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and north-northwesterly winds some parts of the dense water were diverted into the Gdansk Basin instead of the deepest pathway into the EGB. During the deployment period of the ADCPs the wind direction of the regional wind (,38) across the <strong>Baltic</strong> Proper mainly came from a northwesterly direction and only turned towards southwesterly after the 15 November 2006. Meier (2007) experienced a separation of the dense water in his model results when leaving the Stolpe Channel, where one part chose the deepest pathway towards the EGB while the other travelled towards the Gdansk Basin. The position of the Hoburg Channel transect in the model was not ideally chosen for the budget calculations. In its current position (see Fig. 4.18) the eastern end of the transect catches a large eddy with re-circulating water masses, thus creating articially larger transports. Ideally the transect should cover at least the area between the 50 m isobath to create good boundary conditions for the mass balance. For the above mentioned reasons the transect at 56 ◦ N is not taken into an account in the discussions apart from the above mentioned cross-correlations. Volume transports computed by Krauss and Brügge (1991) through the Stolpe Channel for winds from the north amounted to 30 -40 km 3 /d in the mid layers and 20 km 3 /d in the bottom layer. For winds from the east transport volumes produced similar results, but magnitudes are halved. In this study peaks in eastward volume transports reached between 5 and 10 km 3 /d mainly for winds from a northwesterly direction. Only once a strong wind from north-northeast created a volume transport of 15 km 3 /d. Comparisons between volume transports from this study and transports acquired by Krauss and Brügge (1991) are suitable only to a limited extent, since Krauss and Brügge (1991) used idealised wind conditions in their study with continuous winds from a given directions, whereas this study uses realistic wind conditions with uctuating winds. Naturally, transports resulting from constant winds achieve higher magnitudes than transports from uctuating winds. Volume transports estimated below the 7.9 kg/m 3 isopycnal by Borenäs et al. (2007), ranging from 0.32 - 1.69 km 3 /d, are more in the order of magnitude of the transports calculated in this study. Kouts and Omstedt (1993) estimated a transport of 2.16 km 3 /d with an average salinity of 14 g/kg, which are still in the vicinity of estimated transports from the ADCPs. Fluctuating winds blowing over the <strong>Baltic</strong> Proper account for the observed pulse-like deep water currents in the Stolpe Channel. As described by Krauss and Brügge (1991) it was observed that the surface layer and consequential the sea level are acting in the same 98
direction as the wind. The deep layer, however, acts in the opposite direction. Although, during periods of, for example, low eastward winds (the wind was rotated by 180 ◦ to match the currents), eastward currents were observed, where westward currents would be expected instead to match the theory. Krauss and Brügge (1991) concluded that a wind blowing constantly in a certain directions produces a counter current in the lower or bottom layer. By switching the wind o in their model the strong directional transport broke down into eddies and topographically controlled irregular motions. This, however could not be observed in the ADCP data. From the correlations below, the following ow mechanism can be derived: The regional wind steers the sea level (correlation between the wind 38 and sea level dierence: R= 0.89) and to a smaller extend inuences a counter ow of the deep currents between 66 - 71 m (correlation between 38 and SFN/SFS(66-71): R= -0.63). The deep current is more inuenced by changes in the sea level (correlation between SL ∆(VP-SA) and SFN/SFS(66-71): R= -0.68). Correlations of the sea level dierence with estimated transports between 66 - 71 m and modelled transports below the 9.5 kg/m 3 isopycnal are all slightly less correlated (R= -0.65) than the deep velocities. Separate correlations of each ADCP with the regional wind and sea level dierence reveal a stronger inuence of the wind in the upper layer on the norther side of the channel, while on the southern side the Ekman transport induced by the Coriolis force is predominant. Pulse-like currents in the Stolpe Channel are partly driven by the regional wind, i.e. up to 50 % and partly driven by sloping density gradients of dense water masses in the bottom of the channel and therefore resulting geostrophic currents. The height of the eastward ow's upper boundary at SFN (65 m depth) and SFS (52 m) was similar to the slope of the salinity/ density gradient observed in the hydrographic cross-sections. Resulting eects of a sloping density gradient on bottom currents was studied by Paka et al. (1998) and conrm their observations that the current uctuations are density driven, when wind velocities are low. The frequency spectra of the along-slope current of SFN and SFS reveal that the 2 - 4 day long current uctuations originate from changes in the regional wind. Each of these uctuations transport a volume of around 1.78 ± 1.15 km 3 /d eastwards. These 2 - 4 day long uctuations transport nearly the same amount in a single event as the 3-monthly mean of 0.75 ± 2.32 km 3 /d from estimated transports (0.81 ± 3.15 km 3 /d from modelled transports) and are 99
