Around 6 million years ago, the Mediterranean Sea experienced a drastic environmental change. Due to tectonic movements that closed the Gibraltar Strait, isolating it from the Atlantic Ocean, the Mediterranean underwent an unprecedented drying out. Under the effects of a hot and dry climate, the sea level gradually dropped, reaching a critical point.
A Nearly Completely Dry Mediterranean Sea
Approximately 5.5 million years ago, the Mediterranean basin resembled a vast depression, its floor occupied by hypersaline water.
The landscape was similar to that of the current Dead Sea. In total, about 1 million cubic kilometers of salt are thought to have been deposited in the basin!
One can imagine the dramatic repercussions of this drying out on marine biodiversity.
However, the impact on ecosystems remains poorly constrained. A new study published in the journal Science has managed to quantify it. And to say the least, the Mediterranean’s marine ecosystems nearly faced extinction.
Out of the 2,006 endemic species recorded before the Messinian Crisis, only 86 survived this event. Fossil records show a 66.8% difference in species present before and after the crisis, which ended with the abrupt opening of the Gibraltar Strait 5.33 million years ago, allowing Atlantic waters to flood into the dried-up basin.
The current Mediterranean ecosystems were primarily built upon the arrival of species from the Atlantic.
During the time of Bartolomeu Dias, in the latter part of the 15th century, Europeans believed the earth to be flat, with the universe revolving around it. Navigating the high seas was considered foolish, and they had not yet conceived of any maritime route to the Indies. Thus, the adventurers of Portugal, a small nation of one million inhabitants, undertook a significant intellectual, technical, and human achievement by rounding the Cape of Good Hope, the southern tip of Africa. Step by step, over four generations, the Portuguese followed the African coast to reach the Indian Ocean, far from imagining the long voyage that would take them to the Indies.
The Portuguese Dream of New Conquests
Infante Henry the Navigator, son of King John I of Portugal, initiated the Lusitanian expansion. The prince aimed to explore new territories for religious and economic reasons, such as the spice trade, while disengaging from the Ottoman Turks’ control over European commerce. Despite the passing of Henry the Navigator before Bartolomeu Dias’ first mission, the Infante’s exploration of the globe directly benefited the latter. In 1415, Henry the Navigator led his first campaign. He crossed the Strait of Gibraltar and conquered Ceuta, a Spanish enclave in Morocco. Another feat was the crossing of Cape Bojador in 1434. Located 300 km south of the Canaries, this place was the limit of the known world. The Portuguese regarded it as the site of terrifying legends, in which monsters lurking in the deep sea emerged.
To improve navigation, Infante Henry established an academy that brought together astrologers, cartographers, and navigators from across Europe. Together, they invented celestial navigation, oceanic maps, and a lighter ship: the caravel. The coastal ships of the Algarve served as inspiration for the design of this vessel. Dias’s caravel had multiple masts and up to five sails, maneuvered by a crew of 25 men. Importantly, it could sail against the wind, an undeniable advantage for covering long distances.
All these significant efforts paved the way for the conquest of the oceans. To finance these innovations, the Infante, appointed governor of the Order of Christ, received spiritual rights over the African coastline from Pope Calixtus III. Thus, the Order sponsored the voyages of the caravels, whose sails bore their red cross. In 1454, the prince also obtained the pope’s approval to trade Africans as slaves. One last obstacle remained: the Equator, which inspired frightening myths. The navigators feared that their ships would burn up, they would scald, or their skin would turn black. They crossed it in 1474, and exploration continued.
Bartolomeu Dias de Novaes: A Short Biography
A replica of Bartolomeu Dias ship displayed in the Bartolomeu Dias Museum Complex. Image: CC BY-SA 4.0
Bartolomeu Dias was the first explorer to link the Atlantic Ocean and the Indian Ocean via waterways, accomplishing this four years before Christopher Columbus discovered the New World, a revelation that overshadowed the success of Portuguese navigators. Born in Algarve in 1450, Bartolomeu Dias learned navigation from the German geographer and cosmographer Martin Behaim. At the age of 16, he embarked on his first expedition, but it wasn’t until 37 that his efforts yielded a remarkable success: the discovery of the Cape of Good Hope, the southern tip of the African continent. He drowned in a shipwreck in May 1500, during a subsequent expedition.
