Holterman, P.

Morholz, V.

Rehder, G.

Schmale, O.

Tanhua, Toste

Umlauf, L.

Wainek, J.J.

English

OceanRep

Mixing rates in the deep Baltic Sea revealed by a tracer release experimentToste Tanhua, Gregor Rehder, Peter Holtermann, Joanna J. Waniek, Lars Umlauf, Oliver Schmale, Volker Mohrholz.12.9T4 – T311.8T4 – T27.9T3 – T211.2T4 – T16.3T3 – T12.0T2 – T1Kz (10-6m2/s)TimeBackgroundBaltic Sea• Deep water renewal byinflow events• “Natural laboratory” forocean circulationGotland Basin• No tides• Seasonality of mixingKey Questions:Which processes causedeep water mixing duringstagnation periods?How are these processeslinked to atmosphericforcing?LonLat 30’  45’   20oE  15’  30’  36’  48’   57oN  12’  24’  36’ TF271NESESWA1How?OTIS: Ocean Tracer Injection System0.9 kg of SF5CF3  injected in September2007Five MooringsResultsFour Tracer surveysInitial survey (2 weeks) 1 Month later 4 Months later 17 Months later 17 Months laterUmlauf et al., 2008 (EOS)► Fit the data to Gaussian distributions► Calculate the second momentof the fit, i.e. the width ofthe fit as a measure of the vertical mixingKz = S2(T2) – S2(T1) / 2(T2 - T1)Photos: Mario Müller, IFM-GEOMAR► S and T budgetsVertical diffusivity calculated from:► Tracer dist. ► From Literature.Conclusions:► One and a half year of stagnant conditions has beenobserved by moorings, CTD, MSS, and a deliberatelyreleased tracer.► From salt and temperature budgets we find highervertical mixing rates in the winter mixing period, and a stagnant period during the summer with lowermixing rates.► The tracer reveal low vertical mixing in the interiorof the basin, but significant higher rates close to theborder/bottom of the basin. ► Possible signs of interleaving also during the„stagnant“ periodReferencesAxell, L. B. (1998), On the variability of Baltic Sea deepwater mixing, J. Geophys. Res., 103, 21667-21682.Lass, H. U., H. Prandke, and B. Liljebladh (2003), Dissipation in the Baltic proper during winter stratification, J. Geophys. Res., 108, C6, 3187.Stigebrandt, A. (1987), A Model for the Vertical Circulation of the Baltic Deep-Water, J. Phys. Oceanogr., 17, 1772-1785.Umlauf, L., T. Tanhua, J. Waniek, O. Schmale, P. Holtermann, and G. Rehder (2008), Hunting a New Oceanic Tracer, EOS, 89, 43, 419.Contact: Toste Tanhua; ttanhua@ifm-geomar.deT1 = September 2007 T2 = October 2007T3 = January 2008T4 = January 2009Tracer only in the interior basin Tracer “hit” bottom Tracer move outside of basin ..even far away 

Mixing rates in the deep Baltic Sea revealed by a tracer release experiment

Mixing rates in the deep Baltic Sea revealed by a tracer release experiment

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