Colour and Light in the Ocean

Marine ecosystems are open and dissipative systems that rely on an external energy source – light – for their sustenance. The magnitude of the light flux and the spectral quality of the light field (which determines colour) determine the rate of marine photosynthesis by phytoplankton in the ocean, and the types of phytoplankton communities that flourish in different parts of the ocean and in different seasons. Ocean colour – determined by the spectral quality of light scattered out of the sea and back into the atmosphere – can be monitored using satellite sensors, and used to map the distribution of the major phytoplankton pigment, chlorophyll-a, at global scales. Remote sensing of ocean colour, first realised in 1977, has revolutionalised the field of biological oceanography. Over the years, the quality of satellite products have continued to improve, and the range of products available have extended beyond chlorophyll concentration to encompass many variables of interest to biological oceanography and ocean biogeochemistry. The research topic proposed will cover a range of recent developments in ocean colour remote sensing and allied fields.

Particular emphasis will be given to the following topics:
• Ocean colour and phytoplankton as Essential Climate Variables and the use of ocean colour in climate research;
• Algorithms to estimate light flux reaching the sea surface and applications of the information, particularly for calculating marine primary production at large scales;
• Estimation of pools of carbon in the ocean using satellite data;
• Methods to deduce information on phytoplankton community structure using ocean colour and other satellite data; and
• Specialised algorithms for the study of the optical properties and optically-active constituents in optically-complex coastal and inland water bodies.

We envisage papers in this research topic from algorithm providers as well as users of the satellite products, especially the marine ecosystem modelling community, who use the satellite data to validate models and to improve model performance. All contributing authors will be asked to evaluate the current state of the field and to identify the next steps to be taken, to move the field forward.

This Research Topic is sponsored by the European Space Agency. It is the outcome of one of the follow-up actions agreed upon at the "Colour and Light in the ocean from Earth Observation (CLEO)" Workshop held at ESA ESRIN in September 2016, and benefited from a number of ESA projects related to ocean colour.