Influence of Sea-Ice Anomalies on Antarctic Precipitation Using Source Attribution in the Community Earth System Model

We conduct sensitivity experiments using a general circulation model that has an explicit water source tagging capability forced by prescribed composites of pre-industrial sea-ice concentrations (SICs) and corresponding sea surface temperatures (SSTs) to understand the impact of sea-ice anomalies on regional evaporation, moisture transport and sourcereceptor relationships for Antarctic precipitation in the absence of anthropogenic forcing. Surface sensible heat fluxes, evaporation and column-integrated water vapor are larger over Southern Ocean (SO) areas with lower SICs. Changes in Antarctic precipitation and its source attribution with SICs have a strong spatial variability. Among the tagged source regions, the Southern Ocean (south of 50 S) contributes the most (40 %) to the Antarctic total precipitation, followed by more northerly ocean basins, most notably the South Pacific Ocean (27%), southern Indian Ocean (16 %) and South Atlantic Ocean (11 %). Comparing two experiments prescribed with high and low pre-industrial SICs, respectively, the annual mean Antarctic precipitation is about 150 Gt yr1 (or 6 %) more in the lower SIC case than in the higher SIC case. This difference is larger than the model-simulated interannual variability in Antarctic precipitation (99 Gt yr1). The contrast in contribution from the Southern Ocean, 102 Gt yr1, is even more significant compared to the interannual variability of 35 Gt yr1 in Antarctic precipitation that originates from the Southern Ocean. The horizontal transport pathways from individual vapor source regions to Antarctica are largely determined by large-scale atmospheric circulation patterns. Vapor from lower-latitude source regions takes elevated pathways to Antarctica. In contrast, vapor from the Southern Ocean moves southward within the lower troposphere to the Antarctic continent along moist isentropes that are largely shaped by local ambient conditions and coastal topography. This study also highlights the importance of atmospheric dynamics in affecting the thermodynamic impact of sea-ice anomalies associated with natural variability on Antarctic precipitation. Our analyses of the seasonal contrast in changes of basin-scale evaporation, moisture flux and precipitation suggest that the impact of SIC anomalies on regional Antarctic precipitation depends on dynamic changes that arise from SICSST perturbations along with internal variability. The latter appears to have a more significant effect on the moisture transport in austral winter than in summer

Evaluation of modeled land-atmosphere exchanges with a comprehensive water isotope fractionation scheme in version 4 of the Community Land Model

All physical process models and field observations are inherently imperfect, so there is a need to both (1) obtain measurements capable of constraining quantities of interest and (2) develop frameworks for assessment in which the desired processes and their uncertainties may be characterized. Incorporation of stable water isotopes into land surface schemes offers a complimentary approach to constrain hydrological processes such as evapotranspiration, and yields acute insight into the hydrological and biogeochemical behaviors of the domain. Here a stable water isotopic scheme in the National Center for Atmospheric Research's version 4 of the Community Land Model (CLM4) is presented. An overview of the isotopic methods is given. Isotopic model results are compared to available data sets on site-level and global scales for validation. Comparisons of site-level soil moisture and isotope ratios reveal that surface water does not percolate as deeply into the soil as observed in field measurements. The broad success of the new model provides confidence in its use for a range of climate and hydrological studies, while the sensitivity of simulation results to kinetic processes stands as a reminder that new theoretical development and refinement of kinetic effect parameterizations is needed to achieve further improvements. Key Points Water isotope physics have been added to the version 4 of the Community Land Model An imperfect soil moisture simulation has limited impacts on soil water isotopic profiles Soil evaporative kinetic effect alone cannot rectify coupled model discrepancy with respect to water isotopic dat

Comparing methanol-glucose and dimethyl-sulfoxide based extender for milt cryopreservation of brown trout (Salmo trutta)

