David G. Ferris

Onset of deglacial warming in West Antarctica driven by local orbital forcing

The cause of warming in the Southern Hemisphere during the most recent deglaciation remains a matter of debate. Hypotheses for a Northern Hemisphere trigger, through oceanic redistributions of heat, are based in part on the abrupt onset of warming seen in East Antarctic ice cores and dated to 18,000 years ago, which is several thousand years after high-latitude Northern Hemisphere summer insolation intensity began increasing from its minimum, approximately 24,000 years ago. An alternative explanation is that local solar insolation changes cause the Southern Hemisphere to warm independently. Here we present results from a new, annually resolved ice-core record from West Antarctica that reconciles these two views. The records show that 18,000 years ago snow accumulation in West Antarctica began increasing, coincident with increasing carbon dioxide concentrations, warming in East Antarctica and cooling in the Northern Hemisphere associated with an abrupt decrease in Atlantic meridional overturning circulation. However, significant warming in West Antarctica began at least 2,000 years earlier. Circum-Antarctic sea-ice decline, driven by increasing local insolation, is the likely cause of this warming. The marine-influenced West Antarctic records suggest a more active role for the Southern Ocean in the onset of deglaciation than is inferred from ice cores in the East Antarctic interior, which are largely isolated from sea-ice changes.

Cold decade (AD 1810-1819) caused by Tambora (1815) and another (1809) stratospheric volcanic eruption.

Climate records indicate that the decade of AD 1810–1819 including “the year without a summer” (1816) is probably the coldest during the past 500 years or longer, and the cause of the climatic extreme has been attributed primarily to the 1815 cataclysmic Tambora eruption in Indonesia. But the cold temperatures in the early part of the decade and the timing of the Tambora eruption call into question the real climatic impact of volcanic eruptions. Here we present new evidence, based on sulfur isotope anomaly (Δ33S), a unique indicator of volcanic sulfuric acid produced in the stratosphere and preserved in polar snow, and on the precise timing of the volcanic deposition in both polar regions, that another large eruption in 1809 of a volcano is also stratospheric and occurred in the tropics. The Tambora eruption and the undocumented 1809 eruption are together responsible for the unusually cold decade.

Comparison of cyanide exposure markers in the biofluids of smokers and non-smokers

Cyanide is highly toxic and is present in many foods, combustion products (e.g. cigarette smoke), industrial processes, and has been used as a terrorist weapon. In this study, cyanide and its major metabolites, thiocyanate and 2-amino-2-thiazoline-4-carboxylic acid (ATCA), were analyzed from various human biofluids of smokers (low-level chronic cyanide exposure group) and non-smokers to gain insight into the relationship of these biomarkers to cyanide exposure. The concentrations of each biomarker tested were elevated for smokers in each biofluid. Significant differences (p < 0.05) were found for thiocyanate in plasma and urine, and ATCA showed significant differences in plasma and saliva. Additionally, biomarker concentration ratios, correlations between markers of cyanide exposure, and other statistical methods were performed to better understand the relationship between cyanide and its metabolites. Of the markers studied, the results indicate plasma ATCA, in particular, showed excellent promise as a biomarker for chronic low-level cyanide exposure.

Coast-to-interior gradient in recent northwest Greenland precipitation trends (1952–2012)

The spatial and temporal variability of precipitation on the Greenland ice sheet is an essential component of surface mass balance, which has been declining in recent years with rising temperatures. We present an analysis of precipitation trends in northwest (NW) Greenland (1952–2012) using instrumental (coastal meteorological station) and proxy records (snow pits and ice cores) to characterize the precipitation gradient from the coast to the ice sheet interior. Snow-pit-derived precipitation near the coast (1950–2000) has increased (~7% decade−1, p < 0.01) whereas there is no significant change observed in interior snow pits. This trend holds for 1981–2012, where calculated precipitation changes decrease in magnitude with increasing distance from the coast: 13% decade−1 (2.4 mm water equivalent (w.e.) decade−2) at coastal Thule air base (AB), 8.6% decade−1 (4.7 mm w.e. decade−2) at the 2Barrel ice core site 150 km from Thule AB, −5.2% decade−1 (1.7 mm w.e. decade−2) at Camp Century located 205 km from Thule AB, and 4.4% decade−1 (1.0 mm w.e. decade−2) at B26 located 500 km from Thule AB. In general, annually averaged precipitation and annually and seasonally averaged mean air temperatures observed at Thule AB follow trends observed in composite coastal Greenland time series, with both notably indicating winter as the fastest warming season in recent periods (1981–2012). Trends (1961–2012) in seasonal precipitation differ, specifically with NW Greenland summer precipitation increasing (~0.6 mm w.e. decade−2) in contrast with decreasing summer precipitation in the coastal composite time series (3.8 mm w.e. decade−2). Differences in precipitation trends between NW Greenland and coastal composite Greenland underscore the heterogeneity in climate influences affecting precipitation. In particular, recent (1981–2012) changes in NW Greenland annual precipitation are likely a response to a weakening North Atlantic oscillation.

