1,721,051 research outputs found
Glacial Geology and Geomorphology of Terra Nova Bay (Antarctica).
No full textDuring the two first Italian Antarctic Expeditions (1985/86 and 1986/87) glacial-geological and geomorphological research has been carried out in the area of Terra Nova Bay. In particular the Cenozoic glacial sediments, the Holocene raised beaches and the Holocene glacier fluctuations have been investigated. Three main glacial drifts have been recognized. The youngest drift consists of a massive matrix-supported diamict extending up to about 350 m a.s.l. on the Northern Foothills, where it contains fragments of Pelecypods and Serpulids; it was deposited by a grounded ice-shelf during the last glaciation. In the interior mountains the upper limit of the drift rises up to about 1000 m a.s.l. The young glacial drift is characterized by frequent ice-cored topography, initial weathering stages, slightly stained granitic boulders without cavernous weathering, exept in the coastal belt.
The older drift, very thin and discontinuous, occurs above the previous one, up to about 600 m on the Northern Foothills, and it is characterized by red stained granitic boulders affected by cavernous weathering.
A third, oldest drift occurs up to 800 m a.s.l., composed of large and scattered boulders, strongly oxidized and affected by cavernous weathering, locally resting on a strongly developed red paleosol.
At higher elevations up to about 1000 m round topped glacialy abraded reliefs, devoid of any glacial cover, can be observed and represent evidence of a still older glacial stage.
Holocene beaches raised up to 30 m are well known at Terra Nova Bay (Inexpressible Island and Gerlache Inlet). In addition to the ones described by previous authors, other emerged beaches have been found in several localities on the coast of the Northern Foothills, near Evans Cove and at Edmonson Point. It is possible to distinguish two groups of emerged beaches: the first one consists of the beaches at Inexpressible Island and the Northern Foothills, ranging in altitude up to about 30 m a.s.l.; the second group, not higher than 7 m, is present at the foot of northern and eastern slopes of Mt. Melbourne. In our opinion, higher (and older) beaches are lacking in the Mt. Melbourne region because of recent volcanic activity.
Several C-14 ages have been obtained from penguin remains collected in the organic horizons developed on the raised beaches; other C-14 ages were supplied by shells (Pelecypods, Barnacles and Corals) collected in marine sediments. We obtained a range for the glacio-isostatic uplift rate suggesting a value lower than 2.1 mm/yr in the last two millennia and a value lower than 4.5 but greater than 1.8 mm/yr in the four previous millennia.
Evidence of Holocene glacier fluctuations have been observed close to the terminal margins of the outlet glaciers, of the ice shelves and of the local glaciers. Groups of Holocene ice-cored moraines document very small fluctuations of the ice extent of the outlet glaciers. The moraines can be differentiated on the basis of weathering degree, color of staining, development of deflation pavements, lichen cover and development of patterned ground.
The Hells Gate Ice Shelf and the Nansen Ice Sheet (Shelf) advanced, during Holocene, probably because of the isostatic uplift of the coast.
Near the termini of the small local glaciers at least two ice-cored moraines can be observed, showing the same differentiations mentioned above for the outlet glaciers. The moraines of the Strandline Gl. (Tethys Bay) rest on raised beaches and document two advance that were separated by a conspicuous lapse of time. They reached, respectively, a distance of more than 60 m and about 50 m from the present front. On the basis of the relationships between moraines and raised beaches, the oldest moraine has to be younger than about 5800-3800 yr B.P. and both were possibly deposited during the Late Holocene.
At the foot of the eastern slope of Mt. Melbourne, near Edmonson Point, a glacier has been studied. On its south side, a complex of ice-cored moraines is to be found. It consists of a thin cover of marine sediments (laminated sands) that contains several articulated shells of Adamussium colbechi and Laternula elliptica. The fossiliferous sediments appear to have been frozen at the sole of the glacier and then entrained forward and laterally up to the surface (37 m a.s.l.), testifying to an advance of the glacier greater than 130 m that must have occured later than 600-1000 yr B.P
Holocene raised beaches at Terra Nova Bay (Victoria Land, Antarctica)
No full textMore than 40 14C dates for raised beaches at Terra Nova Bay ranging from the present to 7505 ± 230 yr B.P. supply minimum or maximum limiting ages that bracket a relative sea-level curve for this part of Victoria Land. Most samples consist of guano and penguin remains collected from abandoned nesting sites on beach deposits. Up to four 14C dates in stratigraphic sequence have been obtained in two soil profiles. Other samples consist of marine shells collected both within and on the surface of raised beaches. All 14C ages for organisms that lived or fed in circumantarctic waters were corrected for a large reservoir effect. The calibrated ages delimit a first relative sea-level curve for Victoria Land. Rates of uplift ranged from about 10 mm/yr following deglaciation to about 2 mm/yr in the last 3 millennia. Widespread presence of Adélie penguin nesting sites suggests that Terra Nova Bay was deglaciated before 7065 ± 250 yr B.P. ( 7059 6439 cal yr B.P.), when environmental conditions in the coastal area were similar to the present ones. © 1991
Holocene glacier variations in the Terra Nova Bay area (Victoria Land, Antarctica)
No full textInformation on Holocene glacier variations in Antarctica is limited and sometimes contradictory.
