Tracking the rapid pace of a retreating ice sheet

doi:10.1126/science.abc3583

GSTDTAP > 气候变化

DOI	10.1126/science.abc3583
	Tracking the rapid pace of a retreating ice sheet
	Martin Jakobsson
	2020-05-29
发表期刊	Science
出版年	2020
英文摘要	Glaciers and ice sheets that extended from land into the ocean left traces behind on the seafloor called submarine glacial landforms. If mapped in sufficient detail and interpreted correctly, they can provide comprehensive information into past behaviors of glaciers and ice sheets. On page 1020 of this issue, Dowdeswell et al. ([ 1 ][1]) describe the mapping of glacial landforms in the seafloor created by a rapidly retreating ice sheet on the eastern Antarctic Peninsula. The high-resolution data suggest that the retreat rate was paced by ocean tides and at least an order of magnitude faster than modern rates observed in other sensitive areas, such as West Antarctica where the ice sheet drains into the ocean at several locations ([ 2 ][2]). The retreat on the eastern Antarctic Peninsula took place more than 10,000 years ago, pointing out the challenges in predicting the sea-level rise contribution from retreating glaciers and ice sheets in a warming climate. Glacial landforms have long been used to reconstruct ice-sheet extent and, specifically, its retreat pace and dynamics. At a meeting in Stockholm 1889 ([ 3 ][3]), the Swedish geologist Gerard De Geer presented observations of moraines, a general term to describe glacial landforms that consist of a mixture of debris (mainly sediments and rock fragments) deposited and sometimes molded by glacier ice. The moraines were observed in Sweden northwest of Stockholm. They generally took the form of ridges, between 1 and 5 m high and a few to slightly more than 10 m wide, gently winding through the landscape for several kilometers. There were several parallel lines of the moraines mapped in the landscape 200 to 300 m apart. De Geer compared the distances between the parallel moraines with the notion prevailing at the time that Swiss glaciers could retreat up to 70 m during 1 year. He put forward a hypothesis that the moraines were deposited during winter along the margin of the Scandinavian Ice Sheet when it made a seasonal halt during its retreat over the landscape. The distance between the moraines of 200 to 300 m represented therefore a yearly retreat rate of the ice sheet. About 11,000 years ago, when the Scandinavian Ice Sheet's margin was located in the area northwest of Stockholm, land was depressed below the contemporary water level of the Baltic Sea ([ 4 ][4]). This meant that the moraines described by De Geer were formed at the ice margin under water. It would, however, take nearly a century after De Geer's presentation before geophysical seafloor mapping reached the technical capacity to be able to survey features with reliefs of only a meter or so. These “De Geer moraines” are similar in some aspects to the submarine glacial landforms from Antarctica mapped, described, and interpreted by Dowdeswell et al . Dowdeswell et al. describe the appearance of the glacial landforms as if “ladders with numerous rungs” had been left embedded in the seafloor (see the figure). Similar features have been mapped and described previously, although often at lower resolution, around Antarctica ([ 5 ][5]–[ 7 ][6]) and in the Arctic ([ 8 ][7]). However, subtle differences with respect to appearances and settings led to different interpretations of the formation mechanisms. What is common to all previous studies and that of Dowdeswell et al. is that the proposed formation mechanisms involve ocean tides as a “pacemaker.” The glacier ice, either of an iceberg or the margin of an outlet glacier draining an ice sheet into the ocean, can be slightly lifted from the seafloor during high tide. When settling again