snow accumulation

Glacier Snow and Ice Mass Changes

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 mass balance and meltwater flow from the Taylor Valley glaciers. This dataset contains mass balance changes at each stake measured on the glaciers of Taylor Valley. The values are the result of an analysis of the raw data presented in other data files (glacier stake heights, snow depths, and glacier snow densities). Included here for each stake are the change in ice and snow water equivalent (mass) values, and the total mass change. The standard deviation or the range for each total is also given.

Associated Personnel: 

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Dataset ID: 

2006

Short name: 

glmschng

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.

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 the Zone variable: The accumulation zone is the region on the glacier where snow accumulation exceeds ablation, therefore the region is always snow covered, and typically restricted to the higher altitudes of the glacier. The ablation zone is the region where ablation exceeds snow accumulation and the surface is ice, although occasionally covered with seasonal snow. This is important for evaluating the other variables. In the accumulation zone, for example, there will be no height to ice. A Note about Ice WEQ Change: The density used can be calculated from snow height change, or directly examined in the glacier snow density file. 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.

Data sources: 

COM_MSCHNG
HOW_MSCHNG
SUES_MSCHNG
CAN_MSCHNG
HUGH_MSCHNG
TAY_MSCHNG

Maintenance: 

  Data for the glacier snow and ice mass changes 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 found by 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. Based on feedback from Andrew G. Fountain and Karen Lewis, unnecessary fields (such as ice height change, snow height  change, and range) were removed, and others (such as snow WEQ change) were added  to the file.
                        
 In March, 2000, Thomas Nylen revised the existing data, and added new data from the  more recent seasons. Instead of lumping all of the results for each glacier under one file, they were separated into files for each glacier. Results for Hughes and Suess glaciers were also added. Changes made to the original data can be viewed by clicking here. Metadata fields were also revised 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.    
 
In 2006, Chris Gardner and Inigo San Gil standardized the metadata using the EML format.  In addition, metadata was distributed at the LTER Metadata catalogs and Federal metadata clearinghouses.  
 
In 2014, metadata was revamped by Inigo San Gil, using the Drupal Ecological Metadata Language
                    

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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