2. Wochenbericht MSM21/1b

FS Merian Fahrt 21/1b Wochenbericht 2 (11. Juni – 17. Juni 2012

One stop shop web site for TMAs

Establishment of community shared “one stop shop” web site for TMAs where 1) the TMA network as a whole is introduced (partners, common themes, data products); 2) High-level TMA products (volume transport, heat transport) can be obtained; 3) documentation (calculation, error bars) of the products is provided; 4) links to data behind the high-level products (OCEAN SITES); 5) joint cross-TMA network analyses are provided. To achieve this deliverable one workshop will be held (in project month 8)

Adjustment of the basin-scale circulation at 26 degrees N to variations in Gulf Stream, deep western boundary current and Ekman transports as observed by the Rapid array

The Rapid instrument array across the Atlantic Ocean along 26 degrees N provides unprecedented monitoring of the basin-scale circulation. A unique feature of the Rapid array is the combination of full-depth moorings with instruments measuring temperature, salinity, pressure time series at many depths with co-located bottom pressure measurements so that dynamic pressure can be measured from surface to bottom. Bottom pressure measurements show a zonally uniform rise (and fall) of bottom pressure of 0.015 dbar on a 5 to 10 day time scale, suggesting that the Atlantic basin is filling and draining on a short time scale. After removing the zonally uniform bottom pressure fluctuations, bottom pressure variations at 4000 m depth against the western boundary compensate instantaneously for baroclinic fluctuations in the strength and structure of the deep western boundary current so there is no basin-scale mass imbalance resulting from variations in the deep western boundary current. After removing the mass compensating bottom pressure, residual bottom pressure fluctuations at the western boundary just east of the Bahamas balance variations in Gulf Stream transport. Again the compensation appears to be especially confined close to the western boundary. Thus, fluctuations in either Gulf Stream or deep western boundary current transports are compensated in a depth independent (barotropic) manner very close to the continental slope off the Bahamas. In contrast, compensation for variations in wind-driven surface Ekman transport appears to involve fluctuations in both western basin and eastern basin bottom pressures, though the bottom pressure difference fluctuations appear to be a factor of 3 too large, perhaps due to an inability to resolve small bottom pressure fluctuations after removal of larger zonal average, baroclinic, and Gulf Stream pressure components. For 4 tall moorings where time series dynamic height (geostrophic pressure) profiles can be estimated from sea surface to ocean bottom and bottom pressure can be added, there is no general correlation between surface dynamic height and bottom pressure. Dynamic height on each mooring is strongly correlated with sea surface height from satellite observations and the variability in both dynamic height and satellite sea surface height decrease sharply as the western boundary is approached

North Atlantic Ventilation - Cruise No. MSM 21/1b, June 9 - June 22, 2012, Reykjavik (Iceland) - Reykjavik (Iceland)

The R/V MARIA S. MERIAN cruise MSM21/1b was carried out jointly by GEOMAR Kiel and the Institut für Meereskunde at the Centre for Marine and Atmospheric Sciences of Hamburg University. Scientists and technicians from the Atlantic Branch of the P.P. Shirshov Institute for Oceanology (Kaliningrad, Russia) and the Finnish Meteorological Institute (Helsinki; Finland) also participated in the cruise. The measurements mainly contributed to three projects: 1) "Nordatlantik", funded by the German Ministry of Education and Research (BMBF), 2) "THOR", funded by the European Commission within the framework of FP7, 3) "Valley Mixing", funded by the Deutsche Forschungsgemeinschaft (DFG). The main objectives of the cruise were to characterize the spatio-temporal variability of the Denmark Strait overflow and to identify processes responsible for the exchange of the overflow plume with ambient water downstream of Denmark Strait. A multi-platform approach was taken to achieve the goals, based on moorings, an autonomous underwater vehicle (AUV), as well as lowered and vessel-mounted observations. From these platforms, measurements of temperature, salinity, dissolved oxygen, current velocity, dissipation of turbulent kinetic energy, and bottom pressure were obtained. Altogether, twelve moorings were deployed, one mooring was recovered, data from two PIES were uploaded via acoustic telemetry, turbulence measurements on six extended AUV dives were carried out, and 92 CTD / LADCP casts were taken, 25 of which had additionally been equipped with a profiling turbulence (MSS) probe. Along with this, underway data of surface hydrography and current velocity were collected throughout the cruise. Our research was conducted in the spirit of both the "OSPAR Code of Conduct for Responsible Marine Research" and the "Commitment of responsible marine research" by the DFG Senatskommission