Monday, May 12, 2014

Back on land

The Palmer made it to Tahiti safe and sound! Unloading the ship went smoothly and all of the scientists and crew enjoyed celebrating our arrival in Tahiti with some food and beers at the Bora Bora lounge in Papeete. I spent a few days diving and exploring in Tahiti and Moorea and am back in San Diego, ready to get to work on the data from the cruise and on my thesis project.

Here is the movie we made of the cruise. Enjoy!

Sunday, April 27, 2014

Measuring ocean currents with sound!

Well we are more than 5 weeks into the cruise and only 8 days to go! We
are currently at 28 degrees South heading into tropical waters and it
definitely feels like it! After more than a month of clouds, rain and
grey we are finally being rewarded with some warmth and sunshine.
Luckily there is still a nice sea breeze blowing and a few clouds so it
isn't too hot. This week I am going to write a bit about a very cool
instrument that I have been running on board the ship, the Lowered
Acoustic Doppler Current Profiler (LADCP; the blue and yellow instrument
in the photo). That's a bit of a mouthful isn't it?

What is an LADCP?
Let's break it down: Lowered = the instrument is lowered in the ocean
with the CTD package; Acoustic= sound; Doppler = refers to the Doppler
shift. Current = ocean current; Profiler = measures a vertical profile.
So the LADCP measures ocean velocities using sound.

How does it work?
The Doppler effect is the change in frequency of a wave when the
receiver is moving relative to the source of the wave. This often
happens when a vehicle with a siren passes by. As it approaches the
sound waves are "bunched up" and the sound appears higher pitched to
someone listening than when the vehicle is moving away and the waves
appear more "spread out". In the case of the LADCP, it emits a ping
sound at a set interval (usually once or twice a second) into the water,
which is reflected by particles in the water about the same size as the
wavelength of the sound wave, usually plankton and other small
organisms. This reflected wave is read by the LADCP instrument and the
difference in frequency between the emitted wave and the reflected wave
indicates the motion of the water relative to the instrument. This is
complicated by the fact that the LADCP instrument is not motionless but
it moving with the ship and up and down with wave motions. To get
absolute ocean velocities this motion needs to be calculated and removed
from the Doppler signal. The LADCP contains a compass and sensors to
measure the pitch and roll of the instrument so its motion can be
calculated. There are several different methods used to get absolute
horizontal velocities and they each have pros and cons. There is even
some recent work on a method using LADCP data to calculate vertical
velocities in the ocean, which are very difficult to measure because
vertical velocities tend to be very small, compared to horizontal
velocities and vertical wave motion.
The Palmer and most other research ships also have an ADCP (not lowered
with the CTD) mounted on the ship bottom, which constantly measures
velocities in the upper ocean as the ship moves. ADCP's can be used in
many other ways, including measuring the discharge from rivers, locating
underwater "tornadoes" that might damage deep water oil drilling
activities, measuring flow through sewer pipes (gross but important!)
and measuring flow of meltwater from icebergs.

What do the results look like?
The resulting LADCP velocity profile can be noisy and have quite large
errors due to difficulties with removing the ships motion. However, you
can see the speed and direction of velocities from the surface to the
seafloor. The shipboard mounted ADCP measures surface currents so we can
see a map of the surface currents along the ship track and see when we
are crossing sharp fronts with strong currents and other features.

Why measure ocean velocities?
Finally, why do we measure ocean velocities in this complicated way?
Well it is actually very difficult to measure instantaneous velocities
in the ocean. Average velocities can be calculated from the trajectories
of drifters and floats. Also we can use a relationship between the
density gradient in the ocean to velocity to determine geostrophic
velocities in the ocean. But these methods are generally only useful
for very large-scale ocean currents. LADCP data is useful to see
detailed structure in velocity profiles and see how the velocity varies
over time and in space. This is important to understanding physical
processes in the ocean on small and larger scales. It can also be used
to calculate transports of water, which are important for determining
the amount of heat, nutrients, carbon and other properties transported
by the ocean.

Stay tuned next week, as I'll be wrapping up when we arrive in Tahiti
and will be sharing a video of the cruise that I have been working on
with some other scientists on the ship!

