Context: Plastic trash is abundant in our urban refuse, rivers, and forests, from the slopes of the highest peaks to the depths of abyssal trenches. A new study by researchers from Canada, the Netherlands, and the U.S. has reported that coastal lifeforms have also colonised plastic items in the ocean.
Debate on Anthropocene epoch
- This is the name some scientists have proposed for a new period in history characterized by the influence of one species on the planet’s geology, ecosystems and even its fate- none other than Homo sapiens.
- Scientists are still figuring out when this epoch really began; some include the first nuclear weapon test and rapid industrialization after the Second World War.
- For some, this age began with the manufacturing of plastic rubbish, which is widespread in urban waste, rivers, and woods, from the slopes of the highest peaks to the bottoms of abyssal trenches.
- This got established from a study published on April 17, by researchers from Canada, the Netherlands, and the U.S. They have reported that coastal lifeforms have colonized plastic items the in the Great Pacific Garbage Patch.
What is a gyre?
A gyre is a large system of rotating ocean currents.
- There are five major gyres, which are large systems of rotating ocean currents. The ocean churns up various types of currents. Together, these larger and more permanent currents make up the systems of currents known as gyres.
- There are five major gyres: the North and South Pacific Subtropical Gyres, the North and South Atlantic Subtropical Gyres, and the Indian Ocean Subtropical Gyre.
- In some instances, the term “gyre” is used to refer to the collections of plastic waste and other debris found in higher concentrations in certain parts of the ocean. For Example- North Pacific Subtropical Gyre (NPSG).
About North Pacific Subtropical Gyre(NPSG)
- It is located just north of the equator in the Pacific Ocean.
- It consists of the Kuroshio, North Pacific, California, and North Equatorial currents and moves in a clockwise direction. These currents flow adjacent to 51 Pacific Rim countries.
About Great Pacific Garbage Patch
- Inside North Pacific Subtropical Gyre(NPSG), just north of Hawai’i, lies a long east west strip where some of the debris in these currents has collected over the years.
- The eastern part of this is the Great Pacific Garbage Patch.
- Great Pacific Garbage Patch as per one estimate, 1.6 million sq. km big and more than 50 years old. It contains an estimated 45,000 1,29,000 metric tonnes of plastic, predominantly in the form of microplastics.
The Findings of the study
- The tsunami off the Japanese coast in 2011 contributed to the debris in this garbage patch.
- Researchers had found debris washing ashore on the West coast of North America containing live lifeforms originally found in Japan.
- Researchers studied plastic debris from the eastern part of the NPSG and they found that 98% of the debris items had invertebrate organisms. They also found that pelagic species (species of the open ocean) were present on 94.3% of them and coastal species on 70.5%.
The relevance of the findings
- The introduction of a vast sea of relatively permanent anthropogenic rafts since the 1950s” has given rise to a new kind of “standing coastal community” in the open ocean”, called as neo pelagic community.
- According to research “that while coastal species have been found on human made objects in the open ocean before, they were always considered to have been “misplaced” from their intended habitats.
- The neo pelagic community, on the other hand, is not misplaced but lives on plastics items in the garbage patch, including reproducing there.
- The finding recalls a study published on April 3, in which researchers reported that polyethylene films had chemically bonded with rocks in China. This, in turn, is reminiscent, of the “anthropoquinas” of Brazil (sedimentary rocks embedded with plastic earrings) and the “plastiglomerates” of Hawai’i (beach sediment + organic debris + basaltic lava + melted plastic).
About Ocean currents
- They are the continuous, predictable, directional movement of seawater driven by gravity, wind (Coriolis Effect), and water density.
- Ocean water moves in two directions: horizontally and vertically.
- Horizontal movements are referred to as currents, while vertical changes are called upwellings or downwellings.
