Baltic Sea

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Direction Time Hourly Daily 5-Day 5-Day Transport Period VoltrpSF 9.5 VoltrpSF 9.5 VoltrpSF 9.5 VoltrpSF 12 (km 3 /d) % (km 3 /d) % (km 3 /d) % (km 3 /d) % Eastw./Westw. Sep 0.81 100 0.81 100 0.81 99.8 0.92 112.8 Eastward - 1.78 100 1.59 89.1 1.55 86.9 1.08 60.5 Westward Dec 2006 -0.97 100 -0.78 80.0 -0.74 76.1 -0.16 16.7 Eastw./Westw. June 2006 1.54 100 1.54 98.2 1.52 97.2 1.51 96.8 Eastward - 2.18 100 2.04 93.6 2.03 93.1 1.59 73.1 Westward June 2007 -0.64 100 -0.50 78.3 -0.51 79.2 -0.11 17.0 Table 4.5: Hourly, daily, 5-day mean Volume Transports through the Stolpe Channel and their percentage in relation to hourly values. Hourly values considered as 100%. before and therefore is not able to capture the strong storm event (compare Fig. 4.26). Summing up, 5-day means underestimate transport volumes and are not able to precisely reproduce observed uctuations that are on a time scale of 2 − 4 days. But how are these observed uctuations generated? In the following the role of local wind elds will be analysed. 4.3.5 Current uctuations within the Stolpe Channel - steering mechanism Internal and external forcing mechanisms in the Baltic Proper i.e. the EGB, were investigated by Samuelsson and Stigebrandt (1996), using sea level gauges (SL) and a sea level model. They classied uctuations in the sea level with periods between a few days and several years into either internally or externally forced motions. Varying sea level in the Skagerrak/ Kattegat region and freshwater supply from the North Sea were classied by Samuelsson and Stigebrandt (1996) as external forcing and resulted for 50 - 80% of the total sea level variances in the Baltic Proper. Associated periods longer than one month are externally forced, because shorter periods are choked by the narrow straits of the Kattegat (Stigebrandt, 1980). Such long externally forced oscillations are similar to open basin oscillations with increasing amplitudes from the node in the mouth to the inner part (a quarter-wave-length oscillator). In contrast varying air pressure, wind and density in the Baltic Sea are characterised as internal forcing. Seiches for example have periods of two days and/ or shorter and thus may contribute to the daily averages in sea level variations. Hence, Samuelsson and Stigebrandt (1996) 84
discovered that most of the variance for short periods originates from internal forcing but may induce some variance of longer periods. In other words, periods of shorter than 1 month in the sea level are due to internal forcing. Furthermore Samuelsson and Stigebrandt (1996) detected the Baltic Sea oscillates like a closed basin for short periods. From a kinematical point of view these oscillations reect the rst natural seiche mode, with a maximal variability at the extreme ends in the north and south and minimum in the Baltic Proper (a half-wave-length oscillator). Among other things, this is the reason to use records of the Swedish coastal station Landsort to describe changes in the lling level of the Baltic Proper. For longer periods the internal forced oscillations are kinematically similar to an open bay with increasing amplitudes from the mouth and inwards. Samuelsson and Stigebrandt (1996) explain the shift in kinematics of internally forced oscillation with the limited transport capacity of the straits in the mouth for "high frequency" motion. Turning back to the changes in deep currents of the Stolpe Channel, signicant peaks in periods found in the along-slope and across-slope current components of ADCPs SFN, SFS (Fig. 5.10), as well as in the current meter moorings SE and NE deployed in the EGB (Fig. 5.11, Fig. 5.12 in the appendix) are all shorter than one month. An exception is mooring SW (Fig. 5.13 in the appendix) with a peak around 40 days in the across-slope components. Hence, these time series of deep currents point to the conclusion that internal forcing could be the main steering mechanism and therefore investigations, especially in the Stolpe Channel, are focused on internal forcing, i.e. wind and density changes. Accordingly daily eastward currents of ADCPs SFN and SFS (Fig. 4.12) were observed to be pulse-like, with each pulse-like event lasting for about 2 - 4 days, as already discussed in chapter 4.3.3. Here, however, the role of changes in the regional wind conditions will be analysed in more detail to understand the response of deep current uctuations above topographic slopes of the eastern Stolpe Channel. Hypothetically, it is expected that such deep currents follow roughly bathymetric contours due to the conservation of their potential vorticity. Hence, to obtain the along-slope (Fig. 4.27 B, C) and across-slope components of the currents, u and v were rotated anti-clockwise by 28 ◦ to follow the 75 m isobath. These current components were then compared with the regional wind velocity along the main axis of the Baltic Proper, denoted 38 (line between red dots in Fig. 4.28). 38 results from averaging the records of the meteorological stations Arkona Buoy in the Arkona Basin (AB) 85
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No 88 2012 Spatiotemporal Scales of
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Meereswissenschaftliche Berichte MA
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Abstract The Baltic Sea is surround
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Contents Abstract Contents List of
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Acknowledgement 109 Appendix 111 vi
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M-7/M-8 Mesodyn hydrographic snapsh
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List of Figures 1.1 Baltic Sea - ba
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4.32 Regression sea level dierence
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1. Introduction 1.1 Investigations
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circulation above topographic anks
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58 o N 190 230 210 100 75 100 100 7
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y 'new' deep water. For instance, i
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events. During and after such event
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this inow event was classied as 'mo
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Scale (PSS-78), roughly by 0.5%, as
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(Acoustic Doppler Current Proler) a
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for the southernmost zonal section
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whereas the length of the NE time s
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have a thickness of only 1.5 m in o
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dependent salt volumes for the deep
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7 6.5 a Temperature ( o C) 6 5.5 5
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Potential Temperature ( o C) 8 7 6
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inowing waters masses with variable
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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
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: Modelled volume transport through S
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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