VERTIGO (VERtical Transport In the Global Ocean): A study of particle sources and flux attenuation in the North Pacific

Abstract

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 (T eff ) of particulate organic carbon (POC), POC flux 500 / 150 m, at ALOHA (20%) vs. K2 (50%). This efficiency is higher in the diatom-dominated 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 >4000 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.

Particle fluxes associated with mesoscale eddies in the Sargasso Sea

“…A similar conclusion was reached in the NW Pacific based upon enhanced N:Si ratios below the DCM (Buesseler et al, 2007b).…”

Physical and biogeochemical modulation of ocean acidification in the central North Pacific

“…Organic carbon export from the euphotic zone, via gravitational settling of particles and by downward turbulent mixing of dissolved compounds, has varied considerably over our study period (16,18,23). About 60% of this passively exported carbon is converted back to DIC through microbiological respiration between 150-300 m, and another 20% is remineralized between 300-500 m (23,24). An additional contribution to carbon remineralization within the 300-500 m layer is made by the metabolism of vertically migrating mesozooplankton (25,26).…”

Global database of surface ocean particulate organic carbon export fluxes diagnosed from the <sup>234</sup>Th technique

“…In years 1992, 1998 and 2002, the number of 234 Th measurements increased. This is likely due to significant improvements in the 234 Th methodology such as the introduction of the small volume technique (Benitez-Nelson et al, 2001b), and it also highlights dedicated carbon export programmes such as the VERTIGO voyages in the Pacific Ocean (Buesseler et al, 2008b(Buesseler et al, , 2009. It is important to mention that our database only references papers where Th-derived export data are presented in tables, rather than only graphically.…”