Potential Temperature (deg. C)

CTD Data across the Equator

When deciding how to best utilize 5 days for science in a 16-day cruise, we chose to occupy a north-south section across the equator that offered many great research projects from which the seniors could choose. The equatorial currents go east-west and are tightly coupled to the winds. ENSO can introduce variability on interannual time scales, and we are at the end of a prolonged La Niña phase.  Upwelling at the equator brings “older” water to the surface with higher nutrient concentrations which results in higher phytoplankton growth. It also brings waters having higher CO2 concentrations to the surface – resulting in the equator being a source of CO2 to the atmosphere.

The primary method for collecting data and samples for many of these projects is through sampling stations where a rosette containing 24 10-liter bottles to collect water samples, as well as sensors mounted on the frame that continuously measure seawater properties, is lowered and recovered. Due to the pressure limitations of the pH sensor, we had a target depth of 1000 m at most of the stations. One of the sensors, the CTD (conductivity-temperature-depth) is used to determine pressure, temperature and salinity below the ship. Another sensor measures the concentrations of dissolved oxygen.

After processing these data, we can combine them to produce vertical sections of hydrographic properties between 5°N and 5°S.  Hot off the presses, here are sections of temperature, salinity, and dissolved oxygen concentrations from these sensors. South is to the left, the equator at Station 9 (or 300 n. mi. on the lower axis).).