The potential importance of sperm cryopreservation for aquaculture and conservation management seems still undervalued, probably because the available protocols often lead to reduced fertilization success. We experimentally compared the effectiveness of two different freezing extenders for cryopreservation of brown trout (Salmo trutta) semen, controlling for possible male and female effects. The methanol-glucose based extender that we tested was significantly more effective than a common dimethyl-sulfoxide based extender (a commercial cryopreservation kit). We then studied the effectiveness of the methanol-glucose based extender at different sperm-egg ratios and found no significant differences in fertilization ability of fresh and cryopreserved milt at a sperm-egg ratio of at least 110,000:1. We conclude that brown trout sperm cryopreserved with this extender can be used even at low sperm-egg ratios without significant effects on fertilization rates

Growth of brown trout in the wild predicted by embryo stress reaction in the laboratory

Laboratory studies on embryos of salmonids, such as the brown trout (Salmo trutta), have been extensively used to study environmental stress and how responses vary within and between natural populations. These studies are based on the implicit assumption that early life-history traits are relevant for stress tolerance in the wild. Here we test this assumption by combining two datasets from studies on the same 60 full-sib families. These families had been experimentally produced from wild breeders to determine, in separate samples, (i) stress tolerances of singly kept embryos in the laboratory and (ii) growth of juveniles during 6 months in the wild. We found that growth in the wild was well predicted by larval size of their full sibs in the laboratory, especially if these siblings had been experimentally exposed to a pathogen. Exposure to the pathogen had not caused elevated mortality among the embryos but induced early hatching. The strength of this stress-induced change of life history was a significant predictor of juvenile growth in the wild: the stronger the response in the laboratory, the slower the growth in the wild. We conclude that embryo performance in controlled environments can be useful predictors of juvenile performance in the wild

Genetic compatibility exceeds possible ‘good genes’ effects of sexual selection in lake char

Mating is rarely random in nature, but the effects of mate choice on offspring performance are still poorly understood. We sampled in total 47 wild lake char (Salvelinus umbla) during two breeding seasons and used their gametes to investigate the genetic consequences of different mating scenarios. In a first study, 1,464 embryos that resulted from sperm competition trials were raised singly in either a stress- or non-stress environment. Offspring growth turned out to be strongly reduced with increased genetic relatedness between the parents while male coloration (that reveal aspects of male health) was no significant predictor of offspring performance. In a second experiment one year later, block-wise full-factorial in vitro breeding was used to produce 3,094 embryos that were raised singly after sublethal exposures to a pathogen or water only. Offspring growth was again strongly reduced with increased genetic relatedness between the parents while male coloration was no significant predictor of offspring performance. We conclude that the genetic benefits of mate choice would be strongest if females avoided genetic similarity, while male breeding colors seem more relevant in intra-sexual selection

Toxicity of 2 pg ethynylestradiol in brown trout embryos (Salmo trutta)

Endocrine disrupting chemicals are a threat to natural fish populations in the aquatic environment. Their toxicity is usually discussed relative to concentrations in the water the fish are exposed to. In the case of the synthetic compound 17-alpha-ethynylestradiol (EE2), a common and persistent estrogen, concentrations around 1 ng/L have repeatedly been found to induce toxic effects in fish. Here, we used brown trout (Salmo trutta) from a natural population to study EE2 take up and how it affects early life-history. We collected adults during the spawning season, produced 730 families in vitro (to control for potential maternal and paternal effects on embryo stress tolerance), and singly raised 7,300 embryos (in a 2 mL static system) that were either exposed to one dose of EE2 at 1 ng/L (i.e., 2 pg/embryo) or sham-treated. We found that EE2 concentration did not significantly change over a period of 3 months in control containers without embryos. Embryos took up most of the 2 pg EE2 within about 4 weeks at 4.6°C. EE2 treated embryos experienced higher mortality, delayed hatching of the survivors, and had reduced size at hatching. Our findings suggest that the toxicity of EE2 is often underestimated when discussed at the level of concentrations in water only

Investigating the Direct Meltwater Effect in Terrestrial Oxygenâ Isotope Paleoclimate Records Using an Isotopeâ Enabled Earth System Model

