Category: Geography Notes PPT

“The Pelagic zone is the region of the ocean outside the coastal areas and is also known as the open ocean”

Pelagic Waters

The Pelagic waters refer to open and free waters in the oceanic body. It stretches between the ocean surface and ocean bottom. Any marine life residing in the pelagic zone can swim freely without any boundary constraints. 

Pelagic zone, an ecological realm that covers the entire ocean water column. Of the earth’s inhabitants, the pelagic zone has the largest volume. It consists of the water column of the open ocean. It can be further divided into regions by depth. The Pelagic zone or water column can go from the surface of the sea to the entire bottom. As the water column changes with respect to the distance from the surface, its pressure increases, and in turn the temperature and light decrease. It results in a change of salinity, amount of dissolved oxygen, and micronutrients such as iron, magnesium, and calcium.

In addition to changes in the oceanic Pelagic zone, marine life is affected by underwater topography and by the surface of the seafloor or shoreline. Not only the discussed factors are responsible for marine life variations, instead, but the boundary between the ocean and atmosphere is also equally important. It brings the light for photosynthesis but can also bring predation from up and water currents.

Depth and Layers of Pelagic Zone

Depending upon the depth of the sea, the pelagic zone can extend up to five vertical regions in the ocean. These are as follows:

1. Epipelagic – This is the lighter zone where enough light is present for photosynthesis. All primary production in the water occurs here. Plants and animals are concentrated in this layer. Examples of pelagic zone organisms residing here are plankton, seaweed, jellyfish, tuna, and dolphins.

2. Mesopelagic – The pelagic zone organisms residing in the mesopelagic zone are heterotrophic bacteria. Examples of organisms that live here are swordfish, squid, wolffish, and species of cuttlefish.

3. Bathypelagic – At this level of Pelagic water, the ocean is pitch black. No living plant exists here apart from occasional bioluminescent organisms such as anglerfish. Organisms living here survive by consuming detritus falling from the above zone. This phenomenon is also known as marine snow. The inhabitants living in this zone are giant squid, dumbo octopus.

4. Abyssopelagic – This zone starts from around 4000 meters. Very few creatures can reside in cold temperatures, high pressure, and complete darkness. Species found in this zone are several species of squid, swimming cucumber, sea pig, and sea spider. Most of the species living here are transparent and eyeless. The reason being this evolution is the total lack of light.

5. Hadopelagic – This is the deepest part of the ocean lying within oceanic trenches. The zone is found from a depth of 6000 to 11000 meters. Most of the hadal habitat is found in the Pacific ocean. 

Pelagic Environment

The Pelagic environment is based on phytoplankton. They manufacture their own food using photosynthesis. They need sunlight, they inhabit the upper zone. The biodiversity reportedly decreases in the deeper zones. The pelagic zone organisms range from tiny planktons to large mammals. Phytoplanktons provide oxygen for humans and food for many organisms. 

Zooplanktons are found in this zone. It includes heterotrophic planktons consisting of most of the micro and microorganisms.

Invertebrates like squids, jellyfish, octopus, and krill are found in the pelagic zone. Large ocean vertebrates such as crustaceans, sharks, bluefin tuna, sea turtles migrate through the pelagic zone. Pelagic birds live on open seas rather than inland. They feed on planktonic crustaceans, squids, and forage fish. The Pelagic environment consists of the following:

1. Pelagic Invertebrates – Low latitudes invertebrates tend to produce a large number of eggs whereas high latitude invertebrates produce fewer and larger eggs and larger offsprings. 

2. Pelagic Fish – These live in the coastal ocean and lake waters but not on or near the bottom of the sea. These fishes are migratory forage fish. They feed on planktons.

3. Pelagic Reptiles – The pelagic sea snake is the only reptile of one of the 65 species of marine snake to spend its entire life in the pelagic zone. It is helpless on land. Many species of sea turtles spend the first year of life in the pelagic zone and on reaching maturity they move closer to the shore.

