Cruise Report F.S. ALKOR Cruise No. 240

Transcription

1 Cruise Report F.S. ALKOR Cruise No. 24 Dates of Cruise: to Projects: BASEWECS and Student course in phys. oceanogr. Areas of Research: Physical oceanography Port Calls: Warneünde (29.6.; 1.7) and Sassnitz (3.6.) Institute: IFM-GEOMAR Leibniz-Institut für Meereswissenschaften an der Universität Kiel Chief Scientist: Dr. Johannes Karstensen Nuber of Scientists: 1

2 Contents 1 Scientific peronal 3 2 Scientific Background 4 3 Cruise Narrative 5 4 Preliinary results Mooring V431: seventh deployent period Meteorological observations Hydrographic conditions along section C and L CTD - Measureents ADCP - current profiles Equipent/instruents 5.1 CTD/Rosette and Salinoeter Underway Measureents Datadis Navigation Meteorological Data Echo sounder Therosalinograph Vessel ounted ADCP Acknowledgent 19 7 Appendix 2

3 Chapter 1 Scientific peronal Cruise code: AL24 Cruise dates: Port calls: Kiel - Warneünde - Sassnitz - Warneünde - Kiel Table 1.1: Scientific personal on AL24: IFM-GEOMAR: Leibniz-Institut für Meereswissenschaften, Kiel, Gerany; CAU: Cristian Albrechts Universität Kiel, Kiel, Gerany Nae Institute Function Karstensen, Johannes IFM-GEOMAR Chief scientist Schidt, Sunke IFM-GEOMAR Phys. Ocean. Blöhdorn, Björn IFM-GEOMAR Phys. Ocean. Sarz, Christopher IFM-GEOMAR CTD lab. Inga Eisenhardt CAU student Lasse Heuer CAU student Anna Jesußek CAU student Robert Kraeft CAU student To Kwasnitschka CAU student Finn Mielck CAU student Ilka Riepenhausen CAU student Jan R. Riethdorf CAU student Max Schattauer CAU student Christian Schwab CAU student Bianca Willie CAU student Theide Wöffler CAU student Responsible for Report: Johannes Karstensen phone: ++49 () Leibniz-Institut für Meereswissenschaften fax: ++49 () Düsternbrooker Weg, 245 Kiel, Gerany e-ail: jkarstensen@if-geoar.de 3

4 Chapter 2 Scientific Background ALKOR cruise AL24 was four day cruise. It was the second of three cruises in 4 in the fraework of the BMBF project Baltic Sea Water and Energy Cycle Study (BASEWECS), subproject C (grant#. 1LD). The purpose of the cruises is to obtain a rather synoptic picture of the property distribution and velocities in the western Baltic and to aintain a ooring site at the southeastern opening of the Feharn Belt. In general two section are occupied: one section crossing the Feharnbelt (section C ) and one section following the deepest topography fro about 4 E to 21 E (section L ). Along both sections CTD/rosette sapling is perfored as well as continuously recording of current velocities using a vessel ounted ADCP. Mooring site (V431) is aintained, located at the southeastern opening of the Feharn Belt. The ooring consists of a Workhorse-ADCP (3 khz), and a self containing CTD (Type MicoCat) ounted in a coercial shield (Flotation Technology). During AL24 an additional eridional section (although occupied during AL 229) was occupied in the eastern Mecklenburger Bucht. Besides the scientific otivation, the cruises are utilized for educational purposes. Undergraduate students are introduced into odern observational techniques of physical oceanography, basics in instruent calibration and interpretation of the observations. In addition it should give the students to experience the work and life at sea in general and last but not least to explore/investigate the Baltic Sea, the ocean at their back-yard. As scientists (including students) where on board during the cruise, a port call every night was necessary to allow four persons to sleep a shore. 4

