By Craig Carlson and Brandon Stephens / NORTHEAST PACIFIC OCEAN /
Brandon Stephens is a post-doc fellow working with Craig Carlson, a professor at the University of California Santa Barbara’s Marine Science Institute. Their research focuses on the role marine microbes play in the cycling of elements through oceanic dissolved organic matter, which in turn plays a role in the fate of carbon produced in the ocean. They are working aboard the R/V Roger Revelle for the EXPORTS field campaign.
When one thinks of a NASA mission, thoughts of outer space, stars and other astronomic bodies come to mind. The image above could easily be mistaken for one of stars and planets or a nearby galaxy in deep space captured by the Hubble Space Telescope. But really, it’s microscopic life in the ocean.
With the EXPORTS mission, NASA turns it focus, quite literally, from outer space to Earth’s inner space of the subarctic Pacific Ocean. Using ocean optical sensors, microscopes and molecular tools (rather than telescopes), scientists on board the Research Vessel Roger Revelle have been examining microbial life hundreds to thousands of meters below the ocean’s surface.
The microbes that make up the “constellations” represent the some of the Earth’s most abundant organisms: marine bacterioplankton. There are several hundred thousand to one million bacteria in every drop (one milliliter) of ocean water. When scaled to the total volume of the ocean (i.e. ~ 1.5 billion km3), there are approximately 120,000,000,000,000,000,000,000,000,000 (1.2 x 1029) bacterioplankton cells in the global ocean, or ~ 95% of the all the living biomass in the sea. In other words, the total marine bacterioplankton biomass is greater than all of the ocean’s zooplankton, shellfish, fish and whales summed together.
The majority of this unseen marine bacterioplankton grow very fast, dividing every couple of days. To meet their metabolic demands, bacterioplankton must consume vast amounts of organic compounds like carbohydrates and proteins and recycle inorganic nutrients like carbon dioxide, nitrate and phosphate every day. Though each of these microbes live on the timescales of days and work on spatial scales of nanometers (a billionth of a meter), their sheer numbers and high growth rates mean they affect ocean chemistry on the scales of ecosystems. These marine microbes are the true drivers of large scale biogeochemical cycles in oceanic systems as we are witnessing in the subarctic Pacific Ocean.
With EXPORTS, we are examining the intricate mechanisms of the oceanic biological “carbon pump”. The carbon pump describes how photosynthically fixed carbon (usually from atmospheric carbon dioxide that has dissolved in the ocean) is processed and reprocessed through the ocean’s planktonic food web in the surface layers of the ocean. Ultimately a portion of the carbon is exported out of the suface by sinking and mixing to the deep ocean hundreds to thousands of meters below.
How exactly the ocean absorbs and retains carbon largely depends in part on the growth of microbes but also where in the water column (between the ocean surface and abyss) they intercept and consume sinking organic particles or dissolved organic matter. For carbon, and other associated elements, to be stored for long periods of time in the ocean, it first must travese the portion of the ocean’s water column that extends between ~one hundred and one thousand meter depths. This zone is referred to by oceanographers as the ocean’s twilight zone. The twilight zone is so named not only because there is little to no light but also because the chemical budgets and biological processes that occur in this zone are not well understood. If microbes recycle the organic matter too close to the surface, the carbon escapes long-term storage. But if the sinking or mixed organic matter gets deep enough, then that carbon is removed from interaction with the atmosphere for decades to millennia.
Our project is designed to investigate marine microbes and their interaction with organic compounds throughout the water column of the subarctic Pacific Ocean. We are conducting experiments at sea that combine tools from ecology, molecular biology, and marine chemistry to investigate how bacterioplankton consume the organic substrates available to them. By examining microbial behavior, we will learn more about how the ocean’s “inner space” functions and how biology helps govern the movement of carbon within Earth’s systems.