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Ice Core Drilling and Subglacial Lake Studies on the Temperate Ice Caps in Iceland

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Ice Core Drilling and Subglacial Lake Studies on the Temperate Ice Caps in Iceland Ice core drilling and subglacial lake studies on the temperate ice caps in Iceland Iceland astride the Mid-Atlantic ridge Lecture # 36 Astrobiology Winter School Ice drilling projects in Iceland University of Hawaii, Jan. 2005 Thorsteinn Thorsteinsson ([email protected]) National Energy Authority Ice cover during the late glacial period. Combination of hot spot volcanism, spreading on the Mid-Atlantic ridge and glaciation leads to unusual geology. From Thordarson and Höskuldsson (2003). Subglacial volcanism beneath an ice sheet creates unusual landforms: Tuyas (tablemountains) and ridges. Herðubreið, N-Iceland Submarine eruptions create similar formations. Biologicial colonization monitored from the beginning Surtsey eruption, S. of Iceland, 1963-1967. Recent subglacial eruption in Grímsvötn, Vatnajökull ice cap. Jökulsárgljúfur canyons, N. Iceland: Formed in a catastrophic flood from Vatnajökull 2500 years ago. Icelandic analogs to hillside gullies on Mars Mars Mars Iceland Iceland Iceland Temperate ice caps Hofsjökull, 890 km2 cover >10% of Iceland Vatnajökull 2 Langjökull 8000 km 2 920 km Max. thickness: 950 m Mýrdalsjökull 550 km2 - Dynamic ice caps in a maritime climate. - High accumulation rates (2-4 m w.eq. yr-1) - Extensive melting during summer, except at highest elevations (> 1800 m) - Mass balance of ice caps negative since 1995 1972: A 415 m ice core was drilled on the NW-part of Vatnajökull Activities not continued at that time, drill was discarded. Mass balance of Hofsjökull Ice Cap 4 2 0 Winter balance -2 Summer balance H2O Net balance m -4 Cumulative mass balance -6 -8 -10 1987 1992 1997 2002 Climate, Water, Energy: A research project investigating the effect of climate change on energy production in the Nordic countries Temperature increase 1990-2050 °C CWE uses IPCC data to create scenarios for temperature and precipitation change in the Nordic region in the future Modelled change in volume of Hofsjökull ice cap 2000-2002, Modelled glacial meltwater using four different dT and dP discharge (run-off) 2000-2200. scenarios. SINCE 2001: NEW EFFORTS IN ICE CORING AND DRILL DESIGN 100 m ice core drilled at Hofsjökull summit,1790 m above sea level, using a German-built shallow drill. - What kind of drill design is suitable for coring in temperate ice? - Can annual layers be identified in the cores? - Can climate records be retrieved from the temperate ice caps? 16-19 m 40- 43 m 73-76 m Polar ice: Temperature below melting point, borehole dry (Deep coring: Liquid dumped in hole, to prevent closure) Temperate ice: At melting point throughout! Meltwater (and rain) seeps down into snow and firn, and is present in small veins on crystal boundaries below the firn-ice boundary! Water table in ice cap! 1.0 0.9 ] 3 3 Firn-ice boundary ( ! = 0.83 g/cm ) 0.8 Ice becomes impermeable [g/cm 0.7 Density 0.6 Drill hole water-filled 0.5 below firn-ice boundary! 0.4 0 20 40 60 80 100 Depth [m] Hofsjökull – density profile Shallow ice core drill built at the Alfred Wegener Institute in Germany 1 m Antitorque Motor Hatches Core barrel Dry hole: Chips fall through hatches and are collected in upper part of barrel. Core length ~ 1 m. Drill head This system does not work well in a water-filled hole, where: - Motor must be water-protected - Travel time up & down in water column must be > 0.5 m/s - Chips chamber must be designed in a different way A different design was tested with success on the ice shelf covering the Grímsvötn subglacial lake in 2002 1.6 Core length drilled in each run Grímsvötn water table 1.4 Hofsjökull 2001 Grímsvötn 2002 1.2 Hofsjökull water table (m) 1.0 length 0.8 Core 0.6 0.4 0.2 0.0 0 20 40 60 80 100 120 Depth (m) Core length in each drilling run increases with new system! 18O/16O - 18O/16O 18 sample SMOW δ O = x 1000 ‰ 18 16 O/ OSMOW 18 LOCATION ALT Tm δ O SMOW 0.0 ‰ Reykjavík 14 m 4.4 °C - 8.0 ‰ Hofsjökull, Iceland 1800 m ~ - 6 °C - 12.9 ‰ Greenland summit 3200 m - 32 °C - 35.0 ‰ Hofsjökull δ18O profile (0-20 m) 0 2001 5 2000 Summer [m] 1999 surface 10 Depth 1998 15 1997 Summer surfaces determined from: 20 1996 - annual mass balance measurements -16 -14 -12 -10 18 - dust measurements on core ! O [‰] Identification of annual layers from δ18O data not straightforward! 