Comparison of Slopes
There is a close linear relationship between ?H2 and ?O18 from the local
meteoric water line (LMWL) data. This is shown by the equation y = 7.2464x + 4.4204
and R² = 0.92376. The global meteoric
water line (GMWL) also has a close linear relationship as shown by its equation
y = 8x + 10
R² = 1. The slopes are very close. However, the LMWL has a slightly lower slope
as more isotopic fractionation is seen in ?O18 rather than in ?H2
during evaporation and sublimation of rainfall and snowfall. This results in a
uneven proportion of ?O18 compared to ?H2. As well as affecting the slopes the
fractionation of ?O18 and ?H2 is a main aspect of humidity when water vapor is
being evaporated from the ocean (Benjamin et al., 2004). In
regard to atmospheric humidity, all water vapor that is evaporated over oceans
and below 85%, which is the average humidity conditions globally, a d-excess value
will be gotten (Tupa.gtk.fi,
Potential uses of d-excess
D-excess can be used to locate and identify
moisture origins. The level of d-excess present is influenced by the conditions
occurring during the water vapor forming. For example, precipitation during
Winter months coming from the Mediterranean Sea has very high levels of
d-excess. However, a rise in d-excess can also be attributed to re-evaporated
water from continental basins being added to water vapor moving inland (Www-naweb.iaea.org, 2018). D-excess acts as an efficient
isotope tracer in identifying artificial and natural effects occurring in groundwater.
D-excess can provide information on short-term as well as long term patterns (Tupa.gtk.fi,
Long term weighted mean of the d-excess in
The long term weighted mean pf the d-excess
in Valentia is 8.91%. It is much lower than the mean d-excess of the Eastern
Mediterranean Sea and the Western Mediterranean Sea, similar to the North
Atlantic Ocean and Western Subtropical North Atlantic Gyre and considerably
higher than the Arctic Ocean.
Where does rain in Ireland come from?
The polar front is an important aspect of atmospheric
weather. It plays an important role in determining rainfall origins in Ireland.
The polar front is a transitional zone situated between warm air moving in a
northerly direction and cold air moving in a southerly direction. Depressions can
form from disturbances in the front. These depressions commonly pass through
the northwest of Ireland, coming from the North Atlantic. In the depression,
the warm air is pushed in a northern direction and the cold air is pushed in a
southern direction. This pattern of weather gives humid and cloudy conditions followed
by colder weather with rain showers.
Frontal rainfall is common in Ireland in the
Winter months on December and January. This is because Atlantic low-pressure
systems are at their peak in December. As the depressions move in an easterly
direction frontal rainfall and strong winds are common in Ireland. In contrast,
the months of February and June have the least amount of rainfall in Ireland.
This is due to continental and Greenland anticyclones. Rainfall increases in
Ireland in late June and July. This is due to the influence of pressure increasing
over oceans and decreasing over Europe (Met.ie, 2018)
Www-naweb.iaea.org. (2018). Deuterium
excess. online Available at:
Accessed 6 Jan. 2018.
Met.ie. (2018). Climate of Ireland – Met Éireann – The Irish
Meteorological Service Online. online Available at:
https://www.met.ie/climate-ireland/climate-of-ireland.asp?prn=1 Accessed 4
Benjamin, L., L. Knobel, L., Flint Hall, L., DeWayne Cecil,
L. and R. Green, J. (2004). Development of a Local Meteoric Water Line
For Southeastern Idaho, Western Wyoming, and South- Central Montana. Scientific Investigations Report. online U.S. Geological
Survey. Available at: https://pubs.usgs.gov/sir/2004/5126/pdf/sir2004-5126.pdf
Accessed 8 Jan. 2018.
Tupa.gtk.fi. (2018). Deuterium Excess as Tracer
for Seasonal Isotope Variations of Precipitation in Surfacial Groundwaters. online Available at:
http://tupa.gtk.fi/posteri/tp_0394.pdf Accessed 8 Jan. 2018.