R., Straneo, F., Beaird, N. et al. Nutrient release to oceans from buoyancy-driven upwelling at Greenland tidewater glaciers. Nature Geosci 12, 34–39 (2019). https://doi.org/10.1038/s41561-018-0268-4
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