objectives :

Greenland Synthesis project, SASS Seattle meeting 3/06

- Objectives:1) an estimate of the large temporal variations in fresh water output from land-based ice in Greenland 2) an improved understanding of the variability of the ice discharge flux from the Greenland Ice Sheet3) use 1 and 2 to investigate to what extent ice discharge variability from Greenland outlet glaciers is attributable to short term climate variability (e.g., through enhanced basal lubrication from surface melt)

Collaborative Research: A synthesis of rapid meltwater and ice discharge changes: large forcings from the ice with impacts on global sea level and North Atlantic freshwater budgets


The Greenland Ice Sheet in 3D (vertical exaggeration just about right for a glaciologist)


Topography of the Earthat high latitudes, the climate system is at least as effective as plate

tectonics in producing high elevation topography, and it does it quicker (both on the way up and the way down)

If you take fresh water out of the ocean, you have to pile it up somewhere. That growing or shrinking pile is part of the climate system. What are the feedbacks here? What can make the pile shrink the fastest? Is that going on now?


Greenland:

Melt and runoff

Ice flow and calving

Antarctica:

Ice flow and calving


- Objectives:1) an estimate of the large temporal variations in melt water output from land-based ice in Greenland 2) an improved understanding of the variability of the ice discharge flux from the Greenland Ice Sheet3) use 1 and 2 to investigate to what extent ice discharge variability from Greenland outlet glaciers is attributable to short term climate variability (e.g., through enhanced basal lubrication from surface melt)

Collaborative Research: A synthesis of rapid meltwater and ice discharge changes: large forcings from the ice with impacts on global sea level and North Atlantic freshwater budgets


First #2 (#1 has more ties to the other SASS projects, so we will spend more time on it)

2) an improved understanding of the variability of the ice discharge flux from the Greenland Ice Sheet• Driving questions: How has glacier terminus

position and ice thickness varied over the last 100+ years, to the extent that it has been documented? How do present rapid changes compare in this context? How do processes near the termini of glaciers reflect changing climate conditions and/or connections to oceanographic processes?

• Inputs: existing observations (historical, satellite-based, direct measurements of speed up and thinning), models, characterizations of outlet glaciers (condition of calving faces, change in front configuration compared to older observations, present drawdown rates), and understanding of ice discharge processes (position in the tidewater glacier cycle); outputs -> constraints on the variability of ice flow contributions to the fresh water output from the ice sheet


Left out of the last figure is the complexity introduced by the tidewater character of all major outlet glaciers

in Greenland

The tidewater glacier cycle as first described by Austin Post: (tidewater glaciers are those terminating in the ocean)

1) Slow advance of the ice front down the fjord, as the glacier moves a stabilizing moraine shoal ahead of it along the bottom - the longer the low elevation part of the glacier gets, the more susceptible it becomes to warm periods

2) A period where the terminus remains in an extended position against the shoal

3) Rapid retreat after a thinning glacier backs off of the moraine shoal; this retreat can pause or reverse if conditions or geometry favor stability


1) an estimate of the large temporal variations in melt water output from land-based ice in Greenland

• Driving question: What is the spatial and temporal variability in Greenland Ice Sheet surface melt and runoff over the past 125+ years?

• Inputs: ice-core records of melt, coastal station and on-ice meteorological records, glacier survey data (snow pits, ablation stakes), remote sensing, and output from multi-decadal regional and global climate analyses; outputs -> the longest possible reconstruction of estimated surface mass balance, melt and runoff from the inland ice.


Ice (& Firn) Core Records of Melt Amount

Sarah Das

WHOI


0

5

10

15

20

25

1675 1700 1725 1750 1775 1800 1825 1850 1875 1900 1925 1950 1975 2000

D5 Melt 10y

Das1 10y

B9 10y

B2 10y

B6 10y

B7 10y

Das2 10y

D4 10y

D5: C-2473m

Das1: SC-2497m

B2: SW-2226m

D4:C-2731m

Das2: SE-2936m

B9: S-2713m

B6, B7: SE-2439m

10-yr running average melt amount(recent record shows 20yr trends between all sites)

Me

lt (t

ota

l cm

of i

ce/y

ear)


0

5

10

15

20

25

1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

D5 Melt 10y

Das1 10y

B9 10y

B2 10y

B6 10y

B7 10y

Das2 10y

D4 10y

20y cyclesCorrelation between melt and decadal cycles of NAO/AO

1y, 10y NAO (IPCC 2001)

Melt (total cm)


Instrumental period 1983-2002Interannual Melt Highly Variable

0

20

40

60

80

100

120

140

20022001200019991998199719961995199419931992199119901989198819871986198519841983

D5 melt

Meltsite2

Meltsite1

Basin9 Melt

Basin8 Melt

Basin7 Melt

Basin6 Melt

Basin2 Melt

Basin1 Melt

PinatuboEl Chichon

Melt (total cm)


Greenland Ice Core Melt Stratigraphy Records CoreSite - previously analyzedCoreSite - analyzed Jan 2006

