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 extremely effective 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.
We were recently funded by NSF’s Early Career Award program (https://www.nsf.gov/awardsearch/showAward?AWD_ID=1555375) 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. Our earlier focused on nitrification but we also reported the first (molecular) evidence for microbial sulfur cycling in the OMZ of the ETNP (Carolan and Beman 2015, Frontiers in Microbiology). This is suggestive of greater biogeochemical complexity in this region. Our work also examined the overall diversity and composition of bacterial communities found in these low oxygen waters using new DNA sequencing technologies. We found sharp changes in diversity and composition with depth, including significantly reduced diversity as oxygen concentrations decrease to low levels. We built statistical models based on these data and which allow us to model the responses of entire communities—quantitatively—to ocean deoxygenation (BEMAN13_NCOMM).
Our new work will quantify all the microbial processes that consume oxygen, how they interact and regulated by microbial communities, and how this is affected by changes in oxygen concentrations. We will use natural depth gradients, latitudinal gradients, and experimental manipulations to do this. Altogether, these data will contribute to our understanding of marine biogeochemistry and microbial ecology in one of the most ecologically and biogeochemically important regions of the ocean.
Photo taken by Angel White on our research cruise in 2008