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True to its missions, the Oceanographic Institute has been providing its audiences with summaries since 2011 to promote knowledge and protection of the Ocean.
These sheets are written by members of the Institute’s Scientific Council as well as by some of the world’s leading ocean experts. They are offered to help you better understand what is at stake today in terms of the functioning of the Ocean, marine biodiversity and the relationship between Man and the Ocean.
They are classified by number of order of publication and with a color code based on the theme of the file and the related sub-themes linked to it.
Man and the Ocean
- Marine resources
- Environmental risk
- Ocean pollution
- Law of the sea, maritime law, conventions around the sea and international organizations
- Participatory science, mediation
- Scientific innovations and new technologies
- Art and science
How the ocean works
- Geosciences
- Seawater chemistry
- Biogeochemistry
- Climate, Ocean/Atmosphere interactions, ocean dynamics
Marine biodiversity
- Biodiversity studies
- Biological diversity, the appearance of Life
- Current threats to marine biodiversity
- Protection of biodiversity
The climate of northern Africa underwent a rapid change about 10,000 years ago. The Sahara was then a region covered with vegetation, whereas today we only see dry, bare soil. This oscillation, between a humid climate and aridification, is revisited using powerful geochemical tools. This work, covering the last 20,000 years, makes it possible to establish a link between paleo-environmental variations and the phases of human evolution and/or occupation along the Nile watershed.
Rogue waves are isolated waves that are abnormally high compared to the surrounding wave field. They are dangerous because they are unexpected, in a given wave field to which the sailors have spontaneously adapted, and they escape their vigilance. In some cases, they can reach 30 m in height. Seafarers are paying more and more attention to them as they are more frequently reported by sailors nowadays. Recently, they have become the subject of more scientific approaches.
A tsunami is a wave generated by a sudden movement of the sea floor. Characterized by a long wavelength, a tsunami loses very little of its mechanical energy as it travels and can cross an entire ocean: distant tsunamis can be just as devastating as local tsunamis. Their sometimes very high speed of propagation increases the constraints of remote tsunami warning systems and makes it necessary to educate the population, when dealing with local tsunamis. Coastal morphology can enhance or mitigate tsunami amplification processes.
In the Arctic, the warming of the surface and the retreat of the sea ice are exceptional compared to the previous 1,400 years. Dramatic changes are occurring in the cryosphere. On a large scale, human influence currently dominates Arctic warming. On the other hand, one-third of Greenland’s warming is due to human influence, and two-thirds is due to atmospheric circulation patterns. The melting of the Arctic ice will continue, even in the most optimistic scenarios for controlling greenhouse gas emissions.
Cold fluid outflows from the seafloor, particularly within continental margins, are still poorly understood and are likely to be more abundant than those from hydrothermalism. These fluids can be emitted, depending on their depth of origin, at temperatures of several tens of degrees. The importance of these fluids is relatively recent. Locally, these fluids released on the seabed can have a significant impact on the deep environment and the establishment of specific ecosystems.
Plate kinematics is the study of the past and present movements of the tectonic plates that make up the most superficial envelope of the solid earth called the lithosphere. It is simply the quantitative extension of the theory of plate tectonics, which Wegener first predicted as « continental drift » at the beginning of the last century, but whose concepts were definitively established in the mid-1960s.
Ocean ridges are the site of intense tectonic, volcanic and hydrothermal activity. The sea water infiltrates and percolates through the permeable zones thus created. It heats up by several hundred degrees per kilometre, reacts strongly with the rocks it passes through and becomes loaded with many chemical elements, as well as dissolved metals. Warmer, it rises and spurts out onto the sea floor. Its sudden cooling, by mixing with water at 2°C, leads to the crystallization of the dissolved elements which then form metallic sulphides.
The physical oceanography of the Mediterranean Sea depends primarily on the exchange of water between the sea and the atmosphere, but also on the Coriolis effect, due to the rotation of the Earth.
The Mediterranean climate is relatively dry. The losses of the sea by evaporation are not compensated by the contributions of precipitations and rivers, and, if it did not communicate with the Atlantic Ocean, its level would drop by about one meter per year!
The « Mediterranean machine » transforms oceanic waters with relatively variable characteristics into a series of colder and saltier waters with relatively specific characteristics.
The IPCC was created in 1988 with the mission of taking stock of knowledge on climate change. Under the supervision of WMO and UNEP, the experts, divided into three groups, regularly produce a general report. Group I’s contribution to the 5th report was approved at the end of September 2013. For the first time, an entire chapter is devoted to sea level rise. The ocean slows global warming, but absorbs about a quarter of the CO2 released. It will continue to warm in the 21st century, adding to the damage from acidification.
