Equilibrium-line Altitudes of Late Quaternary Glaciers in the Southern Alps, New Zealand

1975 ◽  
Vol 5 (1) ◽  
pp. 27-47 ◽  
Author(s):  
Stephen C. Porter
Keyword(s):  
Late Holocene ◽  
Drainage Basin ◽  
Late Quaternary ◽  
Active Faults ◽  
Vertical Movement ◽  
Area Ratio ◽  
Southern Alps ◽  
Equilibrium Line ◽  
Accumulation Area Ratio ◽  
Geologic Data

AbstractEquilibrium-line altitudes (ELA's) of former glaciers in the Tasman River-Lake Pukaki drainage basin of the Southern Alps were reconstructed from glacial-geologic data on former ice limits by using an assumed accumulation-area ratio of 0.6 ± 0.05. Late Holocene (Neoglacial) ELA's were depressed 140 m below present levels, whereas those of four late Pleistocene ice advances were depressed 500 m (Birch Hill), 750 m (Tekapo), 875 m (Mt. John), and 1050 m (Balmoral). Reconstructed ELA gradients are approximately parallel to one another and range from 19 to 23 m km−1. Although vertical movement on active faults and isostatic tilting due to deglaciation have both contributed to modification of reconstructed ELA gradients from their original values, the maximum resulting effect probably amounts to less than 2.0 m km−1 and is undetectable from present data.

scholarly journals Equilibrium-Line Altitudes and Paleoenvironment in the Merchants Bay Area, Baffin Island, N.W.T., Canada

1985 ◽  
Vol 31 (109) ◽  
pp. 205-213 ◽  
Author(s):  
Fred F. Hawkins
Keyword(s):  
Area Ratio ◽  
Equilibrium Line ◽  
Storm Tracks ◽  
Lateral Moraine ◽  
Baffin Island ◽  
Statistical Comparison ◽  
Bay Area ◽  
The North ◽  
Simple Geometry ◽  
Accumulation Area Ratio

AbstractThe fiordlands south of Merchants Bay contain an extensive, well-preserved moraine record of a late Foxe advance of local valley glaciers. This has allowed accurate reconstruction of former glacier margins and computation of former equilibrium-line altitudes (ELAs) by a variety of methods. Statistical comparison of three methods (maximum lateral-moraine elevation, median elevation, and accumulation area ratio (AAR)) shows that different techniques can give different results for the same glaciers. Lateral moraines gave estimates that were too low, probably due to post-glacial erosion or to non-deposition. Median elevations and the AAR method produced statistically similar results but only for glaciers of simple geometry. The median-elevation method fails to take into account variations in valley morphology and glaciological parameters, and so is not reliable in all situations. The AAR method is supported by empirical evidence and is the best of the three methods for estimating former ELAs.Analysis of trend surfaces of present and late Foxe ELAs shows changes in elevation and orientation through time due to changing environmental factors. Present ELAs are strongly influenced by local factors, southerly storm tracks, and warm maritime conditions. Paleo-ELAs do not show this influence, suggesting that Davis Strait may have been ice-covered during the late Foxe stade and that storm tracks were from the north.

scholarly journals Equilibrium-Line Altitudes and Paleoenvironment in the Merchants Bay Area, Baffin Island, N.W.T., Canada

1985 ◽  
Vol 31 (109) ◽  
pp. 205-213 ◽  
Author(s):  
Fred F. Hawkins
Keyword(s):  
Area Ratio ◽  
Equilibrium Line ◽  
Storm Tracks ◽  
Lateral Moraine ◽  
Baffin Island ◽  
Statistical Comparison ◽  
Bay Area ◽  
The North ◽  
Simple Geometry ◽  
Accumulation Area Ratio

AbstractThe fiordlands south of Merchants Bay contain an extensive, well-preserved moraine record of a late Foxe advance of local valley glaciers. This has allowed accurate reconstruction of former glacier margins and computation of former equilibrium-line altitudes (ELAs) by a variety of methods. Statistical comparison of three methods (maximum lateral-moraine elevation, median elevation, and accumulation area ratio (AAR)) shows that different techniques can give different results for the same glaciers. Lateral moraines gave estimates that were too low, probably due to post-glacial erosion or to non-deposition. Median elevations and the AAR method produced statistically similar results but only for glaciers of simple geometry. The median-elevation method fails to take into account variations in valley morphology and glaciological parameters, and so is not reliable in all situations. The AAR method is supported by empirical evidence and is the best of the three methods for estimating former ELAs.Analysis of trend surfaces of present and late Foxe ELAs shows changes in elevation and orientation through time due to changing environmental factors. Present ELAs are strongly influenced by local factors, southerly storm tracks, and warm maritime conditions. Paleo-ELAs do not show this influence, suggesting that Davis Strait may have been ice-covered during the late Foxe stade and that storm tracks were from the north.

