Electron Spin Resonance Studies of Calcium-Treated Human Erythrocytes and Erythrocyte Ghosts

Biochemistr

Opposing oceanic and atmospheric ENSO influences on the Ross Sea Region, Antarctica

International audienceHere we discuss the cause and effect of opposing atmospheric and oceanic ENSO forcings in the Ross Sea, that lead to a net warming in the eastern Ross Sea and a net cooling in the western Ross Sea during El Niño years. During La Niña years the opposite is observed. The oceanic ENSO effect causes a ~1 K warming with a 3 month lag during El Niño years in comparison to La Niña time periods. During El Niño events, the atmospheric ENSO effect leads to a shift and weakening of the Amundsen Sea Low, causing enhanced import of colder West Antarctic air masses into the western Ross Sea. We find that this indirect ENSO effect is about one order of magnitude stronger (up to 15 K) in the western Ross Sea than the direct effect (~1 K), leading to a net cooling during El Niño and net warming during La Niña events

Deglacial grounding-line retreat in the Ross Embayment, Antarctica, controlled by ocean and atmosphere forcing

Modern observations appear to link warming oceanic conditions with Antarctic ice sheet grounding-line retreat. Yet, interpretations of past ice sheet retreat over the last deglaciation in the Ross Embayment, Antarctica’s largest catchment, differ considerably and imply either extremely high or very low sensitivity to environmental forcing. To investigate this, we perform regional ice sheet simulations using a wide range of atmosphere and ocean forcings. Constrained by marine and terrestrial geological data, these models predict earliest retreat in the central embayment and rapid terrestrial ice sheet thinning during the Early Holocene. We find that atmospheric conditions early in the deglacial period can enhance or diminish ice sheet sensitivity to rising ocean temperatures, thereby controlling the initial timing and spatial pattern of grounding-line retreat. Through the Holocene, however, grounding-line position is much more sensitive to subshelf melt rates, implicating ocean thermal forcing as the key driver of past ice sheet retreat

Mydriasis and heredity *

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65820/1/j.1399-0004.1977.tb00915.x.pd

High-resolution continuous-flow analysis setup for water isotopic measurement from ice cores using laser spectroscopy

Here we present an experimental setup for water stable isotope (&delta;¹⁸O and δD) continuous-flow measurements and provide metrics defining the performance of the setup during a major ice core measurement campaign (Roosevelt Island Climate Evolution; RICE). We also use the metrics to compare alternate systems. Our setup is the first continuous-flow laser spectroscopy system that is using off-axis integrated cavity output spectroscopy (OA-ICOS; analyzer manufactured by Los Gatos Research, LGR) in combination with an evaporation unit to continuously analyze water samples from an ice core. <br><br> A Water Vapor Isotope Standard Source (WVISS) calibration unit, manufactured by LGR, was modified to (1) enable measurements on several water standards, (2) increase the temporal resolution by reducing the response time and (3) reduce the influence from memory effects. While this setup was designed for the continuous-flow analysis (CFA) of ice cores, it can also continuously analyze other liquid or vapor sources. <br><br> The custom setups provide a shorter response time (~ 54 and 18 s for 2013 and 2014 setup, respectively) compared to the original WVISS unit (~ 62 s), which is an improvement in measurement resolution. Another improvement compared to the original WVISS is that the custom setups have a reduced memory effect. <br><br> Stability tests comparing the custom and WVISS setups were performed and Allan deviations (&sigma;_Allan) were calculated to determine precision at different averaging times. For the custom 2013 setup the precision after integration times of 10³ s is 0.060 and 0.070 &permil; for δ¹⁸O and δD, respectively. The corresponding &sigma;_Allan values for the custom 2014 setup are 0.030, 0.060 and 0.043 &permil; for &delta;¹⁸O, δD and &delta;¹⁷O, respectively. For the WVISS setup the precision is 0.035, 0.070 and 0.042 &permil; after 10³ s for δ¹⁸O, δD and &delta;¹⁷O, respectively. Both the custom setups and WVISS setup are influenced by instrumental drift with δ¹⁸O being more drift sensitive than δD. The &sigma;_Allan values for δ¹⁸O are 0.30 and 0.18 &permil; for the custom 2013 and WVISS setup, respectively, after averaging times of 10⁴ s (2.78 h). Using response time tests and stability tests, we show that the custom setups are more responsive (shorter response time), whereas the University of Copenhagen (UC) setup is more stable. More broadly, comparisons of different setups address the challenge of integrating vaporizer/spectrometer isotope measurement systems into a CFA campaign with many other analytical instruments

El Nino Suppresses Aantarctic Warming

Here we present new isotope records derived from snow samples from the McMurdo Dry Valleys, Antarctica and re-analysis data of the European Centre for Medium-Range Weather Forecasts (ERA-40) to explain the connection between the warming of the Pacific sector of the Southern Ocean [Jacka and Budd, 1998; Jacobs et al., 2002] and the current cooling of the terrestrial Ross Sea region [Doran et al., 2002a]. Our analysis confirms previous findings that the warming is linked to the El Nino Southern Oscillation (ENSO) [Kwok and Comiso, 2002a, 2002b; Carleton, 2003; Ribera and Mann, 2003; Turner, 2004], and provides new evidence that the terrestrial cooling is caused by a simultaneous ENSO driven change in atmospheric circulation, sourced in the Amundsen Sea and West Antarctica

