ANALYSIS OF OPTICAL SPIKES REVEALS DYNAMICS OF AGGREGATES IN THE TWILIGHT ZONE

ANALYSIS OF OPTICAL SPIKES REVEALS DYNAMICS OF AGGREGATES IN THE TWILIGHT ZONE

By Nathan Briggs

Thesis Advisor: Dr. Mary Jane Perry

A Lay Abstract of the Thesis Presented

in Partial Fulfillment of the Requirements for the

Degree of Master of Science

(in Oceanography)

August, 2010

            In the ocean, tiny phytoplankton, like plants on the land, use the sun’s energy to convert carbon dioxide (CO₂) into living tissue. As phytoplankton grow and remove CO₂ from the ocean, the ocean can then absorb more CO₂ from the atmosphere. When phytoplankton are eaten or decompose, the CO₂ that they have absorbed is released. Most of the CO₂ absorbed in this way is released near the surface, where phytoplankton live, and quickly returns to the atmosphere. However, some phytoplankton, before they can be consumed, clump together and sink to the deep ocean, where their CO₂ is stored for thousands or even millions of years. This causes a long-term drawdown of CO₂ from the atmosphere, helping to counteract CO₂ emissions. In this thesis I present a method for detecting these sinking clumps of phytoplankton and estimating their sinking speed using small optical instruments aboard low-power automated underwater vehicles. This method revealed a large pulse of phytoplankton sinking at 75 meters per day following the North Atlantic spring phytoplankton bloom in 2008. My results confirm the value of autonomous platforms in studying biological processes in the ocean.