Mass Balance of North Greenland

摘要: The report “North and northeast Greenland ice discharge from satellite radar interferometry” by E. J. Rignot et al . ([9 May, p. 934][1]) concludes that north glaciers are now discharging an excess of 8 cubic kilometers per year glacial into the ocean, causing regional sheet thinning a positive contribution to sea-level rise. This conclusion is based on comparison total across grounding line (49 year) measured with (ERS) interferometry balance grounding-line (41 calculated compilation observed accumulation data ([1][2]) ablation model ([2][3]). We find uncertainties two terms so large relatively small deficit does not permit conclusions about present state sector. The information 251 pits cores spread over (only 30 inside sector in question) retrieved 1913 1990. rate at each locations determined as average varying number annual values (typically between 5 10 values). mean coefficient variation precipitation 0.26 ± 0.06 ([3][4]). Thus, 5- 10-year value may deviate 10% or more long-term value. modeled ablation, depending few air temperature observations ([4][5]), also uncertain. Therefore, discharge, sparse, temporally inhomogeneous data, has uncertainty least ([5][6]). In 1996, field investigations were initiated Nioghalvfjerdsfjord Gletscher Geological Survey Denmark (GEUS) Danish Center for Remote Sensing (DCRS) ([6][7]). study comprises surface mass balance, climate, glacier dynamics, measurements melting bottom floating tongue. Our situ confirmed high melt rates found However, we thickness be no than 600 meters—22% less estimated Their estimate (15.74 appears 3.5 too high. In checking discharges other do exist. our results show reported have magnitude similar discharge. therefore conclude difference significant. question potential deriving accurate velocities using techniques, nor use such assessing ice-sheet comparing discharges. do, however, believe latter requires thickness, accumulation, available. 1. [↵][8]A. Ohmura N. Reeh, Glaciol. 37 , 140 (1991). 2. [↵][9]N. Polarforschung 59 113 3. [↵][10]1. R. Braithwaite Global Planet. Change 9, (1994). [OpenUrl][11][CrossRef][12][Web Science][13] 4. [↵][14]A. Ohmura, Z. Gletscherkun. Glazialgeol. 23 1 (1987). 5. [↵][15]As further illustration uncertainty, flux same models ([1][2], [2][3]) al. used 43 49 resolution applied digital evaluation model. When compared findings this result suggests year. 6. [↵][16]H. H. Thomsen Geol. Surv. Bull. 176 95 (1997). # {#article-title-2} Response: agree Reeh sparse it much above uncertainty. volume was quoted report. budget reads net loss 7 year, suggestive negative balance. We Nioghalvfjerdfjord airborne ice-sounding (ISR) provided continuous, smooth profile measurement points, good agreement laser altimetry portion glacier. As shown report, ISR located close margin, where presumably thinner center 650 meters line. Comparison collected summit core showed within ±10 actual thickness. confident accurate. Glacial vary significantly space, especially near line, basal pronounced. On Petermann Gletscher, 250-meter decrease 20 kilometers, 200-meter peak-to-peak variations immediately past drilled determine must been done point decreasing rapidly. To calculate melt, high-resolution elevation produced colleagues Kort Matrikelstyrelsen institute. their reference (5) consistent calculations. residual simply precision which without data. As state, studies remain essential component efforts sheet. contains early part larger Program Arctic Regional Climate Assessment (PARCA) funded U.S. National Aeronautics Space Administration (NASA). program includes shallow coring snow automated weather stations energy studies, sounding radars measuring repeat-pass noting changes volume. [1]: /lookup/doi/10.1126/science.276.5314.934 [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: #ref-4 [6]: #ref-5 [7]: #ref-6 [8]: #xref-ref-1-1 "View text" [9]: #xref-ref-2-1 2 [10]: #xref-ref-3-1 3 [11]: {openurl}?query=rft.jtitle%253DGlobal%2BPlanet.%2BChange%26rft.volume%253D9%26rft.spage%253D251%26rft.atitle%253DGLOBAL%2BPLANET%2BCHANGE%26rft_id%253Dinfo%253Adoi%252F10.1016%252F0921-8181%252894%252990019-1%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [12]: /lookup/external-ref?access_num=10.1016/0921-8181(94)90019-1&link_type=DOI [13]: /lookup/external-ref?access_num=A1994PZ12700006&link_type=ISI [14]: #xref-ref-4-1 4 [15]: #xref-ref-5-1 [16]: #xref-ref-6-1 6 text"