Influence of regional precipitation patterns on stable isotopes in ice cores from the central Himalayas

Several ice cores have been recovered from the Dasuopu (DSP) Glacier and the East Rongbuk (ER) Glacier in the central Himalayas since the 1990s. Although the distance between the DSP and the ER ice core drilling sites is only 125 km, the stable isotopic record (18O or D) of the DSP core is interpreted in previous studies as a temperature proxy, while the ER core is interpreted as a precipitation proxy. Thus, the climatological significance of the stable isotopic records of these Himalayan ice cores remains a subject of debate. Based on analysis of regional precipitation patterns over the region, we find that remarkable discrepancy in precipitation seasonality between the two sites may account for their disparate isotopic interpretations. At the ER core site, the Indian summer monsoon (ISM) precipitation is dominating due to topographic blocking of the moisture from westerlies by the high ridges of Mt. Qomolangma (Everest), which results in a negative correlation between the ER 18O or D record and precipitation amount along the southern slope of the central Himalayas in response to the “amount effect”. At the DSP core site, in comparison with the ISM precipitation, the wintertime precipitation associated with the westerlies is likely more important owing to its local favorable topographic conditions for interacting with the western disturbances. Therefore, the DSP stable isotopic record may be primarily controlled by the westerlies. Our results have important implications for interpreting the stable isotopic ice core records recovered from different climatological regimes of the Himalayas

The Post-Wildfire Impact of Burn Severity and Age on Black Carbon Snow Deposition and Implications for Snow Water Resources, Cascade Range, Washington

Wildfires in the snow zone affect ablation by removing forest canopy, which enhances surface solar irradiance, and depositing light absorbing particles [LAPs, such as black carbon (BC)] on the snowpack, reducing snow albedo. How variations in BC deposition affects post-wildfire snowmelt timing is poorly known and highly relevant to water resources. We present a field-based analysis of BC variability across five sites of varying burn age and burn severity in the Cascade Range, Washington State, United States. Single particle soot photometer (SP2) analyses of BC snow concentrations were used to assess the impact of BC on snow albedo, and radiative transfer modeling was used to estimate the radiative effect of BC on snowmelt. Results were compared to Snowpack Telemetry (SNOTEL) data from one site that burned in 2012 and another in a proximal unburned forest. We show that post-wildfire forests provide a significant source of BC to the snowpack, and this effect increases by an order of magnitude in regions of high versus low burn severity, and decreased by two orders of magnitude over a decade. There is a shift in the timing of snowmelt, with snow disappearance occurring on average 19 ± 9 days earlier post-wildfire (2013–19) relative to pre-wildfire (1983–2012). This study improves understanding of the connection between wildfire activity and snowmelt, which is of high relevance as climate change models project further decreases in snowpack and increases in wildfire activity in the Washington Cascades

Seasonal and elevational variations of black carbon and dust in snow and ice in the Solu-Khumbu, Nepal and estimated radiative forcings

Black carbon (BC) and dust deposited on snow and glacier surfaces can reduce the surface albedo, accelerate snow and ice melt, and trigger albedo feedback. Assessing BC and dust concentrations in snow and ice in the Himalaya is of interest because this region borders large BC and dust sources, and seasonal snow and glacier ice in this region are an important source of water resources. Snow and ice samples were collected from crevasse profiles and snow pits at elevations between 5400 and 6400 m a.s.l. from Mera glacier located in the Solu-Khumbu region of Nepal during spring and fall 2009, providing the first observational data of BC concentrations in snow and ice from the southern slope of the Himalaya. The samples were measured for Fe concentrations (used as a dust proxy) via ICP-MS, total impurity content gravimetrically, and BC concentrations using a Single Particle Soot Photometer (SP2). Measured BC concentrations underestimate actual BC concentrations due to changes to the sample during storage and loss of BC particles in the ultrasonic nebulizer; thus, we correct for the underestimated BC mass. BC and Fe concentrations are substantially higher at elevations \u3c 6000 m due to post-depositional processes including melt and sublimation and greater loading in the lower troposphere. Because the largest areal extent of snow and ice resides at elevations \u3c 6000 m, the higher BC and dust concentrations at these elevations can reduce the snow and glacier albedo over large areas, accelerating melt, affecting glacier mass balance and water resources, and contributing to a positive climate forcing. Radiative transfer modeling constrained by measurements at 5400 m at Mera La indicates that BC concentrations in the winter–spring snow/ice horizons are sufficient to reduce albedo by 6–10% relative to clean snow, corresponding to localized instantaneous radiative forcings of 75–120 W m−2. The other bulk impurity concentrations, when treated separately as dust, reduce albedo by 40–42% relative to clean snow and give localized instantaneous radiative forcings of 488 to 525 W m−2. Adding the BC absorption to the other impurities results in additional radiative forcings of 3 W m−2. The BC and Fe concentrations were used to further examine relative absorption of BC and dust. When dust concentrations are high, dust dominates absorption, snow albedo reduction, and radiative forcing, and the impact of BC may be negligible, confirming the radiative transfer modeling. When impurity concentrations are low, the absorption by BC and dust may be comparable; however, due to the low impurity concentrations, albedo reductions are small. While these results suggest that the snow albedo and radiative forcing effect of dust is considerably greater than BC, there are several sources of uncertainty. Further observational studies are needed to address the contribution of BC, dust, and colored organics to albedo reductions and snow and ice melt, and to characterize the time variation of radiative forcing

