Understanding oceans
Geetha Iyer
Oceans bring to mind images of water, wind and waves, of sandy beaches and ships. As an afterthought some images of animals, mostly whales, sharks and dolphins, occasionally maybe fishes. That the ocean is home to a vast variety of vintage organisms comes to our mind only when we see a programme on the National Geographic, Animal Planet or David Attenborough’s productions on the BBC.
The ocean is a repository of normal and unique webs of life sustained within a variety of different biomes and ecosystems. Terrestrial ecosystems are easier to describe and understand than ocean ecosystems, because ecosystems found in oceans are governed by factors that are not so easy to relate with, rather abstract to visualize than those that govern terrestrial systems. The boundaries of these ecosystems too are difficult to demarcate unless you are an ocean scientist. But what is irrevocably similar is that humans are directly and indirectly part of the web of life of these systems. The connections are not that obvious, hence more difficult to see ourselves as connected with the organisms within the oceanic biome.
It is important to remove these difficulties. This will enable humans to start paying greater attention to the role played by oceans in sustaining the earth and an understanding of the organisms that live within it. This we know – that with climate change looming large, melting glaciers will raise the sea levels and submerge land leading to the extinction of diverse organisms. What we fail to understand is the effect this climate change will have on oceanic creatures also – that many will face the same fate as the terrestrial ones. Hence the urgency to educate the young and old about the characteristics of the ocean biome and the organisms it holds within. In this first part, I put forth features that make an ocean a dynamic entity. It will then be easy to relate to the bewilderingly diverse and unique flora and fauna.
Characteristics of an ocean
Oceans are governed by a number of factors – biological, chemical and physical, which together give oceans their unique waterprint (like the footprint for terrestrial biomes). The chemical and physical factors that constitute the abiotic factors impact the biological web of life significantly. While some factors may vary, there are some features which are general to all oceans. A basic understanding of these is necessary in order to know what one can do to conserve the biome and the biodiversity.
Saltiness: This is the most obvious feature of the ocean, the presence of sodium chloride in water. Along with this may be present small quantities of other salts such as chlorides of magnesium, potassium and calcium. In the salt pans where salt is extracted from the sea water, care is taken to ensure that the common salt we get is not polluted by the presence of salts other than of sodium. Salt quality is determined by ensuring that the chlorides of other metals are not beyond permissible levels.
Classroom discussion: On land we have cycling of materials such as C,O,N, etc. What are the cycles that operate in the oceans? What about the salt cycle? Salt does get cycled in the ocean. How and what is its significance?
Waves: As energy moves through water, we see them as waves. It’s the wind that primarily causes the formation of waves. So, the energy from the wind is transferred to the water and the result is the waves. But this is a very simplistic statement. There are many factors that govern the formation of waves. Observe the waves the next time you are on a beach and you can see how they rise strongly and as they come towards you they become progressively slow to completely dissipate. You do feel the energy they contain as your feet get surrounded by them, and the difference in the energy too can be felt if you meet the waves at differing distances.
Renewable power can be generated from this mechanical energy – i.e., energy from waves and tides – of the ocean. The enormity of the energy that waves can garner becomes visible during catastrophic events like cyclones, typhoons and tsunami.
Tides: The water in oceans is in constant motion. Tides are waves that periodically rise and fall in response to the forces exerted by the sun and the moon. There is a periodicity to it. Hence we have high tides and low tides. When the crest of a wave, i.e., the highest part of the wave reaches a location, it is high tide and the trough or the lowest part of the wave corresponds to the low tide. The difference between their heights is called the tidal range. The two previous articles in this column discussed how organisms living in this region – the intertidal region – have to adapt to the changing water levels.
