the Antarctic Circle at 66.33°S to the start of the CLIVAR P16S line at
67°S, 150°W a few days ago. Now we are moving slowly northward along the
P16S line, sampling at stations up to four times a day, weather
permitting. So what is it that we are measuring in the ocean and how
are we measuring it?
What:
This cruise is part of a large international repeat hydrography program
(http://www.go-ship.org) that collects measurements along lines across
all of the global ocean basins, repeating the same lines every decade to
see how the ocean is changing. The P16S line was completed in 1991 and
again in 2005. We measure the physical and chemical properties in the
ocean from the surface to the bottom, and this global data is essential
for oceanographers to understand ocean circulation and the carbon cycle
and how it is changing over time. It is also very important to have
high quality ocean measurements to help calibrate sensors and to
validate and improve the performance of global climate models.
The second important role of this cruise is to deploy 12 autonomous
Argo (www.argo.net) profiling floats which drift along with ocean
currents below the ocean surface and come up to the surface every 10
days and send temperature, salinity and pressure data to satellites. We
are also deploying surface drifters that send their location to
satellites to measure currents and a team of NASA scientists is making
measurements of chlorophyll (an indication of how productive the water
is) to validate measurements of ocean color made by satellites.
How:
These sound pretty straightforward right? But it takes a whole team of
scientists, plus the crew members on board the ship many hours of
planning and hard work to collect all these measurements. The ship
operates 24 hours a day (ships are very expensive to run, so we use all
the time we can get!!) so everyone is assigned to a 12 hours shift. The
chief and co-chief scientists (Lynne Talley and Brendan Carter) are in
charge of all the science operations, and communicate with the ship's
Captain and the MPC (Main Point of Contact) to decide where and when the
ship will stop to take measurements.
All of the ocean measurements and water samples are collected using a
CTD (Conductivity, temperature and pressure) mounted on a rosette, which
has 36 bottles that can be closed at specified depths. The winch
operator supervised by the MT's (Marine Techs) lower the rosette into
the water, while members of the science team operate the CTD. This is
where I come in. I work as a CTD watchstander with 2 other graduate
students and our job is to prep the rosette before it goes into the
water, control collection of water samples while the CTD is in the water
and manage the sampling after the CTD is back on deck. When the rosette
is back on the ship, it's a race for water samples! There can be more
than a dozen different chemical properties being measured at a station
and so everyone is competing to collect water samples and it can get
very crowded and confused. One of the other CTD watchstander's or myself
acts as the Sample Cop, policing everyone to make sure they get water
from the right bottle in the right order. It can get very wet while
sampling and on many ships this happens outside on the deck where it can
be very cold. However, the Palmer is super fancy and designed for
working in polar conditions so the CTD is deployed and recovered from a
room with an enormous door so we are able to sample comfortably from
inside (although the sample water can still be below 0°C because the
salt in the water prevents it from freezing at that temperature!). All
the samples are taken to different labs on the ship, some inside the
ship and some on portable containers on the decks outside.
Finally, after the rosette is back on deck and we are leaving a station
we can deploy floats or drifters over the side of the ship. These are
(carefully) thrown overboard and are not recovered. The NASA team also
collects measurements with instruments deployed over the side and the
back deck.
BUT a research cruise is not all hard work! When we are waiting to
arrive at the next station, or the weather is too rough to do anything
we find ourselves with a LOT of spare time on our hands and not many
places to go. Next week I'll be writing about the many ways we spend our
time and keep ourselves entertained on the ship!
(Photos courtesy of Lynne Talley)
