. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography ment layer is too thin for standard conductive heat flow measurements to be made. The purpose of this paper is to examine the im- plications of near-bottom temperature anomalies mea- sured with towed thermistors. Since the crestal zone of the Mid-Atlantic Ridge at 26°N has been studied in some detail [8-10,14-16], the data from this area will be used in discussing the theoretical results. 2. The TAG hydrothermal field During the 1972 and succeeding
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography ment layer is too thin for standard conductive heat flow measurements to be made. The purpose of this paper is to examine the im- plications of near-bottom temperature anomalies mea- sured with towed thermistors. Since the crestal zone of the Mid-Atlantic Ridge at 26°N has been studied in some detail [8-10,14-16], the data from this area will be used in discussing the theoretical results. 2. The TAG hydrothermal field During the 1972 and succeeding cruises of the NOAA Trans-Atlantic Geotraverse (TAG) project, anomalously thick manganese oxide crusts were re- peatedly dredged from the southeast wall of the rift valley at 26°N (Fig. 1). Radiogenic dating of the manganese crusts, which attain thickness of 42 mm only 5 km from the axis of the rift valley, show them to be accumulating at about 200 mm per 106 years, about two orders of magnitude faster than hydrog- enous ferromanganese [8]. The crusts are almost pure manganese (40%), with only trace quantities of Fe, Cu, Ni, and Co [8]. The rapid accumulation rate and pure composition evidence a hydrothermal origin for Fig. 1. Bathymetric map contoured in hundreds of meters [161 showing locations of profiles A and B, along which water tem- perature measurements and bottom photographs were concur- rently made at the southeast wall of the rift valley of the Mid- Atlantic Ridge at 26° N. A water temperature anomaly (AT) was measured between 2950 and 3000 m along profile A [10]. No water temperature anomaly was present along pro- file B. The floor of the rift valley is shaded. The TAG hydro- thermal field is outlined (dashed lines). TABLE 1 Temperature profiles at the TAG hydrothermal field (Fig. 2) Tempera- Cumulative Depth (m) Potential tempe rature (°C). Thermistor position Vertical ture profile distance along in vertical array (m above lowermost thermistor) gradien
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