Winter seal-based observations reveal glacial meltwater surfacing in the southeastern Amundsen Sea

Abstract

Determining the injection of glacial meltwater into polar oceans is crucial for quantifying the climate system response to ice sheet mass loss. However, meltwater is poorly observed and its pathways poorly known, especially in winter. Here we present winter meltwater distribution near Pine Island Glacier using data collected by tagged seals, revealing a highly variable meltwater distribution with two meltwater-rich layers in the upper 250 m and at around 450 m, connected by scattered meltwater-rich columns. We show that the hydrographic signature of meltwater is clearest in winter, when its presence can be unambiguously mapped. We argue that the buoyant meltwater provides near-surface heat that helps to maintain polynyas close to ice shelves. The meltwater feedback onto polynyas and air-sea heat fluxes demonstrates that although the processes determining the distribution of meltwater are small-scale, they are important to represent in Earth system models.

Reversal of ocean gyres near ice shelves in the Amundsen Sea caused by the interaction of sea ice and wind

“…We chose the endpoints following previously published research. The endpoints of mCDW (Θ = 1.044℃ and 𝑆 8 = 34.8795) are consistent with Wåhlin et al (2021), and the endpoints of Winter Water (Θ = −1.86℃, 𝑆 8 = 34.32) and glacial meltwater (Θ = −90.8℃, 𝑆 8 = 0) are the same as used by Zheng et al (2021) and Biddle, Loose, and Heywood (2019).…”

“…The gyre is well defined between the sea surface and about 700-m depth, in front of Pine Island Ice Shelf (Thurnherr et al, 2014;Heywood et al, 2016). Gyres play an important role in local ocean circulation, distributing heat and enhancing water mass exchange in the Amundsen Sea (Zheng et al, 2021;Schodlok 2012). Schodlok et al (2012) use a high-resolution model to infer that the strength of the PIB gyre is the main determinant of heat transport toward the ice shelf and the associated glacial melt rate (Schodlok et al, 2012).…”

“…Schodlok et al (2012) use a high-resolution model to infer that the strength of the PIB gyre is the main determinant of heat transport toward the ice shelf and the associated glacial melt rate (Schodlok et al, 2012). Zheng et al (2021), Mankoff et al (2012) and Tortell et al (2012) also suggest that the PIB gyre entrains water as it exits the ice cavity contributing to the spreading of glacial meltwater and its associated heat, nutrients and freshwater.…”

Impact of Subglacial Freshwater Discharge on Pine Island Ice Shelf

“…Higher melt rates might accelerate grounding line retreat and impact the stability of glaciers upstream, which is an important area for future study. We also note that our model simulation is only conducted for the PIIS austral summer conditions and pathways of glacial meltwater may be different for other seasons and other ice shelves (Zheng et al, 2021). originating from frictional heat and geothermal heat flux at the grounded ice base is added to the simulations, the average melt rate remains largely unchanged but freshwater discharge substantially enhances ice shelf melting close to the discharge location, successfully simulating high ice shelf melt rate, similar to remote-sensing estimates.…”

“…Higher melt rates might accelerate grounding line retreat and impact the stability of glaciers upstream, which is an important area for future study. We also note that our model simulation is only conducted for the PIIS austral summer conditions and pathways of glacial meltwater may be different for other seasons and other ice shelves (Zheng et al., 2021).…”