A polar vortex, also known as a circumpolar vortex is a large area of cold, rotating air that surrounds both of the Earth’s polar regions. It always exists in poles, but strengthens in winters and weakens in summers. 

The term ‘vortex’ in the circumpolar vortex refers to the counterclockwise flow of air that helps to keep the colder air near the poles. Most of the time during winters in the northern hemisphere, the polar vortex will expand, sending cold air southwards through the jet stream. This generally occurs during winters and is often associated with the large outbreaks of Arctic air in the United States. 

Polar Vortex Meaning

Polar vortex, or circumpolar vortex, the polar low, polar cyclone is a large area of persistent low pressure generally located above each of the Earth’s polar regions and containing a mass of extremely cold air. The altitude of this cyclone extends from the middle of the troposphere ( the lowest level of Earth’s atmosphere which spans the region from the surface up to 10 – 18 km [ 6 -11 miles high] km into the stratosphere (the atmospheric layer that extends from 10 -18 km to about 50 km [ 30 miles] high.

The cold air is contained within the polar vortex by the polar front Jet stream. The strength of the polar vortex changes with the season. It is strongest during the winter season in each hemisphere when the Equator is at greatest and temperature contrast between the poles. It may be weaker or entirely diminished during the warmer months of the year.

Polar Cyclone

Polar cyclones, also known as arctic cyclones or polar vortices are very large areas of low pressures. The term polar low should not be confused with the term polar cyclones. Polar cyclones are generally 1000 to 2000 kilometers wide in which the air is moving in the spiral counterclockwise in the northern hemisphere. The reason for this rotation is similar to tropical cyclones, the Coriolis effect. They also exist in the regions such as the Eurasian Arctic area, Greenland, and northern Canada with about 15 cyclones per winter.

Polar cyclones can occur at any time of the year, although summer polar cyclones are weaker than the ones that occur in the winters. 

Strength and Duration of Polar Vortex

The strength and duration of the polar vortex are as follows:

Strength

• Polar vortices or polar cyclones are weakest during summers and strongest during the winters. 

• During the volcanic eruptions in the tropics, a polar vortex will be strengthened and can stay that way for 2 years after the initial eruptions.

• Extratropical cyclones that emigrate into the higher latitudes when the polar vortex is weaker can disturb the single vortex creating small vortices within the polar air mass. Those individual vortices can continue for more than a month.

• The Antarctic polar vortex is more pronounced and persistent than the Arctic polar vortex.

• The climate anomalies La Nina significantly strengthen the polar vortices. 

• Strengthening the polar system within the troposphere that cools down the poles, intensifying the polar vortex.

Duration

• The Northern polar vortex comes about between Mid March Mid May. This event marks the transition from the winter season to the spring season. Hydrological cycles, growing seasons of vegetation, and overall ecosystem productivity are highly impacted by these events.

• The same transition also impacts sea ice, zone, air temperature, and cloudiness immensely.

• Early and late polar break events have occurred due to the variation in stratospheric flow structure and the upward spreading of planetary waves from the troposphere.

• When the polar break up is early, there is one warning period from late February to middle March whereas when the polar break up is late, there are two warning periods, one in January and the other in March.

• Sometimes, a mass polar vortex breaks off before the end of the final warning period. If large enough it can move into Canada and the Midwestern, Central, Southern, and Northeastern United States.

Polar Vortex UPSC Facts and Information

Following are some of the polar vortex UPSC facts and information:

• A polar vortex on Earth is usually in the middle and upper troposphere and stratosphere.

• The Arctic vortex has two main centers: one is over Baffin Island, the other is over Northeastern Siberia.

• Polar vortex and weather impacts due to stratospheric warnings.

Sea caves also known as littoral caves, is a type of cave which is mainly formed by the action of sea. The primary process involved is erosion. Sea caves are found throughout the world. Matainaka cave, on the Otoga coast of New Zealand’ South Island, has been verified as the world’s largest sea cave in length 1.54km or 5.051feet, by a survey in October 2012.

Who Lives in Sea Caves?

