Table of Contents

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

Data for the concentrations of Particulate Acid-Volatile Sulfide (pAVS) (0.8 mm) in depth profiles from in situ McLane pumps at GEOTRACES EPZT Stations 1-5, 7, 9, 11, 13, 17, 18, 20, 21, and 23.

DMO notes:

• changed -9999 values in SAMPNO to nd
• added zeros to pad EVENT_LAT and EVENT_LON where decimal places were not 5 places like most of the dataset.
• orginal name pAVS and pSe(0) changed to conform to GEOTRACES conventions

Samples analyzed for acid-volatile sulfides (AVS) were collected on McLane pumps suspended from a trace metal wire (Hytrel-jacketed Vectran). Pumps filtered for four hours, flowing first over a 51-µm polyester pre-filter, then over paired 0.8-µm pore-size, 142-mm Supor polyethersulfone filters. A small portion of the top Supor filter, representing ~2% of the filter area (0.8-51 µm size-fraction material), was sub-sectioned into polyethylene vials and frozen at -85˚C until shipboard AVS analysis, described below. Filter blanks were held within identical filter housings and submerged on one of the deeper pumps on each cast, but were not actively filtered through. Blanks were handled identically to samples during processing, which was conducted in a HEPA-filtered environment using trace metal procedures.

Particulate elemental samples were collected using McLane in situ pumps (P. Lam, UCSC) with splits (section) from a 0.8 µm Supor filter processed immediately in a N₂-purged glove bag after collection and pump recovery; filter splits were placed and sealed in Tedlar bags and stored at -80°C until analysis. Particulate elemental selenium concentrations were determined using a sulfite leach following Velinsky and Cutter (1990) and analyzed like selenite+selenate following Cutter (1978).  Precision was ca. 10% RSD (n=3). 

Samples analyzed in triplicate and means computed. Standard additions of selenite were used for daily calibration on a representative sample and its slope applied to subsequent samples.

Determinations of acid-volatile sulfide (AVS) were made on-board ship and used the method of Cutter and Oatts (Cutter and Oatts, 1987) that includes acidification, gas stripping and cryogenic trapping/preconcentration of the generated hydrogen sulfide. In this case, the filter slice was placed in a glass stripping vessel, 10 mL of deionized water added, and the stripper purged with He. The cryogenic trap was then immersed in liquid nitrogen, 10mL of 1M HCl added through a septum in the stripping vessel and the evolved and trapped hydrogen sulfide was then quantified using the gas chromatography/flame photometric detection method of Radford-Knoery and Cutter (Radford-Knoery and Cutter, 1993). The system was calibrated with hydrogen sulfide from a permeation tube (calibrated diffusion rate) and assuming a filtration volume of at least 5L (median sample volume: 7.9L), the detection limit was 0.2 pmol/L. It should be noted that AVS determined by this method includes monosulfides of iron, zinc, and nickel, but not those with copper or mercury, or mixed oxidation state sulfides such as greigite or pyrite (Cutter and Oatts, 1987; Radford-Knoery and Cutter, 1993).

From the NSF Award Abstract
The mission of the International GEOTRACES Program (https://www.geotraces.org/), of which the U.S. chemical oceanography research community is a founding member, is "to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions" (GEOTRACES Science Plan, 2006). In the United States, ocean chemists are currently in the process of organizing a zonal transect in the eastern tropical South Pacific (ETSP) from Peru to Tahiti as the second cruise of the U.S.GEOTRACES Program. This Pacific section includes a large area characterized by high rates of primary production and particle export in the eastern boundary associated with the Peru Upwelling, a large oxygen minimum zone that is a major global sink for fixed nitrogen, and a large hydrothermal plume arising from the East Pacific Rise. This particular section was selected as a result of open planning workshops in 2007 and 2008, with a final recommendation made by the U.S.GEOTRACES Steering Committee in 2009. It is the first part of a two-stage plan that will include a meridional section of the Pacific from Tahiti to Alaska as a subsequent expedition.

