MODELS EXPLAINING LONG-TERM PARTICLE EXPORT AT 150 M DEPTH AT STATION ALOHA

Organic particles settling from the surface ocean provide the fuel for enhanced deep-ocean carbon storage, often termed the "biological pump." Small variations in the fraction of primary production that is exported can have large effects on the global carbon cycle. 33y of measured particle export at a depth of 150 m at Station ALOHA in the North Pacific Subtropical Gyre show a clear long-term increase in measured rates of primary production, but no long-term change in export flux, and temporal variation in flux was uncoupled from primary production. Understanding the controls on this flux variation is needed to enable future predictions. Depth-integrated primary production only weakly predicted particle flux, explaining only 10% of the variation in flux with no lagged effects at monthly time scales. Other measured properties, e.g., chlorophyll and particle volume distribution, did not improve the explanatory power. Among-trap deployment error was high; export flux variation measured over short time scales via separate sediment trap deployments showed variation that is 50% of the temporal variation in the time series data, indicating an upper predictive limit of 50%. Simple process-based models of particle settling velocity show large sensitivity to flux based on small variations in settling velocity and particle mineralization rate. Understanding controls on short time-scale (i.e., monthly) variation in particle flux remains elusive, and here we show that combined process and statistical models are needed to understand these controls at various time scales.

Presentation Preference: Oral

Primary Presenter: Robert Hall, University of Montana (bob.hall@flbs.umt.edu)

Authors:

Robert Hall, University of Montana  (bob.hall@flbs.umt.edu)

Emily Zakem, Carnegie Science  (ezakem@carnegiescience.edu)

Zhou Liang, Carnegie Science  (zliang@carnegiescience.edu)

Angelicque White, Univeristy of Hawaii Manoa  (aewhite@hawaii.edu)

Matthew Church, University of Montana  (matt.church@flbs.umt.edu)