However, if the behaviour of the glaciers during the recent past can be clarified, their sensitivity to climatic
changes can be evaluated and their contribution to the sea levelvariation may be predicted. Through the study
of local glaciers and floating ice shelves in the Terra Nova Bay area, new information has been gathered.
Between 7500 and 5000 yr B.P., after the glacial retreat which followed the Last Glacial Maximum, the Nansen
Ice Sheet and the Hells Gate ice shelf were a few kilometres less extensive than they are now. During the second
half of the Holocene, both the local glaciers and the ice shelves advanced to positions that were more extensive
than their present ones, although not all the variations are adequately dated. A retreat phase of the Edmonson
Point glacier occurred during late Middle Ages between 920-1050 A.D. and 1270-1400 A.D. as documented
by ten 14C dates obtained from shells in ice-cored moraines. A subsequent advance occurred after the 15th
century in a period corresponding to the Little Ice Age
Variazioni glaciali e climatiche in Antartide
No full textGli studi geomorfologici e I'analisi di «archivi ecologici» come i siti di nidificazione dei pinguini e delle procellarie hanno consentto di ricostruire I'evoluzione dei margini glaciali negli ultimi 20 000 anni
The alpine Iceman and Holocene climatic change
No full textThe finding of a prehistoric mummified corpse at the upper edge of the accumulation area of an alpine glacier, together with its unique set of artifacts, provided new information on glacier dimensions during the little-known phases of major glacier shrinkage that characterized the warmest parts of the Holocene. The sudden burial of the corpse in a permanent snow cover occurred 5300-5050 cal yr B.P., indicating a significant climatic change that induced glacier expansion at the beginning of Neoglaciation. New geomorphologic data and two AMS 14C ages from buried soils suggest that the present glacier size, following over 100 yr of shrinkage, is comparable to that immediately preceding Neoglaciation. Therefore, we can deduce that the current global climatic warming may have interrupted the environmental conditions prevailing in the Alps during Neoglacial time, restoring characteristics similar to those prevailing during the climatic optimum that were never achieved during the second half of the Holocene. © 1996 University of Washington
Indagini geomorfologiche e glaciologiche nella Terra Vittoria (seconda Spedizione del Programma Nazionale di Ricerche in Antartide, 1986-1987). Geomorphological and glaciological observations at Terra Nova Bay, Victoria Land (Second expedition of the Italian Antarctic Research Program, 1986/87)
No full textDuring the second Italian Antarctic Expedition in 1986/87 geomorphological
and glaciological researches have been carried out, mainly
concerning Cenozoic glacial deposits, Holocene glacier fluctuations and
Holocene raised beaches. Three main glacial drifts have been recognised,
the oldest being associated with well developed red paleosol. The
youngest drift all along the coastal belt is composed of till with a muddy
matrix, locally rich in fragments of Pelecypods and Serpulids
deposited by a grounded ice shelf. At Black Ridge a lateral moraine
is present marking the boundary between the youngest and the older
drifts, elsewhere identifiable only by weathering evidences.
Holocene glacier fluctuations ha ve been recognised, particularly in
the local alpine glaciers: On the basis of the relationships between
moraines and raised beaches at least two glacial advances can be inferred
in Late Holocene. Near Edmonson Point ice-cored moraines composed
of fossiliferous beach sand and gravel testify an advance younger
than 2 200 ± 45 yr B;P.
Holocene beaches raised up to 30 m are well known at Terra Nova
Bay (Inexpressible Island, Gerlache Inlet) . More to the North, raised
beaches have been observed along the coast of Wood Bay, up to an elevation
of about 7 m. Numerous new samples of organic remaines associated
with the raised beaches (penguin guano and bones, Seal bones, Pelecypods,
Barnacles and Corals) have been collected. 14C ages (not corrected) so far
obtained range from 5 770 ± 60 yr B.P. to the present.
Preliminary glaciological observations and measurements have been
conducted on the Strandline Glacier and a geomorphological map at
a scale 1:10 000 has been surveyed for an area of the Northern Foothills
near the Italian Station.
Reconnaissance geomorphological observations have been carried
out in the area extending from the David Glacier to the Tinker Glacier and studies on periglacial and weathering forms have been pursued
Risultati preliminari delle ricerche geomorfologiche e glaciologiche svolte nella seconda spedizione del P.N.R.A
No full textGlacial-geologicql observations have been carried on at Terra Nova Bay. Evidences of at least
four glaciations have been observed: the oldest two are referred to the pre-Pleistocene. AI/long
the coeste! belt the youngest glacial drift contains fragments of marine shells, supporting the
hypothesis of the expansion of a grounded Ross Ice Shelf.
