2008 report
Progress: 45%
Executive summary:
During the second period of the project most of the planned subtasks have been accomplished according to the schedule. Three arrays of moorings in the main gateways: Fram Strait, Barents Sea Opening and Svinøy section were recovered and redeployed. However, due to unexpected logistics problems and heavy ice conditions the Fram Strait array was exchanged only in a half. Data obtained from recovered instruments has been processed and analyzed to provide the volume and heat fluxes in the main gateways. Several CTD sections complementing measurements by moored arrays have been measured in different months in the Greenland Sea and Fram Strait. The first Seaglider mission in Fram Strait was prepared and arranged but due to the instrument failure immediately before deployment it had to be cancelled. A design phase of the acoustic tomography system for monitoring the integrated temperature across Fram Strait had been completed and recommended equipment has been purchased and tested. A numerical study using an acoustic ray trace model has been performed. The tomography field experiment was fully prepared but had to be terminated under rough weather conditions.
During months 13 to 24 following subtasks were accomplished:
1. To recover and redeploy deploy the moored arrays at the Svinøy section, in the Barents Sea Opening and Fram Strait
2. To obtain volume and heat fluxes from the observational arrays and to identify local and remote forcings controlling their variability
a) Fram Strait (progress 40%):
The RV 'Merian' cruise MSM05/6 planned for the exchange of moored array in Fram Strait in September 2007 has been cancelled due to the severe failure of ship engines. The limited ship time obtained in September thanks to a courtesy of the Norwegian Polar Institute on board RV 'Lance' allowed for recovery of 7 and deployment of 8 moorings of the total number of 12 moorings operated in Fram Strait by AWI. The easternmost mooring was damaged in spring 2007, the most likely by a fishing boat, and its remains could not been recovered. Two AWI moorings in the western part of the strait could not be exchanged due to heavy ice conditions. Three of the newly deployed moorings in the eastern part have been equipped with acoustic modems for data transmission. However, the failure of RV 'Merian' suppressed a deployment and necessary tests of the profiling top. Six PIES (Pressure Inverted Echo Sounder) deployed in Fram Strait in 2006 were not recovered and left for the second year of deployment until summer 2008.
The western Fram Strait moorings (4 tall rigs, one ADCP mooring and one tube mooring) operated by NPI have been scheduled for recovery and deployment during the RV 'Lance' cruise in September 2007. Due to the complete coverage of the western strait by the drifting sea ice, extremely compact and thick, none of the moorings' positions could be reached during three weeks of the cruise. All six moorings have been left in the water until a recovery in summer 2008.
Data from recovered instruments from 6 moorings in the eastern Fram Strait and 2 moorings in the central part were processed and analyzed. Total and AW transports in the West Spitsbergen Current domain were calculated; however without data covering the whole array the heat flux could not be properly obtained. This will be done after recovering the rest of the Fram Strait array in 2008.
b) Barents Sea Opening:
The DAMOCLES moorings deployed in June 2006 were exchanged. Four moorings with Aanderaa current meters were recovered and redeployed for the last time in the Fugløya-Bjornøya section. Near the Norwegian coast two bottom mounted ADCPs in trawl proof frames were recovered and redeployed. The northernmost mooring had a downward looking ADCP from Aanderaa Instruments placed at about 50 m above bottom, and measured the outflow of dense bottom water from the Barents Sea to the Norwegian Sea. This type of instrument was tried for the first in this section. The array will be recovered in 2008.
c) Svinøy section (progress 55%):
Two moorings in the Svinøy section were served and redeployed in March and October. The master mooring S1 with a nearly continuous time series since 1995, was recovered with a 100% data recovery and redeployed in the same position (62°49.5'N; 004°17.4'E) at 500 m depth. The backup mooring S2, now moved to 600 m depth, was cut by a trawler again in January. The float and the 100 m current meter were picked up by the Norwegian Coast Guard few days later. The deeper part of the mooring was released in March, but unfortunately not recovered after dragging attempts. So this year we had an instrument loss of 2 RCM current meters and a releaser. The backup mooring was redeployed on the 500m isobath in position 62°49.9'N; 004°15.8'E. Additionally, the deep mooring at 2000 m depth was recovered and redeployed in position 63°58.4'N, 001°38.8'E , now with current meters 100m and 500m above the sea bed. Through the IPY, the Damocles program in the Svinøy section is now completed with contributions from the iAOOS and Poleward programs. Through iAOOS we intend to concentrate on the western branch of the Norwegian Atlantic Current, and 4 Pressure Inverted Echo Sounders (PIES) and 2 additional mooring will be deployed in November 2007 in the vicinity of the 2000 m isobath. A McLane Moored Profiler (MMP) with a profiling CTD to capture the baroclinic transport is scheduled for a deployment in spring 2008. Thus we are close to reach our overall goal of developing the Svinøy section as complete and sustainable, simple and robust upstream reference-system for monitoring the Atlantic inflow (AI) toward the Arctic Ocean.
