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Pine 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, (NG), and oxygen isotopes), collected during a ship‐based campaign in the eastern Amundsen Sea in February–March 2014. (NG) (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. Plain Language Summary: Pine Island Ice Shelf in the Amundsen Sea, Antarctica, is melting due to warm ocean waters. The glacial meltwater that is produced is less salty and carries essential food for biological organisms, so where the glacial meltwater goes once it leaves the front of the ice shelf is important to understand: Less salt in the ocean at the surface makes it easier to form sea ice, and increased productivity from biological organisms can help draw carbon down into the ocean from the atmosphere. We use (NG) to identify where this glacial meltwater is, as the signature that the meltwater leaves in the gases is unique like a fingerprint. We use the noble gas meltwater signature to improve our identification of glacial meltwater using temperature, salinity, and dissolved oxygen (hydrographic observations), which are easier and cheaper to collect so cover a larger area. Using the improved signature from hydrographic observations, we identify the presence of glacial meltwater between 150‐ and 400‐m depths everywhere across the continental shelf. We also show, for the first time, glacial meltwater from the ice shelf flowing off‐shelf in the easternmost channel. These results are important as they show where glacial meltwater is affecting the ocean column most. Key Points: Oxygen isotope and noble gas data identify freshwater in the upper ocean across the Amundsen SeaHydrographic calculations of meltwater are improved using (NG) as ground truthWe identify a new meltwater export pathway in the eastern channel in the Amundsen Sea [ABSTRACT FROM AUTHOR]

Highlights • Tides enhance simulated ice-shelf melting by 1–39% depending on the ice shelf. • Enhanced melting is mostly due to strengthened turbulence near the ice/ocean interface. • Tidal processes occurring seaward are less important than those occurring underneath ice shelves. • A methodology to prescribe tidal effects on ice shelf melt is proposed. Abstract The representation of tides in regional ocean simulations of the Amundsen Sea enhances ice-shelf melting, with weakest effects for Pine Island and Thwaites (< + 10 %) and strongest effects for Dotson, Cosgrove and Abbot (> + 30 %). Tides increase vertical mixing throughout the water column along the continental shelf break. Diurnal tides induce topographically trapped vorticity waves along the continental shelf break, likely underpinning the tidal rectification (residual circulation) simulated in the Dotson–Getz Trough. However, the primary effect by which tides affect ice-shelf melting is the increase of ice/ocean exchanges, rather than the modification of water masses on the continental shelf. Tide-induced velocities strengthen turbulent heat fluxes at the ice/ocean interface, thereby increasing melt rates. Approximately a third of this effect is counterbalanced by the resulting release of cold melt water that reduces melt downstream along the meltwater flow. The relatively weak tide-induced melting underneath Pine Island and Thwaites could be partly related to their particularly thick water column, which limits the presence of quarter wavelength tidal resonance. No sensitivity to the position of Pine Island and Thwaites with respect to the M 2 critical latitude is found. We refine and evaluate existing methodologies to prescribe the effect of tides on ice-shelf melt rates in ocean models that do not explicitely include tidal forcing. The best results are obtained by prescribing spatially-dependent tidal top-boundary-layer velocities in the melt equations. These velocities can be approximated as a linear function of existing barotropic tidal solutions. A correction factor needs to be applied to account for the additional melt-induced circulation associated with tides and to reproduce the relative importance of dynamical and thermodynamical processes. [ABSTRACT FROM AUTHOR]

Abstract: Two coastal polynyas in the Amundsen Sea (Amundsen Polynya and Pine Island Polynya) were studied as part of the DynaLiFe project because of their unusually high rates of biological production and close association with melting ice shelves. In this component of the study, satellite imagery of ocean color (using Reprocessing R2009.1) and passive microwave sea ice distributions were used to characterize interannual changes in polynya dynamics and phytoplankton bloom development between 1997 and 2010. Interannual differences in sea ice cover were large in both polynyas, but especially so in the smaller Pine Island Polynya, and were related to synoptic scale wind patterns rather than climate state (ENSO or SAM). Open water season lasted 10 days longer in the Amundsen Polynya (132 days) than in the Pine Island Polynya (122 days). The phytoplankton bloom in the Amundsen Polynya lasted approximately two weeks longer and was 30% more productive per unit area than the bloom in the Pine Island Polynya. Because Pine Island Polynya was lower in both mean open water area and annual net primary production (NPP) per unit area, total annual NPP averaged over the 13-year time series was only 60% of that in the Amundsen Polynya (1.96 and 3.26TgCyr−1, respectively). Given the high interannual variability and the short time series duration, we did not observe a secular trend in primary production or any relationship with climate indices such as the Southern Annular Mode. However, with increased iron addition from melting ice shelves into the surface waters of the polynyas, we expect that primary production could be enhanced in the future. [Copyright &y& Elsevier]