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Peter,

Thank you for the correction. For 30 years, I have been going around  
with the memory of an undergrad oceanography lecture in which it was  
said that UV only penetrates about a metre. I wonder whether it was  
the lecturer or my memory that was at fault?

Peter A. Nelson wrote:

> Actually, UV light does penetrate to significant depths (in clear  
> oceanic water there is sufficient UV light to, theoretically,  
> provide visual sensitivity at 200 m depth, Losey et al. 1999 J Fish  
> Biol 54:921-943) and marine organisms have evolved physiological  
> and behavioral traits both to take advantage of UV vision and  
> coloration and to protect themselves from its deleterious effects.




I wasn't going to respond to Bill's

> Most phytoplankton sink when they have exhausted their growth  
> potential and do not die on the surface. They are then degraded by  
> bacterial decomposition on the seabed, a process which consumes  
> oxygen and releases CO2 into the water column.

but since Peter has required me to write:

Bill,

My understanding is that most phytoplankton die by being eaten and  
that much of the carbon in their cells is then metabolized by the  
herbivore (or passed up to a predator and metabolized higher in the  
trophic pyramid). My suggestion to the anonymous PtP was based on a  
supposition that hypothetical neustonic phytoplankton would have to  
be eaten at the surface, increasing the chance that their carbon  
would be returned to carbon dioxide at near-surface depths, making it  
that much the more likely that it would return to the atmosphere  
swiftly rather than be passed down to a depth where it might stay for  
a prolonged period.

I realize that that makes some assumptions about the migratory  
behaviour of hypothetical herbivores that graze on hypothetical  
neustonic phytoplankton but, if we may assume that all else is equal  
(a farcical notion, as ever), do you see a fault in my argument for a  
qualitative trend of more rapid return of carbon to the atmosphere  
from neustonic versus merely euphotic-zone primary production?


Trevor Kenchington

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