Using GRACE Data to Estimate Climate Change Impacts on the Earth’s Moment of Inertia

The widely used 15-year Gravity Recovery and Climate Experiment (GRACE) measured mass redistribution shows an increasing trend in the nontidal Earth’s moment of inertia (MOI). Various contributing components are independently evaluated using five high-quality atmospheric reanalysis datasets and a novelty numerical modeling system. We found a steady, statistically robust (passed a two-tailed t-test at p = 0.04 for dof = 15) rate of MOI increase reaching ∼11.0 × 1027 kg m2/yr, equivalent to a 11.45 sμ/yr increase in the length of day, during 2002–2017. Further analysis suggests that the Antarctic ice sheet contributes the most, followed by the Greenland ice sheet, the precipitation-driven land hydrological cycle, mountain glaciers, and the fluctuation of atmosphere, in this order. Short-term MOI spikes from the GRACE measurements are mostly associated with major low/mid-latitude earthquakes, fitting closely with the MOI variations from the hydrological cycle. Atmospheric fluctuation contributes the least but has a steady trend of 0.5 sμ/yr, with horizontal mass distribution contributing twice as much as the vertical expansion and associated lift of the atmosphere’s center of mass. The latter is a previously overlooked term affecting MOI fluctuation. The contribution to the observed MOI trend from a warming climate likely will persist in the future, largely due to the continuous mass loss from the Earth’s ice sheets.

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An ice flow modeling perspective on bedrock adjustment patterns of the Greenland ice sheet

The Cryosphere ◽

10.5194/tc-6-1263-2012 ◽

2012 ◽

Vol 6 (6) ◽

pp. 1263-1274 ◽

Cited By ~ 3

Author(s):

M. Olaizola ◽

R. S. W. van de Wal ◽

M. M. Helsen ◽

B. de Boer

Keyword(s):

Mass Balance ◽

Maximum Yield ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Elastic Response ◽

Delayed Response ◽

Surface Mass ◽

Grace Data ◽

Grace Satellites ◽

Gravity Recovery

Abstract. Since the launch in 2002 of the Gravity Recovery and Climate Experiment (GRACE) satellites, several estimates of the mass balance of the Greenland ice sheet (GrIS) have been produced. To obtain ice mass changes, the GRACE data need to be corrected for the effect of deformation changes of the Earth's crust. Recently, a new method has been proposed where ice mass changes and bedrock changes are simultaneously solved. Results show bedrock subsidence over almost the entirety of Greenland in combination with ice mass loss which is only half of the currently standing estimates. This subsidence can be an elastic response, but it may however also be a delayed response to past changes. In this study we test whether these subsidence patterns are consistent with ice dynamical modeling results. We use a 3-D ice sheet–bedrock model with a surface mass balance forcing based on a mass balance gradient approach to study the pattern and magnitude of bedrock changes in Greenland. Different mass balance forcings are used. Simulations since the Last Glacial Maximum yield a bedrock delay with respect to the mass balance forcing of nearly 3000 yr and an average uplift at present of 0.3 mm yr−1. The spatial pattern of bedrock changes shows a small central subsidence as well as more intense uplift in the south. These results are not compatible with the gravity based reconstructions showing a subsidence with a maximum in central Greenland, thereby questioning whether the claim of halving of the ice mass change is justified.

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A framework for deriving drought indicators from the Gravity Recovery and Climate Experiment (GRACE)

Hydrology and Earth System Sciences ◽

10.5194/hess-24-227-2020 ◽

2020 ◽

Vol 24 (1) ◽

pp. 227-248 ◽

Cited By ~ 2

Author(s):

Helena Gerdener ◽

Olga Engels ◽

Jürgen Kusche

Keyword(s):

