OceanLiNES · Ocean Limiting Nutrients – Examination from Space

Ocean Limiting Nutrients – Examination from Space

Oceanic phytoplankton are the base of the marine food web and contribute significantly to removal of carbon from the atmosphere. Monitoring how their distribution and activity are changing into the future is therefore a major scientific goal. It is widely recognised that nutrient availability is a critical factor regulating phytoplankton distribution in the global ocean, but exactly which nutrients are limiting phytoplankton in different regions is less well resolved. A potential route for synoptic monitoring of phytoplankton nutrient limitation could lie in observations of phytoplankton fluorescence made by sensors on earth orbiting satellites. Prior work—both in the field and laboratory—has repeatedly shown that phytoplankton living under conditions with insufficient availability of the ‘micronutrient’ iron emit significantly more fluorescence per unit biomass than those living under growth limitation by ‘macronutrients’, such as nitrate or phosphate. Therefore, synoptic observations of phytoplankton fluorescence made by sensors on earth orbiting satellites represents a potential approach for distinguishing regions of iron-limited phytoplankton growth from those limited by nitrate or phosphate. This would allow for robust descriptions of where, and how much, of the ocean is currently limited by iron or nitrate/phosphate. Looking to the future, this would allow for a low cost means for monitoring how these distributions are changing with time. A major factor confounding direct application of available satellite fluorescence data lies in correcting the fluorescence signal received by satellite sensors for additional, poorly resolved physiological mechanisms employed by phytoplankton. In particular, down-regulation of fluorescence emission from phytoplankton under different levels of incident irradiance at the instant the fluorescence is emitted/detected by the satellite sensor occurs, and is not the same between phytoplankton communities. The main aim of this project was to perform measurements and experiments throughout the global ocean to determine (i) if there were large regional variations in down-regulation of phytoplankton fluorescence with increasing incident irradiance, and (ii) if the environmental or biological factors that might be driving this. Such understanding might then be used to correct satellite fluorescence signals to reveal patterns of iron-stressed phytoplankton growth at a global scale.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз