Modeling Regional Weather Patterns in Southern Illinois by Integrating Stable Water Isotopes Found in Precipitation to Distinguish Various Controls on the Local Hydrologic Cycle Stephania L. Zneimer1, Liliana Lefticariu1,2, Trenton Ford4, and Mihai Lefticariu3

1Department of Geology, Southern Illinois University, Carbondale, IL 62901 2Environmental Resources and Policy Program, Southern Illinois University, Carbondale, IL 62901

3Department of Chemistry & Biochemistry, Southern Illinois University, Carbondale, IL 62901 4Department of Geography and Environmental Resources, Southern Illinois University, Carbondale IL 62901

Abstract This study pertains to better understanding the water cycle in Southern Illinois by quantifying the temporal variations in the

contribution of different moisture sources to local precipitation. At any given location, precipitation is a mixture of moisture

sources such as evaporated ocean water and local moisture recycled through evapotranspiration at different intervals of depth

within the stratified layers of the atmosphere.

Introduction Fractionation of Oxygen and Hydrogen isotopes occurs in the atmosphere and hydrosphere. Stable water isotopes provide a

powerful tool to track changes in climate and hydrologic cycles. Normally, precipitation is a largely equilibrium process dictated by

temperature. However, real world water cycles, both on the global scale and regional [local] scale establishes other key

parameters that are also involved in the fractionation of H2O isotopes, such as moisture mixing from convective and advective

sources, soil evaporation, transpiration, and recycling.

This study utilizes stable isotopes in characterizing δ18O and δ2H relationships with specific control factors to establish pattern

shifts in isotopic signatures in local weather as it responds to fluctuations in key climatic parameters, such as temperature,

humidity, precipitation and so on. The data refines a Local Meteoric Water Line [LMWL] for Southern Illinois. Explicitly, the LMWL

will be further analyzed to test the hypothesis that differing moisture sources can distinguish the isotopic signature of moisture

sources from Gulf of Mexico and from those of other sources, including local sources.

Meteoric Water Line This plot, referred to as the Global Meteoric Water Line [GMWL] is the effect of Rayleigh-type fractionation driven primarily by equilibrium fractionation during precipitation. This plot, very nearly linear in relation shows the general behavior that 2H and 18O exhibit when hydrologic controls are stressed. Hydrologic controls include mainly temperature, humidity, and even solar radiation.

[Figure 1: General Relationship of δ18O and δ2H]

Additional factors that affect stable isotope composition of precipitation (δ18O and δD) include the source of moisture, local distillation and evaporation processes. Humidity defines the slope in relation to the GMWL. Large amounts of evaporation show a slope that resembles high humidity levels. Higher humidity levels denote less fractionation occurring due to exchange between water and vapor

Methods Starting November 11, 2012, water samples have been collected using a standard rain gouge after each precipitation event and

stored in polyurethane bottles.

In compliance with IAEA (International Atomic Energy Association) which has set standards for water collection for the use of

stable water isotopologues, the authors of the study forwent monthly averages and analyzed every single precipitation event.

Precipitation that was collected was isolated in one specific area, and whose geographic position has remained constant during

the duration of this study.

Each sample was analyzed by liquid injection using a Delta V Plus Isotope Ratio Mass Spectrometer equipped with a Gasbench

II and Costech TC-EA elemental analyzer located in the Mass Spectrometry Lab in Southern Illinois University

Isotopologues were set using V-SMOW (Vienna-Standard Mean Ocean Water). All δ18O and δD values will be expressed relative

to Vienna-Standard Mean Ocean Water (V-SMOW) in ppm.

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Mean Air Temp Total Solar Rad δ18OVSMOW δ2HVSMOW

y = 7.15x + 10.608 R² = 0.8888

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2H

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18O[V-SMOW]

LMWL for Gulf of Mexico moisture source

y = 7.7033x + 10.791 R² = 0.9666

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y = 7.6483x + 4.5361 R² = 0.9861

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LMWL for D-Excess values [-20 to 10]

y = 7.6578x + 15.054 R² = 0.9897

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y = 7.4962x + 24.409 R² = 0.9736

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References 1. Medvigy, David, and Claudie Beaulieu. "Trends in Daily Solar Radiation and Precipitation Coefficients of Variation since 1984." Journal of Climate J. Climate 25.4 (2012): 1330-339. Web. 2. Trenberth, Kevin E., Lesley Smith, Taotao Qian, Aiguo Dai, and John Fasullo. "Estimates of the Global Water Budget and Its Annual Cycle Using Observational and Model Data." J. Hydrometeor Journal of Hydrometeorology: 758-69. Print. 3. Sharp, Zachary. Principles of Stable Isotope Geochemistry. Upper Saddle River, N.J.: Pearson/Prentice Hall, 2007. Print. "Evapotranspiration - The Water Cycle." , from USGS Water-Science School. Web. [Figure 1] Clark, I., and P. Fritz, Environmental Isotopes in Hydrogeology, Lewis Publishers, Boca Raton, 1997.

