Conway Howard

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Conway
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Howard
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  • Article
    Ice sheet record of recent sea-ice behavior and polynya variability in the Amundsen Sea, West Antarctica
    (John Wiley & Sons, 2013-01-25) Criscitiello, Alison S. ; Das, Sarah B. ; Evans, Matthew J. ; Frey, Karen E. ; Conway, Howard ; Joughin, Ian ; Medley, Brooke ; Steig, Eric J.
    Our understanding of past sea-ice variability is limited by the short length of satellite and instrumental records. Proxy records can extend these observations but require further development and validation. We compare methanesulfonic acid (MSA) and chloride (Cl–) concentrations from a new firn core from coastal West Antarctica with satellite-derived observations of regional sea-ice concentration (SIC) in the Amundsen Sea (AS) to evaluate spatial and temporal correlations from 2002–2010. The high accumulation rate (~39 g∙cm–2∙yr–1) provides monthly resolved records of MSA and Cl–, allowing detailed investigation of how regional SIC is recorded in the ice-sheet stratigraphy. Over the period 2002–2010 we find that the ice-sheet chemistry is significantly correlated with SIC variability within the AS and Pine Island Bay polynyas. Based on this result, we evaluate the use of ice-core chemistry as a proxy for interannual polynya variability in this region, one of the largest and most persistent polynya areas in Antarctica. MSA concentrations correlate strongly with summer SIC within the polynya regions, consistent with MSA at this site being derived from marine biological productivity during the spring and summer. Cl– concentrations correlate strongly with winter SIC within the polynyas as well as some regions outside the polynyas, consistent with Cl– at this site originating primarily from winter sea-ice formation. Spatial correlations were generally insignificant outside of the polynya areas, with some notable exceptions. Ice-core glaciochemical records from this dynamic region thus may provide a proxy for reconstructing AS and Pine Island Bay polynya variability prior to the satellite era.
  • Article
    Airborne-radar and ice-core observations of annual snow accumulation over Thwaites Glacier, West Antarctica confirm the spatiotemporal variability of global and regional atmospheric models
    (John Wiley & Sons, 2013-07-26) Medley, Brooke ; Joughin, Ian ; Das, Sarah B. ; Steig, Eric J. ; Conway, Howard ; Gogineni, S. ; Criscitiello, Alison S. ; McConnell, Joseph R. ; Smith, B. E. ; van den Broeke, Michiel R. ; Lenaerts, Jan T. M. ; Bromwich, D. H. ; Nicolas, J. P.
    We use an airborne-radar method, verified with ice-core accumulation records, to determine the spatiotemporal variations of snow accumulation over Thwaites Glacier, West Antarctica between 1980 and 2009. We also present a regional evaluation of modeled accumulation in Antarctica. Comparisons between radar-derived measurements and model outputs show that three global models capture the interannual variability well (r > 0.9), but a high-resolution regional model (RACMO2) has better absolute accuracy and captures the observed spatial variability (r = 0.86). Neither the measured nor modeled accumulation records over Thwaites Glacier show any trend since 1980. Although an increase in accumulation may potentially accompany the observed warming in the region, the projected trend is too small to detect over the 30 year record.
  • Article
    Constraining the recent mass balance of Pine Island and Thwaites glaciers, West Antarctica, with airborne observations of snow accumulation
    (Copernicus Publications on behalf of the European Geosciences Union, 2014-07-31) Medley, Brooke ; Joughin, Ian ; Smith, B. E. ; Das, Sarah B. ; Steig, Eric J. ; Conway, Howard ; Gogineni, S. ; Lewis, Cameron ; Criscitiello, Alison S. ; McConnell, Joseph R. ; van den Broeke, Michiel R. ; Lenaerts, Jan T. M. ; Bromwich, D. H. ; Nicolas, J. P. ; Leuschen, C.
    In Antarctica, uncertainties in mass input and output translate directly into uncertainty in glacier mass balance and thus in sea level impact. While remotely sensed observations of ice velocity and thickness over the major outlet glaciers have improved our understanding of ice loss to the ocean, snow accumulation over the vast Antarctic interior remains largely unmeasured. Here, we show that an airborne radar system, combined with ice-core glaciochemical analysis, provide the means necessary to measure the accumulation rate at the catchment-scale along the Amundsen Sea coast of West Antarctica. We used along-track radar-derived accumulation to generate a 1985–2009 average accumulation grid that resolves moderate- to large-scale features (>25 km) over the Pine Island–Thwaites glacier drainage system. Comparisons with estimates from atmospheric models and gridded climatologies generally show our results as having less accumulation in the lower-elevation coastal zone but greater accumulation in the interior. Ice discharge, measured over discrete time intervals between 1994 and 2012, combined with our catchment-wide accumulation rates provide an 18-year mass balance history for the sector. While Thwaites Glacier lost the most ice in the mid-1990s, Pine Island Glacier's losses increased substantially by 2006, overtaking Thwaites as the largest regional contributor to sea-level rise. The trend of increasing discharge for both glaciers, however, appears to have leveled off since 2008.