lmd_Risi2013_abstracts.html

2013 .

T. Yao, V. Masson-Delmotte, J. Gao, W. Yu, X. Yang, C. Risi, C. Sturm, M. Werner, H. Zhao, Y. He, W. Ren, L. Tian, C. Shi, and S. Hou. A review of climatic controls on δ¹⁸O in precipitation over the Tibetan Plateau: Observations and simulations. Reviews of Geophysics, 51:525-548, December 2013. [ bib | DOI | ADS link ]

stable oxygen isotope ratio (δ¹⁸O) in precipitation is an integrated tracer of atmospheric processes worldwide. Since the 1990s, an intensive effort has been dedicated to studying precipitation isotopic composition at more than 20 stations in the Tibetan Plateau (TP) located at the convergence of air masses between the westerlies and Indian monsoon. In this paper, we establish a database of precipitation δ¹⁸O and use different models to evaluate the climatic controls of precipitation δ¹⁸O over the TP. The spatial and temporal patterns of precipitation δ¹⁸O and their relationships with temperature and precipitation reveal three distinct domains, respectively associated with the influence of the westerlies (northern TP), Indian monsoon (southern TP), and transition in between. Precipitation δ¹⁸O in the monsoon domain experiences an abrupt decrease in May and most depletion in August, attributable to the shifting moisture origin between Bay of Bengal (BOB) and southern Indian Ocean. High-resolution atmospheric models capture the spatial and temporal patterns of precipitation δ¹⁸O and their relationships with moisture transport from the westerlies and Indian monsoon. Only in the westerlies domain are atmospheric models able to represent the relationships between climate and precipitation δ¹⁸O. More significant temperature effect exists when either the westerlies or Indian monsoon is the sole dominant atmospheric process. The observed and simulated altitude-δ¹⁸O relationships strongly depend on the season and the domain (Indian monsoon or westerlies). Our results have crucial implications for the interpretation of paleoclimate records and for the application of atmospheric simulations to quantifying paleoclimate and paleo-elevation changes.

J. Jouzel, G. Delaygue, A. Landais, V. Masson-Delmotte, C. Risi, and F. Vimeux. Water isotopes as tools to document oceanic sources of precipitation. Water Resources Research, 49:7469-7486, November 2013. [ bib | DOI | ADS link ]

The isotopic composition of precipitation, in deuterium, oxygen 18 and oxygen 17, depends on the climatic conditions prevailing in the oceanic regions where it originates, mainly the sea surface temperature and the relative humidity of air. This dependency applies to present-day precipitation but also to past records which are extracted, for example, from polar ice cores. In turn, coisotopic measurements of deuterium and oxygen 18 offer the possibility to retrieve information about the oceanic origin of modern precipitation as well as about past changes in sea surface temperature and relative humidity of air. This interpretation of isotopic measurements has largely relied on simple Rayleigh-type isotopic models and is complemented by Lagrangian back trajectory analysis of moisture sources. It is now complemented by isotopic General Circulation Models (IGCM) in which the origin of precipitation can be tagged. We shortly review published results documenting this link between the oceanic sources of precipitation and their isotopic composition. We then present experiments performed with two different IGCMs, the GISS model II and the LMDZ model. We focus our study on marine water vapor and its contribution to precipitation over Antarctica and over the Andean region of South America. We show how IGCM experiments allow us to relate climatic conditions prevailing in the oceanic source of precipitation to its isotopic composition. Such experiments support, at least qualitatively, the current interpretation of ice core isotopic data in terms of changes in sea surface temperature. Additionally, we discuss recent studies clearly showing the added value of oxygen 17 measurements.

J. Gao, V. Masson-Delmotte, C. Risi, Y. He, and T. Yao. What controls precipitation Î18O in the southern Tibetan Plateau at seasonal and intra-seasonal scales? A case study at Lhasa and Nyalam. Tellus Series B Chemical and Physical Meteorology B, 54:21043, October 2013. [ bib | DOI | ADS link ]