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.

Rapid transport of ash and sulfate from the 2011 Puyehue‐Cordón Caulle (Chile) eruption to West Antarctica

The Volcanic Explosivity Index (VEI) 5 eruption of the Puyehue-Cordon Caulle volcanic complex (PCC) in central Chile, which began 4 June 2011, provides a rare opportunity to assess the rapid transport and deposition of sulfate and ash from a mid-latitude volcano to the Antarctic ice sheet. We present sulfate, microparticle concentrations of fine-grained (~5 μm diameter) tephra, and major oxide geochemistry, which document the depositional sequence of volcanic products from the PCC eruption in West Antarctic snow and shallow firn. From the depositional phasing and duration of ash and sulfate peaks, we infer that transport occurred primarily through the troposphere but that ash and sulfate transport were decoupled. We use Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) back-trajectory modeling to assess atmospheric circulation conditions in the weeks following the eruption, and find that conditions favored southward air parcel transport during 6-14 June and 4-18 July, 2011. We suggest that two discrete pulses of cryptotephra deposition relate to these intervals, and as such, constrain the sulfate transport and deposition lifespan to the ~2-3 weeks following the eruption. Finally, we compare PCC depositional patterns to those of prominent low- and high-latitude eruptions in order to improve multiparameter-based efforts to identify “unknown source” eruptions in the ice core record. Our observations suggest that mid-latitude eruptions such as PCC can be distinguished from explosive tropical eruptions by differences in ash/sulfate phasing and in the duration of sulfate deposition, and from high-latitude eruptions by differences in particle size distribution and in cryptotephra geochemical composition.

Ice Core Records of West Greenland Melt and Climate Forcing

Remote sensing observations and climate models indicate that the Greenland Ice Sheet (GrIS) has been losing mass since the late 1990s, mostly due to enhanced surface melting from rising summer temperatures. However, in situ observational records of GrIS melt rates over recent decades are rare. Here we develop a record of frozen meltwater in the west GrIS percolation zone preserved in seven firn cores. Quantifying ice layer distribution as a melt feature percentage (MFP), we find significant increases in MFP in the southernmost five cores over the past 50 years to unprecedented modern levels (since 1550 CE). Annual to decadal changes in summer temperatures and MFP are closely tied to changes in Greenland summer blocking activity and North Atlantic sea surface temperatures since 1870. However, summer warming of ~1.2°C since 1870–1900, in addition to warming attributable to recent sea surface temperature and blocking variability, is a critical driver of high modern MFP levels. Plain Language Summary Computer models and satellites show that the amount of snow melting each summer on Greenland has increased since the 1990s, but it is difficult to confirm this directly on the ice sheet. When surface snow melts, the water spreads into deeper layers of snow and refreezes as an ice layer. As fresh snow buries each summer’s ice layers, the history of snowmelt is preserved in the ice sheet. We describe seven ice cores collected from western Greenland that contain the history of ice layers back to 1966. We find more ice layers, caused by more summer melting, since the 1990s. By comparing our ice cores to a longer ice core from the same area, we show that today’s melt rates are the highest in this region since at least 1550 CE. Year-to-year changes in the amount of melting are mostly caused by changes in the number of summer high-pressure systems and fluctuating ocean temperatures near Greenland. Although both of these processes have contributed to recent high melt rates, Greenland is 1.2°C warmer today than during similar conditions in the 1890s. This “extra” warming is most likely caused by human greenhouse gas emissions, leading to the unusual melt rates of recent years.

