Dominic Winski

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 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

Centennial-scale variability of the Southern Hemisphere westerly wind belt in the eastern Pacific over the past two millennia

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.