Understanding the spatial and temporal controls of precipitation δ18O in the southern Tibetan Plateau of central Asia is necessary for paleoclimate reconstructions from the wealth of regional archives (ice cores, lake sediments, tree ring cellulose, and speleothems). While classical interpretations of such records were conducted in terms of local precipitation, simulations conducted with atmospheric general circulation models enabled with water stable isotopes have suggested that past changes in south Asia precipitation δ18O may be driven by remote processes linked to moisture transport. Studies conducted at the event scale can provide constraints to assess the drivers of precipitation δ18O and the validity of simulated mechanisms. Here, we take advantage of new event precipitation δ18O monitored from January 2005 to December 2007 at two southern Tibetan Plateau stations (Lhasa and Nyalam). The drivers of daily to seasonal variations are investigated using statistical relationships with local and regional temperature, precipitation amount and convective activity based on in situ data and satellite products. The strongest control on precipitation δ18O at Lhasa during the monsoon season at event and seasonal scales is provided by the integrated regional convective activity upstream air mass trajectories, cumulated over several days. In contrast, the integrated convection appears to be the main driver of precipitation δ18O at Nyalam only in July and August, and the situation is more complex in other months. Local climate variables can only account for a small fraction of the observed δ18O variance, with significant differences between both stations. This study offers a better constraint on climate archives interpretation in the southern Tibetan Plateau. The daily data presented here also provides a benchmark to evaluate the capacity of isotopically enabled atmospheric general circulation models (iGCMs) to simulate the response of precip!

itation δ18O to convection. This is illustrated using a nudged and zo omed simulation with the LMDZiso model. While it successfully simulates some seasonal and daily characteristics of precipitation δ18O in the southern Tibetan Plateau, it fails to simulate the correlation between δ18O and upstream precipitation. This calls for caution when using atmospheric models to interpret precipitation δ18O archives in terms of past monsoon variability.

C. Risi, A. Landais, R. Winkler, and F. Vimeux. Can we determine what controls the spatio-temporal distribution of d-excess and ¹⁷O-excess in precipitation using the LMDZ general circulation model? Climate of the Past, 9:2173-2193, September 2013. [ bib | DOI | ADS link ]

Combined measurements of the H₂¹⁸O and HDO isotopic ratios in precipitation, leading to second-order parameter D-excess, have provided additional constraints on past climates compared to the H₂¹⁸O isotopic ratio alone. More recently, measurements of H₂¹⁷O have led to another second-order parameter: ¹⁷O-excess. Recent studies suggest that ¹⁷O-excess in polar ice may provide information on evaporative conditions at the moisture source. However, the processes controlling the spatio-temporal distribution of ¹⁷O-excess are still far from being fully understood. We use the isotopic general circulation model (GCM) LMDZ to better understand what controls d-excess and ¹⁷O-excess in precipitation at present-day (PD) and during the last glacial maximum (LGM). The simulation of D-excess and ¹⁷O-excess is evaluated against measurements in meteoric water, water vapor and polar ice cores. A set of sensitivity tests and diagnostics are used to quantify the relative effects of evaporative conditions (sea surface temperature and relative humidity), Rayleigh distillation, mixing between vapors from different origins, precipitation re-evaporation and supersaturation during condensation at low temperature. In LMDZ, simulations suggest that in the tropics convective processes and rain re-evaporation are important controls on precipitation D-excess and ¹⁷O-excess. In higher latitudes, the effect of distillation, mixing between vapors from different origins and supersaturation are the most important controls. For example, the lower d-excess and ¹⁷O-excess at LGM simulated at LGM are mainly due to the supersaturation effect. The effect of supersaturation is however very sensitive to a parameter whose tuning would require more measurements and laboratory experiments. Evaporative conditions had previously been suggested to be key controlling factors of d-excess and ¹⁷O-excess, but LMDZ underestimates their role. More generally, some shortcomings in the simulation of ¹⁷O-excess by LMDZ suggest that general circulation models are not yet the perfect tool to quantify with confidence all processes controlling ¹⁷O-excess.

C. Risi, D. Noone, C. Frankenberg, and J. Worden. Role of continental recycling in intraseasonal variations of continental moisture as deduced from model simulations and water vapor isotopic measurements. Water Resources Research, 49:4136-4156, July 2013. [ bib | DOI | ADS link ]

Climate models suggest an important role for land-atmosphere feedbacks on climate, but exhibit a large dispersion in the simulation of this role. We focus here on the role of continental recycling in the intraseasonal variability of continental moisture, and we explore the possibility of using water isotopic measurements to observationally constrain this role. Based on water tagging, we design a diagnostic, named D1, to estimate the role of continental recycling on the intraseasonal variability of continental moisture simulated by the general circulation model LMDZ. In coastal regions, the intraseasonal variability of continental moisture is mainly driven by the variability in oceanic moisture convergence. More inland, the role of continental recycling becomes important. The simulation of this role is sensitive to model parameters modulating evapotranspiration. Then we show that δD in the low-level water vapor is a good tracer for continental recycling, due to the enriched signature of transpiration. Over tropical land regions, the intraseasonal relationship between δD and precipitable water, named D1_iso, is a good observational proxy for D1. We test the possibility of using D1_iso for model evaluation using two satellite data sets: GOSAT and TES. LMDZ captures well the spatial patterns of D1_iso, but underestimates its values. However, a more accurate description of how atmospheric processes affect the isotopic composition of water vapor is necessary before concluding with certitude that LMDZ underestimates the role of continental recycling.

