Geoscience Reference
In-Depth Information
3 Key Findings
Three high-resolution alkenone SST records covering the entire Holocene and
Termination 1 have been completed (44GGC/46JPC, 36JPC, 32JPC). These records
are very similar in both absolute values and variability. So far, AMS
14
C dating has
been carried out only for core KNR176-2 32JPC, but almost identical temperature
evolutions allow for a straightforward correlation of the records. The leading
principal component of the SST records reveals a pronounced cooling of the eastern
tropical Paci
C. Moreover, the alkenone
records suggest a delayed deglacial warming in the region (starting at
c during H1 (Fig.
1
b) in the order of 1
-
2
°
11 ka BP
and possibly related to changes in local winter insolation) and two Holocene cold
events.
The oxygen isotope records from the three cores all reveal a deglacial decrease in
*
18
O
seawater
record (indicative of local SSS changes) from 32JPC, which is located close to the
river mouth of Rio San Juan, indicates higher SSS during the glacial period and a
freshening trend during H1 (not shown). At the same time, the
18
OofG. ruber, but with different timing. The sea-level corrected
δ
δ
18
O difference
between the thermocline dweller N. dutertrei and the shallow dweller G. ruber
increases (not shown), consistent with enhanced upper-ocean strati
δ
cation due to
freshening of the surface layer (cf. Steph et al.
2009
). The results agree with earlier
findings by Pahnke et al. (
2007
) based on
D in alkenones from the same core.
δ
18
O
seawater
records from
Moreover,
the comparison of the sea-level corrected
δ
different sites indicates a pronounced
“
salinity dipole
”
in the tropical eastern Paci
c
during H1, with enhanced SSS (and weaker upper-ocean strati
cation) in the
western Panama Basin (core 44GGC/46JPC) and reduced SSS (and stronger
strati
cation) near the Colombian coast (core 36JPC; Fig.
1
b). These results cor-
roborate the precipitation dipole previously hypothesized for that region (Prange
et al.
2010
).
The CCSM3 model results help interpret the proxy records and set them into a
large-scale dynamical context. Independent of the background climatic state, all
hosing experiments capture a precipitation-anomaly dipole in the Panama Bight
region in response to a weakening of the AMOC, with enhanced rainfall over
western Colombia and reduced rainfall over the Gulf of Panama and west of Costa
Rica (signi
cant at the 0.05 level according to a t-test). The simulation of this
hydroclimatic
dence to the model. As an example, Fig.
2
a
shows the net precipitation response to a substantial AMOC weakening under
preindustrial conditions.
The annual mean net moisture transports from the Atlantic to the Paci
“
“fingerprint”
”
lends con
c were
computed along the 6
N segment for all experiments based on daily model
output. Compared to the pre-industrial simulation, the moisture transport at the Last
Glacial Maximum decreases by 16 % (from 0.31 to 0.26 Sv). An increase of
northeasterly trades is overcompensated by a lower atmospheric moisture content.
The net vapor transport in the early Holocene run is very similar to the pre-
industrial value (0.28 Sv). The net moisture transports across Central America for
°
N
-
14
°
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