EXPORTS (EXport Processes in the Ocean from Remote Sensing) Campaign
Ocean ecosystems play a critical role in the Earth's carbon cycle and the quantification of their impacts for both present conditions and for predictions into the future remains one of the greatest challenges on oceanography. The goal of EXPORTS (EXport Processes in the Ocean from Remote Sensing) Science Plan is to develop a predictive understanding of the export and fate of global ocean NPP (Net Primary Production) and its implications for present and future climates. The achievement of this goal requires a quantification of the mechanisms that control the export of carbon from the euphotic zone as well as its fate in the underlying "twilight zone" where some fraction of exported carbon will be sequestered in the ocean's interior on time scales of months to millennia. In particular, EXPORTS will advance diagnostic and numerical prognostic models by comparing relationships among the ecological, biogeochemical and physical oceanographic processes that control carbon cycling across a range of ecosystem and carbon cycling states. EXPORTS will achieve this through a combination of ship and robotic field sampling, satellite remote sensing and numerical modeling. Through a coordinated, process-oriented approach, EXPORTS will foster insights on ocean carbon cycling that maximizes its societal relevance through the achievement of U.S. and International research agency goals and will be a key step towards our understanding of the Earth as an integrated system. 1) 2) 3)
Figure 1 illustrates the ocean food web processes that drive the transformation and partitioning of carbon among the various particulate and dissolved carbon reservoirs. First, dissolved inorganic carbon (DIC) is photosynthetically fixed into particulate organic carbon (POC) by phytoplankton [and by some phytoplankton into particulate inorganic carbon (PIC)] in the euphotic zone (EZ). Phytoplankton carbon is in turn grazed upon by both micro- and macrozooplankton that respire much of the ingested organic matter back into DIC or release it as dissolved organic carbon (DOC). A fraction of that phytoplankton carbon is exported from the surface ocean either as sinking fecal pellets or as aggregates that are created from the pool of suspended POC and PIC by physical and food-web processes. Zooplankton also contribute to export through their diurnal and seasonal migrations from the EZ to several 100 meters deeper into the twilight zone (TZ), where carbon consumed at the surface is subsequently respired as CO2, excreted as DOC or released as fecal pellets. Further in the TZ, a host of remineralization processes driven by bacteria and zooplankton recycle sinking and suspended organic matter, further influencing the attenuation of the vertical carbon flux.
Figure 1: The EXPORTS conceptual diagram illustrates the links among the ocean's biological pump and pelagic food web and our ability to sample these components from ships, satellites, and autonomous vehicles. Light blue waters are the euphotic zone (EZ), while the darker blue waters represent the twilight zone (TZ). The Figure is adapted from Steinberg and the U.S. Joint Global Ocean Flux Study (JGOFS)
The EXPORTS Science Questions:
• How do upper ocean ecosystem characteristics determine the vertical transfer of organic matter from the well-lit surface ocean?
• What controls the efficiency of vertical transfer of organic matter below the well-lit surface ocean?
• How can the knowledge gained be used to reduce uncertainties in contemporary & future estimates of the export and fates of NPP?
NASA's satellite ocean-color data record has revolutionized our understanding of global marine systems by providing synoptic and repeated global observations of phytoplankton stocks and rates of primary production. EXPORTS is designed to advance the utility of NASA ocean color assets to predict how changes in ocean primary production will impact the global carbon cycle. EXPORTS will create a predictive understanding of both the export of organic carbon from the well-lit, upper ocean (or euphotic zone) and its fate in the underlying "twilight zone" (depths of 500 m or more) where a variable fraction of that exported organic carbon is respired back to CO2. Ultimately, it is this deep organic carbon transport and its sequestration that defines the impact of ocean biota on atmospheric CO2 levels and hence climate.
EXPORTS will generate a new, detailed understanding of ocean carbon transport processes and pathways linking phytoplankton primary production within the euphotic zone to the export and fate of produced organic matter in the underlying twilight zone using a combination of field campaigns, remote sensing and numerical modeling. NASA's upcoming advanced ocean measurement mission, PACE, will be aimed at quantifying carbon cycle processes far beyond today's ocean color retrievals of phytoplankton pigment concentrations, optical properties and primary production rates. The overarching objective for EXPORTS is to ensure the success of these future satellite mission goals by establishing mechanistic relationships between remotely sensed signals and carbon cycle processes. Through a process-oriented approach, EXPORTS will foster new insights on ocean carbon cycling that will maximize its societal relevance and be a key component in the U.S. investment to understand Earth as an integrated system.
