Viral videos circulating on platforms like YouTube and TikTok have recently captured attention by showcasing seemingly distinct lines in the ocean, characterized by contrasting dark and light waters. These videos often erroneously assert that these lines represent an uncrossable boundary between the Pacific and Atlantic Oceans, suggesting that these two vast bodies of water remain separate and unmixed.
However, this portrayal is misleading. Contrary to these viral claims, the Atlantic and Pacific Oceans do indeed meet and continuously mix. As Nadín Ramírez, an oceanographer at the University of Concepción in Chile, explains, “The short answer is yes! The waters are constantly mixing.” While the mixing process varies in speed and intensity across different locations, the fundamental truth remains: these oceans are interconnected and dynamic, not isolated entities. In fact, emerging evidence suggests that climate change is influencing the rate at which these colossal water bodies intermingle.
To understand this phenomenon, consider the analogy of cream swirling into coffee. The two liquids blend, but the process isn’t instantaneous. Similarly, the visual lines observed in the ocean arise from differences in water properties such as salinity, temperature, and density. Water on one side of the line might be saltier, colder, or have a different sediment concentration, leading to a visual distinction. These differences gradually dissipate as mixing occurs.
Factors like strong winds and powerful waves act as natural stirrers, accelerating the mixing process, much like vigorously stirring coffee hastens the dissolution of cream. The point where the Pacific and Atlantic Oceans predominantly meet is near the southern tip of South America, a region fragmented into numerous islands. Within this area, particularly in sheltered passages like the Strait of Magellan and the Beagle Channel, the mixing is less vigorous. Glacial meltwater in these channels further accentuates the visual lines as freshwater meets saltwater, creating striking contrasts similar to those seen in the viral videos.
Map highlighting the Drake Passage between South America and Antarctica, showing the confluence of the Atlantic and Pacific Oceans.
The turbulent Drake Passage, situated between South America and Antarctica, plays a crucial role in facilitating the mixing of the Pacific and Atlantic Oceans. (Image credit: PeterHermesFurian via Getty Images)
Even where the Strait of Magellan opens into the Atlantic, while a sharp visual line may not always be apparent to the naked eye, oceanographers can detect the confluence. Ramírez notes that in oceanographic data visualizations, “You can see a blue tongue of water in the Atlantic,” originating from the Pacific. This Pacific water is less saline due to higher rainfall levels in the Pacific basin. However, this separation is temporary; the relentless action of storms and waves eventually blurs and eliminates these distinctions.
In the open expanse of the Drake Passage, the boundary between the Pacific and Atlantic is renowned for its tumultuous conditions. Characterized by powerful winds and towering waves, sometimes reaching heights of 60 feet (18 meters), the Drake Passage is a highly energetic zone. “That improves the mix,” Ramírez emphasizes, highlighting the role of turbulence in ocean mixing.
Mixing also occurs at the ocean depths. Casimir de Lavergne, a researcher at Sorbonne University and the French National Center for Scientific Research (CNRS), points out the impact of daily tides. The ebb and flow of tides across the irregular seafloor generate significant turbulence, contributing to the vertical mixing of ocean waters.
However, it’s important to distinguish between mixing and exchange. De Lavergne clarifies that mixing implies “that the waters are irreversibly transformed,” akin to cream fully dissolving into coffee until homogeneity is achieved. In contrast, exchange refers to the movement of water masses between oceans without complete homogenization of their properties. The global system of ocean currents ensures a constant exchange of water between the Pacific and Atlantic.
A powerful current encircling Antarctica’s Southern Ocean drives a clockwise flow through the Drake Passage, effectively transporting Pacific water into the Atlantic. This current also draws water from other ocean basins, redistributing it globally. Furthermore, another current system carries Pacific water through the Indian Ocean, around the southern tip of Africa, and into the Atlantic from the east.
While continuous mixing occurs at the edges of these major currents, the ocean also exhibits a layered structure. Ramírez describes the ocean as “like a cake with different layers,” where each layer, or cline, possesses distinct properties based on its origin. Mixing within the mid-layers of the ocean, away from the surface and seafloor turbulence, proceeds at a slower pace due to reduced turbulence.
Alarmingly, climate change is impacting these intricate ocean dynamics. De Lavergne notes a slowing trend in ocean currents, “especially around Antarctica.” Cold, saline water, which is denser, sinks and propels northbound currents. However, polar warming is causing ice melt, introducing warmer, fresher water that is less dense and sinks less readily. This reduced sinking weakens the driving force behind these currents, leading to a slowdown in water exchange.
Furthermore, the rate of water mixing also appears to be decreasing. As ice melt intensifies, “the density difference between the surface waters and the deep waters is increasing,” explains de Lavergne. Larger density differences between water layers impede mixing, prolonging the time it takes for these differences to even out.
These shifts in ocean mixing and circulation patterns are anticipated to have profound consequences for the distribution of oxygen and nutrients in the oceans, with cascading effects on marine ecosystems. Nevertheless, despite these changes, the fundamental processes of ocean mixing and exchange will persist. As de Lavergne concludes, “As long as there are some winds and some tides, there’s going to be mixing. There are going to be currents.” The Atlantic and Pacific will continue their age-old dance of meeting and mingling, albeit under changing environmental conditions.
