Meltwater‐Enhanced Nutrient Export From Greenland's Glacial Fjords: A Sensitivity Analysis

Abstract

As mass loss from the Greenland Ice Sheet accelerates, this modeling study considers how meltwater inputs to the ocean can impact marine ecosystems using a simplified fjord scenario. At marine‐terminating glaciers in Greenland fjords, meltwater can be delivered far below the sea surface, both as subglacial runoff (from atmosphere‐driven surface melt) and as basal melt (from ocean heat). Such delivery can result in buoyancy‐driven upwelling and the upward entrainment of nutrient‐rich deep water, which can support phytoplankton growth in fjord surface waters. For this study, we use an idealized fjord‐scale model to investigate which properties of glaciers and fjords govern the transport of buoyantly upwelled nutrients from fjords. We model the influence of fjord geometry, hydrology, wind, tides, and phytoplankton growth within the fjord on meltwater‐driven nutrient export to the ocean. We use the Regional Ocean Modeling System (ROMS) coupled to a buoyant plume model and a biogeochemical model to simulate physical and biogeochemical processes within an idealized tidewater glacial fjord. Results show that meltwater‐driven nutrient export increases with larger subglacial discharge rates and deeper grounding lines, features that are both likely to change with continued ice sheet melting. Nutrient export decreases with longer residence times, allowing greater biological drawdown. While the absence of a coastal current in the model setup prevents the downstream advection of exported nutrients, results suggest that shelf‐forced flows could influence nutrient residence time within fjords. This simplified model highlights key uncertainties requiring further observation to understand ecological impacts of Greenland mass loss.

Glaciers and Nutrients in the Canadian Arctic Archipelago Marine System

“…There are several physical factors that determine a tidewater glacier's potential influence on the recipient marine environment, such as the proportion of the ice terminus in the water, the depth of meltwater discharge into the ocean, and the meltwater discharge flux (Hopwood et al., 2019; Oliver et al., 2020; Wadham et al., 2019). Based solely on the proportion of the ice terminus in the water, we can broadly classify the marine environment distal to Belcher, Sydkap, and Sverdrup Glaciers as “strongly tidewater‐glacier‐influenced” systems.…”

“…This suggests that the volume of water discharged sub‐glacially is an important determinant of the strength of upwelling and macronutrient delivery to the euphotic zone. The degree of macronutrient enrichment will also depend directly on macronutrient concentrations in the water column at the depth of glacial discharge (Hopwood et al., 2018; Oliver et al., 2020). Our results indicate that even glaciers with shallow grounding lines, provided that they have sufficient glacial discharge below the marine nutricline, can enhance delivery of macronutrients to near‐surface waters (Halbach et al., 2019; Williams et al., 2021).…”

“…By comparison, many outlet glaciers draining the Greenland Ice Sheet terminate into fjords at depths of 600 m or more (Carroll et al, 2016). Previous studies of Greenlandic glacier systems have identified grounding line depth as a primary control on the degree to which the plume-driven entrainment delivers macronutrient-enriched deep seawater to the photic zone through upwelling (Hopwood et al, 2018;Oliver et al, 2020). Using a subglacial discharge plume model for an idealized Greenlandic-like marine-terminating glacier, Hopwood et al (2018) estimate that the optimum grounding line depth for nitrate upwelling into the photic zone occurs at 580-m depth.…”

Freshwater Variability and Transport in the Labrador Sea From In Situ and Satellite Observations

“…increase in melting could have large consequences to the freshwater content in the Labrador Sea, potentially intensifying stratification and impacting winter convection (Hillaire-Marcel et al, 2001;Lazier, 1973;Renssen et al, 2005). In addition, meltwater input can influence the biology of the Labrador Sea by introducing nutrients directly into fjords (Bhatia et al, 2013;Hawkings et al, 2014Hawkings et al, , 2015Hawkings et al, , 2016, by causing buoyancy-driven upwelling inside fjords (Cape et al, 2019;Chu, 2014;Hopwood et al, 2018;Oliver et al, 2020), which can potentially modify nutrient distribution in the coastal ocean (Arrigo et al, 2017), or by modifying surface stratification (Oliver et al, 2018).…”

The 2017 Mission Arctic Citizen Science Sailing Expedition Conductivity, Temperature, and Depth Profiles in Western Greenland and Baffin Bay

“…Mass loss from the Greenland Ice Sheet has increased by a factor of six since the 1980s (Mouginot et al, 2019) and freshwater runoff into adjacent fjord and shelf waters has subsequently increased (Sejr et al, 2017;Boone et al, 2018;Moon et al, 2018;Mankoff et al, 2020). The increase in freshwater discharge impacts marine ecosystems (Meire et al, 2017;Cape et al, 2019;Seifert et al, 2019;Hopwood et al, 2020;Oliver et al, 2020), and density stratification and circulation in fjords and Baffin Bay (Castro de la Guardia et al, 2015;Sejr et al, 2017;Boone et al, 2018;Moon et al, 2018;Monteban et al, 2020;Rysgaard et al, 2020). The contribution of freshwater runoff from the Greenland Ice Sheet to the freshening observed in the North Atlantic remains an area of active research that relies heavily on numerical ocean models (Liu et al, 2018;Dukhovskoy et al, 2019;Zhang et al, 2021).…”