Baltic Sea

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depth, cf. Stigebrandt (1987) and Elken (1996). However, the vertical location of this perennial halocline roughly coincides with that of the persistent pycnocline in all deep Baltic basins. The core depth of the pycnocline varies with the seasonal cycle and acts like a barrier for all vertical exchange processes between upper and deeper layers. In addition, a seasonal thermocline develops in the western and central Baltic Sea at depths between 10 m and 30 m, due to intense solar radiation during summer environmental conditions (Matthäus, 1984). During the rest of the year, however, this shallower thermocline disappears due to downward mixing, released by intense radiative cooling and enhanced wind-stirring at the sea surface. Nevertheless, this downward mixing within intermediate layers is not able to signicantly aect the thermohaline properties of deep water below the perennial pycnocline. In other words, eastward spreading Baltic deep water can be considered to be independent from the seasonal cycle of vertical mixing, observed in intermediate and upper layers. However, thermohaline properties of the deep water persistently change on its path way from one deep basin to the next deep basin (Kouts and Omstedt, 1993). Upward mixing (entrainment) in turn transforms the thermohaline conditions in intermediate and upper layers. These processes involve bottom friction and related vertical sheer in near-bottom currents triggering the breaking of internal waves on dierent time-scales. Because all tidal motions are negligible in the Baltic Sea, core velocities of these deep currents are low and associated upward mixing of water properties is signicantly suppressed through stable stratication conditions. Finally, the thermohaline diusion controls all deep patterns observed by hydrographic eld campaigns and the overall residence time of the Baltic deep water was estimated to be about 25-30 years, cf. Stigebrandt et al. (2002), Meier and Kauker (2003) and Meier (2007). Such a long residence time underlines the importance of sporadically occurring inow events that reach the EGB to maintain and/ or to regenerate the deep benthic ora and fauna in the entire Baltic Proper. These events persist for days up to weeks and interrupt the deep water conditions which are commonly characterised by the so-called 'stagnation periods' lasting frequently for several years. This means, however, that the oxygen content in the Baltic deep water commonly becomes depleted and the tendency increases for the production of hydrogen sulphide, aecting the deep Baltic ecosystem for long periods of time. For example, the slow thermohaline transformation of Baltic deep water is visible by the conservation of their thermohaline characteristics after the replacement of 'old' 6
y 'new' deep water. For instance, in the western Baltic Sea, only 50% of the 'old' Arkona Deep Water can be replaced by inowing 'new' Arkona Deep Water for the case that the exchanged overall volume of deep water exceeds about 100 km 3 . Such drastic inow events are called 'major inows' in the literature, Omstedt and Axell (1998). The nature of involved upward mixing will be studied in more detail in chapter 1.5 and chapter 3. Specic points of the latter also contributed to investigations already presented by Reissmann et al. (2009). 1.4 Pulsating inows The inow of saline waters from the North Sea can penetrate into the south-western Baltic Sea only under certain meteorological circumstances. The transition zone of the Belt Sea has to be either well homogenised (barotropic inows) or stratied (baroclinic inows). Accompanying wind conditions are either very strong or very calm for of several weeks. According to Krauss and Brügge (1991) and Schinke and Matthäus (1998), a high gradient in air pressure with strong easterly winds lasting for more than about ten days are needed to lower signicantly the water level of the central Baltic and to enlarge that in the Kattegat. The established sea level (SL) gradient releases barotropic pressure gradients with down-slope currents towards the western Baltic Sea. Moreover, such a weather situation with prevailing easterlies also reduces the precipitation over Baltic catchment areas as well as the resulting river run-o. This, however, maintains a barotropic pressure gradient with positive sea level anomalies in the Kattegat and negative anomalies in the central Baltic Sea. However, it became also clear that these sea level dierences uctuate on the synoptic scale (2 − 6 d), due to corresponding variations in easterly winds. Thus, pulsating Major Baltic Inows (MBIs) are generated on the synoptic scale (Matthäus and Franck, 1992) especially if these easterlies are suddenly replaced by westerlies lasting for about two weeks. Consequently, such MBIs are characterised by two weather phases: easterly winds dominate the pre-inow period with lower than normal the sea level anomalies in the central Baltic; replaced by strong westerly winds initiating the mature-inow period with the inow of huge amounts of saline, well oxygenated Kattegat water. Such events nally weaken the barotropic pressure gradients between the Kattegat and the central Baltic Sea by pushing their waters into the rst deep basin, the Arkona Basin. Only if this 'new' deep water is denser than ambient deep water of 7
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: 58 o N 190 230 210 100 75 100 100 7
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
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
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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
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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Baltic Sea

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