Baltic Sea

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Die vorliegende Arbeit wurde am 2. Mai 2011 bei der Mathematisch-Naturwisschaftlichen Fakultät der Universität Rostock als Dissertation eingereicht und am 25. Mai 2012 erfolgreich verteidigt. Die Gutachter waren: • Dr. habil. Eberhard Hagen, Leibniz Institut für Ostseeforschung Warnemünde • Prof. Dr. Jüri Elken, Tallinn University of Technology i
Abstract The Baltic Sea is surrounded by land, thus exchanges with the open ocean only take place through the North Sea. The Baltic Sea is divided into dierent deep basins connected by narrow sills and channels. Compared to the open ocean and the North Sea the salinity in the Baltic Sea is generally low due to large amounts of fresh water provided by river discharges. Inowing saline water from the North Sea travels along the bottom and therefore produces a permanent halocline, separating the surface water from the deep water in the basins. Saline and also often oxygen-rich inows are essential for the deep water renewal in the largest basin of the Baltic Sea, the Eastern Gotland Basin (EGB). These inows occur only under certain meteorological conditions and thus so-called stagnation periods (periods without inows) can occur for several years, oxygen depletion can lead to the formation of hydrogen sulde in the Baltic deep water. In this work two dierent inows and their eects on the deep water in the Baltic Proper were investigated. First, the major warm and saline deep inow into the Eastern Gotland Basin, lasting from the end of November 1997 until the beginning of May 1998, was investigated. Temporal uctuations of the deep circulation were monitored at 170 m depth by two current meter moorings deployed at the north-eastern and south-western rim of the EGB between August 1997 - September 1998. Three-dimensional structures of stratication parameters were inferred from comparisons of two high-resolution hydrographic surveys carried out before and during the end of the 1997/1998 inow. Results indicated a lifting of near-bottom isopycnals by more than 50 m during the inow up to a depth of 170 m. Since the basin is enclosed at 170 m depth this implies a complete deep water renewal. Detected warm-water intrusions enhanced the temperature variability on isopycnal surfaces at intermediate depth, creating strong inverse temperature gradients below the halocline. Corresponding Turner angles suggest a signicant contribution of diusive convection to diapycnal mixing in this region. In contrast, for the deepest near-bottom layers which were only marginally aected by intrusions, basin-scale budgets of heat and salinity suggest comparable diusivities (κ s = 1.3 − 2.1 × 10 −5 m 2 /s for salt and κ θ = 1.6 − 2.8 × 10 −5 m 2 /s for potential temperature), implying that double-diusion does not play a major role in mixing there. For intermediate layers between 90-170 m the basin is not closed, thus the budget method could not be adopted. Instead an idealised model for the decay of temperature variance associated with the intrusions was applied. Results indicate that the intrusions decay within a few weeks, corresponding to vertical diusivities of a few times 10 −5 m 2 /s. ii
Page 1 and 2: No 88 2012 Spatiotemporal Scales of
Page 3: Meereswissenschaftliche Berichte MA
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 and 50: 60 80 100 −45 −50 −55 Pressur
Page 51 and 52: Monitoring Station BMP271 60 80 100
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
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Figure 4.11: Modelled current veloc
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SFS and SFN. At the southern ank a
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Mean Volume Transports Mean Volume
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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
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Gdansk Basin happened a few weeks e
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needs some explanation, since the l
Page 93 and 94:
and Fig. 4.24 and displayed in Tabl
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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
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Current speed and direction (cm/s)
Page 131 and 132:
2 1.5 1 Cumulative volume through S
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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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Baltic Sea

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