Warmer, saltier and more acidic oceans threaten human health and the environment
Recent years have seen huge global impacts from Earth’s climate change. In a new study, the result of 40 years of ocean research, scientists have identified changes in the subtropical North Atlantic Ocean off the coast of Bermuda. The research has implications for oceans around the world.
This paper, which appears in the current issue of Frontiers in Marine Science, provides the longest sustained time series in the World Ocean, tracking critical ocean trends over four decades.
The comprehensive study, conducted from 1983 to 2023 at a pair of monitoring sites in the Sargasso Sea surrounding the island of Bermuda, showed a rise in ocean surface temperature of about 1 degree. Celsius (1.80 F). Ocean acidity and salinity also increased by 30% and 136 parts per thousand, respectively, according to the results. Ocean acidity means a decrease in pH, similar to adding lemon juice to water, while a measure of salinity indicates a slight increase in the salt content of the ocean.
The results also show that rising atmospheric carbon dioxide levels caused by human activity have depleted oxygen from the Sargasso Sea’s surface waters by 6%.
The combined effects of these changes negatively impact diverse species, disrupting the food chain of protozoan and higher organisms that rely on this energy source – from fish and marine mammals such as whales to seabirds and other life forms. Likewise, impacts on human communities are expected to be far-reaching, from loss of fishing resources to inundation of coastal areas due to high tides and unpredictable rainfall patterns.
Nicholas Bates
Nicholas Betts, lead researcher on the study, said: “The findings that the current chemistry of the Sargasso Sea’s surface waters is now very different than it was 40 years ago highlight the current and future challenges caused by global ocean change facing this large marine ecosystem in the northern Atlantic Ocean”. Stady.
Bates is a chemical oceanographer and director of research at the Bermuda Institute of Oceanography at Arizona State University. He is also a senior scientist at Global Futures at Arizona State University’s Julie Ann Wrigley Global Futures Laboratory and a professor at ASU’s College of Ocean Futures.
“The information on changes in our oceans gathered from this long-term study is invaluable and can only be obtained through ship-based observations lasting over decades,” said Peter Schlosser, vice president and vice dean of Global Futures and director of the Global Futures Center. many”. Global Futures Lab. “Observed trends in ocean temperature, salinity and carbon chemistry confirm that our oceans are undergoing dramatic change due to human-caused global warming.
“They underscore the urgent need for immediate action to limit this warming to as close to 1.5°C as possible through immediate and profound reductions in greenhouse gas emissions and extraction of carbon dioxide from the atmosphere.”
One of the most dramatic findings of the new study is that the ocean chemistry of surface waters now lies outside the seasonal range observed in the 1980s. Such changes threaten the health of the foundation of the ocean food chain, which consists of tiny organisms known as phytoplankton.
“The ocean ecosystem, including calcified phytoplankton, now lives in a different chemical environment than it experienced just a few decades ago,” Bates said. “Changes in the chemical environment and ocean acidification in the subtropical North Atlantic are due to the uptake of anthropogenic carbon dioxide from the atmosphere.”
Phytoplankton, microscopic plant-like organisms that float in the ocean, are essential to marine ecosystems. They belong to a diverse group of photosynthetic microorganisms that live in the sunlit upper layer of almost all oceans and freshwater bodies. Like terrestrial plants, plants perform photosynthesis, converting sunlight and carbon dioxide into oxygen and biomass, thus producing about half of the world’s oxygen.
This process forms the bedrock of marine food webs, as phytoplankton are primary producers, feeding a wide range of marine life – from tiny zooplankton to whales.
Climate change poses major threats to these vital organisms. Rising sea temperatures and acidification affect the ability of phytoplankton to calcify, a process critical for certain species such as stone coccolithophores. This change in calcification affects not only phytoplankton but the entire ocean carbon cycle.
Warmer waters could also change phytoplankton distribution and bloom patterns, potentially disrupting marine food chains and biodiversity. As phytoplankton dynamics shift, the entire marine ecosystem – including fish populations and overall ocean health – faces significant challenges.
The Atlantic Explorer is a research vessel used to make detailed measurements of critical ocean variables, including temperature, salinity and oxygen content, in the Sargasso Sea surrounding the island of Bermuda. The ship was built in 1982 as a third-class ocean environmental research vessel. It is owned and operated by the Bermuda Oceanographic Institute. Image courtesy of Bermuda Oceanographic Institute
Taking the pulse of the ocean
This study is one of the few projects of its kind that tracks changes in Earth’s ocean systems over several decades. It provides a treasure trove of data of vital importance to both scientists and policy makers grappling with the worsening impacts of climate change.
The project to better understand the physics, biogeochemistry, and ocean acidification in the subtropical North Atlantic began in 1954, with the construction of Hydrostation S. This monitoring station is located about 25 km southeast of the island of Bermuda. Hydrostation S, created by Henry Stommel, a pioneering oceanographer from Woods Hole Oceanographic Institution, has collected vital information about ocean dynamics, from physical variables such as temperature and salinity to biological measurements of phytoplankton over time.
Today, Bates and co-principal investigator Rod Johnson continue this work at a second ocean measurement station known as BATS (Bermuda Atlantic Time Series Study), established in 1983. Both time series were funded by the US National Science Foundation, with BATS being funded by Until 2028.
At the BATS monitoring station, ocean surface temperatures have increased by about 0.24°C per decade since the 1980s. Added to this, the oceans are now about a degree Celsius warmer than they were 40 years ago. The researchers found that in the past four years, ocean temperatures have risen more sharply than in previous decades.
On a crisp autumn afternoon, the campus of Watts College was alive with excitement as friends, family, and faculty gathered to honor the graduating class of fall 2023. The air was filled with a sense of accomplishment and pride as graduates prepared to embark on the next chapter of their lives. The ceremony was a celebration of hard work, dedication, and perseverance, and a testament to the bright futures that awaited these talented individuals. As the sun set on this momentous occasion, the energy and enthusiasm of the graduates filled the air, signaling the beginning of a new and exciting journey for each of them.