Environmental Engineering Reference
In-Depth Information
THE SUBOXIC TRANSITION ZONE IN THE
BLACK SEA
James W. Murray
1
, Evgeniy Yakushev
2
1
University of Washington, School of Oceanography, Box 355351, Seattle WA 98195-5351, USA
2
Russian Academy of Sciences, P.P. Shirshov Institute of Oceanology, Okeanologiya, Gelendzh-
ik-7, 353470, Russia
Abstract
The Black Sea is a classic marine anoxic basin. It has an oxygenated surface layer
overlying a sulfide containing (anoxic) deep layer. At the interface between these
layers there is a suboxic layer in which both oxygen and sulfide are extremely low
and have no perceptible vertical gradients. This condition has evolved because
of the superposition of the flux of organic matter which consumes oxygen during
respiration on the strong density stratification on the water column. The density
stratification is strong because water with high salinity enters the Black Sea
from the Bosporus Strait and mixes with overlying cold intermediate layer (CIL)
water that forms in the winter on the northwest shelf and in the center of the
western and eastern gyres. The rate of CIL formation is also variable over 5 to
10 year periods in response to climate variability on that same time interval.
This variability appears to be driven by the North Atlantic Oscillation. This
mixture of Bosporus outflow and entrained cold intermediate layer water results
in formation the Bosporus Plume which ventilates the layers of the Black Sea
deeper than the CIL. New data about the biogeochemical distributions (oxygen,
sulfide, nitrate and ammonium) were obtained during R/V Knorr research cruises
in 2001 and 2003. The distributions in the upper layers reflect a classic example
of the connection between climate forcing, physical regime, chemical fluxes and
biological response.
1. INTRODUCTION
The Black Sea, Pontus Euxinus to the Greeks because of its stormy weather,
is an inland marine water body with a peculiar layering of oxic, suboxic and
anoxic or sulfidic water that has been of great interest to geochemists and
microbiologists [9, 62]. In this overview we will describe the physical and
chemical distributions and summarize new ideas about how variability in re-
gional climate modulates the physical forcing and circulation, nutrient fluxes
and biological response.
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