Equipment prep

We spent a total of a day and a half getting all of our instruments ready for installing on the reef. That might sound like a long time, but when you think about what it takes to prepare all these things it makes a lot more sense!

We have five different sites around Palmyra where we'll be putting instruments; together, they'll let us get a sense of the overall circulation changes around the island during the course of the El Nino (or at least, of the winter). At each of those spots, we'll be putting in:

- A "CTD", or Conductivity-Temperature-Depth sensor. This measures the pressure, which can be translated into water depth; the conductivity of the water, which is convertible to the salinity; and the temperature of the surrounding water.

- An "ADCP", or Acoustic Doppler Current Profiler. This instrument sends out regular acoustic "pings" like the sonars you see in movies about submarines. Those pings reflect off plankton, dirt, or other debris in the water and return to the instrument; then the change in the frequency of the ping once it gets back to where it started tells you how fast the current is flowing.

The CTD and ADCPs are attached to each other with clamps, then mounted on metal bars and weighed down with 60 pounds of zinc. Then just to make sure they won't go anywhere, they get staked to the reef! The entire setup looks like this:

Then the other thing we are measuring is the isotopic composition of water: both seawater and rainwater. These measurements are really important, because they tell us the relationship of temperature and salinity changes to changes in water composition... which is what the corals we're using to reconstruct El Nino actually 'care' about. To make it simpler: if you think of the seawater around the reef as a big bucket that's affected by

- rain coming in
- water evaporating from the surface
- ocean currents bringing water with different amounts of oxygen isotopes

(credit for background image: Widlansky et al. 2014)

what we're trying to do is measure how important each of those things are during El Nino events. The data we're collecting will be analyzed on its own, then also incorporated into our new, 'isotope-enabled' version of an ocean model (the Regional Ocean Modeling System, or ROMS) so we can get a complete picture of circulation around all of Palmyra, not just the few spots we'll be able to collect data.

In theory it should be really cool! Now to get started on those measurements...