In the left panel we see temperature in blue and oxygen concentration in black. In the right panel we see oxygen concentration again (black) and chlorophyll fluorescence (green). Notice two peaks in chlorophyll, one above the OMZ, and one within it.
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Oxygen Minimum Zones in Chile
Low oxygen regions are common in productive coastal upwelling regions. Oxygen minimum zones (OMZ) located on the eastern boundaries of the North and South Pacific Oceans have expanded in size and intensity over the last 50 years. Unlike the benthic coastal "dead zones" of Oregon and the Gulf of Mexico, the permanent and semi-permanent anoxic (no oxygen) features off Chile and Peru occur at intermediate depths in the water column. The OMZ located off of the northern coast of Chile has been observed at depths as shallow as 50 meters, and can extend down for hundreds of meters in the water column.
Recent work indicates that the Chilean OMZ is maintained by a combination of low oxygen source waters (Equatorial Undercurrent) and high coastal productivity with subsequent bacterial respiration. Anoxic waters that penetrate up into the photic zone (where sunlight can reach) are unusual, and are only recently being investigated in detail. The atypical combination of low oxygen waters with available sunlight results in an intriguing and novel community of microbes with several metabolic pathways. Our understanding of how this fascinating diversity in the microbial community within the OMZ regulates the marine nitrogen cycle is limited, but our group is currently involved in a large collaborative research effort to address this issue (see http://omz.udec.cl).
To give you an idea of what oxygen and chlorophyll levels in an OMZ look like, some initial data from profiling floats deployed off of northern Chile is shown to the left. In the rightmost plot you can see two peaks in chlorophyll. One is above the OMZ in oxygen rich waters. This signal is from common phytoplankton found in most coastal ecosystems. In contrast, the chlorophyll fluorescence peak around 90 meters depth is within the OMZ, and is dominated by marine cyanobacteria (formerly known as "blue-green algae") called Prochlorococcus. Aside from its location within anoxic waters, this peak in Prochlorococcus is unusual because it is found at extremely low light levels, less than 1% surface intensity.
We will be investigating the roles of light and oxygen in the regulation of Prochlorococcus populations with laboratory cultures by using a specialized environmental chamber where we can control light and oxygen levels independently. We hope to shed some light on how oxygen stress and light limitation interact to limit or facilitate the success of Prochlorococcus in the Chilean OMZ. Stay tuned for more details!
- feature story by Amanda Whitmire |
