4.a. Climate change is altering the nature of the ocean’s water

Question 1

Give a brief overview of how climate change is altering the nature of the ocean’s water

Answer 1

• the earth’s climate has changed on many occasions over geological time
• there is an overwhelming evidence that climate is experiencing significant change
• ocean closely connected with the atmosphere, so these changes have a great effect

Question 2

What is ocean acidification

Answer 2

• oceans are a sink for carbon
• estimated 30% of anthropogenic CO2 produced in the last 250 years have been absorbed by oceans
• as surface temperature of the oceans rises, their ability to absorb CO2 reduces
• ocean chemistry being altered by addiction of CO2- known as acidification
• average global surface pH has fallen from 8.2 to 8.1, still alkaline, but this process is known as acidication as this represents a 30% increase in acidity

Question 3

What is the process of ocean acidication

Answer 3

• carbon dioxide from atmosphere absorbed by ocean
• carbon dioxide reacts to sea water to form carbonic acid. Sea water pH lowered
• due to action of carbonic acid, much calcium bicarbonate is formed. Carbonate concentrations are diluted, making it difficult for organusms to form shells, made out of calcium carbonate

Question 4

How has ocean acidification impacted marine ecosystems

Answer 4

• molluscs and crustacea at the bottom of the food chain are unable to build strong shells so they are more susceptible to predators, numbers are reduced, and wildlife higher up the foochain suffer from a reduced diet
• declining number or organisms with shells, affects the carbon cycle, as when they die their shells form a store of carbon in rocks for millions of years. Muscles have difficulty making their shells in acidic water
• some jellfsih thrive in warmer and more acidic conditions and their numbers can increase rapidly until they dominate the equilibrium of marine ecosystem
• adaptations to more acidic oceans exist around underwater volcaoes
• some of the most productive fishing areas exist where water upwells from the depths, bringing CO2 and nutrients to surface

Question 5

How has ocean acidification affected fish stocks

Answer 5

• changes in marine ecosystems could alter marine harvests of shellfish, crustacea and fish- examples of provisioning ecosystem services
• LIDCs and EDCs are most dependent on seafood for protein. In some countries, seafood can account for 50% of dietary protein and many countrues have limited agricultual alterantives
• by 2050, impact of ocean acidification on marine ecosystems are likely to cause stress on fishing in tropics
• changes to fish stocks linked to ocean acidifcation but the overall picture is not clear- some predatory species switch prey and seem to show few negative effects. This puts them in conflict with other predatory species which decline
• marine ecosystems are under increasing pressures from human activity which is adding to the stress coming from ocean acification

Question 6

How have rising temperatures affected warming oceans and coral reefs

Answer 6

• corals are marine polyps which live in symbiosus with algae. Algae release nutrients by photosynethis which the polyps feed on. Algae contain pigments which give coral its colour
• coral require particular living conditions- ideally 26°c, salinity of 30-32,000 ppm, water depth of 25m or less, light for algae to photosynthesise, clean water and some wave action to oxygenate the water
• warming oceans push corals to their thermal limits
• in extreme temperatures, the relationship with the algea is lost and the coral lose their colour- coral bleaching occurs

Question 7

How have rising temperatrures caused coral bleaching

Answer 7

• coral bleaching is evident around the tropics
• it is a complex process associated with salinity
• observations of entire coral communities bleaching have been increasing over the past 30 years
• coral mortality reached up to 80% in Maldives and Seychelles
• satellite measurements of increases in sea surface temperature can be used to predict bleaching events

Question 8

Example of coral bleeching- The Great Barrier Reef- why are coral reefs known as the ‘rainforests of the ocean’

Answer 8

• they have a very high biodiversity- more than 25% of all marine life live on coral reefcs. GBR home to 1500 fish species, 350 coal species, 400 molluse species
• they have effecient recycling of energy and matter, with the vast majority of nutrients tied up in reef organisms

Question 9

Example of coral bleeching- The Great Barrier Reef- what are the threates clinate change poses to coral reefs

Answer 9

• increased sea water temperatures lead to control bleaching events
• sea level rise increases the depth of water over corals and so reduces light levels
• increased wave energy from greater number of more intense tropical storms
• ocean acidification reduces coral’s ability to build carbonate structures

Question 10

Example of coral bleeching- The Great Barrier Reef- direct threats to coral reef communities and ecosystems

Answer 10

• coral reefs act as a buffer for coastlines from high energy waves
• coastal development would cost much more as investment would be required in expensive engineering
• recreational activities attract visitors and generates employment+income for some communities- spreads through the area due to multiplier effect
• white sand beaches associated with coral reefs are made up of broken down fragments of the coral

Question 11

Example of coral bleeching- The Great Barrier Reef- indirect threats to coral reef communities and ecosystems

Answer 11

• coral reefs play a role in acting as ‘nursery locations’ for many species. Loss of this local supply of protein would be detrimental to communities in LIDCs and EDCs already suffering from widespread under nourishment
• these communities have a lack of resources and they are vulnerable to small changes