Following papers summarizing the results from moored arrays were published or are under way:
Schauer U., Beszczynska-Möller A., Fahrbach E., Walczowski W., Piechura J., E. Hansen (2008). Variation of measured heat flow through the Fram Strait between 1997 and 2006. In Arctic-Subarctic Ocean Fluxes: Defining the role of the Northern Seas in Climate. Eds. R. Dickson, J. Meincke and P. Rhines, Springer Verlag.
Schauer U., Beszczynska-Möller A. (2008) Problems with estimating oceanic heat transport into the Arctic Ocean - some conceptual remarks. To be submitted.
Skagseth, Ø., Furevik, T., Ingvaldsen, R., Loeng, H., Mork, K.A., Orvik, K.A., Ozhigin, V. (2008) Volume and heat transports to the Arctic via the Norwegian and Barents Seas. In Arctic-Subarctic Ocean Fluxes: Defining the role of the Northern Seas in Climate. Eds. R. Dickson, J. Meincke and P. Rhines, Springer Verlag.
Orvik, K.A. and Ø. Skagseth (2007). The warming of the Atlantic Inflow toward the Arctic connected to the sub-polar gyre. (to be resubmitted)
Skagseth, Ø, K.A. Orvik, R. Ingvaldsen, K.A. Mork and H. Loeng (2007) Coherent and lagged signal in the Norwegian Atlantic Current toward the Barents Sea (to be resubmitted).
3. To perform CTD sections for complementing the mooring measurements as well as for calibration of the integrated system:
a) Nordic Seas, AREX2007 cruise, RV ’Oceania’, IOPAS, June/July 2007
During the AREX’2007 172 standard CTD/LADCP vertical casts along 11 sections were done. 8 sections were positioned parallelly, perpendicularly to the West Spitsbergen Current flow. The southernmost section were located along the 73º30’N parallel, the northernmost one reached latitude 79º48’N. The position of section EB was coordinated with the mooring line at 78º50’N. One section were performed along the Storfjordrenna, two sections crossed the entrance to the Barents Sea: the Barents Sea Opening and Storfjordrenna. Between stations VMADCP measurements were done. In comparison to the record high summer 2006 temperature and salinity of Atlantic Water in the West Spitsbergen Current, the summer 2007 mean temperatures of Atlantic Water at sections were about 0.6ºC lower, salinity 0.027 psu lower. Also calculated baroclinic transports were in 2007 lower than in 2006. Upstream the Fram Strait Atlantic Water temperature, salinity and baroclinic transports changes suggest decreasing of the volume and heat transport into the Arctic Ocean in the nearest future.
Walczowski, Piechura (2007) Pathways of the Greenland Sea Warming’ Geophysical Research Letters, Vol 34, L10608, doi:10.1029/2007GL029974
b) Fram Strait, FS2007 cruise, RV 'Lance, September 2007
During the Fram Strait 2007 cruise of RV 'Lance' 36 CTD/LADCP stations were performed. In the eastern part of the strait, east of the Greenwich meridian, the CTD section was located next to the moored array at 78°50'N. Due to the dense ice coverage in the western part CTD stations had to follow the ice edge and the section was deviated towards south-west direction, reaching only to 5°W. The short section across the East Greenland shelf slope was also measured at 78°10'N and was continued along the shelf slope southward to 77°40'N. In the eastern part in the WSC temperature and salinity of the Atlantic water were lower than last year while in the central part of the strait water they were higher that year before and the AW covered a bigger area.