R. Winkler, A. Landais, C. Risi, M. Baroni, A. Ekaykin, J. Jouzel, J. R. Petit, F. Prie, B. Minster, and S. Falourd. Interannual variation of water isotopologues at Vostok indicates a contribution from stratospheric water vapor. Proceedings of the National Academy of Science, 110:17674-17679, June 2013. [ bib | DOI | ADS link ]

Combined measurements of water isotopologues of a snow pit at Vostok over the past 60 y reveal a unique signature that cannot be explained only by climatic features as usually done. Comparisons of the data using a general circulation model and a simpler isotopic distillation model reveal a stratospheric signature in the 17O-excess record at Vostok. Our data and theoretical considerations indicate that mass-independent fractionation imprints the isotopic signature of stratospheric water vapor, which may allow for a distinction between stratospheric and tropospheric influences at remote East Antarctic sites.

L. C. Sime, C. Risi, J. C. Tindall, J. Sjolte, E. W. Wolff, V. Masson-Delmotte, and E. Capron. Warm climate isotopic simulations: what do we learn about interglacial signals in Greenland ice cores? Quaternary Science Reviews, 67:59-80, May 2013. [ bib | DOI | ADS link ]

Measurements of Last Interglacial stable water isotopes in ice cores show that central Greenland δ¹⁸O increased by at least 3 compared to present day. Attempting to quantify the Greenland interglacial temperature change from these ice core measurements rests on our ability to interpret the stable water isotope content of Greenland snow. Current orbitally driven interglacial simulations do not show δ¹⁸O or temperature rises of the correct magnitude, leading to difficulty in using only these experiments to inform our understanding of higher interglacial δ¹⁸O. Here, analysis of greenhouse gas warmed simulations from two isotope-enabled general circulation models, in conjunction with a set of Last Interglacial sea surface observations, indicates a possible explanation for the interglacial δ¹⁸O rise. A reduction in the winter time sea ice concentration around the northern half of Greenland, together with an increase in sea surface temperatures over the same region, is found to be sufficient to drive a 3 interglacial enrichment in central Greenland snow. Warm climate δ¹⁸O and δD in precipitation falling on Greenland are shown to be strongly influenced by local sea surface condition changes: local sea surface warming and a shrunken sea ice extent increase the proportion of water vapour from local (isotopically enriched) sources, compared to that from distal (isotopically depleted) sources. Precipitation intermittency changes, under warmer conditions, leads to geographical variability in the δ¹⁸O against temperature gradients across Greenland. Little sea surface warming around the northern areas of Greenland leads to low δ¹⁸O against temperature gradients (0.1-0.3 per degC), whilst large sea surface warmings in these regions leads to higher gradients (0.3-0.7 per degC). These gradients imply a wide possible range of present day to interglacial temperature increases (4 to 10 degC). Thus, we find that uncertainty about local interglacial sea surface conditions, rather than precipitation intermittency changes, may lead to the largest uncertainties in interpreting temperature from Greenland ice cores. We find that interglacial sea surface change observational records are currently insufficient to enable discrimination between these different δ¹⁸O against temperature gradients. In conclusion, further information on interglacial sea surface temperatures and sea ice changes around northern Greenland should indicate whether +5 degC during the Last Interglacial is sufficient to drive the observed ice core δ¹⁸O increase, or whether a larger temperature increases or ice sheet changes are also required to explain the ice core observations.

