Much like crops in a field that need fertilizer to grow, microscopic plants in the oceans (called phytoplankton) also require nutrients from their environment. Growing phytoplankton cells consume nutrients and carbon dioxide from the atmosphere to build their bodies. After these cells die, some of the associated nutrients and carbon sink into the ocean, feeding fisheries and subsurface ecosystems and removing carbon from the atmosphere. Because of the enormous size of the oceans—and the Pacific in particular, which is larger than all the continents combined—phytoplankton growth affects the entire planet’s biological and elemental cycles.  Some nutrients, especially metals such as iron, zinc, nickel, copper and cobalt, are very rare in the oceans because of their solubility and low abundance in terrestrial material, so their availability is known to be a major factor in how much and which types of phytoplankton grow in parts of the ocean. Through our laboratory’s participation in the international GEOTRACES program, funded by this NSF grant award, we studied how organisms in the vast and understudied South Pacific utilize metals and other nutrients in building their bodies. This research allows us and other scientists to better understand how ocean ecosystems of different types (near-shore, offshore, near-surface, deep) function and to predict how the ocean and planet will respond to environmental conditions in the future.

Our lab develops and uses state-of-the-art techniques to collect phytoplankton (and other marine particles) from the ocean and to examine their metal content without contaminating them. In one technique, phytoplankton are filtered from seawater onto clean filters that are later treated with a range of acids and other chemicals to determine the bulk amount of metals associated with particles in a given volume of seawater. In another technique, we examine single phytoplankton cells of a range of types (both large and small cells from a range of taxonomic groups) and examine them individually using x-rays at the Advanced Photon Source, a synchrotron facility run by the Department of Energy. Statistical techniques and data analyses over the large natural gradients of the South Pacific—and comparison with data collected by other GEOTRACES-participating laboratories—showed several surprising trends in metal utilization. We learned that organisms living in the low-oxygen subsurface waters of a huge portion of the east Pacific use much higher levels of metals than phytoplankton growing at the surface. This discovery changes how we think about the biological requirement for these metals in other ocean regions with low-oxygen waters, including many coastal ecosystems important to human industry and health. We showed that different metals are returned to seawater at different rates and depths, which affects how quickly they can be re-used. We also applied new statistical techniques to show the distributions of various chemical forms of the particulate metals. These distributions improve our ability to understand and predict how ocean ecosystems fundamentally work. We also learned that phytoplankton in the open Pacific Ocean have much lower concentrations of some metals such as iron and zinc than phytoplankton collected near the coast. This information helps us to model the behavior of metals and phytoplankton in computer simulations of the ocean.

In addition to the scientific advances, this project helped train several college researchers, local high school students, and post-doctoral researchers in Maine. 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. Public talks and lectures via Bigelow’s Café Scientifique and open house events and a publicly-available webinar program distributed by collaborators at the University of Maine were given as part of the project. 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.

The data collected as part of this project are publically available online:

http://www.bco-dmo.org/dataset/643270

http://www.bco-dmo.org/dataset/648543

http://www.bco-dmo.org/dataset/639847

Last Modified: 01/02/2017
Modified by: Benjamin S Twining