Seasonal microclimate control of calcite fabrics, stable isotopes and trace elements in modern speleothem from St Michaels Cave, Gibraltar - Tufas and Speleothems: Unravelling the Microbial and Physical Controls - page 337

observed seasonal d 13 C variations in coexisting
dripwater, cave air CO 2 and speleothem calcite.
The relationships between stable isotope, Sr
and speleothem fabrics across calcite laminae
deposited between 2000 and 2004 have been
examined at the highest possible resolution using
micromilling, synchrotron m-XRF and electron
backscatter diffraction techniques and shows that
d 13 C and Sr are subtly decoupled from each other
with respect to fabric development. The Sr- d 13 C
topology is consistent with a degassing - calcite pre-
cipitation process where the d 13 C compositions
of drip water and calcite are highly responsive to
seasonally switching cave air pCO 2 whereas
calcite precipitation rates (up to 10 4 slower, see
above) drive the PCP enrichment of Sr at a slower
and more complex manner.
High resolution speleothem fabric, trace element
and isotope records from caves that have been
closely monitored provide crucial links between the
local climate and the way that climate is recorded
during speleothem deposition and remove some of
the assumptions sometimes necessary in climate
reconstruction from speleothem records. In Gibraltar
the low cave air pCO 2 in summer is unusual com-
pared to cave monitoring studies carried out else-
where and shows that caution is needed when
linking paired speleothem fabrics to specific
seasons without knowledge of local processes oper-
ating in the cave. Furthermore, monitoring shows
that the climate recording process may vary among
sites in the same cave resulting in differing bias to
winter and summer growth depending on the inter-
play between ventilation and hydrological cycles.

B AKER ,A.&B RUNSDON , C. 2003. Non-linearities in drip
water

hydrology: an example from Stump Cross

Caverns, Yorkshire. Journal of Hydrology, 277,

151 - 163.
B AKER , A., S MITH , C. L., J EX , C., F AIRCHILD ,I.J.,
G ENTY ,D.&F ULLER , L. 2008. Annually laminated
speleothems: a review. International Journal of

Speleology, 37, 193 - 206.
B ALDINI , J. U. L., M C D ERMOTT , F., B AKER , A.,
B ALDINI , L. M., M ATTEY ,D.P.&R AILSBACK ,
L. B. 2005. Biomass effects on stalagmite growth
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B ANNER ,J.L.,G UILFOYLE ,A.,J AMES ,E.W.,S TERN ,
L. A. & M USGROVE , M. 2007. Seasonal Variations in
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B ORSATO , A., F RISIA , S., F AIRCHILD , I. J., S OMOGIY ,A.
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in annual stalagmite laminae mapped by micrometer-
resolution X-ray fluorescence: incorporation of

colloidally-transported species. Geochimica et

We are indebted to John Balestrino, Joanne McCarthy
and Hela de la Paz for help with the cave monitoring
program, to John Cortes (GONHS) for logistic support,
and Tito Vallejo and the cave guides for their co-operation.
We also thank Jacqui Duffet, Dave Lowry and Rebecca
Fisher for assistance in the laboratory and field during
the project. The manuscript was greatly improved with
the help of comments made by two anonymous reviewers.
This work was supported by the NERC under grant
NE/D005280.

Cosmochimica Acta, 71, 1494 - 1512.
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C RUZ , F. W., K ARMANN ,I. ET AL . 2005. Stable isotope
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