UNIVERSITY OF EAST ANGLIA
School of Environmental Sciences
Main Series Undergraduate Examination 2012-2013
EARTH SYSTEM GEOCHEMISTRY
ENV-2A30
Time allowed: 2 hours
Answer THREE questions in Section A and ONE from Section B.
Each SECTION carries equal weight.
Answer Section A in ONE answer book and Section B in a SEPARATE answer
book.
Provided:

ENV data book
Notes are not permitted in this examination.
Do not turn over until you are told to do so by the Invigilator
ENV-2A30
Module Contact: Prof Julian Andrews, ENV
Copyright of the University of East Anglia
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SECTION A
1. Figure 1, below, shows the Sr isotope curve for seawater over Phanerozoic
time, based on limestone Sr isotope composition. The line is the best estimate
of likely composition and the dots are the individual data points.
Figure 1 (Question 1)
a) Describe why the Sr isotope value of river waters are thought to control much
of the general shape of the curve in Figure 1.
[50%]
b) How does hydrothermal activity at mid ocean ridges affect the curve?
[30%]
c) The River Yare on the UEA campus flow over 80 million year old Chalk
bedrock. What is the likely Sr isotope composition of River Yare water? [20%]
2. Write a realistic reaction that describes sulphate reduction. What will happen
to the products of this reaction in normal marine sediments?
3. a) Describe the process of radiocarbon (14C) production and assimilation.
[40%]
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b) What is the major limitation of
mitigated?
14
C dating and how may this problem be
[60%]
4. Give the definition of primary production, and compare the main controlling
factors for primary production on land and in the oceans.
SECTION B
5. a) Describe the mineralogical and physical features of ophiolites that provide
clues to geochemical reactions occurring in mid-ocean ridge hydrothermal
systems.
[70%]
b) Which two global scale geochemical cycles are most impacted by mid ocean
ridge reactions? Explain why this is.
[30%]
6. How did Sandberg’s seminal work on ooids in the 1980s change our
understanding of variation in ocean chemistry over geological time? How were
his ideas modified by later work on evaporites and hypercalcifying organisms?
7. Describe how and why δ18O values have varied through the late Cenozoic.
8. a) What palaeoclimatic information can be obtained from δ 13C values of
aquatic biomarker alkenone? Explain the main rationale behind this approach.
[70%]
b) Why are alkenones good biomarkers?
[30%]
END OF PAPER
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