TAMU-CC researchers study process that controls greenhouse gas beneath the ocean

TAMU-CC Researchers Study Process that Controls Greenhouse Gas Beneath the Ocean

CORPUS CHRISTI, Texas – The bottom of the ocean is a mysterious place that is almost impossible to visit and study, but researchers at Texas A&M University-Corpus Christi are helping uncover what’s happening at a place that’s even more difficult to reach – the sediments beneath the bottom of the ocean.

Why worry about what’s happening in such an inaccessible place? The answer involves tiny creatures – microbes – that play an important role in a process that helps to regulate the level of harmful greenhouse gases entering oceans and the atmosphere from a huge hidden reservoir. The cycling of these gases by microbes, plants, and fish contributes to an always-changing but healthy Earth.

Texas A&M-Corpus Christi researchers studied part of this process, which starts in the sediment beneath the floor of the ocean. Ocean sediments are a storehouse for massive pockets of methane, a potent greenhouse gas. Often, this methane “leaks” upward from the deep sediments toward the sea floor. In the sediments closer to the sea floor, microbes consume most of the methane as it arrives, converting it into less potent carbon. Some of the carbon stays in the sediments, while some moves upward and enters the water. More is now understood about the importance of these processes to global ocean chemistry through a recent study from a TAMU-CC-led research team.

“Our understanding of the Earth’s climate depends on our ability to track the flow of carbon, especially in the form of greenhouse gases like carbon dioxide and methane in the oceans and atmosphere,” said Sajjad A. Akam, Coastal and Marine Systems Science Ph.D. student at A&M-Corpus Christi.

In addition to Akam, the TAMU-CC research team includes Dr. Richard Coffin, chair of the Department of Physical & Environmental Sciences, and Dr. Hussain Abdulla, Assistant Professor of Chemistry. Dr. Timothy Lyons, Distinguished Professor of Biogeochemistry at the University of California-Riverside, is also on the team. Their work was published last month in the journal Frontiers in Marine Science.

Scientists have good estimates of how much methane enters the seafloor and is put to use by the microbes but there has been less certainty about the fate of the inorganic carbon produced by these interactions.

Coffin has led studies in coastal waters off four continents over the last 20 years to understand deep sediment methane loading and shallow sediment carbon cycling.

“Our recent study fills in this gap by calculating the carbon flow in sediment settings with subsurface methane diffusion,” Akam said. “The results show that while the methane is prevented from entering the ocean water, these shallow sediments host a significant inorganic carbon pool, which is derived from multiple sources, including the microbial conversion of methane.”

Most of the carbon eventually enters the water while some stays behind in the sediment and forms mineral particles. Carbon that enters the water also concerns scientists because it can impact the delicate ocean carbon dioxide balance and cause ocean acidification.

Scientists are working to understand and develop ways to monitor ocean acidification, and the team was assisted by Dr. Xinping Hu, Associate Professor in the Department of Physical & Environmental Sciences at A&M-Corpus Christi. One of Hu’s projects, which seeks out the best places and ways to monitor ocean acidification in the Gulf of Mexico, is being supported by the National Oceanic and Atmospheric Administration.

“Ocean acidification can fundamentally change the ocean chemistry, with significant impacts on marine ecosystems,” Akam said. Increasing ocean acidity can erode the shells of clams, urchins and oysters. Ocean acidity also can affect coral reefs, marine food webs, and ocean-related goods and services.

Akam said coastal areas, like those surrounding the Gulf of Mexico, have an important role in the oceanic carbon cycle, despite their relatively small surface area. Carbon cycling in coastal areas involves processes like freshwater input from rivers, air-sea exchange, coastal dead zones and harmful algal blooms.

“Human activities have a tremendous impact on coastal carbon flows,” Akam said. Most of the carbon activity described in the study is also occurring in coastal settings so results from the study can lead to better understanding of how different processes interact, which can improve predictions on how coastal systems respond to climate change.

Darrell J. Pehr, Texas A&M University-Corpus Christi, 29 May 2020. Article.

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