OCEAN WATERS: CHARACTERISTICS, COMPOSITION, TYPES, EXAMPLES - ENVIRONMENT - 2025

The ocean waters are those contained in the oceans and represent 96.5% of the total water of the planet. They are delimited in 5 oceans that are the Atlantic, Pacific, Indian, Arctic and Antarctic.

The main characteristic of oceanic waters is its salt content, marked blue color, high heat capacity and the system of currents. In addition, they constitute the main source of terrestrial oxygen, are an important carbon sink, regulate the global climate and contain great biological diversity.

Ocean waters. Source: PDphoto

The types of oceanic waters are diverse, depending on how they are classified, either by differences in temperature, salinity, light, geographical location or depth zones. In the vertical dimension, ocean waters form layers that differ in temperature, luminosity, salinity, and biodiversity.

Although ocean waters appear uniform at first glance, the reality is that they form a highly variable system. Both natural processes and human intervention cause ocean waters to be very different from one area to another.

Characteristics of ocean waters

Salinity

Ocean waters are high in salts (30 to 50 grams per liter), depending on the ocean, latitude, and depth. In coastal areas with the mouths of large rivers, salinity is lower and this also decreases with precipitation while it increases with evaporation.

Color

Oceanic waters are seen in blue, although in some seas they can acquire greenish or brown tones. The color is due to the fact that water is capable of absorbing a wide spectrum of solar radiation, blue being the light with the least absorption.

The greenish tones are due to the presence of green microalgae and chestnuts are caused by large amounts of suspended sediment. Red waters are due to the proliferation of microalgae that are toxic (Harmful Algal Proliferations).

Temperature

Oceanic water is capable of absorbing a large amount of heat, that is, it has a high heat capacity. However, the emission of heat is carried out slowly and therefore the oceanic water mass plays an important role in regulating the earth's temperature.

On the other hand, the temperature of ocean water varies with latitude and depth and is affected by winds. In the Arctic the water temperature varies from 10ºC in summer to -50ºC in winter, with a floating ice sheet.

In the case of the Pacific Ocean at the height of the equator, temperatures can reach 29 ºC.

Heat stains

These are large areas of oceanic waters with temperatures 4 to 6 ºC above average, and can reach up to 1 million km². They are caused by areas of high pressure caused by decreased winds that heat the surface layer of the water and can reach up to 50 m below the surface.

This phenomenon has occurred several times near Australia, east of its Pacific coast. Likewise, it has occurred in the oceanic waters of the Pacific between California and Alaska and on the North American west coast.

Density

Due to the high content of dissolved salts, the density of ocean waters exceeds the density of pure water by 2.7%. This makes it easier for an object to float in the ocean compared to a freshwater river or lake.

Oxygenation

Ocean waters produce approximately 50% of Earth's oxygen, but some studies indicate that they have lost about 2% of dissolved oxygen in the last 50 years. The increase in the average global temperature increases the warming of oceanic waters and decreases the dissolved oxygen that goes into colder deep waters.

Movement

Oceanic waters are in constant movement both horizontally and vertically, either on its surface as well as in the depths. This circulation of ocean waters at the planetary level is an important factor for climate regulation.

Surface horizontal circulation

Surface currents are caused by winds, friction between layers of water and by the inertia of the earth's rotational motion. There are warm currents that flow towards the polar zones and cold currents that flow from the poles towards the equatorial zone.

Gulf Stream. Source: User Sommerstoffel on de.wikipedia

These currents form the oceanic gyres or rotating currents, the main ones being those that occur around the Earth's equator. Another expression of the horizontal movement of oceanic waters are the waves generated by the push of the wind towards the coasts.

To the extent that the winds are of greater magnitude, the waves can reach considerable heights. Underwater seismic or volcanic events can cause exceptional waves of great devastating power, called tsunamis.

Deep horizontal circulation

The marine currents that occur in the deep areas are caused by differences in density and temperature between masses of oceanic water.

Vertical circulation

The movements of ascent and descent of oceanic waters are produced by the effect of terrestrial, solar and lunar gravity, generating the tides. As well as differences in temperature, density and confluence of currents, as in descents and outcrops.

The upwellings or outcrops are movements of masses of deep oceanic water towards the surface. These occur due to the differences in movement and temperature of the surface and bottom water masses, coupled with the effect of the marine relief.

These outcrops are of great biological and economic importance because they bring nutrients present in deep layers of ocean waters to the surface. This generates surface areas of high marine productivity.

Composition

Ocean waters are a complex solution of almost all known elements on Earth, both organic and inorganic.

- Inorganic compounds

The most abundant inorganic component in oceanic waters is common salt or sodium chloride, being 70% of the total dissolved solutes. However, practically all known mineral elements are found in ocean waters, only in very small amounts.

