Evidence for a three-phase sequence during Heinrich Stadial 4 using a multiproxy approach based on Greenland ice core records

Abstract

Abstract. Glacial climate was characterised by two types of abrupt events. Greenland ice cores record Dansgaard–Oeschger events, marked by abrupt warming in-between cold, stadial phases. Six of these stadials appear related to major Heinrich events (HEs), identified from ice-rafted debris (IRD) and large excursions in carbon- and oxygen-stable isotopic ratios in North Atlantic deep sea sediments, documenting major ice sheet collapse events. This finding has led to the paradigm that glacial cold events are induced by the response of the Atlantic Meridional Overturning Circulation to such massive freshwater inputs, supported by sensitivity studies conducted with climate models of various complexities. These models also simulate synchronous Greenland temperature and lower-latitude hydrological changes. To investigate the sequence of events between climate changes at low latitudes and in Greenland, we provide here the first 17O-excess record from a Greenland ice core during Dansgaard–Oeschger events 7 to 13, encompassing H4 and H5. Combined with other ice core proxy records, our new 17O-excess data set demonstrates that stadials are generally characterised by low 17O-excess levels compared to interstadials. This can be interpreted as synchronous change of high-latitude temperature and lower-latitude hydrological cycle (relative humidity at the oceanic source of evaporation or change in the water mass trajectory/recharge) and/or an influence of local temperature on 17O-excess through kinetic effect at snow formation. As an exception from this general pattern, stadial 9 consists of three phases, characterised first by Greenland cooling during 550 ± 60 years (as shown by markers of Greenland temperature δ18O and δ15N), followed by a specific lower-latitude fingerprint as identified from several proxy records (abrupt decrease in 17O-excess, increase in CO2 and methane mixing ratio, heavier δD-CH4 and δ18Oatm), lasting 740 ± 60 years, itself ending approximately 390 ± 50 years prior to abrupt Greenland warming. We hypothesise that this lower-latitude signal may be the fingerprint of Heinrich event 4 in Greenland ice cores. The proposed decoupling between stable cold Greenland temperature and low-latitude climate variability identified for stadial 9 provides new targets for benchmarking climate model simulations and testing mechanisms associated with millennial variability.

The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity: insights from climate chamber and climate transect calibrations

“…The 17 O-excess decreases in the evaporating water and increases in the vapor phase when RH decreases at evaporative sites (e.g., sea surface, lake surface, soil surface or leaf surface). Over the last 10 years, a few studies have used the 17 O-excess of water to interpret ice core archives in climatic terms (Guillevic et al, 2014, Schoeneman et al, 2014Winkler et al, 2012;Landais et al, 2008Landais et al, , 2012. They supported that 17 O-excess is a marker of RH, sea-ice extent at the moisture source, and air mass mixing (Risi et al, 2010) except at the very high latitudes of East Antarctica where temperature can have a significant influence.…”

“…They supported that 17 O-excess is a marker of RH, sea-ice extent at the moisture source, and air mass mixing (Risi et al, 2010) except at the very high latitudes of East Antarctica where temperature can have a significant influence. The observed variations of 17 O-excess in Greenland ice cores of ∼ 20 per meg maximum were thus interpreted as variations of RH or sea-ice extent in the source region and coincide with variations in the low-to mid-latitude water cycle as recorded by other proxies (such as CH 4 or δD of CH 4 ) (Guillevic et al, 2014). An even smaller number of studies measured or attempted to model the 17 O-excess of rainwater at low and temperate latitudes (Affolter et al, 2015;Landais et al, 2010b;Li et al, 2015;Luz and Barkan, 2010;Risi et al, 2013).…”

The impact of Last Glacial climate variability in west-European loess revealed by radiocarbon dating of fossil earthworm granules

“…Modeling results show that the European climate was particularly impacted by switches between weakened or enhanced modes of the Atlantic Meridional Overturning Circulation through the transportation of North Atlantic air masses by Westerlies (6). Still, there are growing evidences that Greenland high-resolution climate records do not exhibit the full lowerlatitude climate variability, especially during cold periods (i.e., no distinction of Heinrich events) (7,8). There is thus an urgent need for well-dated high-resolution records of millennial-timescale climatic variability at midlatitudes.…”

Quantifying molecular oxygen isotope variations during a Heinrich stadial

“…A linear interpolation is then performed between match points to calculate the Siple Dome gas age. Green line: NEEM atmospheric δ 18 O, ‰ (±0.03 ‰; Guillevic et al, 2014). Colored areas: GSs.…”

“…For this period of millennial-scale variability, highresolution measurements of δ 18 O atm have been obtained in Greenland and Antarctic ice cores (e.g., Guillevic et al, 2014;Landais et al, 2007aLandais et al, , 2010Severinghaus et al, 2009). In Fig.…”