Data confirms robust weakening of the Gulf Stream

A recently published study in the journal Geophysical Research Letters has revealed that the Gulf Stream transport of water through the Florida Straits has weakened by approximately 4% over the past 40 years. Researchers state with 99% certainty that this is more than what would be expected from random variations, marking the first definitive evidence of significant change in the current.

• The Gulf Stream is a major ocean current located off the East Coast of the United States and a major part of the Atlantic Meridional Overturning Circulation (AMOC). It carries a tremendous amount of seawater and along with it heat, carbon, and other ocean constituents. Because of this, the Gulf Stream plays an important role in weather and climate, influencing phenomena as seemingly unrelated as sea level along coastal Florida and temperature and precipitation over continental Europe. 
• Recent studies have indicated that both the Gulf Stream and the AMOC are showing signs of weakening, which is cause for concern given their vital roles in regulating global and regional climates.
• The Gulf Stream and AMOC system together act as a global conveyor belt, redistributing heat and affecting weather patterns across the world. A weakening of these systems could have severe implications, such as more extreme weather conditions, including increased storms and heatwaves, and altered marine ecosystems. The Gulf Stream’s role in moderating the climate of Western Europe could be compromised, leading to colder winters, while a weakened AMOC could result in a cascade of climatic shifts far beyond the North Atlantic. Thus, the observed weakening of these oceanic currents isn’t just a regional issue but a global concern that may require coordinated international efforts to understand and address.

The Gulf Stream, a critical part of the Atlantic Meridional Overturning Circulation (AMOC), plays a vital role in global weather and climate systems. Its weakening could have far-reaching implications, including changes in European surface air temperature and precipitation, shifts in coastal sea levels along the Southeastern U.S., and altered patterns of North Atlantic hurricane activity, study authors said. The study is based on a synthesis of thousands of data points collected from the Florida Straits, an area between the Florida Keys, Cuba, and The Bahamas. The region has long been the focus of ocean observation campaigns, dating back to the 1980s or earlier.

To arrive at their conclusion, the researchers employed Bayesian modeling techniques to combine data from undersea cables, satellite altimetry, and in-situ observations. This probabilistic approach allowed them to articulate the uncertainty within the model, strengthening the study’s findings. The results consistently indicated a long-term weakening of the Gulf Stream, irrespective of which data sets were included or omitted from the analysis.

While the study provides strong evidence of weakening, it does not identify the cause, leaving the question of whether this is due to climate change or natural variations open for future research. “While we can definitively say this weakening is happening, we are unable to say to what extent it is related to climate change or whether it is a natural variation,” said Chris Piecuch, the study’s lead author and a physical oceanographer with the Woods Hole Oceanographic Institution.

The study has been lauded as a significant milestone in oceanographic research. “I have been studying western boundary currents—primarily the Agulhas Current off South Africa—for 30 years and it is only now that we are able to observe a robust trend in one of these extraordinarily dynamic systems,” said Lisa Beal, a co-author of the article and a professor of Ocean Sciences at the University of Miami, Florida.

The researchers emphasize the necessity of long-term observation systems to detect subtle changes in oceanic conditions. “This paper explicitly demonstrates the value of these long observing systems to tease out very subtle signals. In this case, we showed that we needed more than 30 years of data,” Piecuch added. The study is part of a larger six-year project funded by the National Science Foundation, aimed at extending the observational record of the Gulf Stream at the Florida Straits.

Previous studies have found that AMOC is also weakening over time, but that it’s unlikely to collapse before the end of the century. However, a study published in Nature on July 25, 2023, marks the first time that researchers have tried to pin down when the AMOC could stop working — the authors said it could be anytime between 2025 and 2095.

It is worth noting that AMOC has only been monitored continuously since 2004 through combined measurements from moored instruments, induced electrical currents in submarine cables and satellite surface measurements.

The Gulf Stream and the Atlantic Meridional Overturning Circulation (AMOC) serve as vital components of the Earth’s climate system. The Gulf Stream, for example, significantly influences regional climates by redistributing warm tropical waters northward along the eastern seaboard of the United States and toward Europe. This helps to moderate climates, especially in Western Europe, which experiences milder winters and cooler summers than it otherwise would. The Gulf Stream also plays a role in shaping weather patterns, affecting everything from precipitation to hurricane activity.

The AMOC, of which the Gulf Stream is a part, has even broader implications. This system of ocean currents circulates heat around the globe, acting as a sort of conveyor belt for thermal energy. Its influence extends beyond the North Atlantic, affecting climate systems as far away as the Indian and South American monsoons. Additionally, the AMOC impacts marine ecosystems by facilitating the transport of nutrients and affecting ocean productivity.

If the AMOC were to collapse, the consequences could be dire and far-reaching. One immediate effect would be a dramatic change in climate, especially for regions currently moderated by the system. Europe could experience harsher winters and more extreme weather conditions, affecting everything from agriculture to human health. A collapse could also lead to rising sea levels along the eastern coast of North America, causing increased flooding and erosion. Furthermore, a disrupted AMOC would likely have a cascading effect on global weather patterns, potentially leading to more frequent and severe storms, heatwaves, and droughts worldwide.

There’s also the matter of marine ecosystems, which could be severely impacted by the collapse of the AMOC. The disruption of ocean currents might cause certain species to migrate, decline, or even go extinct, with significant consequences for commercial fishing and biodiversity.

While current models and observations suggest that a complete collapse of the AMOC is not imminent, the system has shown signs of weakening. Understanding the role and functioning of the Gulf Stream and the AMOC is crucial for predicting and potentially mitigating some of these potentially catastrophic effects.

References:

¹ New study definitively confirms gulf stream weakening – Woods Hole Oceanographic Institution – September 25, 2023

² Robust Weakening of the Gulf Stream During the Past Four Decades Observed in the Florida Straits – Geophysical Research Letters – September 25, 2023 – Christopher G. Piecuch and Lisa M. Beal – https://doi.org/10.1029/2023GL105170

³ Warning of a forthcoming collapse of the Atlantic meridional overturning circulation – Nature – July 25, 2023 – Peter Ditlevsen and Susanne Ditlevsen – https://doi.org/10.1038/s41467-023-39810-w

Featured image credit: NASA Earth Observatory