Main salts

These are the ions of chlorine (Cl-), sodium (Na +) and to a lesser extent sulfate (SO₄²-) and magnesium (Mg2 +). Nitrates and phosphates are found in the deep sea that precipitate from the surface layer where they originate from biological activity.

- Organic material

Ocean waters contain large amounts of organic matter both in suspension and deposited on the ocean floor. This organic matter comes mainly from marine organisms, but also from terrestrial organisms that are dragged into the oceans from rivers.

- Gases

Oceanic waters intervene in the development of the oxygen cycle as well as in the carbon cycle, they have a relevant role in them.

Oxygen cycle

The greatest production of oxygen through the photosynthesis process occurs in oceanic waters thanks to the activity of phytoplankton. Most of the oceanic oxygen is found in the upper layer (0-200 m), due to photosynthetic activity and exchange with the atmosphere.

Carbon cycle

Phytoplankton diversity. Taken and edited from: Prof. Gordon T. Taylor, Stony Brook University, via Wikimedia Commons.

Phytoplankton in ocean waters fix organic carbon at an annual rate of 46 gigatons and the respiration of marine organisms releases CO2.

- Anthropic pollutants

Ocean waters also contain a large quantity of pollutants introduced by human activity. The main pollutants are plastics that have formed large islands of ocean plastic.

Types of ocean waters

Ocean waters can be classified according to various criteria, either by oceans, temperature, salinity or the area it occupies.

- By oceans

Oceans of the world

5 oceans are recognized on the planet (Arctic, Atlantic, Antarctic, Indian and Pacific) and in each one the oceanic waters have particular characteristics.

Arctic Ocean

The waters of this ocean are the lowest temperature and depth on the planet, with an average depth of 1,205 m. Likewise, they are the ones with the lowest salinity, because evaporation is low, there are constant contributions of fresh water and in its central part it has ice caps.

Atlantic Ocean

It presents the oceanic waters with the highest content of salts with 12 gr / L on average and is the second largest extension of oceanic water. It has an average depth of 3,646 m and reaches its maximum depth in the Puerto Rico trench at 8,605 m.

Antartic Ocean

The definition of these ocean waters as an ocean is still controversial, but it is the second smallest ocean water body. Like the Arctic Ocean, it has low temperatures and low salinity.

Its average depth is 3,270 m and the maximum is reached in the trench of the South Sandwich Islands at 7,235 m.

Indian Ocean

It contains the third largest volume of oceanic waters after the Pacific and the Atlantic. It has an average depth of 3,741 m and the maximum in the Java Trench with 7,258 m.

Pacific Ocean

This ocean is the largest extension of ocean water on the planet and the one with the greatest average depth at 4,280 m. The deepest point on the globe is found in this ocean, in the Las Marianas Trench at 10,924 m.

- By geographical areas

There are important differences between oceanic waters in their horizontal and vertical distribution, both in temperature, solar radiation, amount of nutrients and marine life. Sunlight does not penetrate deeper than 200 m and determines the density of marine life as well as the temperature gradients.

Oceans and seas

Oceans are large expanses of ocean waters separated from one another by continental configurations and ocean currents. For their part, the seas are part of those, being smaller extensions that are located near the continental shelf.

The seas are delimited by certain geographic shapes such as island chains or peninsulas and are shallower than the oceans.

Gulfs, bays, inlets

They are penetrations of the sea into the land, so they are shallower and receive continental influence. Of these, the cove is the one with the narrowest connection to the open sea.

Estuaries and deltas

In both cases, these are areas where large rivers flow into the sea or directly into the ocean. In both cases, ocean waters are deeply influenced by river waters, lowering salinity and increasing sediments and nutrients.

Albufera

They are accumulations of oceanic water on the coast forming a lagoon separated from the sea by a sandy barrier in almost all its extension. In these geographical features the oceanic water reaches shallow depth, the absorption of solar radiation is maximum and therefore the temperature increases.

- By temperature

There are warm ocean waters and cold ocean waters, which in turn is correlated with nutrient content. Thus, warm ocean waters have fewer nutrients than cold waters.

- By salinity

Salinity of the oceans; lilac / purple areas are the least salty and red areas are the most salty. Source: commons.wikimedia.org

In the world's oceans there is a salinity gradient and those of the Atlantic in the Baltic Sea have lower salinity than those of the equatorial zone. Similarly, the oceanic waters of the Pacific have a higher concentration of salts than those of the Arctic, but less than those of the Atlantic.

Precipitation, relief and salinity

The waters of the Pacific Ocean are less saline than the waters of the Atlantic due to the rainfall pattern determined by the relief. The Andes Mountains in South America and the Rocky Mountains in North America block moisture-laden winds from the Pacific.

