03/17/2013
Latitudinal Patterns Unveiled in Elemental Ratios of Marine Plankton
Summary
Nearly 75 years ago, Alfred C. Redfield observed a similarity between the elemental composition of marine plankton in the surface ocean and dissolved nutrients in the ocean interior. This stoichiometry among carbon (C), nitrogen (N), and phosphorus (P) continues to be a central tenet in ocean biogeochemistry and is used to infer a variety of ecosystem processes, such as phytoplankton productivity and rates of nitrogen fixation and loss. Over the years, however, model, field, and laboratory studies have shown that different mechanisms can explain both constant and variable ratios of C to N and P among ocean plankton communities. The range of C/N/P ratios in the ocean and their predictability are the subject of much active research. In a recent study, partially funded by the U.S. Department of Energy’s Office of Biological and Environmental Research, global patterns in the elemental composition of phytoplankton and particulate organic matter in the upper ocean were assessed using published and unpublished observations of particulate P, N, and C from a broad latitudinal range, supplemented with elemental data for surface plankton populations. The authors showed that the elemental ratios of marine organic matter exhibit large spatial variations, with a global average that differs substantially from the canonical Redfield value. Moreover, elemental ratios exhibit a clear latitudinal trend. Specifically, a ratio of 195:28:1 is observed in the warm, nutrient-depleted low-latitude gyres; a ratio of 137:18:1 in warm, nutrient-rich upwelling zones; and a ratio of 78:13:1 in cold, nutrient-rich high-latitude regions. Thus, it appears that the coupling between oceanic C, N, and P cycles may vary systematically by ecosystem, which, in turn, is reflected in these observed latitudinal tendencies.
References
Martiny, A. C., C. T. A. Pham, F. W. Primeau, J. A. Vrugt, J. K. Moore, S. A. Levin, and M. W. Lomas. 2013. “Strong Latitudinal Patterns in the Elemental Ratios of Marine Plankton and Organic Matter,” Nature Geoscience 6, 279–83. DOI: 10.1038/ngeo1757.