Imagine you’re in a desert, thirsty for water. There’s plenty of precious water just a stone’s throw away, you just can’t get at it. That’s what phytoplankton, the tiny algae supporting life in the ocean, have to face. Except that in their case it’s not the water that is in short supply, but the essential nutrients that allow them to grow and build nutritious biomass in the sunlit surface layer. Those nutrients are plentiful just a couple of hundred metres below. But the strong density gradient in the surface ocean prevents those nutrients from being mixed into the surface layer, where they are desperately needed. That’s the situation in more than 50% of the world ocean.
Bringing those nutrient-rich deep waters to the sunlit surface layer makes a real feast for the hungry phytoplankton. One that all others in the plankton food web will thrive on. That feast has started just now in our mesocosms. Two days ago the first four enclosures received a heavy dose of nutrient-rich deep water collected with RRS James Cook last week. Today another four mesocosms got their first shot. The two sets cover the same range of total nutrient addition, but differ in the number of additions: the first four got it all at once, the next four get twelve small injections over the course of the experiment, one every four days.
Everyone in the team is eager to see the plankton feast develop. Who in the phytoplankton will take the biggest bite of the nutrient load? Will the zooplankton grow fast enough to make efficient use of the sudden surplus in food? Will the fish larvae benefit from a well-fed zooplankton community? Which of our different deep water treatments makes the most efficient transfer of nutrients up the food web? The coming week will tell.
Getting ready to set the table for the big feast – our two working boats loaded with equipment for deep water addition. What is easily said, simulating upwelling of deep water in our mesocosms, takes an incredible effort. Once again, a big THANK-YOU to our KOSMOS core team for their dedication and hard work.
Lifting the heavy underwater pump into a mesocosm. Hard enough on solid ground, a challenge when performed on a swaying boat.
Injecting the nutritious deep water into a mesocosm enclosure