Walter, Maren

OceanRep

TRR 181 Cruise Poseidon 5232 — 23 May 20183. Weekly report (21 May 2018)After the successful recovery of the mooring last week we took a few days to prepare the instruments for the second deployment period. The setup of the mooring is very similar to the first period, with an additional high-frequency acoustic current meter in the upper part of the mooring. The top of the mooring is formed by the head buoy with an upward looking current profiler, designed to monitor the currents and shear in the upper 200m of the water. Below that, in addition to the new current meter, there are seven current meter/temperature logger pairs that will resolve the low mode profiles of currents and stratification, and thus monitor the temporal variability caused by the low-mode internal waves. The re-deployment of the mooring took place on Friday, May 18, at 30°29.33’N, 030°11.90’W, and went smoothly.Turbulence measurements in the form of microstructure profiles in the upper ocean have been taken throughout the cruise during the time series stations with a vertical microstructure profiler (VMP). The VMP on the POS523 cruise is (among other sensors) fitted with two shear probes used to characterize the dissipation of kinetic energy in micro-scale turbulence. VMP deployments occurred in 2h segments between sets of CTD rosette deployments. The VMP is lowered over the stern of the ship, where it then falls freely to its maximum depth, typically around 500-700m. The instrument is recovered using a small electrical winch and then directly re-deployed. As the VMP is designed for continuous autonomous operation, it is not necessary to bring the VMP back on deck between deployments; separate profiles can be extracted in post-processing. Each 2 hour time block is sufficient time to complete 4 or 5 profiles, each profile taking about 20-30 minutes. The deployments are done by a three person team - one person is in charge of operating the winch, helped by the second person, who leads the tether from the spool and passes it to the third person. The third team member’s task consists of ensuring that enough line is in the water at any given time, as the VMP must be deployed on a slack line.  In addition to the main focus of the cruise, the TRR 181, we have a team member from the University of the Azores Horta, Clara Loureiro, who studies the microbial communities through ocean space and time scale in the Azores region. The focus of her work is on bacterioplankton (bacteria and archaea), which represents on of the most important marine organisms for having a crucial role on the global element cycles regulation as to their unique capacity to decompose and remineralise dissolved organic matter. Bacterioplankton distribution and patterns can be shaped by  coupled physical/biological mechanisms (such as nutrient nutrient availability, mesoscale features, etc…) and to understand such dynamic spatial-temporal surveys are needed. The results from Pos523 will be connected to the physical ocean interactions in this region and enlighten our knowledge about who is there, what is their function and how the environment is interacting with them.We finished work in the night from Sunday to Monday, having completed 64 CTD/LADCP profiles on 5 stations (with a total length of 547km!), as well as 17 microstructure FS Poseidon    Malaga - Ponta Delgada    May 2018TRR181       POS523Energy Transfer ET2, Deployment 2018Univ BremenDate: 15-May-2018M-file: TRR1_2018Depth Item S/N Length Rope TimeRDI ADCP + 32" float         w/ Radio & Iridium Beacon192 msrsTRDI DVS (down) 2 m 12 mm DY194 mSea-Bird SBE56 Temperature srs8 mm DY400 msrsNautilus 17'' Float608 m       (4)12 mm DY3.5 msrsSea-Bird SBE56 TemperatureNortek Aquadopp 2 m 12 mm DY612 msrs8 mm DY400 msrsSea-Bird SBE56 TemperatureNortek Aquadopp 2 m 12 mm DY1027 msrs8 mm DY400 msrsNautilus 17'' Float1442 m       (4)12 mm DY3.5 msrsSea-Bird SBE39 TemperatureNortek Aquadopp 2 m 12 mm DY1445 msrs8 mm DY200 msrs8 mm DY400 msrsNautilus 17'' Float2067 m       (2)12 mm DY3.5 msrsSea-Bird SBE39 TemperatureNortek Aquadopp 2 m 12 mm DY2071 msrs8 mm DY400 msrs8 mm DY400 msrsNautilus 17'' Float2899 m       (2)12 mm DY3.5 msrsSea-Bird SBE39 TemperatureNortek Aquadopp 2 m 12 mm DY2903 msrs8 mm DY400 msrs8 mm DY400 msrsNautilus 17'' Float3731 m       (2)12 mm DY3.5 msrsSea-Bird SBE39 TemperatureNortek Aquadopp 2 m 12 mm DY3735 msrs12 mm DY400 msrs12 mm DY400 msrsSea-Bird SBE39 TemperatureNortek Aquadopp 2 m 12 mm DY4554 msrsNautilus 17'' Float4556 m       (3)16 mm DY20 msrsDual Acoustic Releases4577 mSR12 mm DY20 mSAnchor 1500 kg4600 mIridium Beacon: Radio Freq: Releaser 2 Code:Releaser 1 Code: Launch: Release: Anchor Position: Observer: deployments. Now we are all busy packing up and looking forward to arrive in Ponta Delgada.Best wishes to all friends, families and colleagues on shore,Maren Walter and the scientific party of POS523Equipment for on-board filtration of bacterioplankton.Deployment of free-falling microstructure profiler with a tethered rope for recovery.

