
NSF Org: |
OPP Office of Polar Programs (OPP) |
Recipient: |
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Initial Amendment Date: | August 12, 2014 |
Latest Amendment Date: | August 12, 2014 |
Award Number: | 1417678 |
Award Instrument: | Standard Grant |
Program Manager: |
Marc Stieglitz
mstiegli@nsf.gov (703)292-4354 OPP Office of Polar Programs (OPP) GEO Directorate for Geosciences |
Start Date: | January 1, 2015 |
End Date: | December 31, 2019 (Estimated) |
Total Intended Award Amount: | $596,737.00 |
Total Awarded Amount to Date: | $596,737.00 |
Funds Obligated to Date: |
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History of Investigator: |
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Recipient Sponsored Research Office: |
7 LEBANON ST HANOVER NH US 03755-2170 (603)646-3007 |
Sponsor Congressional District: |
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Primary Place of Performance: |
HB 6105 Fairchild BLDG Hanover NH US 03755-3716 |
Primary Place of
Performance Congressional District: |
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Unique Entity Identifier (UEI): |
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Parent UEI: |
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NSF Program(s): | ANS-Arctic Natural Sciences |
Primary Program Source: |
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Program Reference Code(s): |
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Program Element Code(s): |
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Award Agency Code: | 4900 |
Fund Agency Code: | 4900 |
Assistance Listing Number(s): | 47.078 |
ABSTRACT
The stability of the Greenland Ice Sheet is of critical interest to scientists and society
at large in the context of future sea-level rise. The extent to which the Greenland Ice Sheet will lose mass and contribute to rising sea level
in the coming decades depends on the discharge from glaciers at its edges and on the surface mass balance, which is the balance between snow accumulation and surface melt. Estimates of Greenland surface mass balance increasingly utilize climate reanalyses and high-resolution regional climate models to determine snow accumulation, surface melt and runoff/refreeze. These models show significant, and model-dependent, biases (differences from observations) along the steep edges of the Greenland Ice Sheet where the highest and most variable (in space and time) rates of accumulation and surface melt are observed. Thus, the edges of the Greenland Ice Sheet are in critical need of updated accumulation
and melt data to validate models and improve mass balance estimates. The investigators propose a traverse in the Western Greenland percolation zone over two field seasons to develop continuous in-situ snow accumulation and firn density records using ground-based radar and shallow firn cores. The research objectives include: (1) determining the patterns, in time and space, of snow accumulation in Western Greenland over the past 20-40 years; (2) evaluating surface melt refreeze and englacial meltwater storage in the Western Greenland percolation
zone over the past 20-40 years; and (3) quantifying the accumulation and surface melt biases of the most recent climate reanalysis models and their regional climate model counterparts.
This project will advance knowledge and understanding by providing in-situ validation observations for both the mass gain (snow accumulation) and mass loss (surface melt) components of Western Greenland surface mass balance. The western edge of the Greenland Ice Sheet has been losing mass at an accelerating rate since 2005, due mostly to decreasing surface mass balance. However, surface mass balance trends derived from regional climate models differ by a factor of ~2.5 in this region. Western Greenland firn core accumulation records, required for model validation, generally end in 1996-1998, before the most recent period of accelerated mass loss. The investigators will develop continuous records of Western Greenland snow accumulation over the last 20-40 years using ground-penetrating radar validated by frequent snow pits and
firn cores (25-30 m) analyzed for chemistry. They also propose to use a multi-offset radar method to calculate continuous firn density
data, providing a means to assess past surface melt, refreeze and current meltwater storage
in glacier aquifers. Meltwater refreeze shows the largest variability in regional climate
models among surface mass balance components, and thus validation observations are critically needed. The traverse route will crisscross the percolation zone, near-parallel to the steepest accumulation and surface melt gradients, which will increase the value of the dataset for model validation. The traverse will overlap previous traverse routes and reoccupy previously sampled sites to update firn core accumulation records by 18-20 years. In addition, the project will collect cores from new sites in data-poor regions at lower elevations, where both accumulation and surface melt increase and regional climate model validation is most needed. Surface mass balance validation of several climate reanalysis models will lead to more accurate assessments
of current and future Greenland Ice Sheet mass balance trends, which is critical for accurately predicting
future sea-level rise. The project will integrate research with student
learning at multiple levels, with an emphasis on the participation of students from underrepresented groups. The project will fund four graduate students, and incorporate numerous undergraduate researchers recruited through successful programs like the Dartmouth Women in Science Project and the Diversity in Undergraduate Geoscience Alliance. K-12 students will be engaged in this project through inquiry-based, web-hosted climate lessons incorporating the University of Maine Climate Reanalyzer and Environmental Change Model, and through field-based programs in the Boise Mountains focused on snow science. The PIs will continue their active public outreach through established and successful programs like the monthly Upper Valley Science Pub and the biannual Snow Day at the Discovery Center of Idaho, in addition to their frequent public presentations and media interviews through their respective Public Affairs offices.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The overall motivation of this research was to improve our projections of future Greenland Ice Sheet (GrIS) mass loss and sea level rise by understanding the GrIS response to climate change over the past 50-450 years. Recent GrIS melting is a major contributor to global sea level rise, which threatens coastal communities and infrastructure today and into the future. The magnitude of GrIS mass loss depends on its glacial discharge and surface mass balance (SMB), with the later representing the balance between snowfall (mass gain) and surface melting and runoff (mass loss). Regional climate models (RCMs) and remotely sensed data are critical tools for determining SMB, but these models and measurements show significant biases along the steep edges of the ice sheet and only extend back to 1979. Consequently, the edges of the GrIS are in critical need of snowfall and snowmelt field measurements to validate RCMs and remote sensing products, and to extend the SMB record further back in time.
