US GO-SHIP is part of the international GO-SHIP network of sustained hydrographic sections, supporting physical oceanography, the carbon cycle, and marine biogeochemistry and ecosystems. The US program is sponsored by US CLIVAR and OCB. Funded by the National Science Foundation and NOAA.


I09N 2016 Weekly Report 3 Apr 13, 2016

From Leticia Barbero and Carmen Rodreguez **(Co-Chief Scientists)

Ahoy land-dwellers!

This week started off with an issue around the carousel of the rosette. The carousel
is the mechanism that triggers the closing of bottles (bottle tripping) in the rosette
(see pic below). On a couple of stations, problems with communication in the
rosette prevented the surface bottle from tripping. It was determined that there was
damage to the bulk connector of the carousel, which could have forced us to switch
to our spare 24-bottle carousel (thus losing some of our vertical resolution).
Eventually the connector was repaired and we now have reliable communication
with the rosette during the casts. We were also able to keep using the Y-cable that
allows communication between the carousel and the SBE35 reference temperature
sensor. Special kudos to the ODF team, especially Sergey, Matt, Ted and Courtney,
for committing to diagnosing the problem and fixing the connection with minimal
loss of time.

On the same note, we have been forced to take Niskin 12 out of the rosette because
the magnet operating the trigger mechanism is damaged and the bottle was not
tripping. Given that we are now moving towards shallower depths (all the stations
deeper than 4500m are now behind us), we think that the science objectives will not
be significantly impacted.

On this week’s report we want to highlight some of the work being done as an
ancillary project of our regular GO-SHIP work. Scientists from UC Irvine and the
Bigelow Laboratory for Ocean Sciences are conducting biological experiments using
the ship’s underway water line as well as CTD samples. The samples will be
analyzed back on land to determine Particulate Organic Carbon, Nitrogen and
Phosphorous (POC, PON and POP, respectively). POP in particular had never been
measured in these waters prior to our cruise. They are looking at differences in
C:N:P ratios and anticipate that because the South Indian Ocean Subtropical Gyre is
a nutrient poor region, the C:P ratio will be higher here than in regions such as the
equatorial upwelling region, for example. Other samples are collected from the
underway waterline to determine the surface phytoplankton community, and the
presence of genes indicating key nutrient sources. The group is also conducting
incubation experiments to determine nutrient uptake rates. This will allow them to
know whether microbes are using different nutrient sources (nitrate, ammonia or
phosphate, for example). These studies are carried out in combination with results
from trace metal analyses (we are doing roughly one trace metals cast per day) and
data from our CTD nutrient samples.

In the plot below, there is a representation of the preliminary nitrate concentration
values measured so far on the cruise and the location of 2 “regional stations,” where
more intense biological sampling has taken place. One more “regional station” is
planned close to 5 degrees North.

Amanda Fay, one of our CTD watch-standers modified a matlab program previously
coded by Seth Travis and Natalie Freeman (CTD watch-standers on I08S), that
allows us to have a look at the weather conditions predicted along our track. We
continue to enjoy low waves and great weather, and from the privilege of our calm
waters, we can appreciate the weather maps and watch as a huge storm with
predicted wave heights of up to 10 meters forms off the coast of Madagascar.

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I09N 2016 Weekly Report 2 Apr 12, 2016

From Leticia Barbero and Carmen Rodreguez **(Co-Chief Scientists)

Ahoy land-dwellers!

Week 2 of our I09N cruise seems to have flown by as we have settled into our
routine of 3-4 stations per day. The weather has been fantastic and we have been
working under calm seas. We can definitely tell that we have entered tropical waters
now. The temperatures at the sea surface are around 30C (that’s 86 Fahrenheit) and
we can feel the high humidity in the air. No one is complaining if they get splashed
with the cool, refreshing water from the deep bottles anymore.

This past week we have sampled what will be our deepest stations of the cruise,
reaching up to 6122 m depth. That is 3.8 miles deep! The sensors on our Rosie
(nickname for our rosette), however, can only withstand depths of 6000 m, so we
had to stop her short. I am sure she was wondering why we didn’t lower her to the
near-bottom, like we normally do.

While on one of these deep stations, the secondary conductimeter sensor of the CTD
stopped working (not to worry, this is why we have 2 installed). The conductimeter
provides a continuous profile of salinity, so it is an essential piece of equipment in
the package. We replaced the faulty conductimeter while in transit to our following
station, without any waste of ship time. A couple of days later we had to replace the
primary conductimeter as well - so we are now working with two brand new ones.
At the same time, the oxygen sensor started to show increased scatter. Normally,
only one oxygen sensor is installed, so it needs to provide a clean profile. We did
some minor install modifications, tested all our spares, and are now back with a
reliably functioning oxygen sensor.

We have just sailed past Cocos Islands. These small coral atolls belong to Australia
and are located southwest of Christmas Island (see picture below). Unfortunately
we were just a little too far to be able to see the atolls, but that didn’t stop us from
learning about them. Apparently, two British captains (one Scottish, one English)
rediscovered them in the 19th century and planned to settle there. One came with a
harem of 40 women. The second came shortly after with his family for a more
traditional settlement. As you can imagine, these 2 groups didn’t get along,
especially after some women from the harem started deserting to live with the
sailors of the second group. Another interesting fact? Charles Darwin stopped there
during his journey of discovery aboard the Beagle. Participating in a GO-SHIP cruise
always brings with it the chance to learn interesting little facts about remote parts
of our planet!

On Sunday April 3rd, at approximately 16:30 local time, while on station 115, we
had a loss of communications with the CTD which was then at 3000 m depth and
coming up. We recovered the package and determined that one of the conductor
cables had shorted. The winch cable has three electrical conductor cables inside that
are used to communicate with the rosette while it is in the water. Fortunately, only
one conductor is needed, so we switched to an alternate one in the winch and have
proceeded with sampling, redoing a cast on station 115. There will be no impacts to
our science plan as a result of the time invested in reterminating the cables and no
modifications have been made to our station planning.

We have also been deploying ARGO floats at select locations along the way. ARGO
floats are free drifters that stay “parked” at a predetermined depth (normally
around 1000 m). Every 10 days or so, they descend to 2000 m and profile the
temperature and salinity on the way back to the surface. These profiles, along with
the surface GPS position, are then sent via satellite to the labs overseeing the
drifters. There are currently over 3000 ARGO floats providing us with T-S data from
all the world’s oceans, and around 800 need to be deployed every year in order to
keep the array active. By the end of this cruise we will have deployed 8 new floats.