Sub-millennial climate variability from high-resolution water isotopes in the EPICA Dome C ice core

The EPICA Dome C (EDC) ice core provides the longest continuous climatic record, covering the last 800 000 years (800 kyr). A unique opportunity to investigate decadal to millennial variability during past glacial and interglacial periods is provided by the high-resolution water isotopic record (δ18O and δD) available for the EDC ice core. We present here a continuous compilation of the EDC water isotopic record at a sample resolution of 11 cm, which consists of 27 000 δ18O measurements and 7920 δD measurements (covering, respectively, 94 % and 27 % of the whole EDC record), including published and new measurements (2900 for both δ18O and δD) for the last 800 kyr. Here, we demonstrate that repeated water isotope measurements of the same EDC samples from different depth intervals obtained using different analytical methods are comparable within analytical uncertainty. We thus combine all available EDC water isotope measurements to generate a high-resolution (11 cm) dataset for the past 800 kyr. A frequency decomposition of the most complete δ18O record and a simple assessment of the possible influence of diffusion on the measured profile shows that the variability at the multi-decadal to multi-centennial timescale is higher during glacial than during interglacial periods and higher during early interglacial isotopic maxima than during the Holocene. This analysis shows as well that during interglacial periods characterized by a temperature optimum at the beginning, the multi-centennial variability is strongest over this temperature optimum.publishedVersio

High stability in near-infrared spectroscopy: part 1, adapting clock techniques to optical feedback

International audienceOptical feedback is an efficient way to narrow and stabilise semi-conductor lasers. As a step forward for ultra-stable, yet highly tunable sources, we developed a new prototype of a three-mirror V-shaped optical cavity (VCOF). It is made of a precisely machined Zerodur spacer, that holds 3 optical contacted mirrors forming a high finesse V-shaped cavity. This arrangement allows the resonant light to be sent back to the seeding laser, triggering a drastic narrowing of the emission linewidth well below the cavity mode width without the need for high-bandwidth active electronic lock of the laser on the cavity. Low expansion material and precise temperature control of the reference cavity leads to a source with Hz level frequency drift and 70 Hz-level emission linewidth at 215 THz. We discuss the benefits of this new prototype compared to its predecessor for high-sensitivity cavity ring down spectroscopy (CRDS). To serve this purpose, the frequency stabilised laser was characterised on short, mid and long time scales, using a high finesse etalon, a self referenced optical frequency comb and a long term saturated CRDS absorption Lamb dip measurement on water

Water Isotopic Signature of Surface Snow Metamorphism in Antarctica

International audienceIn low accumulation regions of Antarctica, precipitation is so sparse that the processes occurring after snowfall (post-deposition), such as surface metamorphism (Picard et al., 2012), sublimation and solid condensation (Genthon et al., 2017), as well as the redistribution of snow by wind (Groot Zwaaftink et al., 2013; Picard et al., 2019), play a prominent role in how snow accumulates to build the snowpack. These processes strongly affect the physical properties (albedo, density, and grain size) and geochemical composition of snow. For instance, snow grain size, which controls the albedo (Grenfell et al., 1994; Wiscombe & Warren, 1980), is the result of the competition between precipitation which brings small size grains on the surface and metamorphism which coarsens existing grains (Picard et al., 2012). These post-deposition processes influence the snow isotopic composition (δ 18 O or δD for the first order) that are traditionally interpreted as proxies of past temperatures in ice cores. Before deposition, the link between temperature and δ 18 O is due to the Rayleigh distillation of moist air from evaporation sites at low latitudes to the high-latitude precipitation sites (Dansgaard, 1964): When temperature decreases and precipitation occurs, the condensed phase becomes enriched and the remaining moisture depleted of heavy isotopes. In Antarctica, ice cores covering several glacial-interglacial transitions have been retrieved from sites that combine two assets: large ice thickness and low accumulation (EPICA, 2004; Kawamura et al., 2017; Petit et al., 1999). However, the low accumulation lead to the contributions from poorl

Sub-millennial climate variability from high-resolution water isotopes in the EPICA Dome C ice core

International audienc

Sub-millennial climate variability from high-resolution water isotopes in the EPICA Dome C ice core

The EPICA Dome C (EDC) ice core provides the longest continuous climatic record, covering the last 800 000 years (800 kyr). A unique opportunity to investigate decadal to millennial variability during past glacial and interglacial periods is provided by the high-resolution water isotopic record (δ18O and δD) available for the EDC ice core. We present here a continuous compilation of the EDC water isotopic record at a sample resolution of 11 cm, which consists of 27000 δ18O measurements and 7920 δD measurements (covering, respectively, 94 % and 27 % of the whole EDC record), including published and new measurements (2900 for both δ18O and δD) for the last 800kyr. Here, we demonstrate that repeated water isotope measurements of the same EDC samples from different depth intervals obtained using different analytical methods are comparable within analytical uncertainty. We thus combine all available EDC water isotope measurements to generate a high-resolution (11 cm) dataset for the past 800 kyr. A frequency decomposition of the most complete δ18O record and a simple assessment of the possible influence of diffusion on the measured profile shows that the variability at the multidecadal to multi-centennial timescale is higher during glacial than during interglacial periods and higher during early interglacial isotopic maxima than during the Holocene. This analysis shows as well that during interglacial periods characterized by a temperature optimum at the beginning, the multi-centennial variability is strongest over this temperature optimum