Cryosphere Flashcards
What is included in the “cryosphere”?
Mountain/valley glaciers Ice caps and ice sheets Icebergs and sea ice Permafrost Snow cover Lake ice
Give 7 interactions between ice and the Earth
- Surface albedos
- Ice sheet elevation
- Landscape change
- CO2
- Sea level
- Ocean circulation
- Vegetation change
Give descriptions of the 6 major ice masses (how formed, affect on sea level if melt, floating/grounded, area, typical thickness)
Glacier - formed from snow, melts adds to sea level, grounded above sea level, ~100 km2 area, ~100sm thick
Ice cap - snow, melt adds, grounded above, less than 50,000km2, ~500m
Terrestrial ice sheet - snow, melt adds, grounded above, >50,000km2, ~1000s
Marine ice sheet - snow, melt adds, grounded BELOW, >50,000km2, ~1000s
Ice shelf - snow, melt doesn’t add, floating, variable size, 100s-1000s m thick
Sea ice - frozen ocean water, doesn’t add, floating, variable size, 1-5m thick
What ice masses are constrained by topography? Give examples.
Icefield
Valley glaciers
Mountain glaciers e.g. James Ross Island, Antarctic peninsula
What ice masses are unconstrained by topography? Give examples.
Ice sheets - only Antarctic and Greenland (present day); outlet glaciers, ice streams
Ice caps - ice domes, ice divides, outlets, streams e.g. Agassiz ice cap, Canada
Ice shelves - ‘floating’ extensions of glaciers
Ice bergs - calved from shelves/glaciers e.g. MASSIVE Jakobshavn, Greenland (3 miles wide, 1000m thick)
Sea ice - changes seasonally, very dynamic change; max. extent in Arctic reached in March, end of Northern winter, minimum in Sept (inverse for the Antarctic in SH)
What is mass balance in terms of accumulation and ablation?
Positive MB = accumulation > ablation
Negative MB = ablation > accumulation
0 when accumulation = ablation (equilibrium, balanced)
When will a glacier grow in terms of mass balance?
Growth with lower temperatures; more snowfall and less melt so accumulation exceeds ablation, equilibrium line altitude lowers
Shrinkage with higher temps; more melt, a higher ELA
What is accumulation and ablation?
Accumulation = inputs
- Snowfall (snow->firn->ice) with increasing density, eventually cutting of air passages
- Warmer air has larger capacity for moisture, so = faster
- Also wind-blown drift, avalanches, rime, freezing rain
Ablation = outputs
- Surface melt; melting when energy surplus at surface? Debris cover can increase this if THIN as it increases absorption and re-radiation, but not thick
- Calving; ‘dry’ (breaking off in mountains) and ‘wet’ (floating ice/tidewater glaciers) affected by water depth, temp, salinity, tides, crevassing etc.
- Basal melting; ice shelf (water erodes base), grounded (geothermal heat flux) and frictional heating
How does climate influence MB?
Maritime - moist, high accumulation & ablation, gradual gradient and fast flow e.g. Norway
Continental - drier, low acc./abl, steep gradient, smaller MB difference, slower flows e.g. Arctic Canada
What are the 2 main ways in which ice flow occurs? Give 3 factors that control basal sliding.
- Internal deformation - flows via deformation of ice crystals, driven by gravity, the steeper the slope, the faster the flow, so ice is thinner, resistance from friction
- Basal sliding - velocity decreases with depth so top moves a greater distance than the bottom (high basal drag) and velocity also decreases with width so the middle of ice moves fastest (high lateral drag)
- Can also be a result of sediment deformation; underlying soft sediments deform (unlike bedrock), higher the water content, the weaker the sediment (fastest glaciers lubricated at base by water/sediment)
Controlled by bed roughness, quantity/distribution of water at bed, embedded debris
Outline the role of temperature in ice flow, what is Pressure Melting Point - give the 3 glacier types defined by different temp regimes
Ice flow velocity is a function of temperature - ice temp varies with depth according to input type/surface air temp, geothermal heat fluxes, ice flow/advection
PMP = ice not necessarily 0C at base, high pressures can cause ice to melt at lower temperatures (regelation)
- Cold based - ONLY internal deformation, frozen to base, at poles
- Warm based - ice at base at pressure melting point, water is present, warm throughout
- Polythermal - mixture of warm and cold
What is the LGM? How was ice distribution different?
Last Glacial Maximum = peak of last glacial period ~20,000 yrs ago
Former ice sheets; Laurentide, Eurasian, British
Expanded ice sheets; New Zealand, Patagonia, Iceland, Greenland and Antarctica
Sea level; 120-130m lower than today
What is polar amplification? Explain 5 positive feedback systems.
