ice dynamics
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2022 ◽  
Vol 8 ◽  
Author(s):  
Martin Jakobsson ◽  
Larry A. Mayer

The ocean and the marine parts of the cryosphere interact directly with, and are affected by, the seafloor and its primary properties of depth (bathymetry) and shape (morphology) in many ways. Bottom currents are largely constrained by undersea terrain with consequences for both regional and global heat transport. Deep ocean mixing is controlled by seafloor roughness, and the bathymetry directly influences where marine outlet glaciers are susceptible to the inflow relatively warm subsurface waters - an issue of great importance for ice-sheet discharge, i.e., the loss of mass from calving and undersea melting. Mass loss from glaciers and the Greenland and Antarctic ice sheets, is among the primary drivers of global sea-level rise, together now contributing more to sea-level rise than the thermal expansion of the ocean. Recent research suggests that the upper bounds of predicted sea-level rise by the year 2100 under the scenarios presented in IPCC’s Special Report on the Ocean and Cryosphere in a Changing Climate (SROCCC) likely are conservative because of the many unknowns regarding ice dynamics. In this paper we highlight the poorly mapped seafloor in the Polar regions as a critical knowledge gap that needs to be filled to move marine cryosphere science forward and produce improved understanding of the factors impacting ice-discharge and, with that, improved predictions of, among other things, global sea-level. We analyze the bathymetric data coverage in the Arctic Ocean specifically and use the results to discuss challenges that must be overcome to map the most remotely located areas in the Polar regions in general.


2022 ◽  
Author(s):  
Thomas Hudson ◽  
Sofia-Katerina Kufner ◽  
Alex Brisbourne ◽  
Michael Kendall ◽  
Andrew Smith ◽  
...  

Abstract The slip of glaciers over the underlying bed is the dominant mechanism governing the migration of ice from land into the oceans, contributing to sea-level rise. Yet glacier slip remains poorly understood or constrained by observations. Here we observe both frictional shear-stress and slip at the bed of an ice stream, using 100,000 repetitive stick-slip icequakes from Rutford Ice Stream, Antarctica. Basal shear-stresses and slip-rates vary from 10^4 to 10^7 Pa and 0.2 to 1.5 m day^(-1), respectively. Friction and slip vary temporally over the order of hours and spatially over 10s of meters, caused by corresponding variations in ice-bed interface material and effective-normal-stress. Our findings also suggest that the bed is substantially more complex than currently assumed in ice stream models and that basal effective-normal-stresses may be significantly higher than previously thought. The observations also provide previously unresolved constraint of the basal boundary conditions of ice dynamics models. This is critical for constraining the primary contribution of ice mass loss in Antarctica, and hence the endeavour to reduce uncertainty in sea-level rise projections.


2022 ◽  
Author(s):  
Clive Hambler ◽  
Peter A. Henderson

Abstract 1) Globally-representative monthly rates of change of atmospheric carbon dioxide and methane are compared with global rates of change of sea ice and with Arctic and Antarctic air temperatures. 2) Carbon dioxide is very strongly correlated with sea ice dynamics, with the carbon dioxide rate at Mauna Loa lagging sea ice extent rate by 7 months. 3) Methane is very strongly correlated with sea ice dynamics, with the global (and Mauna Loa) methane rate lagging sea ice extent rate by 5 months. 4) Sea ice melt rate peaks in very tight synchrony with temperature in each Hemisphere. 5) The very high synchrony of the two gases is most parsimoniously explained by a common causality acting in both Hemispheres. 6) Time lags between variables indicate primary drivers of the gas dynamics are due to solar action on the polar regions, not mid-latitudes as is conventionally believed. 7) Results are consistent with a proposed role of a high-latitude temperature-dependent abiotic variable such as sea ice in the annual cycles of carbon dioxide and methane. 8) If sea ice does not drive the net flux of these gases, it is a highly precise proxy for whatever does. 9) Potential mechanisms should be investigated urgently.


2022 ◽  
Author(s):  
Ilaria Crotti ◽  
Aurelien Quiquet ◽  
Amaelle Landais ◽  
Barbara Stenni ◽  
David Wilson ◽  
...  

Abstract The response of the East Antarctic Ice Sheet to past intervals of oceanic and atmospheric warming is still not well constrained but critical for understanding both past and future sea-level change. Furthermore, the ice sheet in the Wilkes Subglacial Basin, which is characterized by a reverse-sloping bed, appears to have undergone thinning and ice discharge events during recent decades. By combining new glaciological evidence on ice sheet elevation from the TALDICE ice core with offshore sedimentological records and ice sheet modelling experiments, we reconstruct the ice dynamics in the Wilkes Subglacial Basin over the past 350,000 years. Our results indicate that the Wilkes Subglacial Basin experienced an extensive retreat 330,000 years ago and a more limited retreat 125,000 years ago. These changes coincided with warmer Southern Ocean temperatures and elevated global mean sea level during those interglacial periods, confirming the sensitivity of the Wilkes Subglacial Basin ice sheet to ocean warming and its potential role in sea-level change.


