 |
| Titel |
Carbon cycle dynamics and solar activity embedded in a high-resolution 14C speleothem record from Belize, Central America |
| VerfasserIn |
Franziska A. Lechleitner, Sebastian F. M. Breitenbach, Cameron McIntyre, Yemane Asmerom, Keith M. Prufer, Victor Polyak, Brendan J. Culleton, Douglas J. Kennett, Timothy I. Eglinton, James U. L. Baldini |
| Konferenz |
EGU General Assembly 2015
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250108814
|
| Publikation (Nr.) |
 EGU/EGU2015-8612.pdf |
|
|
|
|
|
| Zusammenfassung |
| Speleothem 14C has recently emerged as a potentially powerful proxy for climate
reconstruction. Several studies have highlighted the link between karst hydrology and
speleothem 14C content, and a number of possible causes for this relationship have been
proposed, such as dripwater flow dynamics in the karst and changes in soil organic matter
(SOM) turnover time (e.g. Griffiths et al., 2012). Here we present a high resolution
14C record for a stalagmite (YOK-I) from Yok Balum cave in southern Belize,
Central America. YOK-I grew continuously over the last 2000 years, and has been
dated very precisely with the U-Th method (40 dates, mean uncertainty < 10 years).
The excellent chronological control for this stalagmite allows us to calculate 14C
activity (a14C) at the time of speleothem deposition (a14Cinit), as well as the dead
carbon fraction (DCF), predominantly a measure of the reservoir effect introduced by
limestone dissolution in the karst (Genty et al., 2001). Both records show striking
similarities to atmospheric a14C (IntCal13) and reconstructions of solar activity and 14C
production rate. We infer close coupling between cave environment and atmosphere, with
minimal signal dampening, an observation supported by monitoring data (Ridley et al.,
in press). DCF fluctuates between approximately 10% and 16% over the entire
record, with distinctly lower DCF values and higher a14Cinit during a period of
reduced rainfall between ca. 700-1100 AD (linked to the Classic Maya Collapse).
This behavior is consistent with observations made elsewhere, and suggests that
DCF responds to karst hydrological variability, specifically open-closed system
transitions. YOK-I a14Cinit typically lags atmospheric values by 10-100 cal years. A
shorter lag appears to be linked to periods of drought, suggesting a response of SOM
dynamics above the cave to rainfall reduction. Specifically, drought is inferred to
lead to reduced bioproductivity and soil carbon turnover, lowering contributions of
old recalcitrant carbon to the soil water, and resulting in closer coupling between
atmosphere and cave environment. The resolution of the record (0.3-0.7 mm/sample)
permits identification of the dominant drivers of stalagmite 14C during different
intervals. For example, hydrologic control on 14C appears dominant during the 11th
century drought, while in the 16th to 18th century a clear solar influence exists. Solar
activity is reflected in YOK-I as lower a14Cinit, reflecting the atmospheric a14C. We
apply simple hydrological models to investigate the different factors influencing 14C
in YOK-I. We estimate the importance of mean SOM age to signal dampening,
and quantify the strength of the solar influence and the global carbon cycle on the
record.
References:
Genty, D., Baker, A., Massault, M., Proctor, C., Gilmour, M., Pons-Branchu, E.,
Hamelin, B. (2001) Dead carbon in stalagmites: carbonate bedrock paleodissolution vs.
ageing of soil organic matter. Implications for 13C variations in speleothems, GCA,
65
Griffiths, M.L., Fohlmeister, J., Drysdale, R.N., Hua, Q., Johnson, K.R., Hellstrom, J.C.,
Gagan, M.K., Zhao, J.-x. (2012) Hydrological control of the dead carbon fraction in a
Holocene tropical speleothem, Quat. Geochron. 14
Ridley, H.E., Baldini, J.U.L., Prufer, K.M., Walczak, I.W., Breitenbach, S.F.M.
(in press) High resolution monitoring of a tropical cave system reveals dynamic
ventilation and hydrologic resilience to seismic activity, Journal of Cave and Karst
Studies |
|
|
|
|
|
|