A new study conducted at the Florida State University (FSU) has revealed that when La Niña brings unusually warm waters and abnormal air pressure to the Pacific Ocean, it leads to a weather pattern that increases the carbon export from the Amazon River.
During a normal year, the Amazon river transfers around 10% of the global riverine dissolved organic carbon into the ocean. The study published in the journal Global Biogeochemical Cycles reveals that the 2011–2012 La Niña occurrences added an extra 2.77 teragrams of dissolved organic carbon (DOC) every year to the outflow from the Amazon River. This volume is equal to the amount exported from the Mississippi River in a normal year.
That’s a big deal, because as global temperature and precipitation patterns continue to change, we’re missing out on this highly sensitive pool of organic carbon coming from the Amazon River that we previously didn’t account for in any of the estimates.
Martin Kurek, Study Lead Author and Doctoral Student, Florida State University
The scientists observed a six-month lag between increased precipitation in the Amazonian headwaters from the La Niña event and a raised DOC export at a sampling station next to the mouth of the Amazon River at Óbidos, Brazil.
Additionally, the DOC arrived from terrestrial sources than in a typical, non-La Niña year, which emphasizes the flushing of materials from land related to a higher rainfall as a result of the La Niña event.
Dissolved organic carbon is considered to be a key intermediary in the global carbon cycle. Gaining better insights into the cycle becomes essential due to the role of carbon on Earth. For instance, the organic matter exported by the Amazon River acts as a food source for microorganisms living in the ocean, while being a source of carbon dioxide to the air, which also affects the Earth’s climate.
A companion manuscript also reported in the Global Biogeochemical Cycles gathered baseline measurements on nutrients, carbon, and trace elements, which enable scientists to form yearly flux estimates and assess the seasonality in the largest river on Earth.
The experiment is similar to a doctor extracting blood samples from a patient to identify the health status, which enables scientists to emphasize when anomalies like La Niña lead to atypical conditions.
We’re using a fairly similar approach to a medical doctor, but in this case, our patient is the Amazon River Basin, and we are taking water samples, not blood samples. This gives us a way to assess the health of the Amazon and to see the effects of human-driven factors, like logging, conversion of lands to agriculture and climate change.
Rob Spencer, Associate Professor of Biogeochemistry, Florida State University
“A big part of understanding all of that is setting a baseline. You have to know what your patient’s typical health is, and in this study, we set the baseline and then caught the impact of a La Niña event,” added Spencer.
Spencer is also the head of the laboratory which hosts the research.
Climate change is anticipated to induce more frequent and severe precipitation phenomena like La Niña. For Spencer and his colleagues, this factor emphasizes the significance of sustained data collection and documentation of the events in the Amazon Basin to help scientists better comprehend the impacts inside the basin and its implication on the receiving Atlantic Ocean.
I think many people are interested in how the Earth works and how it’s changing. If you want to understand how the planet is changing, one of the big things you need to know is how quickly the major river on Earth, the Amazon, is changing.
Rob Spencer, Associate Professor, Biogeochemistry, Florida State University
Scientists from Northeastern University, ETH Zurich, Federal University of Western Para, Woodwell Climate Research Center, University of Oldenburg, and Woods Hole Oceanographic Institution co-authored the first study. The research was financially supported in part by the National Science Foundation and the Harbourton Foundation.
The study co-authors on the baseline measurements study were the researchers from Harvard University, Woods Hole Oceanographic Institution, Woodwell Climate Research Center, Federal University of Western Para, and the International Atomic Energy Agency. Former FSU doctoral student T. W. Drake was the lead author.
Kurek, M R., et al. (2021) Drivers of Organic Molecular Signatures in the Amazon River. Global Biogeochemical Cycles. doi.org/10.1029/2021GB006938.