Copper is a micronutrient that it important for the growth of phytoplankton, which serve as the foundation of the ocean’s ecosystems. However, the majority of copper in the ocean is in a form that isn’t bioavailable (able to be used by living organisms) because it is bound to naturally occurring molecules called ligands. For species of phytoplankton—such as diatoms—that require copper for biological processes, the presence, concentrations, and sources of these ligands are key factors that determine their abundance.
Given this, a group of scientists—including Dr. Kristen Buck, Assistant Scientist at BIOS—undertook an investigation into the sources of copper-binding ligands in the surface waters of the Antarctic Peninsula. They chose this particular location in the Southern Ocean due to its ecological importance, as well as the fact that oceanic mixing and circulation patterns create a natural gradient along which to study copper.
Dr. Buck and her colleagues collected and analyzed water from four distinct water masses during the austral winter (July/August): the Antarctic Circumpolar Current, Southern Antarctic Circumpolar Current Front, Bransfield Strait, and the shelf region of the Antarctic Peninsula. They also took samples from glacier ice, sea ice, and algal sea ice to enhance their investigation into the potential sources of these copper-binding ligands. By using advanced electrochemical methods they were able to determine the concentration of total dissolved copper in each water mass, as well as the concentrations of both strong and weak ligands.
Among their findings:
- A strong class of copper-binding ligands is present throughout Antarctic Peninsula surface waters in the winter. This is likely the result of deep winter mixing that brings elevated copper concentrations to the surface through upwelling.
- The glacial ice had very low levels of dissolved copper, making it unlikely that the land mass is a primary source of copper to the surface ocean in this region.
- Higher concentrations of relatively strong ligands in both the sea ice and the algal-influenced sea ice suggest that resident phytoplankton communities may be a source of these copper-binding ligands.
Dr. Buck notes that, “As the first study to report on dissolved copper and copper-binding ligands during the austral winter in the Southern Ocean, this research significantly increases the number of Cu-binding ligand measurements that have been made in open ocean environments. Continued analysis may shed some light on important sources and sinks of Cu-biding ligands in the Southern Ocean.”