3. Wochenbericht TRR 181 Cruise Poseidon 523 [POS523]

TRR 181 Cruise Poseidon 5232 — 23 May 20182. Weekly report (14 May 2018)On Tuesday, May 8, at seven in the morning our first station was reached and work started in earnest. The position was one we already occupied during the cruise last year, but here, we had the opportunity to study the impact of longer-term tidal variability: the station work last year took place during a spring tide, and this year we reached the position during neap tide, the time of weakest tidal amplitude. The comparison between these two sets of measurements will yield insights into the impact of the spring-neap cycle on the internal wave energy and the energy dissipation. The following time series stations are dedicated to the latitudinal band between 28° and 30°N, where the critical latitude for the semidiurnal tide is located. Theory predicts an increase of non-linear interactions between internal waves of inertial and tidal frequencies in the vicinity of that latitude. We are interested to find signs of this effect in our observations. At the moment, we are nearing the end of our third time series station. At each station, we collect between ten and fifteen full depth profiles of stratification and currents, over a period of 36 to 48 hours. This time frame is needed to resolve both the semidiurnal tidal and the inertial period in our working area. The inertial period at a given latitude is determined by the Coriolis frequency, and rises from 23 hours in the North of our working area to 26 hours in the south. Stratification is determined from CTD casts. The CTD measures temperature, conductivity, and depth, from which the density and hence the stratification of the water column is derived. The internal waves show up in these data as periodic displacements of density surfaces between individual casts. Current and current shear is measured by the Lowered Acoustic Doppler Current Profiler (LADCP). This instrument uses the frequency shift of sound signal that is emitted and subsequently reflected by tiny particles moving with the water to determine the velocity. The energy of the velocity shear on vertical wavelengths between 10 and 500 m serves also as a proxy for the energy of the internal wave field. The internal wave energy flux and the energy dissipation are calculated by using both stratification and shear.On Thursday, May 10, we successfully recovered the mooring in between the first two time series stations. Thanks to the able work of the captain and crew of the Poseidon, all our instruments could be retrieved in good condition, having been in the ocean for nine months since August last year. All instruments have worked fine, and are now serviced and being prepared for the re-deployment of The CTD/LADCP system. The two yellow instruments are the current meter (LADCP), the CTD is installed at the bottom of the package, below the grey water sampling bottles.FS Poseidon    Malaga - Ponta Delgada    May 2018TRR181       POS523the mooring, which is planned for next Friday. The first glimpses on the raw data show both a seasonal signal as well as a strong influence of the spring neap cycle of currents and stratification. On the touristic side of things, we have encountered large groups of the beautiful and dangerous Portuguese man-of-wars passing by the ship during the station work and the mooring recovery.Best wishes to all friends, families and colleagues on shore,Maren Walter and the scientific party of POS523The head buoy housing a current profiler is the first part of the mooring to be recovered after 9 months in the ocean. Photo: T. ReitzPortuguese man-of-war floating close to the Poseidon. Photo: J. KöhlerPressureTemperatureEast VelocityNorth VelocityRaw time series (p, T, u, v) measured by the uppermost current meter in the mooring.

