Abstract
AbstractPine Island Ice Shelf, in the Amundsen Sea, is losing mass due to increased heat transport by warm ocean water penetrating beneath the ice shelf and causing basal melt. Tracing this warm deep water and the resulting glacial meltwater can identify changes in melt rate and the regions most affected by the increased input of this freshwater. Here, optimum multiparameter analysis is used to deduce glacial meltwater fractions from independent water mass characteristics (standard hydrographic observations, noble gases, and oxygen isotopes), collected during a ship‐based campaign in the eastern Amundsen Sea in February–March 2014. Noble gases (neon, argon, krypton, and xenon) and oxygen isotopes are used to trace the glacial melt and meteoric water found in seawater, and we demonstrate how their signatures can be used to rectify the hydrographic trace of glacial meltwater, which provides a much higher‐resolution picture. The presence of glacial meltwater is shown to mask the Winter Water properties, resulting in differences between the water mass analyses of up to 4‐g/kg glacial meltwater content. This discrepancy can be accounted for by redefining the “pure” Winter Water endpoint in the hydrographic glacial meltwater calculation. The corrected glacial meltwater content values show a persistent signature between 150 and 400 m of the water column across all of the sample locations (up to 535 km from Pine Island Ice Shelf), with increased concentration toward the west along the coastline. It also shows, for the first time, the signature of glacial meltwater flowing off‐shelf in the eastern channel.
Highlights
The addition of glacial meltwater (GMW) to the ocean results in cooling and freshening of the water masses that it mixes with
Optimum multiparameter analysis is used to deduce glacial meltwater fractions from independent water mass characteristics (standard hydrographic observations, (NG), and oxygen isotopes), collected during a ship‐based campaign in the eastern Amundsen Sea in February–March 2014. (NG) and oxygen isotopes are used to trace the glacial melt and meteoric water found in seawater, and we demonstrate how their signatures can be used to rectify the hydrographic trace of glacial meltwater, which provides a much higher‐resolution picture
We have demonstrated the value of oxygen isotope ratios and noble gas concentrations in determining freshwater distribution across Amundsen Sea
Summary
The addition of glacial meltwater (GMW) to the ocean results in cooling and freshening of the water masses that it mixes with. Since the 1990s, multiple field campaigns have taken place in this region, operated by the British, U.S, Swedish, German, and Korean research communities (Jacobs et al, 2012; Heywood et al, 2016; Kim et al, 2016; Nakayama et al, 2013) Within these studies, focus has been placed on identifying the mechanisms for the warm water to access the continental shelf and ice shelf (Arneborg et al, 2012; Assmann et al, 2013; Mallett et al, 2018; Thoma et al, 2008; Walker et al, 2007; Wåhlin et al, 2013), and identification of GMW has mainly occurred directly in front of the ice shelves, with the exception of three more recent studies (Biddle et al, 2017; Kim et al, 2016; Nakayama et al, 2013). We combine the GMW content with current velocity data to identify meltwater pathways across the eastern Amundsen Sea (section 6)
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