R. A. Eagle, C. Risi, J. L. Mitchell, J. M. Eiler, U. Seibt, J. D. Neelin, G. Li, and A. K. Tripati. High regional climate sensitivity over continental China constrained by glacial-recent changes in temperature and the hydrological cycle. Proceedings of the National Academy of Science, 110:8813-8818, May 2013. [ bib | DOI | ADS link ]

The East Asian monsoon is one of Earth's most significant climatic phenomena, and numerous paleoclimate archives have revealed that it exhibits variations on orbital and suborbital time scales. Quantitative constraints on the climate changes associated with these past variations are limited, yet are needed to constrain sensitivity of the region to changes in greenhouse gas levels. Here, we show central China is a region that experienced a much larger temperature change since the Last Glacial Maximum than typically simulated by climate models. We applied clumped isotope thermometry to carbonates from the central Chinese Loess Plateau to reconstruct temperature and water isotope shifts from the Last Glacial Maximum to present. We find a summertime temperature change of 6-7 degC that is reproduced by climate model simulations presented here. Proxy data reveal evidence for a shift to lighter isotopic composition of meteoric waters in glacial times, which is also captured by our model. Analysis of model outputs suggests that glacial cooling over continental China is significantly amplified by the influence of stationary waves, which, in turn, are enhanced by continental ice sheets. These results not only support high regional climate sensitivity in Central China but highlight the fundamental role of planetary-scale atmospheric dynamics in the sensitivity of regional climates to continental glaciation, changing greenhouse gas levels, and insolation.

H. C. Steen-Larsen, S. J. Johnsen, V. Masson-Delmotte, B. Stenni, C. Risi, H. Sodemann, D. Balslev-Clausen, T. Blunier, D. Dahl-Jensen, M. D. Ellehøj, S. Falourd, A. Grindsted, V. Gkinis, J. Jouzel, T. Popp, S. Sheldon, S. B. Simonsen, J. Sjolte, J. P. Steffensen, P. Sperlich, A. E. Sveinbjörnsdóttir, B. M. Vinther, and J. W. C. White. Continuous monitoring of summer surface water vapor isotopic composition above the Greenland Ice Sheet. Atmospheric Chemistry & Physics, 13:4815-4828, May 2013. [ bib | DOI | ADS link ]

We present here surface water vapor isotopic measurements conducted from June to August 2010 at the NEEM (North Greenland Eemian Drilling Project) camp, NW Greenland (77.45deg N, 51.05deg W, 2484 m a.s.l.). Measurements were conducted at 9 different heights from 0.1 m to 13.5 m above the snow surface using two different types of cavity-enhanced near-infrared absorption spectroscopy analyzers. For each instrument specific protocols were developed for calibration and drift corrections. The inter-comparison of corrected results from different instruments reveals excellent reproducibility, stability, and precision with a standard deviations of ˜ 0.23 for δ¹⁸O and ˜ 1.4 for δD. Diurnal and intraseasonal variations show strong relationships between changes in local surface humidity and water vapor isotopic composition, and with local and synoptic weather conditions. This variability probably results from the interplay between local moisture fluxes, linked with firn-air exchanges, boundary layer dynamics, and large-scale moisture advection. Particularly remarkable are several episodes characterized by high ( 40) surface water vapor deuterium excess. Air mass back-trajectory calculations from atmospheric analyses and water tagging in the LMDZiso (Laboratory of Meteorology Dynamics Zoom-isotopic) atmospheric model reveal that these events are associated with predominant Arctic air mass origin. The analysis suggests that high deuterium excess levels are a result of strong kinetic fractionation during evaporation at the sea-ice margin.

M. Casado, P. Ortega, V. Masson-Delmotte, C. Risi, D. Swingedouw, V. Daux, D. Genty, F. Maignan, O. Solomina, B. Vinther, N. Viovy, and P. Yiou. Impact of precipitation intermittency on NAO-temperature signals in proxy records. Climate of the Past, 9:871-886, March 2013. [ bib | DOI | ADS link ]

In mid and high latitudes, the stable isotope ratio in precipitation is driven by changes in temperature, which control atmospheric distillation. This relationship forms the basis for many continental paleoclimatic reconstructions using direct (e.g. ice cores) or indirect (e.g. tree ring cellulose, speleothem calcite) archives of past precipitation. However, the archiving process is inherently biased by intermittency of precipitation. Here, we use two sets of atmospheric reanalyses (NCEP (National Centers for Environmental Prediction) and ERA-interim) to quantify this precipitation intermittency bias, by comparing seasonal (winter and summer) temperatures estimated with and without precipitation weighting. We show that this bias reaches up to 10 degC and has large interannual variability. We then assess the impact of precipitation intermittency on the strength and stability of temporal correlations between seasonal temperatures and the North Atlantic Oscillation (NAO). Precipitation weighting reduces the correlation between winter NAO and temperature in some areas (e.g. Québec, South-East USA, East Greenland, East Siberia, Mediterranean sector) but does not alter the main patterns of correlation. The correlations between NAO, δ¹⁸O in precipitation, temperature and precipitation weighted temperature are investigated using outputs of an atmospheric general circulation model enabled with stable isotopes and nudged using reanalyses (LMDZiso (Laboratoire de Météorologie Dynamique Zoom)). In winter, LMDZiso shows similar correlation values between the NAO and both the precipitation weighted temperature and δ¹⁸O in precipitation, thus suggesting limited impacts of moisture origin. Correlations of comparable magnitude are obtained for the available observational evidence (GNIP (Global Network of Isotopes in Precipitation) and Greenland ice core data). Our findings support the use of archives of past δ¹⁸O for NAO reconstructions.

