Initial development and laboratory testing of a ChLorophyll Absorption Meter (CLAM)

Invisible microscopic algae in the ocean and freshwaters (phytoplankton) are plants that photosynthesise by absorbing solar radiation. In doing so, they provide half of the oxygen we breathe, they support marine ecosystem and the fisheries upon which we depend on, and absorb large quantities of CO2 from the atmosphere. Thus phytoplankton are a crucial component of oceanic and freshwater ecosystems that sustains human population.

To be able to effectively predict future changes in phytoplankton and manage environmental resources, it is therefore fundamental to accurately quantify the current stocks and variability of microscopic algae living in marine and freshwater bodies.

Since all phytoplankton are provided with the photosynthetic pigment chlorophyll-a, the concentration of this pigment (chl) is typically used as a proxy for phytoplankton biomass.
However, current methods to determine chl either rely on laborious and expensive collection and laboratory analyses of discrete water samples, or on highly-inaccurate in-situ measurements of chlorophyll fluorescence. Although in-situ fluorescence has the advantage of providing high-resolution measurements, it is affected by phytoplankton physiological processes that render in-situ fluorescence-based estimates of chl highly inaccurate, even if calibrated using collocated discrete data. For example, the ratio of fluorescence to chlorophyll-a concentration can vary by up to a factor 6 due to variations in solar irradiance.

As a consequence, *accurate* chl estimates are currently extremely scarce preventing effective management of water resources.

The overall objective of this project is to develop and test a prototype of an instrument that ultimately will provide high-resolution in-situ estimates of chl in with unprecedented accuracy.

Specifically, we will develop an initial laboratory prototype which will undergo multiple tests and improvements to achieve highly stable and highly accurate measurements of chl.

We envision that this instrument could become the new standard method for automatically measuring chl in situ and in the laboratory.

This instrument could also be deployed in continuous mode on ships and on autonomous platforms such as gliders and profiling floats, thus greatly extending the availability of highly-accurate and high-resolution in-situ measurements of chl.

Who might benefit from this research?
Accurate estimates of chlorophyll-a concentration (chl) are needed to monitor the stocks, dynamics and physiological status of phytoplankton in natural marine and freshwater environments. Furthermore, estimates of chl are needed for many other applications.
We therefore expect that the instrument developed in this project will bring benefits to:
1) scientists interested in rapidly estimating chl with high accuracy and with high-temporal resolution in natural marine and freshwater environments as well as in laboratory settings;
2) governmental agencies required to monitor of the status of natural marine and freshwaters waters;
3) private companies interested in monitoring the quality of waste water treatments
4) private shipping companies interested in quantifying the compliance of ballast water treatments.
5) any entity interested in measuring chl (including aquaculture and algal culturing laboratories).

How might they benefit from this research?
The above entities will benefit from this research by having a new tool to automatically (and thus rapidly) measure chlorophyll-a concentration at high-resolution and with unprecedented accuracy. These features will allow for considerable savings the analyses of chl and would potentially open new avenues of research.