Sea caves are brimmed with life, both on their floors and walls. Such as anemones, starfish and sponges, living under these sea caves with dark zones may harbour organisms not commonly seen in shallow water.

Beach Caves in India

Sea caves are also identified by the ocean cave as well as beach caves.

• Borra caves, Andra Pradesh

• Bhimbetka rock shelters, Madhya Pradesh

• Amarnath cave, Jammu and Kashmir

• Undavalli caves, Andra Pradesh

• Vaishno devi, Jammu and Kashmir

• Udayagiri khandagiri caves, Orissa

• Elephanta cave, Maharashtra

• Badami caves, Karnataka

Avila Sea Caves

Cave Landing Beach is not easily accessible since it’s a hidden gem and thus makes it difficult for one to reach below cave landing in Avila beach CA. Most of the visitors to the Cave Landing parking will make an effort towards the downside of the main trail that leads to Pirates Cove Beach and the best known cave which is actually a tunnel. This tunnel has many nicknames including Smugglers Cave, leads to a viewpoint that looks west toward Port San Luis and the three piers of Avila Beach. This outlook also looks down on a small beach that appears nearly impossible to reach. Well it seems challenging but there is actually a way down.

Back at the parking lot there exists a trail just to the south of the main trail, in close proximity to the ocean, that heads in the same direction as the main trail but then drops down towards the ocean shore. It leads to a point at which a fixed rope is generally in place to provide the necessary support in descending a steep and the cliff. Remember that this descent is not possible without a rope particularly for those of us that are not technical climbers. If the rope is weakened or if one does feel convenient with rappelling, then they should not attempt the downward climb. While performing, wear shoes with good traction help.

How Long is Avila Beach?

Avila Beach consists of 3 piers i.e: Avila Beach Pier, 1,685 feet (514m) in length, and the California Polytechnic State University (Cal Poly SLO) Pier, part of the university’s marine research program, is not publicly accessible.

Not long ago, the pier was enhanced to be the site for whale watching as numbers of grays and humpback whales come into bays around the pier to feed and draw crowds during the seasons.

The Avila Beach Pier got a call to attention in a Super Bowl advertisement on February 7, 2010. Avila Beach was the primary shooting location for California films.

The beach measures less than 0.5 miles (0.8 km) long and is firmly based in San Luis Bay, which is formed by Point San Luis on the west and Fossil Point on the east. Avila Beach faces south and an elevation of 600 foot point at San Luis breaks the prevailing northwesterly winds. It is relatively warmer than the other beaches located on the central coast.

Meyers Beach Sea Caves

These are located in the North of Cornucopia, Wi. There are caves at the Northern end of Mawikwe bay and one caveat at the South end of Mawikwe bay. Meyers Beach Sea Cave trail is 4.6 mile. The trail offers a number of activity options and is rugged with stream crossings and steep slopes which is accessible year round. But in winter it may be snow packed or icy, where skiing is not recommended and use of snowshoes is difficult.

The mainland sea cave of the Apostle Island National Lakeshore, which are the similar caves that turned out to be the world’s most popular ice cave in winter, are easy to reach via boat and hiking trail from Meyers Beach. 

The Meyer’s Beach sea cave trail is extended through 2.3 miles of the Lakeshore Trail, which typically starts at the Meyer’s Beach parking lot near Cornucopia, Wisconsin. “The Bowl” is one of the best views of the hike.

Sea Cave Adventures

Exploring the Mysteries of Earth’s Underwater Caves

• Swimming

• Cave diving

• Scuba diving

• Snorkeling

• Waterrofting

To start with this content featuring the discussion of Sedimentary Rocks we must know there are basically three kinds of rock, namely – igneous, sedimentary, and metamorphic. The Igneous rocks evolve from the molten rock known as magma or lava, this lava cools and thus solidifies. While, the sedimentary rocks generally originate when the particles get settled down in the water or the air, or by the means of precipitation of the minerals from water. They get accumulated in layers.

