Oceans, caught between devil and the deep blue sea… (Pun intended!) – VII

The ocean is a vast and mysterious place, which for many seafarers, is part of its allure. People have always delved into the strangest unsolved ocean mysteries – may it be the Bermuda Triangle, the case of the disappearing island, or the unusual noise that emits from the deepest parts of the ocean – some of these being mere pieces of fiction but some may be a certainty.    

Humanity knows more about the moon’s surface than the depths of the ocean. In fact, 12 people have stepped foot on the planet, but only three have been to the Mariana Trench — the deepest part of the seas, at roughly 7 miles (11 kilometers) deep.  And also about a handful of sounds from the depths of the oceans that scientists cannot explain with any certainty. “The Bloop” may be the most famous underwater sound, captured in 1997 by hydrophones set out by the National Oceanic and Atmospheric Administration (NOAA).  Also, consider this example of coral reefs self-protection technique. Over millions of years, corals in Australia’s Great Barrier Reef developed protective barriers that help them survive in the sun, according to the Commonwealth Scientific and Industrial Research Organisation (CSIRO). Scientists are already working to create UVA/UVB sunscreen filters inspired by the corals’ sunscreen code.


Though 94 percent of life on Earth is aquatic, only about one-third of it is still known to humanity. General populations are entirely ignorant of the majority of the discovered species and pictures of these species appear miraculous to familiar eyes.  New species are continually being identified, raising more questions about marine life and about the origin of life itself.

What are plankton?

Humans and all other animals need oxygen to breathe. Oxygen is produced by plants as they photosynthesize.  Many people know these basic principles, but few people are aware that more than half of the oxygen we breathe comes from the ocean.  However, pollution because of human activities is now reducing the oceans’ ability to produce oxygen.

All autotrophic organisms – which mean plants and bacteria which produce their food by photosynthesis – are oxygen producers.  Plankton are marine organisms which too are autotrophic.  These are the diverse collection of organisms (mostly extraordinarily tiny or even uni-cellular) that live in large bodies of water and are unable to swim against the current. They provide a crucial source of food to many large aquatic organisms like fish.  These organisms include bacteria, archaea, algae, protozoa and other drifting or floating animals. 


Phytoplankton and copepods are the first two steps in the plankton food chain (Pic courtesy – The importance of plankton; 27th March 2015 – Blue Planet Society)

The word plankton comes from the Greek word “planktos” which means “drifting,” descriptive of the billions of single-celled plants that float on the surface of the oceans. Most phytoplankton are unicellular algae. The chlorophyll in the phytoplankton is part of the reason the ocean water looks green. Phytoplankton is very important not only as an oxygen producer and carbon dioxide and temperature regulator but is also essential to the marine food chain. These single-celled organisms are the cornerstone of life in the ocean.  They are eaten by zooplankton, which becomes food for krill, fish and other crustaceans which then become food for larger fish and various marine life and finally by human beings. This food web is an Oceanic food chain.  The unicellular organisms or plankton are susceptible to their surroundings. Temperature changes, ocean acidification, salinity changes and pollution reduce their health and ability to produce oxygen.

Pictures of crustaceans, algae, water-bears and marine reptiles, (Pic Courtesy – World Register of Marine Species)

Air pollutants entering oceans

One of the most important pathways of pollution occurs through the atmosphere. Scientists have a good understanding of how air pollution impacts human health and the terrestrial biosphere, but what impact does air pollution have on oceans? Wind-blown dust and debris, including plastic bags, are blown seaward from landfills and other areas. Dust, for example,  from the Sahara moving around the southern periphery of the subtropical ridge moves into the Caribbean and Florida during the warm season as the ridge builds and moves northward through the subtropical Atlantic. Dust can also be attributed to a global transport from the Gobi and Taklamakan deserts across Korea, Japan, and the Northern Pacific to the Hawaiian Islands. Climate change is raising ocean temperatures and increasing levels of carbon dioxide in the atmosphere.

Besides natural sources like dust, human-induced airborne pollutants, primarily from factories and automobiles, are also responsible for a significant way of contaminants and nutrients entering marine waters. The issue of air pollution and how it relates to our ocean is very complicated.  The constituents of air pollution with the highest potential to harm water quality are nitrogen, mercury, other metals, combustion emissions of fossil fuels, and pesticides. Combustion emissions and particulate matter (PM) mix mingle and react in the atmosphere, often turning into poisonous substances and fall from the air as dust, as a result of gravity or when rain rinses these to the ocean and waterways, which lead into the seas and called as acid rain. Significant contributors to the acid rain are emissions of sulfur dioxide and nitrogen oxides as well as carbon dioxide, released into the atmosphere by burning fossil fuels.

These rising levels of carbon dioxide are acidifying the oceans. This, in turn, is altering entire aquatic ecosystems including plankton kingdom and modifying fish distributions, with impacts on the sustainability of fisheries and the livelihoods of the communities that depend on them.  Ocean water has typically an average pH value of 7.8 – 8.1, which is slightly alkaline.  Scientists believe that the oceans have already become more acidic over the last century. As the water pH approaches 6.0 (more acidic), crustaceans, insects, and some plankton species begin to disappear. As it approaches 5.0, significant changes in the makeup of the plankton community occur, and less desirable species of mosses and plankton begin to invade, and the progressively fish populations start diminishing.

I will not be surprised if fish loving populations of Mumbai are entirely deprived of their favorite Bombay ducks, salmons and mackerels in coming years…

Fish prices in mumbai


  1. See-the-sea; Atmospheric changes and Air pollution
  2. Wikipedia – marine pollution – pathways of pollution
  3. Sea Science: 7 Bizarre facts about ocean; By Kacey Deamer, June 8, 2016
  4. United Nations Environment Programme, 1990
  5. Windows2universe / water-watersheds


Milind Joshi


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