Sunday, April 20, 2014

Happy Easter from the Palmer!

Happy Easter from the Southern Ocean!! Not only are we celebrating
Easter today, but also crossing 40 degrees South latitude heading toward
the tropics!
We had a lot of excitement today- some Easter bunnies came out to
deploy the CTD, there were baskets of eggs, bubbles, and a special hunt
for rainbow wombat droppings filled with candy!

Challenges at Sea

I can't believe that we are already more than 4 weeks into this cruise
already! Once you get into a rhythm and are busy working time really
flies by! Unfortunately though, we are only halfway along the P16S line
to Tahiti and we only have just over 2 weeks to go (remember we did have
11 days of steaming from Hobart before we started the line). This means
that we are quite a bit behind schedule and have had to modify the plan
to sample every 2/3rds of a degree instead of every half degree of
latitude. We have had a series of challenges that have meant a lot of
waiting and troubleshooting that put us behind schedule. This isn't
because the cruise was poorly planned or because of big mistakes, it is
just the nature of working in such a remote and challenging environment.
Our range of options to respond to problems is limited to what materials
and skills we have available on the ship. Luckily, the crew and the
science party have an enormous amount of experience and expertise and so
we have managed to overcome all of the difficulties encountered so far.

Weather has been the biggest challenge so far. The Southern Ocean, no
matter what season, is one of the wildest parts of the global ocean with
intense westerly winds bringing strong storm systems and the world's
largest and strongest current, the Antarctic Circumpolar Current. The
weather also varies across seasons with stronger winds in winter than in
summer. This has meant that historically, most shipboard sampling of
the Southern Ocean has happened in summer (Dec-Jan in the Southern
Hemisphere) meaning that there is a bias in the existing data toward the
calmer (relatively!) summer conditions. This cruise is happening in
Autumn so the weather is probably worse than we might have had in summer
but it is important to get measurements at all times of the year.

We encountered what seemed to be an endless string of low-pressure
systems during the first few weeks of the cruise. Storms like these
happen all the time in this part of the world but it is unusual to have
so many for a continuous period of time. Many people on the ship who
have spend hundreds of days, or even years at sea commented that this
was the worst run of bad weather they had ever had on a cruise.
Unfortunately for us, the weather was too rough to do CTD profiles
during this time so we were stuck with the options of staying put to
wait out the weather, or moving elsewhere in the hope that it might be
better. Another complication is that although we receive weather
predictions from several sources, the predictions are not very accurate
in this region mostly due to the lack of good data included in the
weather forecasting models. So we know what the current weather is but
we really have a very limited idea of what will happen in the next few
hours and next few days. In the end, we spend quite a bit of time going
in circles, fleeing north and then backtracking south rather than just
sitting still to try to get to a spot where we could work and also to
minimize the rocking of the ship.

Another major problem we have encountered on the cruise is damage to
the wire that is used to lower the CTD into the water and transmits data
from the CTD to the ship. The wire has to be able to withstand very high
tensions and large wave motion can cause spikes in the tension, which
puts the wire at risk of damage. We discovered on a very deep cast that
the wire had been damaged at around 4 km along the length of the wire
and after careful examination the crew agreed that the wire was too
damaged to work with as we could risk losing data or losing the whole
rosette at the bottom of the ocean! The ship has a second winch with an
undamaged wire outside so we were left with two options: 1) transfer all
of the 10 km of wire off the spool and roll on the wire from the outside
winch or 2) move the CTD from the inside winch to the outside winch.
Both of these were ambitious tasks and could be very time consuming.
After all of our delays due to weather we couldn't afford to waste any
more time if we want to make it to Tahiti on time! In the end, a
decision was made to attach the CTD to both the inside and outside wires
at the same time and let out the CTD on one wire and bring it back in on
the other (the outside winch is only about 20 feet further down the boat
than the inside winch). No one on the ship had ever done a trick like
this before but it worked perfectly and only took a few minutes! It was
very impressive and I have video footage that I will share at the end of
the cruise. We had a few minor problems with the electronics after that
but once that was resolved nothing has gone wrong for many days! From
now on we will be sampling outside which brings a whole new set of
challenges (getting wet!) but it is great to get outside more,
especially as we move north and the weather improves. Fingers crossed we
don't have any more troubles and it'll be smooth sailing the rest of the
way to Tahiti!

