Processes and patterns of oceanic nutrient limitation

Abstract

Microbial activity is a fundamental component of oceanic nutrient cycles. Photosynthetic microbes, collectively termed phytoplankton, are responsible for the vast majority of primary production in marine waters. The availability of nutrients in the upper ocean frequently limits the activity and abundance of these organisms. Experimental data have revealed two broad regimes of phytoplankton nutrient limitation in the modern upper ocean. Nitrogen availability tends to limit productivity throughout much of the surface low-latitude ocean, where the supply of nutrients from the subsurface is relatively slow. In contrast, iron often limits productivity where subsurface nutrient supply is enhanced, including within the main oceanic upwelling regions of the Southern Ocean and the eastern equatorial Pacific. Phosphorus, vitamins and micronutrients other than iron may also (co-)limit marine phytoplankton. The spatial patterns and importance of co-limitation, however, remain unclear. Variability in the stoichiometries of nutrient supply and biological demand are key determinants of oceanic nutrient limitation. Deciphering the mechanisms that underpin this variability, and the consequences for marine microbes, will be a challenge. But such knowledge will be crucial for accurately predicting the consequences of ongoing anthropogenic perturbations to oceanic nutrient biogeochemistry

Southern Ocean phytoplankton physiology in a changing climate

“…Additionally, Fe is involved in other key cellular processes such as respiration, macronutrient assimilation and detoxification of reactive oxygen species (Sunda, 1989;Morel et al, 1991;Sunda and Huntsman, 1995). Due to their high demand for Fe, primary producers have developed specialised mechanisms to satisfy their needs; resulting in a decoupling between intracellular and dissolved Fe stoichiometry (Morel and Price, 2003;Moore et al, 2013), as well as complex interactions and feedbacks between Fe biology and its chemistry (Hassler et al, 2011a).…”

Diagnosing oceanic nutrient deficiency

“…When combined with the associated carbon fluxes, this cycle of organic matter production, export and remineralization constitutes the biological carbon pump (BCP) [4], which acts to store a large amount of dissolved inorganic carbon in the deep ocean and exerts a major control on atmospheric pCO 2 [5][6][7]. Simultaneously, the availability and supply of a range of nutrients to the upper ocean frequently exerts a fundamental constraint on the rate [8] and/or absolute [9] production of new organic matter in the surface layer [10,11]. Reciprocal interactions between internal oceanic nutrient cycling and upper ocean microbial activity are hence a key driver of global biogeochemical processes [12].…”

“…Reciprocal interactions between internal oceanic nutrient cycling and upper ocean microbial activity are hence a key driver of global biogeochemical processes [12]. In particular, nutrient limitation can set a fundamental constraint on the local strength and overall efficiency of the BCP [10,11,13].…”

How well can we quantify dust deposition to the ocean?

“…Efforts to evaluate the supply of dust to the ocean are motivated in large part by the desire to assess the role of aerosols as a source of iron, an essential nutrient whose abundance is thought to influence rates and geographical patterns of photosynthesis and nitrogen fixation [1][2][3][4][5][6][7]. Ocean productivity, in turn, is a major component of the global carbon cycle [8], so there is a recognized need to include dust supply in global biogeochemical models [9].…”