46
that favor higher and drier conditions. Therefore, if we know the ecological preferences of a species, we can infer (either qualitatively or quantitatively) the elevation
at which a sample from our core must have formed in the past. To make this inference we need to find the modern (i.e., living) analog for the biological assemblage
that is present in the core sample. This is achieved by simply collecting surface sediment (in which foraminifera are living) from salt marshes and measuring the elevation of the salt marsh surface at the same time.
How old is the sediment in each of those 1-cm thick sub-samples of core sediment? The primary means to answer this question is to radiocarbon date preserved
plant remains. When a plant is alive and photosynthesizing, the carbon that it is
made of was in equilibrium with carbon in the atmosphere. But when the plant dies,
one type of carbon (the carbon-14 isotope, which is also called radiocarbon because
it decays radioactively) begins to disappear through time in a systematic fashion. By
measuring how much carbon-14 remains in the sample, the time of its death is
established with a high degree of accuracy and precision. Very few labs have the
instrumentation needed to make this measurement, so the samples are usually
Fig. 3.7 (a) A chartered
float plane used to
transport personnel and
equipment from Kodiak to
Sitkinak Island, Alaska. (b)
Field camp on Sitkinak
Island: home for a week.
Although Kodiak bears live
on these islands they are
(fortunately) rarely seen.
The large yellow tent is
called an Arctic Oven and
is a very comfortable place
to eat and sleep; it even has
a small stove. (Image by
A.C. Kemp)
A. C. Kemp and B. P. Horton
that favor higher and drier conditions. Therefore, if we know the ecological preferences of a species, we can infer (either qualitatively or quantitatively) the elevation
at which a sample from our core must have formed in the past. To make this inference we need to find the modern (i.e., living) analog for the biological assemblage
that is present in the core sample. This is achieved by simply collecting surface sediment (in which foraminifera are living) from salt marshes and measuring the elevation of the salt marsh surface at the same time.
How old is the sediment in each of those 1-cm thick sub-samples of core sediment? The primary means to answer this question is to radiocarbon date preserved
plant remains. When a plant is alive and photosynthesizing, the carbon that it is
made of was in equilibrium with carbon in the atmosphere. But when the plant dies,
one type of carbon (the carbon-14 isotope, which is also called radiocarbon because
it decays radioactively) begins to disappear through time in a systematic fashion. By
measuring how much carbon-14 remains in the sample, the time of its death is
established with a high degree of accuracy and precision. Very few labs have the
instrumentation needed to make this measurement, so the samples are usually
Fig. 3.7 (a) A chartered
float plane used to
transport personnel and
equipment from Kodiak to
Sitkinak Island, Alaska. (b)
Field camp on Sitkinak
Island: home for a week.
Although Kodiak bears live
on these islands they are
(fortunately) rarely seen.
The large yellow tent is
called an Arctic Oven and
is a very comfortable place
to eat and sleep; it even has
a small stove. (Image by
A.C. Kemp)
A. C. Kemp and B. P. Horton