Entry 10
February 27 2025
Arriving at the mid-atlantic ridge, phytoplankton and the carbon cycle
Today was a transit day to our ‘ridge’ site – almost time to test our theory of increased productivity on the mid-Atlantic ridge! We used the afternoon to host another mini-conference of science talks – and today was my turn to present. It was a really supportive and curious atmosphere and, though it was only a 10/15 minute talk, sparked much discussion afterwards. While we’re here, I’ll take the opportunity to tell you a little about my PhD.
My focus is marine phytoplankton and their role in the carbon cycle. Phytoplankton are key players in the biological pump, that is, the flow of carbon from the air, to our oceans, to the deep ocean. This is a key process as it locks carbon out of our atmosphere, reducing the effect of CO2 in warming our planet. However, as our planet is warming and the ocean is absorbing that heat, its surface is increasing in temperature. This causes an increase in the temperature gradient between the surface, low nutrient, high plankton layers, and the lower, high nutrient, low plankton layer. The plankton in the surface rely on mixing between these layers to get the nutrients they need to grow. As the stratification of the ocean increases, there is less mixing, and less nutrients are delivered to the surface. We think this will alter the community structure of phytoplankton in the surface ocean, as a result altering the capacity of the ocean to absorb carbon dioxide.
One theory is that this will shift phytoplankton communities towards smaller phytoplankton, which is where my PhD comes in. With my fieldwork and lab-based study, I am seeking to understand a) how is community structure of phytoplankton in the surface ocean likely to change in response to changing nutrient supply?, b) how and why are picoeukaryotes (particularly a few groups) so well adapted to these conditions (physiological and biochemical mechanisms)? and c) what does photosynthesis and carbon cycling really look like in these organisms - and can we optimise this? As part of this, I’m also looking at specifically-adapted communities, such as those in the deep chlorophyll maxima, and the effect of different nutrient and light regimes, such as those on and off the mid-Atlantic ridge.