ALBERT

Description: Dataset containing surface snow measurements of snow specific surface area (SSA), snow density and snow accumulation. Surface samples were taken from the surface 2.5cm of snow. SSA measurements were determined using an Ice Cube measuring device (Zuanon, 2013). Snow density was measured from the SSA samples with a fixed volume. Snow accumulation describes the change in surface height at each sample site. All measured parameters have 10 daily samples taken at 10m intervals over a 90m transect. Sampling was carried out daily between May and August of 2016-2019, at approximately 24hr time intervals. All measurements were taken at the East Greenland Ice Core Project site (EastGRIP) situated in the accumulation zone of the Greenland Ice Sheet.

Description: Water isotope measurements (i.e. δ18O, δD, and d-excess) of snow and atmospheric vapor were made to document evolution of snow surface water isotopes, with implications for ice core analysis and climate models. Laboratory experiments were used to measure changes in the snow surface in a controlled setting influenced only by sublimation, and field experiments were used to measure changes in the snow surface in a natural setting. Laboratory data includes experiments from 2017-2019, completed at the University of Copenhagen and the University of Colorado Boulder. Eight 4-6 day sublimation experiments were completed, in which 4-6 boxes were filled with well-mixed snow and one box was removed and measured each day. Data includes daily mass and water isotope measurements for snow samples at 0.5 cm intervals from 0-4 cm for all experiments. One experiment includes hourly water isotope and humidity measurements for vapor at 28 and 32 cm above the snow surface, and temperature at 4 cm below the snow surface, the snow surface, and 10 cm above the snow surface. All water isotope measurements were made with a Picarro L-2140i. Field data includes four 40-60 hour experiments completed at the East Greenland Ice Core Project (75.623, 35.96) field site during summer 2019. Data includes hourly mass changes in isolated boxes, water isotope measurements of snow samples (0-4.5 cm) from isolated boxes and natural ice sheet conditions, continuous atmospheric vapor water isotope and humidity measurements at 10 cm above the snow surface, and continuous atmospheric temperature measurements. All water isotope measurements were made with a Picarro L-2140i.

Description: RECAP ice core d18O data from CFA measurements averaged in 5mm depth intervals.

Description: An ice core drilled on the Renland ice cap in east-central Greenland contains a continuous climate record dating through the last glacial period. The Renland record is valuable because the coastal environment is more likely to reflect regional sea surface conditions compared to inland Greenland ice cores that capture synoptic variability. Here we present the δ18O water isotope record for the Holocene, in which decadal-scale climate information is retained for the last 8 kyr, while the annual water isotope signal is preserved throughout the last 2.6 kyr. To investigate regional climate information preserved in the water isotope record, we apply spectral analysis techniques to a 300-year moving window to determine the mean strength of varying frequency bands through time. We find that the strength of 15–20-year δ18O variability exhibits a millennial-scale signal in line with the well-known Bond events. Comparison to other North Atlantic proxy records suggests that the 15–20-year variability may reflect fluctuating sea surface conditions throughout the Holocene, driven by changes in the strength of the Atlantic Meridional Overturning Circulation. Additional analysis of the seasonal signal over the last 2.6 kyr reveals that the winter δ18O signal has experienced a decreasing trend, while the summer signal has predominantly remained stable. The winter trend may correspond to an increase in Arctic sea ice cover, which is driven by a decrease in total annual insolation, and is also likely influenced by regional climate variables such as atmospheric and oceanic circulation. In the context of anthropogenic climate change, the winter trend may have important implications for feedback processes as sea ice retreats in the Arctic.

Description: Ice core water isotope records from Greenland and Antarctica are a valuable proxy for paleoclimate reconstruction, yet the processes influencing the climate signal stored in the isotopic composition of the snow are being challenged and revisited. Apart from precipitation input, post-depositional processes such as wind-driven redistribution and vapor–snow exchange processes at and below the surface are hypothesized to contribute to the isotope climate signal subsequently stored in the ice. Recent field studies have shown that surface snow isotopes vary between precipitation events and co-vary with vapor isotopes, which demonstrates that vapor–snow exchange is an important driving mechanism. Here we investigate how vapor–snow exchange processes influence the isotopic composition of the snowpack. Controlled laboratory experiments under forced sublimation show an increase in snow isotopic composition of up to 8 ‰ δ18O in the uppermost layer due to sublimation, with an attenuated signal down to 3 cm snow depth over the course of 4–6 d. This enrichment is accompanied by a decrease in the second-order parameter d-excess, indicating kinetic fractionation processes. Our observations confirm that sublimation alone can lead to a strong enrichment of stable water isotopes in surface snow and subsequent enrichment in the layers below. To compare laboratory experiments with realistic polar conditions, we completed four 2–3 d field experiments at the East Greenland Ice Core Project site (northeast Greenland) in summer 2019. High-resolution temporal sampling of both natural and isolated snow was conducted under clear-sky conditions and demonstrated that the snow isotopic composition changes on hourly timescales. A change of snow isotope content associated with sublimation is currently not implemented in isotope-enabled climate models and is not taken into account when interpreting ice core isotopic records. However, our results demonstrate that post-depositional processes such as sublimation contribute to the climate signal recorded in the water isotopes in surface snow, in both laboratory and field settings. This suggests that the ice core water isotope signal may effectively integrate across multiple parameters, and the ice core climate record should be interpreted as such, particularly in regions of low accumulation.