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No 88 2012 Spatiotemporal Scales of
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Meereswissenschaftliche Berichte MA
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Abstract The Baltic Sea is surround
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Contents Abstract Contents List of
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Acknowledgement 109 Appendix 111 vi
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M-7/M-8 Mesodyn hydrographic snapsh
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List of Figures 1.1 Baltic Sea - ba
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4.32 Regression sea level dierence
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1. Introduction 1.1 Investigations
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circulation above topographic anks
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58 o N 190 230 210 100 75 100 100 7
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y 'new' deep water. For instance, i
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events. During and after such event
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this inow event was classied as 'mo
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Scale (PSS-78), roughly by 0.5%, as
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(Acoustic Doppler Current Proler) a
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for the southernmost zonal section
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whereas the length of the NE time s
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have a thickness of only 1.5 m in o
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dependent salt volumes for the deep
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7 6.5 a Temperature ( o C) 6 5.5 5
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Potential Temperature ( o C) 8 7 6
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inowing waters masses with variable
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following these bounds will be used
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60 80 100 −45 −50 −55 Pressur
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Monitoring Station BMP271 60 80 100
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Date 31.8.1997, 03.11.1997, 03.11.1
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190 a 200 Depth (m) 210 220 230 240
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Date (ID) 〈S〉 V (g/kg) 〈θ〉
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deviation of the temperature uctuat
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4. The Deep Circulation in the EGB
Page 63 and 64: Depth (m) 50 100 150 200 17 16 4.6
Page 65 and 66: For this reason, the displayed temp
Page 67 and 68: 6.4 6.3 178 m 208 m 223 m Daily Tem
Page 69 and 70: The deep parts of the basin are exp
Page 71 and 72: On the 29 September 2006 between 60
Page 73 and 74: In the geostrophic balance horizont
Page 75 and 76: captured eastward velocities up to
Page 77 and 78: Figure 4.11: Modelled current veloc
Page 79 and 80: SFS and SFN. At the southern ank a
Page 81 and 82: Mean Volume Transports Mean Volume
Page 83 and 84: 160 170 180 Volume of EGB below 170
Page 85 and 86: Basin 55.9 ◦ N. From there the bo
Page 87 and 88: Volume transports (km 3 /d) 15 10 5
Page 89 and 90: Gdansk Basin happened a few weeks e
Page 91 and 92: needs some explanation, since the l
Page 93 and 94: and Fig. 4.24 and displayed in Tabl
Page 95 and 96: Salt (t) 8 6 4 2 0 2 4 6 8 x 10 10
Page 97 and 98: Time Period Stolpe Channel at 17.5
Page 99 and 100: Modelled volume transport through S
Page 101 and 102: discovered that most of the varianc
Page 103 and 104: to the right (perpendicular) to the
Page 105 and 106: of salty and often well oxygenated
Page 107 and 108: Depth (m) 40 45 50 55 60 4 3 2 1 0
Page 109 and 110: a correlation coecient of R=-0.68 a
Page 111 and 112: 5. Discussion and Conclusions 5.1 D
Page 113: graphic cross-sections, conducted i
Page 117 and 118: Bibliography Axell, L. B., 1998: On
Page 119 and 120: Griffies, S. M., R. C. Pacanowski,
Page 121 and 122: Matthäus, W., 1993: Major inows of
Page 123 and 124: Rubio, A., D. Gomis, G. Jordà and
Page 125 and 126: Zhurbas, V., I. Oh and V. Paka, 200
Page 127 and 128: Appendix Current speed and directio
Page 129 and 130: Current speed and direction (cm/s)
Page 131 and 132: 2 1.5 1 Cumulative volume through S
Page 133 and 134: Volume (km 3 ) 2.5 2 1.5 1 0.5 0
Page 135 and 136: 10 3 Regional Wind 7 Power Spectra
Page 137 and 138: NE along−slope at 178m 10 2 10 1
Page 139 and 140: Meereswissenschaftliche Berichte MA
Page 141 and 142: 26 (1997) Lakaschus, Sönke: Konzen
Page 143 and 144: 51 (2002) Wasmund, Norbert; Pollehn
Page 145 and 146: 78 (2009) Wasmund, Norbert; Pollehn
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