Michael Handley

Climate Variability in West Antarctica Derived from Annual Accumulation-Rate Records from ITASE Firn/Ice Cores

Abstract Thirteen annually resolved accumulation-rate records covering the last ~200 years from the Pine Island–Thwaites and Ross drainage systems and the South Pole are used to examine climate variability over West Antarctica. Accumulation is controlled spatially by the topography of the ice sheet, and temporally by changes in moisture transport and cyclonic activity. A comparison of mean accumulation since 1970 at each site to the long-term mean indicates an increase in accumulation for sites located in the western sector of the Pine Island–Thwaites drainage system. Accumulation is negatively associated with the Southern Oscillation Index (SOI) for sites near the ice divide, and periods of sustained negative SOI (1940–42, 1991–95) correspond to above-mean accumulation at most sites. Correlations of the accumulation-rate records with sea-level pressure (SLP) and the SOI suggest that accumulation near the ice divide and in the Ross drainage system may be associated with the mid-latitudes. The post-1970 increase in accumulation coupled with strong SLP–accumulation-rate correlations near the coast suggests recent intensification of cyclonic activity in the Pine Island– Thwaites drainage system.

Nitrogen and Sulfur Input-Output Budgets in the Experimental and Reference Watersheds, Bear Brook Watershed in Maine (BBWM)

Dry (NH4)2SO4 (1,800 eq-1 ha-1 yr-1) has been applied to the western of two contiguous 10 ha catchments at the Bear Brook Watershed in Maine (BBWM) since November, 1989. The initial rapid and significant response in both S and N in West Bear, compared to the reference East Bear, slowed after three years. Annual S retention of the total experimental treatment decreased from 86 to 34%, with a seven year cumulative retention of 59%. Hydrology influences the export flux of S; S is retained more in dry seasons and dry years. The annual retention of N has decreased from 96 to 81%, with a cumulative retention of 82%. The export of N from the reference watershed has declined from 178 to 23 eq-1 ha-1 yr-1 during the treatment period. The treatment N (as NH4) initially stimulated nitrification, and caused pre-existing N to be lost in runoff, rather than the treatment N. Retention of the treatment N has decreased to approximately 80%. The majority of the retained N is stored in the soil, but the reasons for the decreased flux from the reference watershed are not known.

Stable-Isotope and Trace Element Time Series from Fedchenko Glacier (Pamirs) Snow/Firn Cores

In summer 2005, two pilot snow/firn cores were obtained at 5365 and 5206 m a.s.l. on Fedchenko glacier, Pamirs, Tajikistan, the worlds longest and deepest alpine glacier. The well-defined seasonal layering appearing in stable-isotope and trace element distribution identified the physical links controlling the climate and aerosol concentration signals. Air temperature and humidity/precipitation were the primary determinants of stable-isotope ratios. Most precipitation over the Pamirs originated in the Atlantic. In summer, water vapor was re-evaporated from semi-arid regions in central Eurasia. The semi-arid regions contribute to non-soluble aerosol loading in snow accumulated on Fedchenko glacier. In the Pamir core, concentrations of rare earth elements, major and other elements were less than those in the Tien Shan but greater than those in Antarctica, Greenland, the Alps and the Altai. The content of heavy metals in the Fedchenko cores is 2-14 times lower than in the Altai glaciers. Loess from Afghan- Tajik deposits is the predominant lithogenic material transported to the Pamirs. Trace elements generally showed that aerosol concentration tended to increase on the windward slopes during dust storms but tended to decrease with altitude under clear conditions. The trace element profile documented one of the most severe droughts in the 20th century.

A 200 Year Sulfate Record from Sixteen Antarctic Ice Cores and Associations With Southern Ocean Sea-Ice Extent

Abstract Chemistry data from 16, 50–115m deep, sub-annually dated ice cores are used to investigate spatial and temporal concentration variability of sea-salt (ss) SO4 2– and excess (xs) SO4 2– over West Antarctica and the South Pole for the last 200 years. Low-elevation ice-core sites in western West Antarctica contain higher concentrations of SO4 2– as a result of cyclogenesis over the Ross Ice Shelf and proximity to the Ross Sea Polynya. Linear correlation analysis of 15 West Antarctic ice-core SO4 2– time series demonstrates that at several sites concentrations of ssSO4 2– are higher when sea-ice extent (SIE) is greater, and the inverse for xsSO4 2–. Concentrations of xsSO4 2– from the South Pole site (East Antarctica) are associated with SIE from the Weddell region, and West Antarctic xsSO4 2– concentrations are associated with SIE from the Bellingshausen–Amundsen–Ross region. The only notable rise of the last 200 years in xsSO4 2–, around 1940, is not related to SIE fluctuations and is most likely a result of increased xsSO4 2– production in the mid–low latitudes and/or an increase in transport efficiency from the mid–low latitudes to central West Antarctica. These high-resolution records show that the source types and source areas of ssSO4 2– and xsSO4 2– delivered to eastern and western West Antarctica and the South Pole differ from site to site but can best be resolved using records from spatial ice-core arrays such as the International Trans-Antarctic Scientific Expedition (ITASE).

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

Abstract 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.

Dynamics of P, Al, and Fe during High Discharge Episodic Acidification at the Bear Brook Watershed In Maine, U.S.A.

