MBARI researchers have recently measured high concentrations of carbon dioxide in the air that were blown into the sea from cities and agricultural areas, including Silicon Valley. A new article in PLOS ONE estimates that this previously undocumented process could increase the amount of carbon dioxide released in coastal waters by about 20 percent.
Researchers estimate that the oceans could increase their carbon dioxide emissions each year by 25 million tonnes, or about one percent of the ocean's annual carbon dioxide intake. This effect is currently not included in calculations of how much carbon dioxide is released into the ocean due to the burning of fossil fuels.
Less than half of the carbon dioxide that humans have released in the last 200 years has remained in the atmosphere. The remainder was absorbed almost equally by the ecosystems of the ocean and the earth. How quickly carbon dioxide reaches the ocean in a given area depends on a number of factors, including wind speed, water temperature and the relative concentrations of carbon dioxide in surface waters and in the air just above the sea surface.
Chavez continued, "If these measurements had taken place Onboard a ship, the researchers believed that the extra carbon dioxide came from the ship's engine exhaust system and reduced it, but our berths and surface robots do not release carbon dioxide into the atmosphere. "
Early 2018 MBARI Research Assistant Devon Northcott began work on the dataset and analyzed the hourly carbon dioxide concentrations in the air over Monterey Bay. He noticed another eye-catching pattern – carbon dioxide levels peaked in the early morning.
Although atmospheric scientists had already noticed early morning peaks in carbon dioxide concentrations in some cities and agricultural areas, this was the first time that such peaks were measured in seawater. The finding also contradicted a common scientific assumption that carbon dioxide concentrations over marine areas do not vary widely over time or in space.
Northcott was able to detect the sources of this extra carbon dioxide through measurements of a so-called robotic surface ship, a wave glider that moves back and forth across Monterey Bay, carrying out measurements of carbon dioxide in the air and in the ocean for weeks.
"Because we had taken measurements at many different locations in Bay Bay," Northcott explained, "I could use the position of the wave glider and the speed and direction of the wind to determine the direction from which the carbon dioxide comes . "
The data indicated two main sources of morning carbon dioxide spikes – the Salinas and Santa Clara valleys. The Salinas Valley is one of the largest agricultural areas in California. Many plants release carbon dioxide at night, possibly explaining why more carbon dioxide was in the air in this region. Santa Clara Valley [aka Silicon Valley] is a dense urban area where light winds and other atmospheric conditions in the early hours of the morning could concentrate the carbon dioxide released from cars and factories.
Typical morning breezes blow directly from the Salinas Valley over Monterey Bay. Morning breeze also carries air from the Santa Clara Valley south and then west through a gap in the mountains (Hecker Pass) and over Monterey Bay.
"We had this proof that the carbon dioxide comes from an urban area". Northcott explained. "But when we looked at the scientific literature, there was nothing about air from urban areas that affected the coastal ocean, people had thought about it, but nobody had measured it systematically before."
The researchers see this paper not as a last word, but as a "wake-up call" to other scientists. "This raises many questions that we hope other researchers will address," Chavez said. "One of the first and most important things would be to make detailed measurements of carbon dioxide in the atmosphere and ocean in other coastal areas, we need to know if this is a global phenomenon, and we also want to include the atmospheric modeling community."
"We have estimated that this could increase the amount of carbon dioxide entering coastal waters by about 20 percent, "Chavez said. "This could affect the acidity of seawater in these areas, but unfortunately we have no good way to measure this increase in acidity because carbon dioxide takes time to reach the ocean and dramatically vary carbon dioxide levels in coastal waters." [19659018"Theremustbeotherpollutantsinthiscityairthatalsoaffectthecoastalocean"headded
"This is another case in which the data from MBARI's autonomous robots and sensors has led to new insights and unexpected discoveries," Chavez said. "Hopefully other scientists will see these results and want to know if this happens in their own backyards."
Rain is important for the influence of carbon dioxide on grasslands
Devon Northcott et al., Effects of Carbon Dioxide Emissions in the City on Sea Air Flow and Ocean Acidification in Coastal Waters, PLOS ONE (2019). DOI: 10.1371 / journal.pone.0214403
Silicon Valley Carbon Dioxide Affects Monterey Bay Chemistry (2019, April 23)
retrieved on April 24, 2019
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