Mass-balance History Research Articles

Implementation of the RCIP scheme and its performance for 1-D age computations in ice-sheet models

Abstract. Ice-sheet age computations are formulated using an Eulerian advection equation, and there are many schemes that can be used to solve them numerically. Typically, these differ in numerical characteristics such as stability, accuracy, and diffusivity. Furthermore, although various methods have been presented for ice-sheet age computations, the constrained interpolation profile method and its variants have not been examined in this context. The present study introduces one of its variants, a rational function-based constrained interpolation profile (RCIP) scheme, to one-dimensional ice age computation and demonstrates its performance levels via comparisons with those obtained from first- and second-order upwind schemes. Our results show that the RCIP scheme preserves the pattern of input surface mass balance histories in terms of the vertical profile of internal annual layer thickness better than the other schemes.

Recent accelerating mass loss of southeast Tibetan glaciers and the relationship with changes in macroscale atmospheric circulations

The mass balance history (1980–2010) of a monsoon-dominated glacier in the southeast Tibetan Plateau is reconstructed using an energy balance model and later interpreted with regard to macroscale atmospheric variables. The results show that this glacier is characterized by significant interannual mass fluctuations over the past three decades, with a remarkably high mass loss during the recent period of 2003–2010. Analysis of the relationships between glacier mass balance and climatic variables shows that interannual temperature variability in the monsoonal season (June–September) is a primary driver of its mass balance fluctuations, but monsoonal precipitation tends to play an accentuated role for driving the observed glacier mass changes due to their covariation (concurrence of warm/dry and cold/wet climates) in the monsoon-influenced southeast Tibetan Plateau. Analysis of the atmospheric circulation pattern reveals that the predominance of anticyclonic/cyclonic circulations prevailing in the southeastern/northern Tibetan Plateau during 2003–2010 contributes to increased air temperature and decreased precipitation in the southeast Tibetan Plateau. Regionally contrasting atmospheric circulations explain the distinct mass changes between in the monsoon-influenced southeast Tibetan Plateau and in the north Tibetan Plateau/Tien Shan Mountains during 2003–2010. The macroscale climate change seems to be linked with the Europe-Asia teleconnection.

Reconciling the ICE‐6G_C reconstruction of glacial chronology with ice sheet dynamics: The cases of Greenland and Antarctica

AbstractWe describe a theoretical and numerical framework that has been developed to investigate the compatibility of the ICE‐6G_C reconstruction of the glaciation histories of the Greenland and Antarctic ice sheets with the latest understanding of ice physics. The ICE‐6G_C reconstruction has been produced solely on the basis of the theory of the glacial isostatic adjustment (GIA) process, and it has remained an issue as to whether such reconstructions of the time‐dependent thickness variations of grounded continental ice sheets were compatible with physics‐based ice mechanical considerations. Our analyses focus on the evolution over the last glacial cycle of these extent ice sheet complexes and demonstrate that the GIA‐inferred models are entirely consistent with such considerations when uncertainties in (net) mass balance history are taken fully into account.

Constraining the recent mass balance of Pine Island and Thwaites glaciers, West Antarctica, with airborne observations of snow accumulation

Abstract. In Antarctica, uncertainties in mass input and output translate directly into uncertainty in glacier mass balance and thus in sea level impact. While remotely sensed observations of ice velocity and thickness over the major outlet glaciers have improved our understanding of ice loss to the ocean, snow accumulation over the vast Antarctic interior remains largely unmeasured. Here, we show that an airborne radar system, combined with ice-core glaciochemical analysis, provide the means necessary to measure the accumulation rate at the catchment-scale along the Amundsen Sea coast of West Antarctica. We used along-track radar-derived accumulation to generate a 1985–2009 average accumulation grid that resolves moderate- to large-scale features (>25 km) over the Pine Island–Thwaites glacier drainage system. Comparisons with estimates from atmospheric models and gridded climatologies generally show our results as having less accumulation in the lower-elevation coastal zone but greater accumulation in the interior. Ice discharge, measured over discrete time intervals between 1994 and 2012, combined with our catchment-wide accumulation rates provide an 18-year mass balance history for the sector. While Thwaites Glacier lost the most ice in the mid-1990s, Pine Island Glacier's losses increased substantially by 2006, overtaking Thwaites as the largest regional contributor to sea-level rise. The trend of increasing discharge for both glaciers, however, appears to have leveled off since 2008.

