Where are we at?

Biologists at sea sample the water
in several ways depending on the
organisms of interest. A common
method of sampling for small
protists, including phytoplankton
and protozoa, is the CTD cast. A
rosette of Niskin sampling bottles
is lowered into the sea on a coated
steel cable attached to a winch.
The winch used for CTDs on the
N.B. Palmer is about seven feet
tall and can hold more than 3,000
meters of cable, and the crane can
support 22,000 kg (10,000
pounds). The winch and crane are
located in a room on the starboard
side of the ship and a large door is
opened to deploy the rosette.
Within the steel cable that supports
the heavy rosette, there is an
electronic cable that allows the
Niskin bottles to be closed
automatically from the ship with a
flip of a switch. The bottles can be
closed all at once or individually at
selected depths. Electronic
equipment that continuously
records data and relays them to
the ship also is attached to the
rosette. CTD stands for
Conductivity (salinity),
Temperature and Depth which are
always recorded, but other
sensors that measure fluorescence
(an indicator of chlorophyll and
thus photosynthetic organisms),
transmittance and other
oceanographic information are
commonly attached. With this data
scientists can make informed
decisions about the depths at
which they should close the water
bottles.
Our group is particularly interested
in the diversity of protists in the
Ross Sea. We collect some of the
water from the Niskin bottles
directly through a series of filters
that separate different size
fractions of the plankton (>202
µm, >64 µm and > 0.8 µm) for
DNA and RNA analyses. Some of
the water is collected directly into
bottles for microscopic
examination and used to start new
cultures of protists to add to our
Antarctic culture collections.

November 3, 2003