Search

In recent decades, surface melting on the inland Greenland ice sheet has increased, leading to significant meltwater-refreezing in the snow and firn. Increased knowledge of the physical and chemical characteristics of these melt features (i.e., ice layers) is needed to help estimate future global sea-level rise. Here, using a combination of microscopy and spectroscopy, we investigate the size, shape, location, and chemical compositions of inclusions in 12 ice layers of the SIGMA-A ice core in the northwestern Greenland ice sheet (78°03′06″N, 67°37′42″W, 1490 m a.s.l.). In the ice layers, we found inclusions exceeding 30 μm diameter that could only be formed by melting–refreezing, which we classify into columnar-, particle-, and rod-like inclusions. We propose that the smaller columnar- and particle-like inclusions of solid Na2SO4⋅10H2O and CaSO4⋅2H2O form first, within the ice grains, followed by the larger rod-like inclusions of brines with mainly Na+ and Cl− in grain boundaries. Our results suggest a new proxy that may help identify past warm climates in deeper ice cores in Greenland and for studying future ice sheet melting behavior.

Summer sea ice retreat in the high latitude North Atlantic since 2000 is associated with increases in oceanic emissions of dimethyl sulfide, according to a record of methane sulfonic acid fluxes from an ice core in southeast Greenland.

Abstract Previous reconstructions of summer temperatures from ice cores have relied on a statistical relationship between a melt layer and temperature observed at nearby stations. This study presents a novel method for reconstructing summer temperatures from melt layers in ice cores using an energy balance model that incorporates heat conduction and meltwater refreezing in the firn. We use the seasonal patterns in the ERA‐Interim reanalysis data set for an ice core site to calculate the amounts of refreezing water within the firn under various summer mean temperature (SMT) and annual precipitation conditions, and prepared calibration tables containing these three variables. We then estimate the SMTs from the refreezing amount and annual accumulation, both of which can be obtained from an ice core. We apply this method to four ice cores that were recovered from sites with different climates: two sites on the Greenland Ice Sheet, one in Alaska, and one in Russian Altai. The reconstructed SMTs show comparable variations with those of observed temperatures at nearby stations. The nonlinear relationship between SMT and melt layer thickness differs between sites, indicating that a single linear approximation cannot be employed to estimate SMT. Sensitivity analyses suggest that the annual temperature range, amount of annual precipitation, and firn albedo (which is a time‐invariant value in the model) significantly affect the relationship between SMT and melt layer thickness. This new method provides an alternative to existing approaches and yields an independent estimate of SMT from ice cores that have been affected by melting.

The roles and impacts of black carbon (BC), an important aerosol species affecting Earth's radiation budget, are not well understood owing to lack of accurate long-term observations. To study the temporal changes in BC since the pre-industrial period, we analysed BC in an ice core drilled in northwest Greenland. Using an improved technique for BC measurement and a continuous flow analysis system, we obtained accurate and high temporal resolution records of BC particle size and mass/number concentrations for the past 350 years. Number and mass concentrations, which both started to increase in the 1870s associated with inflow of anthropogenically derived BC, reached their maxima in the 1910s-1920s and then subsequently decreased. On the basis of backward trajectory analyses, we found that North America was the dominant source region of the anthropogenic BC in the ice core. The increase in anthropogenic BC shifted the annual concentration peaks of BC from summer to winter-early spring. After BC concentrations diminished to pre-industrial levels, the annual peak concentration of BC returned to the summer. We found that anthropogenic BC particles were larger than biomass burning BC particles. By separating the BC in winter and summer, we reconstructed the temporal variations in BC that originated from biomass burning, including the period with large anthropogenic input. The BC that originated from biomass burning showed no trend of increase until the early 2000s. Finally, possible albedo reductions due to BC are discussed. Our new data provide key information for validating aerosol and climate models, thereby supporting improved projections 31 of future climate and environment. [ABSTRACT FROM AUTHOR]

Ice cores can provide long-term records of black carbon (BC), an important aerosol species closely linked to the climate and environment. However, previous studies of ice cores only analysed BC particles with diameter of <600-850 nm, which could have led to underestimation of BC mass concentrations. Information on the size distribution of BC particles is very limited, and there are no Arctic ice core records of the temporal variation in BC size distribution. In this study, we applied a recently developed improved technique to analyse the BC concentration in an ice core drilled at the SIGMA-D site in northwest Greenland. The improved technique, which uses a modified Single-Particle Soot Photometer and a high-efficiency nebulizer, widens the measurable range of BC particle size. For high-resolution continuous analyses of ice cores, we developed a continuous flow analysis (CFA) system (resolution: 10-40 mm). Coupling of the improved BC measurement technique with the CFA system allows accurate high-resolution measurements of the size distribution and concentration of BC particles with diameter between 70 nm and 4 µm, with minimal particle losses. Using this technique, we reconstructed the size distributions and the number and mass concentrations of BC particles during the past 350 years. On the basis of the size distributions, we assessed the underestimation of BC mass concentrations measured using the conventional method. For the period 2003-2013, the underestimation of the average mass concentration would have been 12%-17% for the SIGMA-D core. [ABSTRACT FROM AUTHOR]

Alpine ice core research has long focused on a few suitable drilling sites at high elevation in the Western European Alps, assuming that the counterparts at lower elevation in the eastern sector are unsuitable for paleoenvironmental studies, due to the presence of melting and temperate basal conditions. However, it has been demonstrated that even in the Eastern Alpine range, below 4,000 m a.s.l., cold ice frozen to bedrock can exist. In fact, millennial-old ice has been found at some locations, such as at the Weißseespitze (WSS) summit ice cap (Ӧtztal Alps, 3,499m a.s.l.), where about 6 kyrs appear locked into 10mof ice. In this work, we present a full profile of the stable water isotopes (δ18O, δ²H), major ions (Na+, K+, Mg2+, Ca2+, NH4+, Cl-, NO3-, SO42-), levoglucosan, and microcharcoal for two parallel ice cores drilled at the Weißseespitze cap. We find that, despite the ongoing ice loss, the chemical and isotopic signatures appear preserved, and may potentially offer an untapped climatic record. This is especially noteworthy considering that chemical signals of other archives at similar locations have been partially or full corrupted by meltwater (i.e., Silvretta glacier, Grand Combin glacier, Ortles glacier). In addition, the impurity concentration near the surface shows no signs of anthropogenic contamination at WSS, which constrains the age at the surface to fall within the pre-industrial age. [ABSTRACT FROM AUTHOR]