Walker
Catherine C.
Walker
Catherine C.
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ArticleEntrainment and dynamics of ocean-derived impurities within Europa's ice shell(American Geophysical Union, 2020-09-20) Buffo, Jacob ; Schmidt, Britney E. ; Huber, Christian ; Walker, Catherine C.Compositional heterogeneities within Europa's ice shell likely impact the dynamics and habitability of the ice and subsurface ocean, but the total inventory and distribution of impurities within the shell are unknown. In sea ice on Earth, the thermochemical environment at the ice‐ocean interface governs impurity entrainment into the ice. Here, we simulate Europa's ice‐ocean interface and bound the impurity load (1.053–14.72 g/kg [parts per thousand weight percent, or ppt] bulk ice shell salinity) and bulk salinity profile of the ice shell. We derive constitutive equations that predict ice composition as a function of the ice shell thermal gradient and ocean composition. We show that evolving solidification rates of the ocean and hydrologic features within the shell produce compositional variations (ice bulk salinities of 5–50% of the ocean salinity) that can affect the material properties of the ice. As the shell thickens, less salt is entrained at the ice‐ocean interface, which implies Europa's ice shell is compositionally homogeneous below ~1 km. Conversely, the solidification of water filled fractures or lenses introduces substantial compositional variations within the ice shell, creating gradients in mechanical and thermal properties within the ice shell that could help initiate and sustain geological activity. Our results suggest that ocean materials entrained within Europa's ice shell affect the formation of geologic terrain and that these structures could be confirmed by planned spacecraft observations.
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ArticleA high resolution, three-dimensional view of the D-28 calving event from Amery Ice Shelf with ICESat-2 and satellite imagery(American Geophysical Union, 2021-01-12) Walker, Catherine C. ; Becker, Maya K. ; Fricker, Helen A.Tabular calving events occur from Antarctica's large ice shelves only every few decades, and are preceded by rift propagation. We used high-resolution imagery and ICESat-2 data to determine the propagation rates for the three active rifts on Amery Ice Shelf (AIS; T1, T2, and E3) and observe the calving of D-28 on September 25, 2019 along T1. AIS front advance accelerated downstream of T1 in the years before calving, possibly increasing stress at the rift tip. T1 experienced significant acceleration for 12 days before calving, coinciding with a jump in propagation of E3. ICESat-2's high resolution and repeat acquisitions every 91 days allowed for analysis of the ice front before and after calving, and rift detection where it was not visible in imagery as a ∼1 m surface depression, suggesting that it propagates as a basal fracture. Our results show that ICESat-2 can provide process-scale information about iceberg calving.
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ArticleGeometry of freezing impacts ice composition: implications for icy satellites(American Geophysical Union, 2023-03-14) Buffo, Jacob J. ; Meyer, Colin R. ; Chivers, Chase J. ; Walker, Catherine C. ; Huber, Christian ; Schmidt, Britney E.Non‐ice impurities within the ice shells of ocean worlds (e.g., Europa, Enceladus, Titan, Ganymede) are believed to play a fundamental role in their geophysics and habitability and may become a surface expression of subsurface ocean properties. Heterogeneous entrainment and distribution of impurities within planetary ice shells have been proposed as mechanisms that can drive ice shell overturns, generate diverse geological features, and facilitate ocean‐surface material transport critical for maintaining a habitable subsurface ocean. However, current models of ice shell composition suggest that impurity rejection at the ice‐ocean interface of thick contemporary ice shells will be exceptionally efficient, resulting in relatively pure, homogeneous ice. As such, additional mechanisms capable of facilitating enhanced and heterogeneous impurity entrainment are needed to reconcile the observed physicochemical diversity of planetary ice shells. Here we investigate the potential for hydrologic features within planetary ice shells (sills and basal fractures), and the unique freezing geometries they promote, to provide such a mechanism. By simulating the two‐dimensional thermal and physicochemical evolution of these hydrological features as they solidify, we demonstrate that bottom‐up solidification at sill floors and horizontal solidification at fracture walls generate distinct ice compositions and provide mechanisms for both enhanced and heterogeneous impurity entrainment. We compare our results with magmatic and metallurgic analogs that exhibit similar micro‐ and macroscale chemical zonation patterns during solidification. Our results suggest variations in ice‐ocean/brine interface geometry could play a fundamental role in introducing compositional heterogeneities into planetary ice shells and cryoconcentrating impurities in (re)frozen hydrologic features.