Thursday, April 10, 2014

Fun at Sea

We are now in the middle of the Antarctic Circumpolar Current at 55°S,
150°W! We had A LOT of bad weather last week but we have managed to make
up to station 25 on the P16S line northward (with a bit of a detour back
south after a storm) and only skipped two stations along the way. Last
week I wrote about the science goals on our research cruise and how we
go about taking measurements of the ocean. This week I am going to talk
about what we do when we are not doing science: having fun! A research
vessel can be a very isolating place, as we can't go outside for a walk
in the park on the weekend, in fact we don't have weekends at all. We
are stuck for 50 days in a confined space with the same people. We also
have very limited connection to the Internet (15 MB each daily which
will last about 3 checks of your Facebook feed…) and only one satellite
phone shared between everyone on board. So we don't have the normal
forms of entertainment that we are used to having on land. However, the
Palmer is well equipped to keep it's crew and scientists entertained and
happy and we find MANY ways to entertain ourselves while we are working
and in our free time. In the past week especially we have had a lot of
foul weather, which meant we couldn't collect any samples, and so there
were many, many hours of free time. Here is an outline of some (but not
a comprehensive list) of the ways we keep ourselves busy and keep morale

Being in such a confined space for a long time means it is very
important for us to get some exercise in the gym to stay fit and healthy
(and for some of us to stay sane!). The ship has a very nice little gym
(in comparison to other ship gym's that I have seen) with a bike, rowing
machine, step machine and a weight machine and dumbbells. There is also
a treadmill and…. wait for it… a sauna!! The sauna is wonderful and
relaxing, especially in a polar climate!

Motivation to work out can be hard out here, especially when you are
tired from working and used to exercising outside in the sunshine (not
much of that in the Southern Ocean). So along with a few other students
on the cruise, I came up with a plan to have a team competition to see
which team could travel the furthest distance on the bike, treadmill,
rowing machine or step machine. We named the competition the "Meters
Club" and the Chief and Co-chief scientists lead the two teams.
Currently the "P16Stacked" team is in the lead but the "Kill-ometers"
aren't far behind and are catching up! The prize for the winning team is
as yet undecided but may involve a chilled beverage when we get off the
ship in Tahiti.

While there are some people on the ship training for a marathon, some
of us are training for ultimate movie marathons! There is a movie lounge
on the ship with extremely comfortable couches (more comfortable than
the beds!), a big screen and an enormous collection of movies on hard
drive, DVD and even VHS!! Also there is a Fussball table and a few
guitars (more about music on board soon). There are movies being played
pretty much 24 hours, although a lot of the time there are more of us
sleeping on the comfy couches in the lounge than actually watching

Board games, cards and puzzles are another popular form of
entertainment at sea. One of the crew members prints a large copy of the
New York Times daily crossword for us to work on as a group but it is
usually finished in less than 10 minutes and if you aren't there in time
you'll miss out (sometimes we do multiple a day so everyone gets their
chance)! There are also a few game tournaments going on: the "Cribbage:
Tournament of Champions" ( if you are like
me and don't know a lot about cards) and the "World Series of Cornhole"
which is yet to commence. There have been a lot of intense Cribbage
games going on around the place!

I have been amazed by the amount of musical talent of the scientists
and crew on board the RV Palmer! Mike (NASA scientist) is lead singer
of a band in D.C., Lynne (Chief Scientist) is a pianist on the side,
Barry (Electrical technician) repairs guitars and plays well and John
Calderwood (CTD deck leader) has the voice of an angel! There are many
more talented musicians amongst us (or at least a lot of us that really
enjoy music, especially singing) and my fellow night shift CTD
watchstander's Tyler and Isa and I do sing-alongs all night long for fun
and to stay awake. I'm not sure how much our talent is appreciated
though as George (Electrical technician) ran into the room and shot us
with a Nerf gun ( one morning after we woke
him with our angelic singing. Mike brought recording equipment on board,
which is totally awesome! I've been recording a lot of video footage
using Go Pro cameras and we are working on some songs to go with the
video so stay tuned for the resulting masterpiece at the end of the