Abstract:Supraglacial lakes form in Antarctic blue ice regions from penetration of solar radiation into the ice in summer. Three lakes were mapped for their structure in summers 2004-05 and 2010-11 in western Dronning Maud Land, and one was also examined for the radiation budget. The lake body consisted of two layers, each ,1 m thick: an upper layer with a thin ice layer on top and main body of liquid water, and a lower layer containing slush and hard ice sub-layers. A sediment-rich slush pocket was found at the bottom… Show more
“…2). This drainage-fed mode of pond formation-involving the accumulation of meltwater from a large catchment via surface drainage-contrasts with in situ ponding of meltwater observed elsewhere in Antarctica 22 . Drainage-fed ponds on ice shelves are common ( Fig.…”
Surface meltwater drains across ice sheets, forming melt ponds that can trigger ice-shelf collapse 1, 2 , acceleration of grounded ice flow and increased sea-level rise 3, 4, 5 . Numerical models of the Antarctic Ice Sheet that incorporate meltwater's impact on ice shelves, but ignore the movement of water across the ice surface, predict a metre of global sea-level rise this century 5 in response to atmospheric warming 6 . To understand the impact of water moving across the ice surface a broad quantification of surface meltwater and its drainage is needed. Yet, despite extensive research in Greenland 7, 8, 9, 10 and observations of individual drainage systems in Antarctica 10, 11, 12, 13, 14, 15, 16, 17, we have little understanding of Antarctic-wide surface hydrology or how it will evolve. Here we show widespread drainage of meltwater across the surface of the ice sheet through surface streams and ponds (hereafter 'surface drainage') as far south as 85° S and as high as 1,300 metres above sea level. Our findings are based on satellite imagery from 1973 onwards and aerial photography from 1947 onwards. Surface drainage has persisted for decades, transporting water up to 120 kilometres from grounded ice onto and across ice shelves, feeding vast melt ponds up to 80 kilometres long. Large-scale surface drainage could deliver water to areas of ice shelves vulnerable to collapse, as melt rates increase this century. While Antarctic surface melt ponds are relatively well documented on some ice shelves, we have discovered that ponds often form part of widespread, large-scale surface drainage systems. In a warming climate, enhanced surface drainage could accelerate future ice-mass loss from Antarctic, potentially via positive feedbacks between the extent of exposed rock, melting and thinning of the ice sheet.
“…2). This drainage-fed mode of pond formation-involving the accumulation of meltwater from a large catchment via surface drainage-contrasts with in situ ponding of meltwater observed elsewhere in Antarctica 22 . Drainage-fed ponds on ice shelves are common ( Fig.…”
Surface meltwater drains across ice sheets, forming melt ponds that can trigger ice-shelf collapse 1, 2 , acceleration of grounded ice flow and increased sea-level rise 3, 4, 5 . Numerical models of the Antarctic Ice Sheet that incorporate meltwater's impact on ice shelves, but ignore the movement of water across the ice surface, predict a metre of global sea-level rise this century 5 in response to atmospheric warming 6 . To understand the impact of water moving across the ice surface a broad quantification of surface meltwater and its drainage is needed. Yet, despite extensive research in Greenland 7, 8, 9, 10 and observations of individual drainage systems in Antarctica 10, 11, 12, 13, 14, 15, 16, 17, we have little understanding of Antarctic-wide surface hydrology or how it will evolve. Here we show widespread drainage of meltwater across the surface of the ice sheet through surface streams and ponds (hereafter 'surface drainage') as far south as 85° S and as high as 1,300 metres above sea level. Our findings are based on satellite imagery from 1973 onwards and aerial photography from 1947 onwards. Surface drainage has persisted for decades, transporting water up to 120 kilometres from grounded ice onto and across ice shelves, feeding vast melt ponds up to 80 kilometres long. Large-scale surface drainage could deliver water to areas of ice shelves vulnerable to collapse, as melt rates increase this century. While Antarctic surface melt ponds are relatively well documented on some ice shelves, we have discovered that ponds often form part of widespread, large-scale surface drainage systems. In a warming climate, enhanced surface drainage could accelerate future ice-mass loss from Antarctic, potentially via positive feedbacks between the extent of exposed rock, melting and thinning of the ice sheet.
