Submitted by Anonymous on Wed, 03/23/2011 - 14:59
Forums
Seawater Property Changes in the Southern Ocean

Do you have a set of "standard" depths at which you are collecting samples with the rosette or is it unique based on previous water profiles collected to each station?

Wed, 03/23/2011 - 18:28

Juan Botella

Hi There, that is a great question! Thanks for sending it. I asked Jim, our chief
scientist and here is what he said.
We do have standard depths, but we have three depth sets that we rotate.
We always get a bottle as close to the surface as possible, around 5 m.
This is sometimes hard to do with large waves, because the rosette should
not be in an out of the water as this creates slack and tension on the
cable which can make it snap.
We always get a bottle 10 m above the bottom, wherever that is, and another
bottle close to this bottom water in case there is an interesting bottom
feature.
We sample roughly every 20 m within the first 100 meters of depth. We then
switch to every 50 m until we reach 500 meters, and then every 100 meter
until 1300 m deep. From there is roughly every 200 to 300 meters until we
get to the bottom. We are somewhat constrained by having only 36 bottles
(although this is an extremely large rosette. Most have a lot less bottles
and smaller).
The surface layers are sampled more because water properties change more
there than in deeper waters.
What I find more interesting is the rotation of three schemes. Jim says
that if we were to sample at exactly the same depth in every station, we
would miss any feature that is in between those depths. What scientists
have figured is that if we have nested depths we can resolve those features
better.
What do I mean by nested depths? Here is what they look like for the first
100 m or so:
Station 1: 5m, 20m, 40m, 65m, 90m
Station 2: 5m, 25m, 50m, 75m, 100m
Station 3: 5m, 35m, 60m, 85m, 110
We have better vertical resolution when we put them all together than
sampling always at the same depth.
Hope that answers your question. Thanks for writing.
Juan.

Thu, 03/31/2011 - 17:56

Anonymous

Thank you for your answer. I know that your location has greater depths than where I worked as a TAS along the California current, so I was attempting to work from within my own sampling experience. Have you captured a photo of the rosette on deck with the deep samples causing condensation as compared to the surface canisters or is it far too cold once it reaches the air? It is one of the images that really impacts my students when we investigate thermohaline circulation.

Thu, 03/31/2011 - 20:44

Juan Botella

Hi there, Surprisingly enough, for me, not for the scientists, the coldest
temperatures we have had are below the mixing layer. This corresponds to
the winter mix layer. The deeper waters are warmer as seen by the XBT.
We do not see the condensation you describe because the air is extremely
dry. I did see that condensation on a WOCE cruise in which I participated
when I was a graduate student back in 1997 on the Caribbean sea.
Thanks for writing,
Juan.