Research on this cruise is a follow-up to the studies begun on the 2004 summer cruise. Waters in areas of the Southern Ocean were tested to determine if they were iron limited or not. Areas in the blue water zone (see illustration Chlorophyll Concentrations: Antarctic Circumpolar Current) of the Antarctic Circumpolar Current were determined to be iron limited. The shelf waters were not limited in iron. Our purpose is to continue our investigations on iron as an explanation for this transition.

We use a PRR, a Profiling Reflecting Radiometer that measures natural light from the sun.

This process is measured in two ways. First we use radioactive CO2 to precisely determine the rate of photosynthesis. This method is laborious and can be done at only a few depths each day. We also use a flurometer to give us a rapid continuous profile.. The flurometer uses a pulsing light to measure sequences of less than a millisecond; the instrument provides information that can be used to estimate the rate of photosynthesis.

We look at the absorption and scattering of different wavelengths of light. Some light that enters the water is absorbed by the phytopigments for use in photosynthesis. Other light is absorbed by other parts of the system. The color of the ocean relates to the material is in the ocean and what wavelengths are being absorbed or reflected.

This process is measured in two ways. First we use radioactive CO2 to precisely determine the rate of photosynthesis. This method is laborious and can be done at only a few depths each day. We also use a flurometer to give us a rapid continuous profile.. The flurometer uses a pulsing light to measure sequences of less than a millisecond; the instrument provides information that can be used to estimate the rate of photosynthesis.

Sometimes you have to wait for weeks to get an image because of the cloud cover. Most of the time, you need to make a composite,  that is, you take parts of an image over several days to get a good image of that area.

One of the advantages is that you are able to look at a large region over a series of time. Ships cannot supply such large time and space scales. We have a 10 year time series for this area. We are able to look at how a region varies both spatially and over a period of years. A disadvantage is that satellites that detect ocean color do not work well in winter when the sun is low on the horizon.

Survey work was done by the American Marine Living Resources (AMLR) organization, sponsored by NOAA (National Oceanographic and Atmospheric Administration). Osmund Holm-Hansen was part of a group that collected data over a period of many years, focusing on krill in the area. People had known for many years that the South Scotia Sea was an area of high density for the whale population, but did not know why. Studies showed that these areas were high in krill. The question arose as to why there were more krill to the east of the STR than to the west.

Have each of them played different roles?  First, AMLR, part of NOAA, did the monitoring that produced a series of observations over many years. However, the observations were limited to one survey track that was repeated year after year. Next, the NSF (National Science Foundation) provided us the funding for process oriented research. We could be more narrowly focused on the physical and chemical control that results in the differences in chlorophyll concentrations from the east side to the west side of the Shackleton Transverse Ridge. Next, NASA provides us with the satellite monitoring that helps us get the images from space of the variations in ocean chlorophyll. Our research cruise is an example of not only interdisciplinary, but also interagency cooperation.

We use the information on radiometry (light measurement) and chlorophyll to make the formulas that translate light observed by the satellite into ecosystem variables of interest scientifically.