Date: Mon, 10 Feb 1997 08:16:25 +0000 (GMT)
From: Jason Goodman <sci5@knorr.whoi.edu>
To: seadiary@MIT.EDU
Subject: February 10
Message-Id: <Pine.SUN.3.91.970210073743.13363C-100000@mike.knorr.whoi.edu>
Mime-Version: 1.0
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57 05' N, 52 30' W
Temp: -9.5 C, Winds 25 m/s
Seas: Y'know, people look really silly standing at a 45 degree angle to 
      the floor.

  More CTD stations today, with XBTs in between.  We're heading toward the 
6th CTD station.  After that, we'll divert to the south, where the 
theoreticians (my advisor and others) think the most likely spot for deep 
convection to occur is.  We're going to be deploying a whole bunch of 
floats and drifters and dropping lots of XBTs in an X pattern.
  We deployed one drifter today.  The idea here is that the ship can only 
measure currents at a few points, and can't really tell where the water 
flows to or what its destination is.  So you drop a dinkus in the water 
and let it float around with the currents.  We've got about six kinds of 
these dinkuses on board.  They are neutrally buoyant so they sink to 
a certain level and hover there, moving with that chunk of water.  They 
listen to a set of sound sources placed in the area, and use those to 
triangulate their position once every couple of hours.  The simplest ones 
do this for several months, then ascend to the surface, stick an antenna 
out of the water, and transmit this sequence of positions back via 
satellite.  The more complicated ones have little CTDs or current meters 
on board, and go to the surface and return once every few days, measuring 
stuff as they ascend and relaying those profiles back, too.  And no, we 
don't retrieve them.  When they die, they float around forever.
  By a rough calculation, I estimate we're going to throw about $200,000 
of electronics overboard over the course of this cruise.  That's counting 
XBTs, floats and drifters, and radiosondes (weather balloons).
  I disassembled a spare radiosonde yesterday.  They're really cool 
inside.  I talked to a meteorologist: they're basically exactly the same 
as the drifters, but in the opposite direction.  And they use radio 
instead of sonar to triangulate.  The parallels between meteorology and 
oceanography are fun to contemplate.
  Somebody asked what exactly we're water-sampling for.  We get data on
dissolved oxygen, salinity, CFCs, and helium-tritium isotope ratios.  The
lab tests for salinity are much more accurate than the sensor on board the
CTD.  Oxygen, CFCs (Freons), and helium-tritium are useful for measuring
how long ago the water was at the surface.  Oxygen gets gradually used by
bacteria, helium-3 decays to tritium slowly (or is it the other way
around?), and CFCs have increased markedly in the atmosphere over the last
several decades, so younger water has more CFCs.  I'm only responsible for
the oxygen and salinity, though I might do the CFCs once in a while.  
  Why do we care how old the water is?  I'll save that one for next time.