The 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.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/rog.20023

A review of climatic controls on δ18O in precipitation over the Tibetan Plateau: Observations and simulations

[1] The most important sources of atmospheric moisture at the global scale are herein identified, both oceanic and terrestrial, and a characterization is made of how continental regions are influenced by water from different moisture source regions. The methods used to establish source-sink relationships of atmospheric water vapor are reviewed, and the advantages and caveats associated with each technique are discussed. The methods described include analytical and box models, numerical water vapor tracers, and physical water vapor tracers (isotopes). In particular, consideration is given to the wide range of recently developed Lagrangian techniques suitable both for evaluating the origin of water that falls during extreme precipitation events and for establishing climatologies of moisture source-sink relationships. As far as oceanic sources are concerned, the important role of the subtropical northern Atlantic Ocean provides moisture for precipitation to the largest continental area, extending from Mexico to parts of Eurasia, and even to the South American continent during the Northern Hemisphere winter. In contrast, the influence of the southern Indian Ocean and North Pacific Ocean sources extends only over smaller continental areas. The South Pacific and the Indian Ocean represent the principal source of moisture for both Australia and Indonesia. Some landmasses only receive moisture from the evaporation that occurs in the same hemisphere (e.g., northern Europe and eastern North America), while others receive moisture from both hemispheres with large seasonal variations (e.g., northern South America). The monsoonal regimes in India, tropical Africa, and North America are provided with moisture from a large number of regions, highlighting the complexities of the global patterns of precipitation. Some very important contributions are also seen from relatively small areas of ocean, such as the Mediterranean Basin (important for Europe and North Africa) and the Red Sea, which provides water for a large area between the Gulf of Guinea and Indochina (summer) and between the African Great Lakes and Asia (winter). The geographical regions of Eurasia, North and South America, and Africa, and also the internationally important basins of the Mississippi, Amazon, Congo, and Yangtze Rivers, are also considered, as is the importance of terrestrial sources in monsoonal regimes. The role of atmospheric rivers, and particularly their relationship with extreme events, is discussed. Droughts can be caused by the reduced supply of water vapor from oceanic moisture source regions. Some of the implications of climate change for the hydrological cycle are also reviewed, including changes in water vapor concentrations, precipitation, soil moisture, and aridity. It is important to achieve a combined diagnosis of moisture sources using all available information, including stable water isotope measurements. A summary is given of the major research questions that remain unanswered, including (1) the lack of a full understanding of how moisture sources influence precipitation isotopes; (2) the stationarity of moisture sources over long periods; (3) the way in which possible changes in intensity (where evaporation exceeds precipitation to a greater of lesser degree), and the locations of the sources, (could) affect the distribution of continental precipitation in a changing climate; and (4) the role played by the main modes of climate variability, such as the North Atlantic Oscillation or the El Nino–Southern Oscillation, in the variability of the moisture source regions, as well as a full evaluation of the moisture transported by low-level jets and atmospheric rivers.

Oceanic and terrestrial sources of continental precipitation

[1] Changes in indices of climate extremes are analyzed on the basis of daily maximum and minimum surface air temperature and precipitation at 71 meteorological stations with elevation above 2000 m above sea level in the eastern and central Tibetan Plateau (TP) during 1961–2005. Twelve indices of extreme temperature and nine indices of extreme precipitation are examined. Temperature extremes show patterns consistent with warming during the studied period, with a large proportion of stations showing statistically significant trends for all temperature indices. Stations in the northwestern, southwestern, and southeastern TP have larger trend magnitudes. The regional occurrence of extreme cold days and nights has decreased by −0.85 and −2.38 d/decade, respectively. Over the same period, the occurrence of extreme warm days and nights has increased by 1.26 and 2.54 d/decade, respectively. The number of frost days and ice days shows statistically significant decreasing at the rate of −4.32 and −2.46 d/decade, respectively. The length of growing season has statistically increased by 4.25 d/decade. The diurnal temperature range exhibits a statistically decreasing trend at a rate of −0.20°C per decade. The extreme temperature indices also show statistically significant increasing trends, with larger values for the index describing variations in the lowest minimum temperature. In general, warming trends in minimum temperature indices are of greater magnitude than those for maximum temperature. Most precipitation indices exhibit increasing trends in the southern and northern TP and show decreasing trends in the central TP. On average, regional annual total precipitation, heavy precipitation days, maximum 1-day precipitation, average wet days precipitation, and total precipitation on extreme wet days show nonsignificant increases. Decreasing trends are found for maximum 5-day precipitation, consecutive wet days, and consecutive dry days, but only the last is statistically significant.