5 Chapter 3 Cruise Narrative 55 3 N CTD Stations 29.Jun 2.Jul N E E Figure 3.1: ALKOR 24 cruise track (black line, based on DATADIS recordings). Red dots are the CTD stations, black star is the location of the V431 ooring. CTD annd vadcp observations have been sapled along the eridional section in the eastern Mecklenburger Bucht (west of Warneünde). AL24 had three port calls: two for Warneünde (29.6.4; 1.7.4), one for Sassnitz (3.6.4) DAY 1 (Tuesday, ): We left IfM-GEOMAR pier (Westufer) at 7:4 (all ties given in the narravtive are ALKOR local tie; MESZ) with scientists on board, of the were students (Geology, Geography). First we had to delivered a Lander to the Ostufer pier. The Lander was on display during the Kieler Woche, which took place in the week before AL24. We left the Ostufer pier 5

6 at 8: and headed for the first station which is also the western ost station of the L section. The equipent was set-up on the day before the cruise (hull ounting of ADCP, intallation of coputer). The first officer (Andreas Pooker) gave an introduction into savetey on board to the students. Then a brief introduction into the progra for the next 4 days was given by the chief scientist. After sapling two CTD stations along L we reached the southern ost station on the C section, crossing the Feharnbelt. The CTD section to the north was followed fro a ADCP section to the south. Finishing the section, we headed for the V431 ooring at the southeastern opening of the Feharnbelt. At :3 and about.2 n away fro the noinal position of the ooring the release code was transitted but the ooring did not appear on the surface iediately. Several trial with the hydrophone in different depth weren t successful either. Unfortunately, the releaser used in the ooring is not able to send a respond signal. Finally the hydrophone was lowered iediately under the surface and the ooring appeared. A final CTD cast was perfored at the ooring site as part of the L-section and for calibration purposes. We left iediately for port call at Warneünde. Warneünde Passagierkai was reached at about 21: and after custos clearance four students left for the Jugendherberge as not enough cabins are available for the persons of the scientific crew (ALKOR has only space for scientists). DAY 2 (Wednesday, 3.6.4): At 6:4 the students who slept in the Jugendherberge were back on board the ALKOR and we left Warneünde heading to coplete the L section. The first station was order n away. The weather cleared and it was was a sunny day with virtually no wind. During the whole day we ade CTD cast, recordings of eteorological paraeters, and analyzing bottle saples fro the first day using the Beckan salinoeter. We reached Sassnitz at : and after costue clearance 4 students again left for a hotel. The nightlife in Sassnitz was doinated by the quarter-final of the European chapionship in soccer Portugal:Netherlands (2:1). It was a nice celebration in particular as one of the seaan was Portuguese. DAY 3 (Thursday, 1.7.4): We left again Sassnitz relatively early (6:5) and headed for the Kadett-Ridge to start a section there at 13:. During transit eteorological observations were ade every half hour and further salinoeter work on the bottle saples were conducted. At Kadett-Ridge we ade 6 stations crossing the ridge. The captain and the officers did a great job during the probing as traffic is quite heavy. After the CTD section crossing the Kadett-Ridge we ade a repeat section acquiring ADCP data with constant 8 kn speed. Than we headed for our second visit at Warneünde port. At :3 we reached the Industrial port of Warneünde as the Passagierkai was occupied by cruise ships. Four student left for a hotel (Jugendherberge was too far away fro the pier). DAY 4 (Friday, 2.7.4): The last day of the cruise. At 6:3 the four students which had to sleep on land were back on the vessel and we left port Warneünde at 7: heading for the Praktikusstation (part of the L section). After occupying a nuber of CTD stations we copleted the L section and approached the ilitary zone of Marienleuchte at 11:5. The assebled shield ooring was re-deployed at :38 at position N/ E for the 8th deployent period. A 6

7 calibration CTD cast was perfored after deployent. A second hydrographic and vadcp occupation of the Feharn Belt section ( C ) followed. This was the end of the scientific progra. During transit to Kiel the equipent was packed for deobilization and soe adinistrative atters were cleared. We reached IfM Pier (Westufer) at : iediately unloading the equipent. 7

8 Chapter 4 Preliinary results 4.1 Mooring V431: seventh deployent period Teperature and conductivity (salinity) near the botto are variable and follow the waring trend of the spring season suer (with a certain tie lag). A noticeable feature is the sudden increase in salinity at the end of April 4. teperature V 435 ooring MicroCat 1st deploy. 3rd deploy. 4th deploy. th 5 th deploy. 6th deploy. 2nd deploy. 7 deploy. 5 Jul 2 Sep Nov Jan Mar May Jul 3 Sep Nov Jan Mar May Jul 4 Jul 2 Sep Nov Jan Mar May Jul 3 Sep Nov Jan Mar May Jul 4 3 salinity Figure 4.1: Mooring V431: Teperature (upper) and salinity (lower) at 28 depth for all V431 deployent periods. 8

