Oceans are a crucial regulator of the climate, absorbing large amounts of the additional planet-warming carbon that humans have pumped into the atmosphere since the mid-1800s, as well as more than 90 percent of the increased heat. Sea surface temperatures have risen significantly—hitting new records earlier this year—while warming is also melting ice sheets in polar regions, spilling huge quantities of freshwater into the ocean.
The ocean covers 71 percent of the planet and holds 97 percent of its water, making the ocean a key factor in the storage and transfer of heat energy across the globe. The movement of this heat through local and global ocean currents affects the regulation of local weather conditions and temperature extremes, stabilization of global climate patterns, cycling of gases, and delivery of nutrients and larva to marine ecosystems. The sun’s heat causes water to evaporate, adding moisture to the air. The oceans provide most of this evaporated water. The water vapor condenses to form clouds, which release their moisture as rain or other kinds of precipitation. All life on Earth depends on this process, called the water cycle. Warmer oceans radically alter the ecosystem. Warmer oceans cause coral reef bleaching and are linked to toxic algae blooms, which can suck oxygen from the water and choke marine life. This deoxygenation of this kind affects biodiversity and food webs. Beyond the impact on animals, changes in these key ocean pumps are also expected to reduce the amount of carbon the ocean can absorb, as well as pulling up to the surface carbon that has been safely stored away in the ocean depths for hundreds of thousands of years.
The ocean plays a vital role in climate and weather. The atmosphere receives much of its heat from the ocean. As the sun warms the water, the ocean transfers heat to the atmosphere. In turn, the atmosphere distributes the heat around the globe.
Because water absorbs and loses heat more slowly than land masses, the ocean helps balance global temperatures by absorbing heat in the summer and releasing it in the winter. The world ocean and atmosphere regulate heat transport across the planet through large scale ocean and atmospheric circulation, keeping earth’s temperatures relatively constant. In general, warm water is transferred from the equator to the poles and cooler water from the poles is transferred back towards the equator. Without the ocean to help regulate global temperatures, ocean currents keep the ocean from becoming extremely hot or cold.
OCEAN CURRENTS ARE DRIVEN BY DENSITY, GRAVITY, WINDS, AND THE ROTATION OF THE EARTH.
The ocean has an interconnected current, or circulation, system powered by wind, tides, Earth’s rotation (Coriolis effect), the sun (solar energy), and water density differences. The topography and shape of ocean basins and nearby landmasses also influence ocean currents. These forces and physical characteristics affect the size, shape, speed, and direction of ocean currents. The oceans of the world are heated at the surface by the sun, and this heating is uneven for many reasons. The Earth’s axial rotation, revolution about the sun, and tilt all play a role, as do the wind-driven ocean surface currents. Two important characteristics of seawater are temperature and salinity – together they control its density, which is the major factor governing the vertical movement of ocean waters. The salinity of the ocean also varies from place to place, because evaporation varies based on the sea surface temperature and wind, rivers and rainstorms inject fresh water into the ocean, and melting or freezing sea ice affects the salinity of polar waters.
THE EBB AND FLOW OF THE TIDE IS NOT THE MOST IMPORTANT PLANETARY PROCESS AT WORK.
What really matters are the ocean currents that circulate the seas from the surface to the depths and the equator to the poles. As aforementioned the ocean’s salinity and temperature and the coast’s geographic features determine an ocean current’s behavior. This process is driven by a combination of winds in the atmosphere and rotation of the Earth. Currents flowing near the surface transport heat from the tropics to the poles and move cooler water back toward the Equator. Earth’s rotation and wind also influence ocean currents. Winds move the surface layers, and the Coriolis force (caused by the spin of the Earth), makes these surface currents curve, either away or towards the coast. Deep, cold currents transport oxygen to organisms throughout the ocean. They also carry rich supplies of nutrients that all living things need. The nutrients come from plankton and the remains of other organisms that drift down and decay on the ocean floor. This cold, dense water also has a vital role in supplying oxygen to deep ocean waters. How and whether deep ecosystems could adapt to less oxygen is unclear.
