Southern Ocean Iron Experiment (SOFeX) Cruise
January 5 - February 26, 2002
January 5, 2002: Day 1
Kenneth Coale writes: The last few days have been extremely busy. Shipments from all over the US arrived in Lyttelton, New Zealand for the first leg of the SOFeX expeditions to the Southern Ocean.Equipment and supply shipments from Moss Landing Marine Labs and the Monterey Bay Aquarium Research institute weighed in at over 30 tons for the two upcoming cruises with total shipping weights of approximately 45 tons. For Revelle alone, the scientific deck load is about 30 tons. This is a lot of equipment for this vessel and the scientists used up about 60 2.54 cm eye-bolts, over 150 meters of 1.25 cm chain, and 50 chain binders, securing the loads to the deck. Lyttelton Engineering welded up more pad eyes to make sure we could attach everything securely. The Southern Ocean is no place to take any chances, especially with this much gear, this many people and with an experiment that is so important.
We seek to develop a mechanistic understanding of the processes that control the productivity of the Southern Ocean waters, the largest body of water containing un-utilized algal nutrients.We hypothesize that the factors which enable phytoplankton to utilize these nutrients will bear directly on climate change.Why? Because as these tiny algae grow, they take up carbon dioxide from the surrounding waters.The gasses in the water in turn equilibrates with the atmosphere.Thus algal growth in the oceans controls atmospheric carbon dioxide and in turn, global warming.There is strong evidence that Antarctic production has been linked to glacial/interglacial climate transitions in the past. But why are there such high levels of un-utilized nutrients in the Southern Ocean?Several factors contribute to this phenomenon including darkness in winter and extremely cold waters, yet even with 24 hour sunlight in the summertime, nutrients remain.We believe the missing ingredient is iron and have devised an experiment to test this hypothesis.
The experimental design is in part responsible for some of our deck load, about 9,000 kilograms of iron sulfate will be mixed on board in two large 19,000 liter tanks and pumped slowly into the ships wake as it enriches two 225 square kilometer patches in areas that represent the two major biogeochemical provinces of the Southern Ocean.These provinces are separated by the Antarctic Polar Fronts Zone (APFZ).Waters to the north of the APFZ are characterized by 4-5 degree C water, high nitrate concentrations yet low silicate concentrations.Waters to the south of the APFZ are cold (-1.5 to zero degrees C) and have both high nitrate and silicate concentrations.
We believe that iron enrichments performed in both locations will yield different results.We anticipate that the northern waters may bloom with phytoplankton species that do not require silicate, whereas southern waters will produce diatoms upon iron enrichment.It is important to understand the difference in these responses because both move carbon through the ecosystem, but in very different ways.For instance, it may be that blooms of smaller phytoplankton in northern waters will not ultimately remove carbon from the atmosphere but blooms of diatoms in southern waters will.We dont yet know.But we intend to find out.
To help us find out are researchers from all over the country.Burke Hales and Taro Takahashi from OSU and Lamont Doherty Laboratories of Columbia University will tow an undulating fish in back of the ship that returns water to labs on the main deck. This fish is like an underwater kite but it looks more like a robotic turkey.They will measure nutrients, temperature, carbon system parameters. Dick Barbers group from Duke University will measure primary production.Mike Landrys group from the University of Hawaii will measure the response of the phytoplankton and take some initial samples for identification. The MBARI group has a big job.They have developed the technology by which the experimental patches will be tracked as they waltz about the Southern Ocean.An instrumented drifting buoydeveloped by Francisco Chavez will serve as the experimental frame of reference.This buoy package will be anchored in the mixed layer with a holey sock drogue (a cylindrical shower curtain, 1.22 meters in diameter and 9.1 meters long).
Using a packet radio, this package will report its position every 5 or 10 minutes to the ship.In addition to its position, the buoy will also report temperature, salinity, oxygen, carbon dioxide, fluorescence (a measure of algal biomass) and beam transmission (a measure of particles in the water).Ken Johnson of MBARI has developed a novel nitrate analyzer that will be used to observe the depletion of this algal nutrient throughout the experiment.The MBARI group will also be responsible for the shipboard determination of iron, navigational logistics and other shipboard measurements of fluorescence and gasses.The MLML group has designed and constructed the iron injection equipment and the corresponding gas tracer mixing tanks.Craig Hunter will be mixing up 19,000 liter tanks of iron sulfate and mixing it with sulfurhexafluoride (an inert chemical tracer).The relatively large amounts of iron (several tons) will be mixed with tiny amounts of tracer (a few hundred grams) and both will be diluted to vanishingly small quantities such that their very detection will comprise a major analytical challenge.Kevin Sullivan from Rikk Wanninkhoffs group will measure the gas tracer to determine how much iron was initially present in the water.As the phytoplankton grow, they will use iron, but not sulfurhexafluoride.The presence of both sulfurhexafluoride and helium-3 will enable Kevin and Rikk to measure gas exchange and mixing in the surface waters. The MLML group will also be responsible for the deployment of sediment traps to catch sinking particles.Although Craig will be deploying these from Revelle, they will be recovered aboard Melville, the next ship to sail from Lyttelton and reach the patch in mid January.
Another unique approach to tracking the experiments will be to deploy autonomous undulating instrument packages.These undulating floats built by Jim Bishops group at Lawrence Berkeley Labs and resemble a gas cylinder with antennae and plexiglass tutu, will enable the measurement of particles, temperature and salinity.The floats themselves vary their volume slightly and are able to broadcast their data and be reprogrammed via satellite. Knowing the current structure, Jim can fly these floats and rest them at different depths much like a hot air balloon navigate its course, and keep the floats profiling in the patch.
Because iron is a vitamin, its availability affects phytoplankton physiology in some measurable ways.To assess the phytoplanktons ability to harvest light energy, researchers from Paul Falkowskis lab at Rutgers University will be measuring the fluorescence response of phytoplankton, an indicator of the efficiency of photosystem II.
This partial list of participants and activities will be supplemented as the experiment continues. For now, we are all hoping for weather that will permit such an ambitious endeavor.
The weather has been variable. From the local perspective, this has been a dry summer, yet we know this is a heavy ice year in the Ross Sea and it has rained every day since arriving here in Lyttelton. Although the locals attribute the unusual weather to forest fires in Australia, others sense the lurking giant of climate change. This gives us little confidence in predicting what is ahead. What we do know is that the equipment was secure and spirits high as the Revelle left Lyttelton harbor, rounded the Banks Peninsula and headed south in a calm sea and light winds.