Geoscience Reference
In-Depth Information
1 Introduction
The Loop Current (LC) is the most prominent surface circulation feature in the Gulf
of Mexico (GoM)
flowing from the Caribbean through Yucatan Channel and
Florida straits into the North Atlantic. Hence, the LC is a component of both, the
western boundary current system of the North Atlantic and the basin- to global-
scale meridional overturning circulation. It is therefore key to both present and past
changes in the wind-driven basin-scale subtropical gyre and the global thermoha-
line circulation (e.g., Bryden et al.
2009
; Lippold et al.
2012
).
Special to the LC is the aperiodic shedding of anticyclonic meso-scale eddies, on
time scales of 3
(cf. The dynamics of the LC, in particular
the mechanism of eddy separation and its possible link to external forcing (e.g. sea
level and wind changes) is still not clear yet, but its role for the large-scale cir-
culation in the North Atlantic is likely of importance (Mildner
2013
). The focus of
this study is therefore to understand the behavior of the LC and its eddy shedding
during the past, in particular during transitional climate stages at the beginning of
interglacials characterized by different sea level, atmospheric circulation, and wind
stress forcing.
Together with the LC, the Mississippi River (MR) discharge in
18 months (cf. Fig.
1
a
-
-
uences the GoM
surface hydrography. Flower et al. (
2004
) described distinct negative excursions in
planktonic foraminiferal stable oxygen isotopes (
18
O) during Heinrich Event 1 and
δ
the B
d, which suggest Laurentide melt water discharge events into the
GoM (e.g., Flower et al.
2004
), although their large-scale impact on the Atlantic
meridional overturning circulation (AMOC) remains ambiguous. Using paleoproxy
records we study how these
ø
lling/Aller
ø
flooding events distribute in the GoM and adjacent
ocean areas.
2 Materials and Methods
We discuss proxy data from the northern GoM (cores MD02-2575, MD02-2576,
M78-181-3), Florida Straits (core KNR166-2-26), and Blake Outer Ridge (ODP
Site 1058C) (Fig.
2
). Details on the chronostratigraphies are given here and in
N
rnberg et al. (
2008
), Kujau et al. (
2010
), Bahr et al. (
2013
), and Schmidt and
Lynch-Stieglitz (
2011
).
Mg/Ca and
ü
18
O analyses were performed on the shallow-dwelling planktonic
foraminifer Globigerinoides ruber white. Sea-surface temperature (SST
Mg/Ca
) was
determined using a common calibration.
δ
18
O
seawater
was calculated combining
δ
18
O and SST
Mg/Ca
and subsequently, corrected for global ice volume
variations yielding
foraminiferal
δ
18
O
ivf
−
sw
as an approximation for sea-surface salinity (SSS).
To investigate the terrigenous input into the northern GoM, we performed high
resolution X-ray
δ
fluorescence (XRF) scanning converted to weight-% by using bulk
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