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1. Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica

   https://doi.org/10.5194/tc-14-3329-2020  

   Thompson, Lisa ; Smith, Madison ; Thomson, Jim ; Stammerjohn, Sharon ; Ackley, Steve ; Loose, Brice ( January 2020 , The Cryosphere)

   null (Ed.)

   Abstract. Katabatic winds in coastal polynyas expose the ocean to extreme heat loss, causing intense sea ice production and dense water formation around Antarctica throughout autumn and winter. The advancing sea ice pack, combined with high winds and low temperatures, has limited surface oceanobservations of polynyas in winter, thereby impeding new insights into theevolution of these ice factories through the dark austral months. Here, wedescribe oceanic observations during multiple katabatic wind events duringMay 2017 in the Terra Nova Bay and Ross Sea polynyas. Wind speeds regularlyexceeded 20 m s−1, air temperatures were below −25 ∘C, and the oceanic mixed layer extended to 600 m. During these events, conductivity–temperature–depth (CTD)profiles revealed bulges of warm, salty water directly beneath the oceansurface and extending downwards tens of meters. These profiles reflect latent heat and salt release during unconsolidated frazil ice production, driven by atmospheric heat loss, a process that has rarely if ever been observed outside the laboratory. A simple salt budget suggests these anomalies reflect in situ frazil ice concentration that ranges from 13 to 266×10-3 kg m−3. Contemporaneous estimates of vertical mixing reveal rapid convection in these unstable density profiles and mixing lifetimes from 7 to 12 min. The individual estimates of ice production from the salt budget reveal the intensity of short-term ice production, up to 110 cm d−1 during the windiest events, and a seasonal average of 29 cm d−1. We further found that frazil ice production rates covary with wind speed and with location along the upstream–downstream length of the polynya. These measurements reveal that it is possible to indirectly observe and estimate the process of unconsolidated ice production in polynyas by measuring upper-ocean water column profiles. These vigorous ice production rates suggest frazil ice may be an important component in total polynya ice production. 

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2. Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica

   https://doi.org/10.5194/tc-2019-213  

   De Pace, L. Smith ( October 2019 , The cryosphere discussions)

   Abstract. During katabatic wind events in the Terra Nova Bay and Ross Sea polynyas, wind speeds exceeded 20 m s−1, air temperatures were below −25 ℃, and the mixed layer extended as deep as 600 meters. Yet, upper ocean temperature and salinity profiles were not perfectly homogeneous, as would be expected with vigorous convective heat loss. Instead, the profiles revealed bulges of warm and salty water directly beneath the ocean surface and extending downwards tens of meters. Considering both the colder air above and colder water below, we suggest the increase in temperature and salinity reflects latent heat and salt release during unconsolidated frazil ice production within the upper water column. We use a simplified salt budget to analyze these anomalies to estimate in-situ frazil ice concentration between 332 × 10−3 and 24.4 × 10−3 kg m−3. Contemporaneous estimates of vertical mixing by turbulent kinetic energy dissipation reveal rapid convection in these unstable density profiles, and mixing lifetimes from 2 to 12 minutes. The corresponding median rate of ice production is 26 cm day−1 and compares well with previous empirical and model estimates. Our individual estimates of ice production up to 378 cm day−1 reveal the intensity of short-term ice production events during the windiest episodes of our occupation of Terra Nova Bay Polynya. How to cite: De Pace, L., Smith, M., Thomson, J., Stammerjohn, S., Ackley, S., and Loose, B.: Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica, The Cryosphere Discuss., https://doi.org/10.5194/tc-2019-213, in review, 2019. 

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3. Upper Ocean Distribution of Glacial Meltwater in the Amundsen Sea, Antarctica

   https://doi.org/10.1029/2019JC015133  

   Biddle, Louise C. ; Loose, Brice ; Heywood, Karen J. ( October 2019 , Journal of Geophysical Research: Oceans)

   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, 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.

