Environmental Engineering Reference
In-Depth Information
TEMPORAL VARIABILITY IN THE NUTRIENT
CHEMISTRY OF THE CARIACO BASIN
Mary I. Scranton
1
, Michelle McIntyre
2
, Yrene Astor
3
, Gordon T. Taylor
1
,
Frank Muller-Karger
2
, Kent Fanning
2
1
Stony Brook University, Marine Sciences Research Center, Stony Brook, NY 11794-5000, USA
2
University of South Florida, College of Marine Science, 140 7th Avenue South, St. Petersburg,
FL 33701, USA
3
Fundaci on La Salle de Ciencias Naturales, Estacion de Investigaciones Marinas de Margarita,
Apartado 144 Porlamar, Isla de Margarita, Venezuela
Abstract
Nutrient data have been collected monthly at the CARIACO time series site in
the Cariaco Basin since 1995, providing a unique picture of the cycling of NO
3
−
,
NO
2
−
,NH
4
+
,PO
4
3
−
and SiO
2
in this permanently anoxic system underlying a
major coastal upwelling zone. Our data indicate that nutrients for phytoplankton
growth are primarily supplied by upwelling of subsurface water on a seasonal
basis. In addition, coastal runoff seems to supply important amounts of silica and
ammonium to surface waters. We saw no indication of local nitrogen fixation
in the Cariaco surface waters. In the suboxic zone, our data to date are not of
sufficiently high enough resolution to resolve all important features. However,
at least partial phosphate removal appears to occur in a zone above the first
appearance of sulfide, and associated with intermittent intrusions of oxygenated
water. In the suboxic zone, there appear to be thin layers where ammonium and
nitrite coexist, potentially permitting anaerobic ammonium oxidation (anammox)
to take place. In the deep waters, concentrations of ammonium, phosphate and
silica continue to increase at a rate consistent with prior studies. However, in the
upper part of the anoxic zone, there is evidence for sulfide removal, probably
associated with oxygen intrusions.
Keywords:
Cariaco Basin, upwelling, nutrients, time series
1. INTRODUCTION
The Cariaco Basin has been known since the mid-1950s to be the world's
largest fully marine system which is permanently sulfidic [28]. As such, it has
been the site of a variety of studies focused on the products of remineralization
of organic matter [13, 27, 28, 30, 31, 37]. This fifty year time series has recently
been greatly enhanced by the establishment of the international (Venezuela and
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