Century-scale relative sea-level changes in West Greenland — A plausibility study to assess contributions from the cryosphere and the ocean

This paper interprets high resolution relative sea-level (RSL) reconstructions obtained from recently deposited salt-marsh sediments in Greenland. The primary aim of this study is to determine the relative contribution to the RSL observations from local to regional ice mass changes as well as density-related (steric) variations in the adjacent ocean. At sites in west Greenland, RSL rise slows from ~3mm/yr to ~0mm/yr at 400years BP and is stable thereafter. In south Greenland, a similar RSL slowdown is also observed but this occurs approximately 200yrs later. Substantial contributions from oceanographic changes are ruled out as dominant drivers of the RSL slowdown in western Greenland but could be more important at Nanortalik. Model sensitivity tests indicate that the RSL data are not compatible with a dominant dynamic ice loss via the Jakobshavn Isbrae outlet glacier as the region of ice loss and the resulting sea-level trends are too localised. Regional changes in ice thickness related to surface mass balance changes can explain the observed RSL signals but only if there is dominant mass loss during the period 400years BP to present. This conclusion is unaffected even when uncertainties in Earth viscosity structure are taken into account. However, it is plausible that some of the RSL fall may be due to reduced ice growth at the onset of the Little Ice Age. A high resolution mass balance history of the Greenland Ice Sheet over the past few millennia and the influence of lateral Earth structure on predictions of RSL change are identified as priority areas of study in order to confidently separate local, ‘transient’ (e.g. elastic and gravitational) RSL changes from the long-term viscous contribution associated primarily with deglacial changes.

Sequence stratigraphy of experimental strata under known conditions of differential subsidence and variable base level

Sequence stratigraphy has been applied from reservoir to continental scales, providing a scale-independent model for predicting the spatial arrangement of depositional elements. We examine experimental strata deposited in the Experimental EarthScape facility at St. Anthony Falls Laboratory, focusing on stratigraphic surfaces defined by discordant contact geometries, surfaces analogous to those delineated in the original work on seismic sequence stratigraphy. In this controlled setting, we directly evaluate critical sequence-stratigraphic issues, such as stratigraphic horizon development and time significance, as well as the internal geometry and migration of the bounded strata against the known boundary conditions and depositional history. Four key stratigraphic disconformities defined by marine downlap, marine onlap, fluvial erosion, and fluvial onlap are mapped and vary greatly in their relative degree of time transgression. Marine onlap and downlap contacts closely parallel topographic surfaces (time surfaces) and, prior to burial, approximate the instantaneous offshore topography. These stratal-bounding surfaces are also robust stratigraphic signals of relative base-level fall and rise, respectively. Marine onlap surfaces are of special interest. They tend to be the best preserved discordance, where widespread, allogenic-based onlap surfaces subdivide otherwise amalgamated depositional cycles amidst cryptic stacks of marine foresets; however, local, autogenic-based marine onlap discordances are present throughout the fill. A critical distinguishing feature of allogenic onlap is the greater lateral persistence of the discordance. Surfaces defined by subaerial erosional truncation and fluvial onlap do not have geomorphic equivalence because channel processes continually modify the surface as the stratigraphic horizons are forming. Hence, they are strongly time transgressive. Last, the stacking arrangement of the preserved bounded strata is found to be a good time-averaged representation of the mass-balance history.

Abrupt tropical climate change: past and present.

