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!
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