A 200 Year Sub-Annual Record of Sulfate in West Antarctica, from Sixteen Ice Cores

Sixteen high-resolution ice-core records from West Antarctica and South Pole are used to examine the spatial and temporal distribution of sulfate for the last 200 years. The preservation of seasonal layers throughout the length of each record results in a dating accuracy of better than 1 year based on known global-scale volcanic events. A dual transport source for West Antarctic sea-salt (ss) SO42- and excess (xs) SO42- is observed: lower-tropospheric for areas below 1000m elevation and mid-/upper-tropospheric/stratospheric for areas located above 1000m. Our XsSO(4)(2-) records with volcanic peaks removed do not display any evidence of an anthropogenic impact on West Antarctic SO42- concentrations but do reveal that a major climate transition takes place over West Antarctica at similar to 1940. Global-scale volcanic eruptions appear as significant peaks in the robust-spline residual xsSO(4)(2-) records from sites located above 1000 m elevation but do not appear in the residual records from sites located below 1000 m

Accelerated Glacier Melt on Snow Dome, Mount Olympus, Washington, USA, due to Deposition of Black Carbon and Mineral Dust from Wildfire

Assessing the potential for black carbon (BC) and dust deposition to reduce albedo and accelerate glacier melt is of interest in Washington because snow and glacier melt are an important source of water resources, and glaciers are retreating. In August 2012 on Snow Dome, Mount Olympus, Washington, we measured snow surface spectral albedo and collected surface snow samples and a 7 m ice core. The snow and ice samples were analyzed for iron (Fe, used as a dust proxy) via inductively coupled plasma sector field mass spectrometry, total impurity content gravimetrically, BC using a single-particle soot photometer (SP2), and charcoal through microscopy. In the 2012 summer surface snow, BC (54 ± 50 μg/L), Fe (367±236 μg/L) and gravimetric impurity (35 ± 18 mg/L) concentrations were spatially variable, and measured broadband albedo varied between 0.67–0.74. BC and dust concentrations in the ice core 2011 summer horizon were a magnitude higher (BC = 3120 μg/L, Fe = 22000 μg/L, and gravimetric impurity = 1870 mg/L), corresponding to a modeled broadband albedo of 0.45 based on the measured BC and ravimetric impurity concentrations. The Big Hump forest fire is the likely source for the higher concentrations. Modeling constrained by measurements indicates that the all-sky 12 h daily mean radiative forcings in summer 2012 and 2011 range between 37–53Wm_2 and 112–149Wm_2, respectively, with the greater forcings in 2011 corresponding to a 29–38mm/d enhancement in snowmelt. The timing of the forest fire impurity deposition is coincident with an increase in observed discharge in the Hoh River, highlighting the potential for BC and dust deposition on glaciers from forest fires to accelerate melt

Recent increase in black carbon concentrations from a Mt. Everest ice core spanning 1860–2000 AD

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95622/1/grl27751.pd

Radiative Forcing by Dust and Black Carbon on the Juneau Icefield, Alaska

Here we present the first known data set on black carbon (BC) and mineral dust concentrations in snow from the Juneau Icefield (JIF) in southeastern Alaska, where glacier melt rates are among the highest on Earth. In May 2016, concentrations of BC (0.4–3.1 μg/L) and dust (0.2–34 mg/L) were relatively low and decreased toward the interior of the JIF. The associated radiative forcing (RF) averaged 4 W/m2. In July, after 10 weeks of exposure, the aged snow surface had substantially higher concentrations of BC (2.1–14.8 μg/L) and dust (11–72 mg/L) that were not spatially distributed by elevation or distance from the coast. RF by dust and BC ranged from 70 to 130 W/m2 (87 W/m2 average) across the JIF in July, and RF was dominated by dust. The associated median snow water equivalent reduction in the July samples is estimated at 10–18 mm/day, potentially advancing melt on the scale of days to weeks. Aging of the snow surface in summer likely resulted in a positive feedback of melt consolidation, enhanced solar absorption and melting, and further concentration of surface particles. Regional projections of warming temperatures and increased rain at the expense of snow make it likely that summer season darkening will become a more important contributor to the high melt rates on the JIF. Further studies are needed to elucidate the spatiotemporal occurrence of various light‐absorbing particles on the JIF, and models of ice field wastage should incorporate their associated RF

