Underway

30^o 13' N

23^o 15' W

... and we're off! Once the a/c was fixed, we wasted no time leaving port late Sunday evening.

After a good night's rest, we ran a couple of test sampling casts on Monday so the new participants could practice their roles before we returned to the A16N line. We worked out a few hiccups, made a few tweaks, and in the end, everyone felt ready for the real work to begin.

Because our teams on the second leg are a little different from the teams on the first leg, we want to make sure that differences in operators do not cause artificial differences in our data. Therefore, we take several precautions to ensure that the data sets from each leg match up seamlessly.

Reference Materials

Reference materials are small subsamples of a larger, well-mixed sample of seawater. These subsamples are specially treated so that the analytes (i.e. things we're measuring) are preserved for a long time. By measuring a reference material, a new operator, method or instrument can be validated against a historical data set of measurements of the same analyte in the same sample. The picture below shows reference materials for the analysis of dissolved nutrients (left) and oxygen, and you can follow this link for more information about trace metal reference materials: http://es.ucsc.edu/~kbruland/GeotracesSaFe/kwbGeotracesSaFe.html.

Reference materials for the analysis of
dissolved nutrients (left) and dissolved oxygen (right)

Crossover Station

Another method of intercalibrating data sets is by sampling and analyzing a set of samples from the same location, referred to as a "crossover station." The first station of our second leg (station 71) is a repeat of the last station from the first leg (station 70). While the surface concentrations for some analytes might vary slightly due to changes in sunlight, temperature, winds and waves, or biological processes, the mid- and deep-water concentrations won't have changed over the time we spent in Madeira. Therefore, each of the two teams should measure the same concentrations throughout the water column at our crossover station. If not, then the new participants can fine-tune their instruments, techniques, standards, etc. to correct for differences in their results.

Several locations that are regularly used as crossover stations are found throughout the world oceans, including BATS in the North Atlantic and ALOHA in the North Pacific.

Bermuda-Atlantic Time Series (Station BATS):  www.bios.edu/research/projects/bats/

Hawaii Ocean Time series (Station ALOHA):  www.soest.hawaii.edu/ALOHA/HOT.html