Variations in terrestrial oxygenâ isotope reconstructions from ice cores and speleothems have been primarily attributed to climatic changes of surface air temperature, precipitation amount, or atmospheric circulation. Here we demonstrate with the fully coupled isotopeâ enabled Community Earth System Model an additional process contributing to the oxygenâ isotope variations during glacial meltwater events. This process, termed â the direct meltwater effect,â involves propagating large amounts of isotopically depleted meltwater throughout the hydrological cycle and is independent of climatic changes. We find that the direct meltwater effect can make up 15â 35% of the δ18O signals in precipitation over Greenland and eastern Brazil for large freshwater forcings (0.25â 0.50 sverdrup (106 m3/s)). Model simulations further demonstrate that the direct meltwater effect increases with the magnitude and duration of the freshwater forcing and is sensitive to both the location and shape of the meltwater. These new modeling results have important implications for past climate interpretations of δ18O.Key PointsA portion of the δ18O signal in landâ based paleoclimate proxies can be attributed to the direct meltwater effect instead of climatic changesThe direct meltwater effect can make up 15â 35% of the δ18O signals in precipitation in Greenland and eastern Brazil for large meltwater eventsThe direct meltwater effect increases with the magnitude and duration of the freshwater forcing and is sensitive to location and shape dependentPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141374/1/grl56782_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141374/2/grl56782-sup-0001-Supporting_Information.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141374/3/grl56782.pd

Tracking the Strength of the Walker Circulation With Stable Isotopes in Water Vapor

General circulation models (GCMs) predict that the global hydrological cycle will change in response to anthropogenic warming. However, these predictions remain uncertain, in particular, for precipitation (Intergovernmental Panel on Climate Change, 2013, https://doi .org/10.1017/CB09781107415324.004). Held and Soden (2006, https://doi.org/10.1175/JCLI3990.1) suggest that as lower tropospheric water vapor concentration increases in a warming climate, the atmospheric circulation and convective mass fluxes will weaken. Unfortunately, this process is difficult to constrain, as convective mass fluxes are poorly observed and incompletely simulated in GCMs. Here we demonstrate that stable hydrogen isotope ratios in tropical atmospheric water vapor can trace changes in temperature, atmospheric circulation, and convective mass flux in a warming world. We evaluate changes in temperature, the distribution of water vapor, vertical velocity (omega), advection, and water isotopes in vapor (delta D-v). Using water isotope-enabled GCM experiments for modern versus high-CO2 atmospheres, we identify spatial patterns of circulation change over the tropical Pacific. We find that slowing circulation in the tropical Pacific moistens the lower troposphere and weakens convective mass flux, both of which impact the delta D of water vapor in the midtroposphere. Our findings constitute a critical demonstration of how water isotope ratios in the tropical Pacific respond to changes in radiative forcing and atmospheric warming. Moreover, as changes in delta D-v can be observed by satellites, our results develop new metrics for the detection of global warming impacts to the hydrological cycle and, specifically, the strength of the Walker circulation

Long-term climate change commitment and reversibility: an EMIC intercomparison

This paper summarizes the results of an intercomparison project with Earth System Models of Intermediate Complexity (EMICs) undertaken in support of the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5). The focus is on long-term climate projections designed to: (i) quantify the climate change commitment of different radiative forcing trajectories, and (ii) explore the extent to which climate change is reversible on human timescales. All commitment simulations follow the four Representative Concentration Pathways (RCPs) and their extensions to 2300. Most EMICs simulate substantial surface air temperature and thermosteric sea level rise commitment following stabilization of the atmospheric composition at year-2300 levels. The meridional overturning circulation (MOC) is weakened temporarily and recovers to near pre-industrial values in most models for RCPs 2.6–6.0. The MOC weakening is more persistent for RCP 8.5. Elimination of anthropogenic CO2 emissions after 2300 results in slowly decreasing atmospheric CO2 concentrations. At year 3000 atmospheric CO2 is still at more than half its year-2300 level in all EMICs for RCPs 4.5–8.5. Surface air temperature remains constant or decreases slightly and thermosteric sea level rise continues for centuries after elimination of CO2 emissions in all EMICs. Restoration of atmospheric CO2 from RCP to pre-industrial levels over 100–1000 years requires large artificial removal of CO2 from the atmosphere and does not result in the simultaneous return to pre-industrial climate conditions, as surface air temperature and sea level response exhibit a substantial time lag relative to atmospheric CO2