Apparent Ages
Oceanic Environments: The Reservoir Ages
Carbon exists in several forms: carbon monoxide CO and
carbon dioxide CO 2 , methane CH 4 , many complex organic
molecules (cellulose, etc.). The dominant forms are the
bicarbonate and carbonate ions (CO 3
2− , HCO 3
− , H 2 CO 3 )
dissolved in water, and calcium, barium and magnesium
carbonates (CaCO 3 , BaCO 3 , MgCO 3 ). Most of the Earth’s
living species directly assimilate the
14
CO 2 from the atmosphere. In the ocean, the organisms incorporate
14 C, which is
not in equilibrium with the atmospheric
14 CO 2 . The benthic
foraminifera are calcareous organisms living on the surface
of marine sediments. When collected alive at a water-depth
of 2000 m in the North Atlantic and Pacific oceans, they will
have
14 C ages of about 600 years and 1400 years, respectively (before the nuclear bomb tests). These
14 C ages are
apparent ages that include the age of the organism and that
of the water body in which the organisms formed their tests
from the dissolved ions according to:
CO 2 þ H 2 O $ H 2 CO 3 $ H
þ
þ HCO
À
3
HCO
À
3 $ H
þ
þ CO
2À
3
ðCa
2 þ
þ 2HCO
À
3 ! CaCO 3 þ H 2 O þ CO 2 Þ:
The
14 C aging of deep waters is the result of the conveyor
(thermohaline) circulation. In the modern ocean, winddriven warm saline surface waters from the North Atlantic
low latitudes flow poleward where they cool and sink to
form the North Atlantic Deep Water (NADW). NADW
flows at depth to the Indian and Pacific Oceans where it
mixes and upwells then flowing back to the North Atlantic.
All the deep waters flow to the Southern Ocean where they
upwell and downwell to form a return flow to the north
through the intermediate waters and the Antarctic bottom
waters. Once isolated from the atmosphere, the dissolved
14 CO 2 in the intermediate and deep waters starts to decrease.
Although in contact with the atmosphere, the sea surface
14 C
is not equal to the atmospheric
14 C, because of the mixing
between the sea surface and the underlying sub-surface
waters. The difference between the apparent
14 C ages of
living organisms in the ocean and the atmospheric
14 C ages
for the same absolute age is termed the reservoir age R. The
sea surface values of R as well as those of the intermediate or
deep waters differ in each one of the ocean basins and
regionally within the basins.
Fig. 4.4 Variations between
14 C and calendar ages between 20,000
and 50,000 cal BP from the calibration record IntCal 13 (Reimer et al.
2013). The straight line represents the 1:1 relation
Fig. 4.5
14
C and calendar ages of the Santorini eruption (modified
from Friedrich et al. 2006). Four groups of rings counted (grey
rectangles) from an olive branch of an approximately ten centimeters
length were dated. The total number of rings equals the number of
calendar years. The
14
C ages match the
14
C variations of the calibration
record (Reimer et al. 2013). The calendar age of the eruption range
between 1621 and 1605 BC at the 1r confidence level (68.2%) and
between 1627 and 1600 BC at the 2r confidence level (95.4%)
4 Carbon-14
59
Oceanic Environments: The Reservoir Ages
Carbon exists in several forms: carbon monoxide CO and
carbon dioxide CO 2 , methane CH 4 , many complex organic
molecules (cellulose, etc.). The dominant forms are the
bicarbonate and carbonate ions (CO 3
2− , HCO 3
− , H 2 CO 3 )
dissolved in water, and calcium, barium and magnesium
carbonates (CaCO 3 , BaCO 3 , MgCO 3 ). Most of the Earth’s
living species directly assimilate the
14
CO 2 from the atmosphere. In the ocean, the organisms incorporate
14 C, which is
not in equilibrium with the atmospheric
14 CO 2 . The benthic
foraminifera are calcareous organisms living on the surface
of marine sediments. When collected alive at a water-depth
of 2000 m in the North Atlantic and Pacific oceans, they will
have
14 C ages of about 600 years and 1400 years, respectively (before the nuclear bomb tests). These
14 C ages are
apparent ages that include the age of the organism and that
of the water body in which the organisms formed their tests
from the dissolved ions according to:
CO 2 þ H 2 O $ H 2 CO 3 $ H
þ
þ HCO
À
3
HCO
À
3 $ H
þ
þ CO
2À
3
ðCa
2 þ
þ 2HCO
À
3 ! CaCO 3 þ H 2 O þ CO 2 Þ:
The
14 C aging of deep waters is the result of the conveyor
(thermohaline) circulation. In the modern ocean, winddriven warm saline surface waters from the North Atlantic
low latitudes flow poleward where they cool and sink to
form the North Atlantic Deep Water (NADW). NADW
flows at depth to the Indian and Pacific Oceans where it
mixes and upwells then flowing back to the North Atlantic.
All the deep waters flow to the Southern Ocean where they
upwell and downwell to form a return flow to the north
through the intermediate waters and the Antarctic bottom
waters. Once isolated from the atmosphere, the dissolved
14 CO 2 in the intermediate and deep waters starts to decrease.
Although in contact with the atmosphere, the sea surface
14 C
is not equal to the atmospheric
14 C, because of the mixing
between the sea surface and the underlying sub-surface
waters. The difference between the apparent
14 C ages of
living organisms in the ocean and the atmospheric
14 C ages
for the same absolute age is termed the reservoir age R. The
sea surface values of R as well as those of the intermediate or
deep waters differ in each one of the ocean basins and
regionally within the basins.
Fig. 4.4 Variations between
14 C and calendar ages between 20,000
and 50,000 cal BP from the calibration record IntCal 13 (Reimer et al.
2013). The straight line represents the 1:1 relation
Fig. 4.5
14
C and calendar ages of the Santorini eruption (modified
from Friedrich et al. 2006). Four groups of rings counted (grey
rectangles) from an olive branch of an approximately ten centimeters
length were dated. The total number of rings equals the number of
calendar years. The
14
C ages match the
14
C variations of the calibration
record (Reimer et al. 2013). The calendar age of the eruption range
between 1621 and 1605 BC at the 1r confidence level (68.2%) and
between 1627 and 1600 BC at the 2r confidence level (95.4%)
4 Carbon-14
59