during low tide, a small ridge is formed on the seafloor by squeezing of sediments along the bottom edge of the iceberg or the outlet glaciers' margin. The submarine glacial landforms mapped in previous studies, referred to as “corrugation ridges” or “washboard patterns,” were interpreted to have been formed in the wake of large grounded icebergs ([ 7 ][6]), or at the trailing end of drifting armadas of mega-sized icebergs calved during an ice shelf break-up ([ 5 ][5]), or underneath a thick ice shelf that floated close above the seafloor but bearing a protruding ice keel that could ground periodically with the tidal movement ([ 6 ][8]). All of these proposed formations of small, extremely regular ridge-like features in seafloor sediments take place at the tail end of the ice or by a bulging ice keel, moving away from the newly formed ridge without running over and destroying them. The ladders and rungs, by contrast, are formed at the front of the grounded ice margin, implying that when the ice moves forward, the features will be destroyed. Glacier ice moves by gravity from higher elevation on land toward the ocean, implying that the ice margin's grounding line must back-step for every formed rung. This can only happen if mass is lost at a regular pace. The precise ice dynamics of this regular mass loss that is paced by tide is not resolved and presents a challenge for the ice-modeling community. Although the mechanical details are yet to be characterized, Dowdeswell et al. have used the idea that the ocean tide-paces the formation of the rungs to convert the distances between the rungs to a retreat rate of the ice sheet. ![Figure][9] Unraveling glacial dynamics Seafloor patterns can reveal grounded ice margin (left), iceberg (right), and under ice (not shown) scenarios. GRAPHIC: C. BICKEL/ SCIENCE Perhaps most importantly, Dowdeswell et al. demonstrate the immense value of high-resolution seafloor mapping in unraveling the complex history of glacial dynamics. Only fractions of the seafloor in the hard-to-access ice-covered polar regions are mapped, and much is left to discover and learn. Scientists working on submarine glacial landforms have experienced a breakthrough in seafloor mapping capabilities similar to what their colleagues working in the terrestrial realm achieved when high-resolution terrain models of the land surface became available through airborne and satellite technology. Indeed, Dowdeswell et al. used the latest geophysical mapping technology mounted on an unmanned mini-submarine to survey the seafloor. Nonetheless, the pace of mapping the oceans, specifically in remote areas, is orders of magnitude slower because of the logistical difficulties and the fact that the ocean is in the way. 1. [↵][10]1. J. A. Dowdeswell et al ., Science 368, 1020 (2020). [OpenUrl][11][Abstract/FREE Full Text][12] 2. [↵][13]1. E. Rignot, 2. J. Mouginot, 3. M. Morlighem, 4. H. Seroussi, 5. B. Scheuchl , Geophys. Res. Lett. 41, 3502 (2014). [OpenUrl][14][CrossRef][15][GeoRef][16][Web of Science][17] 3. [↵][18]1. E. Erdmann , Geol. Foren. Stockh. Forh. 11, 73 (1889). [OpenUrl][19] 4. [↵][20]1. S. Björck , Quat. Int. 27, 19 (1995). [OpenUrl][21] 5. [↵][22]1. M. Jakobsson et al ., Geology 39, 691 (2011). [OpenUrl][23][Abstract/FREE Full Text][24] 6. [↵][25]1. A. G. C. Graham et al ., J. Geophys. Res. Earth Surf. 118, 1356 (2013). [OpenUrl][26] 7. [↵][27]1. R. Lien, 2. A. Solheim, 3. A. Elverhoi, 4. K. Rokoengen , Polar Res. 7, 43 (1989). [OpenUrl][28][CrossRef][29][GeoRef][30] 8. [↵][31]1. K. Andreassen, 2. M. C. M. Winsborrow, 3. L. R. Bjarnadóttir, 4. D. C. Rüther , Quat. Sci. Rev. 92, 246 (2014). [OpenUrl][32][CrossRef][33] [1]: #ref-1 [2]: #ref-2 [3]: #ref-3 [4]: #ref-4 [5]: #ref-5 [6]: #ref-7 [7]: #ref-8 [8]: #ref-6 [9]: pending:yes [10]: #xref-ref-1-1 "View reference 1 in text" [11]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.aulast%253DDowdeswell%26rft.auinit1%253DJ.