A Changing Cryosphere in a Rapidly Warming Arctic: Properties and Processes
Background and Objectives
With recent global warming, air temperatures in the Arctic are rising rapidly at a rate more than three times faster than the global mean. This would accelerate the surface melting of glaciers and ice sheet and shorten the seasonal snow cover duration, thereby contributing to enhanced ice-albedo feedback. As a result, further sea-level rise and changes in the Arctic environment and climate are expected. The aim of this research program is to understand the current state of the changing cryosphere in a rapidly warming Arctic and to elucidate the mechanisms of these changes through the following three Sub Programs (see Fig. 1).
Sub Program 1, “Properties and Processes of Ice Sheet, Glaciers, and Seasonal Snow Cover,” focuses on the changes in the mass balance of the Greenland ice sheet and the Arctic cryospheric environment by means of field observations, satellite remote sensing and numerical modelling. We elucidate the actual conditions and mechanisms of recent mass balance changes in the Arctic cryosphere by quantifying the physical and chemical processes such as snow and ice albedo reduction due to glacial microbes, light-absorbing aerosols and snow grain size growth, which have not been previously considered. Sub Program 2, "Past Warmings and Their Environmental Impacts," investigates past warming trends and environmental changes in Greenland since the Industrial Revolution. In addition, we investigate abrupt climate changes during the last glacial period and their links to the climate and environment in the mid-low-latitudes and the changing rate. We also elucidate the mechanisms and impacts of abrupt warming, which is a prerequisite for preparing for future global warming and socio-economic impacts. Sub Program 3, "Water and Material Circulations in Seasonal Sea Ice Regions and Their Impacts on Environment in the Arctic," aims to quantitatively understand the atmospheric chemical processes involved in the local water cycle in the seasonal sea-ice areas and the release of materials from sea-ice areas to construct a database for incorporating the relevant processes into the atmospheric models. We also elucidate the interannual variations of the relevant processes under the warming climate through aerosol, water vapor and meteorological monitoring, and ice core drilling in the coastal areas of Greenland.
Research Methodology and Main Results
Glaciological, meteorological and microbiological field observations were conducted on glaciers, ice sheet and sea ice areas in northwest Greenland, and glaciers in Alaska and Ny-Ålsund. Ice core drilling was also conducted in the Southeast Dome of the Greenland ice sheet in collaboration with a Grant-in-Aid for Scientific Research project. In addition, data from the previously installed Automatic Weather Stations (AWS) and existing ice core samples were analyzed. Numerical modelling studies were conducted to assess the impact of Arctic warming on the Arctic cryosphere and to understand atmospheric, snow/ice and aerosol processes and the mechanism of cryospheric change using the updated Regional Climate Model and the Earth System Model.
In Sub Program 1, we have achieved the following main results: development of a quality control technique for Greenland AWS data and analysis of the surface energy balance and mass balance at the equilibrium line altitude; understanding and modelling of the glacier surface darkening process due to glacial microbes; development and commercialization of a portable instrument for validation of satellite-derived snow grain size (social implementation); development of a regional meteorology-chemistry-snow-ice coupled numerical model NHM-Chem-SMAP and its implementation in the operational weather forecast model of the Japan Meteorological Agency (social implementation); its validation for snow impurity concentrations with in-situ observation; clarification of the increasing trend of rainfall amount in the Greenland ice sheet; and quantification of effective radiative forcing of anthropogenic black carbon (BC) in the Arctic using the Earth System Model MRI-ESM2.0. In Sub Program 2, we reconstructed the dust composition and concentration over the past 100 years from the SIGMA-D and EGRIP (see Fig. 2) ice cores in the Greenland ice sheet. We also found that the contribution of dust transported from coastal and distant areas varies with the elevation of the drill site and that the mineral composition of dust particles in an ice core at the lower elevation changes between warm and cold periods. We also reconstructed the BC concentration and particle size over the past 350 years from the same ice core and showed that the seasonal pattern differs depending on the origin of fossil fuels and wildfires. In Sub Program 3, we elucidated the winter precipitation process based on observations of the shapes and water isotope ratios of snowfall at Siorapaluk, Greenland. In addition, analysis of the ice core from the Southeast Dome, the highest accumulation area in the Greenland ice sheet, revealed an increase in the release of sulfur compounds with cloud nucleation capability from marine phytoplankton. This is caused by the recent earlier melting of sea ice. We found a significant correlation between changes in summer sulfuric acid concentrations and the cloud amount in the surrounding sea. We also clarified that there has been no significant change in annual precipitation at the Southeast Dome since 1799 and that the snowmelt has increased since 1900 in association with higher summer temperatures.
Summary
Although the COVID-19 pandemic and the Russo-Ukrainian war during the research period had a non-negligible impact on our research activities, the research plans were implemented by changing the research schedules and scope. Collaboration with other research programs was mainly conducted with the Research Programs on Atmosphere, Climate Prediction, and Coastal Environments. Most of the publications in line with the research objectives were carried out. Data release was almost completed and social implementation of research results and contributions to the IPCC and other organizations were also successful. In conclusion, the goals of this Research Program have been achieved. As future issues, for Sub Program 1, we will continue to use the new instruments, numerical models, and satellite observation techniques developed in this program. For Sub Program 2, we need to develop new analytical methods for ice cores and bioaerosol analysis for different time periods and regions. For Sub Program 3, we will continue field observations to incorporate water and material circulation processes in seasonal sea-ice areas into atmospheric chemistry models, improve our understanding of elementary processes through low-temperature chamber simulations, and conduct high-resolution deep ice core drilling and analysis to reconstruct the Little Ice Age.