Ice sheets and information held within them Flashcards
Why are ice sheets good climate archives?
Deposition
Annual
100-700,000 years
Where are the two biggest ice sheets?
Greenland and Antarctic
- 99% of all glacier ice
- 68% of Earth’s freshwater
How do ice sheets tell us about past climates?
Ice sheets trap air bubbles, dust, and other materials that provide clues about past atmospheric conditions, such as temperature, carbon dioxide levels and precipitation patterns
Between 1992 and 2020 what was the loss in ice sheet mass?
Greenland- -4890 Gt (13.6 mm sea level rise)
Antarctica- -2670 Gt (7.4 mm sea level rise)
21 mm sea level rise since 1992
If the ice sheets in Greenland and Antarctica were to melt, how much would that raise global sea level?
Greenland- 7.4 meters
Antarctica- 57.9 meters
How are ice sheets formed?
Ice sheets form from the accumulation of snow over time. When snow builds up, it compresses under its own weight, turning into dense ice
What is the consistency and density of ice sheets?
Snowflakes, 90% air, <0.1g/cm^3
Ice granules, 50% air, 0.3 to 0.5g/cm^3
Firn, 30% air, 400-800kg/m^3
Ice, 20% air as bubbles, 830-923kg/m^3
On average how long does the transformation of firn to ice take?
Takes 100 to 300 years at a depth of 50 to 80 meters
On mountain glaciers how long does the firn take to transform into ice?
Firn can transform into ice in 3-5 years between depths of 10 to 20 meters
How long does firn take to transform to ice in the East Antratice?
Firn is transformed into ice between 280 and 2500 years
Transformation takes place between 64 and 95m depth
What is ice sheet mass balance?
Ice sheet mass balance refers to the difference between the ice gained through snow accumulation and the ice lost through melting, calving and sublimation
Where do meltwater streams and rivers flow on the greenland ice sheet?
Meltwater streams and rivers flow on the surface of the Western area of the Greenland ice sheet
What is iceberg calving?
Iceberg calving is the process where chunks of ice break off from the edge of an ice sheet or glacier, often leading to large icebergs floating away
How can ice sheets be dated?
Ice sheets can be dated using methods like annual layer counting, geochemistry, ash layers, electrical conductivity, and numerical flow models
What is firn in the context of ice sheets?
Firn is an intermediate stage of snow that forms between snow and glacial ice, typically consisting of compacted granular ice
What are wiggle matching and geochemistry used for in ice sheet research?
Wiggle matching of geochemical records is used to match ice core records to past insolation (solar radiation) time series, helping to date the ice sheet layers
What past information can be obtained from ice cores?
Ice cores contain past information on temperature, precipitation, atmospheric composition, volcanic activity, and wind patterns
How can the accuracy of ice sheet dating be improved?
The accuracy can be improved by using multiple methods such as annual layer counting, geochemistry and numerical models
How do ice sheets tell us how temperatures on Earth have changed?
Ice sheets contain layers of ice with trapped air bubbles and isotopes. Scientists anaylse these to reconstruct past temperatures and see how Earth’s climate has changed over time
What can be used with ice sheets to tell us about past air temperature?
Ultra sensitive thermometer
Oxygen and deuterium isotopes
How are isotopes used to estimate past air temperatures from ice sheets?
The ratio of oxygen isotopes (16^O and 18^O) in ice cores reflects past temperatures- more 16^O in ice suggests colder periods, while less 16^O suggests warmer periods
What can be used as an indicator of air temperature?
Isotopes
What hydrogen isotopes are used to study past air temperatures?
The two main isotopes are 1^H (protium) and 2^H (deuterium), with 1^H being more abundant
What do isotopes differ in?
Number of neutrons can vary: giving rise to isotopes. These isotopes differ in relative atomic mass, but not chemical properties
How many stable isotopes does oxygen have?
16^O, 17^O and 18^O
Care most about 16^O and 18^O
Indicators of air temperature
What causes fractionation of water isotopes in the atmosphere?
Fractionation occurs during evaporation and precipitation, where lighter and heavier isotopes behave differently
What happens to isotopes during evaporation?
Evaporated water becomes enriched in lighter isotopes (1^H and 16^O), causing delta deuterium and delta 18^O values to decrease
What happens to isotopes during condensation and precipitation?
Precipitating water becomes enriched on heaver isotopes (2^H and 18^O), so delta deuterium and delta 18^O increase in precipitation, but decrease in the remaining vapor
What is delta deuterium and delta 18^O?
They are measures of isotope ratios in water compared to a standard, indicating changes in climate
What is Rayleigh fractionation?