scholarly journals Testing the area–altitude balance ratio (AABR) and accumulation–area ratio (AAR) methods of calculating glacier equilibrium-line altitudes

2021 ◽  
pp. 1-12
Author(s):  
Rachel P. Oien ◽  
Brice R. Rea ◽  
Matteo Spagnolo ◽  
Iestyn D. Barr ◽  
Robert G. Bingham
Keyword(s):  
Time Series ◽  
Mass Balance ◽  
Area Ratio ◽  
Summer Temperature ◽  
Equilibrium Line ◽  
Field Observations ◽  
Median Difference ◽  
Accumulation Area Ratio

Abstract In this study, we compare equilibrium-line altitudes (ELAs) calculated using the area–altitude balance ratio (AABR) and the accumulation–area ratio (AAR) methods, with measured ELAs derived from direct field observations. We utilise a GIS toolbox to calculate the ELA for 64 extant glaciers by applying the AABR and AAR methods to DEMs and polygons of their geometry. The calculated ELAs (c-ELAs) are then compared to measured zero-net balance ELAs (znb-ELAs) obtained from mass-balance time series held by the WGMS for the same glaciers. The correlation between znb-ELAs and AABR (1.56)/AAR (0.58) c-ELAs is very strong, with an r2 = 0.99. The smallest median difference between znb-ELAs and c-ELAs (i.e. 65.5 m) is obtained when a globally representative AABR of 1.56 is used. When applied to palaeoglacier-climate applications, this difference translates to ~0.42°C, well within the uncertainty of palaeotemperature proxies used to determine mean summer temperature at the ELA. The more widely used mean AABR of 1.75 is shown to be statistically invalid due to the skewness of the dataset. On this basis, when calculating glacier ELAs, we recommend the use of a global AABR value of 1.56.

scholarly journals Altitudinal variations of temperature, equilibrium line altitude, and accumulation-area ratio in Upper Indus Basin

2016 ◽  
Vol 48 (1) ◽  
pp. 214-230 ◽  
Author(s):  
Biswajit Mukhopadhyay ◽  
Asif Khan
Keyword(s):  
Hydrological Modeling ◽  
Area Ratio ◽  
Temperature Data ◽  
Equilibrium Line ◽  
Indus Basin ◽  
Lapse Rate ◽  
Equilibrium Line Altitude ◽  
Upper Indus Basin ◽  
Temperature Equilibrium ◽  
Accumulation Area Ratio

Quantitative measures of adiabatic lapse rate, equilibrium line altitude (ELA), and accumulation-area ratio (AAR) are important to understand the hydrological processes and conduct hydrological modeling in a highly glaciated watershed. We present a detailed analysis of temperature data from 21 climatic stations, hypsometric analyses of glacier distributions, and a method to analyze ablation gradients and runoff curves concurrently to quantify these parameters for the watersheds of the Upper Indus Basin (UIB), with 15,062 km2 of glacierized area and an elevation range of 361–8,611 m. We show that the ELA varies considerably from one watershed to another, implying a highly variable upper elevation limit up to which melting of snows and glaciers takes place throughout the basin. This is in sharp contrast to the assertions made by previous researchers. We show that the ELA is as low as 4,840 m in Astore watershed and it is as high as 6,200 m in Shyok watershed. In accordance with the variation of ELA, the AAR also varies considerably from one watershed to another. It is as low as 0.10 in Gilgit and as high as 0.65 in Zanskar watersheds. We ascribe 15–20% uncertainty to these estimates of ELA and AAR in UIB.

scholarly journals Hypsometry and sensitivity of the mass balance to changes in equilibrium-line altitude: the case of the Southern Patagonia Icefield

2014 ◽  
Vol 60 (219) ◽  
pp. 14-28 ◽  
Author(s):  
Hernán De Angelis
Keyword(s):  
Mass Balance ◽  
Rate Sensitivity ◽  
Area Ratio ◽  
Area Fraction ◽  
Equilibrium Line ◽  
Equilibrium Line Altitude ◽  
First Order ◽  
Southern Patagonia ◽  
Accumulation Area Ratio ◽  
Balance Functions

AbstractWe study the relation between glacier hypsometry and sensitivity of mass-balance rate to changes in equilibrium-line altitude (ELA) to assess whether hypsometry can reliably be used to estimate the sensitivity of unmeasured glaciers to changes in ELA. We express the sensitivity of mass-balance rate to ELA, dḂ/ dELA, as a function of accumulation–area ratio (AAR), its derivative against altitude, dAAR/dELA, and mass-balance functions of ELA. We then apply the concept to 139 glaciers in the Southern Patagonia Icefield for which we derive hypsometry and AAR, and analyze the influence of hypsometry on their mass-balance rate sensitivity. We confirm that glaciers where the bulk of area is located above (below) the ELA are the least (most) sensitive. Glaciers with unimodal hypsometric curves where the peak of area fraction is around the present ELA, and glaciers with bi-or multimodal area distributions, with the ELA located approximately between the bulges, have intermediate sensitivities. We conclude that hypsometry can be used as a first-order estimator of mass-balance rate sensitivity to ELA change.