9 The zero crossing of the low-pass filtered current profiles separate the water colun into the average inflowing/outflowing part. Average depth of this interface is at about with an apparent interannual signal. V431 Feharnbelt, Workhorse ADCP 1962, 48 hours filtered c/s av. 8 c/s av. 5 c/s av. 5 c/s av. 5 c/s av. 4 c/s av. 4 c/s 9 c/s av. 9 c/s av. c/s av. 8 c/s av. 5 c/s av. 5 c/s av. 6 c/s 1.Jul 1.Sep 1.Nov 1.Jan 1.Mar 1.May 1.Jul 1.Sep 1.Nov 1.Jan 1.Mar 1.May Current 132 [c/sec] V431 Feharnbelt, Workhorse ADCP 1962, 48 hours filtered 1 c/s av. 2 c/s av. 4 c/s av. 3 c/s av. 1 c/s av. 2 c/s av. 2 c/s c/s av. c/s av. c/s av. c/s av. c/s av. c/s av. c/s 1.Jul 1.Sep 1.Nov 1.Jan 1.Mar 1.May 1.Jul 1.Sep 1.Nov 1.Jan 1.Mar 1.May Current 42 [c/sec] Figure 4.2: Mooring V431, upward looking Workhorse 3kHz ADCP - along bathyetry velocity (rotated to 132 ) (upper), and perpendicular to bathyetry velocity (lower). Average inand outflow situations are shown: with nubers and interface depth (broken lines). Upper 8 are ignored because of surface interferences. 9

10 4.2 Meteorological observations The weather situation during the four days of our cruise (figure 4.3) was doinated by weak westerly wind. A low pressure syste developed east of Island and oved westward. Air teperature was around C. Figure 4.3: Air pressure distribution over Europe fro 29. June to 2. July 4 (figures fro UK Met Office).

11 4.3 Hydrographic conditions along section C and L CTD - Measureents C section (Feharnbelt) The hydrographic situation in the Feharn Belt was a typical suer situation with a hoogenized war and fresh upper layer (down to about depth) and underlying colder but saline water of North Sea origin. There is not uch of a difference between the first and the second occupation except of soewhat warer surface waters probably through heat gain fro the atosphere. Feharnbelt 29 Jun 4 Feharnbelt 2 Jul Theta [ C] N N N N 54 4 N Theta [ C] N N N N 54 4 N Salinity N N N N 54 4 N Salinity N N N N 54 4 N Siga N N N N 54 4 N Siga N N N N 54 4 N Figure 4.4: Teperature, salinity and density along the Feharnbelt section (C section). (left) First occupation, (right) second occupation. L section Along the way fro the western part of the cruise around Fehran Belt to the eastern ost station off Sassnitz a decrease in teperature, salinity and density can be seen. The clear signal 11

12 of water with North Sea origin can be identified all along the botto. An intrusion of colder water at id-depth (order to 3) can be see in the Arkona Basin. 3 4 Feharnbelt ArkonaBasin, 29.Jun 2.Jul 4 Theta [ C] 5 11 N 11 3 N N 3 N 13 N 13 3 N 3 4 Salinity 5 11 N 11 3 N N 3 N 13 N 13 3 N 3 4 Siga 5 11 N 11 3 N N 3 N 13 N 13 3 N Figure 4.5: Teperature, salinity and density along the zonal section (L section).

