Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics

Abstract

We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993-2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt ⋅ y(-1), equivalent to 0.68 mm ⋅ y(-1) sea level rise (SLR) for 2003-2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004-2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland's outlet glaciers.

Keywords: Greenland Ice Sheet; ice dynamics; laser altimetry; mass balance.

Fig. 1.

Location of GrIS elevation time series according to the main data sets used for SERAC reconstruction. (A) PARCA ATM (1993−2003) and ICESat (purple); (B) PARCA ATM (2003−2009) and ICESat (blue), ICESat crossovers only (brown); (C) OIB ATM/LVIS (2009−2012) and ICESat (red); and (D) combined: all solutions (black). GrIS is shown in gray, and land surface with local ice caps and glaciers is in green/brown hues. Symbols in D mark the locations of elevation change time series shown in Fig. S1.

Fig. 2.

Classification of outlet glaciers based on dynamic thickness change pattern. (A) Thickness change time series derived from the combined ICESat/ATM/LVIS altimetry record (1993−2012) illustrating different dynamic outlet glacier behaviors. Thickening: Store Glacier (6); no dynamic change: Petermann Glacier (78); decelerating thinning: Kjer Glacier (83); accelerating thinning: Zachariæ Isstrom (51) and Ikertivaq NN (46); full cycle thinning: Jakobshavn Isbræ (1); thinning with varying rate: Midgård Glacier (121); thinning, thickening, and thinning with abrupt termination of initial thinning: Helheim (3), Koge Bugt C (4), and A. P. Bernstorff (12) glaciers; unique pattern with periodic thinning and thickening: Daugaard-Jensen Glacier (8). Numbers in parentheses are ID numbers from ref. and in Table S1. Gray box marks the duration of the ICESat mission, and glacier locations are shown in B. Dynamic thickness changes of the four large outlet glaciers, Jakobshavn Isbræ, Kangerlussuaq, Helheim, and Petermann glaciers, underlined in the figure, are modeled in refs. –. (B) Distribution of different outlet glacier behavior types over a background of ice sheet bed elevation from ref. . Inset shows the detailed pattern north of Jakobshavn Isbræ overlain on ice velocities from ref. . Abbreviations mark the following outlet glaciers: Sermeq Avannarleq (SA, 53), Sermeq Kujalleq (SK, 13), Kangilerngata Sermia (KS, 52), Eqip Sermia (ES, 90), Kangiata Nunaata Sermia (KNS, 36), Skinfaxe (S, 82), Rimfaxe (R, 58), and Heimdal (H, 39) glaciers. See Table S1 for a complete list of glaciers and their classification based on 2003–2009 and 1993–2012 dynamic thickness change patterns.

Fig. 3.

Annual total, SMB-related, and ice dynamics-related thickness change rates of the GrIS for 2003–2009 balance years from ICESat, ATM and LVIS laser altimetry observations (see Fig. 1 for locations of elevation change records). Dotted lines on the dynamic thickness change maps mark the ELA (average 2003–2009 SMB = 0). Ice sheet boundary is from ref. , and black regions show weakly or not connected glaciers and ice caps. Balance years start on September 1 and end on August 31 of the following year. See Movie S1 for a higher-resolution, animated version of the figure.

Fig. 4.

Annual mass change rates in gigatons per year for major drainage basins shown in Fig. 2B. Annual total mass change rates from laser altimetry (red) are partitioned into mass changes due to SMB (blue) and ice dynamics (green). Annual mass change rates and their error estimates are listed in Table S5.