OPP-PRF: The Role of Southern Ocean Iron limited Diatoms in Modulating Copper Speciation

University Of Washington, Seattle WA

Investigators

Abstract

Microscopic organisms called phytoplankton that live in the Southern Ocean have the potential to lower atmospheric carbon by transferring it into the ocean through photosynthesis. In order to achieve this, phytoplankton require the vital micro-nutrient iron, but concentrations of iron in the Southern Ocean are generally too low and ultimately inhibit phytoplankton growth. A particular type of phytoplankton called diatoms are disproportionately impacted by low levels of iron, yet they are important members of the phytoplankton community in terms of carbon uptake and transport to the deep ocean. When iron levels get too low to sustain biological processes like photosynthesis, diatoms increase their demand for other micro-nutrients like copper in order to continue to perform various biological functions. To meet their increased copper needed, diatoms may produce organic compounds known as ligands which can bind metals like copper and facilitate its uptake into the cell. These ligands likely help diatoms acquire the extra copper needed to fuel various biological systems. Thus far, little is known about whether diatoms do indeed produce these ligands, what thresholds trigger the production of ligands, and what the chemical structures of these ligands are in the marine environments. This project will focus on answering these questions to increase our understanding of how phytoplankton adapt to low iron levels to sustain their biological systems which can affect atmospheric carbon. The Southern Ocean is an important ocean basin for global carbon uptake. However, phytoplankton and in particular diatom growth is limited by the micronutrient iron in this region, preventing additional photosynthesis and carbon draw down. When diatoms are iron-limited they increase their requirements for copper to fuel their iron transport systems and other biological functions. Diatoms may produce organic copper-binding ligands to facilitate the uptake of additional copper and incorporate it into the cell. Preliminary data from the Western Antarctic Peninsula, a region of the Southern Ocean highlighted by iron limitation in offshore waters, showed these waters contained strong copper binding ligands, while in the iron replete coastal waters there was an absence of strong copper binding ligands. This research will focus on characterizing and identifying the copper ligands within this region as well as determining whether diatoms produce copper ligands when they are limited by iron. The trace metal thresholds that lead to copper ligand production will also be explored. Utilizing archived samples, the chemical structure of the ligands found in this region will be determined through liquid chromatography coupled with an inductively coupled plasma and electrospray ionization mass spectrometry technique, while the binding strength of the ligands will be determined through electrochemical techniques utilizing a competing ligand. Strains of Southern Ocean diatoms will be used in culturing experiments and treated with varying concentrations of copper and iron to determine what strains and under what conditions diatoms produce copper binding ligands. The ligands identified from cultured experiments will be compared to ligands found in the Southern Ocean from archived samples and data collected in the Western Antarctic Peninsula. Findings from this project will lead to a greater understanding of how Southern Ocean diatoms adapt when their copper demands increase, as well as how this affects the region’s ability to store carbon. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.