%2BA.%26rft.volume%253D368%26rft.issue%253D6494%26rft.spage%253D1020%26rft.epage%253D1024%26rft.atitle%253DDelicate%2Bseafloor%2Blandforms%2Breveal%2Bpast%2BAntarctic%2Bgrounding-line%2Bretreat%2Bof%2Bkilometers%2Bper%2Byear%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.aaz3059%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/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEzOiIzNjgvNjQ5NC8xMDIwIjtzOjQ6ImF0b20iO3M6MjI6Ii9zY2kvMzY4LzY0OTQvOTM5LmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ== [13]: #xref-ref-2-1 "View reference 2 in text" [14]: {openurl}?query=rft.jtitle%253DGeophysical%2BResearch%2BLetters%26rft.stitle%253DGeophysical%2BResearch%2BLetters%26rft.aulast%253DRignot%26rft.auinit1%253DE.%26rft.volume%253D41%26rft.issue%253D10%26rft.spage%253D3502%26rft.epage%253D3509%26rft.atitle%253DWidespread%252C%2Brapid%2Bgrounding%2Bline%2Bretreat%2Bof%2BPine%2BIsland%252C%2BThwaites%252C%2BSmith%252C%2Band%2BKohler%2BGlaciers%252C%2BWest%2BAntarctica%252C%2Bfrom%2B1992%2Bto%2B2011%26rft_id%253Dinfo%253Adoi%252F10.1002%252F2014GL060140%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 [15]: /lookup/external-ref?access_num=10.1002/2014GL060140&link_type=DOI [16]: /lookup/external-ref?access_num=2014066126&link_type=GEOREF [17]: /lookup/external-ref?access_num=000337610200024&link_type=ISI [18]: #xref-ref-3-1 "View reference 3 in text" [19]: {openurl}?query=rft.jtitle%253DGeol.%2BForen.%2BStockh.%2BForh.%26rft.volume%253D11%26rft.spage%253D73%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 [20]: #xref-ref-4-1 "View reference 4 in text" [21]: {openurl}?query=rft.jtitle%253DQuat.%2BInt.%26rft.volume%253D27%26rft.spage%253D19%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 [22]: #xref-ref-5-1 "View reference 5 in text" [23]: {openurl}?query=rft.jtitle%253DGeology%26rft_id%253Dinfo%253Adoi%252F10.1130%252FG32153.1%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 [24]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NzoiZ2VvbG9neSI7czo1OiJyZXNpZCI7czo4OiIzOS83LzY5MSI7czo0OiJhdG9tIjtzOjIyOiIvc2NpLzM2OC82NDk0LzkzOS5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30= [25]: #xref-ref-6-1 "View reference 6 in text" [26]: {openurl}?query=rft.jtitle%253DJ.%2BGeophys.%2BRes.%2BEarth%2BSurf.%26rft.volume%253D118%26rft.spage%253D1356%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 [27]: #xref-ref-7-1 "View reference 7 in text" [28]: {openurl}?query=rft.jtitle%253DPolar%2BResearch%26rft.stitle%253DPolar%2BResearch%26rft.volume%253D7%26rft.issue%253D1%26rft.spage%253D43%26rft.epage%253D57%26rft.atitle%253DIceberg%2Bscouring%2Band%2Bsea%2Bbed%2Bmorphology%2Bon%2Bthe%2Beastern%2BWeddell%2BSea%2Bshelf%252C%2BAntarctica%26rft_id%253Dinfo%253Adoi%252F10.1111%252Fj.1751-8369.1989.tb00603.x%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 [29]: /lookup/external-ref?access_num=10.1111/j.1751-8369.1989.tb00603.x&link_type=DOI [30]: /lookup/external-ref?access_num=2004034231&link_type=GEOREF [31]: #xref-ref-8-1 "View reference 8 in text" [32]: {openurl}?query=rft.jtitle%253DQuat.%2BSci.%2BRev.%26rft.volume%253D92%26rft.spage%253D246%26rft_id%253Dinfo%253Adoi%252F10.1016%252Fj.quascirev.2013.09.015%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 [33]: /lookup/external-ref?access_num=10.1016/j.quascirev.2013.09.015&link_type=DOI
领域	气候变化 ; 资源环境
URL	查看原文
引用统计
文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/271745
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	Martin Jakobsson. Tracking the rapid pace of a retreating ice sheet[J]. Science,2020.
APA	Martin Jakobsson.(2020).Tracking the rapid pace of a retreating ice sheet.Science.
MLA	Martin Jakobsson."Tracking the rapid pace of a retreating ice sheet".Science (2020).