Core Site Depth (m) Age Lat (°N) Lon (°E) Elev (m)B1 19.87 1976-2002 71.80 317.56 2904B2 16.88 1980-2002 68.32 315.17 2226B6 24.54 1983-2002 66.96 318.25B7 24.47 1983-2002 67.52 319.59 2439B8 30.07 1958-2002 69.84 323.60 2988B9 30.11 1957-2002 65.01 315.13 2713D4 145.43 1738-2002 71.42 315.97 2731D5 148.10 1675-2002 68.50 317.10 2473Das1 83.35 1908-2002 66.00 316.01 2497Das2 83.97 1936-2002 67.53 323.94 2936ACT1 29.71 (not yet dated) TBD 66.00 313.45 2179ACT2 113.77 1770-2004 66.01 314.99 2412ACT3 144.66 (top 73 m dated) <1934-2004 66.00 316.39 2510ACT4 36.14 1979-2004 65.98 317.21 2345Katie 29.98 1934-2004 Summit 3209

Additional core stragraphy analyzed for ARCSS - 354.22 m


Instrumental-era Greenland Temperature and Ice Sheet

Runoff Reconstructions

J. E. Box

Byrd Polar Research Center

Synthesis of Arctic System Science (SASS) Synthesis of Arctic System Science (SASS) Investigator MeetingInvestigator Meeting26–27 March 200626–27 March 2006

Seattle, WashingtonSeattle, Washington


Surface Air Temperature Data• Coastal temperature records

– Nuuk• Seasonal (1873-2001) and Annual (1873-2004)

– Tasiilaq • Seasonal (1895-2001) and Annual (1873-2004)

– Thule• Seasonal and Annual (1947-present)

– Narsarssuaq• Seasonal (1961-present) and Annual (1873-2004)

– Aasiaat• Seasonal and Annual (1951-present)

– Danmarkshavn (1951-present)• Seasonal (1951-2001) and Annual (1948-2004)

• Polar MM5 – 24 km grid – currently 1988-2005– (by Feb. 2006) 1958-2005


Methodology• Correlate time series from each coastal station records

with time series of each Polar MM5 grid cell– Training period

• currently 1988-2005, (N = 18)• (by Feb. 2006) 1958-2005, (N = 48)

• Rank top two sites for each grid cell based on correlation• Store linear regression coefficients (slope and intercept)

for the top two ranked sites on pixel by pixel basis– Only store coefficients if above significance threshold

• Use full record to reconstruct seasonal ice sheet temperatures– 1873-2004 available for annual means, (N = 132)


Regions of Maximum Correlation

Annual


Highest Rank (Primary)2nd Highest Rank (Secondary)

Dominant Annual Correlations


Thul Uper Ilul Nuuk Nars Danm Tasi

Primary 0.06 0.06 0.49 0.15 0.02 0.07 0.13

Secondary 0.10 0.04 0.21 0.46 0.14 0.01 0.01

Overall 0.08 0.05 0.70 0.31 0.08 0.04 0.07

Ilulissat and Nuuk dominate the annual variance

Results of Annual TrainingFraction of grid ‘belonging to’ each site


Annual Training Conclusions

• Iulissat and Nuuk temperatures are better linked with overall ice sheet temperature variability than other sites

• Tasiilaq and Upernavik variability represents maritime locations better than terrestrial locations


Annual Reconstruction


1873-20041873-2004 mean: mean: -21.89 C-21.89 C


Linear Trend: +0.045 C/ decadeLinear Trend: +0.045 C/ decade, 0.6 K increase over 132 years0.6 K increase over 132 years, r r =0.380=0.380


1873-2004 mean: 1873-2004 mean: -13.16 C -13.16 C Linear Trend:Linear Trend: ++0.0530.053 C/ decade, 0.7 K increase over 132 years, C/ decade, 0.7 K increase over 132 years,

r = 0.472r = 0.472


Climatological Conclusions

• Linear model explains < 2/5 of variance

• Inter-decadal oscillations?

• Warming 0.6 C overall, 0.7 C below 1200 m elevation

• 2003 warmest on record, 1883 coldest


Seasonal Correlations

Seasonal


Primary Secondary

Dominant Seasonal Correlations


Seasonal Training Conclusions

• Need to obtain longer seasonal records– Ilulissat– Narsarssuaq– Ivigtut

• Nuuk series not useful to reconstruct winter temperatures– Nuuk winter temperatures never register as

primary maximum correlator, hardly as secondary correlator


Reconstruction Results

Seasonal


Runoff Reconstruction


3) use 1 and 2 to investigate to what extent ice discharge variability from

Greenland outlet glaciers is attributable to short term climate variability (e.g., through enhanced basal lubrication from

surface melt)


Researchers:

Ice flow/change:

Mark Fahnestock, UNH, Ice flow and surface melt, RS of large ice sheets

Martin Truffer, UAF, Ice flow (field and modeling) - outlet glaciers

Ian Joughin, APL/UW, Ice flow - RS of large ice sheets and modeling

Byron Parizek, PSU, Ice flow modeling of large ice sheets

Melt/change:

Richard Alley, PSU, ice sheets and climate

Sarah Das, WHOI, ice core records of melt, RS of melt

Jason Box, BPRC/OSU, Polar meteorology/met stations/Atm modeling

David Rausch, PSU, ice sheet/climate connections, tools for data analysis

(Overlaps and connections between these two groups omitted for simplicity)


End of slideshow

objectives :

Documents

ice thickness

ice sheetleft

ice discharge flux

ice discharge changes

greenland ice sheet3

landbased ice

greenland outlet glaciers

tidewater glaciers