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There is currently poor scientific agreement on whether the ice–bed interface is frozen or thawed beneath approximately one third of the Greenland ice sheet. This disagreement in basal thermal state results, at least partly, from differences in the subglacial geothermal heat-flow basal boundary condition used in different ice-flow models. Here, we employ seven widely used Greenland geothermal heat-flow maps in 10 000-year spin-ups of the Community Ice Sheet Model (CISM). We perform two spin-ups: one nudged toward thickness observations and the other unconstrained. Across the seven heat-flow maps, and regardless of unconstrained or nudged spin-up, the spread in basal ice temperatures exceeds 10 ∘ C over large areas of the ice–bed interface. For a given heat-flow map, the thawed-bed ice-sheet area is consistently larger under unconstrained spin-ups than nudged spin-ups. Under the unconstrained spin-up, thawed-bed area ranges from 33.5 % to 60.0 % across the seven heat-flow maps. Perhaps counterintuitively, the highest iceberg calving fluxes are associated with the lowest heat flows (and vice versa) for both unconstrained and nudged spin-ups. These results highlight the direct, and non-trivial, influence of the heat-flow boundary condition on the simulated equilibrium thermal state of the ice sheet. We suggest that future ice-flow model intercomparisons should employ a range of basal heat-flow maps, and limit direct intercomparisons with simulations using a common heat-flow map. [ABSTRACT FROM AUTHOR]

Mineral dust can indirectly affect the climate by supplying bioavailable iron (Fe) to the ocean. Here, we present the records of dissolved Fe (DFe) and total Fe (TDFe) in North Greenland Eemian Ice Drilling (NEEM) ice core over the past 110 kyr BP. The Fe records are significantly negatively correlated with the carbon-dioxide (CO2) concentrations during cold periods. The results suggest that the changes in Fe fluxes over the past 110 kyr BP in the NEEM ice core are consistent with those in Chinese loess records because the mineral-dust distribution is controlled by the East Asian deserts. Furthermore, the variations in the dust input on a global scale are most likely driven by changes in solar radiation during the last glacial–interglacial cycle in response to Earth's orbital cycles. In the last glacial–interglacial cycle, the DFe/TDFe ratios were higher during the warm periods (following the post-Industrial Revolution and during the Holocene and last interglacial period) than during the main cold period (i.e. the last glacial maximum (LGM)), indicating that the aeolian input of iron and the iron fertilization effect on the oceans have a non-linear relationship during different periods. Although the burning of biomass aerosols has released large amounts of DFe since the Industrial Revolution, no significant responses are observed in the DFe and TDFe variations during this period, indicating that severe anthropogenic contamination has no significant effect on the DFe (TDFe) release in the NEEM ice core. [ABSTRACT FROM AUTHOR]

The sensitivity of the Arctic precipitation phases (solid and liquid) to the forcings from greenhouse gases (GHGs) and aerosols over 2016–2080 was investigated by using the Community Earth System Model Version 1. Results show that the warming caused by the two forcings results in an increasing trend in total precipitation and a solid‐to‐liquid precipitation transition in the Arctic. Under RCP8.5 scenario, the increased rate of Arctic mean precipitation with global warming forced by aerosol reduction (7.7%/°C) is twice greater than that by increased GHG emission (3.5%/°C). The sensitivity of rainfall to precipitation ratio (RPR) to various forcings is much higher than that of total precipitation in the Arctic. The increased rate of RPR due to global aerosol forcing (8.4%/°C) is approximately 3 times that due to GHG forcing (2.9%/°C) in the Arctic, the differences even larger over Greenland and the eastern Arctic Ocean, resulting in more rainfall in these areas. Plain Language Summary: The precipitation phase is extremely sensitive to temperature changes, especially in the Arctic. Solid and liquid precipitation have almost the opposite effect on the ground energy budget. The changes in precipitation phase can greatly affect snow and ice mass balance, regulating the regional hydrological cycle. The transition from solid precipitation to liquid precipitation can even promote carbon release over the permafrost through changing the rate of snow melting. We evaluated the impacts of the two most important anthropogenic forcing agents (greenhouse gases [GHGs] and aerosols) on the changes of precipitation phases in the Arctic using a state‐of‐the‐art Earth system model. We found that the warming forced by global aerosol reduction and increased GHG emission leads to a solid‐to‐liquid precipitation transition and therefore more rainfall events in the Arctic. Under RCP8.5 scenario, the sensitivity of Arctic precipitation phase to global aerosol forcing is approximately 3 times that to the GHG forcing, and the most sensitive phase changes of Arctic precipitation to the aerosol forcing are observed in Greenland and the eastern Arctic Ocean. Understanding the impact of human activities on the changes in the Arctic precipitation phase will help formulate reasonable emission reduction policies and better adapt to the rapid Arctic climate changes in the future. Key Points: Warming forced by global aerosol reduction and increased GHG emission leads to a solid‐to‐liquid precipitation transition in the ArcticThe sensitivity of Arctic precipitation phase to the aerosol forcing is approximately three times that to the GHG forcingThe most sensitive phase changes of Arctic precipitation to the aerosol forcing are observed in Greenland and the eastern Arctic Ocean [ABSTRACT FROM AUTHOR]

