RRS John Murray JM8/69 Leg1
Cruise summary report
|Ship name (ship code)||RRS John Murray (74MJ)|
|Cruise identifier||JM8/69 Leg1|
|Cruise period||1969-10-02 — 1969-10-11|
|Port of departure||Barry, United Kingdom|
|Port of return||Barry, United Kingdom|
1. Lay the new tide gauge on La Chapelle Bank.
2. Recover NIO moorings 047, 048 and 049 laid during July 1969 on the continental slope of the Bay of Biscay.
3. Drag for lost moorings 040, 041 in the same area.
4. Towing trials on Bath University dummy fish and faired cable.
5. TSO dips in relation to tide gauge and elsewhere as time permits.
Echo sounder fish was streamed and the tide gauge prepared for laying. At the approach of La Chapelle bank sounding lines were run across the area to allow a suitable spot to be chosen. The tide gauge was laid in 162m water depth.
The ship proceeded to the sites of moorings 047 and 048 (approximately 2000 depth) in an attempt to recover them. The repeated attempts to release and recover moorings 047 and 048 were unsuccessful. There was no response from acoustic signals from either mooring and they could not be located by dragging. However, mooring 049 (a near-bottom test mooring, approximately 2800 depth) responded immediately, but it was apparent that the buoyancy of the mooring changed during ascent and it sank to the bottom again. The ship proceeded to the position of mooring 040 (1000m depth) to drag for it. The trawl warp was paid out (2000m) with two sets of cable grapnels on the end. The grapnels were dragged across the mooring area and then recovered with no result. The "hookfish" was tried but its acoustic signals could not be heard beyond 800m, on its first attempt it was dragged with 2000m of wire for 4 hours with no result. Further attempts were made to locate moorings 047 and 048 with the hookfish but nothing was recovered. Two attempts were also made with the hookfish without success to recover the NIO mooring, 040.
The hydrographic winch was tested in the tide gauge area and two TSD dips were made before the Decca was used to locate the tide gauge. Signals were obtained from the tide gauges's pinger. The TSD revealed large fluctuations in the depths of isotherms 40 - 100m. The ship
|Chief scientist||John C Swallow (National Institute of Oceanography)|
|Cruise report||(0.14 MB)|
|General||Bay of Biscay|
|Specific||La Chapelle Bank|
|CTD stations||Quantity: number of stations = 1|
|Sea level (inc. bot. press., inverted echosounder)||Description: every 15 min at 162m 4-24/10|