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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 13 | Copyright

Special issue: Boknis Eck Time Series Station (SW Baltic Sea)

Biogeosciences, 11, 3603-3617, 2014
https://doi.org/10.5194/bg-11-3603-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 04 Jul 2014

Research article | 04 Jul 2014

Summer upwelling at the Boknis Eck time-series station (1982 to 2012) – a combined glider and wind data analysis

J. Karstensen1, T. Liblik1,2, J. Fischer1, K. Bumke1, and G. Krahmann1 J. Karstensen et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany
  • 2Marine Systems Institute at Tallinn University of Technology, MSI, Akadeemia tee 15a, 12618 Tallinn, Estonia

Abstract. Two consecutive summer upwelling events, each lasting for less than 24 h, were surveyed in high temporal and vertical resolution close to the Boknis Eck time-series station (BE) in the western Belt Sea (Baltic Sea) in summer 2010 with an autonomous glider. Driven only by moderate offshore winds both events resulted in more than 5 K cooling of surface waters, while only for the second event were significant irreversible changes in the vertical stratification observed. Generalizing the glider survey observations with hourly wind data from nearby meteorological stations, it is found that upwelling in the BE area occurs for wind directions between 190 to 260° and wind speed exceeding 4 m s−1. Based on these thresholds the wind-induced summer (June to September) upwelling conditions in the BE area for the period 1982 to 2012 are reconstructed. On average about 18 days of upwelling favourable wind conditions are found for the four summer months, with significant interannual variability ranging from 7.7 days (2006) to more than 28 days (1985). By aligning upwelling favourable wind conditions with the monthly BE surveys it is found that extreme anomalies in BE surveys follow extended periods of upwelling favourable winds.

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