A wetter world recorded in Australian coral colony
When climate scientists look to the future to determine what the effects of climate change may be, they use computer models to simulate potential outcomes such as how precipitation will change in a warming world.
But University of Michigan scientists are looking at something a little more tangible: coral.
Examining samples from corals in the Great Barrier Reef, the researchers discovered between 1750 and present day, as the global climate warmed, wet-season rainfall in that part of the world increased by about 10%, and the rate of extreme rain events more than doubled. Their results are published in Nature, Communications Earth and Environment.
"Climate scientists often find themselves saying, 'I knew it was going to get bad, but I didn't think it was going to get this bad this fast.' But we're actually seeing it in this coral record," said principal investigator Julia Cole, chair of the U-M Department of Earth and Environmental Sciences.
"Studies of the future tend to use climate models and those models can give different results. Some may say more rainfall, some they say less rainfall. We're showing that, at least in northeastern Queensland, there is definitely more rainfall, it's definitely more variable and it's definitely already happening."
The study, led by U-M researcher Kelsey Dyez, analyzed core samples drilled from a coral colony situated at the mouth of a river in northern Queensland, Australia. During the summer rainy seasons, rainfall filtering into the river picks up nutrients, organic material and sediments, which are then carried to the river mouth and discharged into the ocean, washing over the coral colony.
As the corals are bathed in this freshwater outflow, they pick up geochemical signals from the river and record them into their carbonate skeletons. The core samples of the corals display faint bands of lighter and darker material. These bands reflect each rainy and dry season the coral lived through. The bands also hold information about the climate in each season, just as trees' rings record climate patterns during the years it grows.
"We want to know, as we warm the earth, are we going to have more rainfall? Less rainfall? Maybe different parts of the Earth will respond differently?" Dyez said. "This project is especially important because we're able to put that warming and changes into context. We are able to record rainfall from the period before we have instrumental records for this part of the world."
To accurately determine how much rain fell each rainy season, and how many extreme rain events occurred during each season, the researchers compared instrumental rainfall records that began in the 1950s to the corresponding years in the coral. This gave the researchers a calibration period that they could use to determine the relationship between the coral characteristics and the amount of rainfall that fell each rainy season as long as the corals were alive, all the way back to 1750.
The coral core was taken from a remote region off northeastern Queensland by the Australian Institute of Marine Science. The land surrounding the river watershed is also in a protected area, meaning that nutrients and sediment flushed into the river by rains are unlikely to be generated by human activity.
"This is a region that has experienced pretty big swings in recent years between floods that have been devastating to communities, and then drier periods," Cole said. "Because northeastern Australia is an agricultural region, how rainfall changes in a warmer world is of real tangible importance. People might not sense a few degrees Celsius of warming, but they really suffer if there's a drought or a flood."
To reconstruct rainfall, the researchers used four different measures. First, the researchers looked at the luminescence of the bands in the coral. When they shine a black light on the coral, organic compounds in the coral cause it to fluoresce. The brighter the band fluoresces, the more organic compounds came down the river and were deposited onto the coral, reflecting a season of heavy rainfall.
The researchers also measured how much of the element barium is contained in each of the bands. The coral skeleton is composed of calcium, but when barium is deposited onto the skeleton, it can replace calcium. The more barium detected in the band, the more river discharge was flowing over the coral.
The researchers then looked at stable carbon isotopes (carbon-12 and carbon-13) within the coral. The more the ratio of these two isotopes favors carbon-12, the more water must have been coming down the river from greater rainfall.
Finally, the researchers examined stable oxygen isotopes (oxygen-16 and oxygen-18). When the ratio of these two isotopes favors oxygen-16, it is a signature of additional precipitation and freshwater coming down the river.
Because the coral record is located off northeastern Australia, the researchers wanted to understand if the whole of Australia experienced similar rainfall. Looking at instrumental rainfall records across Australia, the researchers found that the increased rainfall patterns did not occur evenly across Australia.
