Zenk Walter

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  • Technical Report
    Observations of the Antarctic polar front during FDRAKE 76 : a cruise report
    (Woods Hole Oceanographic Institution, 1976-11) Joyce, Terrence M. ; Dean, Jerome P. ; McCartney, Michael S. ; Millard, Robert C. ; Moller, Donald A. ; Voorhis, A. ; Dahm, C. ; Georgi, Daniel T. ; Kullenberg, G. ; Toole, John M. ; Zenk, Walter
    During March/April 1976 the small-scale structure of the Antarctic Polar Front was observed in the Drake Passage. The observations were part of the International Southern Ocean Studies (ISOS) program called FDRAke 76. The purpose of the program was to obtain densely sampled measurements of temperature, salinity, dissolved oxygen, and chemical nutrients in the Polar Front Zone (PFZ) and pilot measurements of horizontal and vertical velocities in order to explain the above scalar variability. The PFZ is a region where Antarctic and sub-Antarctic waters intermingle and presumably mix to affect the properties of Antarctic Intermediate Water. A report on the third leg of Cruise 107 of the R. V. THOMPSON is presented as well as a description of the measurements and a preliminary report of the data. A feature of interest is the pinching off of a northward meander of the circumpolar current system into a cyclonic ring of Antarctic Waters.
  • Technical Report
    A moored array along the southern boundary of the Brazil Basin for the Deep Basin Experiment : report on a joint experiment 1991-1992
    (Woods Hole Oceanographic Institution, 1994-02) Tarbell, Susan A. ; Meyer, Ralf ; Hogg, Nelson G. ; Zenk, Walter
    The Deep Basin Experiment (DBE) is an international effort and a part of the World Ocean Circulation Experiment with the principal objective of improving our knowledge of the subthermocline circulation. The DBE fieldwork is focussed on the Brazil Basin and this report is concerned with a moored array situated along its southern boundary which was installed in early 1991 to measure the inflow and outflow to the Basin and to investigate the Brazil Current near 30S. This moored array was a joint undertaking by the Institut für Meereskunde of the University of Kiel and the Woods Hole Oceanographic Institution. Moorings were deployed on Meteor Cruise 15, leg 1 and retrieved on Meteor cruise 22, legs 3 and 4. A total of 57 conventional current meters and two Acoustic Doppler Current Profilers were set on 13 moorings with some concentration within the Brazil Current and the Vema Channel. CTDs were taken at each mooring site as well as in between. Some of the recovered instruments were reset in the Hunter Channel, a suspected additional connection between the Argentine Basin and the Brazil Basin. A later report will summarize this data after it is recovered in May 1994.
  • Technical Report
    Horizontal advection of temperature in the seasonal thermocline during Jasin 1978
    (Woods Hole Oceanographic Institution, 1981-05) Joyce, Terrence M. ; Käse, R. H. ; Zenk, Walter
    The temporal changes in the low-frequency thermal structure during a two-week period in August-September 1978 are discussed from moored data collected during the JASIN experiment. While some changes in the thermal structure appear to be related to local winds, the dominant low-frequency variability in the seasonal thermocline can be explained as horizontal ad vection of a spatially varying temperature field, and associated thermal wind, by geostrophic currents with little vertical motion or mixing required.
  • Preprint
    The mid-depth circulation of the northwestern tropical Atlantic observed by floats
    ( 2009-05-29) Lankhorst, Matthias ; Fratantoni, David M. ; Ollitrault, Michel ; Richardson, Philip L. ; Send, Uwe ; Zenk, Walter
    A comprehensive analysis of velocity data from subsurface floats in the northwestern tropical Atlantic at two depth layers is presented: one representing the Antarctic Intermediate Water (AAIW, pressure range 600–1050 dbar), the other the upper North Atlantic Deep Water (uNADW, pressure range 1200–2050 dbar). New data from three independent research programs are combined with previously available data to achieve blanket coverage in space for the AAIW layer, while coverage in the uNADW remains more intermittent. Results from the AAIW mainly confirm previous studies on the mean flow, namely the equatorial zonal and the boundary currents, but clarify details on pathways, mostly by virtue of the spatial data coverage that sets float observations apart from e. g. shipborne or mooring observations. Mean transports in each of five zonal equatorial current bands is found to be between 2.7 and 4.5 Sv. Pathways carrying AAIW northward beyond the North Brazil Undercurrent are clearly visible in the mean velocity field, in particular a northward transport of 3.7 Sv across 16° N between the Antilles islands and the Mid- Atlantic Ridge. New maps of Lagrangian eddy kinetic energy and integral time scales are presented to quantify mesoscale activity. For the uNADW, mean flow and mesoscale properties are discussed as data availability allows. Trajectories in the uNADWeast of the Lesser Antilles reveal interactions between the Deep Western Boundary Current (DWBC) and the basin interior, which can explain recent hydrographic observations of changes in composition of DWBC water along its southward flow.