Ocean currents: This is one of the most important abiotic features of an ocean. Waters in the ocean are not only constantly in motion but there is also a direction to their movements. This directional movement is known as the ocean currents. It could be surface currents or deep ocean currents. They are caused by wind, water density (changes in temperature or salt concentration changes the density of water), gravity or tides. The surface currents are driven by wind and energy from the sun. The deep ocean currents are driven by differences in water density. They are strong physical forces and have a significant impact on the diversity and survival of marine life.
Classroom discussion:
- Organisms living near the surface regions of the ocean have to survive the waves. How are they adapted for the same? Students can be taken for a discussion with people (or these people invited to the class) who are expert ocean swimmers and divers.
- Ocean currents are important for maintaining food webs because they move materials around. What materials do they move around and how is it important for maintaining food webs? [Hint: The sunlight zone in water is where photosynthetic organisms are seen. They need substances such as nitrates and phosphates. The excretory materials from those heterotrophs that feed on these autotrophs sink towards the bottom of the ocean and will remain there if not for ocean currents]1,2 Use materials from the reference given for this discussion.
Ocean zones3: Oceans are quite deep and vertically they are demarcated into three zones based on how far light is able to penetrate. The sunlight zone as the name suggests is the depth to which light can penetrate, which would be roughly about 200 metres. This is the productive region of the ocean as the photosynthesizing autotrophs live in this region. It’s also called the epipelagic zone.
Extending to about 1000 metres below the sunlight zone is the twilight zone or the mesopelagic zone. The light penetration and intensity is minimal reducing as with increasing depth. A small part of the organic food – about 20 per cent – produced in the sunlight zone reaches here. The organisms living in this zone have developed various interesting mechanisms to obtain their food.
Light does not penetrate beyond 1000 metres. From here to the ocean floor is the dark zone or the aphotic zone. Any light found here is generated by the organisms living here, a phenomenon called bioluminescence. About 5 per cent of the organic matter produced in the sunlight zone drifts down here. Recent explorations have shown the presence of some remarkable organisms with unique adaptations for obtaining nutrients and survival.
The ocean floor is not uniform. It is quite uneven and has trenches and ridges. There are underwater mountain chains and volcanoes. The mid-oceanic ridges are a chain of mountains extending to nearly 65,000 km. Given the fact that the oceans are quite deep, exploring creatures in there requires overcoming several physical factors, pressure being the foremost among them along with oxygen availability. For e.g., the Bay of Bengal has an average depth of 2,600 ms with the deepest point being nearly 4000 ms. But with the help of technology, machines such as the bathyscopes have helped facilitate deep sea exploration.
What kind of fauna exist at such depths? Plenty and quite unique. In fact as one moves down from the sunlight zone to the benthic/aphotic zone, the diversity of the organisms, in terms of their structure, function and behaviour, will be quite unique and entirely different from what one is familiar with in terrestrial regions. Life is believed to have evolved in water. Explorations are revealing life to be far more varied and numerous that what one notices on land. What are these biological organisms? What are these sensitive food webs that need to be conserved? These and more on the biodiversity of oceans will be explained in the second part of the ocean saga.
| Some ocean facts • 97% of the earth’s water is in the oceans, about 1.34 billion cubic kilometres of water. • The five major ocean basins are the Pacific, Atlantic, Indian, Arctic and Southern Ocean. • Smaller regions of the oceans are described as seas, gulfs or bays. For e.g., the Bay of Bengal, Gulf of Mannar or the Arabia sea. • The salt concentration in sea water is 3.5%. • Nearly 80 per cent of the ocean is unexplored. • The world’s longest mountain chain is underwater. |
References
- Currents and Marine life: https://oceanexplorer.noaa.gov/edu/learning/8_ocean_currents/activities/currents.html
- Currents: Learning Ocean Science through Ocean Exploration: A Curriculum for Grades 6-12
- Ocean zonation: https://oceanexplorer.noaa.gov/facts/light-distributed.html
- Ideas for activities: https://oceanexplorer.noaa.gov/octonauts/welcome.html
The author is a consultant for science and environment education. She can be reached at scopsowl@gmail.com.
