Characteristic Depths, Fluxes, and Timescales for Greenland's Tidewater Glacier Fjords From Subglacial Discharge‐Driven Upwelling During Summer

Abstract

The Greenland Ice Sheet interacts with the ocean through glacial fjords, which play a key role in moderating multiple components of the regional climate and ecosystem. Fjord-scale transport of ocean heat melts the termini of tidewater glaciers (Sutherland et al., 2019;Wood et al., 2021) in a process understood to have driven half of the ice sheet's mass loss since 1992 (Straneo & Heimbach, 2013; The IMBIE Team, 2020). Freshwater fluxed into the ocean from the ice sheet drives fjord circulation and stratification (Straneo et al., 2011) and enters Greenland's boundary currents and potentially the deep ocean (Böning et al., 2016;Dukhovskoy et al., 2019;Le Bras et al., 2021). Upwelling of deep nutrients in glacial fjords sustains higher productivity marine ecosystems than is typically observed in similar environments receiving only surface runoff (Hopwood et al., 2020), impacting inshore fisheries (Meire et al., 2017). Yet, across each of these disciplines, many of the processes and impacts remain poorly quantified on a pan-Greenland scale.

Subglacial-discharge plumes drive widespread subsurface warming in northwest Greenland's fjords

“…We also do not find a correlation between PMW abundance and distance of the observations from the glacier terminus, or measures of fjord length, width or sill depth. While fjord geometry is expected to influence the dispersal of PMW (Carroll et al, 2017), it may be that this effect is masked by the relatively small sample population and challenges in accurately quantifying PMW presence and complex fjord geometry as simple metrics (Slater et al, 2022).…”

“…Our results illustrate however that subglacial discharge from major tidewater glaciers is typically exported at intermediate depth, with the addition of freshwater counteracted by the upwelling of and mixing with deep, salty AW. As such, while the efficacy of plume entrainment amplifies the export of PMW by two orders of magnitude relative to the subglacial discharge (Slater et al, 2022), it limits the freshening effect of this export. While there is a substantial freshening of the upper layer of the near-glacier profiles relative to the shelf (Figure 2d), this is not explained by the major subglacial discharge inputs modelled in this study, and is instead likely to be driven by a combination of submarine melting of glacier termini and icebergs (e.g.…”

Greenland Subglacial Discharge as a Driver of Hotspots of Increasing Coastal Chlorophyll Since the Early 2000s

“…Our choice of using a uniform coastal distance for Chl processing will also result in differing influences of boundary currents between systems and the coverage of fjord and coastal waters depending on local fjord geometry. For example, SE and CE Greenland glaciers are characterized by relatively long fjords, while Baffin Bay (NW) glaciers often terminate in shorter fjords (Slater et al., 2022). Subsurface subglacial plumes can also result in subsurface Chl maxima, as observed in Godthåbsfjord (Meire et al., 2017), and so subglacial discharge‐driven subsurface maxima may not be detectable to the same extent on a pan‐Greenland scale when using satellite‐derived Chl.…”

“…The physics of the plume model and the physical datasets used are the same as in Slater et al. (2022), which enables us to consider 136 of Greenland's largest marine‐terminating glaciers.…”

Increased sea ice melt as a driver of enhanced Arctic phytoplankton blooming

“…We note that the role glacial meltwater plays in driving bloom processes has also been discussed extensively (Arrigo et al, 2017; Bhatia et al, 2021; Gerringa et al, 2012; Krisch et al, 2020), with an emerging consensus that glacial waters can act as an important source of iron to often iron‐limited polar marine ecosystems (Dierssen et al, 2002; Forsch et al, 2021). Furthermore, glacial discharge can drive upwelling of nutrient‐rich bottom waters (Oliver et al, 2020, 2023).…”