An Important Ocean Current Remains Stable, for Now

Recent findings suggest that the Florida Current's weakening is not as severe as previously believed. This vital current serves as a bellwether for the ocean's climate regulation capabilities. Research published on September 5 in Nature Communications shows that, contrary to earlier assumptions, the Florida Current has remained stable over the years.

A previously reported decline in the Florida Current led to concerns about significant weakening in a major ocean current system. This system regulates climate on Earth through a process known as the Atlantic Meridional Overturning Circulation (AMOC). Some researchers even warned that the AMOC might collapse within this century, which could lead to a drop in temperatures in the northern hemisphere and a sea level rise of up to 70 centimeters along some Atlantic coasts.

Hali Kilbourne, an oceanographer at the University of Maryland Center for Environmental Science, states, "The good news is that the AMOC is slowing down less than we thought, and that means that there's still time to avert a more serious slowdown." However, she emphasizes that the newly assessed data only covers a few decades. This raises the question of whether the AMOC has slowed since preindustrial times, around the mid-1800s.

The AMOC functions as a conveyor belt, circulating heat, salt, and nutrients in the Atlantic Ocean. The upper level transports warm, surface water from the tropics to the North Atlantic. There, the water cools and descends to the ocean floor. It later returns southward along the belt’s lower level, where it gradually warms and rises, completing the cycle.

In the subtropical North Atlantic, a significant portion of the water carried by the AMOC's upper level originates from the Florida Current. This current channels water from the Gulf of Mexico into the Gulf Stream. Since 1982, a telecommunications cable on the ocean floor has been employed to monitor this current, providing the longest ongoing observational record of any AMOC component.

Seawater carries charged atoms called ions; their flow generates a measurable voltage across the cable. By correlating these voltage measurements with direct observations from research cruises, scientists estimate the water flow rate of the current daily.

Despite its efficacy, the monitoring process has limitations, according to Denis Volkov, an oceanographer at the University of Miami. The data collection has been overseen by numerous scientific teams, leading to various processing changes over the years. Volkov's team discovered that following 2000, adjustments to account for the Earth's magnetic field's shifting intensity and orientation were overlooked.

Correcting these geomagnetic influences revealed a decline of approximately 100,000 cubic meters per second in the Florida Current's flow rate since 2000. This represented roughly a quarter of the previously reported reduction and is practically insignificant compared to the average flow of about 32 million cubic meters per second.

The recalibrated data also reduced estimates of the AMOC's recent decline by about 40 percent. Each decade since 2000, the AMOC's flow rate has decreased by around 800,000 cubic meters per second. While it does indicate a decline, Volkov reiterates that it's insignificant. It remains uncertain whether this slowdown results from climate change or reflects a natural fluctuation.

The Florida Current's recent patterns do not suggest that the AMOC is deteriorating because of climate change. This observation is further complicated by the observational record's brevity, which limits clear conclusions.

Kilbourne points out that scientific research constantly evolves, necessitating revisions to data, assumptions, and prevailing beliefs as new information emerges. However, many studies claiming AMOC declines since preindustrial times employ paleoclimate proxy data. This data encompasses sediment grain sizes and coral compositions that span thousands of years. Given that the revised dataset is still comparatively brief, it does not significantly alter the understanding of the AMOC's long-term evolution.

Sophia Hines, an oceanographer at the Woods Hole Oceanographic Institution, emphasizes the importance of ongoing observations. She states, "It’s all important, just different pieces of the puzzle." These continuous efforts may eventually clarify the impact of climate change on the AMOC.

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