A 400‐Year Ice Core Melt Layer Record of Summertime Warming in the Alaska Range

Warming in high-elevation regions has societally important impacts on glacier mass balance, water resources, and sensitive alpine ecosystems, yet very few high-elevation temperature records exist from the middle or high latitudes. While a variety of paleoproxy records provide critical temperature records from low elevations over recent centuries, melt layers preserved in alpine glaciers present an opportunity to develop calibrated, annually resolved temperature records from high elevations. Here we present a 400-year temperature proxy record based on the melt layer stratigraphy of two ice cores collected from Mt. Hunter in Denali National Park in the central Alaska Range. The ice core record shows a sixtyfold increase in water equivalent total annual melt between the preindustrial period (before 1850 Common Era) and present day.We calibrate themelt record to summer temperatures based onweather station data from the ice core drill site and find that the increase inmelt production represents a summer warming rate of at least 1.92 ± 0.31°C per century during the last 100 years, exceeding rates of temperature increase at most low-elevation sites in Alaska. The Mt. Hunter melt layer record is significantly (p< 0.05) correlated with surface temperatures in the central tropical Pacific through a Rossby wave-like pattern that enhances high temperatures over Alaska. Our results show that rapid alpine warming has taken place in the Alaska Range for at least a century and that conditions in the tropical oceans contribute to this warming. Plain Language Summary Warming in mountainous areas affects glacier melt, water resources, and fragile ecosystems, yet we know relatively little about climate change in alpine areas, especially at high latitudes. We use ice cores drilled on Mt. Hunter, in Denali National Park, to develop a record of summer temperatures in Alaska that extends 400 years into the past, farther than any other mountain record in the North Pacific region. The ice core record shows that 60 times more snowmelt occurs today than 150 years ago. This corresponds to roughly a 2°C increase in summer temperature, which is faster than summertime warming in Alaska near sea level. We suggest that warming of the tropical Pacific Ocean has contributed to the rapid warming on Mt. Hunter by enhancing high-pressure systems over Alaska. Our ice core record indicates that alpine regions surrounding the North Pacific may continue to experience accelerated warming with climate change, threatening the already imperiled glaciers in this area.

Denali Ice Core Methanesulfonic Acid Records North Pacific Marine Primary Production

The high-nutrient, low-chlorophyll region of the northeastern (NE) subarctic Pacific is one of the most biologically productive marine ecosystems in the world, supporting fisheries worth over

Evidence of Influence of Human Activities and Volcanic Eruptions on Environmental Perchlorate from a 300-Year Greenland Ice Core Record

5 billion annually. Phytoplankton are the primary producers in this ecosystem and are also a major source of biogenic sulfur emissions, important in Earth’s climate system. However, variability in marine primary production through time is not well constrained. Here we establish methanesulfonic acid (MSA) concentrations in the Denali ice core as a proxy for marine primary production in the NE Pacific. Using Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT; Stein et al., 2015, https://doi.org/10.1178/BAMS-D-14-00110.1) modeling, we identify moisture source regions for the core site and correlate Sea-Viewing Wide Field-of-View Sensor-derived chlorophyll a concentrations with ice core MSA. From 1998 to 2007 we find that areas of significant positive correlation overlap with the HYSPLIT-inferred moisture source region in the western Gulf of Alaska on an annual basis (r = 0.85, p < 0.001). We identify an MSA response to a localized bloom related to ash deposition from a 2009 Mt. Redoubt eruption. An anomalous upwelling-driven bloom in spring 2008 did not impact the ice core MSA record due to unfavorable transport conditions. Despite this, we observe that bloom events are rarely missed in the MSA record, which we attribute to the consistent and high snow accumulation rate at the ice core drill site. Our findings suggest that Denali ice core MSA is a reliable recorder of changes in marine primary production through time in the NE subarctic Pacific. Plain Language Summary The base of the marine food web is composed of single-celled photosynthetic organisms that are collectively termed primary producers. Because these microscopic organisms support all marine life, changes in their biomass can impact the entire food web. Over the past three decades, satellite data have shown that primary producers are declining around the world with some of the greatest declines occurring in the North Pacific Ocean. The reasons for these declines may include changes in ocean temperatures, nutrient availability, and wind-driven ocean mixing, all of which are related to climate. To place these changes within a longer-term context, we seek to validate regionally a proxy tool by measuring a chemical produced by phytoplankton called methanesulfonic acid (MSA). MSA is transported through the atmosphere by storms and deposited on mountain glaciers in the North Pacific region. WemeasuredMSA in a new ice core fromDenali National Park, Alaska. We describe strong, statistically significant correlations between ice core MSA concentrations and chlorophyll concentrations in the western Gulf of Alaska. We suggest that the ice core MSA proxy record can help us understand how primary production in this region has changed through time.