C. Frankenberg, D. Wunch, G. Toon, C. Risi, R. Scheepmaker, J.-E. Lee, P. Wennberg, and J. Worden. Water vapor isotopologue retrievals from high-resolution GOSAT shortwave infrared spectra. Atmospheric Measurement Techniques, 6:263-274, February 2013. [ bib | DOI | ADS link ]

Remote sensing of the isotopic composition of water vapor can provide valuable information on the hydrological cycle. Here, we demonstrate the feasibility of retrievals of the relative abundance of HDO (the HDO/H₂O ratio) from the Japanese GOSAT satellite. For this purpose, we use high spectral resolution nadir radiances around 6400 cm^-1 (1.56 μm) to retrieve vertical column amounts of H₂O and HDO. Retrievals of H₂O correlate well with ECMWF (European Centre for Medium-Range Weather Forecasts) integrated profiles (r² = 0.96). Typical precision errors in the retrieved column-averaged deuterium depletion (δD) are 20-40. We compare δD against a TCCON (Total Carbon Column Observing Network) ground-based station in Lamont, Oklahoma. Using retrievals in very dry areas over Antarctica, we detect a small systematic offset in retrieved H₂O and HDO column amounts and take this into account for a bias correction of δD. Monthly averages of δD in the June 2009 to September 2011 time frame are well correlated with TCCON (r² = 0.79) and exhibit a slope of 0.98 (1.23 if not bias corrected). We also compare seasonal averages on the global scale with results from the SCIAMACHY instrument in the 2003-2005 time frame. Despite the lack of temporal overlap, seasonal averages in general agree well, with spatial correlations (r²) ranging from 0.62 in September through November to 0.83 in June through August. However, we observe higher variability in GOSAT δD, indicated by fitted slopes between 1.2 and 1.46. The discrepancies are likely related to differences in vertical sensitivities but warrant further validation of both GOSAT and SCIAMACHY and an extension of the validation dataset.

D. Noone, C. Risi, A. Bailey, M. Berkelhammer, D. P. Brown, N. Buenning, S. Gregory, J. Nusbaumer, D. Schneider, J. Sykes, B. Vanderwende, J. Wong, Y. Meillier, and D. Wolfe. Determining water sources in the boundary layer from tall tower profiles of water vapor and surface water isotope ratios after a snowstorm in Colorado. Atmospheric Chemistry & Physics, 13:1607-1623, February 2013. [ bib | DOI | ADS link ]

The D/H isotope ratio is used to attribute boundary layer humidity changes to the set of contributing fluxes for a case following a snowstorm in which a snow pack of about 10 cm vanished. Profiles of H₂O and CO₂ mixing ratio, D/H isotope ratio, and several thermodynamic properties were measured from the surface to 300 m every 15 min during four winter days near Boulder, Colorado. Coeval analysis of the D/H ratios and CO₂ concentrations find these two variables to be complementary with the former being sensitive to daytime surface fluxes and the latter particularly indicative of nocturnal surface sources. Together they capture evidence for strong vertical mixing during the day, weaker mixing by turbulent bursts and low level jets within the nocturnal stable boundary layer during the night, and frost formation in the morning. The profiles are generally not well described with a gradient mixing line analysis because D/H ratios of the end members (i.e., surface fluxes and the free troposphere) evolve throughout the day which leads to large uncertainties in the estimate of the D/H ratio of surface water flux. A mass balance model is constructed for the snow pack, and constrained with observations to provide an optimal estimate of the partitioning of the surface water flux into contributions from sublimation, evaporation of melt water in the snow and evaporation from ponds. Results show that while vapor measurements are important in constraining surface fluxes, measurements of the source reservoirs (soil water, snow pack and standing liquid) offer stronger constraint on the surface water balance. Measurements of surface water are therefore essential in developing observational programs that seek to use isotopic data for flux attribution.