Oxygen is fundamental for all life in the sea, from charismatic macrofauna to the tiny microbes that we study. In fact, these groups of organisms are connected because microbes are remarkably efficient at consuming dissolved oxygen in seawater, effectively ‘engineering’ ecosystems by removing oxygen. In key regions of the ocean known as oxygen minimum zones (OMZs), microbes deplete oxygen to extremely low levels (because they feed off high rates of photosynthesis, while there is sluggish circulation at depth). The largest OMZ is found in the eastern tropical North Pacific Ocean (ETNP) off Mexico and Central America, and is expanding as a consequence of climate change.
Mike received an NSF Early Career Award to examine the consumption of oxygen by microbes in OMZs and how this may change as OMZs expand. This builds off our earlier work in the ETNP, which focused on nitrification but also examined the overall diversity and composition of microbial communities in low oxygen waters. We found sharp changes in diversity and composition with depth, including significantly reduced diversity as oxygen concentrations decrease to low levels. We built machine learning-based statistical models which allowed us to model the responses of entire communities—quantitatively—to ocean deoxygenation (BEMAN13_NCOMM).
Our recent work quantifies all the microbial processes that consume oxygen, how they interact and are regulated by microbial communities, and how this is affected by changes in oxygen concentrations. We are using natural depth gradients, latitudinal gradients, and experimental manipulations to do this—and have also capitalized on the unique (and queasy) natural experiment of being at sea during a Category 4 hurricane. Our recent Nature Communications paper demonstrates that nitrite-oxidizing bacteria specialize in the consumption of ultra-low levels of oxygen in these fascinating regions of the ocean.
Photo taken on our research cruise in 2018 *after* Hurricane Bud
Beman Lab, University of California, Merced 