Seawater is filled with ions which are elements that have a positive or negative charge. 99.99% of dissolved elements in seawater are group of 11 ions called major and minor constituents which include sodium and chloride (salt), magnesium, sulfate, calcium, potassium and bicarbonate just to name a few. The other 0.01% of dissolved elements are nutrients and trace elements. Trace elements are dissolved elements in seawater that are found in concentrations less than 1 ppm. “ppm” stand for parts per million; imagine a swimming pool filled with 1 million marbles, if one of those marbles was red and the rest were blue that would be 1 in 1 million red marbles, or 1 ppm. Most of the trace elements that are being analyzed on this cruise are even less than 1 ppm, imagine that marble is only painted 50% red, or 10% red…that’s a really small amount compared to 1 million!
Because trace elements in the ocean are found at such low concentrations, it can be very easy to introduce contamination. Dust and paint from the ship, for example, may contain trace elements that can ruin a sample. Trace metal chemistry on land is done in special clean laboratories that mimic the sterile conditions of an operating room with filtered air and special shoes and gowns for the workers. The solution for a clean lab at sea? Build a giant plastic bubble. Plastic is hung from the ceiling to the floor to create the bubble and special filters are hung from the ceiling that constantly pump in clean particle free air. Plastic mats line the floor and everyone has to change their shoes and wear a lab coat before entering. Every metal surface is covered with plastic, even table legs and chairs.
Despite their ultra low concentrations in seawater, trace elements are an important part of ocean ecosystems. Trace elements such as iron are used in photosynthesis reactions and zinc and copper are used by tiny microorganisms called phytoplankton. Other trace elements such as mercury and lead are pollutants and their ultra low concentrations start to build up when they are absorbed into the food web.