Due to global warming, many marine species, including fish, plankton, and other organisms, migrate to deeper waters and polewards where their physiological needs are better met as surface waters warm. These species are moving into deeper, cooler areas in search of cooler temperatures to avoid thermal stress and more suitable habitats. Record-breaking ocean temperatures are driving these unprecedented shifts in marine life, disrupting ecosystems and economies, and challenging science and policy to keep up with the rapid environmental changes.
Warmer waters hold less dissolved oxygen, and some species may move deeper to find areas with more oxygen, as warmer waters can decrease oxygen levels.
Besides temperature and oxygen, deeper waters may also offer protection from other stressors like strong sunlight or changes in salinity, which can be influenced by global warming.
Migration can disrupt food webs and ecosystems, as species move to areas where their prey or predators are not present, potentially leading to cascading effects throughout the marine environment.
These shifts are upending global fisheries and ecosystems, increasing extinction risks, driving economic disruptions, and sparking geopolitical tensions over access to marine resources.
Marine ecologist Malin Pinsky, Associate Professor of Ecology and Evolutionary at the University of California Santa Cruz, urges action across disciplines and communities, emphasizing sustainable seafood choices, civic engagement, and recognizing that ocean health is fundamental to life on Earth.
Last year was not only the warmest on record for the ocean; it may also have been the warmest in the last 100,000 years. Current ocean temperatures are now similar to those during the Eemian period, which occurred 120,000 years ago, and even resemble conditions from the mid-Pliocene, around 4 million years ago, when giant armadillos roamed North America and beech trees flourished in Antarctica.
This year, 104 countries recorded their highest-ever temperatures, and COâ‚‚ levels have reached 430 parts per million, the highest they have been in at least 2 million years.
Carbon dioxide diffuses from the atmosphere into the ocean's surface waters, especially in cooler regions, in accordance with Henry's Law, which states that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid.
When CO2 in the atmosphere has a higher partial pressure than in the ocean, it dissolves into the water until equilibrium is reached. When CO2 reacts with water molecules, it forms carbonic acid (H2CO3), which releases hydrogen ions into the seawater. This increases acidity and pH levels, making it more difficult for marine organisms such as shellfish, corals, and plankton to build and maintain their calcium carbonate shells and skeletons.
Since the Industrial Revolution, the average ocean pH has decreased from 8.21 to 8.10 and if this continues at the current rate, the surface ocean pH could drop to 7.7 within the next 100 years.
About 90 percent of the excess heat from global warming ends up in the ocean. It is measured in zettajoules—a thousand million million million joules. Without the ocean absorbing this heat, “we’d be very crispy toast, " Professor Pinsky notes.
Since the 1970s, he says, “in the U.S. Northeast alone, blueback herring have shifted 260 miles north, black sea bass 190 miles, and American lobster 150 miles.” And these shifts affect everything: food webs, international supply chains, even geopolitics.
Although these creatures learn fast, they are unaware that the ocean layers are becoming more stratified, trapping warmer, less oxygenated water and the food vital to their survival and reproduction.
Besides relocation, scientists have discovered that clown fish shrink to survive heat stress and social conflict. But with us humans, climate migration is increasingly becoming a source of social conflict. Furthermore, poleward migration of heat is significantly negative for humans. It disrupts local climates and alters weather patterns, which impact agriculture, water supply, and biodiversity. Rising temperatures contribute to health issues, such as heat stress and the spread of diseases usually found in warmer regions. And regions that are used to a specific climate may encounter economic difficulties as they adapt to new agricultural conditions or cope with increased energy demands for cooling.
Heat migration toward the poles can lead to various challenges for humans, necessitating proactive responses.
One such response is to move that heat into deeper water instead of towards the poles.
Differences in pressure cause the ocean/atmospheric heat flux. High pressures produce winds that distribute heat to low-pressure areas around the Earth's surface. The Coriolis effect influences the east/west flow of the Trade Winds, and the Thermohaline Circulation is driven by differences in water density, which are influenced by temperature (thermo) and salinity (haline).
Cold, salty water becomes saltier as seawater freezes at the poles during winter, causing the salt to separate from the ice. This process makes the water denser, causing it to sink and creating pressure gradients. The sinking water initiates a global flow of ocean currents as the water moves to balance these pressure differences. Additionally, surface currents and upwelling bring nutrient-rich water to the surface, supporting marine life. As deep water eventually rises back to the surface, it seeks to move from warmer areas to cooler ones in accordance with the Laws of Thermodynamics and the Law of Conservation of Energy, completing the circulation loop.
The thermally stratified ocean can convert a portion of global warming's heat to work in accordance with the First and Second Laws of Thermodynamics. However, due to buoyancy, a thermally stratified ocean resists the movement of surface heat into deep water.
A heat pipe, a highly effective thermal conductor that transfers heat through the latent heat of boiling and condensation of a low-boiling-point working fluid, can induce vertical movement. The boiling of a working fluid produces pressure that moves the heat to a depth of 1,000 meters, releasing it into the ocean’s deepwater heat sink as the latent heat of condensation.  As the working fluid vapor condenses it produces a vacuum within the heat pipe that sucks heat from the surface at a rate approaching that of sound.
The rapid transfer of heat through heat engines can generate twice the energy currently obtained from fossil fuels and one and a half times the combined energy produced from all sources. Additionally, this process helps mitigate the effects of climate change, allowing natural sinks, including the ocean, to deplete atmospheric CO2 concentrations back to preindustrial levels. This reduction would occur over the course of 13 heat cycles, each lasting approximately 226 years. During this time, the heat not initially converted into work will diffuse back to the surface at a rate of 4 meters per year, at which point it can be recycled to produce more energy.
Surely, we can be no less diligent than fish about our physiological needs?