TY  - UNPB
UR  - https://discovery-pp.ucl.ac.uk/id/eprint/1335899/
A1  - Littler, K.
M1  - Doctoral
ID  - discovery1335899
Y1  - 2011/12/28/
AV  - public
N2  - The Cretaceous (~145?65 Ma) is widely regarded as a greenhouse period with warm,
equable climates and elevated atmospheric CO2 relative to the modern. However, the
earliest Cretaceous (Berriasian?Barremian; 145?125 Ma) is commonly characterised
as a relatively colder ?coolhouse? interval, typified by lower global temperatures
than the mid-Cretaceous. Unfortunately, the lack of absolute sea surface temperature
(SST) estimates prior to the Barremian has hampered efforts to definitively reconstruct Early Cretacous climate. Here, the TEX86 palaeotemperature proxy, for
which a detailed review is provided, has been used to generate a 13 myr record of
SST estimates for the Early Cretaceous, based on sediments from assorted deep-sea
drilling sites. A consistent offset in the TEX86 ratio between transported mudstones
and pelagic carbonates in the low-latitude marine sediments (DSDP Sites 603 and
534) has been identified, which may be linked to post-burial diagenesis or a
difference in organic matter type between lithologies. Mindful of these apparent
lithological effects on TEX86, only the pelagic sediments were used to subsequently
reconstruct Early Cretaceous SSTs. These TEX86 records demonstrate both elevated
SSTs (>27 ÂșC) at low and mid-latitudes relative to the modern, and the apparent
stability of these high temperatures over long timescales. This lack of SST variation
in the low-latitudes during the Valanginian positive carbon-isotope event (CIE; ~135?138 Ma), casts doubt on the warming-weathering feedback model put forward
to explain this major perturbation. Additionally, new paired bulk organic (?13Corg) and bulk carbonate (?13Ccarb) carbon-isotope records from North Atlantic DSDP sites,
have been used to reconstruct relative changes in pCO2 across the CIE. These
observed fluctuations in ?13C imply changes in carbon-cycling and a possible
drawdown in CO2, due to excess organic matter burial associated with the CIE.
TI  - Climate and carbon-cycling in the Early Cretaceous
EP  - 346
N1  - The abstract contains LaTeX text. Please see the attached pdf for rendered equations
PB  - UCL (University College London)
ER  -