MOCNESS-CTD Data from Guaymas Basin vent region, AII-112-28, 1985 from R/V Atlantis II AII-112-28, July 1985

<p>MOCNESS-CTD Data from Guaymas Basin vent region, AII-112-28, 1985 from R/V Atlantis II AII-112-28, July 1985. The first three tows report conductivity in the cond_sal column and thereafter, salinity is reported.</p>

<p>From cruise report:&nbsp;<br />
The MOCNESS, Multiple Opening/Closing Net and Environmental Sensing System, was &nbsp;used to sample the zooplankton in the Guaymas Basin deep sea vents study area (Southern &nbsp;Trough) between 26 July and 1 August 1985. The purpose of the sampling was to characterize &nbsp;the zooplankton populations within 100 meters of the sea floor in the vicinity of the &nbsp;hydrothermal vent activity and to compare animals caught in this region with animals caught in &nbsp;adjacent areas outside the immediate influence of the vents and in the water column above the &nbsp;vents area.</p>

<p>A MOCNESS-1 was used to make these collections. This system was equipped with 9 1-m^2 nets of 333 µm nitex nylon mesh, which presented a 1-m^2 mouth opening when towed with &nbsp;the frame at 45 degrees from the vertical. The system carried Sea Bird temperature and salinity &nbsp;probes, a down welling light sensor, a bottom finding 12 kHz pinger, a pressure transducer, a &nbsp;modified TSK flowmeter, and an angle inclinometer. Data from the sensors were transmitted up &nbsp;to a deck unit via conducting cable where they were displayed and saved on 1/4\" cassette tape. &nbsp;Data were also passed from the deck unit to a CBM microcomputer for real time processing, &nbsp;storage on floppy disc, printing, and plotting.</p>

<p>A variety of towing strategies were used (Figures 1 and 2). Four long horizontal tows &nbsp;with the MOCNESS maintained approximately 100 m above the sea floor in approximately 2000 &nbsp;meters of water were taken both along the axis of the Southern trough above the benthic study &nbsp;area and perpendicular to the axis of the trought. On these tows, the system was traveling above &nbsp;the bottom at between 1 and 2 knots and eight nets were opened sequentially at about fifteen &nbsp;minute intervals. Water filtered by each net was at least 500 m^3.</p>

<p>Three oblique tows were made to 1000 m. While hauling the system back to the surface, &nbsp;nets were opened and closed to sample the following depth strata: 1000-850, 850-700, 700-550, &nbsp;550-400, 400-300, 300-200, 200-100, 100-0m. Volume of water filtered by each net was &nbsp;between 500 and 1000 m3 . Two additional oblique tows were made to sample from within 50 meters of the bottom in the Southern Trough area to 850 m. The depth strata sampled were: &nbsp;1950-1800, `800-1700, 1700-1600, 1600-1450, 1450-1300, 1300-1150, 1150-1000, 1000-850 m &nbsp;and approximately 1000 m3 was filtered by each net. On the second of these tows, batteries in &nbsp;the underwater unit failed, and only depth specific samples from 1950-1800 and 1800-1700 m &nbsp;were obtained. A single oblique tow sampling 25 m intervals from 200 m to the surface was &nbsp;obtained on the last night of the MOCNESS work.</p>

<p>As part of this investigation, F. Manrique made visual and photographic observations of &nbsp;the plankton throughout the water column and especially in the vicinity of the deep-sea floor &nbsp;during ALVIN dive #1609 (1August 1985).<br />
This combination of tows (a total of 85 samples) and ALVIN observations provides a &nbsp;rather complete characterization of the vertical distribution of zooplankton populations from the &nbsp;deep-sea floor to the sea surface in the Guaymas Basin region. In addition, the horizontal &nbsp;distribution of zooplankton in the bottom water zone above this hydrothermal vents area an, for &nbsp;the first time, be studied and the results placed in the larger context of the distribution of the &nbsp;zooplankton in the water column as a whole.</p>