We completed a 4436 km traverse of the western GrIS percolation zone (the GrIS region that experiences surface melt each summer) during which we collected ice-penetrating radar data, high-precision ice elevation data, ice reflectivity (albedo) data, and 16 ice cores. A team of five researchers from Dartmouth College and Boise State University conducted the traverse on snow machines over two field seasons (summer 2016 and summer 2017). We collected four different frequencies of ice-penetrating radar profiles, including a novel multi-offset radar system that provides continuous density and SMB data. Ice cores spanned from the present day to between 23 and 62 years ago, preserving annual melt layers as refrozen ice layers, and preserving annual snowfall layers demarked by snow chemistry. We correlated continuous reflection horizons in the radar profiles with the ice cores to map SMB across the entire field area covered by the traverse.
Our ice core record of summertime melt, when combined with a previous ice core from the study area, shows conclusively that modern GrIS surface melt rates are unprecedented for at least the past 450 years and most likely >5,000 years (Graeter et al., 2018). We find a significant increase in surface melting beginning in the mid 1990s driven by a higher frequency of summertime blocking events, warmer North Atlantic sea surface temperatures, and anthropogenic forcing (Graeter et al., 2018). In terms of snowfall, our measurements indicate that RCMs accurately capture large spatial patterns in GrIS snow accumulation, but we find model-specific differences between RCM snowfall and our measurements on a regional basis (Lewis et al., 2017; 2019). Most notably, we discovered an unexpected decrease in snow accumulation since 1996 across most of the study region. We attribute the snowfall decline to an increased strength and persistence of Greenland blocking highs during summer, which deflect summertime storms towards northwest Greenland where snowfall has been increasing (Lewis et al., 2019). Our results are surprising because most climate models predict a snowfall increase over the GrIS with continued global warming due to higher saturation vapor pressure and declining sea ice extent.
We hypothesize that stronger summertime blocking is also contributing to the well-documented decline in GrIS albedo, further enhancing surface melting. Our measurements show that larger snow grains are statistically associated with lower albedo, but we find no statistically significant relationship between albedo and impurities in the snow. These results suggest that the GrIS darkening was driven by a transition to larger surface snow grains from 1996 to 2017 rather than a change in impurities. We find evidence that enhanced summertime Greenland blocking has significantly contributed to the GrIS albedo decline through two mechanisms: (1) Increased blocking reduces the number of storms that replenish the GrIS surface with high-albedo fresh snow; and (2) increased blocking reduces cloud cover and increases solar radiation that promotes snow grain growth and further reduces albedo.
The broader impacts of this project include a significant impact on graduate and undergraduate training and research. One PhD student and one MS student participated in all aspects of this project, and a second PhD student participated in the 2016 traverse. In addition to graduate students, a total of 16 undergraduate students participated in this project at Dartmouth, one of whom used this project as the basis for her senior honors thesis and presented results at an international conference. Undergraduate students learned how to process, sample, analyze, interpret and disseminate ice core and geophysical data. Twelve of the undergraduate researchers are female, and one is Native American. Results of this project were disseminated to colleagues and the public through peer-reviewed publications, 16 conference presentations, media coverage, a U.S. congressional briefing, and online videos (www.youtube.com/watch?v=eef0_rXvAUU) and blogs (www.Greentracs.blogspot.com) that received tens of thousands of views. Data from this project is available on the National Science Foundation Arctic Data Center.
Last Modified: 05/25/2020
Modified by: Erich Osterberg
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