- Ice/albedo = lower temp, less melt, more snow, advancement, larger area, higher albedo, less radiation for melting & heating = lower temp
- Ice/elevation = thickening ice, higher elevation, local/global climate alteration, orographic rainfall, more snowfall, less melt, +ve MB, more acc. = height
- CO2 = lower in glacial periods (cold water absorbs more), sea ice cover resticts exchange with ocean at poles
- Ocean circulation = ice influences ocean, which influences climate e.g. increased sea ice cover on THC
- Sea level changes = marine regions glaciated, sea levels fall, more land for glaciation, ice sheet growth, amplifies albedo/elevation
Erosional landforms?
Micro (1m) - striations, crescentic gouges
Meso (10-100m) - roche moutonnees, crag & tails
Macro (100-1000+m) - cirques, U-shaped valleys, hanging valleys, fjords
Indirect impacts - outline the 3 types of meltwater, and explain the Zwally Effect (2002)
- Supraglacial - meltwater on top of ice
- Englacial - inside the ice e.g. tunnels
- Subglacial - underneath ice
What ice masses are most affected by the ocean and why? What else affects calving rate and ice sheet extent?
Marine ice sheets, ice shelves, calving rates and tidewater glaciers
Temperature, salinity, tides / sea level changes
Give 3 key elements of marine ice sheets.
- Ice streams (bounded by slower moving ice)
- Outlet glaciers (bounded by topography)
- Grounding line (ice grounded to floating)
What evidence is there for oceans driving the thinning of ice streams (Marine Ice Sheet Instability Hypothesis)
West Antarctica:
- Peninsula ice shelf break-up; melt-water ponds have greater ability to absorb insolation - eventually butresses form at point of break
- Antarctica bedrock largely below sea level
- Instability of ice sheets from reverse slopes and beds below sea level = positive feedback loop relating to continuous retreat
Grounding line decrease -> greater ice thickness at GL -> greater ice discharge -> GL retreat deeper etc.
WAIS = 3m global sea lebel rise in 100yrs from ice shelf breaking, potential collapse but V. COMPLEX
Ice/Ocean interactions - what is the significance of the Amundsen Sea ice streams?
Ice stream thinning driven by the ocean in the Pine Island Glacier & Thwaites Glaciers?
- Ice streams = ‘weak underbelly’ (w/reverse slopes)
- Velocity increase since 1994, retreating GL
- Ice flow modelling; thinning driven by changes in ice shelf, a result of intrusion of warmer CDW?
Ice/Ocean interactions - what is the significance of Circumpolar Deep Water and PIG?
CDW - slightly warmer than AABW, incursion under shelves causes melt
- 1994 acceleration event in Pine Island Glacier
- Modelling shows more CDW on continental shelf at this time, coinciding with velocity increase = wind stress
- ‘Amundsen Sea Low’ (low pressures moved further south/west causing this intrusion and upwelling?)
Ice/Ocean interactions - what is the significance of the Weddell Sea?
Other side of western Antarctic = v. thick ice (would cause dramatic sea level change if melted)
- Potential for rapid change if circulating gyres change, reverse slopes also
Ice/Ocean interactions - what is driving the outlet glacier thinning in Greenland?
- Surface elevation lowering - strong over outlet glaciers (>10m/yr)
- Not just by MB change, what about meltwater/ocena impact?
- Direct contact with ocean (tidewater)
- Marine terminating retreating more than terrestrial (Sole et al., 2008)
Driven by?
Meltwater - more seasonal than long-term
Marine/oceans - changes in NAO, warm water incursion
How does the ice affect the ocean?
Slowing/stopping thermohaline circulation; Greenland melt = influx of freshwater, decreasing salinity, reducing driving factor behind deep water formation in THC (past Heinrich Events show that this has happened before…atmospheric change would NOT BE ENOUGH to make this change)
- But varying results from studies
Depositional landforms?
Moraines - terminal (MB margin), lateral (below ELA), medial (middle), push (bulldozed) Drumlins - subglacial landforms Kames - mound-like hills Eskers - sinuous ridges Kettle lakes - glacial lakes
Ice climate interactions - sun spots and solar irradiance?
- Since 1600s, dark sun spots recorded, a steady increase
- 11-yr cycles of the suns’ outputs correlating subtly
- Small positive correlation with temp
- Solar Irradiance changes have occurred less than 1% since LIA (18th C.)
Ice climate interactions - what are Milankovitch Cycles (1941) and what is the relevance of orbital variations?
Milankovitch Cycles = the elliptical nature of Earth’s orbit, pull creates equatorial bulges
- Insolation receive varies based on time of year (Earth on severe angle and pilled by gravity of Sun, moon and Jupiter…)
- Therefore this must be taken into account when the influence of insolation on ice is studied, looking to energy balance/deficit etc.