The Expedition to the Cape of Good Hope in 1488
The discovery of the Cape of Good Hope was crucial for the upcoming voyages of Portuguese and Spanish explorers. It provided evidence of a maritime route to the Indies and that the African continent indeed had an end. For the first time, cartographers conceived of the oceans as interconnected spaces. The world’s horizon expanded. Under the leadership of Bartolomeu Dias, two caravels and a ship dedicated to carrying supplies carried out this exploration along the African coast. The crew faced a shift in dominant winds between the northern and southern hemispheres. The slow-moving ship hindered their progress. They left it behind with nine guards.
A storm caught the caravels near the southern tip of the African continent, bringing them to the coast near the Bay of St. Blaise (now called Mossel Bay), 370 km east of the southern tip of South Africa. They anchored there on February 3, 1488, realizing they had reached the Indian Ocean and had rounded, without seeing it, the Cape of Good Hope. Bartolomeu Dias wanted to continue the exploration, but his exhausted crew rebelled. Turning back, he identified the point and named it the Cape of Storms. The king would later rename the Cape of Good Hope, seeing it as proof that this maritime route would lead Portuguese explorers to the Indies. Nine months after leaving it, he reunited with the ship with three survivors aboard. One of them, sick, died “of joy” upon seeing them return.
In late 1488, after 16 months of travel, the Portuguese made a triumphant return to Lisbon. Among the crowd welcoming them was a then-unknown Genoese, Christopher Columbus, who came to offer his services to the King of Portugal. In light of Bartolomeu Dias’s success, the king wished to exploit this route that bypassed Muslim lands. He rejected Christopher Columbus’s expedition, which sought to find a passage to the Indies from the West.
All Bartolomeu Dias Expeditions
DestinatIon
Departure
Participants
Sovereign
Southern Congo
in 1466
Pedrarias Davila, accompanied by Bartolomeu Dias, only 16 years old
Alphonse V
Ghana
in 1481
Bartolomeu Dias
John II
Cape of Good Hope
in August 1487
Bartolomeu Dias is 37 years old
John II
Calicut, India
July 8, 1497
Vasco de Gama, accompanied by Bartolomeu Dias
Manuel I
Brazil, then Calicut, India
March 9, 1500
Pedro Alvarez Cabral, accompanied by Bartolomeu Dias
The summit of Mont Blanc is 15,777 feet (4,809 meters) above mean sea level. The height of the sea changes by a few feet due to the tides, and this is something that can be seen by everyone who travels along the Atlantic shore. Despite this, the height of Mont Blanc remains constant throughout time. What could possibly account for such a contradiction? The height of Mont Blanc, for instance, along with all of the other altitudes in metropolitan France, is measured in relation to a reference point located on the Mediterranean, at the Marseille tide gauge, which defines the conventional zero altitude.
This instrument was created in the 19th century and consists of a float that is positioned in a well that looks out over the ocean. The float is placed on the surface of the water where it is shielded from the surge and waves and is attached to a device that keeps track of each of its vertical movements caused by changes in the level of the sea. The measurement of the average sea level that was taken in Marseille between the years 1885 and 1897 provides the basis for the zero height.
A lengthy time span provides the opportunity to break away from the influence of tidal and swell phenomena, the impacts of which, over the long term, cancel one another out and have essentially little effect on the mean sea level. A marking that has been hermetically sealed into the floor of the structure that houses the tidal gauge serves as the physical representation of the zero height. For all intents and purposes, it is situated precisely 5,450 feet (1.661 meters) above the zero point in historical measurement that was established in 1885. However, this standard is not applicable in every situation.
Recent studies of sea level made by the Hydrographic and Oceanographic Service of the French Navy reveal that the zero height designated by the Ajaccio tidal gauge is about 10 cm higher than that of Marseille. These observations were made just on the island of Corsica. In addition, every nation has its own datum, which may be a source of serious issues in situations when many nations are working together on international development initiatives, for instance.
The North American Vertical Datum of 1988 (NAVD 88) is a vertical reference system for North America that uses leveling points spread out throughout the continent from Alaska to Canada and the rest of the United States to provide a common vertical reference. It is referenced to a point in Quebec, Canada.
On a global scale, and particularly at sea, allusions to individual nations are meaningless because of the interconnectedness of the world’s oceans.
The position that the sea would hold if it were standing still is the location that is used to define the zero point. This zero is the basis for a fictitious horizontal surface that is referred to as the “geoid.” Each point on this surface is perpendicular to the vertical direction, which corresponds to the direction of the gravitational field.
