Introduction
It is a well known fact that the oceans cover 70 percent of the Earth’s surface (EPA). It is a storehouse for 1,000 times more heat than the atmosphere, and is the earth’s largest reservoir of water. The hydrological cycle that is caused because of the oceans and is vital to all the living organisms on the earth. It is through evaporation, the ocean transfers huge amounts of water vapor to the atmosphere, where it cools, condenses and eventually falls to the ground as rain or snow (Environmental Defense n.pag).
Even though the ocean and the resources in it seems limitless, today there is obvious evidence that human impacts particularly due to over fishing, habitat destruction, and pollution disturb marine ecosystems and intimidate the long-term productivity of the seas (UNU-IAS Report 10-35, Worm et al. 787 – 790). This paper focuses on the polar oceans and gives a detailed account on the physical environment, the producers and the consumers, and the interaction between various components.
Polar oceans: geographic location
The polar ecosystems are composed of the Arctic and Antarctic regions. This ecosystem is characterized by ice and snow, cold temperatures all through the years, and severe changes in photoperiod that avoid photosynthesis during a large part of the year (NOAA). The water in and around the Antarctic continent is referred to as the Antarctic or Southern Ocean. The Antarctic ecosystem is highly influenced by physical factors such as weather & climate, ice, and ocean currents. The Antarctic Circumpolar Current, at 0 to 200 meters in depth, is the dominant surface-water circulation pattern in this polar region.
The Antarctic Circumpolar Current is a geostrophic current, and is mainly influenced by the existing Antarctic wind patterns and is controlled by the adjoining landmass which is the Antarctic continent. In general, the Antarctic Circumpolar Current is also called the West Wind Drift that flows from west to east around the Antarctic landmass. It is only during the seasonal melting of sea ice, the sunlight is able to penetrate the ocean and enable the vegetative growth. The favorable light conditions stimulate phytoplankton growth and yield surges in primary productivity. Subantarctic Surface Water which is the north of the Antarctic Circumpolar Current is in general the warmer and more saline.
The physical environment of the Antarctic Ocean has also got several unique features. The Antarctic Bottom Water has average salinity, temperature, and density values of 34.65, −0.5°C (31°F), and 1.03 gram per cubic centimeter, respectively. The Antarctic Deep Water which is formed in less extreme latitudes and is less salty and warmer when compared to Antarctic Bottom Water, flows northward near the surface until it reaches the Antarctic Polar Front Zone, where the Antarctic Deep Water sinks and continues to flow northward beneath the warmer, less dense North Atlantic Deep Water.
The Arctic Ocean is yet another part of polar oceans and is divided into the Eurasian and Canadian basins by the Lomonosov Ridge which is a bathymetry feature that runs from Greenland past the North Pole to Siberia. Arctic Ocean surface water is 0–200 meters in depth and mainly flows counterclockwise in the Eurasian basin and clockwise in the Canadian basin.
The physical environment of the artic ocean is also having its own unique features. For instance, there are three distinct marine water masses located within the Arctic Ocean: the Arctic Surface Water which extends from 0–200 meters; the Atlantic Water from 200–900 meters; and the Arctic Deep Water which extends from 900 meters to the seafloor. The Arctic Surface Water is further sub divided into three layers: the surface, subsurface, and lower surface layers. In fact each of these water layers has distinct salinity and temperature characteristics.
The Atlantic Water is situated between the Arctic Surface Water and the Arctic Deep Water. The average temperature of the Atlantic Water is warmer than both that of the Arctic Surface Water and the Arctic Deep Water which is approximately 3°C. The Atlantic Water has a higher salinity range (34.8–35.1) when compared to that of the Arctic Surface Water (28.0–34.0). The Arctic Deep Water, has a salinity range of 34.9 to 34.99 (Advameg Inc). There are fundamental differences that make the two Polar Regions (the Arctic and Antarctic) very different both physically and biologically.
