Comparisons of Nutrients Exported From Greenlandic Glacial and Deglaciated Watersheds. Issue 12 (8th December 2020)

• Record Type: Journal Article
• Authors: Martin, Jonathan B.; Pain, Andrea J.; Martin, Ellen E.; Rahman, Shaily; Ackerman, Philip
• Is Part Of: Global biogeochemical cycles. Volume 34:Issue 12(2020:Dec.)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-12-08
• Subjects: Greenland -- periglacial -- nutrients -- productivity -- Arctic -- discharge; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1029/2020GB006661
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: Recent work demonstrates extensive nutrient exports from outlet glaciers of the Greenland Ice Sheet. In comparison, nutrient exports are poorly defined for deglaciated watersheds that were exposed during ice retreat and retain reactive comminuted glacial sediments. Nutrient exports from deglaciated watersheds may differ from glacial watersheds due to their longer exposure times, more mature chemical weathering, and ecosystem succession. To evaluate nutrient exports from glacial and deglaciated watersheds, we compare discharge and dissolved (<0.45 μm filtered) nutrient concentrations in two glacial and six non‐glacial streams in southwestern and southern Greenland. Glacial streams have orders of magnitude greater instantaneous discharge than non‐glacial streams but their specific discharges are more similar, differing by up to a factor of 10. Compared with non‐glacial streams, filtered water of glacial streams have on average (1) higher inorganic nitrogen (DIN) and PO4 concentrations, lower Si concentrations, and Fe concentrations that are not statistically different; (2) higher DIN and PO4 but lower Si specific yields; and (3) lower DIN/PO4, Si/DIN, and Fe/PO4 ratios, but indistinguishable Fe/DIN. Maximum specific yields occur in early melt season prior to maximum solar radiation for non‐glacial streams, and in mid‐melt season as solar radiation wanes for proglacial streams. Impacts to coastal ecosystems from nutrient exports depend on suspended sediment loads and processing in the estuaries, but landscape exposure during glacial terminations should decrease DIN and dissolved PO4 and increase dissolved Si exports, while increased meltwater runoff associated with future warming should increase DIN and dissolved PO4 and decrease dissolved Si exports. Plain Language Summary: Large ice sheets have advanced and retreated across about 15% of Earth's land surface over the past few million years. Watersheds exposed during ice retreat develop ecosystems and altered chemical reactions of fine‐grained glacial sediment that change stream water chemical compositions. Although individual glacial streams tend to be larger than non‐glacial streams, their discharge volumes per land area are similar within about a factor of 10. Comparisons of chemical compositions of glacial streams draining the Greenland Ice Sheet and nearby non‐glacial streams document different amounts of nutrients discharging from the landscapes. Once filtered to remove particles, stream waters draining the ice sheet contain more nitrogen and phosphorous, less silica, and about equal amounts of iron compared to non‐glacial streams. These differences in nutrient exports affect the abundance of nutrients in coastal ecosystems. Differences in timing of the maximum export relative to daily light levels may also affect photosynthesis. The response of coastal ecosystems to past continental ice sheet advance and retreat, and to increases in meltwater due to Arctic warming, may be affected by relative nutrient contributions from glacial and non‐glacial streams. Key Points: Comparisons of Greenlandic glacial and non‐glacial streams show much greater differences in instantaneous than specific discharge Non‐glacial streams export less dissolved nitrogen and phosphorous and more dissolved silica to coastal zones than glacial streams Dissolved nutrients delivered from Arctic watersheds likely changed since the LGM and may change with increased future melting