On the long-term memory of the Greenland Ice Sheet (original) (raw)

Millions of Years of Greenland Ice Sheet History Recorded in Ocean Sediments

Polarforschung, 2011

glaciation, which is different from all previous well-documented glacial events. The Greenland ice sheet is a remnant of the giant Northern Hemisphere last glacial maximum ice sheets (in our region composed of the Greenland Ice Sheet with the adjacent Innuitian Ice Sheet to the West, which again was connected to the North American Laurentide Ice Sheet) and represents hence a spectacular anomaly. The future of these ice sheets is, because of political, socioeconomic and scientific reasons, subject to intensive debate and much speculation (HUYBRECHTS et al. 2004). In the light of the ongoing discussion of its potential future instability it is of paramount importance for humanity on local (habitats on Greenland), regional (fisheries, fresh water export from Greenland) and global scales (potential for eustatic sea-level rise) to resolve the long-term natural variability of the Greenland ice sheet. In this paper, therefore, we will briefly attempt to review the evidence of the history of the Greenland Ice Sheet based on Quaternary and Tertiary marine sediment cores and their icerafting record of coarse debris because they cover periods with substantially warmer and colder climates as compared to today and because we hope to be able to deduce how the ice on Greenland responded to different climate scenarios. A similar approach had been taken recently by ALLEY et al. 2010; they concentrated on much shorter time scales, but came to conclusions quite similar to our study. The emphasis of the present paper is mostly on longer Pleistocene and Tertiary records because the Greenland ice cores document without doubt that the Greenland Ice Sheet has existed continuously since pre-Eemian times (WILLERSLEV et al. 2007). Geological records from Tertiary and Quaternary terrestrial and oceanic sections have documented the presence of ice caps and sea ice covers both in the Southern and the Northern hemispheres since Eocene times, approx. 45 Ma (THOMAS 2008). Deep-sea sediment cores with their records of icerafting from off NE Greenland, Fram Strait and to the south of Greenland suggest the more or less continuous existence of the Greenland ice sheet since 18 Ma (WOLF & THIEDE 1991), maybe much longer, and thus we need to investigate the history of the natural variability of the Greenland ice sheet over time scales far beyond those presently available from ice cores (VINTHER et al. 2010). The present situation illustrates that the other large northern hemisphere ice sheets vaned during interglacials (cf. VINTHER et al. 2009 for the present interglacial), thereby suggesting that Greenland was and is the main source of coarse terrigenous ice-rafted debris (IRD) during relatively warm climatic scenarios.

Chronology of the last recession of the Greenland Ice Sheet

Journal of Quaternary Science, 2002

A new deglaciation chronology for the ice-free parts of Greenland, the continental shelf and eastern Ellesmere Island (Canada) is proposed. The chronology is based on a new compilation of all published radiocarbon dates from Greenland, and includes crucial new material from southern, northeastern and northwestern Greenland. Although each date provides only a minimum age for the local deglaciation, some of the dates come from species that indicate ice-proximal glaciomarine conditions, and thus may be connected with the actual ice recession. In addition to shell dates, dates from marine algae, lake sediments, peat, terrestrial plants and driftwood also are included. Only offshore and in the far south have secure late-glacial sediments been found. Other previous reports of late-glacial sediments (older than 11.5 cal. kyr BP) from onshore parts of Greenland need to be confirmed. Most of the present ice-free parts of Greenland and Nares Strait between Greenland and Ellesmere Island were not deglaciated until the early Holocene.

Million years of Greenland Ice Sheet history recorded in ocean sediments

Polarforschung 80 Pp 141 149, 2011

Holocene thinning of the Greenland ice sheet

Nature, 2009

On entering an era of global warming, the stability of the Greenland ice sheet (GIS) is an important concern 1 , especially in the light of new evidence of rapidly changing flow and melt conditions at the GIS margins 2 . Studying the response of the GIS to past climatic change may help to advance our understanding of GIS dynamics. The previous interpretation of evidence from stable isotopes (d 18 O) in water from GIS ice cores was that Holocene climate variability on the GIS differed spatially 3 and that a consistent Holocene climate optimum-the unusually warm period from about 9,000 to 6,000 years ago found in many northernlatitude palaeoclimate records 4 -did not exist. Here we extract both the Greenland Holocene temperature history and the evolution of GIS surface elevation at four GIS locations. We achieve this by comparing d 18 O from GIS ice cores 3,5 with d 18 O from ice cores from small marginal icecaps. Contrary to the earlier interpretation of d 18 O evidence from ice cores 3,6 , our new temperature history reveals a pronounced Holocene climatic optimum in Greenland coinciding with maximum thinning near the GIS margins. Our d 18 O-based results are corroborated by the air content of ice cores, a proxy for surface elevation 7 . State-of-the-art ice sheet models are generally found to be underestimating the extent and changes in GIS elevation and area; our findings may help to improve the ability of models to reproduce the GIS response to Holocene climate.

History of the Greenland Ice Sheet: paleoclimatic insights

Quaternary Science Reviews, 2010

Paleoclimatic records show that the Greenland Ice Sheet consistently has lost mass in response to warming, and grown in response to cooling. Such changes have occurred even at times of slow or zero sea-level change, so changing sea level cannot have been the cause of at least some of the ice-sheet changes. In contrast, there are no documented major ice-sheet changes that occurred independent of temperature changes. Moreover, snowfall has increased when the climate warmed, but the ice sheet lost mass nonetheless; increased accumulation in the ice sheet's center has not been sufficient to counteract increased melting and flow near the edges. Most documented forcings and ice-sheet responses spanned periods of several thousand years, but limited data also show rapid response to rapid forcings. In particular, regions near the ice margin have responded within decades. However, major changes of central regions of the ice sheet are thought to require centuries to millennia. The paleoclimatic record does not yet strongly constrain how rapidly a major shrinkage or nearly complete loss of the ice sheet could occur. The evidence suggests nearly total ice-sheet loss may result from warming of more than a few degrees above mean 20th century values, but this threshold is poorly defined (perhaps as little as 2 C or more than 7 C). Paleoclimatic records are sufficiently sketchy that the ice sheet may have grown temporarily in response to warming, or changes may have been induced by factors other than temperature, without having been recorded.