So, we see, if the rocks could talk it would definitely be in these three languages – Igneous, Sedimentary and Metamorphic. This indicates the importance of its classification, sedimentary being among it, we will take up its discussion in this section.   

Siliceous Rocks 

Siliceous rock is one of the groups of sedimentary rocks which consists mainly of silicon dioxide (SiO2), which is either in the form of quartz or amorphous silica and cristobalite. They are included by these rocks which have formed as precipitates of chemical composition and are excluded from those of detrital or fragmental origin.

Among the other siliceous rock, the most common siliceous rock is chert which is a dense, microcrystalline rock that has chalcedony and quartz as its composition. This occurs in beds and in nodules. The Bedded chert consists of siliceous fossils like diatoms and radiolaria. They form the siliceous oozes which are on the seafloor. When these organisms sinks, the portions of their shells get dissolved near the bottom and they reprecipitate in the void spaces between these shell fragments which results in a hard bedded rock. The Bedded cherts are very common in areas that are enriched in silica-bearing organisms, like near volcanoes, they are the volcanic glass that is rapidly altered to produce these high-silica concentrations. Similar processes occur in freshwater lakes that are associated with volcanoes.

Silica Rock 

These rocks are also known as silica sand or even called ‘quartz sand’. The chemical composition of silica is silicon dioxide (SiO2). The Silicon compounds are the significant component lying on the Earth’s crust. The sand is plentiful, they are easy to mine and are relatively easy to process. Sand is the primary ore source of silicon. Other sources are – metamorphic rock, quartzite.

Silicon (Si) is a semi-metallic or a metalloid structure, this property occurs because it has several of its metallic characteristics. The Silicon is never found in its natural state, while found in combination with the oxygen as the silicate ion which is SiO44- in silica-rich rocks like obsidian, granite, diorite, and even in sandstone. Feldspar and quartz account for the most significant silicate minerals. The Silicon alloys include a variety of other metals, which includes iron, aluminium, copper, manganese, nickel and ferrochromium.

Pyroxene Rock 

Pyroxenes are the dark coloured rock-forming type of minerals that are found mainly in igneous and metamorphic rocks worldwide. Pyroxene rocks are formed under acute high temperature or pressure conditions.

Rocks such as Augite, Jadeite, Diopside and Spodumene are the most commonly known members among the pyroxene group. However, the pyroxene group consists of many other members as well.

The minerals of pyroxene are defined by their chemical composition and their crystal structure. The common chemical composition is described by the formula is – XYZ2O6

• Here X may be one or more of the following – Ca, Na, Fe++, Mg, Mn, Zn or Li. 

• While, Y can be – Mg, Fe++, Al, Cr, Co, Sc, Mn or Vn. 

• Z can be Si, Al or even a combination of them both

• There can be a wide range of cations occurring in the X and Y positions. 

Siliceous Sedimentary Rock 

The siliceous sediments are the composition of silica. This silica has precipitated at or near the site of the deposition or this has replaced the pre-existing sediments. These sediments are different from the clastic or the terrigenous sediments. The later sediments are made of grains which are derived from the rocks elsewhere, while physically transported to the site where the deposition took place. 

In the oceans, the siliceous sediments are dominated in the oozes which are composed of microscopic silica particles precipitated biologically by the diatoms. 

Non-Ferromagnesian 

Non-ferromagnesian are the silicates minerals which are without the substantial Fe and also without Mg which is in their crystalline structure. They are generally lighter-coloured in texture than the ferromagnesian silicates.

Siliceous Limestone 

This Limestone very often contains variable amounts of silica which is in the form of chert or the form of siliceous skeletal fragments (like sponge spicules, diatoms, or the radiolarians). Fossils are quite common in the components of limestone. However, the majority of the limestones consists of sand-sized grains which are in a carbonate mud matrix.

Siliceous Shale 

Siliceous Shale is the hard, fine-grained rock that is shaly structured, they are generally believed to be the shale that is altered by the silicification.

