Accumulation Area Ratio Method Research Articles

Long-term estimation of glacier mass balance using geospatial techniques in Western Himalayas, Ladakh, India

All glaciers are subject to mass fluctuations in the current context of climate change. For daily requirements like food, drink, irrigation, and the generation of hydroelectric power, these glaciers provide water to important basins including the Indus, Ganga, and Brahmaputra. Changes in glacier patterns are a blatant sign of local climate variability. Monitoring of glaciers requires long-term studies on glacier dynamics. Himalayan glaciers, because of their disposition in a complex topographic setting and inaccessible terrain render difficulty in the glacier observations in a continuous mode. Glacier mass fluctuations can be associated with glacier area shrinkage or expansion and concomitant snout shift. In the current study, two adjoining glaciers of different sizes, Pensilungpa and Drang Drung glaciers in the Zanskar Valley, Ladakh, India are selected. The period of the study was taken between the years 2000–2022. Earlier studies used a single day per year Accumulation Area Ratio (AAR) method to compute mass balance, which had limitations due to snow cover variability. The present study calculated and averaged all the AAR values for cloud-free images per year during the peak ablation period (mid-July to early September). Digital Elevation Model (DEM) difference technique was also employed for computing the mass budget between 2000 and 2021 b y utilizing two-time period DEMs. It was revealed that in the case of the AAR method, the Pensilungpa glacier showed 7 years of positive and 16 years of negative mass balance. The years 2003–2005 and 2011 to 2016 were depicted with negative mass balance with the highest value up to −0.752-m water equivalent (m.w.e.) for the year 2015. It has negligible areal fluctuations ranging from 0.01 to 0.6 km2. Drang Drung Glacier has shown 12 years of positive and 11 years of negative mass balance. The years 2002–2004 and 2009 to 2012 were depicted with positive mass balance with the highest value up to 0.305 m. w.e. Except, for the year 2009–2012 (areal increment ∼ 2.65 km2), years 2013–2015 showed a negative mass balance with negligible areal fluctuations. Mass balance estimation using DEM differencing method revealed an average estimated mass balance of −0.03 m. w.e. For Pensilungpa glacier though, it is 0.08 m. w.e. For Drang Drung glacier which shows good matches with the mass balance estimated using AAR method in m. w.e. Such contrasting behavior of mass balance suggests higher sensitivity of smaller glaciers to climate change.

LGM glaciers in the SE Mediterranean? First evidence from glacial landforms and 36Cl dating on Mount Lebanon

The hydrological conditions during the Last Glacial Maximum in the Eastern Mediterranean have long been debated. In particular, very little is known about the development of high-altitude glaciers in this region. In the present study, morphological and sedimentological evidence, such as U-shape valleys, glacial cirques, and morainic ridges, are used to identify past glaciers on the western slopes of Mount Lebanon, which is by far the highest topography along the eastern Mediterranean coast (3088 m a.s.l.). The geometry of three paleo-glaciers is reconstructed: one 8-km-long glacial tongue stretching from the highest peak down to an elevation of about 2000 m a.s.l., and two small glacial cirques located at about 2300 m a.s.l. The age of maximum glacier advance is constrained from a 10-m-deep 36Cl depth-profile within the diamicton of one terminal moraine, and yields an early LGM timing (between 25.4 ± 3.1 ka and 31.2 ± 4.5 ka), which agrees with the chronology of the last maximum glacier extension in the Eastern Mediterranean. The three glaciers together form a consistent group, compatible with an Equilibrium Line Altitude (ELA) at 2400 m estimated using the Accumulation Area Ratio method. A degree-day model is further used to infer the temperature and precipitation conditions required to depress the LGM ELA to 2400 m. Our results suggest that the observed glacier extent is compatible with early LGM paleo-temperature records of the area only under the condition of decreased precipitation relative to modern times. These findings thus support an early LGM climate of the Levant region that was drier than today.

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

AbstractIn 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.