This award provides funding for management of the U.S.GEOTRACES Pacific campaign to a team of scientists from the University of Southern California, Old Dominion University, and the Woods Hole Oceanographic Institution. The three co-leaders will provide mission leadership, essential support services, and management structure for acquiring the trace elements and isotopes samples listed as core parameters in the International GEOTRACES Science Plan, plus hydrographic and nutrient data needed by participating investigators. With this support from NSF, the management team will (1) plan and coordinate the 52-day Pacific research cruise described above; (2) obtain representative samples for a wide variety of trace metals of interest using conventional CTD/rosette and GEOTRACES Sampling Systems; (3) acquire conventional JGOFS/WOCE-quality hydrographic data (CTD, transmissometer, fluorometer, oxygen sensor, etc) along with discrete samples for salinity, dissolved oxygen (to 1 uM detection limits), plant pigments, redox tracers such as ammonium and nitrite, and dissolved nutrients at micro- and nanomolar levels; (4) ensure that proper QA/QC protocols are followed and reported, as well as fulfilling all GEOTRACES Intercalibration protocols; (5) prepare and deliver all hydrographic-type data to the GEOTRACES Data Center (and US data centers); and (6) coordinate cruise communications between all participating investigators, including preparation of a hydrographic report/publication.

Broader Impacts: The project is part of an international collaborative program that has forged strong partnerships in the intercalibration and implementation phases that are unprecedented in chemical oceanography. The science product of these collective missions will enhance our ability to understand how to interpret the chemical composition of the ocean, and interpret how climate change will affect ocean chemistry. Partnerships include contributions to the infrastructure of developing nations with overlapping interests in the study area, in this case Peru. There is a strong educational component to the program, with many Ph.D. students carrying out thesis research within the program.

Figure 1. The 2013 GEOTRACES EPZT Cruise Track. [click on the image to view a larger version]

Extracted from the NSF award abstract:

The 2013 GEOTRACES Eastern Pacific Zonal Transect from Peru to Tahiti will cross an entensive oxygen deficient zone typically described as "suboxic"; however, measurements of sulfate reduction in this region suggest it may have some anoxic characteristics due to the presence of free sulfide. Redox conditions influence the solubility/stability of many trace elements which in turn affects their vertical and horizontal transport. A scientist from Old Dominion University plans to analyze water samples collected during the cruise for dissolved iodate/iodide, arsenic [As(III)/As(V)], selenium [Se(IV, VI), particulate Se(0), and nano- to picomolar hydrogen sulfide speciation (total, free/uncomplexed). These measurements, along with nitrate/nitrite, nitrous oxide, and iron species determined by other participants during the cruise, will be used to constrain the range of redox conditions within the oxygen deficient zone, assess the importance of in-situ reduction versus horizontal advection of the redox species, and the changing redox conditions within the hydrothermal plume of the East Pacific Rise. Availability of this data will also enable other researchers to determine the behavior of other redox sensitive trace elements in the ocean.

GEOTRACES is a SCOR sponsored program; and funding for program infrastructure development is provided by the U.S. National Science Foundation.

GEOTRACES gained momentum following a special symposium, S02: Biogeochemical cycling of trace elements and isotopes in the ocean and applications to constrain contemporary marine processes (GEOSECS II), at a 2003 Goldschmidt meeting convened in Japan. The GEOSECS II acronym referred to the Geochemical Ocean Section Studies To determine full water column distributions of selected trace elements and isotopes, including their concentration, chemical speciation, and physical form, along a sufficient number of sections in each ocean basin to establish the principal relationships between these distributions and with more traditional hydrographic parameters;

* To evaluate the sources, sinks, and internal cycling of these species and thereby characterize more completely the physical, chemical and biological processes regulating their distributions, and the sensitivity of these processes to global change; and

* To understand the processes that control the concentrations of geochemical species used for proxies of the past environment, both in the water column and in the substrates that reflect the water column.

GEOTRACES will be global in scope, consisting of ocean sections complemented by regional process studies. Sections and process studies will combine fieldwork, laboratory experiments and modelling. Beyond realizing the scientific objectives identified above, a natural outcome of this work will be to build a community of marine scientists who understand the processes regulating trace element cycles sufficiently well to exploit this knowledge reliably in future interdisciplinary studies.

Expand "Projects" below for information about and data resulting from individual US GEOTRACES research projects.