Precession = season nearest/furthest from sun (~20ka) Eccentricity = how round orbit it (Earth ~100ka)
What are the projected changes for the 2 main ice sheets?
Greenland - increasingly negative surface MB, dynamic retreat, 0.2m SLE
Antarctica - increasingly positive MB, particularly in East where moisture in atmosphere, less land mass, ice/albedo not as strong, western peninsula is most vulnerable
What are some sources of uncertainty surrounding the predictions for the future of the cryosphere?
- Climate forcing; RCPs not guaranteed
- Natural variability; function of NAO/SO, Zwally…
- MISIH; ice stream thermal feedback mech., cliff retreat?
- Geothermal heat flux; subglacial changes
- Models; accuracy/availability of data? Representative? V. complex process, difficulties
What is permafrost, give 3 types?
Perenially frozen ground, overlain by zone of seasonally-thawed ground (active layer) - a belt around North Atlantic (Siberia, Russia, N. Canada)
- Continuous - pervasive permafrost (90-100%), coldest
- Discontinuous - broken up (50-90%), valleys
- Sporadic - isolated blocks, thin, margins (10-50%)
What the recent changes in permafrost and the impacts of this?
Temps at 10-20m depth; gradual warming, greater ALT, good Russian station coverage
- 1930s; active layer thickness decreased by 32m (NH)
- 1970s; in NH, southern limit moving north
- 1980s; temp incresaed by 2C, ALT increased up to 90cm
Impacts on railways/roads, uneven grounds and organic matter thawing/decaying, releasing CO2/CH4, adds to GHG, increasing surface temp, further deepening (positive feedback)
What are the recent changes with regards to snow cover, lake/river ice, sea ice, ice shelves/tongues and ice sheets? (IPCC)
Snow cover; strong negative correlation temp and SCE, 1967-2012 decrease, largest 53% decrease in June
Lake/river ice; contracter Winter ice duration with delays in Autumn, freeze-up more slowly than advances, evidence of acceleration (across NH)
Sea ice; 1970-2012 saw a 3.8% decrease per decade in Arctic but a 1.5% increase for Antarctica! Thinning 2004-2008 in Arctic - mean sea ice thickness decreases by 1.3-2.3m 1980-2008
Ice shelves/tongues; continuing retreat/collapse in Antarctic Peninsula, thinning in Greenland also
Ice sheets; losing mass, adding to sea level over last 20 yrs, rate of loss increased from outlet glaciers
IPCC figures = Antarctic velocity fastest on western peninsula / Greenland fastest in South/West, elevation decrease also
What are the implications for us and our environment? (x3)
Sea level - coastal regions/deltas
Resources - glacial retreat exposing rare Earth elements like in southern Greenland, v. useful for clean technology
Ocean circulation - largely unknown consequences, shutting down of THC, wider impacts?
How are future predictions made and what are they saying?
Representative Concentration Pathways (RCP) by the IPCC - variation of scenarios
- Lowest RCP2.6;
- Highest RCP8.5, ‘business-as-usual’
Then applied to climate models, giving a range of outcomes
How are glaciers directly impacted by the climate?
- Tidewater glaciers most vulnerable
- Some steady declines to neg MB e.g. Himalayas
- General trend of retreat, not constant (Little Ice Age ~16th-19th C.)
- Observed 1980s advancement then 2000s retreat in Europe (strong NAO) and New Zealand (ENSO, IPO) e.g. Franz Josef
How is Greenland directly impacted by the climate?
- Large change in MB spatially e.g. increased ablation at coast, acc. in centre
- Overall neg. MB, is thinning
- 2012 extraordinarily high temps = lots of melting
How is Antarctica directly impacted by the climate?
- Mostly insensitive to small atmospheric tmep changes since most below 0
- Western Antarctic Peninsula - can be above 0C (interacts with warm SO waters and winds), greater levels of change here therefore
How is sea ice extent directly impacted by the climate?
- Arctic sea ice decreasing; global warming but natural variability?
- LT perspective shows derease of nearly 20% since late 1970s
- Antarctic sea ice IS NOT decreasing however
Describe the past trends, the last 1000 years in particular. What are the main climate change forcers?
- Ice cores show natural variability in past temps
- Rapid warming since Last Glacial due to changing solar radiation in NH maybe; range between summer & winter insolation dreatly decreased 6000 y/bp
- Holocene (starting 7000 yrs bp) = peak at 1000 yrs, decline in Medieval Little Ice Age, large spike at 1800s (e.g. 90s recors showing post-industrial spike)
- Volcanic - sulphur in cores, regular spikes/occasional large ones e.g. Krakatoa 550AD, but overall stochastic
- Solar irradiance - sun spots correlate to irradiance so records of these used, showing no dramatic change
- All others - follows temp trend significantly e.g. anthropogenic forcing like GHG