Where the ocean curves away from either the coast or each other, they bring up nutrient rich water from the depths. As winds push surface water away from shore, deep currents of cold water rise to take its place. This upwelling of deep water brings up nutrients that nourish new growth of plankton, providing food for fish. The seasonal cycle of phytoplankton growth is an amazing demonstration of the complex and interwoven physical, chemical and biological processes of the ocean.
Ocean food chains constantly recycle food and energy this way. During the summer, the phytoplankton absorb most of the dissolved inorganic nutrients from the surface waters and are consumed by the zooplankton, decreasing the rate of photosynthesis. Vertical mixing ceases and phytoplankton, which remain in the upper layers, become nutrient-limited. The cycle starts all over in the fall when the surface water cools, churning the deeper, nutrient-rich waters into the depleted surface waters. Nutrients become available again and the phytoplankton blooms in great quantity during the spring after the intense winter mixing. In upwelling currents, vertical water movement and mixing brings cold, nutrient-rich water toward the surface while pushing warmer, less dense water downward, where it condenses and sinks. This creates a cycle of upwelling and downwelling. Prevailing winds, ocean-surface currents, and the associated mixing influence the physical, chemical, and biological characteristics of the ocean, as well as global climate. These upwellings drive some of the most highly productive marine ecosystems.. This whole system is vital for distributing nutrients, food, marine life and heat around the world, thus supporting marine ecosystems and regulating our climate as it moves heat from equator to the poles.
THE ARCTIC OCEAN IS WARMING QUICKLY.
It is about more than rising temperatures; the transformation of the Arctic Ocean from colder, fresher, and ice-capped to warmer, saltier, and increasingly ice-free. It’s a process that is reshaping the physical and chemical conditions of the Arctic Ocean. Because of the oceans’ global circulation patterns, water routinely flows from the Atlantic into the Arctic. This exchange mostly occurs in deeper water, with currents carrying warm and relatively salty Atlantic water north. This warm Atlantic water, however, doesn’t mix well with the Arctic’s surface water, which is relatively cool and fresh. Fresher water is less dense than saltier water, so the Arctic water tends to float on top, trapping the saltier Atlantic water deep below the ocean’s surface.
As sea ice disappears, however, the surface of the Arctic Ocean is heating up. The barrier between the layers is degrading and Atlantic water is mixing more easily into the upper layer. This is kicking off a feedback loop, where warmer surface water melts more sea ice, further exposing the ocean’s surface to sunlight, which heats the water, melts the ice, and allows Atlantic and Arctic water to blend even more.
THE GLOBAL CONVEYOR BELT
Surface currents also connect to deepwater currents to produce what is known as the thermohaline (thermo – heat, haline – salt) conveyor belt. The global conveyor belt’s circulation is the result of two simultaneous processes: warm surface currents carrying less dense water away from the Equator toward the poles, and cold deep ocean currents carrying denser water away from the poles toward the Equator. Deep ocean currents are density-driven and differ from surface currents in scale, speed, and energy. Thermohaline circulation refers to global density-driven circulation of the oceans a global-scale circulation system. Water density is affected by the temperature, salinity and depth of the water. The colder and saltier the ocean water, the denser it is. The greater the density differences between different layers in the water column, the greater the mixing and circulation. The ocean’s global circulation system plays a key role in distributing heat energy, regulating weather and climate, and cycling vital nutrients and gases.
Temperature and density share an inverse relationship so when the surface currents (i.e. the Gulf Stream) flow towards the poles from the equatorial Atlantic Ocean, they are cooled and flow downhill into deep water basins forming the North Atlantic Deep Water. These currents resurface in the northeast Pacific Ocean 1,200 years later. Ocean water from all of the ocean basins mixes thoroughly, carrying heat energy and matter in the form of solids and gases, making Earth’s ocean a global system. The state of this thermohaline circulation, the global conveyor belt, can have an enormous impact on the climate of our planet.
The oceans shield us from the full impacts of the climate crisis. We should thank the ocean for taking up most of what we’ve done to the climate system, otherwise we would be seeing effects that are really 100 times what we’re seeing right now.
But this buffering role comes at a high cost.