Comparisons of Nutrients Exported From Greenlandic Glacial and Deglaciated Watersheds

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 PO 4 concentrations, lower Si concentrations, and Fe concentrations that are not statistically different; (2) higher DIN and PO 4 but lower Si specific yields; and (3) lower DIN/PO 4 , Si/DIN, and Fe/PO 4 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 PO 4 and increase dissolved Si exports, while increased meltwater runoff associated with future warming should increase DIN and dissolved PO 4 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.

Impact of Vertical Mixing on Summertime Net Community Production in Canadian Arctic and Subarctic Waters: Insights From In Situ Measurements and Numerical Simulations

“…Non‐vegetated glaciated regions typically contribute small inputs of DOC (Bhatia, Das, et al., 2013; Pain et al., 2020), but may be important indirect sources of inorganic nutrients to marine surface waters (Bhatia, Kujawinski, et al., 2013; Bhatia et al., 2021; J. B. Martin et al., 2020; Williams et al., 2021). Our sampling in the CAA identified several cor‐NCP hotspots adjacent to the Humboldt and Petermann Glaciers and Devon Ice Cap (labels in Figure 7).…”

“…The Arctic Ocean is heavily influenced by rivers and glaciers, which export variable quantities of freshwater (Carmack et al., 2016), terrestrial material (McClelland et al., 2016), organic matter, macronutrients and trace elements (Bhatia, Das, et al., 2013; Bhatia et al., 2021; J. B. Martin et al., 2020; Williams et al., 2021) to the adjacent marine system. In this study, the influence of freshwater on ML properties was observed as relatively low surface salinity (Figures 3b, 8c, S4–S6c, and S6d in Supporting Information ) near regions of strong freshwater discharge in the QMG, CAA, HB and on the W. Greenland Shelf (markers in Figure 8c).…”

Silicon Isotopes Highlight the Role of Glaciated Fjords in Modifying Coastal Waters

“…There has been a recent focus on understanding how fluxes of glacially derived nutrients impact downstream ecosystems, given that meltwaters are enriched in micro‐ and macro‐nutrients (e.g., Hawkings, 2021; Hendry et al., 2019; Martin et al., 2020; Vick‐Majors et al., 2020). However, the role of fjords in the modulation and drawdown of glacially derived nutrients is still poorly understood.…”

The Biogeochemical Legacy of Arctic Subglacial Sediments Exposed by Glacier Retreat

“…Accelerating glacier recession, inevitable in the coming decades (Bosson et al., 2019; Hugonnet et al., 2021; Zemp et al., 2019), is causing large and irreversible changes to Arctic ecosystems, including the loss of biodiversity and function associated with glacial habitats (Cauvy‐Fraunié & Dangles, 2019; Stibal et al., 2020) and the transition of vast areas of subglacial environment to proglacial habitats subject to rapid ecological succession (Bernasconi et al., 2011; Wojcik et al., 2021). While post‐glacial ecosystem development is largely dependent on allochthonous materials (Rime et al., 2016), the subglacial legacy is likely important as a “starter pack” containing labile crustal nutrients (Hawkings et al., 2014, 2016, 2020; Hatton et al., 2019; Urra et al., 2019), nitrogen (Lawson, Bhatia, et al., 2014; Martin et al., 2020), organic carbon (OC) substrates (Hood et al., 2009; Lawson, Wadham, et al., 2014; Stibal, Wadham, et al., 2012; Wadham et al., 2019), and microbial inocula (Bradley et al., 2016; Řeháková et al., 2010; Rime et al., 2016).…”

“…. While post-glacial ecosystem development is largely dependent on allochthonous materials (Rime et al, 2016), the subglacial legacy is likely important as a "starter pack" containing labile crustal nutrients (Hawkings et al, 2014(Hawkings et al, , 2016(Hawkings et al, , 2020Urra et al, 2019), nitrogen (Lawson, Bhatia, et al, 2014;Martin et al, 2020), organic carbon (OC) substrates (Hood et al, 2009;Wadham et al, 2019), and microbial inocula (Bradley et al, 2016;Řeháková et al, 2010;Rime et al, 2016).…”