This study analyzed 314 unique rain events in Bermuda to better understand the temperature and amount effects on water stable isotope variability. Meteorological data and precipitation samples were collected from three sites on the island. Preliminary results found dips in water vapor isotope values corresponded to rainfall events, and the minimum vapor value positively correlated with the isotope value of the accompanying precipitation sample. Rainfall associated with air mass changes exhibited dips in vapor isotopes that did not rebound after the event, allowing characterization of the new air mass. Further research is needed to examine the role of evaporation and upper atmosphere characteristics on isotope values during rain.

1. Assessing water stable isotope variability in precipitation
during phase changes in the hydrologic cycle
Cothran Harris1,2, Andrew Peters2, Hans Christian Steen-Larsen2,3
1North Carolina State University, 2Bermuda Institute of Ocean Sciences, 3University of Copenhagen
Introduction
Acknowledgements
This research was supported by the NSF-REU grant (OCE-1460686) awarded
to the Bermuda Institute of Ocean Sciences
Two effects have been shown to cause variability in the
isotopic composition of precipitation; the “amount effect”
prevalent in tropical latitudes, and the “temperature
effect” in locations of higher latitude. Using data from
three different locations across Bermuda, this study
studied 314 unique rain events in Bermuda, and how
water vapor isotopic content and other meteorological
parameters affect the isotopic content of each
precipitation sample. Our objective is to attain a better
understanding of the mechanism behind the temperature
and precipitation effect, which will aid out knowledge in
the microphysical processes of the hydrologic cycle.
Methods
• Meteorological data was retrieved from the Tudor Hill
site (B) and L.F. Wade International Airport (C), which
included temperature, humidity, dew point, and
barometric pressure.
• Precipitation samples were collected at BIOS (A).
These samples had their isotopic content
analyzed by a Picarro cavity ring down
spectroscopy (CRDS). The isotopic
content of the water
vapor at Tudor Hill
was also analyzed
with a Picarro
CRDS.
A
B
Figure 3: Tudor Hill. All
meteorological measuring
equipment
Is located at the top of the tower.
Methods and Results Preliminary Results
• Most events analyzed have an observable “dip” in water
vapor d18O values that correspond to an observed rainfall
at Tudor Hill. The minimum d18O value, located at the
nadir of each dip, has a positive correlation with the
accompanying precipitation d18O value from the sample
taken at BIOS for each event. Rainfall events that were
accompanied with a wind shift in particular displayed this
correlation.
• Rainfall events that occur during changes in air mass (i.e.
cold fronts) exhibit d18O dips that never rebound once
the rainfall event had ended. Based on this,
characteristics of the new air mass could be described
using precipitation d18O values from rain events
associated with an air mass change.
Further Research
• Further research is needed to investigate the role
evaporation of rain at the surface has in both
precipitation and water vapor isotope values.
• Further research is needed to analyze radiosondes, and
the characteristics of the upper atmosphere during rain
events.
A B
Figure 1: A map of Bermuda, showing where BIOS (Location A) and
Tudor Hill (Location B) are located.
Figure 2: The rain sampling
site is located in BIOS.
Figure 3: Tudor Hill. All meteorological
measuring equipment
Is located at the top of the tower.
Figure 4: Tudor Hill. An example of a sampled rainfall event.
Wind direction, wind speed, temperature, water vapor d18O
vales, rainfall rate, and absolute humidity are all combined to
produce a “snapshot” of the conditions around a rain event.
Figure 5: The lowest water vapor d18O
value for each rain event plotted against
the accompanying precipitation d18O
value for the rain sampled at BIOS.
Figure 6: The change in water vapor d18O
from after each rain event had concluded
to 24 hours after that, plotted against the
accompanying precipitation d18O value for
the rain sampled at BIOS.
C