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

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.

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

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  the frame at 45 degrees from the vertical. The system carried Sea Bird temperature and salinity  probes, a down welling light sensor, a bottom finding 12 kHz pinger, a pressure transducer, a  modified TSK flowmeter, and an angle inclinometer. Data from the sensors were transmitted up  to a deck unit via conducting cable where they were displayed and saved on 1/4" cassette tape.  Data were also passed from the deck unit to a CBM microcomputer for real time processing,  storage on floppy disc, printing, and plotting.

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

Three oblique tows were made to 1000 m. While hauling the system back to the surface,  nets were opened and closed to sample the following depth strata: 1000-850, 850-700, 700-550,  550-400, 400-300, 300-200, 200-100, 100-0m. Volume of water filtered by each net was  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:  1950-1800, `800-1700, 1700-1600, 1600-1450, 1450-1300, 1300-1150, 1150-1000, 1000-850 m  and approximately 1000 m3 was filtered by each net. On the second of these tows, batteries in  the underwater unit failed, and only depth specific samples from 1950-1800 and 1800-1700 m  were obtained. A single oblique tow sampling 25 m intervals from 200 m to the surface was  obtained on the last night of the MOCNESS work.

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