1. Ben Gurion University of the Negev
Department of Geological and Environemental Studies
The Effect of Silicates Dissolution to the Isotopic Composition of Sr in Sea-Water
Daniel Winkler
Under the supervision of Prof. Jiwchar Ganor and Dr. Yehudit Harlavan [Geological Survey of Israel]
Lookout eastwards from Mizpe Amram. Daniel Winkler

2. The Goal of My M.Sc Study
To contribute to the understanding of the effect of 87Sr/86Sr variations in the oceans, due to the interaction of Sillicates in ocean water
The isotopic composition of Sr in oceans water is dependent on the 87Sr/86Sr of the various minerals and rocks it comes in contact with. The Sr that is released to the oceans water [due to chemical dissolution] is isotopically
homogeneoues up untill it reaches the oceans and is deposited in sedimentary layers of calcium carbonate [and also to a lesser extent, gypsum. Both minerals contain Calcium Ca2+ which is replaceable by Sr2+] 2 2

3. Sr Variation Model Proposed by Gunter Faure [1965] s+v+m=1
s=Sialic (Si+Al) Rocks [Aluminosillicates]
v=Volcanics
m=Carbonates
s+v+m=1
עפ"י הערכים האופיינים של הפרקציות ממקורות סיאליים, וולקנים וקרבונטים – ההרכב האיזוטופי של Sr במי הים כיום, מוגדר עפ"י המשואה שלעיל.
על גבי משולש פאזות, שבה כל מרכיב מהווה פרקציה יחסית, נמצא שהתרומה היחסית של סדימנטים קרבונטיים ימיים להרכב האיזוטופי שלSr במי ים הוא הגבוה ביותר ועל כן הוא גם מהווה מאזן (buffer), על מנת לעמוד בטווח הערכים כפי שהתצפית 87Sr/86Sr מאז הקמבריום מראה. 3 3

4. Sr Budget of the Oceans
1 Sr is homogeneous in ocean water [Long Residence time compared to mixing rate of the oceans
2. There are significant differences in the concentrations and isotopic composition among the different contributors
The oceans are Sr-homogeneous due to the long residence time of Sr in water [tau=5*10^6yr] compared to the mixing rate of the oceans which is only 1000years. ? 4 4

5. The Goal of Research
Determining of Kinetic dissolution of sillicate sediments in interaction with seawater.
Examining the Sr concentration change with time due to the dissolution.
Tracking the variations of 87Sr/86Sr that is contributed along the dissolution stages.
היחס האיזוטופי 87Sr/86Sr במי-האוקינוסים עבר שינויים חדים לאורך ההיסטוריה הגיאולוגית, בעקבות כניסת Sr מבלייה של סלעים בעלי יחסי 87Sr/86Sr שונים. זמן השהות של Sr באוקינוסים (5*106yr) קצר ביחס לזמן הגיאולוגי, כך ששינויים ביחס 87Sr/86Sr מאפשרים תיעוד של השינויים הגיאוכימיים, הטקטוניים והאקלימיים של כדורה"א. 5 5

6. Methodology: Laboratory Experiments: Interaction of sediment with seawater
Laboratory experiments allow controlling of the various parameters [temperature, pH, chemical composition].
Synthetic seawater solution is used, in order to avoid high Sr concnetration which will prevent us from noticing minute changes in Sr concentration over time. 6

7. Sampling Area Amram Rhyolite π Quartz Diorite Roded qδr
Yehoshafat Granite γ
_______________
Tabe Gneiss γν
Eilat Granite γ
Eilat Schist μ
Sachamon Amphibolite a
Alluvium samples of Sillicate rocks will be samped from Eilat Region, from streams that drain single-homogeneous rock-unit. 7 7

8. x8
Methods:
Batch [closed] Experiment. Each tube is representing a single point on the graph.
Each one of the tubes is having the same conditions [temperaure, sediment/solution ratio, pH]
After a specific time period, a separation of solution from the the ‘solution+sediment’ is being done for various chemical analyses
Solution 40gr
Sediment 0.4gr 8 8

