Ice mass balance

Antarctica

Below are updated results continued from our recent paper Harig and Simons [2014], *Earth Planet. Sci. Let.*, 415, 134-141, 2015. http://dx.doi.org/10.1016/j.epsl.2015.01.029. As of the last update January 2015 here, these results use the Release level 5 UTCSR (http://www.csr.utexas.edu/grace/) data solutions from January 2003 up to and including June 2014.

In the latest trend estimate from our paper Antarctica as a whole has lost -92 Gigatons per year since the beginning of 2003 (Fig 1, panel e). We also estimate mass changes for smaller regions within Antarctica (panels a-d), the most dramatic of these being West Antarctica which has lost -121 Gigatons per year of ice mass and has been strongly accelerating.

Figure 1: Total mass change trends for regions around Antarctica. The solid black line is the raw GRACE monthly solution. Here we use a bandwidth of 60 spherical harmonic degrees and a 0.5 degree buffer region. The solid blue line is the best-fitting exponential trend. For more technical details please see the Methods/Code webpage.

Figure 2: Geographical pattern of the cumulative mass change over Antarctica for the period between 1/2003 and 6/2014. The integral value "Int" for the entire epoch is shown in Gigatons. For more technical details please see the Methods/Code webpage.

The Antarctic Peninsula has experienced mass loss of −27 ±2 Gt/yr (see Fig. 1b). Over the last 10 years this trend has shown an acceleration of −5 ±1Gt/yr2. These aggregate values blur distinct changes between the northern and southern halves of the Peninsula. By 2003, several areas of the northern Peninsula had shown speed-up of glaciers visible to remote sensing, including the Larsen A and B areas, and continuous speed-up and retreat of west coast glaciers. This northerly mass loss is consistently detected by GRACE in all years of data availability, in agreement with other remote sensing data. The southern half of the Peninsula has experienced an acceleration towards increasing amounts of mass loss over the past decade. This has increased the overall mass losses, as has been seen in other recent studies as well.

Figure 3: Annual maps of mass change over West Antarctica (top two rows) and the Antarctica Peninsula (bottom two rows) from 2003 to 2013. For every year we show the difference of the signal estimated between January of that year and January of the next. The integral values of the mass change per year are shown as "Int", expressed in Gigatons. For more technical details please see the Methods/Code webpage.

Greenland

Below are updated results continued from our recent paper Harig and Simons [2012]. As of the last update January 2013, these results use the Release level 5 UTCSR (http://www.csr.utexas.edu/grace/) data solutions from January 2003 up to and including January 2013.
The past few years have seen unprecedented melting in Greenland measured by a variety of indicators (see the 2011 Arctic Report Card: Greenland for a good scientific summary). For GRACE mass measurements this means that recent years have increased the trend estimated since 2003. The RL-05 data do not include months from 2002 that appear in the RL-04 data. As a result, Greenland estimates will be somewhat larger than estimates using RL-04 data since the months from 2002 were all below the average melting trend.

The latest trend estimate increased from our paper to -241 Gigatons per year by (1) using more months from September 2011 to January 2013 and (2) the absence of 2002 data. The trend estimate is an average for the middle of the time period. So the slope of the time around 2007 is about -241 Gt/yr. 2003 was actually melting less than this, while 2012 was melting much more than this. The estimate just for 2012 is that Greenland lost 412 Gt of ice mass (see Fig 3).

Figure 1: Total mass change trend for Greenland. The solid black line is the raw GRACE monthly solution. Here we use a bandwidth of 60 spherical harmonic degrees and a 0.5 degree buffer region. The solid blue line is the best-fitting exponential trend. For more technical details please see the Methods/Code webpage. CLICK HERE for a high resolution version of the published figure from Harig and Simons [2012]

Figure 2: Geographical pattern of the cumulative mass change over Greenland for the period between 1/2003 and 1/2012. The integral value "Int" for the entire epoch is shown in Gigatons. The zero cm water contour shown in black. For more technical details please see the Methods/Code webpage. CLICK HERE for a high resolution version of the published figure from Harig and Simons [2012]

