Sampling Seawater from the Arctic Ocean
Outside of the ice pack surface water is collected from a small boat with acid-cleaned plastic tubing and a peristaltic pump. Away from the ship, the small boat slowly moves forward as surface water is pumped into a large carboy. Only water deeper than 20 meters is collected from the ship to avoid contamination from the Healy’s metal hull.
The most abundant elements in seawater are salt ions (sodium, chloride, sulfate, magnesium, calcium, etc.), and on average one liter of seawater contains 35 grams of dissolved salt (one liter of seawater weighs roughly 1000 grams so salinity is measured as parts per thousand). The GEOTRACES program specializes in measuring the least abundant elements in the ocean, referred to as “trace-elements.” Concentrations of the trace-element mercury, for example, are often less than 0.000 000 000 200 grams dissolved in one liter of seawater (parts per trillion). From this perspective, finding a needle in a haystack sounds easier than searching for mercury in the ocean.
Because these elements are found at such low concentrations, even a small amount of contamination can significantly alter a sample. Collecting contamination-free samples is a delicate process – imagine the challenges that arise when looking for trace amounts of iron in seawater collected from a giant rusty ship! The GEOTRACES program has developed specific sampling protocols that include a number of inventive solutions such as plastic shower caps, Kevlar line, and hand carrying 4 ft long GoFlo bottles. The photos below outline the procedure for collecting contamination-free vertical profiles of seawater from the ocean surface to the ocean floor.
Full depth profiles are collected in specially designed GoFlo bottles. The bottles are long cylinders with openings at both ends and are lined with high quality plastic (Teflon) that can withstand acid-washing to remove contaminants. In this image —> Read More