Solar Forcing Recorded by Aerosol Concentrations in Coastal Antarctic Glacier Ice, McMurdo Dry Valleys

Ice-core chemistry data from Victoria Lower Glacier, Antarctica, suggest, at least for the last 50 years, a direct influence of solar activity variations on the McMurdo Dry Valleys (MDV) climate system via controls on air-mass input from two competing environments: the East Antarctic ice sheet and the Ross Sea. During periods of increased solar activity, when total solar irradiance is relatively high, the MDV climate system appears to be dominated by air masses originating from the Ross Sea, leading to higher aerosol deposition. During reduced solar activity, the Antarctic interior seems to be the dominant air-mass source, leading to lower aerosol concentration in the ice-core record. We propose that the sensitivity of the MDV to variations in solar irradiance is caused by strong albedo differences between the ice-free MDV and the ice sheet

Monsoonal Circulation of the McMurdo Dry Valleys, Ross Sea Region, Antarctica: Signal from the Snow Chemistry

McMurdo Dry Valleys (MDV, Ross Sea region, Antarctica) precipitation exhibits extreme seasonality in ion concentration, 3-5 orders of magnitude between summer and winter precipitation. To identify aerosol sources and investigate causes for the observed amplitude in concentration variability, four snow pits were sampled along a coast-Polar Plateau transect across the MDV. The elevation of the sites ranges from 50 to 2400 m and the distance from the coast from 8 to 93 km. Average chemistry gradients along the transect indicate that most species have either a predominant marine or terrestrial source in the MDV. Empirical orthogonal function analysis on the snow-chemistry time series shows that at least 57% of aerosol deposition occurs concurrently. A conceptual climate model, based on meteorological observations, is used to explain the strong seasonality in the MDV. Our results suggest that radiative forcing of the ice-free valleys creates a surface low-pressure cell during summer which promotes air-mass flow from the Ross Sea. The associated precipitating air mass is relatively warm, humid and contains a high concentration of aerosols. During winter, the MDV are dominated by air masses draining off the East Antarctic ice sheet, that are characterized by cold, dry and low concentrations of aerosols. The strong differences between these two air-mass sources create in the MDV a polar version of the monsoonal flow, with humid, warm summers and dry, cold winters

Deglacial evolution of regional Antarctic climate and Southern Ocean conditions in transient climate simulations

Constraining Antarctica's climate evolution since the end of the Last Glacial Maximum (∼18&thinsp;ka) remains a key challenge, but is important for accurately projecting future changes in Antarctic ice sheet mass balance. Here we perform a spatial and temporal analysis of two transient deglacial climate simulations, one using a fully coupled GCM (TraCE-21ka) and one using an intermediate complexity model (LOVECLIM DGns), to determine regional differences in deglacial climate evolution and identify the main strengths and limitations of the models in terms of climate variables that impact ice sheet mass balance. The greatest continental surface warming is observed over the continental margins in both models, with strong correlations between surface albedo, sea ice coverage, and surface air temperature along the coasts, as well as regions with the greatest decrease in ice surface elevation in TraCE-21ka. Accumulation–temperature scaling relationships are fairly linear and constant in the continental interior, but exhibit higher variability in the early to mid-Holocene over coastal regions. Circum-Antarctic coastal ocean temperatures at grounding line depths are highly sensitive to the meltwater forcings prescribed in each simulation, which are applied in different ways due to limited paleo-constraints. Meltwater forcing associated with the Meltwater Pulse 1A (MWP1A) event results in subsurface warming that is most pronounced in the Amundsen and Bellingshausen Sea sector in both models. Although modelled centennial-scale rates of temperature and accumulation change are reasonable, clear model–proxy mismatches are observed with regard to the timing and duration of the Antarctic Cold Reversal (ACR) and Younger Dryas–early Holocene warming, which may suggest model bias in large-scale ocean circulation, biases in temperature reconstructions from proxy records, or that the MWP1A and 1B events are inadequately represented in these simulations. The incorporation of dynamic ice sheet models in future transient climate simulations could aid in improving meltwater forcing representation, and thus model–proxy agreement, through this time interval.</p

A Coastal Transect of McMurdo Dry Valleys (Antarctica) Snow and Firn: Marine and Terrestrial Influences on Glaciochemistry

Samples of snow and firn from accumulation zones on Clark, Commonwealth, Blue and Victoria Upper Glaciers in the McMurdo Dry Valleys (similar to 77-78 degrees S, 161-164 degrees E), Antarctica, are evaluated chemically and isotopically to determine the relative importance of local (site-specific) factors vs regional-scale influences in defining glaciochemistry. Spatial variation in snow and firn chemistry confirms documented trends within individual valleys regarding major-ion deposition relative to elevation and to distance from the coast. Sodium and methylsulfonate (MS-), for example, follow a decreasing gradient with distance from the coast along the axis of Victoria Valley (350-119 mu gL(-1) for Na+; 33-14 mu gL(-1) for MS-); a similar pattern exists between Commonwealth and Newall Glaciers in the Asgaard Range. When comparing major-ion concentrations (e.g. Na-+,Na- MS-, Ca2+) or trace metals (e.g. Al, Fe) among different valleys, however, site-specific exposures to marine and local terrestrial chemical sources play a dominant role. Because chemical signals at all sites respond to particulates with varying mixtures of marine and terrestrial sources, each of these influences on site glaciochemistry must be considered when drawing temporal climate inferences on regional scales