Paleotemps2_worksheet_Fall2023
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School
University of British Columbia *
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Course
340
Subject
Geography
Date
Dec 6, 2023
Type
Pages
2
Uploaded by DukeDragonfly3884
EOSC340 Paleoclimates 2
Paleoclimate Day 2 Worksheet
Goals: Estimate changes in global sea level from changes in
d
18
O in shells and sea water
Extra Qs: practice calculating values of
࠵?
18
࠵?
from sample values of
18
࠵?
and
16
࠵?
and be able
to conceptually explain what part of Earth these samples are most likely to come from.
d
18
O ‰ in sea water
This graph gives the relationship between
the temperature of the ocean water and the
difference in
d
18
O between shells and the
sea water for particular species of forams.
Use this graph (
using the solid black line
)
for questions 1a and 1b below.
Q1a. For the following data, we have
determined the ocean temperature from
other proxies. Calculate the missing d
18
O
values (shell/water) and the average glacial-
interglacial change in d
18
O
water
.
Glacial - Interglacial
d
18
O
water
difference
Date (kya)
Water Temp °C
Shell d
18
O
Water d
18
O
Interglacial
6
28.7
-2.4
Glacial
14.3
28.2
1.34
Interglacial
405
29.7
-2.41
Glacial
427.9
27
-0.44
Average Glacial - Interglacial
d
18
O difference
Q1b. But our estimates of the water temperature have some uncertainty – we don’t know the
temperature exactly. For the first interglacial – glacial period, imagine that we could not tell
what the temperature difference was, and had to assume that both temperatures were the
same, at 28.5C. Complete the missing values in the table below for these temperatures.
Glacial - Interglacial
d
18
O
water
difference
Date (kya)
Water Temp °C
Shell d
18
O
Water d
18
O
Interglacial
6
28.5
0.3
Glacial
14.3
28.5
1.34
Q1c. Based on your answers to part 1a and 1b, what affects the d
18
O of the
shells
most
between glacial and interglacials: changes in water temperature, or changes in water d
18
O?
Q1d. A change of 1‰ in the d
18
O of sea water = 100m change in sea level. What is the
average change in global sea level associated with glacial-interglacial changes in ice volume?
2
(Include direction – check this makes sense – do you expect higher or lower sea levels when
you have large ice sheets on land?)
Extra questions (practice with
d
18
O ‰)
This exercise will help you to understand how scientists calculate
d
18
O from measuring the
percentage of
16
O and
18
O atoms in a sample of water. Columns 1 and 2 in the table below
give you the measurements of the % of O atoms that are
16
O and
18
O respectively
Q2a. Complete the table above using the
d
18
O equation given in the table, where (
18
O /
16
O)
standard
= 0.0020052
Q2b. Put the samples above in order of “heaviest” to “lightest”:
Q2c. Where would you likely find samples with
d
18
O values that match the samples in part 1?
Match the following location with the samples from Q1
Sample #
Rain in the subtropics (latitudes just north/south of the topics) in the summer
Atmosphere over the South Pole in winter
Ocean values in the tropics
Global average ocean water
Snow over the south Pole in winter
Q2d. Explain your reasoning:
Q2e. Given the values of
d
18
O you have calculated, and using the relationship from earlier in
this class:
d
18
O = 0.67T - 13.5 (Johnsen et al., 1989), calculate the temperatures for the
subtropics in summer and the south Pole in winter (CHECK: do these values seem
reasonable? Why/why not?)
%
16
O
sample
%
18
O
sample
(
18
O /
16
O)
sample
࠵?
$%
࠵? = ’
(
)
!"
/
)
!#
)
$%&’()
(
)
!"
/
)
!#
)
$*%+,%-,
− 1. × 1000
1
99.8090
0.1910000
2
99.8010
0.1990000
3
99.79988
0.2001187
4
99.7995
0.2005000
5
99.8110
0.1890000
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