Glacier variations and rising temperature in the Mt. Kenya since the Last Glacial Maximum

High-resolution imagery can be used to reconstruct former glacier boundaries through the identification of glacial erosional and sedimentary geomorphology. We employed moraine mapping and the accumulation–area ratio method (AAR), in conjunction with Landsat, Google Earth, and SRTM imagery, to reconstruct glacier boundaries and equilibrium-line altitudes (ELAs) for Mt. Kenya in the Last Glacial Maximum (LGM), the Little Ice Age (LIA), and at present. Our results show that the areas of Lewis Glacier and the Tyndall-I glacier system were 0.678 km2 and 0.390 km2, respectively, during the maximum of LIA. Those mean that the both glaciers have shrunken by 87.0% and 88.7%, respectively since the LIA. Area change ratios for each glacier were significantly larger in the period of 2000 through 2015 than the former periods, indicating that glacier recession has accelerated. Continuous ice loss in this region has been driven by rising temperature and fluctuating precipitation. Linear regression data for Lewis glacier show that mass balance sensitivity to dry season temperature was–315 mm w.e./°C, whereas the sensitivity to dry season precipitation was 5.2 mm w.e./mm. Our data also show that the ELA on the western slope of Mt. Kenya rose by 716–816 m from the LGM to the modern era, corresponding to that temperature rose by 5.2°C -6.5°C.

GIS analysis of cirques on Vestfirðir, northwest Iceland: implications for palaeoclimate

This study presents the first regional analysis of cirques on Vestfirðir, NW Iceland, using a Geographical Information System (GIS). The length, width, elevation of cirque‐floor, latitude and the distance to the modern coastline (both ocean and fjord coastlines) of cirques were quantified using ArcGIS. The topographical analysis revealed a total of 100 cirques on western and northern Vestfirðir. Several additional cirques are present, but they had poorly defined toewalls, making the cirque‐floor difficult to identify. Mean cirque length is 515 m and mean cirque width is 752 m. The modal orientation of the aspect of cirques is northeast, with a strong secondary mode to the northwest. Cirques at low elevations are more abundant close to the ocean, whereas cirques further from the ocean are present at high elevations. Three techniques were used to reconstruct past equilibrium‐line altitudes (ELAs) of cirque glaciers: the cirque‐floor method, the altitude‐ratio method and the accumulation‐area ratio method. The largest range of past ELAs is generated from the cirque‐floor method with values from 40 up to 730 m. Mean past ELA values range from ∼395 to 423 m depending on the method used to reconstruct former ELAs. A strong positive relationship is observed between past ELA values and distance to the ocean demonstrating the importance of access to a moisture source for glacier survival. This relationship is stronger than the relationship between former ELAs and latitude. Based on the small size of cirque glaciers, it is likely that even minor fluctuations in the Irminger Current and the East Greenland Current influence cirque glaciation on Vestfirðir.

Sledovi pleistocenske poledenitve na Trnovskem gozdu

Trnovski gozd je visoka kraška planota na dinarskem krasu zahodne Slovenije, ki so jo v pleistocenu preoblikovali tudi ledeniški procesi. Ugotovili smo, da je severna pobočja in podnožje najvišjega osrednjega grebena Golaki pokrival ledenik s površino 4,8 km2 in največjo debelino okoli 180 m. V več odtočnih ledenikih je padal preko strme reliefne stopnje v dolini Belce in Trebuše ter na Hudo polje. Prisojna pobočja Golakov niso bila poledenela. Z metodama deleža akumulacijskega dela ledenika ter zgornje meje bočnih moren smo izračunali ravnovesno mejo ledenikov na višini 1240 m.

Modeling Glacier Behavior Under Different Precipitation Seasonalities

To understand the dependence of glacial features on precipitation, glacier behavior was simulated under different precipitation conditions using a glacier fluctuation model that combined a mass-balance model with a glacier flow model. The results reveal a strong dependence of glacier behavior on precipitation conditions. Glacier volume changes in accordance with both precipitation seasonality and annual precipitation amount. Glacier volume also fluctuates in response to changes in precipitation seasonality even if no change in annual precipitation amount occurs, because of changes in glacier albedo and the volume that is able to accumulate. Furthermore, the accumulation area ratio (AAR) depends not only on the annual precipitation amount, but also on precipitation seasonality. These relationships should be considered when the AAR method is used to reconstruct the past equilibrium line of glaciers. Glacier reactions to temperature change become more sensitive as the amount of annual precipitation increases. Response time is different for each glacier type defined by precipitation seasonality: the winter-precipitation-seasonality type had the longest response time, and the summer-precipitation-seasonality type had the shortest. The difference in the response time of glacier types is larger under arid conditions and smaller under humid conditions. The simulation results in this study underscore the importance of including glacier response to precipitation conditions when estimating glacier reactions to climate change.

