The task is to describe the effects of ultraviolet radiation on a biological process, such as photosynthesis. For a particular location, this requires a description of potential photosynthesis as modified by an inhibition function:
where P is daily photosynthesis ( 
),
B is the concentration of chlorophyll-a ( 
),
is chlorophyll-normalized photosynthesis in the
absence of inhibition
,
and the dimensionless inhibition term is a function of
,
spectral irradiance ( 
),
weighted by a wavelength-dependent ( 
)
biological weighting function, 
, discussed below.
In principle, one can calculate the effects of ultraviolet radiation on
aquatic photosynthesis by evaluating Eq.(1) with and without UV wavelengths,
or under different degrees of ozone depletion.
Common simplifications are to ignore variation of chlorophyll with depth (z)
and time (t) and to represent 
as a function of
photosynthetically available radiation (PAR; 400-700 nm), regardless of
spectral quality (units: 
).
A great deal of information is required to assign parameters and functional
relationships to Eq.(1), and at present it serves better as a context for
discussing UV and phytoplankton than as a tool for quantitative analysis.
To evaluate the equation, one must specify:
1) Absolute spectral irradiance, 
( 
) as a function of depth
and time;
2) Photosynthesis as a function of irradiance in the absence of inhibition,
vs. 
;
3) A biological weighting function (BWF), 
, to
convert absolute spectral irradiance to biological effective irradiance,
;
4) A time-dependent function relating inhibition of photosynthesis to
; and
5) An appreciation of how vertical mixing (hence, variable irradiance
exposures of phytoplankton) influences 2) and 4).
In would be quite an accomplishment to evaluate Eq.(1) for one day at one location. To obtain estimates of the effects of ozone depletion on annual marine photosynthesis in large regions of the ocean, variable biomass and changes in populations and their physiological characteristics would also have to be incorporated. Such a detailed calculation is beyond our reach at this time, but as we show below, many aspects of the problem have been studied, and rough estimates of UV effects have been obtained.