After returning from Puerto Rico, Martin garnered the position of acting Assistant Professor in biology with the Hopkins Marine Station of Stanford University. There Martin began his work with trace metals in the ocean, which would come to dominate his career. In the early 1970s, oceanographers held fast to the idea that phosphorus and nitrogen were the only nutrients vital in determining the distribution of the worlds algae populations. They believed that the higher the levels of these non-metallic elements became, the more phytoplankton would grow and the greater the populations of zooplankton and fish would be.
Martin, however, saw this explanation as too simplistic. He wondered what role trace metals such as iron or zinc played in the growth of algae and zooplankton. After all, most land-based life forms, including humans, cannot survive without such metals in their diet. At Hopkins, Martin labored to document the amount of trace metals in zooplankton and phytoplankton specimens. He found that the most common types of plankton contained a regular number of trace metals in their chemical make-up such as zinc, iron, and copper.
Martin pursued his research at the Moss Landing Marine Laboratories where he took the position of Assistant Professor in 1972. By the time he got to Moss Landing he was an expert in trace metals in plankton, says Kenneth Coale, a colleague of Martin and the acting director of Moss Landing. Now that Martin knew what trace metals were in phytoplankton, the next step was to determine the general distribution of these metals in the ocean.
Martin had his work cut out for him. Very few researchers had gone to the trouble of measuring trace metals in seawater samples, and the readings they had taken were likely flawed. The problem with earlier studies on trace metals, Martin realized, was contamination. The iron hull of a ship will raise iron levels in a sample of water by more than 100 times, making it difficult to measure the natural iron levels. Copper tubing or leaded glass test tubes have the same effect on measurements of copper or lead in seawater samples.
He corresponded with Claire Patterson, a geologist at the California Institute of Technology famous for uncovering the age of the Earth by analyzing lead samples in ancient meteorites. Patterson was also one of the few people to successfully isolate trace metals in water. Under Martins direction, Moss Landing began applying Pattersons techniques in their laboratories. As it turned out, the answer lay in one wordplastics. The Moss Landing group rid the lab of all metals that could contaminate a sample of ocean water. They threw out their glass and steel funnels and test tubes and replaced them with Teflon and plastic ones. Copper and glass tubing was replaced by plastic tubing. Everyone there became an expert at welding plastic, says Coale.
When the researchers at Moss Landing ran tests for trace metals in the newly renovated lab, they found that metal concentrations in the ocean were orders of magnitude lower than previously thought. Iron concentrations alone were thousands of times less than any measurement taken in the past. At the same time the researchers tested for trace metals that had never been documented, such as zinc, cobalt, and manganese. They found nearly an entire periodic table in the oceans.
A slew of discoveries followed their cataloging effort. Among these was the realization that trace amounts of copper and zinc actually decrease measurements of algae growth in seawater. This news did not go over well with the science community at first. Essentially the Moss Landing researchers were telling many oceanographers that the measurements on phytoplankton growth they had taken over the years may have been incorrect. But Martin enjoyed these kinds of reactions. He liked to see himself as the underdog, says Coale. His results were eventually accepted.