Figure 3: Yearly-resolved maps of mass change over Greenland from 2003 to 2011. For every year we show the difference of the signal estimated between January of that year and January of the next. The integral values of the mass change per year are shown as "Int", expressed in Gigatons. The zero cm/yr water contours are shown in black. For more technical details please see the Methods/Code webpage. CLICK HERE for a high resolution version of the published figure from Harig and Simons [2012]

The Arctic: Alaska, Canadian Archipelago, and Greenland

Below are the results continued from our recent paper Harig and Simons [2016], *Geophys. Res. Let.*, 2016. http://dx.doi.org/10.1002/2016GL067759. As of the most recent update January 2016 here, these results use the Release level 5 UTCSR (http://www.csr.utexas.edu/grace/) data solutions from January 2003 up to and including February 2015.

In the latest trend estimate from our paper Antarctica as a whole has lost -92 Gigatons per year since the beginning of 2003 (Fig 1, panel e). We also estimate mass changes for smaller regions within Antarctica (panels a-d), the most dramatic of these being West Antarctica which has lost -121 Gigatons per year of ice mass and has been strongly accelerating.

Figure 1: Map of the total ice mass change [mass corrected using the GIA model by Paulson et al., 2007] for the regions (black dashed lines) around a) Greenland and b) Gulf of Alaska. Coastlines are shown in light grey. Glaciated regions, as determined from the Randolph Glacier Inventory (RGI) version 3.2, are outlined in dark grey.
For more technical details please see the Methods/Code webpage.

Figure 2: Slepian eigenfunctions that are optimally concentrated within regions (grouped by row) outlining a) Ellesmere Island, b) Baffin Island, c) Gulf of Alaska North, and d) Gulf of Alaska South. Dashed lines indicate the regions of concentration. Functions are bandlimited to L=60 and are scaled to unit magnitude. The parameter alpha denotes which eigenfunction is shown. The parameter lambda is the corresponding eigenvalue for each function, indicating the amount of concentration. Magnitude values whose absolute values are smaller than 0.01 are left white. For more technical details please see the Methods/Code webpage.

Figure 3: Ice mass changes [mass corrected using the GIA model by Paulson et al., 2007] in gigatons (Gt) for a) North and b) South regions of the Gulf of Alaska. The regions covered by each localization are shaded in red in the top right inset. The black lines are monthly GRACE observations with two sigma error bars determined from our analysis. The solid blue lines are the best-fit estimates including a quadratic curve and the periodic annual and semi-annual terms. For each year in the analysis two numbers indicate the maximum (top) and minimum (bottom) difference between the observations and the fitted curves. For more technical details please see the Methods/Code webpage.

Figure 4: Ice mass changes [mass corrected using the GIA model by Paulson et al., 2007] in gigatons (Gt) for regions of a) Ellesmere Island, b) Baffin Island, and c) Greenland. The regions covered by each localization are shaded red in the top right inset. The black lines are monthly GRACE observations with two sigma grey error bars determined from our analysis. The solid blue lines are the best-fit estimates including a quadratic curve and the periodic annual and semi-annual terms. Estimates are fit using data prior to June 2013 (left of vertical grey lines), and then extrapolated forward through 2014 (right of vertical grey lines) to show the departure of recent data from the long-term trends. For more technical details please see the Methods/Code webpage.

Figure 5: Ice mass changes found after removing the long-term trend and accelerations from the curves shows in Fig. 4, leaving only the annual and semiannual components (blue lines) fitted from the data (black lines). The regions covered by each localization for a) Ellesmere, b) Baffin, and c) Greenland are shaded red in the insert. As in Fig. 4, estimates are fit using data prior to June 2013 (left of vertical grey lines), and then extrapolated forward through 2014 (right of vertical grey lines) to show the departure of recent data from the long-term trends. The grey bands around the blue lines represent the two sigma confidence intervals for the prediction of new data points. Yearly numbers indicate the maximum (top) and minimum (bottom) difference between the observations and the fitted curves. For more technical details please see the Methods/Code webpage.