High-frequency climate variability in the Holocene from a coastal-dome ice core in east-central Greenland

Abstract

Abstract. 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.

5 kyr of fire history in the High North Atlantic Region: natural variability and ancient human forcing

“…RECAP levoglucosan flux shows high fluxes at 1.5 kyr BP, with a declining trend until 1 kyr BP, where values remain low until 0.2 kyr BP ( Figure 2). This agrees with higher RECAP summer δ 18 O trend (Hughes et al, 2020). Marcott et al (2013) and (Mann et al, 2008) document a cooling trend from a warm interval (~1500 -1000 kyr BP) to a cool interval (~500 -100 years BP).…”

“…Since Levoglucosan, BC and NH 4 + can be deposited in snow and glaciers by both wet and dry deposition (Stohl et al, 2007), fluxes were calculated as the product of concentration with annual accumulation and expressed in µg m -2 y -1 . Renland accumulation (Hughes et al, 2020;Corella et al, 2019;Simonsen et al, 2019) shows a stable profile, indicating that wet deposition didn't undergo drastic changes over the period covered by our record (Vinther et al, 2009). Levoglucosan flux (Figure 2a) exhibits the same major features observed in the concentration record, indicating that variations in the levoglucosan series reflect changes in the atmospheric concentration, rather than a change in snow accumulation (Grieman et al, 2018).…”

“…Greater-than-present summer insolation resulted in warmer and drier summers in the Northern Hemisphere with a consequent increasing of fire as showed by records from North America and Europe. Renland, being located at a high latitude, receives minimal or no insolation throughout the winter, meaning that summer insolation dominates (Hughes et al, 2020). Thus, summer solar input along with temperatures may have the major influence in controlling fire activity in the HNAR.…”

The Community Firn Model (CFM) v1.0

“…Several firn densification models have been developed without invoking Sorge's law. Some of these have used firn strain-rate data; these include work by Arthern et al (2010), who measured firn compaction rates in real time in Antarctica using "coffee-can" type strain gauges (Hulbe and Whillans, 1994), and by Morris and Wingham (2014), who inferred firn compaction rates by tracking layering in repeated high-resolution density logs of boreholes. Other studies have worked to develop a model based on the microphysical processes driving densification; e.g., Alley (1987) developed a model for zone 1 densification by applying grainboundary sliding theory.…”

Supplementary material to "5 kyr of fire history in the High North Atlantic Region: natural variability and ancient human forcing"

“…Figure S2. RECAP annual accumulation (in kg m -2 y -1 ) calculated from diffusion and seawater corrected δ 18 O (Hughes et al, 2020;Corella et al, 2019).…”