Holocene glacier fluctuations have been studied and two minor neoglacial advances have
been observed. Near Edmonson Point a glacier advance has been dated to about 1000 years
BP .
14C ages have been obtained for Holocene raised beaches, ranging from 5770 + 60 to the
present. A rate of 3 mm1year can be preliminarly estimated for the isostatic uplift during the last
4500 years.
A geomorphological map at a scale 1:10.000 has been produced for the area surrounding the
Italian station
Glaciers and ice sheets: Current status and trends
No full textAbout 10 % of the land surface on Earth is covered by glacier ice, with an estimated total volume equivalent to about 66 m of potential sea-level rise. Almost the totality (99 %) of this volume is locked in the polar ice sheets, while less than 1 % forms all the other mountain glaciers and ice caps. In the last three decades, the general retreat of the mountain glaciers and the accelerated flow and ice loss from several outlet glaciers draining the Greenland and the Antarctic ice sheets came to general attention as a major evidence of climate warming and as a potential contribution to the sea-level rise, to local shortage of water resources and to other environmental risks. Here, we present a short review of the most recent data and assessments on the present status and on trends of glaciers and polar ice sheets. The Greenland ice sheet (12 % of total glacier ice volume) over the last three decades showed an increase of the extent of the surface melt area and an acceleration of many marine-terminating glaciers; as a consequence, the ice sheet is losing ice at an increasing rate that reached -263 ± 30 Gt/year in the 2005-2010 time interval, equivalent to a sea-level rise of 0.72 ± 0.08 mm/year. The much larger, higher and colder composite Antarctic ice sheet (87 % of total glacier ice volume), in the same 2005-2010 time interval, had an ice loss of -81 ± 37 Gt/year. Mountain glaciers and ice caps are retreating in all the major glacierized regions, with the exception of a few mountain areas where contrasting patterns have been observed. Although containing less than 1 % of the total glacier ice, mountain glaciers and ice caps suffered a total ice loss of -259 ± 28 Gt/year in the period 2003-2009, equivalent to a sea-level rise of 0.71 ± 0.08 mm/year. The overall contribution of glaciers and ice sheets is estimated equivalent to a sea-level rise of 1.50 ± 0.16 mm/year for the period 2003-2009, or about 60 % of the total sea-level rise in the same period. Various estimates of the total glacier contribution to the sea-level rise by the end of the twenty-first century have been recently proposed, ranging from a few decimeters to 2 m, with most plausible projections at about 0.5 m. Most probably Greenland, the Antarctic Peninsula and the West Antarctic ice sheet will continue to lose ice, while the sign of the East Antarctica contribution is uncertain. Mountain glaciers will most likely continue to lose ice, although at different rates in the various mountain regions. For the European Alps and the Southern Alps (New Zealand), a loss of more than 70 % of their present volume is expected by the end of the twenty-first century. The glaciers' contraction in the mountain areas may cause slope failures, debris mobilization, outburst floods from glacial lakes, and water deficits, particularly in the summer season, in the arid zones in the coming decades. Together with other changes occurring in the cryosphere such as the Arctic sea-ice reduction, the snow cover decline and the permafrost degradation, the glacier retreat is considered part of a larger picture of environmental changes, directly or indirectly caused or increased by the human impact, leading to new environmental conditions, thus deserving to be indicated as the Anthropocene. Still more open to future responses is the consideration if the ongoing glacier reduction and the rise of the sea level will contribute to leave such a footprint in the geologic record as to require a new stratigraphic unit, a new time epoch in the billion years long history of the Earth. © 2013 Accademia Nazionale dei Lincei
Il ghiacciaio Strandline (Baia Terra Nova, Antartide). The Strandline Glacier, Terra Nova Bay, Antarctica.
No full textThe 'Strandline Glacier is a small local alpine glacier (0.79 km-)
on the coast of Gerlache Inlet, Terra Nova Bay, Victoria Land. It is
a cold glacier with accumulation and ablation areas controlled by wind
and irregularly distributed. The main ablation area coincides with the
terminal convex zone, crossed by transverse and splaying crevasses.
The AAR is of about 0.8. The front of the glacier in the central part
is an ice cliff 25 m high, changing laterally into a short dome and ramp
margin. The foliation is well evident along the frontal margin, showing
a syncline structure. A small and discontinuous apron of snow and
ice is present at the foot of the ice cliff . Inner moraines, ice cored
moraines and a sheet of basal melt out till (sublimation till) are present
along the marginal zone, partially resting on Holocene raised
beaches. Two Holocene ice advances, possibly younger than 4 500 yr
B.P., can be recognized. The front of the glacier advanced of more
than 60 m the first time and about 50 m the second time, the two
advances being separated by a consistent lapse of time, judging from
weathering and lichen development. The glacier is presently in a retreat
phase, although small push moraines near the front document minor
recent advances
Geologia. L'istituto Lombardo. Accademia di Scienze e Lettere. II - Storia della Classe di Scienze Matematiche e Naturali. Libri Schweiwiller
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