By Carly Menker, Dec. 14, 2021 –
Columbia University Ph.D. student Celeste Pallone devotes her research time observing Eastern Equatorial Pacific dwelling planktonic foraminifera – very tiny creatures that can give huge clues into the pace of ocean climate change.
“Marine sediment cores act as an archive of sea surface temperatures, past environments, including past temperatures, and general environmental factors, such as past global ice volume,” she said of the single-celled, shelled organisms she studies at Columbia’s Lamont-Doherty Earth Observatory high in the Palisades outside New York City. “I examine these proxies, which can be biological or chemical or physical, and then using them I reconstruct oceanographic conditions in the past helping craft record of the El Niño-Southern Oscillation [ENSO].”
Climate change threatens El Nino and other ages-old weather systems with severe disruptions. ENSO varies on 2–7 year timescales and has major influences on temperature, wind patterns, biological productivity and rainfall across the tropical Pacific and far beyond. This also includes crop yields, floods and droughts at multiple locations, said Jerry McManus, field researcher and professor at Columbia’s Department of Earth and Environmental Sciences and Lamont-Doherty. Understanding the baseline influences on this system is key to gauging how it may be altered through climate changes.
The latest report from the U.N.’s International Panel on Climate Change expresses continued uncertainty about how the El Niño-Southern Oscillation will respond to continued warming, although the consequences that play out in the global water cycle are likely to be greater (more rain and flooding in some areas, with increased drought in others). South American countries such as Peru rely on the periodic El Niño to bring warmer ocean waters and rainfall. The uncertainly over El Niño is unsettling. Additionally, the Special Report on the Ocean and Cryosphere in a Changing Climate projected that over the 21st century, the ocean will transition to unprecedented conditions with increased temperatures, further acidification and oxygen decline. It predicts more frequent marine heatwaves along with extreme El Niño and La Niña events.
Pallone is seeing how she can reconstruct the oceanography of the eastern equatorial Pacific Ocean (the region of the open ocean directly south of Mexico and Central America) during a particularly interesting time in Earth’s past as she reported at the annual Comer Climate Conference, an international gathering hosted in southern Wisconsin but held virtually this fall.
According to WHO, the warming of the central to eastern tropical Pacific Ocean in the El Niño 2015-2016 event is affecting more than 60 million people, particularly in eastern and southern Africa, the Horn of Africa, Latin America and the Caribbean and the Asia-Pacific region.
El Niño is an oceanic climate pattern that characterizes unusual warming of surface waters in the eastern tropical Pacific Ocean. Considered the warm phase of a larger phenomenon called the El Niño-Southern Oscillation, the system marks a periodic warming of ocean surface temperatures. Its opposite, La Niña, is marked by an unusual cooling of oceanic surface temperatures. El Niño brings drier warmer weather to the northern United States and wetter conditions to the south. Arriving in the Americas around Christmas time in the cycle described below, it was given the name El Niño (meaning Little Boy or the Christ child) by Spanish fishermen.
Each climate pattern lasts about 9-12 months, and both tend to develop during the spring (March-June), reach peak intensity during the late autumn or winter (November-February) and then weaken during the spring or early summer (March-June) according to the National Oceanic and Atmospheric Administration.
“If you have a strong El Niño event, that might be followed by a strong La Niña event as well – but it is a consistent oscillation that we’ve observed,” Pallone said.
El Niño/La Niña’s hydrological effects are the most important implications on the human population. It can affect rainfall patterns impacting agriculture or even flooding and monsoonal seasons. With satellite measurements of sea surface temperature since the 1980s, there are historical records that indicate the same kind of variability that we observe today suggesting that the ENSO system has been occurring for certain at least the past several thousand years, perhaps even more.
“If we can kind of identify periods that had recurrent warming episodes, for example, or a really large range of temperature variability, we can associate those periods with stronger or more frequent El Niño events,” Pallone said.
McManus highlighted the importance of why Pallone chose to focus on a particular time period, Marine Isotope Stage 5. The marine isotope stages offer a way of tracking ice ages and the periods between them based on the oxygen isotopes found in sediment cores.
