BATS 295 Day 4

Dr Meg Estapa is a post doc at WHOI who is currently working on a project studying how much particulate carbon gets exported into the deep sea. I spoke to her yesterday about her new project and this is what it’s all about…

What is particulate carbon and how is it being measured?
Particulate carbon falls through the water column to the deep sea. It is comprised of dead phytoplankton cells, faecal matter from zooplankton and other substances. As it falls though the twilight zone (0-1000m) a lot of this carbon gets remineralized and only a small amount makes it to the deep sea. Meg is currently trying to measure the particulate carbon flux that gets exported into the deep sea  by using and comparing two different methods. She is also going to compare her sediment trap data with the BATS data.

What is going to be used to measure this particulate carbon in the deep sea?
They are going to be using both neutrally buoyant sediment traps (NBSTs) and profiling floats. NBSTs operate like the BATS traps however instead of the sediment traps being attached to rope the NBSTs are free floating allowing them to drift with the ocean currents reducing hydrodynamic effects. They have four tubes which collect the falling particles. 

one of the NBSTs being deployed

They also deployed two profiling floats which have transmissometers attached to them. Transmissometers shine a beam of light through the water to tell the concentration of suspended particles. Particles that fall onto the upward-facing window of the instrument block the light beam, causing a measurable signal we can relate back to flux. 

Profiling float in the water

The floats can drift in the ocean for months and measure other parameters such as salinity and oxygen. The data from the float is relayed via satellite to Meg's computer. The NBSTs also have transmissometers attached to them so they can compare the sediment trap flux data with the flux data from the transmissometers. This will allow them to see whether transmissometers accurately determine particulate carbon flux. 

One of the four sediment trap tubes contains a gel – what does this gel do?

The gel in the tube is a soft landing for particles that fall in the trap. It preserves the size and shape of the particles so you can identify and chemically analyze the particles.

Close up of a sediment trap tube - the transmissometer is on the left! 

Why is it important to monitor this carbon flux in the ocean?

It is important to monitor the particles that are raining down from the ocean because they are an important part of the carbon cycle. It is difficult to measure carbon flux frequently and if it is possible to measure flux using just profiling floats then this would reduce the need for vessels which are expensive and allow more continuous measurements. There are large parts of the ocean where there is very little data on particulate carbon flux which is why it is important for more continuous monitoring.   

A big thank you to Meg for taking the time to talk to me about her project! Tomorrow we will be recovering the floats, NBSTs and BATS sediment traps – even more photos to come!

Bye Bye NBST number three! See you soon!