Quantifying climate and glacier mass balance in north Norway during the Younger Dryas

Øksfjordjøkelen is located at ∼ 70° N on the Troms–Finnmark border in North Norway. During the Younger Dryas, it was decoupled from and sat just beyond the margin of the Scandinavian Ice Sheet. At this time the major fjords in Troms and Finnmark were ice-free with outlet glaciers from the icefield filling a number of smaller side valleys. Only one outlet from the icefield, Sörfjorddalen, is temporally well-constrained by 14C dating and association with the Main Shoreline (associated with a period of minimal crustal rebound dated to the Younger Dryas). Sörfjorddalen is reconstructed using a valley centre-line iterative model and assuming a no-slip basal boundary condition. This assumption of cold-based ice is supported by the geomorphological evidence of angular bouldery fronto-lateral moraines formed during the Younger Dryas. The equilibrium line altitude for the Sörfjorddalen is calculated using both the Balance Ratio and Accumulation Area Ratio methods, and this is used to constrain the snout positions (generally to mapped moraines) of the other outlets. This approach assumes similarity of mass balance gradients and geometries of the outlet glaciers which is supported by present-day symmetry of the icefield. This method is extremely useful in such environments where dateable material is often difficult, if not impossible, to find. Some margins terminated in deep water where bathymetry was lacking, making calving quantification problematic with subsequent impacts on equilibrium line altitudes poorly constrained. These deep-water terminating snouts were discounted from subsequent palaeo-climate reconstructions. An empirical equilibrium line altitude temperature-precipitation relationship was used to define limits of climate change required to sustain the reconstructed icefield. Palaeo-precipitation estimates were refined using a palaeo-temperature estimate for the Younger Dryas from Andøya. Calculations of ice flux through the equilibrium line altitude were used to further constrain the mass balance characteristics of the reconstructed icefield and these suggest similarities with ice masses found in the northern (Nordaustlandet) regions of Svalbard.

Late Pleistocene climate inferred from the reconstruction of the Taylor River glacier complex, southern Sawatch Range, Colorado

Ice surface topography of a late Pleistocene glacier complex, herein named the Taylor River Glacier Complex (TRGC), was reconstructed on the basis of detailed mapping of glacial landforms combined with analyses of aerial photos and topographic maps. During the last glacial maximum (LGM), the TRGC covered an area of 215 km 2 and consisted of five valley or outlet glaciers that were nourished by accumulation in cirques basins and/or upland ice fields. Equilibrium-line altitudes (ELAs) for the glaciers of the TRGC were estimated using the accumulation-area ratio method, assuming that ratio to be 0.65 ± 0.05. ELAs thus derived ranged from about 3275 to 3400 m, with a mean of 3340 ± 60 m. A degree-day model (DDM) was used to infer the climatic significance of the LGM ELA. With no appreciable differences in precipitation with respect to modern climate, the ELA implies that mean summer temperatures during the LGM were ∼7.6 °C cooler than today. The DDM was also used to determine the temperatures required to maintain steady-state mass balances for each of the reconstructed glaciers. The required reductions in summer temperature vary little about a mean of 7.1 °C. The sensitivity of these results to slight (± 25%) changes assumed for LGM precipitation are less than ± 0.5 °C. Even under an LGM climate in which precipitation is assumed to be substantially different (± 50%) than the present, mean summer temperatures must be on the order of 7.0 to 8.5 °C lower to depress equilibrium lines to LGM altitudes. The greater sensitivity of the ELA to changes in temperature suggests that glaciation in the region was driven more by decreases in summer temperature rather than increases in precipitation.

Equilibrium‐line altitudes during the Last Glacial Maximum across the Brooks Range, Alaska