Types of Currents
Based on depth
| Surface currents | Sub Surface currents |
| Found up to 400 m of depth. | Beyond 4oo m depth. |
| Constitute around 10% of the total water in ocean. | 90% of the total water. |
| Formed at lower latitudes as higher temperature reduces the density,expands the water and hence the water floats on the surface. | Mainly formed at higher latitudes as lowertemperature increases the density and cause them to sink. |
Based on Temperatures
| Warm Currents | Cold currents |
| Bring warm water into cold water areas | Bring cold Water into warm water areas. |
| Observed on the east coast of continents in the low and middle latitudes (both hemispheres) | Found on the west coast of the continents in the low and middle latitudes (bothhemispheres). |
| In the northern hemisphere they arefound on the west coasts of continents in high latitudes. | Found on the east coast in the higher latitudes in the Northern Hemisphere. |
| Thermal expansion and floatation drive these currents. | Thermal contraction and sinking drive these currents. |
Factors Affecting Currents
Originating factors
- Earth’s rotation: the rotational force of the earth causes movement of ocean water near the equator in opposite direction to the west to east rotation of the earth and thus Equatorial currents are generated.
- Oceanic factors: Temperature, salinity and density differences are responsible for expansion, floatation and sinking of water. E.g. – Labrador current moves as sub surface currents from pole towards equator.
- Atmospheric factors: Winds drive ocean current in direction in which they move. Rainfall and evaporation create level differences and thus moves the water.
Modifying factors
- Direction, shape and configuration of coastline: currents flow parallel to coastline. equatorial current after being obstructed by Brazilian coast gets bifurcated into two branches and then moves along the coast.
- Bottom reliefs: North Atlantic drift is deflected to the right when it crosses Wyville Thompson ridge.
- Coriolis effect: deflective force affects the direction. Currents flowing from north pole towards equator deflects towards right.
- Seasonal changes: They alter the direction of motion. E.g. – Indian ocean currents show regional shifts under the influence of monsoonal winds.
Temperature & salinity affecting Ocean circulation:
Temperature and salinity affect the density of water, resulting in water moving up or down through the ocean layers and moving as currents around the ocean.
- Salinity increases the density of ocean water. This denser water sinks and moves as subsurface current whereas less saline water moves towards greater saline water as surface current. Ex: The current flowing from the Atlantic Ocean to the Mediterranean Sea via Gibraltar Strait is caused by salinity difference.
- Due to high temperature in the equatorial region the water density decreases because of greater expansion of water particles whereas the density of sea water becomes comparatively greater in the polar areas. Consequently, water moves due to expansion of volume from equatorial region of higher temperature to polar areas of relatively very low temperature. Ex: The Gulf Stream and Kuroshio warm currents move from equator towards north due to the temperature difference.
- As warm water flows northwards it cools and some evaporation occurs, which increases the amount of salt. Low temperature and a high salt content make the water denser, and this dense water sinks deep into the ocean. The cold, dense water slowly spreads southwards, several kilometers below the surface. Eventually, it gets pulled back to the surface and warms in a process called “upwelling” and the circulation is complete. Ex: Atlantic Meridional Overturning Circulation (AMOC).
Significance of ocean currents
Geomorphic
- Ocean current along with waves erode, modify and develop coastal as well as submarine landforms.
- Longshore currents carry along with themselves vast quantities of material and sediments.
- Currents help to move eroded debris and deposit it as silt, sand, and gravel along the coasts
- Desert formation: Cold Ocean currents have a direct effect on desert formation in west coast regions of the tropical and subtropical continents.
Climatic
- Manage global climate by transporting excessive heat from equator towards pole.
- Modify the coastal climate. E.g.- Gulf stream brings heat to the north-western Europe and lead to moderate conditions.
- Phenomenon like El-Nino and La-Nina are associated with oceanic currents.
- Currents along with the wind lead to regional climatic changes. E.g.- Currents along the Indian coast impact the monsoon.
- Rainfall and fogs are also associated with oceanic currents.
Ecological
- Distribute oceanic heat and balances the temperature conditions.
- Carry nutrients and food to organisms that live permanently attached in one place and carry reproductive cells and ocean life to new places. E.g.- Upwelling Benguela current brings the nutrients to the coast of Africa
- Oceanic gyres are known to trap pollutants thus causing garbage patches. Ex. Great Pacific Garbage Patch.
Economic
- Commercial fishing grounds are formed where warm and cold current mix. E.g.- Labrador current mixing with Gulf stream near newfoundland.
- Aids as well as hinder navigation. Current support ships moving in the same direction, but it blocks their way when they carry large amount of ice bergs along with them, especially the colder currents.
- Currents offer a vast potential to be transformed into energy sources.
Social
- Play an important role in determining settlements in a coastal region.
- Impact health of population by altering climatic conditions.