Three lines of evidence for abrupt tropical climate change, both past and present, are presented. First, annually and decadally averaged delta(18)O and net mass-balance histories for the last 400 and 2,000 yr, respectively, demonstrate that the current warming at high elevations in the mid- to low latitudes is unprecedented for at least the last 2 millennia. Second, the continuing retreat of most mid- to low-latitude glaciers, many having persisted for thousands of years, signals a recent and abrupt change in the Earth's climate system. Finally, rooted, soft-bodied wetland plants, now exposed along the margins as the Quelccaya ice cap (Peru) retreats, have been radiocarbon dated and, when coupled with other widespread proxy evidence, provide strong evidence for an abrupt mid-Holocene climate event that marked the transition from early Holocene (pre-5,000-yr-B.P.) conditions to cooler, late Holocene (post-5,000-yr-B.P.) conditions. This abrupt event, approximately 5,200 yr ago, was widespread and spatially coherent through much of the tropics and was coincident with structural changes in several civilizations. These three lines of evidence argue that the present warming and associated glacier retreat are unprecedented in some areas for at least 5,200 yr. The ongoing global-scale, rapid retreat of mountain glaciers is not only contributing to global sea-level rise but also threatening freshwater supplies in many of the world's most populous regions.

Tree-ring-based mass-balance estimates for the past 300 years at Peyto Glacier, Alberta, Canada

Tree rings were used to reconstruct mass balance for Peyto Glacier in the Canadian Rocky Mountains from A.D. 1673 to 1994. Summer balance was reconstructed from tree-ring estimates of summer temperature and precipitation in the Canadian Rockies. Winter balance was derived from tree-ring data from sites bordering the Gulf of Alaska and in western British Columbia. The models for winter and summer balance each explain over 40% of the variance in the appropriate mass-balance series. Over the period 1966–1994 the correlation between the reconstructed and measured net balances is 0.71. Strong positive mass balances are reconstructed for 1695–1720 and 1810–1825, when higher winter precipitation coincided with reduced ablation. Periods of reconstructed positive mass balance precede construction of terminal moraines throughout the Canadian Rockies ca. 1700–1725 and 1825–1850. Positive mass balances in the period 1845–1880 also correspond to intervals of glacier readvance. Mass balances were generally negative between 1760 and 1805. From 1673 to 1883 the mean annual net balance was +70 mm water equivalent per year (w.e./yr.), but it averaged −317 mm w.e./yr from 1884 to 1994. This reconstructed mass balance history provides a continuous record of glacier change that appears regionally representative and consistent with moraine and other proxy climate records.

The impact of glaciers on the runoff and the reconstruction of mass balance history from hydrological data in the tropical Cordillera Blanca, Perú

A 41 years series of runoff and precipitation data from the Peruvian Cordillera Blanca demonstrates the high hygric seasonality in this tropical high mountain range. In this area, glaciers have a crucial impact on runoff which is of essential importance for the highly populated and cultivated valley of the Callejon de Huaylas particularly during the dry season. Whereas the mid latitudes glacier runoff amplifies the seasonal variation of runoff, the effect of glaciers in the low latitudes is a smoothing one. It decreases clearly with the decreasing degree of glaciation. In addition, particular circumstances of this tropical environment allow the reconstruction of a glacier mass balance history from the hydrological data for the second half of the 20th century. It shows a high synchronicity with the global trend of periods with glacier mass loss and gain. Comparison with length variations of three individual glaciers indicate a rather fast reaction of these glaciers to changes in mass balance. Although the mass balance variations show some differences among the individual catchment basins, the over all trend is uniform. A general positive correlation of mass balance variations with SOI is obvious but not regular.

