Environmental Controls on Carbon:Nitrogen Variability in Surface Ocean Plankton

Previous studies have indicated that variability in C:N is controlled by several factors including phylogeny of dominant plankton, N-limited growth, live:dead particulate matter, light, and time of day. To glean a deeper understanding of how environmental factors might control variability in C:N across ocean basins, we collected samples of surface ocean plankton (<30 um diameter) at high-resolution time scales (1-4 hr) along two north-south cruise transects in the Indian (IO9) and Atlantic Oceans (AMT28). Similar to other global-scale data sets, C:N was high in oligotrophic gyres relative to that in nutrient rich waters. In some localized regions, however, daily oscillations in the C:N of surface ocean plankton was higher than basin-scale variability. For example, variability in the 48-hour moving mean C:N in the southern (5.8-7.5) and northern regions (6.4-7.2) along AMT28 was lower than diel shifts in C:N in some localized hotspots (5.5-7.7). To identify environmental factors that control diel changes in C:N, we used a non-linear statistical model focusing on independent and interactive effects of nutrient supply and temperature, two factors that are predicted to experience dramatic relative changes within and between biogeographical provinces in the future. Our across-basin approach to analysis may be robust in identifying environmental controls of diel variability in surface ocean plankton C:N.