Patterns of the Deep convection in the Nordic Seas

Aleksandr M Fedorov, Nansen International Environmental and Remost Sensing St Petersburg, Saint Petersburg, Russia; St. Petersburg State University (SPbSU), Institute of Earth Science, Oceanology, Saint-Petersburg, Russia, Igor Bashmachnikov, St. Petersburg State University (SPbSU), Institute of Earth Science, St. Petersburg, Russia; Nansen International Environmental and Remote Sensing Center, St. Petersburg, Russia and Tatyana V Belonenko, Saint Petersburg State University, Oceanology, Saint Petersburg, Russia
Abstract:
The most probable region of the deep convection (DC) development, in the central Greenland basin, was first detected by Nansen (1912), its boundaries specified in further studies (Fedorov et al., 2018, Bashmachnikov et al., 2018). The convection depth is detected from vertically homogeneous upper ocean density profiles (the mixed layer depth - MLD) or high oxygen concentration. Variations in the winter MLD maxima are used for evaluation of interannual variability of the DC intensity.

A primary sources of data for this study was ARMOR 3D data-set. This data-set provides monthly mean values of temperature and salinity on 1/4̊x1/4̊ spatial grid and standard oceanographic depth levels, obtained optimal interpolation algorithm of in-situ and satellite data. The MLD was calculated using Dukhovskoy's method (Bashmachnikov et al. 2018): the mixed layer depth is fixed on a potential density profile when the local potential density gradient exceeds three standard deviations in a 100-meter layer, centred at the study level. Daily MLD from GLORYS were averaged to monthly means. Spatial distributions of the MLD were used for further analysis.

It is shown that variability of DC intensity in the Greenland Sea can be efficiently described by the winter maximum MLD together with the area of the region with MLD over 800m (SDC). Cluster analysis demonstrates three types of convection conditions: deep MLD and large SDC, deep MLD and small SDC, shallow MLD and small SDC. With intensification of the DC, the maximum winter MLD increases until reaching a threshold value, after which SDC starts increasing, while winter maximum MLD remains nearly constant. This dependency is observed in both datasets used in this study.

References

A.M. Fedorov, I. L. Bashmachnikov, T. V. Belonenko Localization of areas of deep convection in the Nordic seas, the Labrador Sea and the Irminger Sea. Vestnik of Saint Petersburg University. Earth Sciences, 2018, 63(3), 345–362.

I.L. Bashmachnikov; A.M. Fedorov; A.V. Vesman; T.V. Belonenko; A.V. Koldunov; D.S. Dukhovskoy, Thermohaline convection in the subpolar seas of the North Atlantic from satellite and in situ observations. Part 1: Localization of the deep convection sites. Sovremennye Problemy Distantsionnogo Zondirovaniya Zemli iz Kosmosa, 2018, 15(7), 184-194.

Acknowledgements: The research is funded by the Russian Scientific Foundation: Project number – 18-17-00027

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