Subject: FOCE review
From: "Edward Peltzer" <[email-masked]>
To: "Adina Paytan" <[email-masked]>
Cc: "Bill Kirkwood" <[email-masked]>, "Kent Headley" <[email-masked]>, "Peter Brewer" <[email-masked]>, "Jim Barry" <[email-masked]>
Date: Tue, 15 May 2012 10:50:47 -0700 (PDT)

Adina:

Good to see you yesterday and thanks for coming to the review and
contributing to the discussion.

You are, of course, correct that two CO2 parameters are needed to fully
qualify the CO2 system.  We will add that to the x-FOCE requirements.

After you left I spoke with a few folks at MBARI about this and a couple
of ideas came to mind:

1. The Contros pCO2 sensor is a good candidate for real-time measurements
especially of the background water in situ.  And there is the new Aanderaa
sensor coming-out soon; someone should have a look at that and see if it
is adequate.  We have had bad luck with the SAMI sensors in terms of
producing usable data; plus their need for reagents limits both the length
of deployment and frequency of measurement.  One of these sensors
(whichever folks choose) per site should suffice.

2. For sw-FOCE at HMS, I think we should consider adding a small CO2
equilibrator to the inlet line so that we can measure pCO2 in real-time.
I built one of these with Catherine Goyet many years ago and ran it at
sea.  By cycling between different sources, one can measure pCO2 of the
surface seawater, xCO2 of the air (both inside and outside the pump
house), and reference gases to keep things calibrated.  Combine this with
an inline pH sensor and we can have the CO2 system on the ESW supply line
pretty well nailed down.

3. Adding a Contros (or other sensor) to the experimental chambers will
get expensive if we do everyone, but having it in one might be useful.  We
will need to talk about this more with the team.

On another topic, I've attached some screen grabs from our CO2 release
trials to show how fast conditions can change inside the flume and from
this you can infer how often we need to sample.  In each figure, the top
trace is the six pH sensors, the bottom is the CTD temp outside (blue) and
inside (red) the flume.  The 174...bmp figure shows temperature drifting
along slowly and then a very abrupt 0.1 deg C shift in about 5 mins.  The
pH_w_Temp.bmp shows the temperature cycle over a 5 day period and one can
clearly see the tidal influence on temperature cycling and a daily range
of 0.5 deg C -- which is quite a lot at 890m depth.  In both figures, the
CTD sampling is once per minute (0.01666... Hz).  For our SeaBird CTDs,
this is the fastest rate they go in the non-profiling mode.  WE could go
slower but I think then we will lose some of the finer detail.  I think it
is better to log all this data and then box-car average in post processing
to suit the individual investigators needs.

Just some thoughts.

Ed.

--------------------------------
Dr. Edward T. Peltzer
Monterey Bay Aquarium Research Institute
7700 Sandholdt Road
Moss Landing, CA  95039-9644

Phone: 831-775-1851
Fax:   831-775-1620

Email: [email-masked]
http://www.mbari.org/staff/etp3/ <http://www.mbari.org/staff/etp3/> 
--------------------------------

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