Rayleigh fractionation is the process where an air mass loses heavy isotopes (2^H, 18^O) over time through precipitation, making the remaining vapor more depleted (more negative delta deuterium and delta 18^O)
How do delta deuterium and delta 18^O values relate to air temperature?
Lower delta deuterium and delta 18^O values in ice cores suggest colder climates, while higher values indicate warmer climates
What affects ice sheet stable isotopes ?
Moisture source
Transport path
Season of precipitation
How do ice sheets tell us about how dustiness and atmospheric greenhouse gases have changed on Earth?
Ice sheets trap air bubbles and dust particles they form. Analyzing these reveals past levels of greenhouse gases (like Co2, CH4) and dustiness, which reflect changes in climate, wind patterns and aridity
How are ice cores important archives?
They are important archives of past greenhouse gases
Air trapped in ice: important source of information about past greenhouse concentrations
What can be a faithful recorder of atmospheric concentrations?
Co2 and CH4 trapped in air bubble in ice
Are the shifts in distribution of sun energy enough?
No
Changes in atmospheric greenhouse gas concentrations, in particular Co2, play a large role in the development of cold conditions during ice ages, and warm conditions during interglacials. Co2 amplifies changes induces by orbital variations
What is an example of feedback to cooling and ice growth?
Initial change
Climate cooling
Increased snow and ice: higher reflectivity
Less solar radiation absorbed at surface
Greater cooling
What is an example of a feedback involving bedrock?
Ice sheet grows
Bedrock sinking delayed for thousands of years
Ice sheet, stays at higher, colder deviations
More positive ice mass balance
Ice grows faster
In total what is the measurement of the carbon reservoirs?
All in pg = 10.000.000.000.000.000 g
What reservoirs are involved in the carbon cycle and how are they weighted in pg?
Reservoirs small to big:
Atmosphere (750)
Surface ocean (700)
Plants and soils (2000)
Deep ocean (37,300)
Earth’s crust (100,000)
What processes are involved in the carbon cycle?
Ocean-atmosphere gas exchange: Co2 dissolves in the upper layer of the ocean, and under natural conditions, the same amount would be vented out
Photosynthesis (marine and terrestrial)
Respiration and decomposition
Combustion
Volcanic eruptions
Weathering of silicate rocks
What reservoirs are most important in the carbon cycle?
Atmosphere
Terrestrial biosphere
Ocean
Sediments and rocks
What is glacial Co2 lowering in the carbon cycle?
During ice ages, atmospheric Co2 drops due to greater ocean storage, more dust-driven productivity, and colder temperatures, which shift carbon from the air into the ocean and land reservoirs
How did terrestrial carbon vegetation differ between the current interglacial and the last glacial maximum?
During the LGM, terrestrial carbon was lower due to reduced vegetation from colder, drier conditions, and more ice cover. It is higher in the current interglacial because of warmer, wetter climate and more plant growth
What does modelling suggest about terrestrial carbon (soil and vegetation) during deglaciation?
Depending on assumptions, models suggest that up to 400 Gt of carbon could have been released to the atmosphere, or there may have been a small increase in soil and plant organic carbon storage
What are the different types of terrestrial carbon?
Vegetation carbon
Soil organic carbon (SOC)
Litter and dead biomass
Peatlands and permafrost carbon
How does glacial Co2 lowering affect different earth system reservoirs?
Atmosphere: Co2 decreases, cooling climate
Terrestrial biosphere: Less vegetation and soil carbon
Oceans: Take up more Co2, store it in deep water
Sediments: More burial of carbon
Rocks: Minimal short-term effect, long term weathering may change slowly
What is the biological pump in the carbon cycle?
Its the process by which Co2 is absorbed by ocean phytoplankton, turned into organic matter through photosynthesis, and then exported to the deep ocean as organisms die and sink- helping to isolate Co2 from the atmosphere
How does ocean productivity and export affect atmospheric Co2?
Increased productivity (more phytoplankton growth) and export (more sinking organic carbon) enhance the biological pump, leading to more Co2 removal from the atmosphere and greater carbon storage in the deep ocean
What is the role of calcification in ocean inorganic carbon?
Calcification (e.g. by coral reefs, coccolithophores) forms calcium carbonate (CaCO3) and releases Co2 back into the water and atmosphere
How did glacial periods affect reef calcification?
During glacials, exposed continental shelves reduced reef habitats, leading to a decline in reef calcification and potentially lower Co2 release from this process
What are the causes for lower glacial atmospheric Co2?
Cooler seawater temperatures: increased Co2 solubility: likely glacial Co2 sink
Terrestrial biosphere: likely not a glacial Co2 sink
Ocean inorganic carbon: likely glacial Co2 sink
Ocean biological carbon: likely glacial Co2 sink
