Baltic Sea

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the Bornholm Basin, it enters further basins in the northeast (Hagen and Feistel, 2001). Such favourable inow conditions usually occur in late autumn, winter, and early spring when the saline water of the Kattegat is vertically well ventilated/ oxygenated due to downward convection and wind-stirring. According to Matthäus and Franck (1992), associated volume transports through the Belts and the Sound must exceed 10 km 3 /d to renew completely all deep water of the central Baltic Sea. Hydrographic long-term observations clearly show that such MBIs happen on the multi-year scale. Their irregular repetition occurs all 3-5 years. Following Wyrtki (1954), Franck et al. (1987), Matthäus and Franck (1992), Fischer and Matthäus (1996) and Feistel et al. (2003a) such MBIs convey about 200 km 3 deep water with about 2 Gt salt and about 1 Mt Oxygen towards the western Baltic Sea. In contrast, the nature of baroclinic inows is mainly determined by lateral occurring salinity gradients in the Kattegat. They maintain corresponding baroclinic pressure gradients, especially during calm wind conditions in the late summer. Associated inow events already described by Knudsen (1900), Thiel (1938), Hela (1944), Wüst et al. (1957), Welander (1974), Jacobsen (1980), Matthäus et al. (1983), Feistel et al. (2003c), Feistel et al. (2004) and Mohrholz et al. (2006) suggest that the frequency of such phenomena increased, probably due to changes in prevailing wind directions during the last two decades. Once triggered, these baroclinic inows reveal a somewhat weaker volume transport and prefer the pathway through the Great Belt via the Darss Sill. They reach the Arkona Basin after several days. Consequently, salt is frequently transported from the western Baltic Sea towards the Baltic Proper, however, on a much lower level as that released by the barotropic MBIs. Nevertheless, via triggered entrainment, they are able to change prevailing hydrographic conditions and ventilate intermediate and/ or deep layers to a certain degree. This follows from observations showing a somewhat better oxygenation of much lower eciency. Thus, they also contribute to the development/ maintenance of the deep marine ecosystem in the Baltic Proper (Reissmann et al., 2009). Multi-year current records which have been carried out above the eastern topographic slope of the EGB (Hagen and Feistel, 2004). Their results suggest an overall velocity of 3 cm/s for the cyclonic deep circulation. Its core velocity reects a topographically steered rim current, which is highly geostrophic and accelerates up to a factor of 3 during such baroclinic inow 8
events. During and after such events, large lateral pressure and salinity gradients between the central EGB (low pressure) and its rim (high pressure) cause saline water to follow the bottom topography and circulate cyclonically within it (Lehmann and Hinrichsen, 2000). Internal pressure gradients react to changes in wind forcing and river discharges releasing vertical and lateral meanders into the rim currents (Elken, 1996). Such current meanders are thought to be formed by rhythmic inows and temporal changes in the actual windstress curl as well as by the conservation of the potential vorticity of the deep current eld behind irregularities in the bathymetry like that of the well known Klints Bank in the EGB. In hydrographic elds within and below the main pycnocline, these meanders form eddy-like features with diameters between 5 km and 15 km and a vertical thickness of several decametres. Repeated hydrographic surveys suggest that their life time exceeds one week (Elken, 1996). These meso-scale features rotate cyclonically or anti-cyclonically with core velocities reaching up to 20 cm/s, although their lateral displacement velocity is only 2 − 3 cm/s (Hagen, 2004). However, when hitting such obstacles as that of the Klints Bank, these features can also be destroyed on much shorter time-scales. Recently, there is some speculation that the decay of such phenomena also contributes to the erosion of the main pycnocline on the basinscale. Following Kuzmina et al. (2005), a great portion of their kinetic energy should be lost through turbulent mixing when these features collide with the boundaries of the basin. From the methodical point of view, Reiÿmann (2005) developed objective methods for an adequate recognition of such meso-scale patterns in the mass-eld. He called these Baltic eddies 'Beddies', in analogy to the so-called 'Meddies' observed at the latitude of the Strait of Gibraltar in the Atlantic Ocean. 1.5 Recent inow history Matthäus and Franck (1992) show that the so-called MBIs mainly appear between October and April. Their frequency of occurrence is very irregular, from once per year to once per ten years separated by infamous stagnation periods. The longest observed stagnation period of nearly 16 years occurred between 1976 and 1993, during which only some weak inow events were observed between 1976 and 1983. Therefore, they were classied to be insucient for renewing the near-bottom water of all basins. This long stagnation period was 9
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: y 'new' deep water. For instance, i
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
Page 77 and 78:
Figure 4.11: Modelled current veloc
Page 79 and 80:
SFS and SFN. At the southern ank a
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Mean Volume Transports Mean Volume
Page 83 and 84:
160 170 180 Volume of EGB below 170
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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
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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
Page 99 and 100:
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
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
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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Baltic Sea

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