Sediment Trap Recovery Cruise - TTN-055

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Date: Fri, 12 Jan 1996 17:41:00 +0000 (GMT)


Believe it or not, there is another "last" JGOFS Arabian Sea cruise.  Even
though folks from the previous leg ran off with the charts, we still
managed to find our way to the mooring sites.  Steve Manganini, Chris Moser
and the WHOI/OSU teams have once again shown their stuff by successfully
recovering the moorings at sites 1-5.  In spite of some pretty fuzzy
wuzzles (challenging snarls), the recovery team (including Brooksforce,
Billings, Peterson, Gann, Hart and Bogue) maintained high spirits and
good humor throughout.  They are a joy to work with.  We are also
lucky to have Susan Kadar with us.  She was a much needed and experienced
hand with plankton tows, CTDs, and trap processing.

In all, we recovered a complete set of samples at each depth of deployment
covering every time period over the last 6 months at trap stations 1 through
4.  Combined with the results from the first trap recovery cruise, this   
gives us a year-long uninterrupted record.  Redundancy of traps and trap
types (see below) allowed this remarkable collection.  Perhaps this
redundancy is a lesson to consider in Southern Ocean planning.  Results
from the sediment traps show a clear pattern of seasonal flux and will help
us greatly in linking surface water processes and benthic carbon fluxes. 
We are all enthusiastic about getting these samples back to the lab, and
to tying in our results with those from the process cruises!

The recovered moorings included 16 OSU/WHOI (OW) time-series sediment
traps.  The sample changers of all 16 of the OW traps functioned
perfectly.  All traps collected material through the beginning of the SW
monsoon.  As expected, fluxes were extremely high at that time.  The
cups were timed to advance more quickly during the high flux periods, but
the peak flux was later than expected.  Clogging occurred in 21-cup
traps in the uppermost waters due to the extremely high influx of material
at this time.  This possibility had been forseen and "redundant" 13-cup
MK7 traps with larger delivery spouts that did not clog had been
placed just above the smaller-aperture traps.  A total of 255 samples were
returned to the surface.  Collections from mooring 5 were sub-sampled for
trace metals and nutrients immediately, and heights of sediment in
the collection cups recorded for all mooring samples.  Sediment heights
provided an exciting first glimpse of flux patterns.  

The recovered moorings also included 8 UW/SKIO/SUNY (USS) arrays.  The USS
arrays held 4 traps each, 3 with swimmer exclusion (IRS) valves, and 1
open trap without a valve.  Two of the USS IRS traps also had time-series
carousels.  A complete set of time-series samples was collected at each
depth and site, with one or both of the IRS traps with carousels working
perfectly on each array.  Time-integrated IRS and open traps also collected
samples at each depth and site for direct comparison and analysis of
the contribution of swimmers.  Swimmers were rampant in the shallow (ca.
500 m) open traps, and present in deeper open traps as well, whereas the
exclusion valves were effective at minimizing visible swimmers in the IRS
traps.  The Hedges/Lee/Montlucon splitting team managed to work up a lather
with more than 200 samples returned that were split, filtered and frozen on
board.

Initial surveilance of samples (height of material in the sample cups)
shows a dramatic pulse-like delivery of material during the SW monsoon. 
Fluxes appear to be roughly 2-3 times those of the previous 6-month
deployment.  Agreement between duplicate 13- and 21-cup OW traps was excellent
when comparison was possible.  The USS traps showed a clear attenuation of
material with depth and hint at a decrease in surface flux away from the
coast.  Both the  OW and the USS traps show a single influx of material
closest to the coast with multiple, but distinct, pulses further from
land.  Microscopic analysis by Misho Stirn and his crew, Adnan and Khamis,
from Sultan Qaboos University indicated that smaller diatoms found in
surface waters were not present in material collected by mid-depth traps,
and even robust, larger diatoms were gone at deeper depths.  Calcareous
material apparently was well preserved, as expected.

Mike R. was busy on the CTD  with 20 casts completed.  Suspended particles
were collected at trap stations for Bob Bidigare for stable carbon isotope
measurement, and for the organic geochemistry group (Wakeham/Hedges/Lee)
for biochemical analyses.  Roger Francois collected particles at trap
stations and throughout the cruise for stable nitrogen isotope measurements
of PON.  He also collected seawater for nitrogen isotope analysis of
nitrate, while samples were taken for Bidigare for carbon isotope analyses
of DIC.

Plankton was collected at each trap site and daily during transit to the
Seychelles.  Just after recovering the mooring at Station 4, we were
treated to a Noctiluca bloom.  It was great fun looking at all the
symbiotic flagellates inside them.  Plankton will be analyzed for
species composition and abundance as well as chlorophyll biomass
(Stirn).  At the trap sites, plankton will also be analyzed for organic
composition.  Brenda Boleyn was a big help with the plankton tows and
identifying creatures of the deep.

Goldendale Middle School (WA) 7th-graders are getting a daily feed of
ship position and weather data courtesy of marine-tech Neil Bogue who is
also answering questions the students send over email.  Some future
oceanographers may result!

Major inroads into training for the next international ping-pong
championship were made during the steam south to the Seychelles, not to
mention a visit from King Neptune.  As usual, Captain Al and the crew of the
Thompson have been outstanding.  We continue to be impressed with their
efficiency, competence and geniality.


cindy lee is sci-01@thompson.ocean.washington.edu