9. Sr,Ca,Mg,Fe,K Analysis [at the Geological Survey in Jerusalem]
0.22μm filter
[via Vacuum pump]
t0+t
Sr,Ca,Mg,Fe,K Analysis [at the Geological Survey in Jerusalem]
Perkin Elmer SCIEX ELAN
Precision ±10%
Si, Al Analysis
Spectrophotometer
Perkin Elmer Lambda 2S
Precision ±5%
הפרדת התמיסה מהמבחנה עם הסדימנט תעשה בעזרת מערכת משאבת וואקום דרך פילטר PVDF (Millipore™ Durapore 0.22um). התמיסה תשמר במבחנה חדשה עם רישום של תאריך ההפרדה.
Seperation of solution from the solution+sediment found in the tube will be done by vacuum pump via 0.22um filter
The tube will be saved with the date and time of seperation
Si and Al will be analyzed colorimetrically with Perkin Elmer 2S spectrophotometer, by using wavelengths of 810nm and 585nm [respectively]. The metod is based on adding reagents of molybdate blue and catechol-violet for Si and Al respectively which forms a complex which its absorbance values the device can measure. Using a calibration curve [concentration versus absorbance least-squares fitting line] can allow one to deduce the concentration of a unknown solution [by analyzing the absorbance values one gets from a series of known standards] 9 9

10. Sr-seperation in resin-columns in the clean-laboratory at the Geological Survey in Jerusalem
87Sr/86Sr Analysis
Nu Plasma MC-ICP-MS
Precision ±0.002% 10 10

11. Initial Results of the following minerals:x8
Albite (63µm<f<75µm)
Amram Rhyolite (0<f<63µm)
Roded Quartz Diorite (63<f<90µm)
Yehoshafat Granite (63<f<90µm)
Logarithmic-scale sampling [fator2]
[2.5d,5d,10d…320d].
Solution 40gr
Sediment 0.4gr 11 11

12. Albite (size fraction 63µm<f<75µm)
The mineral Albite was chosen, because:
Its dissolution kinetics is known from previous studies [Blum1995,Brantley1998]
Its interaction with seawater solution was never studied before
Since the size fraction was not size-homogeneous and so that small particles were adhered to the larger ones, the sample was Ultrasonically-shaken.
Results are indeed satisfactory, as the SEM photos below are showing
Before
After 12 12

13. Surface Area of the minerals Albite [before and after ultrasonic-cleansing]13 13

14. Results show that indeed Albite is dissolving in seawater solution
10/2/2012
30/4/2012
Via Spectrophotometer
T=25c
pH=8.2
Surface Area=0.277m2/gr
Vol SW Solution=0.04L
Alb=0.4gr 14

15. 10/2/2012
21/3/2012
Via ICP-MS 15 15

16. Via Spectrophotometer16 16

17. My experiments will contribute to the understanding of:
1.Which minerals are the major Sr contributors during sediment-seawater interaction process.
2.Which of the Eilat region rocks unit are the major Sr contributors.
3.The results of my ressearch will contribute to the understanding of the Sr budget of the oceans. 17 17

18. Next assignments:
Finishing of experimental work and Thesis writing.
Chemical analysis of all the experiments up to this day.
New experiments for samples: Taba Gneiss, Eilat Granite, Eilat Schist, Sachmon Amphibolite
Mineral separation of the various minerals found within the alluvium sample. Bulk samples BET surface-area measurement
87Sr/86Sr analysis, as well as Ca,Mg,K,Fe,Sr analysis for the various experiments solution up to present date.
October
September
August
July
June
May
April
Mars
February
January
December
November
2013
2012 18

19. Thanks for listening…
Lookout from top of Har Zfachot to the northern part of Eilat gulf. End of Israel Trail.
Daniel Winkler 19