Kanzow, Torsten

Karstensen, Johannes

Krahmann, Gerd

Schlundt, Michael

English

OceanRep

Results from a Glider Swarm Experiment near Cape VerdeG. Krahmann, T. Kanzow, J. Karstensen and M. SchlundtIFM-GEOMAR Kiel/Germanyin collaboration with colleagues from INDP / Cape Verde5th EGO Meeting / Las Palmas   17.3.2011Experiment goals- observe the meso- to submesoscale variability  near the Tenatso mooring site- connect glider biogeochemical  observations to physical   observations and to external  forcing (e.g. dust input)  to further our understanding of the coupling between the  various processes- make use of the mooring data for intercalibration- collect experiences   conducting an  experiment with  a group of glidersExperiment design‘Boundary conditions’:- 6 Slocum gliders using lithium batteries  equipped with T, S, O2, Chl-A, Turb sensors- observe area ‘around’ Tenatso mooringTarget:- cover the area as synoptically as possible- be able to determine covariance length scales- use regular sampling strategy (not adaptive)Chosen setup:- area of 45 x 45 km for 7 weeks- pattern optimized to cover area and space/time scales- 500 m dive depth for deep gliders to increase repeat rate- deployment location according to sea conditionsExperiment designOptimizing the glider tracks- short repeat time- even area coverage- even glider distance  distribution- many mooring   passings- easy steeringExperiment designvs execution- designed tracks were largely followed- biofouling led to significant drop in speed in second half  leading to a near-loss of steerability- some sensors were also adversely affected by biofoulingExperiment designvs executionunexpected effects of biofouling:a diurnal cycle in the glider’s vertical velocitiesDust observations from Aqua Modis1/2/101/7/101/12/101/17/101/22/101/27/102/1/102/6/102/11/102/16/102/21/102/26/103/3/103/8/103/13/103/18/103/23/103/28/104/2/104/7/104/12/104/17/104/22/104/27/105/2/105/7/105/12/105/17/105/22/105/27/106/1/10time00.40.81.21.62AOD 550 nmGebiet 1: Zielgebietumgebung 1°Gebiet 2: Zielgebietumgebung 2°einschließlich AuslegungsortAerosol optical thickness at 550 nmArea used for black lineArea used for red lineExperimentDust from Aqua Modisand turbidity from gliders20.03 29.03 07.04 16.04 25.04 04.05time00.40.81.21.62AOD 550 nmGebiet 1: Zielgebietumgebung 1°Gebiet 2: Zielgebietumgebung 2°einschließlich Auslegungsort- Several dust events were   observed during the  experiment.- The first two events appear  to correlate to some (?) of  the (nearly) unprocessed  glider turbidity data.- During the last third of the  experiment the data gets  noisy again because of   biofouling.upper 50 m average turbidityDust from Aqua Modisand turbidity from gliders20.03 29.03 07.04 16.04 25.04 04.05time00.40.81.21.62AOD 550 nmGebiet 1: Zielgebietumgebung 1°Gebiet 2: Zielgebietumgebung 2°einschließlich Auslegungsort - Likely culprits for the    noisy data towards the end   of the experiment are  biofouling on the sensor  or fish near the sensor.A chance discovery during a detour- Background current in the area is  generally westward with a  slight intensification near the islands- To evade this current  we steered    ifm11 on a more northerly course   towards the experiment area- The new course led us directly into  a subsurface eddyA chance discovery during a detour- The (uncalibrated) oxygen  concentrations in this eddy are  extremely low for this region.- It is unclear where this watermass  comes from.Variability- Shown are 3 repeat cycles of the  track pattern by glider ifm11.- Variability is found on various   temporal and spatial scales.- Phases with strong internal wave  activity alternate with more  quiet times.- Mesoscale changes appear to  drift by with the background   current.Summary- In spring 2010 we conducted a 7 week long experiment   north of Cape Verde employing 6 Slocum gliders.- The experiment was designed to observe the submeso- and   mesoscale variability near the Tenatso mooring site.- The experiment plan was executed successfully with some   setbacks mainly stemming from very strong biofouling.- Nevertheless the collected data (3000 profiles, 3800km)   exhibit a wealth of variability on various temporal and  spatial scales.- Could we collect ‘promising’ practice against biofouling ? All photographs courtesy of M. MüllerResults from a Glider Swarm Experiment near Cape Verde

Results from a Glider Swarm Experiment near Cape Verde

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