Dataset: zoo_bongo
Deployment: TT050

See Platform deployments for cruise specific documentation

   PI:        Karen Wishner (University of Rhode Island),
              Marcia Gowing (University of California-Santa Cruz)
   dataset:   Zooplankton carbon by size fractions at 0-200m using
              bongo net tows
   dates:     August 19, 1995 to September 13, 1995
   location:  N: 22.5076  S: 15.2486  W: 57.3112  E: 68.733
   project:   Arabian Sea
   cruise:    TTN-050, Process 5 (Late SW Monsoon)
   ship:      R/V Thomas Thompson

 
 

Mesozooplankton Biomass Documentation: JGOFS Arabian Sea

PIs:  Karen Wishner (URI), Marcia Gowing (UCSC)
Data Base Organizer and Chief Technician:  Celia Gelfman
Assistants:  Chelsea Donovan, Heidi Franklin, Maureen Koneval, Lauren
Lankau, John Maccario, Jennifer Saltzman, Dorothee Schreiber, Cynthia
Venn, Kathleen Vignes.

	Samples were collected with a double 1 m2 MOCNESS (two 1 m2
	MOCNESS systems side-by-side), a multiple opening-closing net
	system with environmental sensors and control of the nets from
	shipboard (Wiebe et al. 1976, 1985).  The nets were 153 micron
	mesh with a 1 m2 mouth opening (when towed at a 45 degree
	angle). The net was towed usually at 1.5 - 2.5 kts behind the
	ship.  Wire was payed out at 10 - 25 m/min and hauled in at 5 -
	20 m/min.  Environmental data from the MOCNESS included time,
	depth, temperature (Sea-Bird SBE 3), salinity (Sea-Bird SBE 4),
	light transmission (SeaTech 25 cm beam transmissometer), and
	oxygen (Sea-Bird SBE 13).  The volume filtered through each net
	was determined by the MOCNESS program, taking into account flow
	past the system (measured with a modified TSK flowmeter mounted
	on the net frame) and the towing angle.  In some cases, the
	volume filtered per time from trouble-free portions of a tow
	was extrapolated to time intervals with electronic problems.

	Usually 16 discrete samples were collected in an oblique haul
	from about 1000 m to the surface.  Typically a day and a night
	tow were taken at each of the six long stations during four
	seasonally-spaced process cruises (TN043, TN045, TN050,
	TN054).  Occasional additional tows and samples to deeper
	depths were also done.  During the monsoon cruise (TN050),
	there were often problems with knotted or ripped nets because
	of the rough seas; data from this cruise should be treated with
	caution. Tow times and geographic locations can be found in the
	cruise event log.

	Cod ends were placed on ice immediately after retrieval.  Nets
	were hosed down with filtered (nominally 2 micron) seawater.
	For most day tows, the entire sample was preserved in 4%
	borate-buffered formaldehyde.  For most night tows, the samples
	were split in a NMFS-style (flat-bottomed) plankton splitter.
	Half the sample was preserved as above for displacement
	volumes, wet weights, and distributions; one quarter (or the
	entire remaining half for very small samples and for surface
	samples) was set aside in a refrigerator for dry weight and CHN
	subsampling several hours later; and one quarter (when
	available) was preserved in paraformaldehyde for electron
	microscopy of zooplankton gut contents.

	For dry weights, the sample was size-fractionated through a
	sieve series (2000, 1000, 505, 202 micron) and each size
	fraction was resuspended in a known volume of filtered
	seawater.  Aliquots were taken with a Stempel piston pipette,
	filtered onto combusted pre-weighed GF/D 25 mm glass fiber
	filters, rinsed with distilled water, loosely wrapped in
	aluminum foil, placed in an oven (60 degrees C) for several
	days, and stored in a desiccator for shipment home.  Two
	replicates were done for each size fraction.  Four blanks
	(aliquots of filtered seawater treated as above) were done for
	each tow.  In the lab, filters were dried in an oven (60
	degrees C) for 8 - 10 hr, weighed for dry weight on a Cahn
	microbalance, ashed in a muffle furnace (500 degrees C) for 4
	hr, and weighed for ash. For dry weights, the pre-cruise filter
	weight and the mean dry weight blank for the cruise (a single
	value for each cruise) were subtracted from the measured
	post-cruise dry weights. The ash-free dry weight was calculated
	as the post-cruise dry weight minus the post-cruise ash weight
	and the cruise mean ash weight blank.  For carbon values, a
	conversion factor from the literature was used [log (dry
	weight) = 0.499 + 0.991 (log carbon)] (Wiebe et al. 1975, Wiebe
	1988).  The mean of the 2 replicate filters from each sample
	was used. In cases where no measurements were made and in cases
	where the weight of a filter with sample was less than the
	blank and pre-cruise filter weight, the data were recorded as
	ND (no data).  Carbon values from CHN measurements were also
	obtained by Roman from some of these same samples in the upper
	200 m on cruises TN043, TN045, and TN050.


	Displacement volumes and wet weights were measured several
	months after the cruise on preserved samples.  Either the
	entire sample or a half split was used.  Large singular
	organisms (large fish or jellyfish) were removed beforehand.
	Displacement volumes were done with no size fractionation. Wet
	weights were done on the large (> 2 mm) and small (