After 6 long hours processing the phytoplankton profile from last night’s CTD, we decided to stay on this station for the remainder of our trip. The profile showed a distinct (and stable) maximum of phytoplankton. Interestingly, this maximum isn’t at the top as you might expect for sun-loving organisms.
The phytoplankton maximum occurs at around 91 m depth. No one’s entirely sure why and a couple of the side experiments happening on ship are meant to tackle this question. The going theory has three possibilities (not mutually exclusive): the light intensity at the top is too high for the phytoplankton (called phototoxicity), the grazer productivity is also higher at the top so overall abundance is down because the phytoplankton is being eaten, or the nutrient level at the very top (for a number of reasons) is low enough to limit abundance.
Everyone on board seems to take that as a given and we use the chlorophyll maximum to determine the other intervals at which we collect water samples. It’s an important layer in terms of biological function and theoretically drives pelagic productivity.
On a more personal level, it’s also the first day we’re all on shifts. We completed the first full CTD measurements together to make sure everyone was one the same page and happy with the place we decided to stop. After a short nap by nearly everyone on board, we started a diel experiment, which will be measuring the same things we have been, but on the hour every hour for the next 24. We’ve also been kindly fueled by the mess crew with gigantic brownies and steak and potatoes for dinner and I currently smell cinnamon somethings baking for those of us up for the night shift. All of this wonderfulness and the only place to exercise being laps around the ship
~Bluegrass Blue Crab