Baltic Sea

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example, accepting the geostrophic adjustment within such eddy-like features, the shape of the isopycnals suggests dierently rotating features in and below the main halocline, Fig. 3.6 b. Here, the feature with an anticyclonic rotation occurred at 19.65 ◦ E in the halocline (70 - 90 m), while the cyclonic one was placed directly beneath it in 90 - 120 m. Their generation mechanisms are considered to be outside the scope of this study, but were examined in more detail by Reiÿmann (2002), Reiÿmann (2005) and Zhurbas and Paka (1997). Looking for associated mixing conditions, all estimated values of Tu suggest that there was a predominance of the diusive convective regime in the whole deep domain (Fig. 3.6 b). All Tu values between −90 ◦ < Tu< −60 ◦ (or 0.25 < R ρ < 1), indicated a large tendency for diusive convection, were generally found on top of the warm intrusions. This is nicely illustrated for the particularly strong intrusion in Fig. 3.6 b (between 19.99 ◦ E and 20.15 ◦ E). This intrusion was topped at around 161 m depth by a single cell with a peak value of Tu = −83.9 ◦ (or R ρ = 0.81). The lateral extension of this patch stretched over the distance of 10 km (19.99 − 20.15) ◦ E. 3.2.3 Vertical and temporal variability The temporal evolution of temperature and salinity between the two basin-scale eld campaigns M7 and M8 discussed above is illustrated by a series of CTD proles taken at or near the central monitoring station BMP271 (see Fig. 3.7). The initial three proles measured in August and November 1997 show very little vertical and temporal variabilities, and comparatively low bottom temperatures. No signs of inow activity could be identied at this early stage. However, the proles taken on 17-18 February 1998, more than 3 months later, exhibit a dramatically dierent picture. The potential temperature had strongly increased below 60 m, and peak values near the bottom increased from 5.3 ◦ C (31 August 1997) to 7.2 ◦ C (18 February). The near-bottom potential densities rose from σ θ = 9.55 kg/m 3 to σ θ = 9.85 kg/m 3 , and water denser than the pre-inow maximum were then found in the entire depth range below 165 m (not shown). The inowing water masses are seen to occur as intrusions, causing high vertical and temporal variability in the temperature proles. Note that only very little vertical/ temporal variability was observed below approximately 210 m depth. This suggests that the renewal of the nearbottom waters was already completed on the 18 February 1998. Above this level, however, 34
Monitoring Station BMP271 60 80 100 120 Depth (m) 140 160 31.8.97 21:12 180 03.11.97 7:31 03.11.97 8:52 200 17.02.98 18:07 17.02.98 20:49 220 18.02.98 7:09 27.03.98 1:20 21.04.98 14:57 240 3 3.5 4 4.5 5 5.5 6 6.5 7 Potential temperature ( o C) Figure 3.7: Potential temperature vs. depth of the monitoring station BMP271 below 50 m to the bottom, see Fig. 1.2. Sampling time given as dd.mm.yy HH:MM UTC. especially in the intermediate layer (90-170 m), these intrusions generated strong vertical temperature gradients which may have aected the stability parameters in the double-diusive regime. To investigate this eect, the Turner angles dened in (3.2) were computed for all measured proles. The results are displayed in Fig. 3.8, and illustrate that diusive-convective conditions prevail, consistent with the stabilising eect of salinity and the destabilising eect of high temperatures from the inowing water. According to Zhurbas and Paka (1999) and Kuzmina et al. (2005) active turbulence in diusive convection requires values of R ρ ∼ 1/15 = 0.067 (Tu = −48.81 ◦ ). Resulting vertical averages were computed for R ρ and TU with corresponding standard deviations for the fully enclosed part of the basin below 170 m depth (Table 3.2). Here, vertically averaged θ and S gradients were used to calculate R ρ and Tu. In general, all averages suggest a shift of Tu towards values reecting diusive convective conditions triggered by the deep warmwater intrusion. The only exception results from the prole sampled in March, Fig. 3.8. Its R ρ values exhibits the highest standard deviation (see Fig. 3.8) of all proles with Tu values pointing to the above mentioned cases (ii) and (iii), i.e. to the stable and salt-ngering mixing domains. However, such extreme values of Tu near the bottom are irrelevant for double-diusive processes given the fact that the dominating process here is bottom boundary mixing. The two proles from 17 February 1998 had the highest values of the density ratio 35
Page 1 and 2: No 88 2012 Spatiotemporal Scales of
Page 3 and 4: Meereswissenschaftliche Berichte MA
Page 5 and 6: Abstract The Baltic Sea is surround
Page 7 and 8: Contents Abstract Contents List of
Page 9 and 10: Acknowledgement 109 Appendix 111 vi
Page 11 and 12: M-7/M-8 Mesodyn hydrographic snapsh
Page 13 and 14: List of Figures 1.1 Baltic Sea - ba
Page 15 and 16: 4.32 Regression sea level dierence
Page 17 and 18: 1. Introduction 1.1 Investigations
Page 19 and 20: circulation above topographic anks
Page 21 and 22: 58 o N 190 230 210 100 75 100 100 7
Page 23 and 24: y 'new' deep water. For instance, i
Page 25 and 26: events. During and after such event
Page 27 and 28: this inow event was classied as 'mo
Page 29 and 30: Scale (PSS-78), roughly by 0.5%, as
Page 31 and 32: (Acoustic Doppler Current Proler) a
Page 33 and 34: for the southernmost zonal section
Page 35 and 36: whereas the length of the NE time s
Page 37 and 38: have a thickness of only 1.5 m in o
Page 39 and 40: dependent salt volumes for the deep
Page 41 and 42: 7 6.5 a Temperature ( o C) 6 5.5 5
Page 43 and 44: Potential Temperature ( o C) 8 7 6
Page 45 and 46: inowing waters masses with variable
Page 47 and 48: following these bounds will be used
Page 49: 60 80 100 −45 −50 −55 Pressur
Page 53 and 54: Date 31.8.1997, 03.11.1997, 03.11.1
Page 55 and 56: 190 a 200 Depth (m) 210 220 230 240
Page 57 and 58: Date (ID) 〈S〉 V (g/kg) 〈θ〉
Page 59 and 60: deviation of the temperature uctuat
Page 61 and 62: 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 and 114:
graphic cross-sections, conducted i
Page 115 and 116:
direction as the wind. The deep lay
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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