What is it?
Why is this important:
Why is it such a big deal?
Water in the polar regions has a lower salinity level than tropical regions. This circulation allows for a distribution of water to level out salinity levels in certain areas. Also, the movement of the warmer water from the tropical regions to the polar regions allows for a warming of the polar areas of the world (while also allowing cooler water to be brought to tropical regions to assist with cold, deep water currents that also flow-->these areas must remain at their temperature levels to allow for nutrient growth and specie survival)
Concerns about affecting the circulation:
-->Polar regions traditionally experience minor shifts in salinity throughout the year-the warming and cooling of seasons allow for a freezing and melting of water. More recently, the continual warming of polar regions has allowed for ice to melt. This ice is made of freshwater, which is less dense than salt water. When the ice melts, the freshwater in the polar regions of the ocean is increased, thus decreasing the salinity. This freshwater also slows the circulation as it does not sink due to the lack of density (in comparison to salt water) and thus doesn't continue the continual movement of water sinking in polar regions to continue the circuit.
-->Tropical regions experience an increase in salinity due to the warmer temperatures (caused through global warming) causes an increase in evaporation. This evaporation leads to a higher level of salinity (left behind when water evaporates) in tropical regions.
Decrease Circulation and CO2 levels:
Oceans act as a carbon sink (an area where carbon is absorbed and stored). With a decrease in circulation, the top layer of water becomes saturated with CO2 until they reach a maximum of what they can absorb. The bottom regions, on the other hand, are CO2 poor as they are not being circulated to the surface level where they can play a part in absorbing CO2. This ends up leaving more CO2 in the atmosphere due to a reduction in a major carbon sink.
Impact on organisms:
Upwelling is the vertical movement of ocean currents, bringing nutrients and colder water to the surface and the movement of warmer water down (assists with temperature distribution in the middle region of the ocean). This upwelling is important as it brings food to many organisms that are not deep sea dwellers.
In addition, the warming of the tropical regions and the cooling of the polar regions due to a disruption in circulation leads to a huge impact on organisms in both areas.
To check this out, courtesy of Al Gore, watch this video: