Greenland Ice Sheet Mass Balance Reconstruction. Part II: Surface Mass Balance (1840-2010)

Meteorological station records, ice cores, and regional climate model output are combined to develop a continuous 171-yr (1840-2010) reconstruction of Greenland ice sheet climatic surface mass balance (B-clim) and its subcomponents including near-surface air temperature (SAT) since the end of the Little Ice Age. Independent observations are used to assess and compensate errors. Melt water production is computed using separate degree-day factors for snow and bare ice surfaces. A simple meltwater retention scheme yields the time variation of internal accumulation, runoff, and bare ice area. At decadal time scales over the 1840-2010 time span, summer (June-August) SAT increased by 1.6 degrees C, driving a 59% surface meltwater production increase. Winter warming was +2.0 degrees C. Substantial interdecadal variability linked with episodic volcanism and atmospheric circulation anomalies is also evident. Increasing accumulation and melt rates, bare ice area, and meltwater retention are driven by increasing SAT. As a consequence of increasing accumulation and melt rates, calculated meltwater retention by firn increased 51% over the period, nearly compensating a 63% runoff increase. Calculated ice sheet end of melt season bare ice area increased more than 5%. Multiple regression of interannual SAT and precipitation anomalies suggests a dominance of melting on B-clim and a positive SAT precipitation sensitivity (+32 Gt yr(-1) K-1 or 6.8% K-1). The B-clim component magnitudes from this study are compared with results from Hanna et al. Periods of shared interannual variability are evident. However, the long-term trend in accumulation differs in sign.