The gravitational field is the force that keeps us rooted to the surface of the earth and gives objects their weight. The gravitational field is not uniform over the surface of the Earth, which results in its surface having an uneven, potato-like shape. Using gravimeters located either on the ground or on satellites, scientists may calculate the contours of the geoid by determining how the Earth’s gravity field varies over a large number of locations.
However, the behavior of the seas is not nearly the same as that of a glass of water sitting on a table. As a result, they have a substantial angle of departure from the geoid. Because of shifts in water density, winds, and dominant currents like the Gulf Stream, as well as shifts in air pressure, the average level of the sea can shift by several feet relative to this point of reference. Therefore, the water level in the Mediterranean Sea is 6 inches (15 centimeters) lower than the water level in the Atlantic Ocean.
The geoid is modeled on a worldwide scale nowadays, and the precision of the model may vary from as little as 4 inches to as much as a few feet, depending on the location. But our GPS can’t handle the complexity of this modeling. Because of this, they employ a streamlined version that provides approximations of elevations determined in reference to a global zero. Carry out the examination in the mountainous region. On a peak, the height that is indicated by the GPS and the official altitude are not always the same.
Large, coiled shells of sea snails are a common memento brought back from beach vacations because they bring to mind the sun, the sea, and the sand. These shells can be found in both freshwater and saltwater environments. However, the shells of these marine animals do more than just bring the aesthetic beauty of the ocean into our homes through their acoustic properties. Even when you are located thousands of miles away from the closest body of water, if you hold the shell’s enlarged aperture up to your ears, you may be able to hear a soft murmur that is reminiscent of the ocean. But what exactly is it that’s causing all of this oddity?
According to seasoned beachcombers, the best noise-makers are not mussel shells but rather the enormous shells of sea snails. This is because sea snail shells are hollow inside. This is due to the fact that its cavity, in contrast to those of other shells, is sufficiently large enough to produce this noise effect. On the other hand, if we put our ear to the bottom of a cup or glass that is empty, we might hear the same thing again. But how could something like a cup or a seashell sound like this?
Is it the beat of your heart, or the sound of the wind coming in?
A good number of people believe that the noise they were hearing was actually their own blood pulsing through their veins. It was said that the shell made the faint pulsing that normally occurs in the veins of our skull significantly more audible. This is not the case at all, as demonstrated by the fact that a microphone, when placed in close proximity to the opening of a seashell that is resting on a table, will pick up the same sound as when the microphone is placed elsewhere in the room. Despite the fact that none of our blood vessels are located near the ear, which is the typical spot for a seashell.
If it wasn’t the blood, then what could it be? Is it possible that the noise is caused by air moving around inside the shell, similar to the way that the wind makes a sound in the trees? An experiment can be used to disprove this hypothesis as well. Just placing the seashell or jar on your ear in a soundproof room results in the listener hearing… nothing. However, if the noise was caused by air movement, you would still be able to hear it since air flows even in a soundproof environment.
Shell serves as a resonance chamber
But where does the noise come from? The answer that you are looking for is “our surroundings”. This is because we are constantly subjected to a variety of different kinds of background noise in our daily lives. The seashell can be used as a resonating chamber by placing it near your ear and then holding it there. When sound waves from the outside are reflected again and again by the shell’s walls, the air inside the shell begins to vibrate and resonate.
This is causing some frequencies of the background noise to become louder while simultaneously causing others to become quieter. The overall effect of the higher frequencies makes a noise that is reminiscent of waves crashing against the shore.
However, the volume of the noise made by shells of varying sizes and shapes is quite distinct from one another. This is because the acoustic frequencies at which the air resonates have a relationship that can be positive or negative depending on the size of the cavity inside the seashell. When compared with their smaller counterparts, larger seashells have the effect of magnifying a more specific frequency range. This provides an explanation for why their noise sounds muffled.
Motion sickness affects both humans and some animals, including fish.
Motion sickness is caused by a conflict between sensory information.
Fish can experience symptoms similar to human motion sickness, including vomiting and loss of orientation.
When a ship pulls out of port and the ship begins to rock in open water, many passengers start to feel sick. They frequently suffer from headaches, vertigo, and cold sweating in their palms. It frequently extends beyond these few symptoms. Motion sickness quickly develops into nausea, frequent vomiting, and the desire to pass out, which makes the journey impossible to complete. Those who have been affected only want to get to land. But is motion sickness something that only humans are susceptible to, or can animals also get it? For example, are fish susceptible to getting seasick?