AbstractEquilibrium‐line altitudes (ELAs) were estimated for 383 reconstructed glaciers across the Brooks Range, northern Alaska, to investigate their regional pattern during the Last Glacial Maximum (LGM). Glacier outlines were delimited based on published field mapping and the original interpretations of aerial photographs. Glacier margins were digitised from 1:63 360‐scale maps into a geographic information system (GIS) with a digital elevation model on a 60‐m grid. ELAs were calculated for each reconstructed glacier using the accumulation area ratio method (AAR = 0.58). The analysis was restricted to relatively simple cirque and valley glaciers that deposited clearly identifiable LGM moraines, and that did not merge with the complex transection glacier ice that filled most troughs of the range. The glaciers used in this analysis had areas ranging from 0.14 to 120 km2. Their ELAs rose from 470 m a.s.l. in the western Brooks Range to 1860 m a.s.l. in the east, over a distance of 1000 km. The ELAs were fitted with a third‐order polynomial trend surface to model their distribution across the range, and to investigate the source of local‐scale variations. The trend surface lowers toward the west and south, similar to previously derived trends based on glaciation thresholds. In addition, ELAs in the northeastern part of the range lower northward toward the Beaufort Sea, which has not been reported as strongly in other studies. Modern glacier ELAs also lower toward the southwest. The depression of LGM ELAs from modern glacier ELAs is greatest in the central Brooks Range (a maximum of 700 m), and decreases to the east (200 m). The regional pattern of LGM ELAs points to the primary source of moisture from the North Pacific, as it is today. The unexpected trend of LGM ELAs in the northeast part of the range is supported by recent field mapping, where anomalous ice distribution and ELAs reflect complicated LGM climate patterns and possibly late Quaternary tectonism. Copyright © 2005 John Wiley & Sons, Ltd.

Modern and Little Ice Age Equilibrium-Line Altitudes on Outlet Valley Glaciers from Jostedalsbreen, Western Norway: An Evaluation of Different Approaches to Their Calculation

The modern and Little Ice Age (LIA) equilibrium-line altitude (ELA) of 20 outlet valley glacier from Jostedalsbreen, western Norway, has been calculated using different approaches. Using an accumulation area ratio (AAR) of 0.6 [+-] 0.05 gave a mean little Ice Age ELA depression of 70 m. A method developed by M. Kuhle, taking the influence by topography into account gave a mean ELA depression of 35-255 m, the median elevation of glaciers 115 m, and the toe-to-headwall altitude ration 140 m. Differences in the ELA estimates can be attributed to the differences in topography and morphology of the glaciers. The AAR method appears to provide the most reliable results. This will aid in determining mean global temperatures during the LIA. 34 refs., 9 figs., 5 tabs.

Mass balance of Himalayan glaciers using AAR and ELA methods

AbstractThe accumulation area ratio (AAR) for Himalayan glaciers representing zero mass balance is substantially lower than for North America and Europe. Regression analysis suggests 0.44 for the AAR representing zero mass balance in the western Himalaya. A good correlation was observed when this method was applied to individual glaciers such as Gara and Gor-Garang in Himachal Pradesh, India. The correlation coefficients (r), using 6 and 7 years of data, respectively, were 0.88 and 0.96 for Gara and Gor-Garang Glaciers, respectively. However, when data from six western Himalayan glaciers were correlated, the correlation was 0.74. The AAR was also estimated by using Landsat images which can be useful in obtaining a trend in mass balance for a large number of Himalayan glaciers for which very little information exists.A higher correlation was observed between equilibrium-line altitude (ELA) and mass balance. The field data from Gara and Gor-Garang Glaciers shows a high correlation coefficient, i.e. −0.92 and −0.94, respectively. The ELA values obtained from the Landsat satellite images combined with topographic maps suggest positive mass balance for the year 1986–87 and negative for 1987–88.

Mass balance of Himalayan glaciers using AAR and ELA methods

AbstractThe accumulation area ratio (AAR) for Himalayan glaciers representing zero mass balance is substantially lower than for North America and Europe. Regression analysis suggests 0.44 for the AAR representing zero mass balance in the western Himalaya. A good correlation was observed when this method was applied to individual glaciers such as Gara and Gor-Garang in Himachal Pradesh, India. The correlation coefficients (r), using 6 and 7 years of data, respectively, were 0.88 and 0.96 for Gara and Gor-Garang Glaciers, respectively. However, when data from six western Himalayan glaciers were correlated, the correlation was 0.74. The AAR was also estimated by using Landsat images which can be useful in obtaining a trend in mass balance for a large number of Himalayan glaciers for which very little information exists.A higher correlation was observed between equilibrium-line altitude (ELA) and mass balance. The field data from Gara and Gor-Garang Glaciers shows a high correlation coefficient, i.e. −0.92 and −0.94, respectively. The ELA values obtained from the Landsat satellite images combined with topographic maps suggest positive mass balance for the year 1986–87 and negative for 1987–88.

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

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.

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

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.