Environmental Engineering Reference
In-Depth Information
until the anthropogenic enhancement in recent times, respiration rates in this
region were probably not high enough to trigger SO
4
2
−
reduction.
There are as yet no data on N
2
O from the Namibian upwelling zone. Off
Peru and Chile, enhanced N
2
O production does occur in the O
2
deficient
waters [9, 12], but with peak values generally occurring within the transition
zone between the oxic and suboxic layers (associated with low NO
2
−
[9]). This
is at variance with the trend observed off India where N
2
O often attains the
highest concentrations in suboxic (NO
2
−
bearing) waters, implying different
mechanisms of N
2
O production.
With regard to benthic processes, SO
4
2
−
reduction rates over the Indian
shelf appear to be greatly subdued, with correspondingly lower concentrations
of free sulphide in porewaters, than off Namibia. These differences, tentatively
attributed to a combination of lesser availability of organic matter and greater
abundance of reactive iron over the Indian shelf [S.W.A. Naqvi and V. Br uchert,
unpublished data], should be investigated in detail.
Acknowledgements
This manuscript was prepared when SWAN was on leave from NIO as a
Fellow at the Hanse Wissenschaftskolleg (HWK), Delmenhorst, Germany; the
help and support of the HWK staff is gratefully acknowledged. We also wish
to record our gratitude to Dr. M.D. George, Dr. S.G.P. Matondkar, Dr. D.M.
Shenoy, Dr. V.V.S.S. Sarma, Ms. Witty D' Souza and Mr. Anil Pratihary for
their contribution to collection of the data used here. The IFP data were kindly
supplied to us by Prof. Karl Banse, who should also be thanked for generously
sharing with us his vast knowledge of the oceanography of the Arabian Sea. Our
guru of oceanic nitrogen cycling, Dr. Lou Codispoti, along with an anonymous
reviewer made excellent suggestions that have greatly improved this article.
References
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