Preprints
https://doi.org/10.5194/os-2022-19
https://doi.org/10.5194/os-2022-19
 
01 Apr 2022
01 Apr 2022
Status: this preprint is currently under review for the journal OS.

The role of tides and sea ice on the carbonate chemistry in a coastal polynya in the south-eastern Weddell Sea

Elise Sayana Droste1, Mario Hoppema2, Melchor González-Dávila3, Juana Magdalena Santana-Casiano3, Bastien Y. Queste1,4, Giorgio Dall'Olmo5, Hugh J. Venables6, Gerd Rohardt2, Sharyn Ossebaar7, Daniel Schuller8, Sunke Trace-Kleeberg2,9, and Dorothee C. E. Bakker1 Elise Sayana Droste et al.
  • 1School of Environmental Sciences, University of East Anglia, Norwich Research Park, NR4 7TJ Norwich, United Kingdom
  • 2Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Postfach 120161, 27515 Bremerhaven, Germany
  • 3Instituto de Oceanografía y Cambio Global, IOCAG, Universidad de Las Palmas de Gran Canaria, ULPGC, 35017 Las Palmas de Gran Canaria, Spain
  • 4Department of Marine Sciences, University of Gothenburg, Carl Skottsbergs Gata 22B, SE-413 19 Gothenburg, Sweden
  • 5Plymouth Marine Laboratory, Prospect Place, PL1 3DH Plymouth, United Kingdom
  • 6British Antarctic Survey, High Cross, Madingley Road, CB3 0ET Cambridge, United Kingdom
  • 7NIOZ Royal Netherlands Institute for Sea Research, department of Ocean Systems, P.O. Box 59, 1790 AB, Den Burg, Texel, The Netherlands
  • 8Scripps Institution of Oceanography, UC San Diego, 8622 Kennel Way, La Jolla, CA 92037, United States
  • 9School of Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, SO14 3ZH, United Kingdom

Abstract. Tides significantly affect polar coastlines by modulating ice shelf melt and modifying shelf water properties through transport and mixing. However, the effect of tides on the marine carbonate chemistry in such regions, especially around Antarctica, remains largely unexplored. We address this topic with two case studies in a coastal polynya in the south-eastern Weddell Sea, neighbouring the Ekström Ice Shelf. The case studies were conducted in January 2015 (PS89) and January 2019 (PS117), capturing semi-diurnal oscillations in the water column. These are pronounced in both physical and biogeochemical variables for PS89. During rising tide, advection of sea ice melt water from the north-east created a fresher, warmer, more deeply mixed water column with lower dissolved inorganic carbon (DIC) and total alkalinity (TA) content. During ebbing tide, water from underneath the ice shelf decreased the polynya's temperature, increased the DIC and TA content, and created a more stratified water column. The variability during the PS117 case study was much smaller, as it had less sea ice melt water input during rising tide and was better mixed with sub-ice shelf water. The contrasts in the variability between the two case studies could be wind and sea ice driven, and underline the complexity and highly dynamic nature of the system.

The variability in the polynya induced by the tides results in an air-sea CO2 flux that can range between a strong sink (-20 mmol m-2 day-1) and a small source (7 mmol m-2 day-1) on a semi-diurnal time scale. If the variability induced by tides is not taken into account, there is a potential risk of overestimating the polynya's CO2 uptake by 98 % or underestimating it by 108 % (mistaking it for a source instead of a variable sink), compared to the average flux determined over several days. Given the disproportionate influence of polynyas on heat and carbon exchange in polar oceans, we recommend that future studies around the Antarctic and Arctic coastlines consider the timing of tidal currents in their sampling strategies and analyses. This will help constrain variability in oceanographic measurements and avoid potential biases in our understanding of these highly complex systems.

Elise Sayana Droste et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2022-19', Anonymous Referee #1, 29 Apr 2022
  • RC2: 'Comment on os-2022-19', Anonymous Referee #2, 21 May 2022
  • RC3: 'Comment on os-2022-19', Anonymous Referee #3, 12 Jun 2022

Elise Sayana Droste et al.

Elise Sayana Droste et al.

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Short summary
Tides affect the marine carbonate chemistry within a coastal polynya neighbouring the Ekström Ice Shelf by movement of seawater with different CO2 content. The result is that the coastal polynya in the summer can cycle between being a sink and a source of CO2 several times a day. We encourage consideration of tides when collecting measurements in polar coastal regions to account for variability and to avoid over- or underestimations of CO2 exchange between the atmosphere and ocean.