Carbon 6.2 Flashcards
How does the biological carbon pump sequester atmospheric carbon and contribute to the carbon pump?
- CO2 dissolves into the ocean
- The ocean’s surface layer contains tiny phytoplankton – they contain chlorophyll and need sunlight to live.
- Phytoplankton photosynthesise and removes carbon from ocean (5-15Gt a year). They have shells and sequester CO2 which creates calcium carbonate as their shells develop.
- They use carbon to grow
- Zooplankton (animal-based plankton) consumer Phytoplankton both support the marine food web
- Respiration of Zooplankton releases CO2 back into the ocean. Faecal pellets and dead zooplankton fall into the ocean floor unless eaten
- Marine organisms (such as some plankton, coral, shellfish) use carbon to build carbonate shells
- When these organisms die, they may decompose but their shells fall to the ocean floor. And build up (sedimentation) eventually form limestone rocks – this is the carbonate pump.
Thermohaline circulation
an ocean current that produces both vertical and horizontal circulations of warm and cold water around the world’s oceans.
How does thermohaline circulation create a physical pump of carbon out of the atmosphere?
-Since colder water and deep water under pressure can hold more gas than warm or shallow water – the Southern Ocean around Antarctica is an important carbon sink
-The deep cold water rises very gradually to the surface, where it absorbs CO2 from the atmosphere – this is slowing so may not be an effective carbon sink in the future
Where you have ocean currents, it helps carbon to sink with it = the physical pump
-The Southern Ocean shows that there is a solubility or physical carbon pump involving upwelling and downwelling currents, which move dissolved CO2.
-Cold, denser seawater sinks into the deep ocean, where slow-moving deep ocean currents hold C02
-These deep currents eventually return to the surface, where the seawater is warmed, and CO2 is diffused back into the atmosphere
-Carbon compounds are transported between the world’s ocean in this way along the deep ocean conveyor known as the thermohaline circulation
-The water in the far North Atlantic is cold and very saline (salty) which makes it denser and heavier, causing it to sink
-By sinking, it draws warmers water in from the ocean surface from the tropics/equatorial region
-Eventually, this movement from the tropics draws cold water up from the ocean bottom, ready to be warmed again
-As the water moves, it takes down the carbon with it, by moving the dead organisms
Why is it useful for the food web and the sequestration of carbon in the ocean?
-The circulation allows upwelling which delivers many nutrients upwards to be consumed, this supports the food web and allows sequestration and the carbonate pump to continue
Why are the cold waters around the poles good as carbon sinks?
The cold oceans around Antarctica and Greenland are huge carbon sinks as colder denser water can hold more dissolved carbon. The sinking of water here as part of the thermohaline circulation is important in delivering the carbon to deeper levels to be sequestered.
What is thermohaline circulation?
Thermohaline circulation forms ocean currents that cause sinking and flowing of water horizontally and vertically.
Why does water sink in the north Atlantic?
In the North Atlantic, cold salty water sinks as it is denser.
What does the sinking water do that helps to start the circulation?
This sinking pulls in warmer surface water and in turn pulls warmer water from the tropics across the Atlantic.
Why is this sinking, and circulation of water known as a ‘physical pump’ of carbon?
The movement of this warmer water north pulls the deep, colder water south and pulls it upwards to be warmed again to complete the circulation in the Atlantic creating a physical pump that carries the carbon with it.
Why is the circulation vulnerable? What might happen in the future?
The circulation is vulnerable and there are signs it may be slowing as more freshwater enters the ocean from melting ice caps. This could switch off the pump and Europe could plummet into an ice age!
the Gulf Stream - thermohaline circulation
- In 2004, the gulf stream had stalled for 10 days
- There was concern that the ocean currents were slowing and there was data that showed that the speed of ocean circulation between the Gulf of Mexico and Europe had slowed by 30% since 2000
the Gulf Stream - thermohaline circulation
-Scientists results for the cause was:
- Melting Arctic ice was increasing the amount of freshwater entering the North Atlantic
- The Ocean’s salinity was declining as a result, preventing cold water from sinking there
- This meant that there was nowhere for the warm water of the Gulf Stream to go – the North Atlantic was losing its pulling effect
Carbon sequestration
the removal and storage of carbon from the atmosphere – usually occurs in oceans, forests and soils through photosynthesis.
Short term biological processes
- Surface and deep ocean waters
- Main stores in the biological process is the ocean and there are significant fluxes due to photosynthesis and respiration
- Oceans are also a small natural source of methane gas, especially shallow coastal offshore areas, where gas seeps from a nutrient rich seabed through the ocean to the atmosphere
the biological pump
-Phytoplankton in surface waters use sunlight to turn carbon into organic matter through photosynthesis and carbon enters the food web via other organisms that use carbon to make their shells and skeletons (Calcium carbonate) such as corals, oysters, crabs and zooplankton.
