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Comet Supercomputer Used to Simulate Environmental Changes in Chesapeake Bay

XSEDE Allocates Scientists HPC Time to Compare Conditions from Early 1900s to Early 2000s

By Kimberly Mann Bruch, SDSC Communications

Seasonal changes taking place in Chesapeake Bay according to computer simulations conducted at SDSC via an XSEDE allocation. DJF is December-February, MAM is March-May, JJA is June-August, and SON is September-November. The figure shows exchanges of carbon dioxide with the atmosphere (air-sea flux, bottom right) and other related fields.  (Dissolved inorganic carbon (DIC), Total alkalinity (TA), and CO2 partial pressure) Credit: St-Laurent et al (2020)

Encompassing more than 4,000 square miles, the Chesapeake Bay is the largest estuary in the continental U.S., providing an excellent testbed for scientists to better understand long-term changes occurring in coastal waters by using high-performance computing (HPC) resources to create detailed simulations.

The National Science Foundation-funded Extreme Science and Engineering Discovery Environment (XSEDE) initiative recently allocated time on Comet at the San Diego Supercomputer Center (SDSC) at UC San Diego for Virginia Institute of Marine Science (VIMS) Research Scientist Pierre St-Laurent and colleagues to examine impacts of both regional and global changes affecting the Chesapeake Bay. They discovered that historical increases in fertilizers and atmospheric carbon dioxide concentrations have forced the bay to behave increasingly like a small sea on a continental shelf rather than a traditional estuary.

"Upon using this XSEDE allocation to study what happened during the last 100 years, we determined that the bay now absorbs slightly more carbon dioxide than it releases into the atmosphere," said St-Laurent. "This result exemplifies the particularity of the continental U.S.'s largest estuary, but also may be indicative of the magnitude of the changes that are ongoing in coastal waters throughout the world."

St-Laurent and his colleagues published their detailed findings in Volume 17 (issue 14) of the Biogeosciences journal.

"Our study provides valuable perspective to watershed managers as it compares the long-term impact of fertilizer usage with other global changes," said St-Laurent. "Not only is the health of the Chesapeake Bay important for ecological reasons, but also for economic purposes as the seafood industry driven by these waters is estimated to contribute around two billion dollars in sales each year and approximately 40,000 jobs, according to the Chesapeake Bay Foundation."

Additionally, the bay has long been a popular tourist destination with its variety of sandy beaches, wetlands, and open waters.

"XSEDE expands the realm of possibilities by allowing us to conduct longer simulations and examine additional scientific aspects," said Pierre St-Laurent, a research scientist at the Virginia Institute of Marine Science.

"Without our XSEDE allocation on Comet, we would have had to scale down our experiments drastically, affecting the scientific scope of the study and leaving important questions unanswered," added St-Laurent. "Because our research spanned two periods of time covering the early 1900s to the early 2000s, our computational requirement vastly exceeded the resources available at our local research center, but they were well within the computing capacities at SDSC."

In addition to these long-term overview comparison models, the researchers are also interested in specifics regarding the bay's health; specifically, they're studying hypoxia, or lack of oxygen, within the waters. Their Chesapeake Bay Hypoxia Forecast, which was developed by the study's second author and VIMS Research Professor Marjy Friedrichs, simulates present-day levels of dissolved oxygen and pH in the Chesapeake Bay, levels of dissolved oxygen and pH in the bay two days from now, and the percentage difference during that short time span.

Using this modeling system, the researchers also assess how the low-oxygen waters have changed over the past 35 years. Historically, the duration of low-oxygen waters in the bay has ranged between 93-143 days. Despite a general downward trend in hypoxic duration due to management actions reducing nutrient inputs to the bay, the past two years have had relatively severe hypoxia lasting 123 days in 2018 and 136 days in 2019.

"These unusually long durations of hypoxia are due to the high precipitation levels we've seen over the past two years," said Friedrichs. "One of our goals with this work is to help decision makers put recent data into a long-term context so that they can better understand how their clean-up efforts are improving the health of the bay."

As Friedrichs and St-Laurent work to refine these simulations by increasing the horizontal resolution of their model grid, resources such as Comet will be needed to continue running these long-term (35+ years) simulations.

St-Laurent and Friedrichs were funded by grants from the NSF (OCE-1537013), NASA (NNX14AF93G), and the National Oceanic and Atmospheric Administration's National Centers for Coastal Ocean Science (NA16NOS4780207). Access to Comet was via XSEDE (OCE-160013).  William & Mary Research Computing also provided computational resources and technical support.


At a Glance:

  • This XSEDE allocation provided scientists with an opportunity to use SDSC's Comet supercomputer to examine impacts of the Chesapeake Bay's changes
  • Virginia Institute of Marine Science researchers found that the bay now absorbs slightly more carbon dioxide than it releases into the atmosphere
  • The scientists also determined that the Chesapeake Bay experienced relatively severe hypoxia in 2018 and 2019