Deep Thoughts

The oceans encompass the most important ecosystems for the health of our planet, most of it unseen and at depths unimaginably remote and little explored. It is there that microbial communities pulse to the ancient rhythms of life on earth. Researchers are beginning to plumb these mysterious depths to learn what organisms are there and how they interact to shape the global cycles of macronutrients, such as carbon, nitrogen, and oxygen, upon which all life relies. From 2009 to 2013, the ocean-going vessel Tara collected seawater from 210 sites around the globe at a range of water depths, generating a total of 35,000 samples (morphological, genetic, and environmental) with which to analyze the composition and diversity of microbial ecosystems. A key discovery arising from this epic effort is that the single most important determinant of microbial community taxonomic structure and gene composition is temperature (Sunagawa et al., 2015), at least in the sunlit zones where photosynthesis occurs. Other environmental factors, such as dissolved oxygen and geographic location, play more minor roles. Understanding this key contributor to ocean microbiomes may facilitate more accurate modeling of the ecologically critical sunlit zone, how it changes with seasonal variations in temperature or as a result of climate change, and how it interacts with deeper ocean layers.