Hydrological Cycle ◽

Water Storage ◽

Synthetic Data ◽

Satellite Gravity ◽

Spatially Correlated ◽

Grace Data ◽

Spatial Noise ◽

Drought Indicators ◽

Gravity Recovery ◽

Linear Trends

Abstract. Identifying and quantifying drought in retrospective is a necessity for better understanding drought conditions and the propagation of drought through the hydrological cycle and eventually for developing forecast systems. Hydrological droughts refer to water deficits in surface and subsurface storage, and since these are difficult to monitor at larger scales, several studies have suggested exploiting total water storage data from the GRACE (Gravity Recovery and Climate Experiment) satellite gravity mission to analyze them. This has led to the development of GRACE-based drought indicators. However, it is unclear how the ubiquitous presence of climate-related or anthropogenic water storage trends found within GRACE analyses masks drought signals. Thus, this study aims to better understand how drought signals propagate through GRACE drought indicators in the presence of linear trends, constant accelerations, and GRACE-specific spatial noise. Synthetic data are constructed and existing indicators are modified to possibly improve drought detection. Our results indicate that while the choice of the indicator should be application-dependent, large differences in robustness can be observed. We found a modified, temporally accumulated version of the Zhao et al. (2017) indicator particularly robust under realistic simulations. We show that linear trends and constant accelerations seen in GRACE data tend to mask drought signals in indicators and that different spatial averaging methods required to suppress the spatially correlated GRACE noise affect the outcome. Finally, we identify and analyze two droughts in South Africa using real GRACE data and the modified indicators.

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Basal Drainage System Response to Increasing Surface Melt on the Greenland Ice Sheet

Science ◽

10.1126/science.1235905 ◽

2013 ◽

Vol 341 (6147) ◽

pp. 777-779 ◽

Cited By ~ 102

Author(s):

T. Meierbachtol ◽

J. Harper ◽

N. Humphrey

Keyword(s):

Conceptual Models ◽

Ice Sheet ◽

Drainage System ◽

Greenland Ice Sheet ◽

System Response ◽

Mountain Glaciers ◽

In Situ Observations ◽

Key Aspects ◽

Conduit Development

Surface meltwater reaching the bed of the Greenland ice sheet imparts a fundamental control on basal motion. Sliding speed depends on ice/bed coupling, dictated by the configuration and pressure of the hydrologic drainage system. In situ observations in a four-site transect containing 23 boreholes drilled to Greenland’s bed reveal basal water pressures unfavorable to water-draining conduit development extending inland beneath deep ice. This finding is supported by numerical analysis based on realistic ice sheet geometry. Slow meltback of ice walls limits conduit growth, inhibiting their capacity to transport increased discharge. Key aspects of current conceptual models for Greenland basal hydrology, derived primarily from the study of mountain glaciers, appear to be limited to a portion of the ablation zone near the ice sheet margin.

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The meltwater feedbacks on ice dynamics, influence of melt amplitude, duration and extent.

10.5194/egusphere-egu21-1099 ◽

2021 ◽

Author(s):

Basile de Fleurian ◽

Petra M. Langebroeke ◽

Richard Davy

Keyword(s):

Water Pressure ◽

Ice Sheet ◽

Drainage System ◽

Greenland Ice Sheet ◽

System Model ◽

Ice Dynamics ◽

Mountain Glaciers ◽

Different Characteristics ◽

Crucial Parameter ◽

Subglacial Drainage

In recent years, temperatures over the Greenland ice sheet have been rising, leading to an increase in surface melt. This increase however can not be reduced to a simple number. Throughout the recent years we have seen some extreme melt seasons with melt extending over the whole surface of the ice sheet (2012) or melt seasons of lower amplitudes but with a longer duration (2010). The effect of those variations on the subglacial system and hence on ice dynamic are poorly understood and are still mainly deduced from studies based on mountain glaciers.Here we apply the Ice-sheet and Sea-level System Model (ISSM) to a synthetic glacier with a geometry similar to a Greenland ice sheet land terminating glacier. The forcing is designed such that it allows to investigate different characteristics of the melt season: its length, intensity or the spatial extension of the melt. Subglacial hydrology and ice dynamics are coupled within ISSM is coupled to a subglacial hydrology model, allowing to study the response of the system in terms of subglacial water pressure and the final impact on ice dynamics. Of particular interest is the evolution of the distribution of the efficient and inefficient component of the subglacial drainage system which directly impacts the water pressure evolution at the base of the glacier.We note that the initiation of the melt season and the intensity of the melt at this period is a crucial parameter when studying the dynamic response of the glacier to different melt season characteristics. From those results, we can infer a more precise evolution of the dynamics of land terminating glaciers that are heavily driven by their subglacial drainage system. We also highlight which changes in the melt season pattern would be the most damageable for glacier stability in the future.

