Project Outcomes Report: Arctic GEOTRACES

The Arctic Ocean lies at the intersection of the Atlantic and Pacific Oceans, providing a direct link between these two ocean basins. In addition, six major rivers from North America and Eurasia supply the surface of the Arctic with large volumes of freshwater. For much of the year, the surface of the Arctic Ocean is covered with a layer of floating sea ice, thick enough to walk on and for organisms – from microscopic plants to polar bears – to call home. Ongoing measurements have shown that Arctic ice is melting, shrinking, and thinning, which will endanger the habitats of plants and animals that depend on the ice for survival. We participated in a 75-day research expedition with other chemical and physical oceanographers, focusing our attention on the relationship between microscopic Arctic plants and the nutrients that stimulate their growth and productivity.

Marine plants have many of the same nutritional requirements as terrestrial plants: nitrogen, phosphorus, carbon dioxide, sunlight, and trace concentrations of metals such as iron, zinc, nickel, copper and cobalt that they use to drive biochemical reactions. While terrestrial plants extract much of their metals from the soil, marine plants are often limited by low concentrations of essential metals. These metal concentrations are low due to limited inputs from the land (where they are plentiful) or low solubilities in seawater. The Arctic is unique among the major oceans in that most of the ocean is bordered by coastal shelves that collect material that rinses from the land. Arctic currents resuspend these nutrient-rich sediments and carry them far into the central basin, potentially providing remote regions of the Arctic with precious trace metals to fuel the growth of microorganisms.

We measured metal concentrations in marine particles and individual phytoplankton cells, discovering that chemically ‘labile’ particulate metal concentrations vary greatly across the Arctic Ocean, by a factor of 10-100. The highest concentrations of particles were found where the Pacific Ocean enters the Arctic over the shallow Bering and Chukchi shelves. There was also a plume of particulate manganese just below the ice near the North Pole. Manganese is an essential nutrient for phytoplankton, but the size and intensity of the plume suggested that marine bacteria or fungi were converting dissolved manganese supplied from rivers into particles in the ocean. These reactive manganese particles then adsorb other metals from the ocean, which aggregate and sink through the water to collect in large quantities on the ocean floor sediments. While the metals “scavenged” by these manganese particles are not directly being used by marine microorganisms, they are being removed through biological processes.

When we compared the bulk labile metal concentrations against the individual plankton metal contents, we found that the two different analytical approaches produced different results. Of the seven primary metals we studied, only cobalt and copper were similar between the two treatments. This finding suggests that the labile fraction includes a significantly higher amount of metals from non-living sources such as manganese oxides.

The metal contents of Arctic phytoplankton differed from those of the algae that grow within the ice. While the cellular iron fractions were similar, the sea ice algae were found to contain higher relative concentrations of the other trace metals. The higher contents in sea ice algae could indicate a greater demand for these metals, or the algae could simply be storing the metals internally in preparation for possible metal-limiting conditions in the future. Overall, the metal contents of Arctic phytoplankton were most like those of phytoplankton from the North Atlantic Ocean, where phytoplankton were found to contain high iron concentrations and required more zinc than nickel to perform at their biochemical optimum.

In addition to enabling scientific advances, this project helped train several college researchers, local high school students, and post-doctoral researchers in Maine and Florida. Students and researchers attended international science meetings to present their findings. The project strengthened inter-state and international research collaborations and allowed participation by American scientists in worldwide research efforts including GEOTRACES. Several public talks and lectures were given via Bigelow’s Café Scientifique and FSU’s Science Café, open house events, and local homeschool cooperatives. These activities advanced public understanding of the scientific process and the environment. Data gathered by the project was also incorporated into college course materials via Bigelow’s collaboration with Colby College. Data collected as part of this project are archived and available through the Biological and Chemical Oceanography Data Management Office, US Arctic GEOTRACES project page (https://www.bco-dmo.org/project/638812).

Last Modified: 03/29/2019
Modified by: Peter Morton