Instead, we've got rain by the bucket! Literally!
Day 11
This day was a bit of a bipolar experience. Since the night
before, we were heading further south in search of rain. For much of the
day, people were just sitting around. We caught up on some lab work,
thought out some contingency plans, and kept an eye on the radar. It was
quiet and a bit tense as the rain system we were chasing kept moving south and
we couldn't quite catch up with it.
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| Our chief scientist keeping an eye on the radar as it begins to rain |
Then, around 5pm, we started getting a few sprinkles. The
sky wasn't too dark and we weren't sure we had really found the rain we were looking
for. Gradually, the rainfall began to increase and it rained steadily for
good, long time. A wave of relief and energy swept through the ship.
Our rain gauge recorded about 1.2cm of rainfall, and, due to the low wind
conditions, we managed to completely fill our rain bucket! And there was
much rejoicing.
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| Gazing out at the stormy seas |
A few hours later, after the rain had stopped, we jumped into
action. We hadn't done any before sampling of this location, having
prioritized the quest for rain. We made up for it by doing two CTD casts:
one right outside the area that had been rained on, and one right smack in the
middle of it. After we did the second cast, we deployed one drifter to
keep track of that water mass so we could sample it again later. Then we
dropped the towfish in the water and circled the drifter for a few hours
collecting water late into the evening.
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| Sampling the CTD cast in wet weather |
Day 12
After a late night of sampling, it was back up and at it again
early this morning. We did another series of CTD casts, one normal and
one trace metal, followed by a PAR cast before pulling the drifter back on
board and heading north. After the rain stopped the day before, the winds
picked up a good bit, creating some decent waves. Getting the drifter out
of the water proved to be a bit of a challenge, and everyone involved ended up
wet.
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| Catching the drifter in some decent sized waves |
Thankfully we had the rest of day to recover from the intense
sampling and lack of sleep. We are steaming back to our eddy #2 to pick
up sampling there again tomorrow. Everyone is using the time wisely to
catch up on lab work and prepare for our last spurt of sampling the next few
days before heading home.
Aerosol sampling
I've mentioned that we've been sampling aerosols most nights we've
been out. In order to sample, we must be headed into the wind so that
there is no contamination from the ship's smoke stacks. Since we can't do
much other sampling while we are moving, we've been doing aerosols at night
while most people are asleep.
The aerosol sampling is run by a graduate student who is using the
data as part of a Masters project, and is assisted by a visiting undergraduate
trainee. These lucky two stay up all night keeping an eye on the sampling
and sleep during the day while the rest of us are running around making noise.
It's a tough job being on the opposite schedule of everyone else, but
they've done great so far.
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| Preparing the aerosol sampler to run |
The aerosols we are interested in are basically different types of
land-based pollutants. Our scientific equipment isn't measuring the types
of aerosols - its collecting iron particles that are present in the air.
That means this project falls under the trace-metal clean category.
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| Setting up the aerosol sampler |
The aerosol sampler consists of a series of filters. Air is
pulled through the filters, and each filter collects particles of different
sizes, from large to small. It takes several hours of continual running
to collect enough to measure. Once enough air has been filtered, each
filter is taken out and cut into smaller pieces. Then, the samples are
"leeched" with deionized water (clean water), so that the particles
on the filter are released into the water and dissolved. Now the iron
from the air is in a form to be analyzed in a trace metal clean lab.
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| The aerosol crew working in the lab |
We already know that iron is a micronutrient for phytoplankton. Even if it isn't limiting, we are still
interested in where the iron comes from that gets in the surface ocean.
We think a lot of it is deposited from the atmosphere, but there aren't
many measurements. The goal of the aerosol sampling is to get a better
idea of how much iron is deposited. There are several questions we can
answer with this analysis.
By comparing the amount of iron in the air to the amount in the
rain, we can see if iron is more likely to be deposited in wet or dry
conditions. There is another aerosol sampler running on the Eastern Shore
area of Virginia,
collecting the same types of samples. If we compare the two, we can
determine how much iron leaves the air between the coast and the open ocean.
We can also determine potential types of pollution and source locations
by using pollutant maps to track where the aerosols originated.
Most of this work will be done after the cruise is over, as part
of a Masters project. But for now, the data we collect on aerosols here
will help us specifically understand this system, and understand the importance
of rain in depositing iron to the surface ocean.
As always, thanks for reading. Stay tuned for the (most
likely) exciting end to our cruise - see how it all works out!
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