“MIS5 was approximately 130,000 to 70,000 years ago and the last interglacial interval that was subsequently followed by a major global ice age, and then the deglacial warming that led to the Holocene interglacial interval of the last 10 or 11 thousand years, the time when all of human agriculture and civilization has developed,” McManus said.
He emphasized that MIS5 is the interval of time when Earth was last as warm as it is today before the most recent ice age, offering the potential to provide insights into natural variability during a warm interval. “The 60,000 years of MIS5 were characterized by three large cycles in the seasonal distribution of sunlight based on the progression of the seasons around Earth’s elliptical orbit,” he said. This time period can help differentiate between natural climate events and what is going on now because of the climate similarities between the time periods of past and present.
Pallone’s research is tri-fold. She uses multiple methodologies to reconstruct the surface and subsurface oceanography of the eastern equatorial Pacific Ocean during a particularly interesting time in Earth’s past, according to McManus.
“She makes many measurements of the oxygen isotope ratios in individual specimens of surface-dwelling planktonic foraminifera shells preserved in deep-sea sediments deposited at that time to learn about the temperature each one experienced during its month or so lifetime, and to compare the range of temperatures that characterized different intervals in the past,” he said. “That tells us something about El Niño-Southern Oscillation (ENSO) variability.”
Another piece of her research is an analysis of multiple specimens of foraminifera species that live at a range of depths below the sea surface to assess their shells and biology as a way to assess where and how fast the temperature changes beneath the surface ocean, hallmarks of El Niño and La Niña events. She studies thermocline structure as another clue to temperature change. The thermocline is the transitional layer between warmer mixed water at the ocean’s surface and cooler deep water below.
Pallone also measures uranium, thorium and protactinium isotopes in the bulk sediment to estimate the amount of material that rained down due to biological productivity in the past.
“A shallower thermocline means that more nutrient-rich waters were moving toward the surface ocean at a particular time, potentially enhancing productivity,” McManus said.
Ultimately, by combining these three main methods, this enables Pallone to make a richer and more robust reconstruction of the ocean state in the EEP at different times throughout history.
The strength or frequency of an El Niño event can be influenced by small changes in Earth’s orbital geometry, with the main factor being changes in solar insulation that are driven by orbital shifts. Teleconnections, climate anomalies related to each other over long distances, also come into play because of how the atmosphere and oceans talk to each other.
“Because of the global circulation of the atmosphere in the ocean, if you have an event happening in the equatorial Pacific, for example, you’ll have effects in other parts of the world,” Pallone said.
Pallone started her research thinking that by using the foraminifera as a proxy and the MIS5 time period, she could create a good analog for modern warning.
“If we can reconstruct the environment during [MIS5], maybe it will inform about what changes could be coming in the future,” she said. “This, with most comparisons between the paleo record and the modern, we’re going to have kind of changes in temperature that might have been or that might be quicker than anything that we’ve seen in the past. But the past is still a useful analog for what could happen in the system.”
For the future, global efforts are needed to curb climate change. At the 2021 Glasgow Climate Conference, the United Nations called for a worldwide response to accelerate climate action to limit global temperature rise at a 1.5 degree C tipping point. The goal called for cutting global fossil fuel emissions by 45% compared to 2010 levels and doing so by 2030. The goal was not adopted.
Going forward, U.N. Secretary-General António Guterres deemed that the world is in emergency mode, meaning we must end fossil fuel subsidies, phase out coal, put a price on carbon, protect vulnerable communities, and deliver the $100 billion climate finance commitment.
Pallone’s research is a small but crucial step in reaching toward this goal.
El Niño events are the dominant source of like this kind of decades scale climate variability today,” Pallone said. “It’s unsettling that we’re not so confident in what could happen to them in the coming years or in the coming century.”
Photo at top: El Niño is anchored in the tropical Pacific, but it affects climate “downstream” in the United States. This shows the U.S. impacts of the climate patterns. (NOAA)
Carly Menker is a health, environment and science reporter for the Medill News Service and a Comer Scholar at Medill. Follow her on Twitter @carlymenker.