Week 1: Stories of the CTD

Written by Marianna Karagiannis

It's already been a full week since we woke up at 3:30 am to drive to San Diego and load up the ship. Time flies! It's been smooth sailing so far, which I am incredibly grateful for as I am quite prone to seasickness. Why I decided to become an oceanographer while knowing this about myself is a mystery, but being out here in the ocean is so magical that I think it's worth it! As long as I have a steady supply of medication and ginger chews.

Our CTD rosette getting lowered into the water

Since getting on the ship, we've been slowly making our way to our first sampling region, stopping along the way to collect data about the water column. We use an instrument called a CTD (Conductivity, Temperature, and Depth) that we lower down through the ocean. The CTD also has sensors that measure oxygen, turbidity, and fluorescence (which tells us where the phytoplankton are). While these sensors record data in real time, we also have bottles (called Niskin bottles) attached to the rosette (the metal frame) that we use to collect water from specific depths. By looking at the live data, we can decide which depths we want water from. Most of our analyses are really time intensive and require careful laboratory work, so it's really nice to get some beautiful data so easily!

Checking that everything looks good before sending it out

By measuring conductivity and temperature, we can start to understand where the deep and surface water mix and better map out ocean circulation. For example, the water at the surface might have a characteristic temperature and salinity that tells us it is being carried by a particular current. Stay tuned for another blog post to learn more about these currents!

We love data! And we love it when technology cooperates!

Oxygen is one of the most important parameters we are measuring this trip. This part of the ocean has a persistent feature called an Oxygen Minimum Zone (OMZ), where part of the water column has very little oxygen. While this feature is natural, we think it might be expanding, so we want to compare our data to previous research and see how they compare.

Attaching filters to our bottles to try to keep microbes out of our samples

When we take the rosette back out of the water, we try to work quickly. If we leave the bottles sitting out for too long, oxygen could seep into the anoxic bottles, microbes could start growing, or temperature changes could mess with the water chemistry. With these water samples, we can get much more detailed information than just what the sensors can detect as it is in the water. This includes analyzing what microbes and phytoplankton are present, the concentration of particular nutrients that are critical for plankton growth, pH, concentrations of trace metals, the amount of dissolved inorganic carbon (DIC), and the amount of dissolved organic carbon (DOC). It can get a bit tight when we are all trying to squeeze in and get our samples at the same time, but we make it work!

Sampling can require getting in some strange positions

I really enjoy sampling from Niskin bottles, but I often find myself contorting in weird positions and accidentally spraying myself with water. It's pretty cool to remember that the water I'm spilling all over myself took a journey from miles beneath me, and hasn't seen the surface in hundreds of years!