“…In this simple geometry, a frozen lid covers a slushy, water-covered surface when there is sufficient incoming solar radiation to support melting. This concept is based on observations of supraglacial lakes in Dronning Maud Land, Antarctica, in a flat area near a nunatak (Leppäranta and others, 2012; Jarvinen and Leppäranta, 2013). Fig.…”
Section: Thermal Model Of the Ice Shelfmentioning
confidence: 99%
“…Unlike the ablation zones in Greenland, where steep surface topography drives immediate movement of meltwater as it is created, flat ice-shelf surfaces allow surface and subsurface meltwater to build-up in bog-like areas where the topography is subtle, but heterogeneous (Banwell and others, 2014). Flat surface topography and the absence of firn also promotes subsurface melting driven by solar radiation that penetrates the surface (Leppäranta and others, 2012; Jarvinen and Leppäranta, 2013; Lenaerts and others, 2017). While the collapse of the Larsen B Ice Shelf in 2002 was preceded by a well-developed surface expression of meltwater (Sergienko and MacAyeal, 2005; Glasser and Scambos, 2008), the collapse of the Wilkins Ice Shelf in 2008 was attributed to the presence of water below the surface that enabled hydrofracture (Scambos and others, 2009).…”
Seismograms acquired on the McMurdo Ice Shelf, Antarctica, during an Austral summer melt season (November 2016–January 2017) reveal a diurnal cycle of seismicity, consisting of hundreds of thousands of small ice quakes limited to a 6–12 hour period during the evening, in an area where there is substantial subsurface melting. This cycle is explained by thermally induced bending and fracture of a frozen surface superimposed on a subsurface slush/water layer that is supported by solar radiation penetration and absorption. A simple, one-dimensional model of heat transfer driven by observed surface air temperature and shortwave absorption reproduces the presence and absence (as daily weather dictated) of the observed diurnal seismicity cycle. Seismic event statistics comparing event occurrence with amplitude suggest that the events are generated in a fractured medium featuring relatively low stresses, as is consistent with a frozen surface superimposed on subsurface slush. Waveforms of the icequakes are consistent with hydroacoustic phases at frequency $ {\bf \gt} \bf 75\,{\bf Hz}$ and flexural-gravity waves at frequency $ \bf {\bf \lt}25\,{\bf Hz}$. Our results suggest that seismic observation may prove useful in monitoring subsurface melting in a manner that complements other ground-based methods as well as remote sensing.
“…A necessary condition for the formation of cold-environment supraglacial lakes is that solar radiation is able to accumulate heat below the surface enough to warm up and melt ice. Therefore, these lakes are found in blue-ice areas (Winther and others, 1996; Hoffman and others, 2008; Leppäranta and others, 2013b) where albedo is low and transparency of ice is good. In the Dronning Maud Land, such blue-ice areas are typically found on the lee side of mountains.…”
Section: Introductionmentioning
confidence: 98%
“…Resulting from local glacial melt, the lake water is very clear and possesses extremely low levels of geochemical impurities (Lehtinen and Luttinen, 2005) and biota (Keskitalo and others, 2013). The lake body is an ice/water mixture and consists of two layers: an upper water/slush layer, and a lower layer with soft and hard sub-layers and sediments at the bottom (Leppäranta and others, 2013b).…”
ABSTRACT. Thermodynamics of a seasonal supraglacial lake were examined based on field data from three summers. At maximum, the lake body consisted of an upper layer with thin ice on top, and a lower layer with slush, hard ice and sediment at the bottom. Sublimation from the upper ice surface averaged to 0.7 mm d −1 , and melting in the ice interior averaged to 9.1 mm d −1 during summer. Albedo was on average 0.6 and light attenuation coefficient was ∼1 m −1. Averaged over December and January, and over 3 different years, we found that the net solar heating was 137 W m The potential winter growth is more than summer melting, and thus the lake freezes up completely in winter in the present climate.
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