Better understand climate change by studying the oceans

Climate change and its impact on human society have become a global concern. Faced with this question, scientists are trying to pinpoint the climate’s evolution, but are still struggling to reach a consensus about the magnitude of global warming in the future. The difficulty arises in particular from the fact that the phenomenon involves a great number of natural and human parameters, linked by complex interactions.

Thermal regulation is not based solely on atmospheric processes. It is also closely linked to the dynamics and the biology of oceans, which cover about 70% of the earth’s surface and are constantly exchanging energy (heat) and matter (gas, water, aerosols) with the atmosphere. In order to best predict climate change, it has become essential to refine the description, quantification, and monitoring of exchange mechanisms between these vast expanses of salt water and our aerial environment.

Follow the Gulf Stream and gather scientific data from both water and air

The PlanetSolar DeepWater expedition is exploring the ocean processes that interact with the atmosphere by taking water and air measurements for over 8,000 km along the Gulf Stream. This ocean current helps to carry heat from the tropics to the polar regions in the North Atlantic, making it one of the most important regulators of the European and North American climates.

During this expedition, special attention is paid to ocean vortexes, whirlpools that carry large amounts of energy, as well as to areas of deep water formation, strategic locations where surface waters dive down to the seafloor, helping to fuel what is commonly called the “ocean conveyor belt” – a three-dimensional global current that connects all the ocean basins on the planet.

The data collected will be used to refine numerical weather and ocean modeling.

Energy exchanges between the ocean and the atmosphere

Oceans and atmosphere are constantly exchanging thermal energy. Oceans influence the climate by altering the distribution of heat around the globe over time. This impact is due to the thermal inertia of water, which warms up or cools off less quickly than air. The ocean’s thermal “memory” is substantially longer than the atmosphere’s; it modulates temperatures by gradually releasing any previously stored heat. This feature helps to balance the overall allocation of our planet’s thermal energy by redistributing it from warmer areas to colder areas through marine currents. It is believed that the ocean contributes up to 30 % of the heat transfer carried out by the climate system from the equator towards the poles.

Modeling of the North Atlantic’s surface marine temperature
Source : EU/FP6 « SEOS » Project, http://www.seos-project.eu »

Matter exchanges between the ocean and the atmosphere

Oceans absorb and release very large quantities of carbon dioxide (CO₂) into the atmosphere. This greenhouse gasCriticalThe greenhouse effect is a natural phenomenon that allows the Earth to retain some of the energy transmitted by the sun. Functioning as a bidirectional filter, the atmosphere lets through a large part of the solar radiation that strikes the ground. Warmed up, it emits infrared radiation towards space, which is specifically retained by certain gases and atmospheric particles, mainly water vapor and CO₂. The retained energy reappears in the form of heat. is soluble in sea water, where it is sometimes contained by the activity of a multitude of micro-algae in suspension, phytoplankton. To grow, it uses sunlight to produce organic matter from CO₂ (photosynthesis). At the end of its life, phytoplankton sinks to the ocean floor and forms sediment, sequestering carbon for hundreds of years.
Atmospherics aerosols, tiny dust and micro-droplets suspended in the air, can form from sulfurized molecules produced by phytoplankton. We know that aerosols, copious in the atmosphere, are involved in climate mechanisms in a variety of ways. In accordance with their nature, they reflect solar radiation and infrared heat in different manners, thereby modulating our planet’s greenhouse effectCriticalThe greenhouse effect is a natural phenomenon that allows the Earth to retain some of the energy transmitted by the sun. Functioning as a bidirectional filter, the atmosphere lets through a large part of the solar radiation that strikes the ground. Warmed up, it emits infrared radiation towards space, which is specifically retained by certain gases and atmospheric particles, mainly water vapor and CO₂. The retained energy reappears in the form of heat.. They also form from condensation nucleiCriticalSome aerosols act as condensation nuclei. Upon contact, the atmospheric water vapor molecules condense and accumulate. When the mass of the nucleus and its condensation become significant, they become visible and fall in the form of precipitation. , essential to the formation of clouds, which are heavily involved themselves in climate modulation. Despite these recognized critical roles, aerosols are still studied very little, and there is considerable uncertainty about the extent of their influence on our planet’s thermal balance.

Several species of phytoplankton color the polar seas in the summer
(Barents Sea, satellite image).
Source: NASA Earth Observatory

Areas of deep water formation

The Gulf Stream is brought about by winds carrying warm tropical water along the North American coast. This surface current, called the North Atlantic Drift, then flows through the ocean and reaches the Arctic Ocean. Throughout this journey, the water gradually cools down, becoming denser. When the freezing point is reached, some of the water turns to ice, releasing salt into the surrounding water, increasing its density. Gravity causes this cold salty water to plunge down 2,000-3,500 meters deeps and form a deep current called the North Atlantic Deep Water, which flows toward the southern polar regions. This loop contributes to global ocean circulation, comparable to a giant conveyor belt in a delicate balance. Global warming could affect deep water formation in the North Atlantic, with consequences that still remain poorly assessed.

Frozen sea
Source: Thinkstock

Ocean vortexes

Large ocean vortexes are regularly observed off the coast of North America. These ascending cyclonic formations (cold water rising from the depths) or descending anticyclonic formations (warm water plunging to the depths) are caused by turbulence, still poorly understood, associated with the circulation of the Gulf Stream. The vortexes alter the vertical distribution of nutrients, and therefore influence both heat exchanges with the atmosphere and the growth of phytoplankton.

Satellite image of an ocean vortex, with a high concentration of phytoplankton.
Source: NASA Earth Observatory