Numerical modelling of historical front variations and dynamic response of Sofiyskiy glacier, Altai mountains, Russia

AbstractThe recent fluctuation of the central Asian climate, and its effect on the region’s glaciers, is poorly known, largely because of a lack of knowledge of the dynamic behaviour of so-called summer-accumulation-type glaciers. In this study, a one-dimensional numerical glacier model is used to simulate the dynamic response of Sofiyskiy glacier, Altai mountains, Russia, to climate forcing. A successful simulation of the observed historical front variations was accomplished by dynamic calibration. This resulted in a reconstruction of the recent mass-balance history of the glacier, showing a distinct decline in surface mass balance in the second half of the 19th century, a slightly higher mass balance at the beginning of the 20th century, followed by a steady decline towards present conditions. The future response of Sofiyskiy glacier was projected for six 21st-century climate scenarios. Under a “no-change” scenario, the glacier will retreat > 2 km by 2100. If air temperature gradually rises by > 5°C during this century, the glacier will vanish around 2100. Basic response characteristics of Sofiyskiy glacier were determined. These indicate rather low mass-balance sensitivity to temperature change, but a strong front reaction due to geometric conditions.

Mass balance and streamflow variability at Place Glacier, Canada, in relation to recent climate fluctuations

AbstractAlthough a great deal of research has focused on the hydrologic effects of climate variability and change, relatively little research has examined the effects on streamflow of interactions between climate variability and change and resulting glacier response. Place Glacier, in the southern Coast Mountains of British Columbia, Canada, has been monitored for mass balance since 1965, and a stream gauge was operated just below the glacier terminus from 1969 to 1989. This paper presents analyses of the mass balance history and streamflow variations in relation to recorded climatic variability.Place Glacier's winter and net balances are correlated with the Pacific Decadal Oscillation (PDO). Summer balance is positively correlated with summer temperature and negatively with the preceding winter balance, which enhances the effects of changes in winter balance on net balance. The well‐documented post‐1976 shift from the PDO cold phase to the present warm phase initiated a significant and persistent period of more negative net balance and terminal retreat. A reconstruction of net balance extending back to the 1890s, based on a regression with winter precipitation and summer temperature, displays decadal‐scale fluctuations consistent with the PDO. Summer streamflow responded to interannual variations in winter snow accumulation and summer temperatures, which control the rate of rise of the glacier snowline and melt rates. After accounting for these influences via regression analysis, August streamflow displayed a negative trend in total runoff. Examination of air photographs and the reconstructed mass balance history suggest that significant firn depletion had occurred prior to 1965, such that the dominant effect of glacier changes was a reduction in ice area, resulting in decreased meltwater production. Copyright © 2001 John Wiley & Sons, Ltd.

20th century mass balance and thermal regime change at Scott Turnerbreen, Svalbard

AbstractThe changing geometry and thermal structure of Scott Turnerbreen, a 3.3 km2 glacier located at 78° N in the Svalbard archipelago, is documented. A net mass balance of–0.58 m a–1w.e. is determined for the period 1936–93, by comparing a recent topographic survey with earlier maps. The thermal regime was investigated with multifrequency radar and borehole thermistors. Basal temperatures of–4.1° and –3.3°C were measured, and observed temperature gradients indicate that the entire bed is frozen. This interpretation is confirmed by continuous radar profiling, which demonstrates the absence of high-frequency scattering from temperate ice. However, with the reconstructed 1936 ice- thickness distribution, at least 2 km of the length of the glacier bed would be at the pressure-melting temperature. The 20th century mass-balance history of Scott Turnerbreen is likely to have been influenced by a surge occurring around 1930, which meant that the glacier was already in a state of disequilibrium before the abrupt climate perturbation marking the termination of the Little Ice Age. A significant loss of mass has been accompanied by a transition from inferred polythermal to entirely non-temperate thermal conditions. Current driving stress and velocity are very low, and the glacier has almost certainly fallen out of the surge cycle. Within 60 years, there has therefore been a wholesale transformation in the geometry, thermal structure and dynamics of Scott Turnerbreen.