Low Silica Rocks

The Ultramafic rocks (which is also referred to as the ultrabasic rocks, they are although the terms which are not totally equivalent) but they are the igneous and meta-igneous rocks which have a very low silica content (that is less than 45%), they are generally >18% MgO, with high FeO, low in the potassium content, and they are composed of greater than 90%of the mafic minerals (which are dark coloured, high magnesium).

 

Examples of Siliceous Rocks

Examples of Siliceous rocks are as follows:

• Chert and flint.

• Diatomaceous earth.

• Tripoli.

• Porcellanitic.

• Novaculite.

• Radiolarian earth.

• Chemical rock.

• Nodular chert.

The spit coastal feature or the spit geography is largely formed by the deposition of sediments like the sand by the huge water bodies such as the oceans or seas. It is usually a sandpit, a type of deposition bar forming a part of the beach landform off the coasts or the shores of the lakes. The spit geography is developed at places where there is re-entrance of the water from the water bodies like the cove’s headlands. This is generally aided by the process of longshore drift carried by the longshore currents. The drift generally occurs when the waves meet the beach at an oblique angle and move the sediment down the beach in a zigzag pattern.

Factors Affecting the Spit Geography Definition

It is clear that spit geography is formed from the deposition of sediments by the longshore currents carrying a longshore drift. The drift that forms the main factor of the spit geography definition happened due to the waves meeting the landforms of the beach at oblique angles and then moving the sediments down from the beach to the ocean in a zigzag manner. This entire process forming the core of the spit geography definition is also complemented by the longshore currents as well which increase the transport of the sediment by the water alongside the beach. These longshore currents and the longshore drifts are both caused by the same set of waves coming from the water body. 

The Spit Geography is Depicted by the Following Diagram:

The longshore current generated by the waves spreads out and dissipates at places where the direction of the inland shore re-enters or changes its direction for example at places like headlands. Thus, as the longshore current which is already carrying enough load of sediments dissipates near the coastal features like the headlands, it is unable to carry the same load and so drops much of the sediments. This process is known as a deposition. The submerged bar of the sediment allows the longshore drift to continue to transport the sediment towards the direction of the waves breaking and form an above-water spit. Without any of the complementary processes of the longitudinal drift, the sandbar would not have been formed above the water leading to the formation of a spit geography but instead would have been run off by the water or levelled off by it. 

An Image of the Spit in Contrast With Other Coastal Landforms is Shown in the Following:

Formation of a Spit Geography

Now, it is very well established that the reason for the formation of spit geography is the longitudinal drifts and longshore currents generated by the waves of the water bodies. These coastal features arise when the longitudinal drifts reach the section of a headland where the turn is greater than the angle of 30 degrees. The longitudinal drifts or the longshore waves continue the process of deposition above the water until water pressure from the sea or the ocean becomes more than the required amount for the formation of a spit geography. The spit and the geographic events influenced by the water become less pronounced as the spit stabilizes by the growth of vegetation as it grows more and more fertile. As the spits grow further the water behind them or rather trapped by them gets sheltered by the dynamic activities of the waves and the wind making it more suitable for a salt marsh to be developed. The growth of this vegetation is because of the sediments making up the spit which come from different sources, such as rivers, oceans, seas, etc. Whenever there is an increase in logging and activities like farming upstream of the water bodies can cause an increase in the sediment deposition as it increases the sediment load of the rivers as well. When the supply of the sediment is usually interrupted at the neck of the spit, the spit starts moving away from the land and it leads to the formation of an island. 

Spits Around the World

The two of the famous spits around the world are shown in the below list of diagrams:

• Curonian Spit: It is a spit divided between Russia and Lithuania.
  

• Dungeness Spit: This spit is located in the Strait of Juan de Fuca on the US pacific coast.
  

• Farewell Spit on the South Island of New Zealand
  

Other famous spits around the world include the longest spit in the world which is the Arbat Spit located in the Sea of Azov with a length of 110 kilometers approximately. The longest spit found in a freshwater body is in Long Point, Ontario extending approximately 32 km into Lake Erie.