EXPORTS is a large-scale NASA-led field campaign that will provide critical information for quantifying the export and fate of upper ocean net primary production (NPP) using satellite observations and state of the art ocean technologies. In the upper sunlit ocean (or euphotic zone), the ocean teems with microscopic organisms known as phytoplankton that provide food for zooplankton - tiny oceanic animals. 4) 5)
EXPORTS scientists will strive to understand how the carbon makes it to the twilight zone and deep ocean interior, and how long it stays there, which is vital to understanding present and future ocean ecosystems and global climate.
Figure 2: Some of the phytoplankton, the zooplankton, and their waste products are transported from the surface of the ocean to the deeper, dimly lit "twilight zone", taking the carbon they are made of with them. Some of that carbon will eventually make it to the deeper ocean interior where it will remain for time scales of months to millennia. - During the EXPORTS campaign, the Imaging Flow Cytobot will give scientists a continuous view of plankton diversity in the northeast Pacific. This collage represents just a small number of the different plankton types that inhabit Earth's ocean [image credit: WHOI (Woods Hole Oceanographic Institution),Heidi Sosik]
Figure 3: The Pacific Ocean teems with phytoplankton along the West Coast of the United States, as captured by the MODIS instrument on NASA's Aqua satellite. Satellites can track phytoplankton blooms, which occur when these plant-like organisms receive optimal amounts of sunlight and nutrients. Phytoplankton play an important role in removing atmospheric carbon dioxide (image credit: NASA)
In August 2018, a large multidisciplinary team of scientists, equipped with advanced underwater robotics and an array of analytical instrumentation, will set sail for the northeastern Pacific Ocean. The team's mission for NASA and the NSF (National Science Foundation) is to study the life and death of the small organisms that play a critical role in removing carbon dioxide from the atmosphere and in the ocean's carbon cycle. 6)
More than 100 scientists and crew from more than 20 research institutions will embark from Seattle for NASA's EXPORTS (Export Processes in the Ocean from Remote Sensing) oceanographic campaign. EXPORTS is the first coordinated multidisciplinary science campaign of its kind to study the fates and carbon cycle impacts of microscopic plankton using two research vessels and several underwater robotic platforms.
The research vessels, the R/V Revelle and R/V Sally Ride, operated by the SIO (Scripps Institution of Oceanography), University of California San Diego, will sail west 200 miles into the open ocean. From these seaborne laboratories, researchers will explore the plankton, as well as the chemical and physical properties of the ocean from the surface to half a mile below into the twilight zone, a region with little or no sunlight where the carbon from the plankton can be sequestered, or kept out of the atmosphere, for periods ranging from decades to thousands of years.
Figure 4: The R/V Revelle (left) and the R/V Sally Ride will leave Seattle for a month-long expedition in the northeast Pacific, where a multidisciplinary team of scientists will study the life and death cycles of phytoplankton and plankton for the benefit of future ocean satellite missions (image credit: UC Santa Barbara/Norm Nelson)
"By employing two ships we'll be able to observe complex oceanographic processes that vary both in space and time that we wouldn't be able to capture with a single ship," said Paula Bontempi, program manager for Ocean Biology and Biogeochemistry at NASA Headquarters.
Phytoplankton are tiny, plant-like organisms that live in the sunlit upper ocean. They use sunlight and dissolved carbon dioxide that enters the upper ocean from the atmosphere to grow through photosynthesis, which is one way that ocean organisms cycle carbon. As primary producers, phytoplankton play an important role in removing atmospheric carbon dioxide and producing oxygen. When phytoplankton are consumed by plankton or die, their remains sink and some fraction of their carbon is exported to depth.
While the major export pathways of how carbon moves through the ocean are known, the magnitude of the carbon flows in the different oceanic pathways and their dependence on ecosystem characteristics are poorly known. Scientists on the EXPORTS team are investigating how much carbon moves through the ocean within the upper sunlit layer and into the twilight zone and how ocean ecological processes affect carbon fate and sequestration. This information is needed to predict how much carbon will cycle back into the atmosphere over what time scales, or how much carbon is exported to ocean depths (Figure 2).
"The carbon humans are putting into the atmosphere is warming Earth," says Mike Sieracki, program director in the National Science Foundation's Division of Ocean Sciences. "Much of that carbon eventually finds its way into the ocean and is transported to the deep ocean, where it is sequestered and will not return to the atmosphere for a long time. This project will help us understand the biological and chemical processes that remove the carbon, and establish a foundation for monitoring these processes as the climate changes."
Seven years in the making, the 2018 campaign has been a huge undertaking, said David Siegel, EXPORTS science lead from the University of California, Santa Barbara. "The impact the EXPORTS data will have for understanding how our planet is changing will be significant," Siegel said. "NASA's ocean color satellite record shows us these ecosystems are highly sensitive to climate variability. Changes in phytoplankton populations affect the marine food web since phytoplankton are eaten by many animal species big and small. The stakes are high."
