If you want to see our cruise track and current location, you can check out this website that tracks most ships, including ours.
Below are our normal daily updates. Since not too much
happened, I've included a section at the end to start explaining the science
that is happening on board in more detail. This time, I'll be talking
about trace metal chemistry.
Day 5
For the most part, this day looked a lot like day 4. We had
the aerosol sampler out overnight, and were headed south, into the wind.
Around 2am, we turned it off and returned to the center of the eddy we've
been in for the past few days. After another sunrise CTD cast, we
deployed the towfish and began towing it in a circle around our drifters.
At one point, it began raining really hard while the towfish was
out. So there was a mad scramble to get the rain collector out to catch
more rain. It ended up being only a brief shower, but we got a bit of
rain out of it. Then, we finished up with the towfish and proceeded to do
the daily noon PAR cast. After that, we completed another shallow CTD
cast to get the conditions after the brief rain event.
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| Rather wet scientists after dashing out in the rain to turn on the rain collector |
Up until this point, we hadn't been getting quite as many surface
samples as we wanted from the towfish. So when we did the shallow CTD
cast, we decided to sample from the ship's underway system at the same time.
The underway system is always on and samples at the bottom of the ship.
However, there is a good chance that the samples wouldn't be
representative of the surface water, since there are probably extra organisms
growing in or near the sampling system. We compared the samples to the
CTD surface cast, and it turned out the values did not match, so we probably
won't use the underway system for sampling nutrients or chlorophyll.
Our final task of the day was to retrieve two of the three
drifters. We decided to leave one out to continue collecting data, but
didn't want to risk more than one with Bertha approaching. We will return
for the last one after Bertha has passed.
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| Pulling the drifter and attached drogue out of the water |
Day 6
Not much went on today. We used this time to catch up on lab
work and relax. We arrived back in port at around 2pm, and spent time
calling friends and family and catching up with the internet while the crew
fueled up the ship and did some maintenance work.
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| Passing the lighthouse on our way back into port |
Trace metal oceanography
In the cruise updates, I've mentioned deploying our trace metal
CTD, at least until the winch for it broke. Now, I'd like to give you a
general idea of what I mean when I say "trace metal".
I've already talked a bit about nutrients and phytoplankton. Measuring nutrients is one of the main activities for this
cruise. Major nutrients in the ocean are essentially various forms of
nitrogen, phosphorus, and carbon. If enough nutrients of each type are
available, phytoplankton will grow and reproduce. If one type is missing
or used up, growth will slow and stop. We call the missing type the
"limiting nutrient". In oceanographic history, scientists
discovered a quandry. They found large amounts of all nutrients, but for
some reason, the phyotplankton weren't growing and using them up. The
regions where this phenomenon occurred became known as High Nutrient Low
Chlorophyll (HNLC) regions. Something besides the nutrients was acting as
the limiting factor.
It was eventually discovered that along with the major nutrients,
phytoplankton also need incredibly small amounts of other nutrients, called
micronutrients. One of these was iron. There is not a lot of iron
floating around in the ocean, but it normally doesn't act as a limiting factor
except in certain HNLC regions.
So, once it was discovered that iron was another important, albeit
small, nutrient, scientists set out to measure it as well. This was where
they ran into problems. Iron is available is such low concentrations that
any measurements were contaminated. The ship itself contaminated the
water, any metal on the CTD or the chain or the winch also contaminated the
water. Basic laboratory equipment and normal lab coats and gloves
contaminated samples. It was virtually impossible to get an accurate iron
measurement with standard oceanographic equipment.
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| Working in the trace metal clean laboratory on board - Photo courtesy of Bettina Sohst. |
This was where "trace metal clean" protocols came in.
Scientists figured out how to make their working environment clean enough
that accurate iron measurements could be made. They set up clean
laboratories with special ventilating systems to keep any traces of iron out.
Plastic bottles used to collect samples are rigorously cleaned, using
acid baths that leave no trace behind. Special CTD set-ups were designed
to ensure no contamination of the ocean during sampling.
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| Trace metal CTD about to be deployed |
In our case, we have a trace metal clean CTD and the towfish is
also trace metal clean. There is a clean laboratory set up in a
"van" on the ship - it is a portable lab the size of a shipping
container that can be attached to the back deck. When we do a trace metal
cast, the trace metal CTD goes in on the opposite side of the ship as the
normal CTD, so there is no contamination. The trace metal CTD doesn't
collect any samples in the upper 10m of the water, to avoid any contamination
from the ship. In order to sample the surface water for iron, we use the
towfish. It is put in the water while the ship is moving, and is held out
to one side, so that it collects water untouched by the ship. Every time
we use it, it gets flushed with seawater before any samples are collected.
When not in use, all nozzles and openings are covered with disposable
plastic to keep contamination to a minimum.
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| Preparing to deploy the towfish |
Now, when I mention our trace metal CTD, you will know that I
really mean a "trace metal clean" CTD where samples can be taken to
measure the micronutrient iron.
Coming up, we're back out at sea, taking more measurements and
we’ll be deciding soon where to go next.
More posts in this series:
Upcoming Cruise
Cruise Delays
Upcoming Cruise, Part II
Update #1
Update #2
Update #3
Update #5
Update #6
Update #7
Update #8
Update #9
More posts in this series:
Upcoming Cruise
Cruise Delays
Upcoming Cruise, Part II
Update #1
Update #2
Update #3
Update #5
Update #6
Update #7
Update #8
Update #9
