Preprints
https://doi.org/10.5194/tc-2021-13
https://doi.org/10.5194/tc-2021-13

  05 Mar 2021

05 Mar 2021

Review status: a revised version of this preprint was accepted for the journal TC and is expected to appear here in due course.

Changes in the Area, Thickness, and Volume of the Thwaites B30 Iceberg Observed by Satellite Altimetry and Imagery

Anne Braakmann-Folgmann1, Andrew Shepherd1, and Andy Ridout2 Anne Braakmann-Folgmann et al.
  • 1Centre for Polar Observation and Modelling (CPOM), University of Leeds, Leeds, LS2 9JT, UK
  • 2Centre for Polar Observation and Modelling (CPOM), University College London, London, UK

Abstract. Icebergs account for half of all ice loss from Antarctica and, once released, present a hazard to maritime operations. Their melting leads to a redistribution of cold fresh water around the Southern Ocean which, in turn, influences water circulation, promotes sea ice formation, and fosters primary production. In this study, we combine CryoSat-2 satellite altimetry with MODIS and Sentinel-1 satellite imagery to track changes in the area, freeboard, thickness, and volume of the B30 tabular iceberg between 2012 and 2018. We track the iceberg elevation when it was attached to Thwaites Glacier and on a further 106 occasions after it calved using Level 1b CryoSat data, which ensures that measurements recorded in different modes and within different geographical zones are consistently processed. From these data, we mapped the icebergs freeboard and estimated its thickness taking snowfall and changes in snow and ice density into account. We compute changes in freeboard and thickness relative to the initial average for each overpass and compare this time series to precisely located tracks using the satellite imagery. This comparison shows that our time series of iceberg freeboard change is in good agreement with the geolocated overpasses (correlation coefficient 0.87), and suggests that geolocation reduces the uncertainty by 1.6 m. We also demonstrate that the snow layer has a significant impact on iceberg thickness change. Changes in the iceberg area are measured by tracing its perimeter and we show that alternative estimates based on arc lengths recorded in satellite altimetry profiles and on measurements of the semi-major and semi-minor axes also capture the trend, though with a 48 % overestimate and a 15 % underestimate, respectively. Since it calved, the area of B30 has decreased from 1500 +/− 60 to 426 +/− 27 km2, its mean freeboard has fallen from 49.0 +/− 4.6 to 38.8 +/− 2.2 m, and its mean thickness has reduced from 315 ± 36 to 198 ± 14 m. The combined loss amounts to an 80 +/− 16 % reduction in volume, two thirds (69 ± 14 %) of which is due to fragmentation and the remainder (31 ± 11 %) is due to basal melting.

Anne Braakmann-Folgmann et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on tc-2021-13', Xuying Liu, 05 Apr 2021
    • AC3: 'Response to Xuying Liu', Anne Braakmann-Folgmann, 21 May 2021
  • RC1: 'Comment on tc-2021-13', Anonymous Referee #1, 08 Apr 2021
    • AC1: 'Response', Anne Braakmann-Folgmann, 21 May 2021
  • RC2: 'Comment on tc-2021-13', Jessica Scheick, 13 Apr 2021
    • AC2: 'Response', Anne Braakmann-Folgmann, 21 May 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on tc-2021-13', Xuying Liu, 05 Apr 2021
    • AC3: 'Response to Xuying Liu', Anne Braakmann-Folgmann, 21 May 2021
  • RC1: 'Comment on tc-2021-13', Anonymous Referee #1, 08 Apr 2021
    • AC1: 'Response', Anne Braakmann-Folgmann, 21 May 2021
  • RC2: 'Comment on tc-2021-13', Jessica Scheick, 13 Apr 2021
    • AC2: 'Response', Anne Braakmann-Folgmann, 21 May 2021

Anne Braakmann-Folgmann et al.

Anne Braakmann-Folgmann et al.

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Short summary
We investigate the disintegration of the B30 iceberg using satellite remote sensing and find that the iceberg lost 378 km3 of ice in 6.5 years, corresponding to 80 % of its initial volume. About two thirds are due to fragmentation at the sides and one third is due to melting at the iceberg's base. The release of fresh water and nutrients impacts ocean circulation, sea ice formation and biological production. Moreover, we show that adding a snow layer is important when deriving iceberg thickness.