How NASA detected that El Niño changed the salinity of coastal waters| Trending Viral hub

New findings have revealed a coastal area very sensitive to changes in runoff and rainfall on land.

After helping to generate record heat in 2023 and drenching large areas of the United States this winter, the current El Niño is losing strength this spring. Scientists have observed Another way in which the climate phenomenon can leave its mark on the planet: by altering the chemistry of coastal waters.

A team at NASA’s Jet Propulsion Laboratory in Southern California used satellite observations to track the content of dissolved salt, or salinityof the global ocean surface for a decade, from 2011 to 2022. At the sea surface, salinity patterns can tell us a lot about how fresh water falls, flows and evaporates between land, ocean and atmosphere, a process known as The water cycle.

The JPL team showed that year-to-year variations in salinity near coasts are strongly correlated with the El Niño Southern Oscillation (ENSO), the collective term for El Niño and its counterpart, La Niña. ENSO affects climate around the world in contrasting ways. El Niño, linked to warmer-than-average ocean temperatures in the equatorial Pacific, can bring more rain and snowfall than normal to the southwestern United States, as well as drought in Indonesia. These patterns reverse somewhat during La Niña.

During the exceptional El Niño event of 2015, for example, scientists detected a particularly distinctive effect on the global water cycle: lower precipitation over land caused a decrease in river discharge on average, which in turn led to noticeably higher salinity levels in such distant areas. about 125 miles (200 kilometers) from the coast.

On other occasions, the opposite was found: Areas with above-normal land rainfall experienced increased river discharge, reducing salinity near those coasts.

“We are able to show the response of coastal salinity to ENSO on a global scale,” said lead author Severine Fournier, an ocean physicist at JPL.

The team found that salinity is at least 30 times more variable in these dynamic nearshore zones than in the open ocean. The link between rain, rivers and salt is especially pronounced at the mouths of large river systems like the Mississippi and Amazon, where plumes of freshwater can be mapped from space as they flow into the ocean.

With global warming, researchers have been observing changes in the water cycle, including increases in extreme precipitation and runoff. At the intersection of land and sea, coastal waters may be where impacts are most detectable.

“Given the sensitivity to precipitation and runoff, coastal salinity could serve as a kind of indicator, indicating other changes that are developing in the water cycle,” Fournier said.

He noted that some of the world’s coastal waters are not well studied, even though about 40% of the human population lives within about 60 miles (100 kilometers) of the coast. One reason is that river gauges and other in-situ monitors can be expensive to maintain and cannot provide coverage of the entire planet, especially in more remote regions.

That’s where satellite instruments come in. Launched in 2011, the Aquarium The mission made some of the first global space-based observations of sea surface salinity using extremely sensitive radiometers to detect subtle changes in ocean microwave radiation emissions. Aquarius was a collaboration between NASA and the Argentine space agency, CONAE (National Commission for Space Activities).

Today, two higher resolution tools: soil moisture and ocean salinity from ESA (European Space Agency) (SMOS) mission and passive active soil moisture (SMAP) mission: will allow scientists to get within 25 miles (40 kilometers) of the coasts.

Using data from all three missions, the researchers found that surface salinity in coastal waters reached a global average maximum (34.50 practical units of salinity, or PSU) every March and fell to a global average low (34.34 PSU) around September. (The PSU is approximately equal to parts per thousand grams of water.) The discharge of rivers, especially the Amazon, drives this moment.

In the open ocean, the cycle is different: surface salinity reaches a global average minimum (34.95 PSU) from February to April and a global average maximum (34.97 PSU) from July to October. The open ocean does not show as much variability between seasons or years because it contains a significantly larger volume of water and is less sensitive to river discharge and ENSO. Instead, changes are governed by planetary-scale precipitation minus total global evaporation, plus other factors such as large-scale ocean circulation.

The study was published in the journal Geophysical Research Letters.

Jane J. Lee / Andrew Wang
Jet Propulsion Laboratory, Pasadena, California.
818-354-0307 / 626-379-6874
jane.j.lee@jpl.nasa.gov / andrew.wang@jpl.nasa.gov

Written by Sally Younger

2024-035

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