Preprints
https://doi.org/10.5194/os-2021-50
https://doi.org/10.5194/os-2021-50

  18 Jun 2021

18 Jun 2021

Review status: this preprint is currently under review for the journal OS.

Atmospherically-forced sea-level variability in western Hudson Bay, Canada

Igor Dmitrenko1, Denis Volkov2,3, Tricia Stadnyk4, Andrew Tefs4, David Babb1, Sergei Kirillov1, Alex Crawford1, Kevin Sydor5, and David Barber1 Igor Dmitrenko et al.
  • 1Centre for Earth Observation Science, University of Manitoba, Winnipeg, Manitoba, Canada
  • 2Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, Florida, USA
  • 3NOAA, Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida, USA
  • 4Department of Geography, University of Calgary, Calgary, Alberta, Canada
  • 5Manitoba Hydro, Winnipeg, Manitoba, Canada

Abstract. In recent years, significant trends toward earlier breakup and later freeze‐up of sea-ice in Hudson Bay have led to a considerable increase in shipping activity through the Port of Churchill, which is located in western Hudson Bay and is the only deep-water ocean port in the province of Manitoba. Therefore, understanding sea level variability at the Port is an urgent issue crucial for safe navigation and coastal infrastructure. Using tidal gauge data from the Port along with an atmospheric reanalysis and Churchill River discharge, we assess environmental factors impacting synoptic to seasonal variability of sea-level at Churchill. An atmospheric vorticity index used to describe the wind forcing was found to correlate with sea level at Churchill. Statistical analyses show that, in contrast to earlier studies, local discharge from the Churchill River can only explain up to 5 % of the sea level variability. The cyclonic wind forcing contributes from 22 % during the ice-covered winter-spring season to 30 % during the ice-free summer-fall season due to cyclone-induced storm surge generated along the coast. Multiple regression analysis revealed that wind forcing and local river discharge combined can explain up to 32 % of the sea level variability at Churchill. Our analysis further revealed that the seasonal cycle of sea level at Churchill appears to be impacted by the seasonal cycle in atmospheric circulation rather than by the seasonal cycle in local discharge from the Churchill River, particularly post-construction of the Churchill River diversion in 1977. Sea level at Churchill shows positive anomalies for September–November compared to June–August. This seasonal difference was also revealed for the entire Hudson Bay coast using satellite-derived sea level altimetry. This anomaly was associated with enhanced cyclonic atmospheric circulation during fall, reaching a maximum in November, which forced storm surges along the coast. Complete sea-ice cover during winter impedes momentum transfer from wind stress to the water column, reducing the impact of wind forcing on sea level variability. Expanding our observations to the bay-wide scale, we confirmed the process of wind-driven sea-level variability with (i) tidal-gauge data from eastern Hudson Bay and (ii) satellite altimetry measurements. Ultimately, we find that cyclonic winds generate sea level rise along the western and eastern coasts of Hudson Bay at the synoptic and seasonal time scales, suggesting an amplification of the bay-wide cyclonic geostrophic circulation in fall (October–November), when cyclonic vorticity is enhanced, and Hudson Bay is ice-free.

Igor Dmitrenko et al.

Status: open (until 13 Aug 2021)

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  • RC1: 'Comment on os-2021-50', Anonymous Referee #1, 14 Jul 2021 reply

Igor Dmitrenko et al.

Igor Dmitrenko et al.

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Short summary
Significant trends of sea-ice in Hudson Bay have led to a considerable increase in shipping activity. Therefore, understanding sea level variability is an urgent issue crucial for safe navigation and coastal infrastructure. Using the sea level, atmospheric and river discharge data, we assess environmental factors impacting variability of sea-level at Churchill. We find that it is dominated by wind forcing, with the seasonal cycle generated by the seasonal cycle in atmospheric circulation.