Supplementary Table 3.
Exclusion of datasets from deep ocean circulation analysis
Site
Reason for exclusion in analysis
549
This site contains a 1 meter gap in carbonate sedimentation at the core of the
CIE, rendering identification of the core of the CIE difficult. Anomalously low
13C persists throughout the recovery period. We believe that the isotope
record is extensively overprinted. Additional data is needed in the postexcursion period to reliably identify the inflection point where values return to
pre-excursion patterns.
577
Site 577 contains a hiatus through the CIE. Without a tie point for the core of
the CIE, and with no data point available to identify the end of the recovery
period, a reliable chronology could not be constructed
865
Site 865 contains only 4 points in the time interval of interest, and only one
value in the CIE interval. The value is unlikely to be representative of the 13C
plateau and probably represents a value in the recovery. An unpublished highresolution stable isotope record of bulk carbonates suggests that this site is
missing the entire plateau interval.
690
Benthic foraminiferal 13C data for Site 690 published by Thomas and
Shackleton (1996) were excluded from this analysis (total = 28 data points, out
of 91 published data points). These data were systematically offset towards
more positive values (~0.5‰ to 1‰) from the data published by Kennett and
Stott 1990, Stott et al., 1990 and Thomas et al, 2002. We note that exclusion
of these data does not affect our conclusions and we highlight two
observations: (1) Since the offset is towards more positive values, the inclusion
of these data would increase the interbasinal aging gradient between the
Southern Ocean and other basins during the pre-excursion and post-excursion
values, supporting our interpretation of overturning in the Southern Ocean
during these time intervals. (2) The Thomas and Shackleton data contain only
1 value during the carbon isotope excursion interval, and this value does not
significantly lower the Site 690 13C average, or the Southern Ocean basin
average for that interval. The inclusion of these data would not change our
main conclusions, yet because of the uncertainty in the cause of the offset of
this dataset compared to three other sources, we have chosen not to include
these data in our deep ocean circulation analysis.
1221
Site 1221 contains a carbonate dissolution horizon in which dolomite rhombs
compose a significant portion of the fine fraction. Some benthic foraminifera
contained dolomite rhombs on their tests, although these specimens were not
selected for carbon isotope measurements. Foraminifera below the carbonate
dissolution horizon have a sugary surface texture. 18O values from the core of
the CIE display an inverse pattern than that observed in all other PETM sites 18O values become more positive. It is unlikely that these values represent
true oceanic conditions, since the PETM is a time of ubiquitous global warmth.
We attribute these unusual features in the stable isotope record of this site to
diagenesis.
1258
The sediments in this site were partially lithified, and it was very difficult to
obtain foraminifera free of matrix. The 13C values from this site also appear to
be systematically shifted towards more negative values than any other deep sea
site not only within the CIE but also before and after it. The P/E boundary in
this site overlays black shales that have very negative 13C values owing to
their high organic carbon content. These observations have led us to believe
that some geochemical overprinting has taken place in foraminifera from this
site, perhaps due to fluid flow above the black shale horizon. The record at Site
1258 does appear to record the same basic features of the 13C seen in some of
the most complete records of the PETM, but given the poor fossil preservation
and the consistent offsets from all other data sets, we regard the absolute
values as suspect.