Baltic Sea

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of eects on the small-scale do saline inows have on ambient water masses in the EGB? How do hydrographic parameters change due to dierent inows? On what kind of spatiotemporal scale do dense water masses travel through the Stolpe Channel and what eect do they have on the deep EGB? What kind of pathways are used? How much water and salt is transported through the Baltic Proper and into the EGB? How can these dense pathways be modelled accurately? What steers these dense water masses? These questions will be attended to in the two main Chapters: Chapter 3: A case study of thermal variability following deep water intrusions in the Eastern Gotland Basin and in chapter 4: The Deep Circulation in the EGB (Inter-basin communication of deep Baltic basins and their eects for the deep circulation). In Chapter 3 the eects of exactly such a warm inow on water masses in the EGB will be investigated and their role in small-scale dynamics and mixing. Its waters can be clearly distinguished from those of the ambient water of the EGB by positive temperature anomalies. However, this hydrographic situation resulted in a number of unusual stratication properties in the deep EGB that have so far received only little attention. Chapter 3 focuses on changed stratication conditions due to upward mixing within near-bottom layers. Realistic mixing parameters will be discussed, especially under the aspect of double-diusive processes. The data is based on results from the rather unique data set sampled by the MESODYN (MESO-scale DYNamics) project. These results were already published in Wieczorek et al. (2008). In contrast to those of previous intrusion studies, which were based on two-dimensional hydrographic transects as in Kuzmina et al. (2005) this approach enables a three-dimensional analysis of the mixing conditions. Two densely spaced CTD surveys with a station spacing of 2.5 nm (dots in Fig. 1.2) were carried out before and after the inow event and some aspects of the thermohaline deep water transformation were described by Wieczorek et al. (2008) as well as in chapter 3. However, temporal changes of the nature of such mixing conditions still remained unanswered and will be investigated in chapter 4. Therefore, two ADCPs measured currents and temperature simultaneously for three months between September and December 2006. This time span is characterised by the inow event described in Matthäus and Franck (1992). The instruments were deployed at 75 m depth in the north and in the south of the eastern gate-way of the Stolpe Channel. Simultaneously, records of three subsurface moorings, each equipped with three current meters, were used to study associated uctuations in the deep 2
circulation above topographic anks of the deep EGB between May 2006 and March 2007. The Stolpe Channel, which connects the deep Bornholm Basin like a trench with the deep Eastern Gotland Basin, is thought to be a key area for the generation of pulse-like deep water intrusions forcing corresponding uctuations in the deep water circulation of the EGB. In this key area the time scales of detected uctuations will be analysed, as well as related steering mechanisms. The quantication of transports through the Stolpe Channel could be estimated from these records and obtained volume transports were compared with those obtained from model simulations. For the rst time high spatial resolution current and hydrographic modelled data from MOM4 is going to be analysed in comparison with measured data. Some attention is drawn to the salt transport and pathways from the Stolpe Channel into the EGB. Thus, the question will be answered of how much of the salt then arrives in the largest basin of the Baltic Sea, the EGB, and how the resulting overall salt content varies over time. An important question is what kind of spatiotemporal resolution is required for exact model simulations, to model transports accurately. The deep water ventilation is discussed by the observations of a cold, oxygen-rich intermediate inow in the Stolpe Channel and along two diagonal hydrographic transects crossing the EGB. 1.2 Topography of deep Baltic basins The Baltic Sea is mainly surrounded by land, thus water exchanges with the North Atlantic Ocean take place indirectly through transition areas such as the Kattegat (K), which connects the Baltic Sea with the North Sea. To reach the western Baltic Sea, its waters have to pass three straights, the narrow Øresund (Øs) in the east and the Little Belt and Great Belt (GrB) in the west. Behind this entrance area, all inowing water is topographically trapped for a certain time in several deep basins, which are connected by channels and separated by shallow sills of dierent depth, Fig. 1.1 and Fig. 2.1. Before entering the Arkona Basin (AB), the westernmost of a chain of deep basins, the inowing water from the two Belts has to pass the only 18 m deep Darss Sill (DaS). While the water owing through the Øresund has to pass the 7 m deep Drogden Sill (DrS) to spread into the next deep basin. The AB has a maximum depth of about 45 m and is connected with the Bornholm Basin (BB) by the Bornholm Channel (BCh). The somewhat deeper BB has a maximum depth of approximately 100 m. Its topographic contours are almost circular with a diameter of about 80 km. Further to the east, the adjacent 3
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: 1. Introduction 1.1 Investigations
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
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On the 29 September 2006 between 60
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In the geostrophic balance horizont
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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
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Basin 55.9 ◦ N. From there the bo
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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
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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
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Time Period Stolpe Channel at 17.5
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Modelled volume transport through S
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discovered that most of the varianc
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to the right (perpendicular) to the
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of salty and often well oxygenated
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Depth (m) 40 45 50 55 60 4 3 2 1 0
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a correlation coecient of R=-0.68 a
Page 111 and 112:
5. Discussion and Conclusions 5.1 D
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graphic cross-sections, conducted i
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direction as the wind. The deep lay
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Bibliography Axell, L. B., 1998: On
Page 119 and 120:
Griffies, S. M., R. C. Pacanowski,
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Matthäus, W., 1993: Major inows of
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Rubio, A., D. Gomis, G. Jordà and
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Zhurbas, V., I. Oh and V. Paka, 200
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Appendix Current speed and directio
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Current speed and direction (cm/s)
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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
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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
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51 (2002) Wasmund, Norbert; Pollehn
Page 145 and 146:
78 (2009) Wasmund, Norbert; Pollehn
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Baltic Sea

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