Project: Twilight Zone EXplorer

Carbon Flux Through the Twilight Zone - New Tools to Measure Change

Building upon the success of the VERTIGO project, we continue to work to improve our understanding of how materials travel from the surface to the deep ocean. This pathway is called the "Biological Pump" which refers to the combined activities that lead to a quick pathway for plant and animal debris (molts, fecal pellets, loose aggregated material) to sink as marine "snow" or a particle into the deep ocean. In the open ocean, this cycle is largely a biological one, though in some settings, transport of material delivered by dust may matter (e.g. TENATSO - Cape Verde time series project).

The "twilight zone" is a region of low light below the ocean's sunlit surface "euphotic" zone, and above the deep ocean boundary (around 1000m or 3000 feet). It is in this mysterious layer where most of the sinking particles of the world's ocean are consumed by the animals that live at depth.

In a new project starting in late 2006, we are designing an autonomous vehicle called the "Twilight Zone EXplorer" (TZEX) to sample the ocean particle flux and make remote measurements in the twilight zone. Beginning in 2007, we will be starting to sample on a monthly basis at Bermuda, as part of the BATS (Bermuda Atlantic Time-Series) program using our existing particle flux collectors, the Neutrally Buoyant Sediment trap.

The biological pump and processes regulating the flux of particles in the ocean. Carbon dioxide fixed during photosynthesis by phytoplankton in the upper ocean can be transferred below the surface mixed layer via three major processes: i) passive sinking of particles, ii) physical mixing of particulate and dissolved organic matter (DOM), and iii) active transport by zooplankton vertical migration. The sinking flux includes senescent phytoplankton, zooplankton fecal pellets, molts and mucous feeding-webs (e.g., larvacean houses) and aggregates of these materials. The sinking particle flux decreases with depth as aggregates are fragmented into smaller, non-sinking particles, decomposed by bacteria, and consumed and respired by zooplankton. This remineralization returns carbon and nutrients to dissolved forms. The structure of the planktonic community affects the composition and the sinking rates of particles. Particle size, form, density, and the content of biogenic minerals affect sinking and remineralization rates.

Funding

The TZEX project is funded as part of the NSF Carbon and Water in the Earth System crosscutting solicitation aimed at closing significant gaps in our understanding of the complex relationships between and within the global water and carbon cycles.

NSF link: http://www.nsf.gov/funding/pgm_summ.jsp?pims_id=13651&org=OCE

References:

Dehairs, F., A. de Brauwere, M. Elskens, U. Bathmann, S. Becquevort, S. Blain, P. Boyd, K. Buesseler, E. Buitenhaus, M. Gehlen, G. Herndl, C. Klass, R. Lampitt, D. Lefevre, U. Passow, H. Plous, F. Primeau, L. Stemmann and T. Trull (2008). Controls on Organic Carbon Export and Twilight Zone Remineralization: An Overview of the EUROCEANS Workshop . Oceanography, 21(3): 92-95.

Dehairs, F., A. de Brauwere and M. Elskens (2008). Organic Carbon in the Ocean's Twilight Zone. EOS, Transactions American Geophysical Union, 89 (38): doi:10.1029/2008EO380004.