A flowline model for Nigardsbreen, Norway: projection of future glacier length based on dynamic calibration with the historic record

Historic glacier-length variations are used to constrain a computer model for Nigardsbreen, Norway. A mass-balance history is derived that, when imposed on the flow model, gives an almost perfect match between observed and simulated glacier length since AD 1748. Being calibrated with past changes, the model predicts an 800 m advance of the glacier snout if mass-balance conditions remain as they were for the period 1962–93. Several greenhouse-warming scenarios are imposed to project the glacier’s behaviour into the next century. For a uniform heating rate of 0.02 K a–1, Nigardsbreen would advance slightly until AD 2020, but then a very rapid retreat would start: in AD 2100 glacier volume would be only 10% of the 1950 volume.

Simulation of the historical variations in length of Unterer Grindelwaldgletscher, Switzerland

AbstractThe historical length variations in Unterer Grindelwaldgletscher have been simulated by coupling a numerical mass-balance model to a dynamic ice-flow model. As forcing functions, we used (partly reconstructed) local climatic records, which were transformed by the mass-balance model into a mass-balance history. The ice-flow model then computes the length variations that have occurred over the course of time.In a model run from AD 1530 to the present, with both seasonal temperature and precipitation variations as forcing functions, the observed maximum length of the glacier around AD 1860 and the subsequent retreat are simulated. The observed AD 1600 maximum, however, does not show up in the simulation. This is probably due to an incorrect reconstruction of the mass balance for this period, as detailed climatic data are available only since 1865. The root-mean-square difference between the simulated and the observed front positions is 0.28 km. The simulated glacier geometry for 1987 fits the observed geometry for that year reasonably well.Because of the success of the historical simulation, an attempt is made to predict future glacier retreat on the basis of two different greenhouse-gas scenarios. For a Business-as-Usual scenario, only 29% of the 1990 volume would remain in AD 2100.

A flowline model for Nigardsbreen, Norway: projection of future glacier length based on dynamic calibration with the historic record

Historic glacier-length variations are used to constrain a computer model for Nigardsbreen, Norway. A mass-balance history is derived that, when imposed on the flow model, gives an almost perfect match between observed and simulated glacier length since AD 1748. Being calibrated with past changes, the model predicts an 800 m advance of the glacier snout if mass-balance conditions remain as they were for the period 1962–93. Several greenhouse-warming scenarios are imposed to project the glacier’s behaviour into the next century. For a uniform heating rate of 0.02 K a–1, Nigardsbreen would advance slightly until AD 2020, but then a very rapid retreat would start: in AD 2100 glacier volume would be only 10% of the 1950 volume.

Simulation of the historical variations in length of Unterer Grindelwaldgletscher, Switzerland

AbstractThe historical length variations in Unterer Grindelwaldgletscher have been simulated by coupling a numerical mass-balance model to a dynamic ice-flow model. As forcing functions, we used (partly reconstructed) local climatic records, which were transformed by the mass-balance model into a mass-balance history. The ice-flow model then computes the length variations that have occurred over the course of time.In a model run from AD 1530 to the present, with both seasonal temperature and precipitation variations as forcing functions, the observed maximum length of the glacier around AD 1860 and the subsequent retreat are simulated. The observed AD 1600 maximum, however, does not show up in the simulation. This is probably due to an incorrect reconstruction of the mass balance for this period, as detailed climatic data are available only since 1865. The root-mean-square difference between the simulated and the observed front positions is 0.28 km. The simulated glacier geometry for 1987 fits the observed geometry for that year reasonably well.Because of the success of the historical simulation, an attempt is made to predict future glacier retreat on the basis of two different greenhouse-gas scenarios. For a Business-as-Usual scenario, only 29% of the 1990 volume would remain in AD 2100.