"It's not actually that well correlated to western Australia. That's too far away. But for most of eastern Australia, there is a significant correlation. And that's where many people live," Dyez said. "It's especially strong across Queensland, which is where a lot of these rainfall extremes are happening right now."
Study: Rainfall variability increased with warming in northern Queensland, Australia over the past 280 years (DOI: 10.1038/s43247-024-01262-5) (available when embargo lifts)
JOURNAL
Communications Earth & Environment
DOI
Unlocking clearer views of our water worlds: A Landsat legacy
AEROSPACE INFORMATION RESEARCH INSTITUTE, CHINESE ACADEMY OF SCIENCES
IMAGE:
LOCATIONS OF IN SITU DATA FOR FOUR WATER PARAMETERS EXAMINED IN THIS STUDY.
view moreCREDIT: JOURNAL OF REMOTE SENSING
A study highlights the significant advancements in water environment analysis facilitated by the Landsat missions. This research, for the first time, offers a comprehensive global assessment of cloud-free observations (NCOs) from Landsat, underscoring its pivotal role in environmental and hydrological studies.
Satellite remote sensing is vital for monitoring marine and freshwater ecosystems, leveraging missions like SeaWiFS, MODIS, MERIS, Landsat, and Sentinel for tracking water parameters such as chlorophyll, sediment, and temperature. The dynamic nature of water bodies demands high-frequency observations for accuracy, with limitations highlighted by factors like clouds and sunglint. Despite its longer revisit cycle, Landsat's observations are invaluable for inland and coastal waters, emphasizing the need for more frequent data to effectively monitor the dynamic changes in aquatic ecosystems.
A recent study (doi: 10.34133/remotesensing.0110) published in the Journal of Remote Sensing on 22 February 2024, advancements in analyzing water environments via Landsat missions are revealed. For the first time, this research offers a global assessment of cloud-free observations (NCOs) from Landsat, emphasizing its critical contribution to environmental and hydrological studies, marking a significant leap in our capability to monitor and understand water bodies on a global scale.
The study embarked on an ambitious journey to unravel the intricacies of NCOs via the Landsat missions. By meticulously analyzing over 4.8 million Landsat images spanning from Landsat 5 through Landsat 8, they uncovered striking spatial and temporal variations in cloud-free data across the globe. Their research illustrated Landsat-8's superior performance, offering nearly double the mean annual NCOs compared to its predecessors. This leap in data quality is particularly pronounced in areas with orbital overlaps, especially above the 45°N latitude, where observation quality is significantly enhanced. Furthermore, this work delves into the vital role of these overlaps in augmenting the quantity and quality of observations, presenting a game-changer in how we monitor and understand the dynamics of the Earth's water environments.
The study's lead researcher emphasized, "Our analysis not only showcases Landsat-8's superior capability in providing nearly twice as many mean annual NCOs as its predecessors but also highlights the importance of adjacent orbit overlaps in improving observation quality, particularly above 45°N latitude."
The findings hold profound implications for enhancing the accuracy of long-term environmental change detection and monitoring. By leveraging improved NCOs, researchers and policymakers can make more informed decisions, particularly in managing water resources and addressing ecological challenges.
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References
DOI
Original Source URL
https://doi.org/10.34133/remotesensing.0110
Funding information
This work was supported by the National Natural Science Foundation of China (nos. 42271322 and 42321004) and Guangdong Provincial Higher Education Key Technology Innovation Project (2020ZDZX3006).
About Journal of Remote Sensing
The Journal of Remote Sensing, an online-only Open Access journal published in association with AIR-CAS, promotes the theory, science, and technology of remote sensing, as well as interdisciplinary research within earth and information science.
JOURNAL
Journal of Remote Sensing
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Quantifying Cloud-Free Observations from Landsat Missions: Implications for Water Environment Analysis
