WHP Ref. No.: AR15/ACM3/ACM12/ACM13 Last updated: March, 1993 METEOR Finished Her Second DBE Cruise Cruise Report Background Within WOCE, the Deep Basin Experiment DBE aims to observe and model the deep water exchange between two ocean basins. The sparely investigated Brazil Basin was chosen for this study. The observational part of the DBE reqires two year- long measurements with moored current meters at the basin's deep connections in the north and south as well as Langrangian measurements with neutrally buoyant floats at mid depths of the basin. The current measurements at the basin's southern margin and the RAFOS float project are coordinated efforts of the Institut fuer Meereskunde in Kiel, IFMK, and the Woods Hole Oceanographic Institution, WHOI. An intensification of the Lagrangian component is planned by IFREMER, Brest, in 1993. During her first DBE cruise (M15/1-2) in January and February 1991, FS METEOR had launched 13 current meter moorings along the western part of the southern boundary of the Brazil Basin from the shelf break across the Santos Plateau towards the Vema Channel. The section of moorings combines WOCE arrays ACM3 on the western part of the heat flux section A10 and the DBE array ACM12 in the Vema Channel. A bathymetric survey of the the Vema sill with the ship's multibeam echosounding system HYDROSWEEP supported the selection of mooring sites in the channel and will help in the interpretation of the interaction between the observed currents and the bottom topography. The bathymetry of the Hunter Channel at the eastern part of the southern boundary was not yet well known in detail. Actually, many detailed features in available bottom charts appeared to be wrong. Deep CTD stations during that first DBE cruise however showed that a significant part of bottom water must flow northwards through the Hunter Channel, and a bathymetric survey, although incomplete, served to identify passages in the channel for placement of current meter moorings of array ACM13 during the next cruise. Thus, the second DBE cruise of METEOR had three main objectives: to recover all current meter moorings from array ACM3/ACM12 after 23 months deployement, and to launch six new current meter moorings in the Hunter Channel array ACM13 and one in the outflow extension on the eastern flank of the Rio Grande Rise. In addition, the acoustic array for the RAFOS float experiment within the Antarctic Intermediate Water, AAIW, had to be installed. Further, CTD sections across the Brazil Current and along the mooring sections and selected XBT drops were planned. Narrative METEOR cruise M22/3-4 consisted of two legs. Leg M22/3 began in Recife November, 18, 1992. Heading south towards mooring array ACM3, some hydrographic measurements within the Brazil Current were made south of the Vitoria Trinidade Ridge and two test floats were placed at the 850 m depth level within the AAIW. On November, 25, we reached position 29 S, 44.5 W, where the first of four IFMK moorings carrying sound sources was launched for the float experiment. During the following two days, three IFMK current meter moorings from ACM3 were recovered completely after 23 months. With three CTD sections across the Brazil Current, 120 Km apart, leg M22/3 finished. For a short interruption of the cruise, METEOR called into port in Santos November, 30, where Walter Zenk took over as chief scientist from Thomas Mueller. Leg M22/4 started from Santos December, 2. Initially, four WHOI moorings linking ACM3 and ACM12 were recovered after 23 months without problems. To our surprise, the acoustic release of a fifth mooring on the eastern side of the Santos Plateau responded but failed to release. After numerous trials we started preparations to drag for that mooring. However, we had to disrupt this because the weather became worse. Facing the substantial mooring work ahead of us, we had to give up this mooring and proceeded to the Vema Channel. On December, 2, the second IFMK sound source mooring was deployed on the western Vema terrace. Next, two IFMK moorings from the Vema sill were recovered, but one was lost. Neither was it possible to communicate with its acoustic release nor did it come into sight after several release commands had been sent. Two further moorings from the Vema Channel array were recovered without problems, and thus the mooring work within the line ACM3/ACM12 was completed. We reached the Hunter Channel on December, 11. Due to bad wheather conditions with a gale blowing up to Beaufort 12, launching of the 6 current meter moorings of array ACM13 and the third IFMK sound source mooring was sometimes distressing. Again, due to unfavourable weather conditions we were unable to add significant information to the Hunter Channel bathymetry with HYDROSWEEP. By December, 15 we left the Hunter Channel region for a site on the eastern flank of the Rio Grande Ridge where a near-bottom mooring was launched. During the first DBE cruise in 1991, METEOR had discovered a deep western boundary current on the eastern flank which will be monitored by the current meters in this mooring. A final mooring K3 with two near-bottom current meters and the fourth sound source was set into a channel which we believe to be a northward extension of the Vema Channel. METEOR called into port in Rio de Janeiro December, 22, 1992. Summarizing, 11 of 13 current meter moorings from the ACM3/ACM12 array were successfully recovered after 23 months deployement. As some consolation with respect to the two lost moorings, we note that there is still some hope that one of these can be dragged successfully later because we know its exact position, and that the second one was a short mooring mainly deployed for redundance close to a recovered, more heavily equipped one. Six current meter moorings were deployed in the Hunter Channel array ACM13, two moorings with near bottom current meters into the extensions of the Hunter Channel and Vema Channel outflows, and an acoustic array with four sound sources for the RAFOS float experiment in the AAIW level was set up. In addition 20 RAFOS floats and 16 satellite tracked drifting buoys drogued at 100 m were launched. Walter Zenk and Thomas J. Mueller Institut fuer Meereskunde an der Universitaet Kiel, Germany Telemail/Omnet: IFM.KIEL Nelson G. Hogg Woods Hole Oceanographic Institution Woods Hole, MA, USA Telemail/Omnet: N.HOGG .