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ArticleFoehn winds at Pine Island Glacier and their role in ice changes(European Geosciences Union, 2023-07-25) Francis, Diana ; Fonseca, Ricardo ; Mattingly, Kyle S. ; Lhermitte, Stef ; Walker, CatherinePine Island Glacier (PIG) has recently experienced increased ice loss that has mostly been attributed to basal melt and ocean ice dynamics. However, atmospheric forcing also plays a role in the ice mass budget, as besides lower-latitude warm air intrusions, the steeply sloping terrain that surrounds the glacier promotes frequent Foehn winds. An investigation of 41 years of reanalysis data reveals that Foehn occurs more frequently from June to October, with Foehn episodes typically lasting about 5 to 9 h. An analysis of the surface mass balance indicated that their largest impact is on the surface sublimation, which is increased by about 1.43 mm water equivalent (w.e.) per day with respect to no-Foehn events. Blowing snow makes roughly the same contribution as snowfall, around 0.34–0.36 mm w.e. d−1, but with the opposite sign. The melting rate is 3 orders of magnitude smaller than the surface sublimation rate. The negative phase of the Antarctic oscillation and the positive phase of the Southern Annular Mode promote the occurrence of Foehn at PIG. A particularly strong event took place on 9–11 November 2011, when 10 m winds speeds in excess of 20 m s−1 led to downward sensible heat fluxes higher than 75 W m−2 as they descended the mountainous terrain. Surface sublimation and blowing-snow sublimation dominated the surface mass balance, with magnitudes of up to 0.13 mm w.e. h−1. Satellite data indicated an hourly surface melting area exceeding 100 km2. Our results stress the importance of the atmospheric forcing on the ice mass balance at PIG.
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ArticleInfluence of physical factors on restratification of the upper water column in Antarctic coastal polynyas(American Geophysical Union, 2024-03-03) Xu, Yilang ; Zhang, Weifeng Gordon ; Maksym, Ted ; Ji, Rubao ; Li, Yun ; Walker, Catherine C.Antarctic coastal polynyas are hotspots of biological production with intensive springtime phytoplankton blooms that strongly depend on meltwater-induced restratification in the upper part of the water column. However, the fundamental physics that determine spatial inhomogeneity of the spring restratification remain unclear. Here, we investigate how different meltwaters affect springtime restratification and thus phytoplankton bloom in Antarctic coastal polynyas. A high-resolution coupled ice-shelf/sea-ice/ocean model is used to simulate an idealized coastal polynya similar to the Terra Nova Bay Polynya, Ross Sea, Antarctica. To evaluate the contribution of various meltwater sources, we conduct sensitivity simulations altering physical factors such as alongshore winds, ice shelf basal melt, and surface freshwater runoff. Our findings indicate that sea ice meltwater from offshore is the primary buoyancy source of polynya near-surface restratification, particularly in the outer-polynya region where chlorophyll concentration tends to be high. Downwelling-favorable alongshore winds can direct offshore sea ice away and prevent sea ice meltwater from entering the polynya region. Although the ice shelf basal meltwater can ascend to the polynya surface, much of it is mixed vertically over the water column and confined horizontally to a narrow coastal region, and thus does not contribute significantly to the polynya near-surface restratification. Surface runoff from ice shelf surface melt could contribute greatly to the polynya near-surface restratification. Nearby ice tongues and headlands strongly influence the restratification through modifying polynya circulation and meltwater transport pathways. Results of this study can help explain observed spatiotemporal variability in restratification and associated biological productivity in Antarctic coastal polynyas.
