[L&O Featured Article] L&O Featured Article, Vol 52(1) (correction)

[L&O Feature Articles Announcements]

With apologies- the article referenced below is in the January 2007 issue of
Limnology and Oceanography, Vol 52, Issue 1.

 

Paul Kemp

ASLO Web Editor

 

 

  _____  

 

The Featured Article in the November 2005 issue of L&O is:

 

Morel, André, Bernard Gentili, Hervé Claustre, Marcel Babin, Annick Bricaud,
Joséphine Ras, and Fanny Tièche. 2007. Optical properties of the "clearest"
natural waters. Limnol. Oceanogr. 52: 217-229.

 

The article is freely available at:

 

http://aslo.org/lo/toc/vol_52/issue_1/0217.pdf

 

 

Introductory comments by Heidi Sosik (L&O Associate Editor)

 

Just over 25 years ago, Smith and Baker (1981) published a seminal paper on
the optical properties of the clearest natural waters.  The premise that
they had indeed observed the clearest natural waters stood nearly
uncontested until now.  Morel and co-workers report on measurements in the
South Pacific gyre that, in the words of one reviewer, are
“amazing—literally of another planet.”  The optical measurements presented
in this paper not only show these waters to be exceptionally clear, but also
refute widely-used laboratory-based standards for “pure water” absorption
coefficients. These observations bear on the ecology and biogeochemistry of
a vast region of the South Pacific and have fundamental implications for
physical optics, photochemistry, and photobiology in aquatic systems.  

 

At first glance, this paper may seem principally about optical methods and
the challenges of making observations when signals are exceedingly small.
There are much broader implications, however.  First, the results provide
characterization of a poorly known, but vast region of the open ocean that
proves to be hyper-oligotrophic, with chlorophyll concentrations typically
less than 0.03 mg m-3 and euphotic zone depths greater than 150 m.  The
optical clarity is rivaled only by a permanently ice-covered polar lake
studied by Vincent et al. (1998).  These in situ observations confirm
results from ocean color satellite missions that routinely show the South
Pacific gyre to have the lowest surface chlorophyll concentrations on the
globe.  They are also consistent with nitraclines as deep as 200 m in the
area.  The full interplay of ecological, biogeochemical, and physical
factors contributing to these conditions remains to be explored.  

 

As mentioned above, Morel et al.’s results have a second major implication
that involves fundamental knowledge of the optical properties of pure water.
Surprisingly, these natural ocean waters seem to more “clean” (or free of
non-water materials) than has been possible to generate reliably in the
laboratory to date.  The evidence for this is that the ocean waters have
lower absorption at certain ultraviolet wavelengths than “pure” water
measured in noteworthy laboratory studies.  The consequences of this finding
extend well beyond abstract interest in pure water properties.  The direct
implication for all natural aquatic systems is that more ultraviolet
radiation than previously thought is absorbed by organisms and other
materials such as dissolved organic compounds subject to photochemical
transformation.  This knowledge will undoubtedly motivate renewed efforts to
characterize pure water optical properties as well as reassessments of the
effects of ultraviolet radiation in natural waters bodies.  

 

In this work, Morel et al. acknowledge inspiration by borrowing the title of
Smith and Baker’s 1981 influential paper.  They make only one change for
this new classic: “clearest” is now in quotation marks, prudently awaiting
another revelation.  

 

References

 

Smith, R. C., and K. S. Baker. 1981. Optical properties of the clearest
natural waters (200-800 nm). Appl. Opt. 20: 177-184.

 

Vincent, W. F., R. Rae, I. Laurion, C. Howard-Williams, and J. Priscu.
1998.  Transparency of Antarctic ice-covered lakes to solar UV radiation.
Limnol. Oceanogr. 43: 618-624.  

 

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