Mesopelagic Zooplankton and Particle Flux
VERTIGO, for VERtical Transport In the Global Ocean, is a collaborative international venture studying processes affecting particle flux in the mesopelagic zone (depths of ~100-1,000 m). Knowing the fate of organic material as it sinks from the ocean's surface to its depths is important because it represents a potentially large sink for carbon dioxide, the main greenhouse gas implicated in global warming. A primary goal of VERTIGO is to quantify the fraction of sinking particles that reach the depths and to identify the biological and chemical processes that transform them along the way. Little is known about processes that affect particle flux in the deep "twilight zone" of the ocean, or about the organisms living there.
In VERTIGO we are testing 2 basic hypotheses regarding the fate of sinking particles leaving the upper ocean and the factors that influence the rate at which different types of sinking particles are remineralized on the way down to the deep-sea (the "efficiency" of transport):
- The environment where particles are formed in the upper ocean (particle source characteristics) is the dominant control on the efficiency of transport
- Midwater processing, either by zooplankton or bacteria, controls transport efficiency.
Our zooplankton ecology lab is primarily concerned with hypothesis 2 and is investigating how mesopelagic zooplankton affect sinking particles.
We are examining changes in particle composition and flux with depth at two study sites: the Hawaii Ocean Time-series (HOT) site and a moored time series site in the subarctic NW Pacific (Japanese site K2; 47°N 160°E). These two sites differ greatly in particle composition and rates of production and export. We are using a suite of specially designed oceanographic instruments including "neutrally buoyant sediment traps" to catch sinking particles and a MOCNESS plankton net to sample zooplankton at discrete depth zones.
Our goal is to identify the types of zooplankton in the twilight zone, estimate their abundance, and quantify their role in particle transformation. We are using a number of different approaches, including examining gut contents and fecal pellets of mesopelagic zooplankton to look for evidence of feeding on sinking particles, examining changes in types of fecal pellets with depth to look for evidence of "repackaging" by zooplankton at depth, and determining the contribution of zooplankton to remineralization of sinking particles by comparing the loss of sinking particle carbon with depth (as measured by sediment traps) with zooplankton metabolic requirements.
VERTIGO is a collaboration between our laboratory and colleagues at the
- Woods Hole Oceanographic Institution (WHOI)
- University of California (Santa Barbara and Santa Cruz)
- Lawrence Berkeley National Laboratory
- University of Tasmania
- New Zealand's National Institute of Water and Atmospheric Research (NIWA)
- India's Physical Research Laboratory
- University of Brussels, Belgium
Funding for this project is primarily provided by National Science Foundation (NSF) Biological and Chemical Oceanography programs. VERTIGO is also supported by the Antarctic Climate & Ecosystems Cooperative Research Centre, the U.S. Department of Energy, Woods Hole Oceanographic Institution, the Fund for Scientific Research-Flanders (Belgium), and other national and international sponsors.