Known Examples of Seasickness in Fish
Yes, but it’s possible that they wouldn’t be seasick in their natural habitat. Because if there is turbulence on the surface of the water where a fish is swimming, the fish will simply dive to avoid it.
However, when fish are snared in a fishing net in a short amount of time, this unique situation arises. Seasickness may sometimes occur even when ornamental fish are transported from one location to another in an enclosed vehicle.
The same can be said for some animals, which are sent into space as “animal space tourists” for scientific research purposes and are able to survive there despite the absence of gravity.
A conflict between visual information and the organs of balance causes motion sickness, which affects all higher animals to varying degrees. Although they can’t throw up, certain animals like rats and horses still experience the discomfort of seasickness.
How to Tell If a Fish is Seasick
A school of fish swimming in a loop. (Credit: Michael Haluwana)
But how can you tell which fish are seasick? For example, are they able to throw up as well? The animals eventually develop symptoms that are identical to those seen in people at this point.
They would begin to spin and make a variety of gestures in an attempt to reassert their authority over their surroundings. Animals who occasionally experience feelings of nausea may even turn somersaults while swimming in the water, similar to a swimming loop.
There is evidence that fish can also throw up. For instance, fish breeders will withhold food from their animals before transporting them so that they will not engage in this behavior.
There was another attempt to learn whether fish experience motion sickness. After placing almost 50 fish in a tank and boarding an aircraft, the researchers watched the fish undergo a steep dive to simulate zero gravity. A few of the fish then swam in circles, seemingly bewildered.
During the test, eight free-falling fish demonstrated seasickness. The fish looked to be vomiting and swimming in circles after their release by the scientists. This demonstrates, much like with humans, that certain fish are prone to motion sickness while others are not. This “seasick” fish would be easy prey in the wild.
According to Stuttgart zoologist Dr. Reinhold Hilbig:
“The fish lost their orientation… They completely lost their sense of balance, behaving like humans who get seasick.”
Dr. Reinhold Hilbig
This also applies to the fish in a tank on the ship during wavy seas that show signs of distress. Their distress appears to be related to the vibrations in the tank and their loss of eye contact with the motion of the water.
Why Does Seasickness Happen?
But what exactly causes humans and other animals to experience motion sickness in the first place? This frequently occurs when the input the sense organs receive does not coincide with the body’s movement and spatial location. Scientists refer to this phenomenon as a conflict between the senses.
After a brief period of time, the brain loses its bearings and is unable to determine which piece of information to trust. This is something that can happen on a rocking ship as well as in the back seat of a moving car or on the drooping wings of an airplane.
(Credit: Emory University)
Imagine that you’re on a train that’s stopped in the middle of nowhere. A train is about to leave the station on the nearby track. When this occurs, the organ of balance in the ear reports that you are not moving, whereas the eyes report that you are moving.
The brain at first has trouble making sense of this apparent contradiction. However, it eventually comes to the conclusion that the train has come to a stop and that everything has returned to its usual state after analyzing the signals from other sensory organs.
However, motion sickness is possible if the predicament lasts for an extended period of time, such as when one is on a ship experiencing a significant surge.
Due to the nature of the brain, it is likely that an individual will incorrectly diagnose themselves as having food poisoning. Then they would throw up in order to get rid of the allegedly revolting food. That can be considered a hypothesis, at the very least.
Even fish have organs to help them keep their balance. They are positioned, one on each side of the head, specifically on the left and right sides. A fish may momentarily lose its sense of orientation and feel dizzy or ill if a vortex or strong wave movement rocks it back and forth.
The investigation into the phenomenon in both people and fish is by no means complete. It is unknown, for instance, why some organisms experience seasickness even when making only very slight movements, while others do not experience this phenomenon.
The Reason for Motion Sickness in Animals
The causes of seasickness in animals are still a mystery. Many hypotheses attempt to explain why our species developed such a robust reaction. There’s some speculation that this helps shield nerve cells from neurotoxins.
Because back in the day, the only time our senses were at odds with one another, as they are during motion sickness, was when we were poisoned. Therefore, to expel the toxins, one could only vomit.
Ernest Shackleton, the intrepid explorer of the Antarctic, carried ponies with him on his journey by sea and wrote in his journals of the terrible hardships they endured in the midst of the storms. It’s rather common to see seasickness in our dog and cat friends.
