[L&O Featured Article]L&O Vol. 46, No. 2 (March 2001): Featured Article now available

[lo-feature-admin@aslo.org]

The featured article in the March 2001 issue of L&O is:

Duarte, Carlos M., Susana Agusta, Javier Aristegui, Natalia Gonzalez, and
Ricardo Anadon. 2001. Evidence for a heterotrophic subtropical northeast

Atlantic. Limnol. Oceanogr. 46: 425-428.

This article is freely available on the Web at

          http://aslo.org/lo/toc/vol_46/issue_2/0425.pdf

Instructions for reading PDF files are located on the ASLO web page:

          http://aslo.org/help/loonline.html

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Introductory comments by Erik Smith (one of the two people that reviewed
this paper for L&O)

This month's L&O featured article by Duarte et al. (2001) contributes to an
ongoing debate regarding the balance between gross primary production (P)
and total community respiration (R) in oligotrophic ocean environments.
Recent studies have suggested that R exceeds P over large areas of the
oceans, with the greatest deficits occurring in the most oligotrophic
regions (del Giorgio et al. 1997; Duarte and Agusti 1998; Duarte et al.
1999). This conclusion has profound implications for our understanding of
the oceanic carbon cycle. In addition to calling into question the belief
that the ocean's pelagic food webs are necessarily based on autochthonous
production, these findings indicate that the biota of the oligotrophic
regions acts as a source, rather than a sink, for atmospheric CO2. These
studies have met with some well-considered skepticism, however, on the
basis of both the form of the data analysis and on the apparent difficulty
in balancing the proposed regional deficits with non-local sources
(Williams 1998; Williams and Bowers 1999).

As both sides of the debate agree, uncertainties in oceanic P-R balances
partly result from the emphasis on P, and a relative neglect for R, in most
large-scale oceanographic programs. This paucity of coupled P and R
measurements has particularly hampered the debate with respect to the
oligotrophic ocean. In their present contribution, Duarte et al. (2001)
move away from generalized relationships across different oceanic provinces
and focus on the subtropical NE Atlantic. Compiling O2-based P and R rate
data from several cruises conducted in this region, the authors find the
mean depth-integrated value for P to be significantly lower than that for
R, with two-thirds of the stations investigated having a net heterotrophic
euphotic zone. While the data available do not allow for an estimate of the
net P-R balance at the annual time scale, the results certainly add to the
body of evidence arguing for an excess organic carbon demand relative to
production in this oligotrophic area. To account for this imbalance, the
authors cite evidence for lateral inputs from the productive upwelling
areas of the NW African coast and substantial atmospheric deposition to
this area of the ocean.

This contribution will likely continue to stimulate debate on this
fundamental issue. Hopefully, it will also promote further efforts to
expand the presently meager empirical basis for coupled P and R estimates
in the open oceans.

REFERENCES

del Giorgio, P. A., J. J. Cole, and A. Cimbleris. 1997. Respiration rates
in bacteria exceed plankton production in unproductive aquatic systems.
Nature 385: 148-151.

Duarte, C. M., and S. Agusti. 1998. The CO2 balance of unproductive
aquatic ecosystems. Science 281: 234-236.

Duarte, C. M., S. Agusti, P. A. del Giorgio, and J. J. Cole. 1999. Is the

open ocean heterotrophic? Science 284: 1735b.

Duarte, C. M., J. Aristegui, N. Gonzalez, S Agusti, and R. Anadon.
 2001.
Evidence for a heterotrophic subtropical northeast Atlantic. Limnol.
Oceanogr. 46: 425-428.

Williams, P. J. leB. 1998. The balance of plankton respiration and
photosynthesis in the open ocean. Nature 394: 55-57.

Williams, P. J. leB., and D. G. Bower. 1999. Determination of organic
carbon balance in the oceans from field observations: a re-evaluation.
Science 284: 1735a.