2. Wochenbericht TRR 181 Cruise Poseidon 523 [POS523]

TRR 181 Cruise Poseidon 5232 — 23 May 20181. Weekly report (7 May 2018)The Poseidon cruise Pos523 is part of the TRR 181, an interdisciplinary research program of the Deutsche Forschungsgemeinschaft (DFG). The topic of TRR181 ‘Energy transfers in atmosphere and ocean’ is the representation of the oceanic and atmospheric energy cycles in climate models. Pos523 is the second expedition to the area south of the Azores within the TRR181 after last years’ Pos516. The shipboard party is formed by 10 scientists of the Universities Bremen and Hamburg, the University of Victoria and the University of the Azores Horta.The oceans’ interior is not at rest. Movement exists in all direction and on a variety of scales that range from basin wide current systems to the millimetres of small scale turbulent motion. The main energy sources for these motions are wind and tides. The interaction between the different scales and the exchange of energy is not well understood. Tidal forcing, for example, excites so-called internal tides at steep topography as seamounts and the continental shelf. These internal tides have the form of underwater waves that may travel hundreds of kilometres across ocean basins. Along their paths, the waves lose their energy by a range of processes and interactions, but the how and where is mostly unknown.Our project has the aim to better understand the fluxes and dissipation of this tidal energy in the ocean interior to improve the representation of these processes in climate models. We do this by observing the distribution of internal wave energy along a path, a so-called tidal beam emanating from the seamount chain south of the Azores toward the Cape Verde Islands. Our main instrumentation is a CTD probe. CTD stands for Conductivity, Temperature, Depth, the main parameter the instrument measures and records. The CTD is part of an instrument package that is lowered from the ship to the seafloor, thus delivering full depth profiles of the water column. The rest of the package consists of a water sampling carousel and a set of acoustic current meters (Lowered acoustic Doppler current meter, LADCP). During this cruise, we will occupy several longterm stations of up to 48 hours, where we will alternately measure full depth CTD/LADCP profiles and shallow (approximately 500m) profiles of turbulence measurements in the upper ocean. Further, we will recover and redeploy a long term mooring designed to record the temporal variability in the internal Schematic of the tidal beam south of the Azores (red/blue), and our instrumentation to observe it: the CTD/LADCP below the ship, and the mooring to observe temporal variability.FS Poseidon    Malaga - Ponta Delgada    May 2018TRR181       POS523wave energy fluxes and the upper ocean turbulence. The mooring was deployed during last years’ Poseidon 516 cruise and is equipped with several current meters and temperature loggers. On Wednesday, May 2, we left Malaga in the morning in calm and sunny weather, passed the Strait of Gibraltar in the afternoon and set course towards our working area. The 5-day trip to the position of our first station leaves plenty of time to install and test our instruments, and fortunately everything is working fine. We are all looking forward to Tuesday morning, when we will finally start our first time series station with CTD, LADCP, and microstructure profiling. Best wishes from the subtropical Atlantic to all friends, families and colleagues on shore,Maren Walter and the scientific party of POS523Leaving Malaga.Preparing the winch for microstructure turbulence observations.

1. Wochenbericht TRR 181 Cruise Poseidon 523 [POS523]

http://oceanrep.geomar.de/43105/1/POS523_Wochenbericht3.pdf

3. Wochenbericht TRR 181 Cruise Poseidon 523 [POS523]

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