Earth’s estuaries are warming, consistent with climate change

Estuaries, where the tides combine ocean waters with freshwater from land, are critical natural environments to many marine species. According to the National Oceanic and Atmospheric Administration, estuaries provide habitats for roughly 68% of the U.S. commercial fish catch and 80% of recreational catch. Ensuring these ‘nurseries’ thrive is essential to environmental health and many local economies.

Water temperature influences many aspects of estuary ecosystems. Due to ongoing climate change, estuary temperatures are warming, which could negatively impact the animals, plants, and plankton that rely on these habitats. Most estuaries around the globe, however, lack surface water temperature data, which is needed to study the sensitivity of these systems to warming water temperatures, particularly in remote regions, or places lacking historical data.

To that end, a team of scientists at the University of Maryland Center for Environmental Sciences (UMCES) and the University of Pittsburgh developed a spatially explicit database for 1,060 estuaries around the world using satellites. Their findings were published April 5, 2024 in the journal, Limnology and Oceanography Letters.

Lora Harris, an estuarine ecologist and professor at UMCES’ Chesapeake Biological Laboratory; John Gardner, an assistant professor at the University of Pittsburgh and UMCES alum, and Pittsburgh Ph.D. student, Punwath Prum, collaborated on this effort to characterize temperature change in estuaries.

"The data can be used to develop conceptual and statistical models that will help predict the relative sensitivity of different estuarine ecosystems to increasing water temperatures, and then inform strategies for protecting the estuaries most susceptible to climate change," said Harris.

The team’s analysis indicates that estuaries with extreme warming are located largely near the Arctic, which is the most rapidly warming region on Earth. Rising air temperature is a first-order control of warming estuaries followed by factors such as freshwater inflow, or estuary size. Landsat records were utilized to conduct this study.

"The satellite products NASA and U.S. Geological Survey can provide, combined with faster computing are enabling a new wave of science that is truly global," said Gardner. "We can measure changes in every estuary, and within every estuary, over the last few decades."

According to the team, both ocean and estuary warming rates show that the east coast of the U.S. and southeast Australia are more susceptible to warming with global climate change. Moreover, sea surface temperature increases are higher in the northern hemisphere than in the southern hemisphere, similar to estuary trends.

"We calculated the warming rate of 737 estuaries and found 47% of them are, indeed, warming," said Prum, lead author on the paper. "Our results show that the warming rate of estuaries was faster at higher latitudes, and we could identify the estuaries most vulnerable to climate change."

Harris said: "Global patterns in ocean warming coincided with patterns of estuary warming rates when we compared our results with spatial patterns in the European Space Agency-Climate Change Initiative Sea Surface Temperature trends. So, the estuaries, in a sense, act as a barometer for the health of other waters."

Indeed, the consequences of estuary warming are important to understand, Gardner said. "They can help us identify at-risk ecosystems."

There is something to learn from those estuaries that are not warming, as well. "What is it about them that makes them perhaps more resilient to warming?" said Gardner. "Finding this out may help us better manage, or protect, both at risk and ‘sanctuary’ ecosystems, but ultimately, climate change is global so both global and local actions are needed to slow the estuarine warming and mitigate its consequences."

This project, entitled, "Widespread warming of Earth's estuaries," was supported by NASA-NIP grant No. 80NSSC21K0921.