/pdf/changes-in-daily-climate-extremes-in-the-eastern-and-central-1bbr59ldxv.pdf

Changes in daily climate extremes in the eastern and central Tibetan Plateau during 1961–2005

https://geosci.uchicago.edu/~rowley/Rowley/Publications_files/Polissar%20et%20al%20EPSL%202009.pdf

Paleoaltimetry of the Tibetan Plateau from D/H ratios of lipid biomarkers

Groundwater recharged by meteoric water supports human life by providing two billion people with drinking water and by supplying 40% of cropland irrigation. While annual groundwater recharge rates are reported in many studies, fewer studies have explicitly quantified intra-annual (i.e., seasonal) differences in groundwater recharge. Understanding seasonal differences in the fraction of precipitation that recharges aquifers is important for predicting annual recharge groundwater rates under changing seasonal precipitation and evapotranspiration regimes in a warming climate, for accurately interpreting isotopic proxies in paleoclimate records, and for understanding linkages between ecosystem productivity and groundwater recharge. Here we determine seasonal differences in the groundwater recharge ratio, defined here as the ratio of groundwater recharge to precipitation, at 54 globally distributed locations on the basis of 18O/16O and 2H/1H ratios in precipitation and groundwater. Our analysis shows that arid and temperate climates have wintertime groundwater recharge ratios that are consistently higher than summertime groundwater recharge ratios, while tropical groundwater recharge ratios are at a maximum during the wet season. The isotope-based recharge ratio seasonality is consistent with monthly outputs from a global hydrological model (PCR-GLOBWB) for most, but not all locations. The pronounced seasonality in groundwater recharge ratios shown in this study signifies that, from the point of view of predicting future groundwater recharge rates, a unit change in winter (temperate and arid regions) or wet season (tropics) precipitation will result in a greater change to the annual groundwater recharge rate than the same unit change to summer or dry season precipitation.

/pdf/the-pronounced-seasonality-of-global-groundwater-recharge-3dzkc5giom.pdf

The pronounced seasonality of global groundwater recharge

[1] In this study, individual precipitation samples, collected over 2 years at stations in different climatic regions of west China (Tibetan Plateau region, Tianshan region, and Altay) were analyzed for the stable isotopes of precipitation to improve our understanding of how vapor transport impacts the modern stable isotopic distribution. Our results identify regional patterns in both δ18O and deuterium excess (D excess, defined as δD – 8δ18O), and in particular we have identified the northward maximum extent of the southwest monsoon over the Tibetan Plateau. This demarcation is also the boundary for the fractionation effect of temperature on stable isotopes in precipitation. The patterns we have identified are as follows: (1) In the southern Tibetan Plateau, along the southern slope of the Himalayas, our results show a distinct seasonality for both δ18O and D excess as a result of the shift of summer monsoon moisture and winter westerly moisture transport. The signals of δ18O in the western Tibetan Plateau reveal that the region receives southwest monsoonal moisture. In the east of the plateau, stable isotopic variation shows alternation between monsoon intrusion and recycling of northern moisture. (2) In contrast, in Tianshan there is an apparent “temperature effect” in δ18O, with enriched values occurring in summer and depleted values occurring in winter. Seasonal D excess values, opposite to those observed in the southern Tibetan Plateau, are controlled by differing seasonal evaporation conditions. (3) In Altay, the most northern mountain region, the seasonal δ18O shows the same variation with that in Tianshan region. However, D excess shows no apparent seasonal variation.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2006JD007718

