Gravity Variation in Siberia: GRACE Observation and Possible Causes

We report the finding, from the GRACE observation, of an increasing trend in the gravity anomaly in Siberia at the rate of up to 0.5 ugal yr-1 during 2003/1 - 2009/12, in the backdrop of a negative anomaly of magnitude on the order of ~-10 mgal. In consideration of the non-uniqueness of the gravitational inverse problem, we examine in some detail the various possible geophysical causes to explain the increasing gravity signal. We find two geophysical mechanisms being the most plausible, namely the melting of permafrost and the GIA post-glacial rebound. We conclude that these two mechanisms cannot be ruled out as causes for the regional gravity increase in Siberia, based on gravity data and in want of ancillary geophysical data in the region. More definitive identification of the contributions of the various causes awaits further studies

Characterizing three-dimensional features of Antarctic subglacial lakes from the inversion of hydraulic potential—Lake Vostok as a case study

To estimate basal water storage beneath the Antarctic ice sheet, it is essential to have data on the three-dimensional characteristics of subglacial lakes. We present a method to estimate the water depth and surface area of Antarctic subglacial lakes from the inversion of hydraulic potential method. Lake Vostok is chosen as a case study because of the diverse and comprehensive measurements that have been obtained over and around the lake. The average depth of Lake Vostok is around 345±4 m. We estimated the surface area of Lake Vostok beneath the ice sheet to be about 13300±594 km2. The lake consists of two sub-basins separated by a ridge at water depths of about 200–300 m. The surface area of the northern sub-basin is estimated to be about half of that of the southern basin. The maximum depths of the northern and southern sub-basins are estimated to be about 450 and 850 m, respectively. Total water volume is estimated to be about 4658±204 km3. These estimates are compared with previous estimates obtained from seismic data and inversion of aerogravity data. In general, our estimates are closer to those obtained from the inversion of aerogravity data than those from seismic data, indicating the applicability of our method to the estimation of water depths of other subglacial lakes

GRACE RL05-based ice mass changes in the typical regions of antarctica from 2004 to 2012

The Antarctic ice sheet is the largest block of ice on Earth, a tiny change of its ice sheet will have a significant impact on sea level change, so it plays an important role in global climate change. The Gravity Recovery and Climate Experiment (GRACE) mission, launched in 2002, provides an alternative method to monitor the Antarctic ice mass variation. The latest Release Level 05 (RL05) version of GRACE time-variable gravity (TVG) data, derived from GRACE observations with improved quality and time-span over 10 years, were released by three GRACE data centers (CSR, JPL and GFZ) in April 2012, which gives us a chance to re-estimate the ice mass change over Antarctic more accurately. In this paper, we examine ice mass changes in regional scale, including Antarctic Peninsula (AP, West Antarctica), Amundsen Sea Embayment (ASE, West Antarctica), Lambert-Amery System (LAS, East Antarctica) and 27 drainage basins based on three data sets. The AP mass change rates are −12. 03±0. 74 Gt/a (CSR, 2004–2012), −13. 92±2. 33 Gt/a (JPL, 2004 −2012), −12. 28±0. 76 Gt/a (GFZ, 2005-2012), with an acceleration of −1.50±0. 25 Gt/a2, −1.54± 0. 26 Gt/a2, −0. 46±0. 28 Gt/a2 respectively, the ASE mass change rates are −89. 22±1. 93 Gt/a, −86. 28± 2. 20 Gt/a, −83. 67±1. 76 Gt/a with an acceleration of −10. 03±0. 65 Gt/a2, −8. 74±0. 74 Gt/a2 and -5. 69 ±0. 68 Gt/a2, and the LAS mass change rates are −4. 31±1. 95 Gt/a, −7. 29±2. 84 Gt/a, 1. 20±1. 35 Gt/a with an acceleration of −0. 18±0. 62 Gt/a2, 3. 55±0. 95 Gt/a2 and 0. 97±0. 49 Gt/a2. The mass change rates derived from the three RL05 data are very close to each other both in AP and ASE with the uncertainties much smaller than the change rates, and mass losses are significantly accelerated since 2007 in AP and 2006 in ASE, respectively. However, the mass change rates are significantly different in LAS, negative rate from CSR and JPL data, but positive rate from GFZ data, the uncertainties are even larger than the correspondent change rates. With regard to the 27 drainage basins, seven basins (basin 3–9) located in the east Antaxctica show positive mass change rates, and the rest twenty basins are chamcterizecl by negative mass change rates during the time span of the three RL05 data

On Tide Aliasing in GRACE Time-Variable Gravity Observations

Aliasing error induced by tide-related high frequency mass variations is one of the most significant errors in the Gravity Recovery and Climate Experiment (GRACE). In the present work, we evaluated the 161.0-day S2, 171.2-day P1, and 322.1-day S1 ocean tide aliasing in GRACE latest RL06 data based on nearly 15 years of observation from 2002 to 2017. Tide aliasing was still obvious for current GRACE observations, especially for S2 and P1 aliasing. S2 aliasing was mostly evident over West Antarctica, and was a clearly eastward propagation that travelled around Antarctica in about 2 years, while P1 showed strongest aliasing over South Greenland. More seriously, we found that GRACE mascon data showed an extremely large aliasing error. The mascon data may have unintentionally amplified the aliasing error on land due to the regularization (or constraint) applied for reducing signal leakage. Enough attention must be paid to tide aliasing when using GRACE for assessing mass variations at high latitudes (e.g., glaciers in polar regions) which can cause potential obstacles to estimation of actual seasonality