Volcanic influence on centennial to millennial Holocene Greenland temperature change

Abstract

Solar variability has been hypothesized to be a major driver of North Atlantic millennial-scale climate variations through the Holocene along with orbitally induced insolation change. However, another important climate driver, volcanic forcing has generally been underestimated prior to the past 2,500 years partly owing to the lack of proper proxy temperature records. Here, we reconstruct seasonally unbiased and physically constrained Greenland Summit temperatures over the Holocene using argon and nitrogen isotopes within trapped air in a Greenland ice core (GISP2). We show that a series of volcanic eruptions through the Holocene played an important role in driving centennial to millennial-scale temperature changes in Greenland. The reconstructed Greenland temperature exhibits significant millennial correlations with K⁺ and Na⁺ ions in the GISP2 ice core (proxies for atmospheric circulation patterns), and δ¹⁸O of Oman and Chinese Dongge cave stalagmites (proxies for monsoon activity), indicating that the reconstructed temperature contains hemispheric signals. Climate model simulations forced with the volcanic forcing further suggest that a series of large volcanic eruptions induced hemispheric-wide centennial to millennial-scale variability through ocean/sea-ice feedbacks. Therefore, we conclude that volcanic activity played a critical role in driving centennial to millennial-scale Holocene temperature variability in Greenland and likely beyond.

Figure 1

Greenland temperature anomalies relative to averages of 1988–2015 at the Summit and four coastal stations. (a) Temperature anomalies from 1988 to 2015. (b) Same as (a) but from 1850 to 2015. Green line with 2σ error bands is the reconstructed temperature anomaly. The reconstructed temperature (snow temperature) was adjusted to have the same value in 1993 as an average of the observed Summit temperature (air temperature) for 1988–1998 by adding 1.0 °C. The names and timings of large volcanic eruptions are according to Box et al.. RMs represents running means.

Figure 2

Greenland Summit temperature and its proxies over the Holocene. (a) Reconstructed temperature from argon and nitrogen isotopes with 2σ error bands. (b) Melt-layer frequency (times per years) in 100 and 500-year RMs with light blue and blue lines, respectively. Note that the data before 9000 B.P. has low confidence. (c) δ¹⁸O_ice and a calibrated temperature scale in 20-year RMs with 2σ error bands from GISP2, GRIP, and NGRIP (Methods) (d) GRIP borehole temperature inversion. Blue shades are Greenland cold episodes. E.H.T.R. = Early Holocene Temperature Rise, M.H.C. = Mid-Holocene Cooling, M.H.O. = Mid-Holocene Optimum, B.A.C.E. = Bronze Age Cold Epoch, B.A.O. = Bronze Age Optimum, I.A.C.E. = Iron Age Cold Epoch, I.A.O. = Iron Age Optimum, M.C.A. = Medieval Climate Anomaly. The names are given according to the Greenland temperature changes or common usages if available.

Figure 3

Holocene climate forcing. (a) Reconstructed Greenland temperature. (b) Reconstructed and modeled Greenland temperatures over the Holocene from various climate model experiments. Experiments without volcanic and solar forcing that exhibit long-term trends similar to that of full forcing are not shown for the sake of simplicity. (c) Modeled NH average temperatures with full forcing (blue) and without volcanic forcing (green) both relative to the average of the past 1000 years from the full forcing run. (d) Modeled high (60–90°N), middle (30–60°N), and low (0–30°N) latitude average temperatures. (e) Annual insolation at 72°N (orange) and solar activity (red), GHG (blue; include CO₂, CH₄, and N₂O, Methods) and volcanic forcing as raw (black) and 101-year RMs (green) (Methods). Note that the raw volcanic forcing has a different scale. Values are relative to averages of the past 1,000 years. Model outputs are from individual runs and smoothed by 21-year RMs. Blue shades are the Greenland cold episodes as in Fig. 2.

Figure 4

Centennial to millennial-scale volcanic impacts on climate over the past 10,000 years. (a) Raw volcanic forcing, (b) Volcanic Impact Index (VII), the difference between two curves in Fig. 3c. (c) ΔNH sea-ice cover (y-axis is reversed) is calculated as differences between experiments with full forcing and without volcanic forcing (ensemble means) in 21-year RMs, (d) as in (c) but for ocean temperature (54–484 m) in 40°N–90°N. Red dotted lines in (e–i) show bandpass-filtered Greenland temperatures, which are compared to (e) modeled NH average temperatures (Methods), and VII, (f) Na⁺ ion in GISP2 (a proxy for atmospheric circulation), (g) K⁺ ion in GISP2 (proxy for atmospheric circulation), (h) Oman cave stalagmite δ¹⁸O, (i) Dongge cave stalagmite δ¹⁸O^,. Different bandpass filters were applied for (e,f,g,h) and (i) with 400–4000 year bands and 200–2000 year bands after linear detrending, respectively (Methods). Red areas in (b–d) indicate periods under relatively strong volcanic influence. Blue shades are the Greenland cold episodes as in Fig. 2.