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ArticleThe extraordinary March 2022 East Antarctica “Heat” Wave. Part I: observations and meteorological drivers(American Meteorological Society, 2024-01-09) Wille, Jonathan D. ; Alexander, Simon P. ; Amory, Charles ; Baiman, Rebecca ; Barthelemy, Leonard ; Bergstrom, Dana M. ; Berne, Alexis ; Binder, Hanin ; Blanchet, Juliette ; Bozkurt, Deniz ; Bracegirdle, Thomas J. ; Casado, Mathieu ; Choi, Taejin ; Clem, Kyle R. ; Codron, Francis ; Datta, Rajashree ; Di Battista, Stefano ; Favier, Vincent ; Francis, Diana ; Fraser, Alexander D. ; Fourre, Elise ; Garreaud, Rene D. ; Genthon, Christophe ; Gorodetskaya, Irina V. ; Gonzalez-Herrero, Sergi ; Heinrich, Victoria J. ; Hubert, Guillaume ; Joos, Hanna ; Kim, Seong-Joong ; King, John C. ; Kittel, Christoph ; Landais, Amaelle ; Lazzara, Matthew ; Leonard, Gregory H. ; Lieser, Jan L. ; Maclennan, Michelle ; Mikolajczyk, David ; Neff, Peter ; Ollivier, Ines ; Picard, Ghislain ; Pohl, Benjamin ; Ralph, F. Martin ; Rowe, Penny ; Schlosser, Elisabeth ; Shields, Christine A. ; Smith, Inga J. ; Sprenger, Michael ; Trusel, Luke D. ; Udy, Danielle ; Vance, Tessa ; Vignon, Etienne ; Walker, Catherine C. ; Wever, Nander ; Zou, XunBetween 15 and 19 March 2022, East Antarctica experienced an exceptional heat wave with widespread 30°–40°C temperature anomalies across the ice sheet. This record-shattering event saw numerous monthly temperature records being broken including a new all-time temperature record of −9.4°C on 18 March at Concordia Station despite March typically being a transition month to the Antarctic coreless winter. The driver for these temperature extremes was an intense atmospheric river advecting subtropical/midlatitude heat and moisture deep into the Antarctic interior. The scope of the temperature records spurred a large, diverse collaborative effort to study the heat wave’s meteorological drivers, impacts, and historical climate context. Here we focus on describing those temperature records along with the intricate meteorological drivers that led to the most intense atmospheric river observed over East Antarctica. These efforts describe the Rossby wave activity forced from intense tropical convection over the Indian Ocean. This led to an atmospheric river and warm conveyor belt intensification near the coastline, which reinforced atmospheric blocking deep into East Antarctica. The resulting moisture flux and upper-level warm-air advection eroded the typical surface temperature inversions over the ice sheet. At the peak of the heat wave, an area of 3.3 million km2 in East Antarctica exceeded previous March monthly temperature records. Despite a temperature anomaly return time of about 100 years, a closer recurrence of such an event is possible under future climate projections. In Part II we describe the various impacts this extreme event had on the East Antarctic cryosphere.
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ArticleThe extraordinary March 2022 East Antarctica “Heat” Wave. part II: impacts on the Antarctic ice sheet(American Meteorological Society, 2024-01-09) Wille, Jonathan D. ; Alexander, Simon P. ; Amory, Charles ; Baiman, Rebecca ; Barthelemy, Leonard ; Bergstrom, Dana M. ; Berne, Alexis ; Binder, Hanin ; Blanchet, Juliette ; Bozkurt, Deniz ; Bracegirdle, Thomas J. ; Casado, Mathieu ; Choi, Taejin ; Clem, Kyle R. ; Codron, Francis ; Datta, Rajashree ; Di Battista, Stefano ; Favier, Vincent ; Francis, Diana ; Fraser, Alexander D. ; Fourre, Elise ; Garreaud, Rene D. ; Genthon, Christophe ; Gorodetskaya, Irina V. ; Gonzalez-Herrero, Sergi ; Heinrich, Victoria J. ; Hubert, Guillaume ; Joos, Hanna ; Kim, Seong-Joong ; King, John C. ; Kittel, Christoph ; Landais, Amaelle ; Lazzara, Matthew ; Leonard, Gregory H. ; Lieser, Jan L. ; Maclennan, Michelle ; Mikolajczyk, David ; Neff, Peter ; Ollivier, Ines ; Picard, Ghislain ; Pohl, Benjamin ; Ralph, F. Martin ; Rowe, Penny ; Schlosser, Elisabeth ; Shields, Christine A. ; Smith, Inga J. ; Sprenger, Michael ; Trusel, Luke D. ; Udy, Danielle ; Vance, Tessa ; Vignon, Etienne ; Walker, Catherine C. ; Wever, Nander ; Zou, XunBetween 15 and 19 March 2022, East Antarctica experienced an exceptional heat wave with widespread 30°–40°C temperature anomalies across the ice sheet. In Part I, we assessed the meteorological drivers that generated an intense atmospheric river (AR) that caused these record-shattering temperature anomalies. Here, we continue our large collaborative study by analyzing the widespread and diverse impacts driven by the AR landfall. These impacts included widespread rain and surface melt that was recorded along coastal areas, but this was outweighed by widespread high snowfall accumulations resulting in a largely positive surface mass balance contribution to the East Antarctic region. An analysis of the surface energy budget indicated that widespread downward longwave radiation anomalies caused by large cloud-liquid water contents along with some scattered solar radiation produced intense surface warming. Isotope measurements of the moisture were highly elevated, likely imprinting a strong signal for past climate reconstructions. The AR event attenuated cosmic ray measurements at Concordia, something previously never observed. Last, an extratropical cyclone west of the AR landfall likely triggered the final collapse of the critically unstable Conger Ice Shelf while further reducing an already record low sea ice extent.