Abstract
Records of chemical impurities from ice cores enable us to reconstruct the past deposition of aerosols onto the polar ice sheets and alpine glaciers. Through that, they allow us to gain insight into changes of the source, transport and deposition processes that ultimately determine the deposition flux at the coreing location. However, the low concentrations of the aerosol species in the ice and the resulting high risk of contamination poses 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 90s. Here we present continuous records of calcium (Ca2+), sodium (Na+), ammonium (NH4+), nitrate (NO3−1) 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. Both of the records have previously been used in a number of studies but have never been published in the 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.
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; 20 and the records of past aerosol deposition onto the polar ice sheets, preserved in the ice as wide range of chemical impurities
Innovative sampling and measurement techniques are necessary to 25 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 cm to mm-scale variability along the depth in the icecore record
Summary
Proxy records from polar ice cores have allowed us to gain detailed insight into the past climate and its variability. The CFA data of NGRIP and NEEM at annual to multi-annual resolution has, for example, been used to investigate the timing of the rapid warming events during the Last Glacial period and at the onset of the Holocene in multiple studies They have revealed the abruptness and the decadal scale delays between warming in Greenland, changes in the North Atlantic and Asian climate (Steffensen et al, 2008; Erhardt et al, 2019a), and the diversity of these events (Capron et al, 2021) due to the natural variability in 75 the climate system. These 10 yr-averaged datasets on the current age model are provided alongside the 1 mm data as well (Erhardt et al, 2021)
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