4. To prepare and perform the first field test of Seaglider in Fram Strait and to analyze achieved data:
The AWI Seaglider SN127 was purchased from the SFC Seattle in spring 2007. The Seaglider was equipped with SeaBird temperature and conductivity sensors, Wetlab scatterometer and fluorymeter and Aanderaa oxygen optode. Before delivery the instrument had been thoroughly tested in a tank and during field tests in the Pudget Sound by the manufacturer and finally trimmed (ballasted) for the Fram Strait water density ranges. A plan of the first Seaglider mission in Fram Strait was worked up in details, including different recovery scenarios and backup solutions (for more information see deliverable D8.3-7). The Iridium account (SIM card) for 'DAMOCLES Seaglider' was aquired from DAMOCLES resources and activated. After arriving to Bremerhaven the glider went successfully through all pre-deployment tests in lab conditions and was loaded onboard the ship. The deployment in Fram Strait was scheduled for the MSM05/5 cruise of RV 'Merian'. However, the Seaglider unexpectedly failed to pass the pre-deployment tests performed on board prior a final launch in spite of successful tests on land (for details see D8.3-7). To avoid the possible loss of instrument due to communication problems the deployment was cancelled and the glider was returned to the manufacturer for repairs. The planned Seaglider operations had to be postponed until the next year.
5. To continue work on the acoustic tomography array:
6. To select/develop/adapt appropriate inversions methods for ocean acoustic tomography to obtain reliable estimates of the average temperature profiles across the eastern Fram Strait:
The work with the design of the tomography moorings and planning of the field experiment has been followed up. This work is described under WP 8.2, and correspondingly reported under that work package.
A numerical study using interpolated oceanographic fields (2003-2005) from AWI as input to the acoustic ray trace model RAY has been performed for the East Greenland Current. In the calculations the source was positioned at 78°50'N, 5°W and receiver at 78°50'N, 1°E. The acoustic modeling show a clear correspondence between changes in the EGC and the arrival time structure. The study also shows that the source should be inside the duct to provide information about changes in the EGC. A more detailed analysis of the numerical results will be performed. Study of inversion method for the analysis of tomography data in the eastern part of the Fram Strait in the West Spitsbergen Current was completed. Tomographic travel times (clock-drift and mooring-motion corrected) will be analyzed using the matched-peak inversion approach seeking to maximize the agreement between theoretical and observed arrival times, and extended to cover the case of multiple receivers.
We have been working with additional funding for the EGC source. Several proposals, including one or two additional sources, have been generated and submitted, but we have not yet any answer. As the situation is now we plan for recovery of the existing moorings and a redeployment of the moorings in the EGC 1-2- months after recovery.
In the second half of reported period the main focus was on attending FAT testing of the equipment, leading, organizing and following up transportation/logistics issues and planning the tomography experiment. Activities are described under WP8.2. The tomography experiment had to be terminated before deployment of the tomography moorings due to bad weather. Next experiment is under planning. A consequence is that there will not be time (or man-months) for planning or carry out a third experiment in the East Greenland Current. Only preliminary investigations will be carried out next summer, for detailed description see WP8.2.
A follow up four year long project ACOBAR –“ACoustic technology for OBserving the interior of the ARctic Ocean" has been accepted for negotiations. Expected project starts late spring /early summer 2008. ACOBAR introduce two additional sources in the Fram Strait. Sources will be used together with the DAMOCLES source and receiver array to establish an array both for tomography and for navigation of gliders and floats. ACOBAR is coordinated by NERSC, and partners are AWI, UPMC, SCRIPPS.WHOI, OPTIMARE, ENSIETA, Aquatec and ACSA.
