Abstract
Abstract. Records of chemical impurities from ice cores enable us to reconstruct the past deposition of aerosols onto polar ice sheets and alpine glaciers. Through this they allow us to gain insight into changes of the source, transport and deposition processes that ultimately determine the deposition flux at the coring location. However, the low concentrations of the aerosol species in the ice and the resulting high risk of contamination pose a formidable analytical challenge, especially if long, continuous and highly resolved records are needed. Continuous flow analysis, CFA, the continuous melting, decontamination and analysis of ice-core samples has mostly overcome this issue and has quickly become the de facto standard to obtain high-resolution aerosol records from ice cores after its inception at the University of Bern in the mid-1990s. Here, we present continuous records of calcium (Ca2+), sodium (Na+), ammonium (NH4+), nitrate (NO3-) and electrolytic conductivity at 1 mm depth resolution from the NGRIP (North Greenland Ice Core Project) and NEEM (North Greenland Eemian Ice Drilling) ice cores produced by the Bern Continuous Flow Analysis group in the years 2000 to 2011 (Erhardt et al., 2021). Both of the records were previously used in a number of studies but were never published in full 1 mm resolution. Alongside the 1 mm datasets we provide decadal averages, a detailed description of the methods, relevant references, an assessment of the quality of the data and its usable resolution. Along the way we will also give some historical context on the development of the Bern CFA system. The data is available in full 1 mm and 10-year-averaged resolution on PANGAEA (https://doi.org/10.1594/PANGAEA.935838, Erhardt et al., 2021)
Highlights
Proxy records from polar ice cores have allowed us to gain detailed insight into the past climate and its variability
Among the records from polar ice cores, the most prominent ones are those of past atmospheric gas composition, preserved in the bubbles enclosed in the ice; the isotopic composition of the water, preserved in the ice itself; and the records of past aerosol deposition onto the polar ice sheets, preserved in the ice as a wide range of chemical impurities
Innovative sampling and measurement techniques are necessary to obtain the required analytical precision and resolution. The latter is important for aerosol records as the concentration of impurities in the ice varies on the seasonal time scales, translating into centimeter to millimeter scale variability along the depth in the ice-core record
Summary
Proxy records from polar ice cores have allowed us to gain detailed insight into the past climate and its variability. Among the records from polar ice cores, the most prominent ones are those of past atmospheric gas composition, preserved in the bubbles enclosed in the ice; the isotopic composition of the water, preserved in the ice itself; and the records of past aerosol deposition onto the polar ice sheets, preserved in the ice as a wide range of chemical impurities Together, these proxies contain information about different parts of the Earth system, all recorded in the same archive, allowing for detailed multi-parameter studies of the past climate. Together with the dating by annual layer counting, the high-resolution CFA aerosol data can, for example, be used to study episodic aerosol signals This has been done for the NGRIP and the upper part of NEEM NH+4 records, where changes in the occurrence rates of wildfire plumes reaching the Greenland ice sheet from North America were studied (Fischer et al, 2015; Legrand et al, 2016) building on previous work on the NH+4 seasonality and its temporal change in the GRIP ice core (Fuhrer et al, 1996). These 10-year-averaged datasets on the current age model are provided alongside the 1 mm data as well (Erhardt et al, 2021)
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