13 Kadett Ridge section Crossing the Kadett Ridge quite one can identify the North Sea Water signal fro the salinity stratification. However, the vertical gradients are diinished copared to the Feharnbelt section. Overall the salinity is uch lower than in the Fehranbelt section. KadettRinne 1 Jul 4 Theta [ C] N N 54 N N N N N Salinity N N 54 N N N N N Siga N N 54 N N N N N Figure 4.6: Teperature, salinity and density section Feharnbelt (C section). (left) First occupation, (right) second occupation. 13

14 4.3.2 ADCP - current profiles During the cruise there were no heading inforation recorded in the appropriate files and heading inforation which is needed to process the data have been retrieved for the DATADIS data. However, allocating the right heading to the ADCP saple was tricky as there where in addition certain synchronization proble between the ADCP clock and the DATADIS clock. Both occupation of the Feharnbelt (C section) showed outflowing water ore or less over the whole section. No core of the inflowing water at the botto, which is typically found, can be seen Current 5 degree rotated Current 5 degree rotated 4 3 Depth () current [c/sec] Depth () current [c/sec] N N N N N N N N 5 Figure 4.7: Currents (roatated to align with the bathyetry (5 ) in Feharnbelt (C section). (left) First occupation, (right) second occupation. The Kadett ridge section shows eastward flow at depth, probably associated with the spreading of high salinity water of North Sea origin. Depth () 5 Eastward current current [c/sec] N N N N 5 Figure 4.8: Eastward currents for Kadett Ridge section.

15 Chapter 5 Equipent/instruents Mooring deployent site V431 is located in the ilitary zone of Marienleuchte at the southeastern opening of the Feharnbelt. Water depth is about 29. V431 consists of a Workhorse ADCP (3kHz) and a self containing T/S recorder of type SBE-MicroCat. Table 5.1: V431: Suary on 7th recovery and 8th launch of trawl resistant botto ooring V431. year; tie (UTC) latitude longitude depth coent ; :1 recovery, after several release coands have been send. Successful after sending coand near the surface ; : N E 28.2 deployed, no coents During the aintenance days (.9. and 17.9.) data has been uploaded fro the ooring instruents (MicroCat, ADCP). Maintenance include checking for possible cracked etc., cleaning of instruents and sensors. New batteries were installed in the releaser, ACDP had battery exchange on 23 January 4, MicroCAT on. Septeber 3. Finally the shield is assebled again and ade ready for the next deployent 5.1 CTD/Rosette and Salinoeter During AL24 an OTS-Multisonde was used with dissolved oxygen and chlorophyll (fluoroeter) senors attached. The frae of the sonde allow to ount sapling bottles. As the bottle saples are used for salinity calibration only (oxygen was not calibrated) we used/attached on ost stations only two bottles. An electronic theroeter and a pressure sensor have been ounted on these two bottles to verify the release depths. Teperature and pressure sensors of the OTS sonde have been lab calibrated in 1 and these coefficients are used during AL24. Fro the standard calibration of the conductivity cell a preliinary (uncalibrated) salinity is

16 calculated. The salinity is later calibrated using the bottle saples salinities easure with a Beckan type salinoeter. The therosalinograph is an autoated sea surface teperature and salinity easureent syste. The easureents are ade on board and the ship uses a water intake. A conductivity cell and a theristor cell provide conductivity and teperature easureents. Salinity is derived fro these two paraeters conductivity and teperature. The ship s position is given by a GPS. A coputer akes the data acquisition, data processing, recording, and controls the real-tie transission of the data. The therosalinograph (TSG) on ALKOR is a Salzgitter Elektronik and peranently installed. It easures the water teperature and salinity fro about 4 depth. The data is streaed into DATADIS. For the calibration of the therosalinograph water saples have been taken for each CTD station. This revealed an offset of about.1 in salinity between TSG and saples. A teperature offset could not be detected. We started to easure the water saples with the Beckann-Salinoeter on the second cruise day in order to adapt the saples to lab-teperature. But before starting with the easureents of the sea water saples the salinoeter was calibrated with IAPSO Standard Seawater which has an precisely known electrical conductivity ratio. Possible trends in the conductivity sensor of the Beckan salinoeter is estiated fro a nuber of easureents of a reference water. We used a volue of Baltic Sea water which was drawn on the first day. This saple is called substandard as it is used like a standard. Then the first substandard easureent was done. After easuring a few bottle saples the substandard is easured again. This has to be repeated periodically after five easureents. Plotting substandard salinity versus the tie of substandard salinity substandard saple teperature (in lab) day (July 4) substandard salinity Figure 5.1: (left) Substandard salinities versus tie of easureent in lab. (right) Substandard salinity versus teperature of the saple in lab. A best linear fit (broken line) and the regression equation is given. the easureent (Figure 5.1, left) reveals a jup in the salinity between the two days of the easureents. A possibility for the jup ight be different teperatures of the saples on day 2 and day 3. However, a clear linear dependency between the saples teperature and the easured salinity can not be seen (Figure 5.1, right). The overall average value for the substandard was (edian ) and we see the.33 as the uncertainty in the salinities easure with the salinoeter.