The long-term removal of organic carbon from the atmosphere to the ocean depths is known as the biological pump, which operates through three main processes. First, carbon-laden particles from the ocean's surface sink through gravity, as happens with dead phytoplankton or feces produced by small animals called zooplankton. Second, zooplankton migrate daily close to the ocean's surface to feed on phytoplankton and return to the twilight zone during nighttime. Third, physical processes in the ocean, such as the large global overturning circulation of the oceans and smaller-scale turbulent eddies, transport suspended and dissolved carbon to great depths.
NASA's satellites provide a variety of measurements of the ocean's uppermost layer, such as temperature, salinity and the concentration of a pigment found in all plants called chlorophyll. EXPORTS will provide data on the role of phytoplankton and plankton in the biological pump and the export of carbon, information important to planning observations and technologies needed for future Earth-observing satellite missions.
"We've designed EXPORTS to observe simultaneously the three basic mechanisms by which carbon is exported from the upper ocean to depth," Siegel said. "We're trying to better understand the biology and ecology of phytoplankton in the surface water, how those characteristics drive the transport of carbon to the twilight zone, and then what happens to the carbon in the deeper water."
Among the many technologies being used is an autonomous platform called a "Wirewalker" that uses wave energy to move instruments along a taut wire from the surface to 500 m in depth while measuring temperature, salinity, oxygen, carbon, and chlorophyll concentration.
A 2 m long remote-controlled underwater vehicle called the Seaglider will gather similar measurements, but at depths as much as 1,000 meters.
On board the ship, samples will be collected for genomic sequencers to assess the composition of the phytoplankton, zooplankton, bacterial and archaeal communities.
New microscopic imaging tools also will be used by EXPORTS scientists, including a high throughput microscope called the Imaging FlowCytobot that will provide realtime, high-resolution images of billions of individual phytoplankton. 7) The UVP (Underwater Vision Profiler) will measure the sizes of sinking aggregate particles and collect images of zooplankton organisms.
Mounted on the ship's superstructure will be optical instruments that will measure the ocean's color at very high spectral resolution, from the ultraviolet wavelengths to the shortwave infrared bands of the electromagnetic spectrum. Phytoplankton have distinct spectral "signatures" — colors of light they absorb and scatter. By identifying those signatures scientists will be able to develop algorithms for future satellite ocean color missions such as NASA's PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) mission. From space, PACE will use similar optical instruments to distinguish the type and amount of phytoplankton present in the ocean.
"What we will learn from EXPORTS will give us a deeper understanding of how plankton species and other microorganisms such as bacteria interact with their environment," said Bontempi. "Not only will we be able to use this information to develop new approaches to identifying and quantifying plankton species from space, we'll be able to predict how much carbon will cycle back into the atmosphere and how much will be transported to the ocean depths for the long term."
1) "EXPORTS (EXport Processes in the Ocean from Remote Sensing)," NASA, 2018, URL: http://oceanexports.org/about.html
2) David A. Siegel, Ken O. Buesseler, Michael J. Behrenfeld, Claudia R. Benitez-Nelson, Emmanuel Boss, Mark A. Brzezinski, Adrian Burd, Craig A. Carlson, Eric A. D'Asaro, Scott C. Doney, Mary J. Perry, Rachel H. R. Stanley, Deborah K. Steinberg, "Prediction of the Export and Fate of Global Ocean Net Primary Production: The EXPORTS Science Plan," Frontiers in Marine Science, 08 March 2016, https://doi.org/10.3389/fmars.2016.00022, URL: https://www.frontiersin.org/articles/10.3389/fmars.2016.00022/full
3) Adrian Burd, Alison Buchan, Matthew Church, Michael Landry, Andrew McDonnell, Uta Passow, Deborah Steinberg, Heather Benway, "Towards a transformative understanding of the biology of the ocean's biological pump: Priorities for future research," Report of the NSF Biology of the Biological Pump Workshop, 19-20 February, 2016, Hyatt Place New Orleans, New Orleans, LA, 67 pp., DOI:10.1575/1912/8263
5) "Updates and Plans for the First EXPORTS Field Campaign," OCB Project Office, WHOI (Woods Hole Oceanographic Institution), 1 Feb. 2018, URL: https://www.us-ocb.org/updates-and-plans-for-the-first-exports-field-campaign/
6) Steve Cole, Cheryl Dybas, "NASA, NSF Plunge Into Ocean ‘Twilight Zone' to Explore Ecosystem Carbon Flow," NASA Release 18-052, 18 June 2018, URL: https://www.nasa.gov/press-release/nasa-nsf-plunge-into-ocean-twilight-zone-to-explore-ecosystem-carbon-flow
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (email@example.com).