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Volume 12, issue 3
Ocean Sci., 12, 715-732, 2016
https://doi.org/10.5194/os-12-715-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Operational oceanography in Europe 2014 in support of blue...

Ocean Sci., 12, 715-732, 2016
https://doi.org/10.5194/os-12-715-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 27 May 2016

Research article | 27 May 2016

Multi-sensor in situ observations to resolve the sub-mesoscale features in the stratified Gulf of Finland, Baltic Sea

Urmas Lips, Villu Kikas, Taavi Liblik, and Inga Lips Urmas Lips et al.
  • Marine Systems Institute at Tallinn University of Technology, Akadeemia Road 15a, 12618 Tallinn, Estonia

Abstract. High-resolution numerical modeling, remote sensing, and in situ data have revealed significant role of sub-mesoscale features in shaping the distribution pattern of tracers in the ocean's upper layer. However, in situ measurements are difficult to conduct with the required resolution and coverage in time and space to resolve the sub-mesoscale, especially in such relatively shallow basins as the Gulf of Finland, where the typical baroclinic Rossby radius is 2–5km. To map the multi-scale spatiotemporal variability in the gulf, we initiated continuous measurements with autonomous devices, including a moored profiler and Ferrybox system, which were complemented by dedicated research-vessel-based surveys. The analysis of collected high-resolution data in the summers of 2009–2012 revealed pronounced variability at the sub-mesoscale in the presence of mesoscale upwelling/downwelling, fronts, and eddies. The horizontal wavenumber spectra of temperature variance in the surface layer had slopes close to −2 between the lateral scales from 10 to 0.5km. Similar tendency towards the −2 slopes of horizontal wavenumber spectra of temperature variance was found in the seasonal thermocline between the lateral scales from 10 to 1km. It suggests that the ageostrophic sub-mesoscale processes could contribute considerably to the energy cascade in such a stratified sea basin. We showed that the intrusions of water with different salinity, which indicate the occurrence of a layered flow structure, could appear in the process of upwelling/downwelling development and relaxation in response to variable wind forcing. We suggest that the sub-mesoscale processes play a major role in feeding surface blooms in the conditions of coupled coastal upwelling and downwelling events in the Gulf of Finland.

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Multi-platform high-resolution observations in the Gulf of Finland in the summers of 2009–2012 revealed pronounced variability at the sub-mesoscale in the presence of mesoscale features, such as upwelling/downwelling events, fronts, and eddies. The analysis suggests that the sub-mesoscale processes could contribute considerably to the downscale energy cascade and play a major role in phytoplankton growth enhancement via vertical transport and re-stratification of the surface layer.
Multi-platform high-resolution observations in the Gulf of Finland in the summers of 2009–2012...
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