John Martin (1935-1993)

In 1975, Martin became director of the Moss Landing Marine Laboratories. Previously the research center had switched directors every four years. Martin held onto the position for nearly 18 years. It was during his term as director that the lab became a force to be reckoned with.

Many attribute his success as both a scientist and an administrator to his charisma and his ability to think creatively. “John had a knack for stumbling into difficult problems and then coming up with simple solutions to them. That is the mark of a great scientist,” says Coale. Martin's disabilities from polio didn't always allow him to sit in a lab for hours on end and work out all the technical details. His innovative ideas, his attention to his colleagues' needs, and his good nature, however, attracted the interest of scientists from all over the country. In the end, he always managed to get the best from people who worked for him in the lab.

As director, Martin turned his attention to the issue of phytoplankton's role in global climate. Not only do these tiny plants give much of the ocean its green color, but they also collectively draw down millions of tons of carbon dioxide, one of the most abundant greenhouse gases, from the atmosphere each year. Phytoplankton take in carbon through the process of photosynthesis and incorporate it into their cell structure. When phytoplankton die, many will sink to the bottom of the ocean. Since the carbon is no longer allowed to roam freely in the atmosphere, it cannot contribute to the greenhouse effect and the warming of the planet. Understanding this process is vital to understanding how we affect our climate through carbon dioxide emissions.

This research was right up Martin's alley. It was complex, involved the fundamental processes of life, and was full of unanswered questions. Martin organized the Vertical Transport and Exchange of Oceanic Particulate Program (VERTEX) in 1981 to determine just how much carbon in the form of deteriorated phytoplankton sank to the sea floor over a given period of time. With the cooperation of scientists from many institutions, the Moss Landing researchers placed sediment traps all across the North Pacific to measure the amount of carbon settling to the sea floor. They then compared their measurements to the phytoplankton growth levels on the surface. The project became the blueprint for nearly every future large-scale effort to measure the role of phytoplankton in the Earth's carbon cycle such as the Joint Global Ocean Flux Study (JGOFS) program.

Map of Global Chlorophyll Concentration

The distribution of phytoplankton in the ocean is largely governed by the availability of nutrients. However, vast stretches of ocean are almost devoid of phytoplankton, despite the presence of adequate phosphorous and nitrogen (the same nutrients in garden fertilizer). Martin discovered that the missing ingredient was iron—a trace element in the waters of the open ocean. The above image shows the concentration of chlorophyll from phytoplankton, compiled from 3 years of data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). Purple and blue indicate low chlorophyll levels, and green, yellow, and red indicate high levels. (Image courtesy the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE.)

It was also through his work in VERTEX that Martin came to the iron hypothesis for which he is so well known. While examining the growth levels of phytoplankton in the Earth's oceans, Martin decided to revisit one of the oldest, greatest mysteries of oceanography concerning “the desolate zones.” Formally dubbed HNLC (high-nutrient, low-chlorophyll) zones, these enormous tracts of water in the sub-arctic North Pacific, the equatorial Pacific, and the Antarctic Ocean contain very little phytoplankton, or for that matter any other type of marine life, despite high levels of nutrients. Lacking a solid explanation, most scientists believed that hungry zooplankton populations kept burgeoning phytoplankton levels low.

Again, Martin's instincts told him that there was something amiss with this textbook explanation. The phytoplankton in the HNLC zones behaved as they did in areas of the ocean where the levels of the standard nutrients were low. He was sure there was something else that caused the absence of phytoplankton in these areas other than low nitrogen or phosphorus levels. In the 1930s, Joseph Hart, an English scientist, speculated that these HNLC areas might be due to an iron deficiency. Though iron is typically not a key ingredient in phytoplankton growth, they do need some to grow.

Previous measurements, of course, turned up no iron deficiency. Using the lab he developed at the Moss Landing, Martin measured the iron levels in seawater collected from these regions again and found that they were exceedingly low or non-existent. He came up with the hypothesis that iron acts as a sort of micronutrient in phytoplankton reproduction, and therefore the lack of iron was the sole cause for such low phytoplankton levels in HNLC waters. He reasoned that the seas only get their iron from the dust originating in windswept lands, and that wind currents weren't carrying enough iron to these “desolate zones."

To test his hypothesis, Martin sent his team to Antarctica where they collected clean water and added iron to some samples and left others untreated. The samples were placed in baths on the deck of the ship. The phytoplankton in the iron-dosed jar flourished after a few days.

graph of phytoplankton growth

The above graph shows the amount of phytoplankton in two flasks of ocean water, one seeded with iron, the other untreated. After several days, the phytoplankton population in the flask with iron had exploded, while that in the other flask remained stable. (Graph courtesy U.S. Joint Global Ocean Flux Study, based on data from K. Johnson and K. Coale.)

With these results in hand, Martin then went a step further and claimed that the iron levels could in part be responsible for past ice ages. During an ice age much of the fresh water on the continents is locked up in the ice caps, and the exposed landmasses become drier than they are today. If large amounts of iron were swept off these arid landmasses by wind and dumped into the ocean's “desolate zones,” the resulting growth of phytoplankton would effectively pump vast amounts of carbon dioxide from the atmosphere deep into the seas. The lower levels of carbon could, in turn, prolong the ice age. In 1989, Nature magazine published the results of Martin's experiments as well as his speculations on climate change. Within months the news had reached all the major science magazines and the press wires and even landed Martin on Good Morning America, CNN, and the United Kingdom's BBC.

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On the Shoulders of Giants

John Martin
Personal life
An ocean full of metal
The Iron Hyphothesis
Following the vision
References

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