Hintereisferner, Austria: mass-balance reconstruction and numerical modelling of the historical length variations

AbstractIn this study, an attempt is made to simulate the historical length variations of Hintereisferner (Austria). Key elements in the model are: (1) reconstruction of the local climate (Vent); (2) multiple linear regression analysis between measured climate and mass-balance variations; (3) reconstruction of the mass balance with (1) and (2); (4) a one-dimensional numerical ice-flow model forced by the mass-balance history. Progress relative to the previous, similar studies can be summarized as two points: (1) the mass balance is reconstructed more carefully, and (2) sensitivity experiments show that uncertainties and assumptions in the flow model hardly affect the response of the glacier to climate fluctuations with a time-scale of the order of (or larger than) the response time of the glacier (around 100 year).In the regression equation, mass-balance fluctuations are determined by the temperature during the ablation season and the annual precipitation. Cloudiness has no effect. The local temperature can be reconstructed as far back as 1755 with the temperature series from Basel, but the reconstruction of precipitation is unreliable prior to 1900. Mainly due to this point, a simulation starting in 1755 failed completely. However, in a run starting in 1894, the total retreat since then (2.2 km) was reproduced within 10%.

Hintereisferner, Austria: mass-balance reconstruction and numerical modelling of the historical length variations

AbstractIn this study, an attempt is made to simulate the historical length variations of Hintereisferner (Austria). Key elements in the model are: (1) reconstruction of the local climate (Vent); (2) multiple linear regression analysis between measured climate and mass-balance variations; (3) reconstruction of the mass balance with (1) and (2); (4) a one-dimensional numerical ice-flow model forced by the mass-balance history. Progress relative to the previous, similar studies can be summarized as two points: (1) the mass balance is reconstructed more carefully, and (2) sensitivity experiments show that uncertainties and assumptions in the flow model hardly affect the response of the glacier to climate fluctuations with a time-scale of the order of (or larger than) the response time of the glacier (around 100 year).In the regression equation, mass-balance fluctuations are determined by the temperature during the ablation season and the annual precipitation. Cloudiness has no effect. The local temperature can be reconstructed as far back as 1755 with the temperature series from Basel, but the reconstruction of precipitation is unreliable prior to 1900. Mainly due to this point, a simulation starting in 1755 failed completely. However, in a run starting in 1894, the total retreat since then (2.2 km) was reproduced within 10%.

Predicted time-scales for GISP2 and GRIP boreholes at Summit, Greenland

AbstractTwo deep-drilling projects (GISP2 and GRIP) in central Greenland will provide ice cores for paleoclimate studies. Drilling decisions and preliminary interpretations require age-depth curves (time-scales). Using a finite-element momentum-balance model, we calculate the modern ice-flow pattern on the flowline through the two drill sites. Our model appears to require relatively soft ice either throughout the ice sheet or below the Wisconsinan-Holocene transition in order to match the modern geometry and mass balance. By scaling the ice velocity to an assumed mass-balance history throughout the past 200 000 years, we estimate the time-scales at both sites. At GISP2, a flank site, we place the 10 000 years BP isochrone (representing the Wisconsinan-Holocene transition) at 1535 m ice-equivalent depth. At GRIP, on the ice divide, the corresponding depth is 1377 m. Our calculations show ice older than 200 000 years at 100 m above the bed at both coring sites. The time-scale calculation can be used for drilling decisions and preliminary interpretations. It should be refined as more regional-survey and ice-core data become available.

Predicted time-scales for GISP2 and GRIP boreholes at Summit, Greenland

AbstractTwo deep-drilling projects (GISP2 and GRIP) in central Greenland will provide ice cores for paleoclimate studies. Drilling decisions and preliminary interpretations require age-depth curves (time-scales). Using a finite-element momentum-balance model, we calculate the modern ice-flow pattern on the flowline through the two drill sites. Our model appears to require relatively soft ice either throughout the ice sheet or below the Wisconsinan-Holocene transition in order to match the modern geometry and mass balance. By scaling the ice velocity to an assumed mass-balance history throughout the past 200 000 years, we estimate the time-scales at both sites. At GISP2, a flank site, we place the 10 000 years BP isochrone (representing the Wisconsinan-Holocene transition) at 1535 m ice-equivalent depth. At GRIP, on the ice divide, the corresponding depth is 1377 m. Our calculations show ice older than 200 000 years at 100 m above the bed at both coring sites. The time-scale calculation can be used for drilling decisions and preliminary interpretations. It should be refined as more regional-survey and ice-core data become available.