HOT-36: Chief Scientist Report
Chief Scientist: C. WINN
HOT-36 Cruise Report
4/15/92 - 4/20/92
We left Snug Harbor on schedule on Wednesday the 15th. We arrived at
Kahe Point at approximately noon, and departed at approximately 1700.
We deployed the sediment traps at 02:00. The traps were recovered
after an approximately 72 hour deployment. Stations 3, 4 and 5 were
occupied after station Aloha and we arrived at Snug Harbor at 07:00 on
Monday the 20th.
The weather was excellent during the entire cruise making operations
relatively simple. As a result we had very few problems on this
cruise.
In general CTD operations went smoothly on HOT-36, and we had only a
few problems. At Kahe Point the transmissometer and the fluorometer
cable connections were reversed. This was corrected upon arrival at
station Aloha. However, it was not possible to display the
transmissometer data in real time during HOT-36. Apparently, the
configuration files were not set up properly for the transmissometer.
Also, at Kahe Point the CTD was left on during the test cast.
Although this did no cause any problems at Kahe Point, the CTD was
again left on while the system was being re-terminated at Station
Aloha. As a consequence, the Wecoma Marine Technician received an
electrical shock during the re-terminated process. The practice of
leaving the CTD on between casts in order to keep the oxygen sensors
powered requires that special care be used to ensure that the CTD
turned off when minor adjustments are made to the system. Fernando
made a small sign to place on the CTD when it is on deck and turned
on. This seemed to be a reasonably good way to avoid problems with the
CTD being powered up while on deck. In the long run however, it would
probably be best to avoid leaving the system powered up on deck as much
as possible.
The JGOFS sediment trap and primary production measurements were made
without problems on HOT-36, however one primary production depth was
lost because of a problem with a Go-Flo bottle. In addition, the WOCE
36 hour burst sampling was completed and all chemical samples were
obtained at all of five stations. XBT's were dropped during transit
from station 3 to station 5. The shipboard ADCP was run during the
entire cruise, and the 300 m isobath was followed between station five
and Kaena Point in order to provide for ADCP calibration.
A few minor repairs and documentation updates should be made before the
next HOT cruise. One of the Go-Flo bottles did not close properly
during the primary production cast. This bottle should be repaired
before HOT 37. The other Go-Flo bottles should probably be inspected
for problems. The documentation for the in situ sedimentation array
should be updated to reflect the new spar buoy design. We almost
deployed the spar with too much bottom weight because the sediment trap
array drawing were not clear. In addition, the HOT cruise prospectus
should be modified to include the definition of Station Aloha as a 10
km radius around the nominal HOT site coordinates. There was some
confusion on the part of the ship's crew regarding the size of the area
that we define as station Aloha.
We encountered a small accumulation of Trichodesimium sp. in the
surface waters for a brief period on HOT-36. This occurred in the
afternoon of the 17th, after surface winds were extremely light for an
extended period. Bucket samples showed that the surface waters
appeared to be enriched in Trichodesimium sp., colonial radiolarians,
copepods etc. This surface manifestation seemed to disappear after the
winds picked up in the late afternoon and evening. There was no
obvious evidence of this feature on the morning of the 18th.
Station 2 casts 1, 16 & 17:
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Regarding the deep salinity offset from HOT-36: My suspicion is that
one of two things happened to cause this. Either the salinity cell was
allowed to dry out during the transit between Kahe Point and ALOHA, or
else some biological fouling occurred somewhere on the downcast of cast
1. Things to do: Check with people on the cruise about the first
possibility. Plot the deep theta-s versus our historical theta-s from
HOT. Is it really the first cast that is off, or are the two later
casts somehow offset? Casts 16 & 17 look very consistent with each
other, but that does not make them right. Final thing is, if you are
convinced that cast 1 is offset, check the bottle salts and their
difference from the CTD for evidence of a shift somewhere during the
downcast.
We will just have to make some cast-by-cast adjustments for salinity on
HOT-36. My guess is that casts 15 & 16 will have the same adjustment
which is due to the slow drift of the calibration of the c-cell, but
that cast 1 will require a special offset. I don't know about oxygen,
but it sounds similar to a problem we had on a previous cruise. Jef
and I will have to look at it. (rbl)
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