RESEARCH HIGHLIGHT

SAFE Cruise:   IARC Researchers participate in a Multi-institutional Collaboration on Iron Sampling and Analysis

February 18, 2005

IARC Researcher Dr. Jingfeng Wu and Post-Doctoral Fellow Yihua Cai participated in the SAFE Research Cruise during October/November of 2004.   The cruise was a joint effort directed at resolving differences in the measurement of dissolved iron in seawater.   SAFE, or Sampling and Analysis of Iron (Fe), is a multi-institutional collaboration, which included 14 groups of experienced iron analysts whose goal is to establish standards for the measurement of dissolved iron in seawater.   In addition, they will study the reasons for measurement discrepancies to assess and resolve differences that occur between laboratories.

The SAFE cruise track went from Honolulu, Hawaii to San Diego, California (Fig. 1).   From the departure point in Hawaii, the vessel traveled to 30º N and 140ºW, where researchers spent 8-9 days collecting water samples.

Fig. 1. Cruise track and Station Map.

Their newly developed 2-L ATE/Vane sampler was used to collect uncontaminated seawater samples (Fig. 2).   Samples are measured in the IARC lab by a procedure called the magnesium hydroxide coprecipitation isotope dilution Mass Spectrometry, using the Finnigan Element2 High Resolution Inductively Coupled Plasma Mass Spectrometer, located (HR-ICPMS) at IARC (Fig. 3).   Water samples enter a high temperature chamber where the elements are broken down into charged particles called ions.   The charged particles pass through a magnetic field and are separated by the difference in charge to mass ratios for different ions.   A detector then counts the number of ions and quantifies the composition of the water.  

IARC Research Technician Robert Rember notes that the mass spectrometer "is capable of measuring concentrations of trace elements in water from the part per million to part per quadrillion level."   They are currently taking measurements of iron (Fe) and lead (Pb) concentrations in seawater samples from the Atlantic, Pacific, and Arctic Oceans.   Using the new HR-ICPMS method, the IARC researchers hope to provide benchmark Fe data to compare with shipboard results by cruise participants using other techniques.

Figs. 2 & 3. LATE/Vane sampler and High Resolution Inductively Coupled Plasma Mass Spectrometer (HR-ICPMS) at IARC.

This project is a preface to a new 10-year NSF program called "Geotraces," which aims to map global distribution of trace metals and isotopes ( http://www.ldeo.columbia.edu/res/pi/geotraces/ ).   Measurement of Fe in seawater will be the central part of the project because of its important implications to phytoplankton growth, atmospheric CO₂ and climate over geological time.