Coupling carbon and energy fluxes in the North Pacific Subtropical Gyre

Abstract

The major biogeochemical cycles of marine ecosystems are driven by solar energy. Energy that is initially captured through photosynthesis is transformed and transported to great ocean depths via complex, yet poorly understood, energy flow networks. Herein we show that the chemical composition and specific energy (Joules per unit mass or organic carbon) of sinking particulate matter collected in the North Pacific Subtropical Gyre reveal dramatic changes in the upper 500 m of the water column as particles sink and age. In contrast to these upper water column processes, particles reaching the deep sea (4000 m) are energy-replete with organic carbon-specific energy values similar to surface phytoplankton. These enigmatic results suggest that the particles collected in the abyssal zone must be transported by rapid sinking processes. These fast-sinking particles control the pace of deep-sea benthic communities that live a feast-or-famine existence in an otherwise energy-depleted habitat.

Fig. 1

Mass and carbon fluxes. Flux profiles of a mass, b total carbon (TC), and c organic carbon (OC). The magenta curves are the best fits to a log–log transformed normalized power function of the form F_z = F₁₀₀ (z/100)^b where F_z is flux at depth z(m), F₁₀₀ is flux at 100 m and b is the coefficient of flux attenuation (ref. ; Supplementary Fig. 1). The best fit parameters are: mass flux, F₁₀₀ = 158.5 mg m⁻² d⁻¹, b = −0.60, r² = 0.85; TC flux, F₁₀₀ = 45.71 mg C m⁻² d⁻¹, b = −0.80, r² = 0.93; OC flux, F₁₀₀ = 42.66 mg C m⁻² d⁻¹, b = −0.89, r² = 0.93. Vertical fluxes of d OC, e IC and f BC expressed as percentages of TC for each depth

Fig. 2

Energy fluxes. a Energy flux and b specific energy of SPM expressed in mass-specific (blue symbols) and OC-specific (magenta symbols) units. The magenta curve on the left is the best fit for the equation presented in Fig. 1 (also see Supplementary Fig. 2). The best fit parameters are: F₁₀₀ = 2701.6 J m⁻² d⁻¹, b = −1.81, r² = 0.90. The horizontal magenta dashed line on the right is the approximate depth of the photosynthetic compensation irradiance (see text for details). c Schematic representation of the flux profiles and flux attenuation coefficients for mass (blue curve, b = −0.60), OC (green curve, b = −0.89), and energy (magenta curve, b = −1.81)

Fig. 3

Energy capture, flux, and dissipation. a Carbon and energy flux processes showing specific energy of photosynthetic production (green bar), depth-dependent changes in energy of SPM as particles sink and age (magenta symbols) and mean ± s.d. specific energy for SPM collected at 4000 m (blue symbol). The horizontal magenta dotted line at 175 m depicts the photosynthetic compensation irradiance (see text for details). b Profiles of photosynthetic production (green symbols) and concentration of dissolved inorganic carbon (blue symbols) at Station ALOHA. c Schematic representation of the major processes controlling carbon and energy fluxes at Station ALOHA