IGPP Seminar Series

Coordination of nutrient cycles by Southern Ocean climate

by Curtis Deutsch
Atmospheric and Oceanic Sciences UCLA

Abstract

The elemental composition of plankton is central to understanding the limits to marine biological productivity and its role in the global carbon cycle. The major bio-limiting nutrients, nitrate and phosphate, exhibit one of the strongest correlations in the ocean with a slope (16N:1P) remarkably similar to the average biomass of plankton, a fact that Alfred Redfield understood to imply either an acclimation of plankton to average nutrient availability or an adjustment of the ocean nutrient reservoirs to plankton metabolism. However the N:P ratios at the species and organism levels are highly variable, and the processes through which the global N:P relationship emerge from that biological flexibility are not known. We use an ocean circulation model combined with observed distributions of nitrate and phosphate to detect large-scale deviations from the "Redfield" N:P ratio of biological nutrient removal in surface waters of the Southern Ocean, a region with global influence on the productivity of low latitudes and the storage of carbon at depth. The Southern Ocean nutrient data, situated in the mean circulation, require a latitudinal gradient in the N:P ratio of biological uptake with values below the canonical 16:1 ratio in the Antarctic zone increasing to high values in the Subantarctic. These variations do not follow the N:P of nutrient supply, indicating that plankton communities with distinct metabolic requirements are selected by the physical environment, with significant apparent effects from sea surface temperature and iron-bearing atmospheric dust. The average N:P ratio of plankton therefore does not adjust to the availability of these nutrients, but reflects a regional balance between environmental factors that vary with climate.
Tuesday, 24 November 2009
3853 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM