---TITLE:  Thule Ecosystem Flux

---AUTHORS:
	-Jeff Welker (PI), Michael Jones (co-PI), Jace Fahnestock (co-PI)
	-Natural Resource Ecology Laboratory, Colorado State University, Fort 
Collins, CO 80523-1499
	-jwelker@nrel.colostate.edu, jace@nrel.colostate.edu
	-970)491-1796 (Jeff), 970)491-5262 (Jace), 970)491-1965 (Fax)

---DATA SET OVERVIEW:
	-This data represents estimates of net carbon dioxide exchange, 
respiration and photosynthesis (umol m-2 s-1) from high arctic ecosystems on 
the northwest coast of Greenland, near Thule (76°31'N, 68°30'W).  Measurements 
were taken in six different ecosystems: Polar desert, Polar semi-desert, Polar 
oasis, Polar desert deglaciated < 2years, Polar desert deglaciated ~50 years, 
Polar desert deglaciated >100 years.

---INSTRUMENT DESCRIPTION
	-LI-COR LI-6200 infrared gas analyzer (IRGA) coupled to a clear 
polycarbonate hemispherical bubble (60 cm diameter, 20 cm high) of the type 
used in playground structures (Miracle Recreation Equipment, Indianapolis, IN). 
 The chamber was sealed to the ground at the time of measurement with medium 
density closed-cell foam that was placed between the weighted chamber and the 
ground.  Measurements of carbon dioxide exchange are corrected for prevailing 
atmospheric pressure and temperature within the IRGA.  Respiration measurements 
were made by covering the chamber with an opaque cloth and photosynthesis was 
calculated as the difference between NEE and respiration.

---DATA COLLECTION and PROCESSING:
	-Data were collected plus or minus two hours of solar noon on 26-27 
July 1999.  Three consecutive 30-second measurements of net carbon dioxide 
exchange are taken on each plot at the time of measurement to ensure steady 
state conditions within the chamber.  The chamber is subsequently covered with 
an opaque cloth and three more measurements of respiration (photosynthesis 
eliminated by covering the chamber) are taken.  Photosynthesis is calculated as 
the difference between net flux and respiration.  There are eight replicate 
plots for each of the six ecosystems that we sampled.  The three consecutive 
measurements are averaged for each plot and the data for the plots are 
subsequently averaged to produce a mean carbon dioxide exchange estimate for 
each treatment for each time period.  In this notation, negative numbers 
indicate net carbon loss by the tundra to the atmosphere during the measurement 
time period while positive numbers indicate net carbon gain by the tundra 
during the measurement period.  Thus, respiration is always negative and 
photosynthesis is always positive or zero.

---DATA FORMAT:
	-Data is column delimited ASCII
	-Column headers, in order, are: site, plot (replicate), temperature (C, 
each point is the mean of two measurements, net ecosystem CO2 exchange (umol 
m-2 s-1, each point is the mean of three measurements), plant and soil 
respiration (umol m-2 s-1, each point is the mean of three measurements), and 
gross photosynthesis (umol m-2 s-1, each point is the mean of three 
measurements).
	- DATA VERSION= 1.0 (28 February 2002) FINAL.

---DATA REMARKS:
	-Data are initially stored in the LI-6200.  Both BINARY and ASCII 
versions of the data are subsequently transferred to a PC where we primarily 
use Microsoft Excel to manipulate the data.  Because the LI-6200 operating 
parameters are calibrated and set before each measurement period, we do very 
little manipulation of the data following collection except to average the 
replicate measurements and plots. The three replicate measurements on each plot 
help to ensure no outliers.

---REFERENCES
	-Jones, MH, JT Fahnestock, PD Stahl and JM Welker. 2000. A note on 
summer CO2 flux and soil microbial biomass from multiple high arctic ecosystems 
in northwestern Greenland. Arctic, Antarctic, and Alpine Research 32:104-106.