Table of Contents

• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Program Information
• Funding

Sulfide; oxygen and peroxide; from CTD casts

   PI:        George Luther and Brent Lewis
   of:        University of Delaware
   dataset:   Sulfide; peroxide ratio
   dates:     March 15, 1995 to March 29, 1995 
   location:  N: 21.8328  S: 15.2382  W: 62.4017  E: 67.918
   cruise:    TN045, Arabian Sea Process cruise #2 (Spring Intermonsoon)
   ship:      R/V Thomas Thompson
 
   Note: Zero values for sulfide represent less than the    analytical detection limit of 0.2 nM.


Sulfide, Oxygen, and peroxide

COLLECTION
	Samples for sulfide were measured aboard ship by voltammetry.
Sulfide samples were drawn anaerobically via syringe at the CTD
rosette from bottles not previously sampled for Winkler oxygen.
Samples were analyzed by voltammetry (both linear sweep and cathodic
stripping square wave) within ten minutes according to the methods of
Luther (1991). [also described in Farrenkopf et al., in press and
Theberge et al., in press special Deep-Sea Research Arabian Sea Dutch
volume.]
 
 

ANALYSES
Oxygen and peroxide can be determined without deposition by applying a
negative potential scan from 0.0 V to -1.5 V using the linear sweep or
square wave voltammetry.  Oxygen and peroxide have peaks near -0.09 V
and -0.95 V, respectively (Meites, 1965).  After first scanning the
samples in linear sweep mode to determine the ratio of oxygen to
peroxide sulfide was determined by subsequent scans from -0.1 to -0.8 V
in the cathodic stripping square wave voltammetry (CSSWV) mode without
deposition.  The analyses was repeated with up to 120 second
deposition.  There is approximately one minute time lag between
measurement techniques.   Depths chosen at each station coincided with
levels of high iodide and/or high nitrite.  Sulfide was not measureable
at any of the stations for any of the depths sampled.  Depths chosen at
each station coincided with levels of high iodide and/or high nitrite.
The method detection limit for sulfide in seawater samples is 0.2 nM.
Measurements were undertaken to acertain that oxygen was present in the
samples.  Concentrations of oxygen and peroxide were not quantitated.

EQUIPMENT Electrochemical measurements were made in 10 mL glass
polarographic cells.  EG & G Princeton Applied Research model 384 B
polarographic analyzers equipped with 303A hanging mercury drop working
electrode (HDME) stands were used throughout.  Potentials were measured
vs. a saturated calomel reference electrode (SCE). A platinum counter
electrode was used for current measurements in a standard three
electrode voltammetric arrangement.  A blanket of nitrogen gas is
maintained over the sample so oxygen will not dissolve into the sample
from the laboratory atmosphere.

REFERENCES:

Farrenkopf, A.M., G.W. Luther, III, V.W. Truesdale and C.H. van der
Weijden (in press) Sub-surface iodide maxima: Evidence for biologically
catalyzed redox cycling in Arabian Sea OMZ during the SW intermonsoon.
Deep-Sea Research.
 
Luther, G.W., III (1991) Sulfur and iodine speciation in the water
column of the Black Sea, in Black Sea Oceanography, E. Izdar and J. W.
Murray, Editors.  Kluwer Publishers:  Netherlands. p. 187-204.

Meites (1965) Polarographic Techniques 2nd Edition.  Inter Science
Publications: New York, 752 pp.

Theberge, S.M., III G.W. Luther and A.M. Farrenkopf (in press)  On the
existence of free and metal complexed sulfide in the Arabian Sea and
it's Oxygen Minimum Zone. Deep-Sea Research.

The U.S. Arabian Sea Expedition which began in September 1994 and ended in January 1996, had three major components: a U.S. JGOFS Process Study, supported by the National Science Foundation (NSF); Forced Upper Ocean Dynamics, an Office of Naval Research (ONR) initiative; and shipboard and aircraft measurements supported by the National Aeronautics and Space Administration (NASA). The Expedition consisted of 17 cruises aboard the R/V Thomas Thompson, year-long moored deployments of five instrumented surface buoys and five sediment-trap arrays, aircraft overflights and satellite observations. Of the seventeen ship cruises, six were allocated to repeat process survey cruises, four to SeaSoar mapping cruises, six to mooring and benthic work, and a single calibration cruise which was essentially conducted in transit to the Arabian Sea.

The United States Joint Global Ocean Flux Study was a national component of international JGOFS and an integral part of global climate change research.

The U.S. launched the Joint Global Ocean Flux Study (JGOFS) in the late 1980s to study the ocean carbon cycle. An ambitious goal was set to understand the controls on the concentrations and fluxes of carbon and associated nutrients in the ocean. A new field of ocean biogeochemistry emerged with an emphasis on quality measurements of carbon system parameters and interdisciplinary field studies of the biological, chemical and physical process which control the ocean carbon cycle. As we studied ocean biogeochemistry, we learned that our simple views of carbon uptake and transport were severely limited, and a new "wave" of ocean science was born. U.S. JGOFS has been supported primarily by the U.S. National Science Foundation in collaboration with the National Oceanic and Atmospheric Administration, the National Aeronautics and Space Administration, the Department of Energy and the Office of Naval Research. U.S. JGOFS, ended in 2005 with the conclusion of the Synthesis and Modeling Project (SMP).