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A comparison of late glacial-early Holocene fluctuations of Greenland Ice Sheet outlet glaciers with nearby mountain glaciers in central east Greenland

Quaternary International ◽

10.1016/j.quaint.2012.08.549 ◽

2012 ◽

Vol 279-280 ◽

pp. 240

Author(s):

Meredith Kelly

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Late Glacial ◽

Early Holocene ◽

East Greenland ◽

Mountain Glaciers

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Earth's ice imbalance

10.5194/egusphere-egu21-2399 ◽

2021 ◽

Author(s):

Thomas Slater ◽

Isobel Lawrence ◽

Inès Otosaka ◽

Andrew Shepherd ◽

Noel Gourmelen ◽

...

Keyword(s):

Sea Ice ◽

Numerical Models ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Arctic Sea Ice ◽

Ice Shelf ◽

Ice Shelves ◽

Mountain Glaciers ◽

Arctic Sea ◽

The Antarctic

Satellite observations are the best method for tracking ice loss, because the cryosphere is vast and remote. Using these, and some numerical models, we show that Earth lost 28 trillion tonnes of ice between 1994 and 2017. Arctic sea ice (7.6 trillion tonnes), Antarctic ice shelves (6.5 trillion tonnes), mountain glaciers (6.1 trillion tonnes), the Greenland ice sheet (3.8 trillion tonnes), the Antarctic ice sheet (2.5 trillion tonnes), and Southern Ocean sea ice (0.9 trillion tonnes) have all decreased in mass. Just over half (58 %) of the ice loss was from the northern hemisphere, and the remainder (42 %) was from the southern hemisphere. The rate of ice loss has risen by 57 % since the 1990s &#8211; from 0.8 to 1.2 trillion tonnes per year &#8211; owing to increased losses from mountain glaciers, Antarctica, Greenland, and from Antarctic ice shelves. During the same period, the loss of grounded ice from the Antarctic and Greenland ice sheets and mountain glaciers raised the global sea level by 34.6 &#177; 3.1 mm. The majority of all ice losses were driven by atmospheric melting (68 % from Arctic sea ice, mountain glaciers ice shelf calving and ice sheet surface mass balance), with the remaining losses (32 % from ice sheet discharge and ice shelf thinning) being driven by oceanic melting. Altogether, these elements of the cryosphere have taken up 3.2 % of the global energy imbalance.

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Improved GRACE regional mass balance estimates of the Greenland ice sheet cross-validated with the input–output method

The Cryosphere ◽

10.5194/tc-10-895-2016 ◽

2016 ◽

Vol 10 (2) ◽

pp. 895-912 ◽

Cited By ~ 7

Author(s):

Zheng Xu ◽

Ernst J. O. Schrama ◽

Wouter van der Wal ◽

Michiel van den Broeke ◽

Ellyn M. Enderlin

Keyword(s):

Mass Balance ◽

Climate Model ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Mass Change ◽

Input Output ◽

Surface Mass ◽

Ice Cloud ◽

The Difference ◽

Gravity Recovery

Abstract. In this study, we use satellite gravimetry data from the Gravity Recovery and Climate Experiment (GRACE) to estimate regional mass change of the Greenland ice sheet (GrIS) and neighboring glaciated regions using a least squares inversion approach. We also consider results from the input–output method (IOM). The IOM quantifies the difference between the mass input and output of the GrIS by studying the surface mass balance (SMB) and the ice discharge (D). We use the Regional Atmospheric Climate Model version 2.3 (RACMO2.3) to model the SMB and derive the ice discharge from 12 years of high-precision ice velocity and thickness surveys. We use a simulation model to quantify and correct for GRACE approximation errors in mass change between different subregions of the GrIS, and investigate the reliability of pre-1990s ice discharge estimates, which are based on the modeled runoff. We find that the difference between the IOM and our improved GRACE mass change estimates is reduced in terms of the long-term mass change when using a reference discharge derived from runoff estimates in several subareas. In most regions our GRACE and IOM solutions are consistent with other studies, but differences remain in the northwestern GrIS. We validate the GRACE mass balance in that region by considering several different GIA models and mass change estimates derived from data obtained by the Ice, Cloud and land Elevation Satellite (ICESat). We conclude that the approximated mass balance between GRACE and IOM is consistent in most GrIS regions. The difference in the northwest is likely due to underestimated uncertainties in the IOM solutions.

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