Today I wanted to share a little bit about the big-picture behind this project and how we choose where to sample. A bit of history to begin…
As I mentioned before, the international World Ocean Circulation Experiment (WOCE) was a “comprehensive global hydrographic survey of physical and chemical properties, of unprecedented scope and quality, and represents the ‘state of the oceans’ during the 1990s” (http://woceatlas.ucsd.edu/). This line (P16N) was occupied in its entirety, for the first time, in April 1984. Since then, many portions of it have been resampled, with the last time being in 2006. However, there is still one small section that has never been sampled! We are in that water now so things are exciting here- everything we are collecting is new!
As we move north, we stop every ½ degree of latitude to sample, which is roughly every 50 miles. At each stop (station) we put the rosette in and take samples at 24 different depths. This water is over 5000m deep and we only get 24 samples. So how do we choose our depths?
From what I can tell, each cruise does it somewhat differently, but the idea is to rotate through 3 different depth “schemes” to get a full picture of the entire water column every 3 stations. In the deeper water we collect a sample every 400-500m, while above 1000 meters, we sample much more frequently (every 25-100 m). By rotating through schemes we attempt to not leave any gaps unsampled within a 2-degree space. With these samples, scientists are able to extrapolate using algorithms and other information to create section maps, which cover the entire North Pacific, like those included below. It’s pretty incredible stuff. Each time this region is reoccupied we can create new maps and look for changes between them. This always leads to further investigations about what causes those changes and if the trend is expected to continue. The maps shown here are from 1992 so we are comparing them with signals we are seeing on our stations. |
First of all, the North Pacific contains the oldest water on Earth as it is the “end” of the thermohaline circulation which begins in the North Atlantic and carries water around the globe (Atlantic Ocean to Southern Ocean to the Pacific). The water in the deep Pacific hasn’t been exposed to the atmosphere for over 1,000 years. That is why it’s so important to measure the concentration of gases in this water- it tells us something about the atmosphere a long time ago.
Starting with something simple, here is a plot of the temperature throughout the water column. As you would expect, it is warmest at the surface (pinks) and gets colder as you go to depth (blues). The top plot in each of these figures is simply a zoomed-in version of the top 1000m from the bottom plot. (Note- all plots were produced by the WOCE atlas project).
It looked something like this…