January 5 - February 26, 2002
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 ships 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).
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 asmarkers 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.
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 ofnutrients, 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.
SEASOAR, Fe FISH & SF6 SHIPBOARD MAPPING: The SeaSoaris 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.
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.
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.
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.
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.
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.
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. They provide a shipboard access to rate process experiments.
USCGC POLAR STAR EQUIPMENT: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
- 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