    

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4. Summer Carbonate Chemistry in the Dalton Polynya, East Antarctica

   https://doi.org/10.1029/2018JC014882  

   Arroyo, M. C. ; Shadwick, E. H. ; Tilbrook, B. ( August 2019 , Journal of Geophysical Research: Oceans)

   The carbonate chemistry in the Dalton Polynya in East Antarctica (115°–123°E) was investigated in summer 2014/2015 using high‐frequency underway measurements of CO₂fugacity (fCO₂) and discrete water column measurements of total dissolved inorganic carbon (TCO₂) and total alkalinity. Air‐sea CO₂fluxes indicate this region was a weak net source of CO₂to the atmosphere (0.7 ± 0.9 mmol C m⁻²day⁻¹) during the period of observation, with the largest degree of surface water supersaturation (ΔfCO₂= +45 μatm) in ice‐covered waters near the Totten Ice Shelf (TIS) as compared to the ice‐free surface waters in the Dalton Polynya. The seasonal depletion of mixed‐layer TCO₂(6 to 51 μmol/kg) in ice‐free regions was primarily driven by sea ice melt and biological CO₂uptake. Estimates of net community production (NCP) reveal net autotrophy in the ice‐free Dalton Polynya (NCP = 5–20 mmol C m⁻²day⁻¹) and weakly heterotrophic waters near the ice‐covered TIS (NCP = −4–0 mmol C m⁻²day⁻¹). Satellite‐derived estimates of chlorophylla(Chla) and sea ice coverage suggest that the early summer season in 2014/2015 was anomalous relative to the long‐term (1997–2017) record, with lower surface Chlaconcentrations and a greater degree of sea ice cover during the period of observation; the implications for seasonal primary production and air‐sea CO₂exchange are discussed. This study highlights the importance of both physical and biological processes in controlling air‐sea CO₂fluxes and the significant interannual variability of the CO₂system in Antarctic coastal regions.

    

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5. Enhanced moisture delivery into Victoria Land, East Antarctica, during the early Last Interglacial: implications for West Antarctic Ice Sheet stability

   https://doi.org/10.5194/cp-17-1841-2021  

   Yan, Yuzhen ; Spaulding, Nicole E. ; Bender, Michael L. ; Brook, Edward J. ; Higgins, John A. ; Kurbatov, Andrei V. ; Mayewski, Paul A. ( January 2021 , Climate of the Past)

   Abstract. The S27 ice core, drilled in the Allan Hills Blue IceArea of East Antarctica, is located in southern Victoria Land, ∼80 km away from the present-day northern edge of the RossIce Shelf. Here, we utilize the reconstructed accumulation rate of S27covering the Last Interglacial (LIG) period between 129 ka and 116 ka (where ka indicates thousands of years before present) to infer moisture transport into the region. Theaccumulation rate is based on the ice-age–gas-age differences calculatedfrom the ice chronology, which is constrained by the stable water isotopesof the ice, and an improved gas chronology based on measurements of oxygenisotopes of O2 in the trapped gases. The peak accumulation rate in S27occurred at 128.2 ka, near the peak LIG warming in Antarctica. Even the mostconservative estimate yields an order-of-magnitude increase in theaccumulation rate during the LIG maximum, whereas other Antarctic ice coresare typically characterized by a glacial–interglacial difference of a factorof 2 to 3. While part of the increase in S27 accumulation rates mustoriginate from changes in the large-scale atmospheric circulation,additional mechanisms are needed to explain the large changes. Wehypothesize that the exceptionally high snow accumulation recorded in S27reflects open-ocean conditions in the Ross Sea, created by reduced sea iceextent and increased polynya size and perhaps by a southward retreat of theRoss Ice Shelf relative to its present-day position near the onset of the LIG.The proposed ice shelf retreat would also be compatible with a sea-levelhigh stand around 129 ka significantly sourced from West Antarctica. Thepeak in S27 accumulation rates is transient, suggesting that if the Ross IceShelf had indeed retreated during the early LIG, it would have re-advancedby 125 ka. 

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