Ocean Circulation and the Marine Food Web

Increasing ocean temperatures and the addition of significant amounts of fresh water from melting ice caps and glaciers may cause a disruption in weather patterns and a breakdown in the marine food web.

Great Ocean Conveyor Belt (Hugo Ahlenius, UNEP/GRID-Arendal)

The movement of water through the oceans is very important because it circulates heat and nutrients around the globe. The mild temperatures of England, which is on the same latitude as Canada, are due to the heat released to the atmosphere by water that is moving from the tropics towards the Arctic. Water is moved around the globe by the great ocean conveyor belt. As warm surface water is moved away from the tropics it cools and releases its heat to the atmosphere. This heat then warms parts of Europe. The further north this water moves the cooler and heavier it becomes, eventually sinking to the lower level of the conveyor belt. This cooler water is then carried along the depths of the ocean picking up nutrients that have gathered there as it moves.

Marine food web (NOAA) Click to enlarge

As winds move the top layers of the oceans, cold, nutrient rich waters from the depths are brought to the top at "upwelling sites". These areas are important feeding grounds for phytoplankton - microscopic plants that float in the light filled waters at the top of the ocean. Phytoplankton feed on the nutrients that come from the deep ocean waters and many other species then feed on them. They are the primary producers of the ocean and form the base of many marine food chains.

Fresh water is less dense than sea water. Therefore the addition of significant amounts of fresh water from melting ice caps and glaciers may result in a slowing of the ocean conveyor belt, leading to cooler winters in Western Europe and a disruption of the circulation of vital nutrients to phytoplankton. Phytoplankton may also be cut off from their food supply as surface temperatures warm causing the mixing between the warmer top layers and cooler bottom layers to diminish. A decrease in phytoplankton can lead to a collapse of marine food webs, affecting marine mammals (whales, seals and dolphins), sea birds (albatross), and important commercial fish species (cod, salmon and tuna).

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Heavy Extinction Risk for King Penguins

Climate change strikes again - this time, King Penguins.  With temperatures projected to increase in the Antarctic by 0.4ºC over the next two decades, King Penguins' chances of survival have dropped by 15%.  King Penguins feed on small fish and squid, which subsequently are declining because of warming in the Southern Ocean.  These penguins inhabit islands to the north of Antarctica, but warming temperatures are diminishing their food supply and forcing them to travel further in search for something to eat.  This extra effort, in turn, is taking its toll on their overall health and ability to survive.  Temperature increases jeopardize the future wellbeing of this species, and only time will tell if the King Penguin will be able to cope with the stresses of climate change. To find out more, read an article from the Telegraph or the scientific report from The National Academy of Sciences.

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