Hydrographic and Current Measurements in the Area of the Angola–Benguela Front

H. U. Lass Institut für Ostseeforschung Warnemünde, Rostock-Warnemunde, Germany

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M. Schmidt Institut für Ostseeforschung Warnemünde, Rostock-Warnemunde, Germany

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V. Mohrholz Institut für Ostseeforschung Warnemünde, Rostock-Warnemunde, Germany

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G. Nausch Institut für Ostseeforschung Warnemünde, Rostock-Warnemunde, Germany

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Abstract

The structure and flow in the area of the Angola–Benguela front was studied under the auspices of BENEFIT (Benguela Environment–Fisheries Interaction and Training) during one of the starting cruises of the program with the R/V P. Kottzov from 20 April to 13 May 1997. The dataset acquired in the shelf area between 13°30′S and 17°S consists of CTD casts down to 1200 dbar, two sections of towed CTD, and seven tracks of towed acoustic Doppler current profiler measurements. Throughflow measurements of the temperature and salinity were performed continuously during the cruise. Daily National Aeronautics and Space Administration scatterometer (NSCAT) wind data with ½° resolution were analyzed for April and May 1997 in the area bounded by 5°N, 35°S and 10°W, 20°E.

The Angola–Benguela Front was observed at 16°30′S separating 40-m thick, tongue-shaped, warm and saline Angola Current water in the north from the cold and less-saline water of the Benguela in the south. In contrast to temperature, the pattern of salinity distribution in the tongue split northward into a northwestern and a coastal branch.

Strong downwelling was observed between 60- and 500-m depth on the shelf at 15° and 17°S. The core of the Antarctic Intermediate Water was found at a depth of 800 m throughout the whole region with a salinity of about 34.50 psu decreasing poleward.

A poleward current of 1 Sv entered the studied area through the northern boundary at 13°30′S. Additionally, an eastward directed geostrophic current of 6 Sv driven by the cyclonic wind stress curl entered the region from the northwest in the upper 400 m bending southward along the shelf edge at 15°S and exited the cruise area at 17°S as a coastal boundary current with a volume transport of about 7 Sv. The importance of this current as a link between the cyclonic gyre in the Angola Dome area and the source region of the Benguela Current is discussed.

Corresponding author address: H. U. Lass, Institut für Ostseeforschung Warnemünde, Seestr. 15, D-18119 Rostock-Warnemünde, Germany.

Email: lass@io-warnemuende.de

Abstract

The structure and flow in the area of the Angola–Benguela front was studied under the auspices of BENEFIT (Benguela Environment–Fisheries Interaction and Training) during one of the starting cruises of the program with the R/V P. Kottzov from 20 April to 13 May 1997. The dataset acquired in the shelf area between 13°30′S and 17°S consists of CTD casts down to 1200 dbar, two sections of towed CTD, and seven tracks of towed acoustic Doppler current profiler measurements. Throughflow measurements of the temperature and salinity were performed continuously during the cruise. Daily National Aeronautics and Space Administration scatterometer (NSCAT) wind data with ½° resolution were analyzed for April and May 1997 in the area bounded by 5°N, 35°S and 10°W, 20°E.

The Angola–Benguela Front was observed at 16°30′S separating 40-m thick, tongue-shaped, warm and saline Angola Current water in the north from the cold and less-saline water of the Benguela in the south. In contrast to temperature, the pattern of salinity distribution in the tongue split northward into a northwestern and a coastal branch.

Strong downwelling was observed between 60- and 500-m depth on the shelf at 15° and 17°S. The core of the Antarctic Intermediate Water was found at a depth of 800 m throughout the whole region with a salinity of about 34.50 psu decreasing poleward.

A poleward current of 1 Sv entered the studied area through the northern boundary at 13°30′S. Additionally, an eastward directed geostrophic current of 6 Sv driven by the cyclonic wind stress curl entered the region from the northwest in the upper 400 m bending southward along the shelf edge at 15°S and exited the cruise area at 17°S as a coastal boundary current with a volume transport of about 7 Sv. The importance of this current as a link between the cyclonic gyre in the Angola Dome area and the source region of the Benguela Current is discussed.

Corresponding author address: H. U. Lass, Institut für Ostseeforschung Warnemünde, Seestr. 15, D-18119 Rostock-Warnemünde, Germany.

Email: lass@io-warnemuende.de

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