Environmental Engineering Reference
In-Depth Information
phide followed by turquoise discolouration and suggested an abrupt injection
of hydrogen sulphide-containing water triggered by methane eruptions from
the sediment. According to Emeis et al. [14], methane gas and hydrogen sul-
phide in the unconsolidated sediments may be released following changes in
the physical regime of the overlying water or the sediment. So far, studies have
been largely descriptive and only qualitative assessments have been possible.
For a quantitative analysis of the various potential sources of hydrogen sul-
phide - sediment or water column - regional and temporal distribution patterns
of fluxes, concentrations, and budgets of hydrogen sulphide and oxygen are
required. In this respect leading questions are:
1.
What is the oceanic circulation pattern over the shelf and how does the
chemistry of the water masses entrained in the upwelling affect overall
oxygen levels on the shelf?
2.
What is the rate of oxygen consumption in the water column and how does
this rate compare to oxygen consumption rates at the sediment-water
interface?
3.
What is the regional and temporal variation in hydrogen sulphide flux in the
upwelling zone and what regulates the flux from the sediments?
4.
How does the gas distribution in the shelf sediment affect the flux of hydro-
gen sulphide from the sediment?
2. DATA AND METHODS
Water column and sediment data were acquired between May 1997 and May
2004 on cruises with the research vessel of the Namibian Ministry of Fisheries
RV Welwitchia
and during expeditions of the research vessels
RV Meteor, cruises
M48-2 and M57-3, RV Poseidon, cruise 250/2, RV Petr Kottsov, Benefit cruise
and
RV Alexander von Humboldt, cruise legs AHAB-3 and AHAB-4.
Station
locations on the different cruises and water depths are shown on Fig. 1. A
summary of the measurements is listed in Table 1. A complete table of sample
locations, sampling times, and types of measurement is available from the
senior author upon request. Altogether, sediment and water column data were
acquired from over 130 stations.
In addition, over the course of a period of three years (May 2001 until May
2004) sediment and water column data were obtained from a shallow-water
station (Station 1) at 22
◦
50.9' S, 14
◦
28.4' E (27 m water depth).
Continuous data records on water column physics and chemistry were ob-
tained from a mooring that was deployed at 22
◦
59.7'S, 14
◦
02.8'E (131 m water
depth) from December 12, 2002 until April 1, 2003 and again from January 7,
2004 until May 5, 2004.
