2 August 2022 The Mighty CTD

Journal

Sea Surface Temperature: 43 degrees F

Depth: 46 feet

PolarConnect Event Coming Up August 4

On August 4th I will be hosting a live zoom from the Norseman II! You can tune in to learn about the research, see some benthic organisms, check out Alexandrium and other plankton, and meet some of the scientists!

It will be at 9:00 AM Alaska Time/ 10:00 AM Pacific Time / 11:00 AM Mountain Time / 12:00 PM Central Time / 1:00 PM Eastern Time. I would love for you to join!

You can register at: https://www.polartrec.com/polar-connect/register

What's Down There?

Every single time we stop at a station, the CTDA research tool that is submerged in the water to measure conductivity (salinity), temperature, and depth. is lowered to the seafloor. By the time we return to Nome, it will have gone overboard over 200 times. Given how important it is to the research on board the Norseman II, I thought I would take some time to describe what it does and why it is so useful.

The ocean under the ship is not uniform. It is made out of different water masses that are moving alongside, above, and below each other. Each of these water masses is made out of a unique type of water and unique characteristics, such as:

Temperature
Salinity (how much salt is in the water)
What nutrients are present

Landing the CTD — The CTD is mounted on a frame called a Rosette. It sits at the bottom of the frame. Above it are Niskin bottles, used to collect water from different depths.

What is the CTDA research tool that is submerged in the water to measure conductivity (salinity), temperature, and depth.?

The CTDA research tool that is submerged in the water to measure conductivity (salinity), temperature, and depth. is basically a bundle of sensors (called a “package”). All CTDs can measure:

Conductivity - how easily electricity can travel through the seawater, which is used to measure how salty the water is.
Temperature
Depth

Our CTDA research tool that is submerged in the water to measure conductivity (salinity), temperature, and depth. also has sensors to measure:

The amount of chlorophyll in the water – chlorophyll is the pigment used in photosynthesis, so the amount of chlorophyll in the water gives a sense of how many phytoplankton are in the water
How murky or clear the water is (this is called “beam attenuation” and it is a measure of how many particles are in the water)
Height above the seafloor
The amount of oxygen dissolved in the water
Light

Close up of CTD — The CTD is mounted at the bottom of the rosette. The grey cube-like shapes above it are lead weights to help it sink down the water column.

CTDA research tool that is submerged in the water to measure conductivity (salinity), temperature, and depth. Casts

When we cast the CTDA research tool that is submerged in the water to measure conductivity (salinity), temperature, and depth. over the side, the sensors transmit data to computers onboard. The computers then graph the information so that we can understand it easily and quickly.

Scientists studying the CTD readout — The CTD sends data back to the ship as it descends through the water column. This data is used to decide from which depths to collect water samples.

CTD data screen — The CTD generates quite a lot of data!

What does it all mean?

Taken all at once, the CTDA research tool that is submerged in the water to measure conductivity (salinity), temperature, and depth. data is pretty overwhelming. Let's take a closer look at a few of the plots to see what they tell us about the water under the ship.

Some tips for reading the graphs:

Depth is plotted on the left hand side. The surface is at the top of the graph, and the depth increases going down
The wiggles in the graph are due to the Norseman II moving in the waves. Every time the boat rocks on a wave, the CTDA research tool that is submerged in the water to measure conductivity (salinity), temperature, and depth. rises and falls a small amount.

Temperature and Salinity Graph — In this graph, water temperature (measured in degrees Celsius) is plotted in red, and salinity (the amount of salt in the water) is plotted in blue. The units for water temperature are on the top of the graph. The units for salinity are in blue. You don’t need to pay attention to the black line.

From this temperature and salinity data, you can see that there are two distinct water masses under the ship. The upper water mass is warmer and less salty, and the lower water mass is colder and saltier.

Chlorophyll plot — The green line shows the amount of chlorophyll in the water. You can ignore the black line.

Chlorophyll is used for photosynthesis, so the amount of chlorophyll in the water tells how many phytoplankton are down there. You can see that the water 18 meters (60 feet) deep has the greatest amount of phytoplankton. This zone is called the Chlorophyll Maximum. It is right at the transition between the two water masses. This happens quite often.

Details