Due to this, the water vapor that comes from the oceanic waters of the Pacific, precipitates in the ocean itself. But in the case of the Atlantic, the water vapor that is generated over the Caribbean Sea surpasses Central America, precipitating in the Pacific Ocean.

All this determines a greater dissolution of the concentration of salts in Pacific ocean waters compared to those of the Atlantic.

- By light

Depending on the depth, ocean waters are more or less exposed to the penetration of the visible spectrum of solar radiation. Based on this, we speak of the euphotic zone and the aphotic zone for those depths where sunlight does not reach.

Euphotic zone

The mass of oceanic water reached by sunlight is between the surface and 80-200 m deep and depends on the degree of turbidity of the water. In this area there are photosynthetic organisms, phytoplankton and macroalgae that define the food chains.

Aphotic zone

The aphotic zone ranges from 80-200 m to the abyssal depths, photosynthesis is not carried out and the living beings that inhabit it live on the debris that falls from the upper zone.

Likewise, there are food chains that start from chemosynthesizing primary producers such as archaea. These produce energy by processing chemical elements from hydrothermal vents on the seabed.

- Vertical zoning

Oceanic waters can be classified according to their vertical distribution in the water body, which affects their physical-chemical characteristics. In this sense, we speak of the littoral zone that goes from the coast to where the solar radiation reaches about 200 m deep.

The deep zone is located from 200 m to the sea trenches, 5,607 to 10,924 m. The ocean waters in each of these zones vary in temperature, sunlight, salinity, type and quantity of marine life, among other factors.

Examples of ocean waters

The ocean waters of the coral reef

Coral reef. Source: I, Kzrulzuall

Coral reefs are rich in biological diversity, despite being warm waters and initially low in nutrients. This is due to the fact that coral colonies become life attractors that form a complex ecosystem.

Coral colonies are found in shallow water, receive sufficient light and are a refuge against currents, generating a complex food web.

The oceanic waters of the Chilean and Peruvian coasts

These coasts are west of South America, in the Pacific Ocean, and are one of the outcrop points of oceanic waters on the planet. These oceanic waters are cold and rich in nutrients from the deep layers.

This outcrop forms the Humboldt Current that runs south towards the equator and is caused by various factors. These are the inertial effect of the earth's rotation, the equatorial centrifugal force and the relief of the marine platform.

These oceanic waters allow the concentration of large schools of fish and other marine organisms. Therefore, they are centers of high biodiversity and areas of high fishing productivity.

The ocean waters of the Gulf of Mexico dead zone

In the Gulf of Mexico there is the so-called Gulf Dead Zone, an area of ​​20,277 km², where marine life is greatly reduced. This is due to the eutrophication phenomenon caused by the incorporation into oceanic waters of nitrates and phosphates from agrochemicals.

These polluting products originate in the extensive North American agricultural belt and are washed into the ocean by the Mississippi River. Excess nitrates and phosphates cause unusual growth of algae that consume dissolved oxygen in ocean waters.

The ocean waters of the plastic islands

Plastic islands. Source: North_Pacific_Gyre_World_Map.png: Fangz (talk) derivative work: Osado

Ocean waters with high concentrations of plastic have been discovered in the so-called ocean gyres of the Pacific, Atlantic and Indian Oceans. These are small pieces of plastic, most of them microscopic, that cover large areas of the ocean.

This plastic comes mainly from continental areas and has been partially degraded during its movement through the ocean. The marine currents are concentrating it in the center of the current rotation system that makes up these oceanic gyres.

These concentrations of plastic negatively affect ocean life and the physico-chemical properties of ocean waters in the area.

References

1. Asper, VL, Deuser, WG, Knauer, GA and Lohrenz, SE (1992). Rapid coupling of sinking particle fluxes between surface and deep ocean waters. Nature.
2. Fowler, SW and Knauer, GA (1986). Role of large particles in the transport of elements and organic compounds through the oceanic water column. Progress in Oceanography.
3. Kanhai, LDK, Officer, R., Lyashevska, O., Thompson, RC and O'Connor, I. (2017). Microplastic abundance, distribution and composition along a latitudinal gradient in the Atlantic Ocean. Marine Pollution Bulletin.
4. Mantyla, AW and Reid, JL (1983). Abyssal characteristics of the World Ocean waters. Deep Sea Research Part A. Oceanographic Research Papers.
5. Montgomery, RB (1958). Water characteristics of Atlantic Ocean and of world ocean. Deep Sea Research.
6. Perillo, GME (2015). Chapter 8: Oceanography. In: Vallés, E. State and perspectives of the exact, physical and natural sciences in Argentina. National Academy of Sciences.
7. Rosell-Melé, A., Martínez-García, A. and Núñez-Gimeno, N. (2009). The role of the oceanic carbon cycle in atmospheric CO2 changes. The incidence of the biological pump in the climate. Security and environment.