2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Juan Pablo Corella ◽  
Niccolo Maffezzoli ◽  
Andrea Spolaor ◽  
Paul Vallelonga ◽  
Carlos A. Cuevas ◽  
...  

AbstractIodine has a significant impact on promoting the formation of new ultrafine aerosol particles and accelerating tropospheric ozone loss, thereby affecting radiative forcing and climate. Therefore, understanding the long-term natural evolution of iodine, and its coupling with climate variability, is key to adequately assess its effect on climate on centennial to millennial timescales. Here, using two Greenland ice cores (NEEM and RECAP), we report the Arctic iodine variability during the last 127,000 years. We find the highest and lowest iodine levels recorded during interglacial and glacial periods, respectively, modulated by ocean bioproductivity and sea ice dynamics. Our sub-decadal resolution measurements reveal that high frequency iodine emission variability occurred in pace with Dansgaard/Oeschger events, highlighting the rapid Arctic ocean-ice-atmosphere iodine exchange response to abrupt climate changes. Finally, we discuss if iodine levels during past warmer-than-present climate phases can serve as analogues of future scenarios under an expected ice-free Arctic Ocean. We argue that the combination of natural biogenic ocean iodine release (boosted by ongoing Arctic warming and sea ice retreat) and anthropogenic ozone-induced iodine emissions may lead to a near future scenario with the highest iodine levels of the last 127,000 years.


2022 ◽  
Author(s):  
John Erich Christian ◽  
Alexander A. Robel ◽  
Ginny Catania

Abstract. Many marine-terminating outlet glaciers have retreated rapidly in recent decades, but these changes have not been formally attributed to anthropogenic climate change. A key challenge for such an attribution assessment is that if glacier termini are sufficiently perturbed from bathymetric highs, ice-dynamic feedbacks can cause rapid retreat even without further climate forcing. In the presence of internal climate variability, attribution thus depends on understanding whether (or how frequently) these rapid retreats could be triggered by climatic noise alone. Our simulations with idealized glaciers show that in a noisy climate, rapid retreat is a stochastic phenomenon. We therefore propose a probabilistic approach to attribution and present a framework for analysis that uses ensembles of many simulations with independent realizations of random climate variability. Synthetic experiments show that century-scale climate trends substantially increase the likelihood of rapid glacier retreat. This effect depends on the timescales over which ice dynamics integrate forcing. For a population of synthetic glaciers with different topographies, we find that external trends increase the number of large retreats triggered within the population, offering a metric for regional attribution. Our analyses suggest that formal attribution studies are tractable and should be further pursued to clarify the human role in recent ice-sheet change. We emphasize that early-industrial-era constraints on glacier and climate state are likely to be crucial for such studies.


Molecules ◽  
2021 ◽  
Vol 27 (1) ◽  
pp. 258
Author(s):  
Elzbieta Pach ◽  
Albert Verdaguer

Scanning electron microscopy (SEM) is a powerful imaging technique able to obtain astonishing images of the micro- and the nano-world. Unfortunately, the technique has been limited to vacuum conditions for many years. In the last decades, the ability to introduce water vapor into the SEM chamber and still collect the electrons by the detector, combined with the temperature control of the sample, has enabled the study of ice at nanoscale. Astounding images of hexagonal ice crystals suddenly became real. Since these first images were produced, several studies have been focusing their interest on using SEM to study ice nucleation, morphology, thaw, etc. In this paper, we want to review the different investigations devoted to this goal that have been conducted in recent years in the literature and the kind of information, beyond images, that was obtained. We focus our attention on studies trying to clarify the mechanisms of ice nucleation and those devoted to the study of ice dynamics. We also discuss these findings to elucidate the present and future of SEM applied to this field.


2021 ◽  
pp. 1-15
Author(s):  
Yin Fu ◽  
Qiao Liu ◽  
Guoxiang Liu ◽  
Bo Zhang ◽  
Rui Zhang ◽  
...  

