On the relationship between stratification and primary productivity in the North Atlantic

Abstract

Recent observational studies linking variability in global ocean productivity with upper ocean warming are based on the paradigm that warming produces a more stable water column which, in turn, inhibits primary productivity for a large fraction of the global ocean, namely the tropics and subtropics. Though seemingly straightforward, this paradigm relies on the assumption that an increase in the stratification of the upper ocean water column decreases the vertical mixing or overturning of the surface waters such that the supply of nutrients to the euphotic zone is reduced, and so too the primary productivity. Here we show, using observational data in the North Atlantic subtropical gyre, that while upper ocean stratification and primary productivity are strongly linked on seasonal time scales, they have at most a weak correlative relationship on interannual time scales over the modern observational record. We suggest that interannual variability in ocean biomass and primary productivity depends on a host of variables that are not easily predicted from the expected temperature response to climate variability and change. These variables include the strength of local and remote wind and buoyancy forcing and the surface or subsurface advective supply of nutrients.

Water column stratification structures viral community composition in the Sargasso Sea

“…This is consistent with prior studies, which have de monstrated that physical processes drive bacterial dynamics at the BATS site (Carlson et al 1996, Steinberg et al 2001, Nelson et al 2004, Palter et al 2005, Lozier et al 2011. During mixing periods, bacterioplankton den sities are redistributed homogeneously within the mixed layer (Carlson et al 1996, Steinberg et al 2001.…”

Summer primary productivity and phytoplankton community composition driven by different hydrographic structures in the East/Japan Sea and the Western Subarctic Pacific

“…Although nutrient concentrations in the euphotic zone (<75 m) were higher in the WSP than in the EJS, the integrated primary productivity was higher in the EJS than in the WSP [Shiomoto, 2000;Yamada et al, 2005;Kwak et al, 2013aKwak et al, , 2013b [Lozier et al, 2011]. Iron limitation may be another cause as suggested by Nishioka et al [2003] and Harrison et al [2004].…”

Picoeukaryote distribution in relation to nitrate uptake in the oceanic nitracline

“…This supports the view put forward by Bienfang et al (1984) and Banse (1987) that nutrient fluxes to the upper ocean are biologically regulated within the lower euphotic zone rather than due to physical processes alone. This mechanism is additional to density-driven stratification that separates the upper euphotic zone from deep ocean nu trient reservoirs, and may explain why only weak correlations between stratification and primary production have been found on interannual timescales (Dave & Lozier 2010, Lozier et al 2011.…”