0 5 10 15 20 0 0 0 0 0 0 0 5 5 5 5 5 10 10 10 10 10 15 15 15 15 15 20 20 20 20 20 20 20 0 200 400 600 800 0 400 800 1200 0 100 200 300 0 50 100 150 200 0 50 100 150 200 + - 2- ++ - Na Cl SO4 Ca NO3 Marine aerosol dominates. 40 40 Washout occurs during first melting season! 60 60 80 80 100 100 0 20 40 60 80 100 0 5 10 15 20 Meltlayer % DEP conductivityx10 -6 (µS/m) Lava fields and sandy deserts in the interior are snow covered in winter, but snowfree 2-3 months during summer: Windblown dust covers ice caps in late summer! (Ó. Arnalds et al. 1997) Temperature, stratigraphy and dust concentration in a 15 m snow core at drill site May 2003 0 0 0 2 2 F 2 1 2 4 4 4 3 F 6 4 6 6 [m] 5 8 8 8 D_pi 6 F 10 710 10 8 2002 summer 12 12 12 G surface 9 F G 14 1014 14 11 G -6 -4 -2 0 0 5 10 15 20 0 5 10 15 20 H18 F 12 F 13 G 2001 summer 14 G surface 15 T [°C] Ryk 10 cm [ppmv] Ryk 20 cm [ppmv] Dust [ppmv] 40 Hekla 17. janúar 1991 1990 Dustpeaks allow identification 45 1989 of annual layers. Volcanic ash layers provide 50 1988 reference horizons. 1987 55 1986 1985 D_pi (m) 60 1984 1983 ? 65 1982 1981 70 Hekla 17. ágúst 1980 0 2 4 6 8 10 Grímsvötn eruption November 2 2004 Dust concentration (ppmv) Hofsjökull 2001: Dust concentration and oxygen isotopes 0 20 40 D?pi (m) 60 Net accumulation from ice core Accumulation - yearly mass balance measurements Hveravellir precipitation 80 Comparison with the precipitation record from 100 0 1 2 3 4 5 Hveravellir weather station (650 m a.s.l.), 35 km ?ykkt árlags (m) west of drilling site. Measured annual layer thicknesses. Correction for density differences and plastic thinning of layers with depth yields net mass balance at drilling site 1970-2000. Hveravellir -11.5 Mean annual temperature (Sept-Aug) - Hveravellir 0.0 core -12.0 mean ice -0.5 -12.5 temperature -1.0 Hofsjökull - -13.0 -1.5 [‰] [ O -13.5 °C 18 -2.0 ! 18 ] ! O values - Hofsjökull ice core -14.0 1975 1980 1985 1990 1995 2000 Year (September-August) -12.0 18 ! O = 0.37 * T - 12.62 [‰] 18 -12.5 Mean annual values of δ O in ice core correlate with mean annual temperature -13.0 at Hveravellir. 2 O [‰] - Hofsjökull ice core -13.5 r = 0.29 18 ! -2.0 -1.5 -1.0 -0.5 0.0 Mean annual T (Sept-Aug), Hveravellir [ °C ] How many annual layers are preserved in the Icelandic ice caps? Sandwich model – simple model that describes the thinning of annual layers with depth. Assumes vertical strain rate constant throughout ice sheet. H H Change in t(y)= ln ë y annual layer H thickness (λ) with depth ! y y H H ë H ë ë = y H y H 0 x λ λΗ Dansgaard-Johnsen model: More sophisticated model that does not assume constant vertical strain rate. Melting at the bed can be assumed in model y y h !v !v " y " y !y !y Sandwich model: Dansgaard-Johnsen model: Vertical strain rate constant Vertical strain rate constant from surface to bedrock down to distance h above bed, (unrealistic in lower part) but decreases linearly with depth to 0 below h. Age vs depth relationship according to the Dansgaard-Johnsen model ' ' 2a $ 1 $ % %kh + k 0 "H ( kh 2 + a " % " 0 & & 2a # 1 # 1 % & k # 2 " $ 0 2 ! t ln h y H $kh + k !H ' kh + a0 = % " ! ! $ $ k ! 2 ! 2a0 % ' 2a $ 1 " 1 % " kh + k %kh + k 0 "y'( kh 2 + a t' = ln$ ! k % % " 0 " k 2 2a0 $ & 2a # 1 ! & & # # kh + k $kh + k 0 !h ' kh 2 + a k $ $ ! 0 ! ' $ % k " 2 % " % " 2 1 1 t ' $% " t' 0 y h = % "% ( " + ! ! & k # 2a0 2a0 % y'+ h + " & k k # Results for Hofsjökull summit (H = 300 m, λH = 3.6 m ice) x 500 year record could be retrieved, and annual layers still detectable at 270 m! Bárðarbunga, NW Vatnajökull (2000 m a.s.l.) Model results at 700 m depth: 1100 years old ice Annual layers 17 cm thick 0 0 Bár!arbunga 200 200 400 400 Depth (m) Depth (m) 600 600 Bár!arbunga 800 800 0 400 800 1200 0.0 0.5 1.0 1.5 2.0 2.5 Age (yr) Annual layer thickness (m) - New drill being built in Iceland, operational in 2005. The drill could be made available for coring efforts on temperate or polythermal ice caps elsewhere (Svalbard, Scandinavia, Patagonia) - Ice cores from temperate ice caps in Iceland can be accurately dated - Proxy records for precipitation and temperature can be obtained - A 500 year record could be retrieved with a 300 m drilling at the summit of Hofsjökull - A record covering historical time in Iceland (870 AD – present) could be retrieved with a deep drilling (>700 m) in the ice-filled caldera at Bárðarbunga, Vatnajökull ice cap * Vatnajökull (8000 km2) The Grímsvötn volcanic caldera beneath the Vatnajökull ice cap: Powerful geothermal system, frequent eruptions.
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