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2004 ). This net export of freshwater helps to maintain relatively high salinities
within the Atlantic and has been argued to exert a strong in
uence on the strength
and stability of the Atlantic meridional overturning circulation (AMOC) (e.g.,
Zaucker et al. 1994 ; Romanova et al. 2004 ). So far, only three paleoceanographic
studies were devoted to past changes in the cross-isthmus vapor transport during the
Late Quaternary (Benway et al. 2006 ; Leduc et al. 2007 ; Pahnke et al. 2007 ). In
these studies sea-surface salinity (SSS) reconstructions from the eastern tropical
Reconstructed local salinity increases (decreases) were basically interpreted as
decreased (increased) cross-isthmus moisture transport, which however led to
seemingly contradictory results,
c were used to infer changes in the Atlantic-to-Paci
c moisture
in particular during Heinrich Stadial 1 (H1).
Increasing eastern Paci
c SSS off Costa Rica (Benway et al. 2006 ; Leduc et al.
2007 ) and decreasing SSS in the Panama Bight (Pahnke et al. 2007 ) were later
reconciled by postulating the development of an anomalous precipitation dipole in
the eastern tropical Paci
a situation (Prange
et al. 2010 ). This analog would be associated with reduced Atlantic-to-Paci
c during H1, similar to a modern La Ni
c vapor
export (Schmittner et al. 2000 ) and hence a positive feedback on the H1 AMOC
slowdown due to anomalous Atlantic Ocean freshening. In the framework of our
study, a transect of sediment cores along the Colombian and Panamanian margins
in combination with climate model studies provides an opportunity to improve our
understanding of the role of the tropical hydrological cycle as a potential driving
force for global climate change through Termination 1 and the Holocene.
2 Materials and Methods
In order to reconstruct past variations of the hydroclimate in the Panama Bight region,
we use high-deposition rate sediment cores retrieved during R/V Knorr cruise 176-2
in 2004 (Fig. 1 a; ) . Located along the rim of the
basin, these cores allow for the reconstruction of temporal changes in spatial hy-
droclimatic patterns by means of well-established geochemical methods. Coring sites
from the Colombian margin are ideally located to sensitively monitor changes in
continental river runoff. Using stable-isotope analyses on planktonic foraminifera
(Globigerina ruber, Neogloboquadrina dutertrei) in combination with alkenone sea-
surface temperatures (SSTs; Mg/Ca SST reconstructions were not possible due to the
sparsity of G. ruber in most samples), a history of SSS changes and thermocline depth
in the Panama Bight is developed for Termination 1 and the Holocene.
The proxy studies are accompanied by simulations of Holocene and deglacial
(H1) climate states, using the atmosphere-ocean general circulation model CCSM3
(Collins et al. 2006 ). A reliable simulation of the regional climatic features in the
eastern tropical Paci
c with correct position of the Choco Jet
a low-level westerly
wind jet centered at 5
requires the use of a relatively high spatial resolution of the atmospheric compo-
nent. We therefore employed the T85 (1.4
N which transports Paci
c moisture towards Colombia
transform grid) version of the model.
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