The Arctic Vs the Antarctic
The Antarctic marine ecosystem is situated in the circumpolar Southern Ocean surrounding the central continent of Antarctica. As a result there is no inflow from rivers or sediment as in the case of the Arctic. But nutrient rich water rises to the surface and fertilizes the Antarctic surface waters. The Antarctic fauna is much richer than the Arctic and has a high degree of endemism and biomass. In fact the Antarctic benthic communities generally have several dominant species. The fish fauna present in this region is generally endemic and tailored to below-freezing water temperatures. The bird communities are similar at given latitude in all parts of the Southern Ocean basin.
The Arctic Ocean system is an isolated sea, permanently covered by ice in the center, and surrounded by landmasses. The Arctic Ocean has several large rivers that bring in a large quantity of sediment into the basin resulting in a substrate of particulate matter and a low-saline stratified surface layer. The Arctic fauna is poor and mainly depends on the Atlantic Ocean. Arctic benthic communities are habitually dominated by one or only a few species and the fish fauna is generalized. Additionally there are also strong differences between the bird communities at similar latitudes in different parts of the ocean basin (NOAA).
Primary producers and secondary consumers in the Antarctic Ocean
The extent of ice cover in the Antarctic Ocean affects competition between species of phytoplankton which are the primary producers. As a result of this competition, there exist competitions between zooplankton species which are primary consumers. For instance colder winters mean greater ice cover than warmer winters and colder winter favor larger phytoplankton, like diatoms. Diatoms are the favored food of krill, which are sequentially eaten by many other animals in this food web. Therefore, when winters are very cold and the ice is more, nearly every group in the food web has enough of food because more food energy is transferred from lower to higher feeding or tropic levels.
On the other hand when the winters are not so cold, and more of the ice melts, it favors different species of phytoplankton growth and reproduction. Warmer winters in general favor smaller phytoplankton such as cryptophytes. However, the krill does not consume this smaller phytoplankton and therefore less of the food energy from cryptophytes gets into the food web. Researchers have found that during the past five decades, cold winters that has extensive sea ice development have been less frequent. This has resulted in reduced krill populations. Therefore it can be side that in the Antarctic, the food web is directly affected by climate factors.
It is generally believed that anthropological activities have had a major impact on the changing climatic pattern. In recent years the burning of fossil fuels has greatly increased the amount of carbon dioxide and other green house gases in the atmosphere. It is well known that carbon dioxide gas is a principal warming agent in the atmosphere that is causing global warming. Therefore, if this pattern of warming continues and goes unchecked, the cost could be devastating not only for the Antarctic regions, but for the entire planet (Botos n.pag).
Primary producers and secondary consumers in the Arctic ecosystem
The Arctic ecosystem has an exclusive, complex food web that is designed by its unique plankton, animal species, and environmental factors. Phytoplankton and algae that are the primary producers take up carbon dioxide from seawater and utilize it for photosynthesis. The Arctic ecosystem is covered with a formidable ice and snow cover. As a result this ocean is plunged into total darkness during the winter, banged by blizzard winds, and is very cold. The Arctic Ocean is however considered as one of the most inaccessible and yet beautiful environments on Earth.
Great polar bears are among the uniqueness in this region. They roam over the Arctic ice and swim the Arctic seas and are on the top most part of the food web. Supporting these top predators is a complex ecosystem that includes plankton, fish, birds, seals, walruses, and even whales. Phytoplankton and algae that produce organic material using energy from the sun are the main producers of this food web that support all of this life.
In recent years, the scientists have reported that the warming temperatures are affecting the Arctic Ocean and are producing changes that may not only effect on the Arctic’s interlink but also its delicately balanced food web. Any small change in the food web not only threatens life in the Arctic region, but also could have impacts on the entire Earth’s climate. For instance, the populations of Arctic plankton not only provide food at the base of the food web in the Arctic region but also serve to convert carbon dioxide from the atmosphere into organic matter that eventually sinks to the ocean bottom thus effectively extracting a heat-trapping greenhouse gas from the atmosphere (Woods Hole Oceanographic Institution).