Phosphorus (P), aluminum (Al), and iron (Fe) stream chemistry were assessed for high discharge snowmelt events at the Bear Brook Watershed, Maine (BBWM) during December 2001 and February 2002 and compared with results from a January 1995 study of the same streams. The West Bear catchment has been subjected to artificial acidification since 1989. The East Bear catchment is the untreated reference. Total (acid soluble) Al, Fe, and P were positively correlated with discharge during the 2001–2002 events. However, dissolved P concentrations remained low (≤0.1 μmol L−1) during high discharge events as pH decreased in both streams. For example, in 2001, total P concentration increased to 1.7 μmol L−1 during the rising limb of the hydrograph in West Bear, approximately five times the value in East Bear. During the same event, in West Bear and East Bear dissolved Al concentrations increased to 21 and 6.3 μmol L−1, respectively, while total Al concentrations increased to 166 and 30 μmol L−1, respectively. Dissolved Fe concentrations remained ≤0.9 μmol L−1 in both streams during all study events. However, total Fe concentrations in 2001 increased to 239 and 4.1 μmol L−1 for West Bear and East Bear, respectively. Total Al and Fe declined parallel to total P after peaking during all study periods. Nearly all of the base cations were in dissolved form during the three events, indicating that total Al in West and East Bear Brooks is not associated with primary minerals such as feldspars. We conclude that particulate Al, Fe, and ` are chemically linked during transport at high discharge in these episodically and chronically acidified streams.

Next‐generation ice core technology reveals true minimum natural levels of lead (Pb) in the atmosphere: Insights from the Black Death

Abstract Contrary to widespread assumptions, next‐generation high (annual to multiannual) and ultra‐high (subannual) resolution analyses of an Alpine glacier reveal that true historical minimum natural levels of lead in the atmosphere occurred only once in the last ~2000 years. During the Black Death pandemic, demographic and economic collapse interrupted metal production and atmospheric lead dropped to undetectable levels. This finding challenges current government and industry understanding of preindustrial lead pollution and its potential implications for human health of children and adults worldwide. Available technology and geographic location have limited previous ice core investigations. We provide new high‐ (discrete, inductively coupled plasma mass spectrometry, ICP‐MS) and ultra‐high resolution (laser ablation inductively coupled plasma mass spectrometry, LA‐ICP‐MS) records of atmospheric lead deposition extracted from the high Alpine glacier Colle Gnifetti, in the Swiss‐Italian Alps. We show that contrary to the conventional wisdom, low levels at or approaching natural background occurred only in a single 4 year period in ~2000 years documented in the new ice core, during the Black Death (~1349–1353 C.E.), the most devastating pandemic in Eurasian history. Ultra‐high chronological resolution allows for the first time detailed and decisive comparison of the new glaciochemical data with historical records. Historical evidence shows that mining activity ceased upwind of the core site from ~1349 to 1353, while concurrently on the glacier lead (Pb) concentrations—dated by layer counting confirmed by radiocarbon dating—dropped to levels below detection, an order of magnitude beneath figures deemed low in earlier studies. Previous assumptions about preindustrial “natural” background lead levels in the atmosphere—and potential impacts on humans—have been misleading, with significant implications for current environmental, industrial, and public health policy, as well as for the history of human lead exposure. Trans‐disciplinary application of this new technology opens the door to new approaches to the study of the anthropogenic impact on past and present human health.

Re-evaluation of colorimetric Cl− data from natural waters with DOC

Colorimetric Cl− data from natural solutions that contain dissolved organic carbon (DOC) may be biased high. We evaluated aquatic Cl- concentrations in ecosystem compartments at the Bear Brook Watershed, Maine, and from lakes in Maine, using ion chromatography and colorimetry. DOC imparts a positive interference on colorimetric Cl− results proportional to DOC concentrations at approximately 0.8 µeq Cl−/L per mg DOC/L. The interference is not a function of Cl− concentration. The resulting bias in concentrations of Cl− may be 50% or more of typical environmental values for Cl− in areas remote from atmospheric deposition of marine aerosols. Such biased data in the literature appear to have led to spurious conclusions about recycling of Cl− by forests, the usefulness of Cl− as a conservative tracer in watershed studies, and calculations of elemental budgets, ion balance, charge density of DOC, and dry deposition factors.

Industrial-age doubling of snow accumulation in the Alaska Range linked to tropical ocean warming

Future precipitation changes in a warming climate depend regionally upon the response of natural climate modes to anthropogenic forcing. North Pacific hydroclimate is dominated by the Aleutian Low, a semi-permanent wintertime feature characterized by frequent low-pressure conditions that is influenced by tropical Pacific Ocean temperatures through the Pacific-North American (PNA) teleconnection pattern. Instrumental records show a recent increase in coastal Alaskan precipitation and Aleutian Low intensification, but are of insufficient length to accurately assess low frequency trends and forcing mechanisms. Here we present a 1200-year seasonally- to annually-resolved ice core record of snow accumulation from Mt. Hunter in the Alaska Range developed using annual layer counting and four ice-flow thinning models. Under a wide range of glacier flow conditions and layer counting uncertainty, our record shows a doubling of precipitation since ~1840 CE, with recent values exceeding the variability observed over the past millennium. The precipitation increase is nearly synchronous with the warming of western tropical Pacific and Indian Ocean sea surface temperatures. While regional 20th Century warming may account for a portion of the observed precipitation increase on Mt. Hunter, the magnitude and seasonality of the precipitation change indicate a long-term strengthening of the Aleutian Low.

A New Multielement Method for LA-ICP-MS Data Acquisition from Glacier Ice Cores

To answer pressing new research questions about the rate and timing of abrupt climate transitions, a robust system for ultrahigh-resolution sampling of glacier ice is needed. Here, we present a multielement method of LA-ICP-MS analysis wherein an array of chemical elements is simultaneously measured from the same ablation area. Although multielement techniques are commonplace for high-concentration materials, prior to the development of this method, all LA-ICP-MS analyses of glacier ice involved a single element per ablation pass or spot. This new method, developed using the LA-ICP-MS system at the W. M. Keck Laser Ice Facility at the University of Maine Climate Change Institute, has already been used to shed light on our flawed understanding of natural levels of Pb in Earths atmosphere.