Introduction to Optical Constituents of the Ocean
In-water constituents that aﬀect its optical properties are traditionally lumped into the following:
1. Sea water (water + inorganic dissolved materials)
3. Colored (or chromophoric) dissolved organic material (CDOM)
3. Non-phytoplankton organic particles (sometimes referred to as detritus or tripton).
4. Inorganic particles.
The constituents are identiﬁed operationally based upon how we measure their optical properties and often are grouped by like optical properties. For example, the distinction between particulate and dissolved is operationally deﬁned by the ﬁlter type/pore size. It is essential to remember (1) that the strict chemical deﬁnition is quite diﬀerent and (2) ﬁlter pore size varies from author to author and (3) keep track of pore sizes to ensure closure (i.e. don’t deﬁne dissolved organic matter by the ﬁltrate of a 0.2 micron pore sized ﬁlter and then measure particulates on a 0.7 micron pore size GF/F ﬁlter). Similarly, often all the non-phytoplankton particles are lumped into a single compartment as their optical properties are quite similar. Sometime all the particulate material is lumped together into suspended particulate material (SPM) or part of it into the particulate organic material (POM). This is often done when studying a speciﬁc bio-geochemical property using optics.
The diﬀerentiation of dissolved and particulate materials (using a ﬁlter) does not imply that the dissolved material is organic, though this is most often the assumption. For example, inorganic dissolved substances such as iron oxides (rust) could contribute in certain cases.