We conducted a 2 m snow pit study in July 2017 at the East GRIP (Greenland Ice-Core Project; northeastern Greenland) deep ice-coring site. We collected snow samples at intervals of 0.05 m and analyzed their iron (Fe) and rare earth element (REE) concentrations. Pronounced seasonal variations in trace elements were observed during 2012–2017. The results indicated that the dissolved Fe (DFe), total dissolved Fe (TDFe), and total dissolved REEs (TDREEs) largely originated from mineral dust, which peaked in winter to early spring. In particular, the 2014–2015 Holuhraun eruption (31 August 2014 to 27 February 2015) can be clearly observed in the data at a depth of 90–125 cm. This event not only provided abundant acidic material (sulphate), but also released a large amount of DFe. Therefore, these results provide a possible way to use Greenland deep ice core data to construct a much longer history and better understand the relationship between eruptions and the release of iron in future studies. [ABSTRACT FROM AUTHOR]

Ice core records from polar regions are of great value to study long-term climate and environmental change. Greenland ice-core records are celebrated for their high resolution and have provided very important knowledge for understanding the late Quaternary palaeoclimate, especially in reference to millennial-scale abrupt climatic flips during the last glaciation. Recently, a new project to retrieve a deep ice-core from Greenland known as NEEM for North Greenland Eemian Ice Drilling, has been launched with the main target being the last interglacial period. The new core will help us understand further details of climate changes during a period of warmth as the present. Antarctic ice cores have a unique advantage in providing recovery of longer time-scale paleclimate information and hence are regarded as a crucial pillar to examine climatic cycles on the time-scale of Earth-orbital phenomena. Since the bottom ice in Dome A is estimated to be older than a million years, a deep drilling there be- comes a new focus for ice core studies. [ABSTRACT FROM AUTHOR]

Understanding the changes in Greenland's temperature is important for assessing and predicting the mass of the Greenland ice sheet, which plays an important role in sea level rise. In this study, we analyzed the annual and seasonal coastal Greenland's temperatures during the period 1952–2017 (focusing on the period 2013–2017) based on a dataset obtained from the Danish Meteorological Institute (DMI). Overall, the annual coastal Greenland's temperature increased during 1952–2017 at a rate of 0.23 °C decade−1, especially in the southeastern (0.70 °C decade−1) and northern (0.42 °C decade−1) regions of the island. From the changes in the seasonal coastal Greenland's composite temperature (CT), winter exhibited the largest change rate (0.28 °C decade−1), and the summer CT increased by 0.25 °C decade−1, while the spring CT increased by 0.17 °C decade−1 with less variation. The temperature increase accelerated during 2013–2017 according to Mann-Kendall (M-K) tests, especially in the northeastern and northern regions of the island. The seasonal temperature change of the whole island decreased in the following order: annual > autumn > summer > winter > spring. We also analyzed the annual inland temperature change during the period 1997–2017 based on a dataset obtained from the Greenland Climate Network; the results indicated that the inland temperature increased by 0.13 °C decade−1. Pearson correlation analysis was used to determine the teleconnection relationship between the coastal temperatures and large-scale atmosphere-ocean climate indexes, and we found that the Greenland Blocking Index (GBI), Atlantic Multidecadal Oscillation (AMO), Tropical Northern Atlantic Index (TNA), North Tropical Atlantic Index (NTA), Caribbean Index (CAR), Atlantic Meridional Mode (AMM), East Atlantic (EA) and Western Hemisphere warm pool (WHWP) have significant positive correlations with the coastal temperature in most months, except in February and May. However, the North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and Eastern Asia/Western Russia (EAWR) show significant negative correlations with temperature. Overall, there exists a time lag effect between the climate indexes (except for the GBI, AO and NAO) and temperature. From the application of the random forest model, we found that the GBI, NAO, CO 2 , AMO, N 2 O, SF 6 , CH 4 , and Northern Oscillation Index (NOI) are the most important variables that influenced the CT changes during 1979–2017. Finally, we calculated the contribution rates of the most important variables to temperature change during the period 1979–2017 and showed that the contribution rates of the GBI, CO 2 and NOI to temperature change were 47.30%, 35.68%, and 17.02%, respectively. • The temperature increase accelerated during 2013–2017 in Greenland. • The GBI, NAO, AMO, CO 2 , N 2 O, SF 6 , and CH 4 are important variables influencing coastal Greenland's temperature change. • The contribution rates of the GBI, CO 2 and NOI to coastal Greenland's temperature change are 47.30%, 35.68%, and 17.02%. [ABSTRACT FROM AUTHOR]

We report the first high-resolution record of arsenic (As) observed in Greenland snow and ice for the periods 1711-1970 and 2003-2009 AD. The results show well-defined large-scale atmospheric pollution by this toxic element in the northern hemisphere, beginning as early as the 18th century. The most striking feature is an abrupt, unprecedented enrichment factor (EF) peak in the late 1890s, with an ∼30-fold increase in the mean value above the Holocene natural level. Highly enriched As was evident until the late 1910s; a sharp decline was observed after the First World War, reaching a minimum in the early 1930s during the Great Depression. A subsequent increase lasted until the mid-1950s, before decreasing again. Comparisons between the observed variations and Cu smelting data indicate that Cu smelting in Europe and North America was the likely source of early anthropogenic As in Greenland. Despite a significant reduction of ∼80% in concentration and ∼60% in EF from the 1950s to the 2000s, more than 80% of present-day As in Greenland is of anthropogenic origin, probably due to increasing As emissions from coal combustion in China. This highlights the demand for the implementation of national and international environmental regulations to further reduce As emissions.