CTD’s and why we filter water

Throughout the cruise, we have cast a lot of CTD’s. CTD stands for conductivity (or salinity), temperature, and depth. In oceanography, a CTD is a regularly used instrument that is dropped vertically in the water column to measure water properties (the C, T, and D) at different depths. CTD’s are usually attached to large bottles that collect sea water at different depths. In the video below, the crew brings up the CTD rosette, and Martí and Peter begin filtering water.

Why do we need to know the properties of ocean water? To learn more about where certain animals live in the ocean, we use instruments like CTD’s to determine different water properties at various depths. We can then use this type of data and correlate it to the type of animlas or plants we find there, and further study how tiny marine critters can survive in different areas (or habitats) of the ocean.

Phytoplankton (tiny ocean plants) are essential for many marine animals. By filtering sea water, we can collect these small plants (as well as dead organic material) on filters with microscopic holes. Therefore, filtering water can give an indication of the amount of food available to small marine life (as Coralie mentioned in her post). Martí filters water for his project to learn more about the microbial food web during the polar night.

CTD data can also be used to compare water properties at similar locations through time. The water in western Svalbard is influenced by warmer and saltier water from the Atlantic Ocean moving its way northward into the Arctic Ocean. To determine if some of the fjords in western Svalbard will be ice-covered this year, researchers can investigate water temperatures using a CTD (see figure below). Some of the researchers on our cruise have summarized their findings on this University Centre in Svalbard (UNIS) page.

A temperature profile obtained from a CTD. Here you can see that surface water temperatures in 2016 were colder than in 2017 in Isfjord (IsK). What this indicates is that there is more Atlantic water inside Isfjord than last year, so the chances of an ice-covered Isfjord is unlikely this winter. Graphic credit: Ragnheid Skogseth/UNIS.
Coralie, Peter, and Martí around the CTD rosette.
Peter is boss when it comes to water filtration!

-Erin Kunisch (PhD candidate, UiT)