Geoscience Reference
In-Depth Information
2 Materials and Methods
Gravity core SO164-03-4 (16
W; 2,744 m) was recovered
during RV SONNE cruise SO164 in 2003 in the Columbian Basin of the central
Caribbean Sea. All interpretations in this study are based on trace element and
isotope measurements on the tropical spinose symbiont-bearing foraminifera spe-
cies G. sacculifer and G. ruber. G. sacculifer mainly occurs during the summer
season in water depths from 30 m down to
*
50 m (Regenberg et al.
2009
),
whereas G. ruber tends to calcify in the warmer surface waters (shallower than
30 m when compared to G. sacculifer). The Mg/Ca-temperature calibrations of
N
°
32.37
′
N; 72
°
12.31
′
ü
rnberg (
2000
) and of were applied to G. sacculifer and G. ruber, respectively.
Approximately 0.5
30 fora-
miniferal tests are needed for Mg/Ca analysis. The measurement of the Mg/Ca
ratios followed standard protocols based on earlier studies (c.f. Kisak
1.2 mg sample material usually consisting of 20
-
-
rek et al.
2008
). The statistical uncertainty of the analytical procedure is in the order of 0.3 %
representing one standard deviation of the mean. From the same sample aliquot
about 15 single specimens of planktonic foraminifera are required for
ü
18
O mea-
δ
surements. The analytical reproducibility for the samples of this study is
0.07
‰
*
18
O.
Calcium isotope measurements are following the procedure of Heuser et al.
(
2002
). The isotopic variations are expressed as
for
δ
44/40
Ca-values using NIST
SRM915a as standard material following the notation as proposed in Eisenhauer et al.
(
2004
). In order to convert
δ
44/40
Ca-values into temperature, the
44/40
Ca-temperature
δ
δ
calibration of Hippler et al. (
2006
) was applied.
3 Key Findings
The Mg/Ca records of two different planktonic species although different in their
absolute temperature estimates (Fig.
1
) show that their glacial/interglacial Termi-
nations I is at
13 thousand years (ka) before present (BP) and at
9 ka BP,
*
*
18
O-Termination I of G. sacculifer. Hence, there is general
respectively, for the
δ
accord of a
4 ka-offset from our observation and the earlier observation of Visser
*
et al. (
2003
).
There is a general agreement of the
44/40
Ca- with the Mg/Ca-based temperature
reconstructions (Fig.
1
) in phase and time for the Holocene after Termination I.
Notably, there is no systematic temperature difference between the Holocene and
the Last Glacial in the
δ
44/40
Ca-temperature record, hence no Termination can be
attributed to this record. For the time interval before Termination I the
δ
44/40
Ca-
temperature relationship indicate no lower glacial temperatures and tend to be
1
δ
C warmer when compared to the corresponding Mg/Ca record. Latter
observation is challenging pending future reconciliation.
2
°
-
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