Stable isotopic variations in west China: A consideration of moisture sources

[1] This research presents the most spatially complete data set depicting average monthly δ18O precipitation values across the United States (isoscapes). Average monthly isoscapes were calculated by analyzing 5 consecutive years of precipitation samples collected at 73 collection sites from the United States Network for Isotopes in Precipitation. Three patterns across the United States emerged from the analysis: (1) the most 18O-depleted precipitation was not confined to the higher elevations of the Rocky Mountain region but were also found in the upper Great Lakes; (2) clear latitudinal gradients were observed in the Mississippi River valley: steeper during cold months than during warm months; and (3) coastal latitudinal gradients were significantly shallower than continental gradients. The average monthly isoscapes were significantly correlated with surface temperatures, particularly in winter but less so in summer. The Rayleigh distillation model, however, produced uniformly steeper monthly isotope temperature coefficients (δ18O‰/°C) than those calculated from empirical δ18O values. Our analysis suggests that differences in model/observation isotope temperature coefficients result from the contiguous United States having two primary moisture sources: the Gulf of Mexico and the northeast Pacific Ocean regions. A significant proportion of precipitation sourced from the Gulf of Mexico (northeast Pacific Ocean) occurs in warm (cool) regions resulting in more (less) isotopic depletion than if all moisture had originated from one source for the entire United States. These two primary precipitation source scenarios result in a smaller variation in oxygen isotopic variation for the distribution of temperatures in a given month, yielding lower than predicted isotope temperature coefficients. The results of this study highlight the importance of understanding environmental factors affecting regional precipitation isotope values, particularly if one wishes to use isotopic analysis for paleoclimate interpretation or as a measure of a modern day hydrologic process.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2010JD014105

Monthly precipitation isoscapes (δ18O) of the United States: Connections with surface temperatures, moisture source conditions, and air mass trajectories

[1] Understanding and modeling precipitation isotope (δ 18 O and 6D) patterns for large regions of the globe requires quantifying processes governing continental-scale climatology and hydrology. In this study, we have evaluated the extent to which inclusion of monthly moisture source temperature and moisture source locations in the Rayleigh distillation model aid in reproducing the relationships between monthly time series of precipitation isotope (δ 18 O) values and temperature across the contiguous United States. The steepest isotope-temperature slopes (0.5‰-0.6‰ δ 18 O/°C) and greatest δ 18 O value correlations with temperature (r 2 = 0.5-0.8), derived from 5 continuous years of the data from the United States Network for Isotopes in Precipitation, occurred in the high altitudes of the Rocky Mountains and the upper Great Lakes region. The isotope-temperature slopes derived from the site-specific time series were consistently lower along the coastal regions of the United States as were the coefficients of determination. The low coastal isotope-temperature slopes are not easily explained by the simple Rayleigh model that uses condensation temperatures as the primary driver of precipitation isotopes. However, the Raleigh model equipped with moisture source temperatures defined by seasonal temperature oscillations and migrating moisture source locations provides a robust replication of the δ 18 O-temperature slopes along coastal regions. These findings emphasize the importance of moisture sources conditions when interpreting palaeoclimate proxies (i.e., tree rings, ice cores, etc.), and argue that moisture source dynamics should always be included in models that use isotopes as diagnostic tools in testing hydrologic models.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009WR008558

Moisture source temperatures and precipitation δ18O-temperature relationships across the United States

Strong compressive and shear stresses generated by glacial loading and unloading have a direct impact on near‐surface geological processes. Glacial stresses are constantly evolving, creating stress perturbations in the lithosphere that extend significant distances away from the ice. In the Arctic, periodic methane seepage and faulting have been recurrently associated with glacial cycles. However, the evolution of the Arctic glacial stress field and its impact on the upper lithosphere have not been investigated. Here, we compute the evolution in space and time of the glacial stresses induced in the Arctic lithosphere by the North American, Eurasian and Greenland ice sheets during the latest glaciation. We use glacial isostatic adjustment (GIA) methodology to investigate the response of spherical, viscoelastic Earth models with varying lithospheric thickness to the ice loads. We find that the GIA‐induced maximum horizontal stress (σH) is compressive in regions characterized by thick ice cover, with magnitudes of 20–25 MPa in Fennoscandia and 35–40 MPa in Greenland at the last glacial maximum. Simultaneously, a tensile regime with σH magnitude down to −16 MPa dominates across the forebulges with a mean of −4 MPa in the Fram Strait. At present time, σH in the Fram Strait remains tensile with an East‐West orientation. The evolution of GIA‐induced stresses from the last glaciation to present could destabilize faults along tensile forebulges, for example, the west‐coast of Svalbard. A more tensile stress regime as during the Last Glacial Maximum would have more impact on pre‐existing faults that favor gas seepage from gas reservoirs.

R. W. Vachon

Papers

Stable isotopic variations in west China: A consideration of moisture sources

Monthly precipitation isoscapes (δ18O) of the United States: Connections with surface temperatures, moisture source conditions, and air mass trajectories

Moisture source temperatures and precipitation δ18O-temperature relationships across the United States

Glacially Induced Stress Across the Arctic From the Eemian Interglacial to the Present—Implications for Faulting and Methane Seepage

Impact of Far-Field Glacially-Induced Stresses on Fault Stability in the Eastern Paris Basin