15Glaciers

15Glaciers - 11/20/2007 Science magazine (22 Dec 2006),...

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Unformatted text preview: 11/20/2007 Science magazine (22 Dec 2006), breakthroughs of the year ESM 203: Ice in the Climate System Jeff Dozier & Thomas Dunne Fall 2007 1. 2. 3. Proof of the Poincar conjecture Digging out fossil DNA gg g Shrinking ice "Glaciologists nailed down an unsettling observation this year: The world's two great ice sheets--covering Greenland and Antarctica--are indeed losing ice to the oceans, and losing it at an accelerating pace...." ( l see N York Ti (also New Y k Times, 01 O 2007 f a cool graphic on Oct 2007, for l hi sea ice: http://tinyurl.com/2ne94h) Components of the cryosphere Seasonal snow (covered in Lecture 7) Glaciers Formed from snow through metamorphism, possibly melt & refreeze, and compression Mountain glaciers to continental-scale ice sheets, which account for 2% of Earth's water, and ~80% of fresh water Global water stores Oceans Glaciers, ice sheets and snow Groundwater (750-4000m) Groundwater (<750m) Lakes Soil Atmosphere Rivers Biosphere 97.2% 2.0 0.4 0.3 0.01 0.005 0.001 0.0001 0.00004 Sea ice Formed from freezing of sea water and incremented by snow on the ice Expulsion of brine drives thermohaline circulation Permafrost: perennially frozen soil Lake and river ice Black, P. E. (1995) On the critical nature of "useless" resources, Water Resources Bulletin ESM 203: Ice in the climate system 1 11/20/2007 Formation of glacier ice Metamorphism makes snow denser after it falls Transfer toward bonds sinters crystals Melt-freeze cycles further increase snow density Where some snow survives melt season, layers pile up and squeeze lower layers (increase density), causing snow to turn to ice Typical densities, kg m3 new snow older, unmelted snow 10300 glacier ice 650900 917 1000 Mass balance of a mountain-valley glacier mountainMore net accumulation at higher elevations because accumulation (snow fall) is greater ablation (snow melt and sublimation) is smaller head snow at end of accumulation season midway thru ablation season end of ablation season 250400 pure water ice glacier ice terminus bed 5 melted and refrozen snow 300600 liquid water (nv or firn) equilibrium line 7 Formation of sea ice or lake ice Ice layers in glacier (Hindu Kush) Each layer represents annual accumulation Ice and gas bubbles in layers enable measurements of past atmospheric t f t t h i composition and temperature 18O in ice (and in ocean sediments) allows estimate of temperature at time of snowfall ratio of 18O/16O, compared to ocean water standard, more 18O in evaporated H2O when warmer oceans enriched, ice depleted during glacial periods Isotopes of other elements (15N, 40Ar) confirm temperatures 6 8 ESM 203: Ice in the climate system 2 11/20/2007 Accumulation and ablation zones Glacier flow Ice is a plastic Gravity causes it to flow slowly downhill Mass balance = Accumulation Ablation If glacier is in equilibrium accumulation = ablation (i.e., mass balance = 0) flow from accumulation zone to ablation zone boundaries stable If glacier has positive mass balance elevation of equilibrium line decreases glacier advances (but then area of ablation increases) If glacier has negative mass balance elevation of equilibrium line q increases glacier retreats (but then area of ablation decreases) (Koh-i-Bandaka, Hindu Kush, ~6000m) 9 11 Supraglacial stream (ablation zone) Advance and retreat related to mass balance snow glacier ice equilibrium line Accumulation Ablation Accumulation < Ablation Accumulation > Ablation (Capps Glacier, Wrangell Mountains, Alaska) 10 12 ESM 203: Ice in the climate system 3 11/20/2007 Sea level and glacier changes in last 100 years Types of glaciers (morphological) Cirque: all Sierra glaciers today, e.g. Dana, Palisade Mountain Valley: Baltoro, Yosemite in Pleistocene Piedmont: Malaspina Floating: Glacier Bay, Ross Ice Shelf Mountain icecap: Patagonia, Tuolumne in Pleistocene Continental: today only Greenland and Antarctica Sea level increasing ~1.8 mm/yr, perhaps