Decoupling of net community and export production on submesoscales in the Sargasso Sea

Abstract

Determinations of the net community production (NCP) in the upper ocean and the particle export production (EP) should balance over long time and large spatial scales. However, recent modeling studies suggest that a horizontal decoupling of flux-regulating processes on submesoscales (≤10 km) could lead to imbalances between individual determinations of NCP and EP. Here we sampled mixed-layer biogeochemical parameters and proxies for NCP and EP during 10, high-spatial resolution (~2 km) surface transects across strong physical gradients in the Sargasso Sea. We observed strong biogeochemical and carbon flux variability in nearly all transects. Spatial coherence among measured biogeochemical parameters within transects was common but rarely did the same parameters covary consistently across transects. Spatial variability was greater in parameters associated with higher trophic levels, such as chlorophyll in >5.0 μm particles, and variability in EP exceeded that of NCP in nearly all cases. Within sampling transects, coincident EP and NCP determinations were uncorrelated. However, when averaged over each transect (30 to 40 km in length), we found NCP and EP to be significantly and positively correlated (R = 0.72, p = 0.04). Transect-averaged EP determinations were slightly smaller than similar NCP values (Type-II regression slope of 0.93, standard deviation = 0.32) but not significantly different from a 1:1 relationship. The results show the importance of appropriate sampling scales when deriving carbon flux budgets from upper ocean observations.

Ecosystem metabolism in salt marsh tidal creeks and ponds : applying triple oxygen isotopes and other gas tracers to novel environments

“…McGillicuddy et al 2007, Estapa et al 2015, Ferrón et al 2015. For example, we find that the dissolved gas tracers vary substantially with biological activity over the timescale of hours, not weeks as would be expected from the gas exchange timescale (see section 2 and supplementary information).…”

“…A growing body of literature suggests that physical variability is an important determinant of community structure , production , and export [Ayers and Lozier 2012]. In particular submesoscale to mesoscale (kilometers to hundreds of kilometers) variability may play an important role in increasing phytoplankton community diversity [Clayton et al 2013, Lévy et al 2014 and concentrating or enhancing biological activity [McGillicuddy et al 2007, Klein and Lapeyre 2009, Estapa et al 2015 at small scales.…”

Prediction of the Export and Fate of Global Ocean Net Primary Production: The EXPORTS Science Plan

“…This corresponds to a time scale of roughly 10 days assuming a trap at 500 m is sampling slowly sinking particles (50 m d −1 ). Recent work by Estapa et al (2015) provides additional clues for the duration of an ECC state sampling period. These authors made simultaneous determinations of POC export (via 234 Th disequilibrium) and net community production (NCP; via O 2 /Ar gas tracers) on ∼2 km spatial scales over eight 30-40 km transects.…”

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

“…Monthly, multiyear time-series of productivity, based on incubations measuring the uptake of 14 C-labeled dissolved inorganic carbon (DIC) and 15 NO − 3 have been reported previously (Pennington and Chavez, 2000;Wilkerson et al, 2000), and numerous process-oriented biological studies have been conducted (Pilskaln et al, 1996;Kudela and Dugdale, 2000;Ward, 2005;Ryan et al, 2009;Johnson, 2010;Smith et al, 2014aSmith et al, , 2016 , but can be challenging to apply in systems where recently-upwelled water is observed at the surface; this low O 2 water may bias estimates low if not accurately accounted for (Munro et al, 2013;Teeter, 2014;Haskell et al, 2016b). Furthermore, inferring carbon export below the mixed layer from techniques within the mixed layer is complicated by the fact that lateral transport of surface waters and oceanic fronts may cause a spatial and/or temporal decoupling between carbon fixation and export (Olivieri and Chavez, 2000;Estapa et al, 2015;Nagai et al, 2015).…”