Two back-to-back expeditions in the Southwest Atlantic Ocean have highlighted the key role played by deep-sea organisms in locking away carbon and buffering against climate change.
This includes the mysterious creatures that take part in the world’s biggest animal migration, not to mention the microscopic algae that live in murky waters.
Supported by the Schmidt Ocean Institute, the missions set out to fill major gaps in the understanding of the biological pump – the process by which the ocean transfers carbon from the surface to the deep sea.
The first expedition, completed in February, focussed on the fish, shrimps, jellies and other creatures which rise from the deep every night and then return to the dark at daybreak. This is the world’s largest animal migration.
“These animals feed at the surface daily, effectively capturing carbon, and then they carry that carbon in their guts down to 1,500 metres, which they eventually excrete,” says expedition leader Anitra Ingalls from the University of Washington.
The animals consume carbon, then excrete carbon, but what happens inbetween these two steps is unclear.
Scientists want to understand the influence of the animals’ gut bacteria, so they collected samples from waters far off the east coast of South America. Now, they are using their data to create models that predict how the animals are likely to influence current and future climate change.
The second expedition, which finished in April, examined how nutrients and carbon are cycled by microscopic algae, called phytoplankton.
Most phytoplankton live in the upper, sunlit layer of water, but the team were interested in those living lower down at depths of about 100m, where the sunlight starts to dim.
No one really knows how these phytoplankton get the nutrients that they need, but one idea is that when surface-dwelling phytoplankton die and sink, they effectively provide 'compost' for the microorganisms that live below them.
Matthew Church from the University of Montana hopes to test this theory using the samples that he and his team collected from the Southeastern Atlantic Gyre. This includes water samples taken from the tail end of a surface phytoplankton bloom, collected around 320km (200 miles) off the coast of Brazil.
“The outcomes of this cruise will specifically improve understanding of the biological and chemical interactions taking place in the dimly lit portion of the upper ocean and the role they play in carbon export to deeper waters,” says Church.
In pictures: Atlantic Ocean expeditions
Top image: Squid documented by ROV SuBastian. Credit: ROV SuBastian / Schmidt Ocean Institute | All Images and videos used under creative commons Attribution-NonCommercial-ShareAlike CC BY-NC-SA, creativecommons.org/licenses/by-nc-sa/4.0/
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