Atmospheric Soluble Dust Records From a Tibetan Ice Core: Possible Climate Proxies and Teleconnection with the Pacific Decadal Oscillation

In autumn 2005, a joint expedition between the University of Maine and the Institute of Tibetan Plateau Research recovered three ice cores from Guoqu Glacier (33°34′37.8″N, 91°10′35.3″E, 5720 m above sea level) on the northern side of Mt. Geladaindong, central Tibetan Plateau. Isotopes (δ18O), major soluble ions (Na+, K+, Mg2+, Ca2+, Cl−, NO3−, SO42−), and radionuclide (β‐activity) measurements from one of the cores revealed a 70‐year record (1935–2005). Statistical analysis of major ion time series suggests that atmospheric soluble dust species dominate the chemical signature and that background dust levels conceal marine ion species deposition. The soluble dust time series have interspecies relations and common structure (empirical orthogonal function (EOF) 1), suggesting a similar soluble dust source or transport route. Annual and seasonal correlations between the EOF 1 time series and National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis climate variables (1948–2004) suggest that the Mt. Geladaindong ice core record provides a proxy for local and regional surface pressure. An approximately threefold decrease of soluble dust concentrations in the middle to late 1970s, accompanied by regional increases in pressure and temperature and decreases in wind velocity, coincides with the major 1976–1977 shift of the Pacific Decadal Oscillation (PDO) from a negative to a positive state. This is the first ice core evidence of a potential teleconnection between central Asian atmospheric soluble dust loading and the PDO. Analysis of temporally longer ice cores from Mt. Geladaindong may enhance understanding of the relationship between the PDO and central Asian atmospheric circulation and subsequent atmospheric soluble dust loading

Taxonomic decomposition of the latitudinal gradient in species diversity of North American floras

Aim: To test the latitudinal gradient in plant species diversity for self-similarity across taxonomic scales and amongst taxa. Location: North America. Methods: We used species richness data from 245 local vascular plant floras to quantify the slope and shape of the latitudinal gradients in species diversity (LGSD) across all plant species as well as within each family and order. We calculated the contribution of each family and order to the empirical LGSD. Results: We observed the canonical LGSD when all plants were considered with floras at the lowest latitudes having, on average, 451 more species than floras at the highest latitudes. When considering slope alone, most orders and families showed the expected negative slope, but 31.7% of families and 27.7% of orders showed either no significant relationship between latitude and diversity or a reverse LGSD. Latitudinal patterns of family diversity account for at least 14% of this LGSD. Most orders and families did not show the negative slope and concave-down quadratic shape expected by the pattern for all plant species. A majority of families did not make a significant contribution in species to the LGSD with 53% of plant families contributing little to nothing to the overall gradient. Ten families accounted for more than 70% of the gradient. Two families, the Asteraceae and Fabaceae, contributed a third of the LGSD. Main Conclusions: The empirical LGSD we describe here is a consequence of a gradient in the number of families and diversification within relative few plant families. Macroecological studies typically aim to generate models that are general across taxa with the implicit assumption that the models are general within taxa. Our results strongly suggest that models of the latitudinal gradient in plant species richness that rely on environmental covariates (e.g. temperature, energy) are likely not general across plant taxa

The spectral and chemical measurement of pollutants on snow near South Pole, Antarctica

Remote sensing of light-absorbing particles (LAPs), or dark colored impurities, such as black carbon (BC) and dust on snow, is a key remaining challenge in cryospheric surface characterization and application to snow, ice, and climate models. We present a quantitative data set of in situ snow reflectance, measured and modeled albedo, and BC and trace element concentrations from clean to heavily fossil fuel emission contaminated snow near South Pole, Antarctica. Over 380 snow reflectance spectra (350–2500 nm) and 28 surface snow samples were collected at seven distinct sites in the austral summer season of 2014–2015. Snow samples were analyzed for BC concentration via a single particle soot photometer and for trace element concentration via an inductively coupled plasma mass spectrometer. Snow impurity concentrations ranged from 0.14 to 7000 part per billion (ppb) BC, 9.5 to 1200 ppb sulfur, 0.19 to 660 ppb iron, 0.013 to 1.9 ppb chromium, 0.13 to 120 ppb copper, 0.63 to 6.3 ppb zinc, 0.45 to 82 parts per trillion (ppt) arsenic, 0.0028 to 6.1 ppb cadmium, 0.062 to 22 ppb barium, and 0.0044 to 6.2 ppb lead. Broadband visible to shortwave infrared albedo ranged from 0.85 in pristine snow to 0.62 in contaminated snow. LAP radiative forcing, the enhanced surface absorption due to BC and trace elements, spanned from \u3c1 W m­–2 for clean snow to ~70 W m­–2 for snow with high BC and trace element content. Measured snow reflectance differed from modeled snow albedo due to specific impurity-dependent absorption features, which we recommend be further studied and improved in snow albedo models