scholarly journals Characterization of Snow and Ice Reflectance Zones On Glaciers Using Landsat Thematic Mapper Data

1987 ◽  
Vol 9 ◽  
pp. 104-108 ◽  
Author(s):  
D.K. Hall ◽  
J.P. Ormsby ◽  
R.A. Bindschadler ◽  
H. Siddalingaiah
Keyword(s):  
Surface Temperature ◽  
Area Ratio ◽  
Thematic Mapper ◽  
Landsat Thematic Mapper ◽  
Ablation Area ◽  
Thematic Mapper Data ◽  
Glacier System ◽  
Accumulation Area Ratio ◽  
Snow And Ice

Landsat Thematic Mapper (TM) data have been analyzed to study the reflectivity characteristics of three glaciers: the Grossglockner mountain group of glaciers in Austria and the McCall and Meares Glaciers in Alaska, USA. The ratio of TM band 4 (0.76–0.90 μm) to TM band 5 (1.55–1.75 μm) was found to be useful for enhancing reflectivity differences on the glaciers. Using this ratio, distinct zones of similar reflectivity were noted on the Grossglockner mountain group of glaciers and on the Meares Glacier; no distinct zones were observed on the McCall Glacier. On the TM subscene containing the Grossglockner mountain group of glaciers, 28.2% of the glacierized area was determined to be in the zone corresponding most closely to the ablation area, and 71.8% with the location of the accumulation area. Using these measurements, the glacier system has an accumulation area ratio (AAR) of approximately 0.72. Within the accumulation area, two zones of different reflectivity were delineated. Radiometric surface temperatures were measured using TM band 6 (10.4–12.5 μm) on the Grossglockner mountain group of glaciers and on the Meares Glacier. The average radiometric surface temperature of the Grossglockner mountain group of glaciers decreased from 0.9 ± 0.34 °C in the ablation area, to −0.9 ± 0.83 C in the accumulation area.

scholarly journals Late Holocene intensification of the westerly winds at the subantarctic Auckland Islands (51° S), New Zealand

2017 ◽  
Author(s):  
Imogen M. Browne ◽  
Christopher M. Moy ◽  
Christina R. Riesselman ◽  
Helen L. Neil ◽  
Lorelei G. Curtin ◽  
...  
Keyword(s):  
New Zealand ◽  
Late Holocene ◽  
Drainage Basin ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Ice Age ◽  
The Pacific ◽  
Westerly Winds ◽  
Latitudinal Position ◽  
Paleoclimate Records

Abstract. The Southern Hemisphere westerly winds (SHWW) play a major role in controlling wind-driven upwelling of Circumpolar Deep Water (CDW) and outgassing of CO2 in the Southern Ocean on interannual to glacial-interglacial timescales. Despite their significance in the global carbon cycle, our understanding of millennial-scale changes in the strength and latitudinal position of the westerlies during the Holocene (especially since 5000 yr BP) is limited by a scarcity of paleoclimate records from comparable latitudes. Here, we reconstruct middle to late Holocene variability in the SHWW using a fjord sediment core collected from the subantarctic Auckland Islands (51° S, 166° E), located in the modern centre of the westerly wind belt. Drainage basin response to variability in the strength of the SHWW at this latitude is reconstructed from downcore variations in magnetic susceptibility (MS) and bulk organic δ13C and atomic C/N, which monitor influxes of lithogenous and terrestrial vs marine organic matter, respectively. The hydrographic response to SHWW variability is reconstructed using benthic foraminifer δ18O and δ13C, both of which are influenced by the isotopic composition of shelf water masses entering the fjord. Using these data, we provide marine and terrestrial-based evidence for increased wind strength from ~ 1600–900 yr BP at subantarctic latitudes that is broadly consistent with previous studies of vegetation response to climate at the Auckland Islands. Comparison with a SHWW reconstruction using similar proxies from Fiordland suggests a northward migration of the SHWW over New Zealand at the beginning of the Little Ice Age (LIA). Comparison with paleoclimate and paleoceanographic records from southern South America and the western Antarctic Peninsula indicates a late Holocene strengthening of the SHWW after ~ 1600 yr BP that appears to be broadly symmetrical across the Pacific basin, although our reconstruction suggests that this symmetry breaks down during the LIA. Contemporaneous increases in SHWW at localities either side of the Pacific in the late Holocene are likely controlled atmospheric teleconnections between the low and high latitudes and by variability in the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO).

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