Abstract Most glaciers on the Tibetan Plateau have experienced continuous mass losses in response to global warming. However, the seasonal dynamics of glaciers on the southeastern Tibetan Plateau have rarely been reported in terms of glacier surface elevation and velocity. This paper presents a first attempt to explore the seasonal dynamics of the debris-covered Dagongba Glacier within the southeastern Tibetan Plateau. We use the multitemporal unoccupied aerial vehicle images collected over the lower ablation zone on 8 June and 17 October 2018, and 13 May 2019, and then perform an analysis concerning climatic fluctuations. The results reveal that the mean surface elevation decrease of the Dagongba Glacier during the warm season ( $2.81\pm 0.44$ m) was remarkably higher than the cold season ( $0.72\pm 0.45$ m). Particularly notable glacier surface elevation changes were found around supraglacial lakes and ice cliffs where ice ablation rates were $\sim$ 3 times higher than the average. In addition, a larger longitudinal decline of glacier surface velocity was observed in the warm season than that in the cold season. In terms of further comparative analysis, the Dagongba Glacier experienced a decrease in surface velocity between 1982–83 and 2018–19, with a decrease in the warm season possibly twice as large as that in the cold season.


2021 ◽  
Vol 9 ◽  
Author(s):  
Anna Wendleder ◽  
Andreas Schmitt ◽  
Thilo Erbertseder ◽  
Pablo D’Angelo ◽  
Christoph Mayer ◽  
...  

The existence of supraglacial lakes influences debris-covered glaciers in two ways. The absorption of solar radiation in the water leads to a higher ice ablation, and water draining through the glacier to its bed leads to a higher velocity. Rising air temperatures and changes in precipitation patterns provoke an increase in the supraglacial lakes in number and total area. However, the seasonal evolution of supraglacial lakes and thus their potential for influencing mass balance and ice dynamics have not yet been sufficiently analyzed. We present a summertime series of supraglacial lake evolution on Baltoro Glacier in the Karakoram from 2016 to 2020. The dense time series is enabled by a multi-sensor and multi-temporal approach based on optical (Sentinel-2 and PlanetScope) and Synthetic Aperture Radar (SAR; Sentinel-1 and TerraSAR-X) remote sensing data. The mapping of the seasonal lake evolution uses a semi-automatic approach, which includes a random forest classifier applied separately to each sensor. A combination of linear regression and the Hausdorff distance is used to harmonize between SAR- and optical-derived lake areas, producing consistent and internally robust time series dynamics. Seasonal variations in the lake area are linked with the Standardized Precipitation Index (SPI) and Standardized Temperature Index (STI) based on air temperature and precipitation data derived from the climate reanalysis dataset ERA5-Land. The largest aggregated lake area was found in 2018 with 5.783 km2, followed by 2019 with 4.703 km2, and 2020 with 4.606 km2. The years 2016 and 2017 showed the smallest areas with 3.606 and 3.653 km2, respectively. Our data suggest that warmer spring seasons (April–May) with higher precipitation rates lead to increased formation of supraglacial lakes. The time series decomposition shows a linear increase in the lake area of 11.12 ± 9.57% per year. Although the five-year observation period is too short to derive a significant trend, the tendency for a possible increase in the supraglacial lake area is in line with the pronounced positive anomalies of the SPI and STI during the observation period.


2021 ◽  
Vol 9 ◽  
Author(s):  
Theresa Diener ◽  
Ingo Sasgen ◽  
Cécile Agosta ◽  
Johannes J. Fürst ◽  
Matthias H. Braun ◽  
...  

The dynamic stability of the Antarctic Ice Sheet is one of the largest uncertainties in projections of future global sea-level rise. Essential for improving projections of the ice sheet evolution is the understanding of the ongoing trends and accelerations of mass loss in the context of ice dynamics. Here, we examine accelerations of mass change of the Antarctic Ice Sheet from 2002 to 2020 using data from the GRACE (Gravity Recovery and Climate Experiment; 2002–2017) and its follow-on GRACE-FO (2018-present) satellite missions. By subtracting estimates of net snow accumulation provided by re-analysis data and regional climate models from GRACE/GRACE-FO mass changes, we isolate variations in ice-dynamic discharge and compare them to direct measurements based on the remote sensing of the surface-ice velocity (2002–2017). We show that variations in the GRACE/GRACE-FO time series are modulated by variations in regional snow accumulation caused by large-scale atmospheric circulation. We show for the first time that, after removal of these surface effects, accelerations of ice-dynamic discharge from GRACE/GRACE-FO agree well with those independently derived from surface-ice velocities. For 2002–2020, we recover a discharge acceleration of -5.3 ± 2.2 Gt yr−2 for the entire ice sheet; these increasing losses originate mainly in the Amundsen and Bellingshausen Sea Embayment regions (68%), with additional significant contributions from Dronning Maud Land (18%) and the Filchner-Ronne Ice Shelf region (13%). Under the assumption that the recovered rates and accelerations of mass loss persisted independent of any external forcing, Antarctica would contribute 7.6 ± 2.9 cm to global mean sea-level rise by the year 2100, more than two times the amount of 2.9 ± 0.6 cm obtained by linear extrapolation of current GRACE/GRACE-FO mass loss trends.


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