 |
| Titel |
Changes in the balance of soil respired CO2 (root vs. soil organic matter) during the Younger Dryas event; evidence from three European cave sites |
| VerfasserIn |
Dominika Rudzka, Frank McDermott |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043274
|
|
|
|
|
|
| Zusammenfassung |
| The main goal of this study was to understand better the response of soil carbon to a major
climate transition and to examine the influence of variable temperature sensitivity of different
carbon sources. New radiocarbon measurements for portions of three speleothems from
European cave sites (La Garma and El Pindal caves, N. Spain; Sofular cave, Turkey)
deposited during the late-Glacial to early Holocene were used to investigate these processes.
These data were used to improve the interpretation of δ13C in stalagmites, which can be
influenced not only by the temperature and moisture changes (reflected in major climatic
transitions), but also by several different processes (e.g. variable degassing and limestone
dissolution, soil evolution, hydrological effects). Pollen data indicate that C3 plants persisted
at all three sites since the late-Glacial. There is however a marked increase in δ13C
during the Younger Dryas (YD) in all three stalagmites, indicating a climate driven
change in carbon cycling dynamics. In principle this change could reflect stronger
degassing due to drier conditions or more closed system behaviour (higher ‘dead carbon
proportion’ (dcp) due to greater limestone dissolution). Closed system modeling
indicates that greater limestone dissolution should result in higher δ13C and lower
initial 14C activity as a result of dilution by ‘dead’ carbon. In practice, initial 14C
activity of stalagmite carbonate during the YD in all three speleothems follows the
atmospheric 14C age plateau, indicating open system behaviour, with little evidence for
lowering of 14C activity that would be expected to result from enhanced limestone
dissolution. This is interpreted as a change in the balance of soil-respired CO2. Soil CO2
is a combination of soil organic matter (SOM) and plant-root respiration. In the
latter process, plants cycle only ambient atmospheric CO2 (relatively high 14C
activity). By contrast, microbial decomposition of soil organic matter typically
involves breakdown of older (low 14C activity) carbon. Our data indicate that there is a
change in the balance between these two sources as a result of temperature and
moisture change during the YD. Overall, soil respiration rates were reduced during the
YD (less biogenic C input and therefore higher δ13C), and were dominated by
live root respiration of ambient atmospheric carbon. In the Holocene, CO2 from
decomposition of soil-stored carbon overwhelms CO2 from root respiration at all three
sites. This is consistent with an analysis of published speleothem 14C data from
several European cave sites. Speleothems from cold-wet sites in N. Europe show
clear evidence for progressive ageing and storage of recalcitrant carbon in soils,
resulting in lower 14C activity and dcp-time trends that are consistent with radioactive
decay of soil-stored carbon. By contrast, at warmer S. European sites, there is no
evidence for build-up and storage of recalcitrant SOM (high 14C activity, low dcp
in speleothems), indicating that organic matter is rapidly cycled through the soil.
Global warming is likely to impact high latitude northern hemisphere sites that can
release large quantities of stored carbon, resulting in a positive climate feedback. |
|
|
|
|
|
|