half from melting glaciers From Global Change Electronic Edition 13 15 Top: rate of seasealevel rise, showing recent acceleration Bottom: sea level (0 at 1990) Dana Glacier (cirque) 1978 (mine) 1908, from the Berkeley Geography Collection S. Rahmstorf Science 315, 368 -370 (2007) Published by AAAS 16 ESM 203: Ice in the climate system 4 11/20/2007 Cirque headwall in Hindu Kush Patagonian Icecap 17 19 Malaspina Glacier, example of a piedmont glacier Ice sheets, shelves 18 http://www.glacier.rice.edu/ 20 ESM 203: Ice in the climate system 5 11/20/2007 Faster flow from West Antarctica because of thinning sea ice? IceIce-cored moraine, Capps Glacier, Alaska Bed topography (left) and thinning rate (right) Enough to raise sea level 0.24 mm/yr (Thomas et al., Accelerated sea-level rise from West Antarctica, Science, 8 October 2004) 21 23 Medial moraines, Barnard Glacier, Alaska Lateral moraines of tributary glaciers combine to form medial moraines Looking down on moraine-covered glacier moraine- 22 24 ESM 203: Ice in the climate system 6 11/20/2007 Glacier polish, Tuolumne Meadows The Milankovitch (1920) hypothesis Long-term variations in climate depend on seasonal and geographic variations in solar radiation, which are caused by orbital variations 25 27 U-shaped valley Orbital causes of climate variability Eccentricity period 95125 kyr 147M km 152M km orbit varies between more eccentric and more circular Obliquity period 41 kyr tilt of Earth's axis varies from 21.824.4o Precession period 21-23 kyr date of perihelion cycles through calendar Jan 5 July 4 There is also a 100 kyr variation in the orbital inclination, 2+ from the plane of the ecliptic 26 28 ESM 203: Ice in the climate system 7 11/20/2007 Example: finding periodicity in data I. Ice Stream Dynamics Forcing II. Ice thickness Surface slope Resistance Internal stiffness Basal and marginal resistance III. Velocity Synthetic time series of periods 100, 41 & 22 kyr Add together Add random noise to the sum Apply spectral analysis to the noisy sum Periods recovered LongLong-term variability in ocean 18O: why the shift from 41 Kyr to 100 Kyr? 41 kyr cycle dominated 1.5-2.5 million years ago 100 kyr cycle dominated in last million years Discoveries New ice streams R. A. Muller & G. J. MacDonald, Glacial Cycles and Astronomical Forcing, Science, 277, 215-218, July 11, 1997 30 Radarsat Antarctic Mapping Mission (RAMP) 1997 ESM 203: Ice in the climate system 8 11/20/2007 Discoveries Ice shelf disintegration Ice stream velocity variations Not "plug flow" Basal flow important 100 km Direct response to regional warming 700 m/a 2000 km2 of Larsen Ice Shelf disintegrated in 2 days. (from Bindschadler et al., 1996) 0 m/a Glaciers feeding lost ice shelves accelerate (up to 8X) "ice-shelf buttressing" Monitoring Velocity Fingerprint of Collapse Jakobshavns Isbrae Centerline Speed Thinning increasing towards coast (satellite altimetry) Flow acceleration (InSAR) Retreat of grounding line (Landsat) Calving of large icebergs (MODIS) Elevation Change Pine Island Gl. Thwaites Gl. Smith/Kohler Gl. All data from satellites (from Joughin et al, 2001) Oceanic forcing is inescapable ESM 203: Ice in the climate system 9 11/20/2007 Monitoring Mass Glacier/Ice Sheet web sites Byrd Polar Research Center (Ohio State) http://www-bprc.mps.ohio-state.edu/ Lamont Doherty Lamont-Doherty Earth Observatory Climate Data Library http://lola.ldgo.columbia.edu:81/ University of Washington Quaternary Research Center http://weber.u.washington.edu/~qrc/ National Snow and Ice Data Center http://nsidc.org/glaciers/ Data from GRACE Seasonal variations of Greenland mass from GRACE (from Luthcke et al., submitted) 40 As these time series lengthen, historical data sets often increase in scientific and societal value. Arctic Sea Ice Extent ESM 203: Ice in the climate system 10 ...
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This note was uploaded on 08/06/2008 for the course ESM 203 taught by Professor Dozier,dunne during the Fall '07 term at UCSB.

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