MSC 112 Lab 3, Deep Sea Sediments, Microfossils, and Global Climate Change
September 26, 2019
Sophia Fernandes
Purpose
It is important to understand the relationship between sediments and sea surface
temperature, since sediments that collect on the ocean floor record many of the characteristics of
the ocean at the time they were living. Distributions of many planktonic groups, especially
planktonic foraminifers, are closely related to sea surface temperature and their presence in
different depths of sediment reveals a great deal of information about the ocean at the time they
were living. Globoratalia Menardii is a specific species of foraminifer that inhabits warm, tropic
water. G. Menardii is used to determine climatic conditions in the history of the Earth. This
exercise demonstrated how to use G. Menardii to determine glacial and interglacial periods and
the different characteristics of these periods by determining its presence at different depths.
Methods
Prior to receiving the actual climate stratigraphy’s that were used for the data table, each
student received a “practice stratigraphy” to ensure their ability to distinguish the correct
planktonic foraminifera under a microscope from the others. After receiving approval from either
the lab instructor or the TA, each student received two climate stratigraphies from a Caribbean
sediment core, P6304-7, at the point of location 15o 06' N, 69 o 3 8' W in the 1960s by a Miami
research vessel. Using the microscopes provided, students scanned their samples to determine
whether they contained specimens of G. Menardii or not. The class data was then combined and
recorded in a table with depths ranging from 0cm-390cm.
Results
Table showing the presence of G. Menardii at different depths:
Sample
G. menardii
Sample
Depth (cm)
present?
Depth (cm)
0
yes
210
10
yes
220
20
Yes
230
30
Yes
240
40
Yes
250
50
Yes
260
60
No
270
70
No
280
80
No
290
90
No
300
100
No
310
110
No
320
120
No
330
130
no
340
140
No
350
150
Yes (1)
360
160
No
370
170
No
380
180
No
390
190
no
200
no
G. menardii
present?
No
no
Yes (1)
Yes (1)
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
yes
Yes
Yes
No
No
no
Calculations of the sedimentation rates of each glacial and interglacial period
0-10,000 years ago (current interglacial period):
50cm/10,000 years = .005cm per year
.005 x 1,000 = 5 cm per 1,000 years
10,000-75,000 years ago (glacial period):
75,000-10,000= 65,000 years
220-60= 160 cm
160cm/65,000 = .00246 cm per year
00.246 x 1,000 = 2.46 cm per 1,000 years
75,000-128,000 years ago (interglacial period):
128,000-75,000 = 53,000 years
360-230 = 130 cm
130/53,000 = .00245 cm per year
.00245 x 1,000 = 2.45 cm per 1,000 years
Christopher Columbus calculations:
2019-1492= 527 years
527 x .005 (sedimentation rate for the current interglacial period per year) = 2.635 cm
Conclusions
Sediments are extremely valuable in regards to determining and dating the different
glacial and interglacial periods in the history of the earth. Ocean depths where the Globorotalia
Menardii, a specific species of foramineifera, is found signifies that the sediment layer is from an
interglacial period. During interglacial periods there are no continental ice sheets present, the
water is warmer, there is a lower 18O concentration, and the lack of ice sheets results in a higher
sea level. Alternatively, depths with no Globorotalia Menardii present signifies a glacial period.
Four different glacial periods were determined using the data table that was completed
using the data collected by the class. Two interglacial periods were identified due to the presence
of the specimen; one ranging from 75,000 years ago to 128,000 years ago with G. Menardii
present from 230-360 cm, and the current interglacial period that spans back 10,000 years with
G. Menardii present from 0-50 cm deep. Two glacial periods were determined from the data. The
most recent glacial period occurred 10,000 years ago to 75,000 years ago with the specimen not
present at depths of 60-220 cm; although the specimen did appear at the depth of 150 cm, this
was likely due to the short rise of temperature during the glacial period. The earliest glacial
period that was revealed by the data collected from the depth of 370 ended about 128,000 years
ago but the start of the period is unclear since there is no prior switch of the presence of the
specimen in the table given.
The sedimentation rates appear to be constant between the two full periods in the data.
There is one full interglacial period and one full glacial period recorded and both have very
similar sedimentation rates that differ by only .01 cm per 1,000 years. The most recent period in
the data is an ongoing glacial period that currently has a sedimentation rate of .5 cm per 1,000
years but is inconclusive since the period is ongoing. The data collected from 370-390 is also not
useable when comparing the sedimentation rates of glacial and interglacial periods because there
is no shift in presence of the specimen to mark the beginning of that glacial period.
Sedimentation rates will greatly vary based on the location in the ocean. For example, a
main characteristic of continental rises is that they are covered by a thick layer of sediment due
to the turbidity currents that flow from land. Further out in ocean in the abyssal plains will have
much lower rates of sedimentations since they are further from land and therefor do not receive
as much of the sedimentary runoff as areas closer to continents do.