Contact authours: Stephania Zneimer: slenora@siu.edu

Liliana Lefticariu: lefticariu@geo.siu.edu Trenton Ford: twford@siu.edu

Mihai Lefticariu: mihailefticariu@siu.edu

LMWL of Distinct Advective Moisture Sources

Deuterium Excess [D-Excess] Parameter

The D-excess parameter is the defined as d = δD − δ18O. This parameter is sensitive to the conditions during the evaporation and interaction of air/water masses [recycling] from moisture origins [such as oceanic source] to the site of precipitation.

Control Factors The fractionation within the hydrological cycle is theoretically controlled by the following factors;

δ18O and δ2H in air masses become lighter with increasing latitude because as humid air cools adiabatically, water molecules condensate and precipitate out of the air mass. δ18O and δ2H are heavier molecules and air masses

lose relatively more and more of the water molecules that contain the heavier isotopes.

δ18O and δ2H becomes lighter toward continent interior as air masses produce more than one precipitation event, the remaining vapor in the air mass is continuously depleting δ18O and δ2H isotopes.

HYSPLIT Model HYSPLIT is used to establish source-receptor relationships of particle trajectory paths between multiple air masses as well as the sources. These relationships are modeled based off of calculations for atmospheric advection and

diffusion and combines it with a nested meteorological grid to produce a three-dimensions particle distribution model.

Using HYSPLIT modeling of backwards trajectories of precipitation events which incorporated altitudes of 300, 500 and 850 meters above ground, demonstrated five advective moisture sources, namely: (1) The High Pressure Jet

Stream/the Pacific Ocean, (2) the Low Pressure Arctic Jet Stream and the upper continent of the Northern Rockies and Plains, (3)the lower continent in the South and Southwest, (4) the Gulf of Mexico, and (5) the Atlantic ocean .

Convective moisture sources are regarded as occurring locally, which in this study is defined geographically as the area extending from 35.00° N to 45.00° N and -87.00° W to -95.00° W.

The HYSPLIT model’s setup used the multiple heights clustering method, which traced back-trajectory paths for up to 72 hours. Of the total precipitation events that were analyzed in the HYSPLIT model, terminations as shown in

Figure 2, were the clearest to identify and localize. About forty-four percent of back trajectories terminated in only the Gulf of Mexico. D-excess values clustered around a range from 5 to 25. Oxygen-18 values clustered in more enriched

isotopic regimes [-10 to 0]. Terminations that plotted in the other sources mentioned compromised forty-one percent of storm events. (15% of storm events had terminations in “other” sources and the Gulf of Mexico). The Oxygen-18

values were comparable to Gulf precipitation, in that values spread around values of depleted isotopic regimes [-25 to 0], however D-excess values clustered around a range from -5 to 15.

2012/2013 y = 7.9141x + 15.585

2014 y = 7.7692x + 10.194

2015 y = 7.3914x + 6.9364

2016 y = 7.949x + 22.547

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δ2 H

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δ18O[V-SMOW]

LMWL Change in Time

2013 2014 2015 2016 Linear (2013) Linear (2014) Linear (2015) Linear (2016)

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Controls on Hydrologic Cycle

δ18OVSMOW δ2HVSMOW Relative humidity D-Excess

[Figure 2]

Further Research HYSPLIT Modeling results generated significant results about differentiating moisture sources, specifically the Gulf of Mexico. Constructing the line for the MWL when considering the high deuterium excess values, shows a line similar to the MWL that was event-separated based solely on the Gulf of Mexico. In addition, humidity values with low peaks are opposed with high peaks of Deuterium Excess, which strongly suggests moisture recycling taking place. Further research is needed to refine an isotope-based climate model that accounts for 18O-enriched values, that explain the influence of air masses originating from the Gulf of Mexico, of low humidity values, the fraction of moisture incurred from evapotranspiration [advective versus convective moisture sources] and other meteorological conditions.