VERTIGO (VERtical Transport In the Global Ocean): A study of particle sources and flux attenuation in the North Pacific
Buesseler, KO and Trull, T and Steinberg, DK and Silver, MW and Siegel, DA and Saitoh, SI and Lamborg, CH and Lam, PJ and Karl, DM and Jiao, NZ and Honda, MC and Elskens, M and Dehairs, F and Brown, SL and Boyd, PW and Bishop, JKB and Bidigare, RR, VERTIGO (VERtical Transport In the Global Ocean): A study of particle sources and flux attenuation in the North Pacific, Deep Sea Research Part II: Topical Studies in Oceanography, 55, (14-15) pp. 1522-1539. ISSN 0967-0645 (2008) [Refereed Article]
The VERtical Transport In the Global Ocean (VERTIGO) study examined particle sources and fluxes
through the ocean’s ‘‘twilight zone’’ (defined here as depths below the euphotic zone to 1000 m).
Interdisciplinary process studies were conducted at contrasting sites off Hawaii (ALOHA) and in the NW
Pacific (K2) during 3-week occupations in 2004 and 2005, respectively. We examine in this overview
paper the contrasting physical, chemical and biological settings and how these conditions impact the
source characteristics of the sinking material and the transport efficiency through the twilight zone.
A major finding in VERTIGO is the considerably lower transfer efficiency (Teff) of particulate organic
carbon (POC), POC flux 500/150m, at ALOHA (20%) vs. K2 (50%). This efficiency is higher in the diatomdominated
setting at K2 where silica-rich particles dominate the flux at the end of a diatom bloom, and
where zooplankton and their pellets are larger. At K2, the drawdown of macronutrients is used to assess
export and suggests that shallow remineralization above our 150-m trap is significant, especially for N
relative to Si. We explore here also surface export ratios (POC flux/primary production) and possible
reasons why this ratio is higher at K2, especially during the first trap deployment. When we compare
the 500-m fluxes to deep moored traps, both sites lose about half of the sinking POC by 44000 m, but
this comparison is limited in that fluxes at depth may have both a local and distant component.
Certainly, the greatest difference in particle flux attenuation is in the mesopelagic, and we highlight
other VERTIGO papers that provide a more detailed examination of the particle sources, flux and
processes that attenuate the flux of sinking particles. Ultimately, we contend that at least three types of
processes need to be considered: heterotrophic degradation of sinking particles, zooplankton migration
and surface feeding, and lateral sources of suspended and sinking materials. We have evidence that all
of these processes impacted the net attenuation of particle flux vs. depth measured in VERTIGO and
would therefore need to be considered and quantified in order to understand the magnitude and
efficiency of the ocean’s biological pump.