17 The difference between CTD and bottle saples is shown versus depth in figure 5.2 (left). In general largest difference, up to -.8 (CTD is.8 higher than bottle saple salinity), occur. These difference can be explained by the difference in sapling depth between CTD (lower) and bottles (rosette is higher up in the water colun). The CTD sensor is deeper in the water colun and saples the typical ore saline water at greater depth. We decided not to apply any corrections fro the coparison between CTD and bottle saples as only a few value can be assued to saple the sae body of water. 5 Pressure Bottle CTD salinity Figure 5.2: Difference between bottle saple salinity and CTD salinity versus depth (pressure). For the calibration of the therosalinograph water saples have been taken for each CTD station. This revealed an offset of about.1 in salinity between TSG and saples. No teperature offset could be detected. 5.2 Underway Measureents Datadis ALKOR has a central data collection syste, called DATADIS. Here data fro a nuber of sources (sensors) is erged into a single file which can be used fro other devices or/and stored for later processing. Recently there was an update of the DATADIS syste by Maritec Engineering. Apparently, the old BW onitors in the labs were reoved but unfortunately not replaced. Currently only one onitor is available in the dry lab. In addition a nuber of shortcoing were found during our cruise: There is no UTC (e.g. fro the GPS syste) available at the output (screen/file). Currently there is no depth sounding (SIMRAD) at the output (screen/file). There is only a onitor in the dry lab which akes the reading of critical data during work at deck soeties laborious. 17

18 5.2.2 Navigation ALKOR has a GPS navigational syste as well as a gyro copass available. Unfortunately the data is only in part fed into the DATADIS syste and therefore the inforations are not readily available for other devices (see DATADIS section) Meteorological Data ALKOR is well equipped with eteorological sensors easuring air teperature, wind (speed and direction), wet-teperature, air-pressure, shortwave radiation. However, the longwave radiation sensor does not deliver any data at all. Radiation sensors are cleaned at the beginning of the cruise Echo sounder During AL 24 ER 6 SIMRAD echo sounder easured the depth. Unfortunately the instruent is yet not ipleented into the DATADIS syste and besides its display in the drylab, the data is stored at an instruent own hard disc. Measured depth are based on the sound speed of 53 as calculated fro a teperature (8 C) and salinity (11) Therosalinograph The therosalinograph (TSG) on ALKOR is peranently installed at about 4 depth and a S/MT 8 type of Salzgitter Elektronik GbH. TSG data is directly fed into the DATADIS. Calibration was done after the cruise through bottle saples Vessel ounted ADCP A 3 khz workhorse ADCP fro RD Instruents was ounted in the ships hull. After a nuber of recent iproveent in ters ounting the instruent (ALKOR cruise AL4/3) the data was still questionable, in particular a nuber of large data gaps near the botto occurred. The vadcp is used with botto tracking ode. At AL24 no heading data was recorded and the heading was retrieved after the cruise fro the recorded navigational data. However, there is a proble in allocating the exact tie of the heading to the saple nuber of the ADCP and substantial errors are possible.

19 Chapter 6 Acknowledgent Herzlichen Dank an Kapitän Jan Lass und die Offiziere Andreas Pooker, Rainer Nannen und Peter Strehlow sowie der gesaten Besatzung der ALKOR für ihre professionelle Unterstützung und die nette Atosphäre an Bord. BASEWECS ist ein BMBF Projekt das zu DEKLIM Progra gehört und die Fördernuer 1LD besitzt. 19

20 Chapter 7 Appendix FileNae = ifk_4_6_info.ctd Cruise = NF SS 4 Instruent = OTS StartDate = 4/6/29 EndDate = 4/7/2 Coluns = NR:LAT:LON:D:YY:MM:DD:HH:lg:fb:r:rg:kd

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