disturbance

Disturbances often shape ecosystems by periodically reorganizing or destroying them, allowing for significant changes in plant and animal populations and communities.

Summarized glacier mass balance measurements, McMurdo Dry Valleys, Antarctica (1993-2020, ongoing)

Abstract: 

As part of the Long Term Ecological Research (LTER) project in the McMurdo Dry Valleys of Antarctica, a systematic sampling program has been undertaken to monitor glacial mass balance and meltwater flow. This data package contains total mass balance changes at each stake measured on six glaciers (Canada, Commonwealth, Hughes, Suess, Howard, and Taylor) in Taylor Valley and one glacier (Adams) in Miers Valley, all of which are located in the McMurdo Dry Valleys region of Antarctica. These values are the result of an analysis of the raw data presented in other data files (glacier stake heights, snow depths, and snow densities). Included here for each stake is the total water equivalent mass change. The standard deviation or the range for each total is given. Most measurements began during the 93-94 field season. Adams measurements were established during the 14-15 field season. Measurements are ongoing except at Hughes and Suess Glaciers where monitoring ceased following the 08-09 field season. Monitoring the changes in these measurements over time provides a record of mass balance, and aids in determining the role of glaciers in the polar hydrologic cycle.

LTER Core Areas: 

Dataset ID: 

2005

Associated Personnel: 

1150
1149
2
134
136

Short name: 

glcrweq

Purpose: 

The goal of each summer season is to take measurements in early spring (Oct/Nov) and late summer (late January). This provides a measure of seasonal winter/summer changes of glacier mass.

Data sources: 

ADAWEQ
CANWEQ
COMWEQ
HOWWEQ
TAYWEQ
HUGH_WEQ
SUES_WEQ

Methods: 

The methods of data collection are described in the glacier stake heights, snow depths and glacier snow density metadata files. To convert the data to mass values, the total change in ice height (usually negative) and snow height (depth for snow covered ice) at each stake are multiplied by their respective densities. The density for ice is 0.9 g/cm3 and the density for snow is measured in nearby snowpits. The final error of the mass balance measurement is based on the errors in the stake heights and snow depths found by replicated measurements. The errors were carried through the calculations based on Baird, D.C., 1962. Experimentation: An Introduction to Measurement Theory and Experiment Design. Prentice Hall, Englewood. We assume no error in the snow density measurements. A Note about Stake names A stake with an H or V indicates a stake along the ice cliff that forms the boundary of the glacier terminus. An H is a horizontal stake placed into the vertical wall of the glacier terminus, and V is a stake placed into the ice apron at the base of the ice cliff. The vertical stakes were installed to support the horizontal stakes and provide a nearby measure of ablation for a surface with a much different slope. A Note about Standard Deviation Calculations: During the early years only one or two measurements of surface height were taken at each stake. If two measurements were taken, the average was used and the range expressed as the error; note of this was made in "comments" field. If greater than 2 measurements of surface height and snow depth were taken, standard deviation of Total WEQ Change was based on a calculation of errors.

Maintenance: 

 Data for the glacier mass balance summaries was submitted by Andrew G. Fountain to the data manager in August, 1997. The column showing "file name" identifies the original file containing that record. These are provenance ascii text files and can be asked to the the McMurdo LTER data manager's  office. 
 
Once submitted, the data manager used Microsoft Excel and Access software to produce files that were in more of a relational mode.
                        
In March, 2000, Thomas Nylen revised the existing data, and added new data from the more recent seasons. Instead of lumping all of the mass balance results for each glacier under one file, they were separated into files for each glacier. Results for Hughes and Suess glaciers were also added. Metadata fields were also completed at this time.
                        
 In April, 2000, Denise Steigerwald added fields for dataset code and glstkid. Dataset code would allow  the data to be linked to the metadata in a relational database. Glstkid is a code that ties stake records to points on a GIS base map being developed by Michael Prentice at the University of New Hampshire.     
                    
Metadata was standardized in 2006 using the EML format and distributed throughout LTER and federal clearing houses (Chris Gardner, Inigo San Gil).  in 2014, metadata was revamped using the Drupal Ecological Information Management system (Inigo San Gil)

Additional information: 

In some circumstances we have the opportunity or need to measure the glaciers in mid-season (Dec). View the dates the measurements were made at the following URL:

http://www.mcmlter.org/data/glaciers/timing/weqdates.pdf

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