Brief communication
Greenland's shrinking ice cover: "fast times" but not that fast

The Cryosphere, 2012

ABSTRACT A map of Greenland in the 13th edition (2011) of the Times Comprehensive Atlas of the World made headlines because the publisher's media release mistakenly stated that the permanent ice cover had shrunk 15% since the previous 10th edition (1999) revision. The claimed shrinkage was immediately challenged by glaciologists, then retracted by the publisher. Here we show: (1) accurate maps of ice extent based on 1978/87 aerial surveys and recent MODIS imagery; and (2) shrinkage at 0.019% a-1 in ~50 000 km2 of ice in a part of east Greenland that is shown as ice-free in the Times Atlas.

250 000 years in history of Greenland's ice sheet

1996

C a lcul a ti ons ha\'e bcc n co ndu cted ro r th c geome tri c e\'o luti o n o r the G ree nl a n d ice sh ee t throug h th e las t 250000 \'Ca rs or its clim a te hi stor y, .\ n exte nd ed \'C rsio n o f Ca lo\"s three-dim e nsio n a l ice-shee t m od el is w,ed . i, e, ice is m od e ll ed as a \'iseo us th er momeeh a n ica 11 y co u plrd fl u id \I'i t h pOlI'(~r-I a w rh eo logy u nd erla i n b y a h eat-co nd uc ting lith osp h ere susce pt ibl e to bed rock sin king. Th e sh a ll OlI'-i ee ap proxima ti o n is im posed a nd th e simplifi cd equ at io ns a rc nLlm eri ca ll l' integra ted b y ri nitcd ifle re nce a p p rox im at io n usin g a cc ntred staggered A ra ka\\'a g rid . Thi s sys tem is d ri \T n b y d a ta o bta in ed fro m th e E uropea n G ree nl a nd I ce Co re Projec t (G RIP ). Th e pa ra m cteriza ti o n o f th e a tmos ph e ri c tempe ra ture is b ased o n d ata fro m Oh m ura, preeipi ta ti o n da ta a rc ta ken fi'o m 0 h m u ra a nd R ee h a nd i m plrm e n ted as 5h Ol\'l1 by Ca lOl', T o pogra phi c da ta [o r th e p rese nt o bse n 'ed con d iti o ns a re th ose of L e trcguilh', T h e res ult a nt 250 kyea r m od el integra ted to pogra ph y is quite cl ose to th a t o bt a in ed fi'o m a stead y-sta te ca lcul a ti on und er prese nt co nditi o ns, For th e ca lcul at io ns prese nted . Green land's no rth d o m e see m s to be mo re sel1siti n' to ch a n ges in prec ip it a ti o n th a n its so uth d ome. \\' hil e t he h eig ht o f th e no nh d o m e is direc t'" rel a ted to th e a tm os ph eri c tempe ra ture, th e h eig ht o f th e so uth d o m e is ilwe rsel y rela ted to thi s \'a ri a bl e. In th e sou th , c ha nges in ice d yn am ics du e to a c h a nge in ice tempe ra ture oppose ch a n ges in prec ip ita ti o n, Th e ca lcul a ti o n s a re \'isua li zed in a sh o rt \'id eo c lip th a t is ke pt o n file with th e a uth o rs.

A persistent and dynamic East Greenland Ice Sheet over the past 7.5 million years

Nature, 2016

Limited data constrain the multi-million year behavior of ice sheets because repeated ice advances overrun and erode the land-based record of prior glaciations 1-3. Terrestrial deposits of ancient glacial and interglacial periods are rare, isolated, and poorly dated 4 ; thus, they cannot provide a continuous record of ice sheet behavior 2. In contrast, material shed from continents is preserved as marine sediment that can be analyzed to infer glacial process and history. Here we capitalize on the marine record to show that East Greenland experienced deep, ongoing glacial erosion over the past 7.5 Myr. Our conclusions are based on a progressive, order-of-magnitude decline in the concentration of in situ-produced cosmogenic 10 Be and the changing ratio of 26 Al to 10 Be of quartz sand, isolated from icerafted debris in sediment cores 5,6 and corrected for radiodecay on the sea floor. The 26 Al to 10 Be ratio indicates that early Pleistocene East Greenland ice cover was dynamic; in

Brief communication Greenland’s shrinking ice cover:“fast times” but not that fast

2012

A map of Greenland in the 13th edition (2011) of the Times Comprehensive Atlas of the World made headlines because the publisher's media release mistakenly stated that the permanent ice cover had shrunk 15 % since the previous 10th edition (1999) revision. The claimed shrinkage was immediately challenged by glaciologists, then 5 retracted by the publisher. Here we show: (1) accurate maps of ice extent based on 1978/1987 aerial surveys and recent MODIS imaging; and (2) shrinkage at 0.019 % a −1 in ∼ 50 000 km 2 of ice in a part of east Greenland that is shown as ice-free in the Times Atlas. Abstract 5, Abstract 5, Abstract 5, Abstract 5,

On the long-term memory of the Greenland Ice Sheet (original) (raw)

Related papers