Summer warmth of the past six interglacials on Greenland

Abstract

The relative warmth of mid-to-late Pleistocene interglacials on Greenland has remained unknown, leading to debates about the regional climate forcing that caused past retreat of the Greenland Ice Sheet (GrIS). We analyze the hydrogen isotopic composition of terrestrial biomarkers in Labrador Sea sediments through interglacials of the past 600,000 y to infer millennial-scale summer warmth on southern Greenland. Here, we reconstruct exceptionally warm summers in Marine Isotope Stage (MIS) 5e, concurrent with strong Northern Hemisphere summer insolation. In contrast, "superinterglacial" MIS11 demonstrated only moderate warmth, sustained throughout a prolonged interval of elevated atmospheric carbon dioxide. Strong inferred GrIS retreat during MIS11 relative to MIS5e suggests an indirect relationship between maximum summer temperature and cumulative interglacial mass loss, indicating strong GrIS sensitivity to duration of regional warmth and elevated atmospheric carbon dioxide.

Keywords: Arctic; Greenland Ice Sheet; Last Interglacial; Marine Isotope Stage 11; interglacial.

Fig. 1.

Map of study region. Location of Eirik Drift core sites (black point), including Ocean Drilling Program Site 646 used in this study. Dotted lines separate silt provenances as in Fig. 2H (5, 12). White is the modern glacier extent. Solid lines are the modern schematic surface ocean currents: the West Greenland Current (WGC), Baffin Island Current (BIC), and Irminger Current (IC). The dashed line is the Deep Western Boundary Undercurrent (WBUC). Points are the Greenland ice cores (27), with ice dated to peak (dark red) or late (light red) MIS5e (–31) and Holocene δ²H_C28 records (yellow) (17, 24). The inset map is of Lake El’Gygytgyn (Lake E) (9), Arctic Ocean core HLY-06 (10), and the Faroe Islands (FI) (25).

Fig. 2.

Interglacial records from MIS13 to MIS1. Datasets are plotted on their own age scales and not synchronized, except those from the same sites. Formally defined MIS and peak substage (22) (as in Fig. 4) are shaded. (A) June 21st insolation at 65°N (6). (B) Atmospheric CO₂ concentration (7). (C) Site 646 δ²H_C28 (this study). Analytical error is smaller than point size (SI Appendix). (D) Site 646 δ²H_C28 as an anomaly relative to the last millennium. (E) Global benthic (blue) and Site 646 planktic foraminifera δ¹⁸O (black) (4, 22). (F) Stable carbon isotopes (δ¹³C, ‰ VPDB [Vienna Pee Dee Belemnite]) of Cibicidoides wuellerstorfi from U1305 (34). (G) SSTs from U1305 (summer: black and red error envelope; winter: black and blue error envelope) (11) and Site 646 (summer: red; winter: blue) (4). (H) Provenance of MD99-2227 silts as in Fig. 1 (5, 12). (I) Mean temperature of the warmest month (MTWM) from Lake El’Gygytgyn (9). (J) Site 646 pollen concentrations (4).

Fig. 3.

Comparison of paleoclimate constraints from MIS1, MIS5e, and MIS11, contextualized by insolation (A) (6) and atmospheric CO₂ (B) (7) forcings. δ²H_C28 from this study (646) is plotted as absolute values in comparison to absolute values of western Greenland (N3, Pluto [PLO]) and Faroe Island (FI) lake sediment δ²H_C28 from MIS1 (C, right-hand y-axis in green) (17, 24, 25). Site 646 δ²H_C28 is additionally presented as an anomaly relative to the last millennium (D, left-hand y-axis in black) for comparison to Greenland ice core δ¹⁸O anomalies (y-axis in blue) through MIS1 and MIS5e (E) (–31). Southern and eastern Greenland ice core δ¹⁸O records are plotted in MIS1, whereas all Greenland ice cores with semicontinuous sequences are included in MIS5e. The ice core δ¹⁸O axis is scaled by eight times for comparison to δ²H. Isotope records are compared to a synthesis of Arctic summer temperature (26) and estimated peak Arctic MIS5e temperature (43) (F).

Fig. 4.

Climate forcings and southern Greenland response during peak Marine Isotope substages. Both substages were included for MIS13 and MIS7, when peak substages are poorly defined. Comparison of δ²H_C28 (A), 65°N insolation (B) (6), and CO₂ (C) (7) between peak Marine Isotope substages. Boxplots represent distribution of values within the substage. Dashed lines indicate the mean for 1 to 0 ka, and right axes present values as anomalies relative to this mean.