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IRON TANKS &
DISTRIBUTION
 | Seawater will be added to 15,000 liter (4000 gallon) tanks
containing 3,175 kilograms (7000 pounds) of iron sulfate. This
will be distributed, along with the inert gas
sulferhexafluoride (SF6), by a pumping system into
the ship’s wash at an approximate depth of 5m. The iron
patch will be laid out in a square pattern covering an area of
15 km x 15 km. This should result in an initial iron
concentration of approximately 1 nM (10-100 times ambient).
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DRIFTERS
 | A
Lagrangian drifter attached
to a holey sock drogue,
instrumented with GPS, optical and chemical sensors and
telemetry will be deployed to mark the center of the patch.
The ship will use the buoy position, in combination
with SF6 concentration as
markers for sampling sites. The drifter will provide
continuous reference positioning as well as fluorescence and
nitrate, and CTD (Conductivity, Temperature & Depth) data.
If the drifter buoy should slip relative to the center of the
patch, a second buoy will be deployed in the center of the
"marked" patch and the original buoy recovered.
In addition, an instrumented drifter will be placed in
a proximal control area not enriched with iron to monitor
ambient changes in the above parameters.
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TM
& STANDARD ROSETTE
 | We
will occasionally stop to take vertical profile samples both
in and out of the patch.
We were recently able to show that our “mini TM
(Trace Metal) Rosette”, employing 2.5 L Teflon coated niskin
bottles and teflon spigots could collect uncontaminated iron
samples on a trip across the N. Pacific central gyre. A
standard CTD Rosette (20 L bottles) will
also be used for the collection of
nutrients, phytoplankton, oxygen, and other samples.
These vertical profile measurements will provide insight as to
how the chemical, physical and biological parameters are
distributed throughout the water column.
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SEASOAR,
Fe FISH & SF6 SHIPBOARD MAPPING
 | The SeaSoar is
basically a towed, undulating platform that will be outfitted
with various physical, biological and chemical sensors, as
well as a pumping system to deliver seawater to the ship. It
will provide real time information from the sensors as well as
seawater for shipboard mapping of nutrients, SF6,
pCO2, FRRF (Fast Repetition Rate Fluorometry).
A CTD, fluorometer, and ISUS (In Situ Ultraviolet
Spectrometer) are among the many sensors that will be put on
the SeaSoar to provide real time data. ISUS was developed here
at MBARI. It is a chemical sensor that relies on the
absorption of UV light by various constituents in seawater. We
are particularly interested in its ability to measure nitrate
in real time. Most shipboard mapping techniques have some lag
time associated with them.
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 | The shipboard mapping of nutrients will be performed using
standard FIA (Flow Injection Analysis) techniques. We expect
to see a decrease in nutrient concentrations in the patch
relative to outside of the patch as the bloom develops.
Likewise we expect to see a decrease in pCO2
concentrations. The FRRF measures the efficiency with which
photosynthetic pigments in phytoplankton cells harvest and
utilize light. FRRF was the first parameter to show a response
to iron additions in previous experiments. Measurements of SF6
(by gas
chromatography) will provide a quick means of insuring that we
are either in or out the patch and that the drifter is
remaining central to it. SF6, unlike iron, is
inert and can be measured at extremely low levels (fM) making
it an ideal tracer.
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 | Seawater
for the shipboard mapping of iron will be pumped
using an all Teflon pump, from an intake on a separate towed
platform (The mighty TowFish), and delivered to a trace metal clean
manifold. Iron concentrations will be determined using FIA
with a detection limit near 0.02 nM. We expect to see iron
concentrations decrease rapidly due to biological uptake.
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PITS
& LARGE VOLUME FILTRATION PUMPS
 | MLML
Muti-Particle Interceptor Traps (PITS) will be deployed at a
depth of 75 both in and out of the patch. These traps provided
a wealth of new information about carbon and trace metal flux
during the multiyear VERTEX (Vertical Exchange and Transport)
program. The R/V Melville will retrieve the PITS at the end of
the experiment.
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 | Multiple Large Volume Filtration Systems will also be
deployed to collect sinking particulates. These are individual
in situ pumping/filtration that can be deployed at multiple
depths per cast to provide information on how particle flux
changes with depth. If iron fertilization is truly a means of
sequestering carbon to the deep ocean then we should see an
increase in carbon flux in the patch relative to out.
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RAD
VAN & INCUBATORS
 | The Radiation Van is a fully self-contained portable
laboratory where all isotope work will be conducted. Primary
production, the rate at which phytoplankton cells are
incorporating carbon into organic matter, is of special
interest. Samples are collected and inoculated with a small
amount of low level radioactive inorganic carbon. They will
then be placed in decktop incubators at ambient light and
temperature levels for a period of time in which
photosynthetic processes will convert the inorganic carbon
into organic carbon. The samples are then filtered to capture
the cells and the amount of radioactive carbon incorporated
into organic carbon can be determined using a liquid
scintillation counter (LSC).
The LSC measures the amount of light produced when
radioactive carbon decays which is directly proportional to
the amount incorporated.
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Decktop Incubators are simply large boxes in which surface
seawater is circulated to maintain seawater temperature. They
are usually covered to various degrees with fine mesh netting
to allow light levels from different depths to be mimicked.
T-hey provide a shipboard access to rate process experiments.
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Additional Information for USCGC Polar Star
Methods
include:
Natural Thorium-234 for particle export
Major elements of upper ocean C cycle
DIC, DOC, POC & Nutrients, Fe, Si
Biological indicators
Pigments, stable C & N isotopes, Fv/Fm,
productivity
Physical patch tracer- SF6
Operations
include:
Finding patch (drogue with satellite positioning)
Surface survey (seawater line- chemistry and tracers)
Water catching
standard CTD/Rosette
trace metal clean bottles/Kevlar
In-situ battery powered pumps for filtration
Towed fish for TM sampling |
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