Response To Lundie

Hi Lundie:

When we see humpbacks, we see groups of several. Sometimes it is
difficult to count them. The last group looked to be about 5 animals?

As for your Secchi disk question, let’s first make sure all our readers
know what a Secchi disk is. It is a device used to measure water
transparency. The disk, usually made of wood or plastic, is divided into
quarters which are painted alternating black and white for contrast. It is
lowered into the water at mid-day until it can no longer be seen. The
depth where it appears to disappear is recorded.

Now, we’ll admit you stumped us. It is not a measurement we normally make
and none of us could remember the conversion from oceanography 101. After
surveying most everyone on board and not finding an answer to your
question, we did what any self respecting undergraduate would do. We
searched the copy of Wikipedia that is maintained on the ship’s server.
It says that multiplying the Secchi depth by 3 will approximately give the
depth of the euphotic zone. During most of our CTD casts, measurable PAR
is reaching 50-60 meters depth. Dividing by three gives us a Secchi depth
on the order of 17-20 meters. Whew, we almost had to get out the
calculator for that one!

1 Comment:

  1. Lundie Spence, PhD., Director said...
    How did the Secchi experiment go? How deep was the disk and you could still see it?
    Once in the mid Atlantic we lowered a large Secchi to about 100 feet and could still see it. Very transparent water.
    I assumed that the Antarctic waters were rich with life. Not as clear.


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