Oxygen%20Isotope

1
Oxygen Isotope and
Paleoclimatic Information
2
(No Transcript)
3

• Paleoclimatic information from biological
• material in ocean cores

B. Oxygen Isotope studies of calcareous
marine fauna
C. Oxygen Isotope stratigraphy
D. d18O / Ice volume / Sea-level changes
4

• Paleoclimatic information from biological
• material in ocean cores

1. Paleoclimatic inferences from biogenic
material in ocean sediments derive from
assemblages of dead organisms
(thanatocoenoses). However, thanatocoenoses may
not be representative of the biocoenoses in
the overlying water columnselective
dissolution of thin-walled specimens at
depth, differential removal of easily
transported species by scouring bottom currents,
and occasional contamination by exotic
species transported over long distances by
large-scale ocean currents.
5
ACD
Lysocline
CCD
6
(No Transcript)
7
2. Biogenic oozes are made up primarily of the
calcareous or siliceous skeletons (tests) of
marine organisms, which may have been
planktic (passive floating organisms living
near the surface 0-200m) or benthic
(bottom dwelling). (a) Calcareous materials
foraminifera, coccolith, dinoflagellate
(b) Siliceous materials radiolarian,
silicoflagellate, diatom
8
3. Paleoclimatic influences from the remains of
calcareous and siliceous organisms have
resulted from basically three types of
analysis (a) the oxygen isotopic composition
of calcium carbonate in foram test (b)
the relative abundance of warm and cold water
species or quantitative interpretations
of species assemblages and their spatial
variations through time (c) morphological
variations in a particular species resulting
from environmental factors
9
(No Transcript)
10
G. bulloides
N. pachyderma
11
dino-flagellate
coccolith
diatom
12
B. Oxygen Isotope studies of calcareous marine
fauna

• Urey(1948) if an animal deposits calcium
  carbonate in
• equilibrium with the water in which it lies,
  and the shell
• sinks to the bottom of the seait is only
  necessary to
• determine the ratio of the isotopes of oxygen
  in the shell
• today in order to known the temperature at
  which the
• animal lived.

2. Isotopic composition of a sample
13
3. Isotopic composition of the ocean
T16.9?4.2(dc?dw)?0.13(dc ? dw)2
4. Changes in the d18O of the ocean (a)
Emiliani(1955, 1966) Amplitude of isotopic
variation related to glacial and
interglacial periods is 1.8. 70?changes
in temperature (56?C) 30?changes in
the isotopic composition of ocean
water.
14
(b) Shackleton(1967) Analyzed benthic
foraminifera to show an increase of bottom
water in d18O during glacial times being
similar to that of surface water (between
1.41.6 ).
(c) Dansgaard and Tauber(1969) They estimated
the isotopic composition of glacial age
ocean water as 1.2 , thus accounting for
70 of the observed isotopic change in
foraminiferal carbonate at that time.
15
(No Transcript)
16
The isotopic changes recorded in benthic
foraminiferal tests are primarily a record of
changing terrestrial ice volumes, or a
paleo-glaciation record.
17
5. problems (a) the isotopic composition of
the water is unknown (b) vital effect
In some cases, the carbonate would not be formed
in isotopic equilibrium with the water.
(ex Globigerinoides ruber give isotopic
values 0.5 lighter than expected.) (c)
variations in the depth habitat Water
density is of prime importance to individual
species, as the same species may be found in
different areas living at different
depths, but in water of the same
temperature and salinity.
18
(No Transcript)
19
(d) gametogenesis Foram tests from sea
floor are significantly enriched with 18O
compared to their living counterparts. This
is apparently due to calcification of the tests
at depth (gt300m) considerably below the
upper mixed layer. It may count for 20 of
foram test weight in sample from the sea
floor, because calcium carbonate has been
extracted from water which is much cooler
than that nearer the surface, the overall d18O
values indicate a mean temperature
significantly lower than the near-surface
temperature.
20
(No Transcript)
21
(e) salinity effect Any change in salinity
due to large-scale dilution effects (because
of ice sheet melting) or to local changes in
the precipitation-evaporation (P-E) relationship
will also be recorded in foraminifera.
(f) dissolution The effect of dissolution
in the thanatocoenoses is a pervasive
factor with implications not only for isotopic
studies, but for all paleoclimatic studies
based on floral and faunal assemblages.
Most importantly, dissolution does not
effect all species uniformly, selective removal
of the more fragile.
22
(No Transcript)
23
(No Transcript)