IMR: During the last period mooring is recovered and deployed again for the last time in the Fugløya – Bjørnøya section. The results from the last year are added to the results from previous years and are shown in the figure below. The results are included in the summary of the ASOF-project
Volume flux of Atlantic Water Into the Barents Sea
Reference
Øystein Skagseth, Tore Furevik, Randi Ingvaldsen, Harald Loeng,Kjell
Arne Mork, Kjell Arild Orvik and Vladimir Ozhigin, 2008. Volume and heat transports to the Arctic Ocean via the Norwegian and Barents Seas. In Dickson, R.R., Meincke, J. and Rhines, P. (eds) Arctic-Subarctic Ocean Fluxes: Defining the role of the Northern Seas in Climate. Springer Verlag (in press)
FORTH ( 70% of total work done):
During the second year FORTH developed a near-real-time discrete inversion scheme (DI) for the analysis of the anticipated travel-time data from the eastern section (1o-7oE, 78o50'N) of the Fram-Strait experiment (design described in deliverable D3.1-3). DI is based on the matched-peak approach applying directly to travel times and seeking to maximize agreement between theoretical and observed peaks. To enhance the information available for the inversion, the possibility of using early bottom-reflected arrivals, in addition to the waterborne arrivals, was examined. For the parameterization of the temperature distribution, the EOFs obtained and made available by AWI, relying on 3-year long data (2002–2005) from the ASOF array, were used. The model relations between temperature distributions and travel times were implemented using a ray-tracing code and a discretization of the parameter space. The calculation results are stored in a database so that they can be used for subsequent inversions. The data base structure allows for easy expansion, e.g. decrease of discretization steps or increase of the number of EOFs. In the absence of real measurements DI was tested using synthetic data relying on the above 3-year long time series from the ASOF array. The inversion scheme and the results from the simulation study are described in deliverable D3.1-05. Besides DI, an alternative inversion scheme was developed in which the discretization of the parameter space is replaced by random search using the Markov Chain Monte Carlo method (MCMC). Even though MCMC is significantly slower than DI it offers a continuous sampling of the parameter space which in some pathological cases may be of advantage. For this reason MCMC is also included as an alternative option in the streaming mode tomographic analysis system (SMTAS).
NERSC : 86%
Activities Month 13-18:
1) Followed up the work with the design of the tomography moorings and planning of the field experiment. This work is described under WP 8.2, and correspondingly reported under that work package.
2) A numerical study using interpolated oceanographic fields (2003-2005) from AWI as input to the acoustic ray trace model RAY has been performed for the East Greenland Current. In the calculations the source is positioned at 78 50 N 5 W and receiver at 78 50 N 1 E. The acoustic modeling show a clear correspondence between changes in the EGC and the arrival time structure. The study also shows that the source should be inside the duct to provide information about changes in the EGC. A more detailed analysis of the numerical results will be performed.
3) We have been working with additional funding for the EGC source. Several proposals, including one or two additional sources, have been generated and submitted, but we have not yet any answer. As the situation is now we plan for recovery of the existing moorings and a redeployment of the moorings in the EGC 1-2- months after recovery.
Activities Month 19-24
1) Attending FAT testing of the equipment. Leading, organizing and following up transportation/logistics issues and planning the tomography experiment. Activities are described under WP 8.2.
2) Plan, organize and carry out the first field operation in the Fram Strait to deploy the two tomography moorings.
3) Prepare and update deliverables D8.2-2 and D8.2-3.
4) Prepare presentations for (1) conference Crete, June; (2) at WHOI, (July) and (3) Polar conference in Bergen, August
5) A follow up four year long project ACOBAR –“ACoustic technology for OBserving the interior of the ARctic Ocean" has been accepted for negotiations. Expected project start late spring /early summer 2008. ACOBAR introduce two additional sources in the Fram Strait. Sources will be used together with the DAMOCLES source and receiver array to establish an array both for tomography and for navigation of gliders and floats. ACOBAR is co-ordinated by NERSC, and partners are AWI, UPMC, SCRIPPS.WHOI, OPTIMARE, ENSIETA, Aquatec and ACSA.
The tomography experiment had to be terminated before deployment of the tomography moorings due to bad weather. Next experiment is under planning. See description under WP 8.2. This delay has several consequences.
- The major consequence of delaying the experiment in the Fram Strait is that there will not be time (or man-months) for planning or carry out a third experiment in the East Greenland Current. Only preliminary investigations will be carried out next summer if extra hydrophones and data recorders can be provided without significant costs, see WP 8.2.
- Another consequence will be to switch focus of the acoustic modelling activities at NERSC to support the planned experiment in the eastern part of the Fram Strait and the development of data assimilation (= model based inversion) schemes. Major modelling/model based inversion (=assimilation) activities will be done in WP 4.2. Main activity in WP 3 .1 will be to plan carry out the work defined under WP 8.2 including carry out the field experiment and to process and analyse acoustic data from modems and raw data after modem recovery.