Primary productivity in the polar oceans
Primary productivity is affected by the availability of sunlight, carbon dioxide, and inorganic nutrients such as nitrates, phosphates, and trace elements. In the polar marine environment, nutrients are recycled from phytoplankton to animals to decomposers such as bacteria before returning to phytoplankton and this cycle goes on and on. In the polar oceans, phytoplankton blooms happen during the summer months. As a result of this phytoplankton blooms under favorable light conditions lead to short-term improved primary productivity. In fact studies have found that during these summer months, the Antarctic Ocean’s upwelling zone exhibits some of the Earth’s highest primary productivity.
As mentioned earlier, in the polar oceans, the sea-ice formation and melting processes play important roles in primary productivity. Frazil ice is mixed with surface and subsurface water, entrapping phytoplankton between ice crystals that are ultimately integrated into pack ice. The phytoplankton particularly the diatoms will proliferate within the sea-ice brine channels, resulting in the pack ice to appear greenish-brown. During the yearly ice melt process, the diatoms are released back into the water, resulting in local increased primary productivity.
Marine biodiversity normally decreases towards high latitudes, reaching a minimum in the polar oceans. Additionally, the few marine species that exist in the polar oceans are likely to grow at slower rates, live longer lives, attain larger sizes, and have fewer offspring than their tropical counterparts. Besides, some of the marine species that are able to survive the comparatively harsh polar conditions tend to exist as larger populations than their more diverse tropical counterparts.
In contrast, to the Antarctic, the Arctic Ocean is mainly dominated by shallow marginal seas. This is a major factor that has resulted in the different biota spatial distributions in these two oceans. While the greater part of the Antarctic Ocean Polar habitats sustain populations of diving birds such as penguins and puffins, and marine mammals such as whales, seals, and polar bears, these animals are more visible than the invertebrate and microscopic communities found in the water column, on the seafloor, and in sea ice. The Arctic Ocean biota resides and feed throughout the water column and along the seafloor.
Among the larger populations of biota present in the Antarctic region are the five types of seals (namely the crabeater, elephant, leopard, ross, weddell), six varieties of penguins (namely adelie, chinstrap, emperor, gentoo, macaroni, king), and five whale species (namely blue, sperm, orca, mink, southern bottlenosed). These are present in addition to a variety of seabirds, squid, fish, krill, copepods, and diatoms.
On the other hand the major sea mammals linked with the Arctic Ocean are whales (namely the beluga, orca, bowhead, California gray, narwhal), polar bears, sea otters, seals (namely ringed, ribbon, bearded, spotted), and walruses (Figure 1). Additionally arctic birds such as the tufted puffin, laysan albatross, and spectacled eider mainly depend on the Arctic Ocean as a primary food source. These birds feed by diving into the water for fish, crustaceans, and/or mollusks.
As mentioned earlier in the Arctic Ocean, the dominant types of phytoplankton and zooplankton are diatoms and copepods, respectively. Water-column productivity of the shallow Arctic marginal seas promotes the growth of productive benthic communities which include mollusks, polychaetes, brittle stars, and amphipods, which support bottom feeding by the spectacled eider, walrus, bearded seal, sea otter, and the California gray whale (Advameg Inc).
Summary
The polar oceans form the most unique ecosystems on the planet earth. However, with the present day human activates, this fragile ecosystem is also affected. As it is a well known fact that the Arctic is an important indicator of the state of global well-being. Studies have predicted that the impacts of climate change will be felt most extremely in the Arctic. There are also problems due to the over hunting. Populations of some whales are dangerously low after centuries of hunting even though most commercial whaling has legally being ceased. It is also reported that fish stocks in some arctic waters are at its extinction.
Sea birds and even polar bears suffer from over-hunting in parts of the Arctic. The problems in the polar oceans are increasing due to the climate changes both due to human activities as well as due natural reasons. These fragile ecosystems are among the most unique ecosystems on this planet that holds unique importance. It is the duty of each and every one of us to protect these environments through sustainable development.
Arctic marine food web
Work cited
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Worm, B. et al. Impacts of Biodiversity Loss on Ocean Ecosystem Services, Science 3 November (2006) Vol. 314. no. 5800, pp. 787 – 790.