<i>δ</i><sup>13</sup>C decreases in the upper western South Atlantic during Heinrich Stadials 3 and 2
Abrupt millennial-scale climate change events of the last deglaciation (i.e. Heinrich Stadial 1 and the Younger Dryas) were accompanied by marked increases in atmospheric CO<sub>2</sub> (CO<sub>2atm</sub>) and decreases in its stable carbon isotopic ratios (<i>δ</i&g...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-04-01
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| Series: | Climate of the Past |
| Online Access: | http://www.clim-past.net/13/345/2017/cp-13-345-2017.pdf |
| Summary: | Abrupt millennial-scale climate change events
of the last deglaciation (i.e. Heinrich Stadial 1 and the Younger Dryas)
were accompanied by marked increases in atmospheric CO<sub>2</sub> (CO<sub>2atm</sub>)
and decreases in its stable carbon isotopic ratios (<i>δ</i><sup>13</sup>C),
i.e. <i>δ</i><sup>13</sup>CO<sub>2atm</sub>, presumably due to outgassing from the
ocean. However, information on the preceding Heinrich Stadials during the
last glacial period is scarce. Here we present <i>δ</i><sup>13</sup>C records
from two species of planktonic foraminifera from the western South Atlantic
that reveal major decreases (up to 1 ‰) during Heinrich
Stadials 3 and 2. These <i>δ</i><sup>13</sup>C decreases are most likely related
to millennial-scale periods of weakening of the Atlantic
meridional overturning circulation and the consequent increase (decrease) in
CO<sub>2atm</sub> (<i>δ</i><sup>13</sup>CO<sub>2atm</sub>). We hypothesise two mechanisms
that could account for the decreases observed in our records, namely
strengthening of Southern Ocean deep-water ventilation and weakening of the
biological pump. Additionally, we suggest that air–sea gas
exchange could have contributed to the observed <i>δ</i><sup>13</sup>C decreases.
Together with other lines of evidence, our data are consistent with the
hypothesis that the CO<sub>2</sub> added to the atmosphere during abrupt
millennial-scale climate change events of the last glacial period
also originated in the ocean and reached the atmosphere by outgassing. The
temporal evolution of <i>δ</i><sup>13</sup>C during Heinrich Stadials 3 and 2 in
our records is characterized by two relative minima separated by a relative
maximum. This <q>w structure</q> is also found in North Atlantic and
South American records, further suggesting that such a structure is a
pervasive feature of Heinrich Stadial 2 and, possibly, also Heinrich Stadial 3. |
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| ISSN: | 1814-9324 1814-9332 |