Silicon is abundant on the planet Earth, mainly in the form of silica, which is a component of many minerals. Si is one of the key elements involved in the biosphere. The leaching of siliceous minerals by rainwater produces soluble silicic acid (Dsi). Many living organisms are capable of absorbing Dsi: diatoms, silicoflagellates, radiolarians, several species of choanoflagellates and some sponges. As the first link in the food web, diatoms contribute nearly 50% of the primary production of the world’s oceans, and through photosynthesis produce about a quarter of the oxygen we breathe.
Sea level rise is a global issue because half of the world’s population lives within 200 km of a coastline, and 1 in 10 people live less than 10 metres above sea level. Various compilations confirm an acceleration of the rise in sea level with an average rate of less than 1.5 mm/year before the 1950s, up to more than 3 mm/year today. Altimetry data confirmed the rise in sea level. Current trends are expected to continue due to global warming.
In the absence of oxygen in the atmosphere and ocean, iron is soluble. With the development of photosynthesis, iron is only transiently present in the oceanic water column. Microparticles carried by the wind enter the food chain very quickly. The atmosphere of the ice ages was much richer in dust than that of the warm periods, and scientists have speculated that a more abundant supply of iron to the ocean may account in part for the lower carbon dioxide content of the atmosphere.
Hydrothermal » springs are outlets of fluids on the seabed, whose temperature is higher than that of the surrounding water. These emissions reflect the circulation of seawater through fractured rocks under the influence of a heat source. Although the geochemical composition of hydrothermal fluids is highly variable, with a few exceptions they share common characteristics: acidity, « reducing » properties, characterized by the absence of oxygen, and above all high concentrations of sulphide and metals.
Of the solar energy that enters the Earth system, 56% is absorbed by the ocean, which in turn gives some of it back to the atmosphere. This coupling between the ocean and the atmosphere means that the oceanic surface circulation is an imitation of the atmospheric circulation. The thermohaline circulation corresponds to currents produced not by wind but by differences in density between oceanic water masses. A complete turn of the oceanic general circulation takes about a thousand years. This is the so-called « conveyor belt », which plays an important role in climate dynamics.
The ocean is the main regulator of the global climate. Its interaction with the atmosphere and its consequences are central to the climate system. First of all, it is the great thermal inertia of the ocean, compared to the atmosphere, which allows it to store solar radiation in summer and to release this thermal energy to the atmosphere in winter…
The ocean is the main regulator of the global climate. Its interaction with the atmosphere and its consequences are central to the climate system. The great thermal inertia of the ocean, compared to the atmosphere, allows it to store solar radiation in summer and to release this thermal energy to the atmosphere in winter. The ocean has been warming in recent decades. 90% of the excess heat accumulated in the climate system over the past 50 years due to anthropogenic warming is stored in the ocean.
During the last glacial maximum, the sea level was about 130 metres lower. With the melting of the ice caps that covered northern America and Europe, the sea rose and then stabilized about 3,000 years ago. Tide gauge observations indicate that the sea has begun to rise again. All evidence suggests that the current sea level rise is related to global warming. Thermal expansion of the oceans explains part of the observed rise in sea level…
This small marine area, which has seen the birth of many religions and most of the great civilizations around it, is a very fragile domain, inherited from a very long geological history, and inexorably condemned to disappear like its great ancestors, to which the many mountain ranges surrounding it still bear witness
The sea is in constant exchange with the atmosphere. The wind deforms the surface of the sea and transmits energy to it. Air, and even more so water, absorbs solar radiation. The sea is a reservoir of heat, some of which is returned to the atmosphere. The spray washes away the components of the surface layer. Gases can pass through the surface of the sea. The oxygen produced by phytoplankton diffuses into the atmosphere when it is supersaturated. Carbon dioxide, produced by respiration, is consumed by phytoplankton. It enters as an element in the buffer system that determines the pH of the sea…
A dead zone is characterized by a deficit of dissolved oxygen in the water, causing the death by asphyxiation of marine fauna with low mobility and the migration of fish. Tolerance to low-oxygen waters varies greatly depending on the type of organism. Dead zones have grown exponentially since the 1960s, with serious consequences for ecosystems. The main cause is the massive application of fertilizers. Some dead zones are permanent; others are episodic. The ecological and economic consequences are significant.
The air-sea interface covers more than 70% of the Earth’s surface and plays an important role in global biogeochemical processes. At this interface, a micro-layer is formed by the accumulation of surfactants, proteins, amino acids, carbohydrates, lipids, phenols and various inorganic and organic pollutants in the contaminated zone. It constitutes a particular ecosystem, where various forms of life called neuston develop. A polluted micro-layer constitutes an unfavourable environment for the development of eggs and larvae.
