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Fig. 1 a
c Eddy separation process in CONTROL shown by sea-surface elevation (in meters)
depicted as composite from the last 20 model years (18 events in total); contour lines are 0.8 (1.2 m
with 10 cm interval). a Scenario 3 months before shedding; b the eddy has just separated from the
LC; c scenario 6 months after shedding. Locations for sediment cores MD02-2575/-76, M78-181-
3, EN32-PC6, KNR166-2-26, ODP-1058C, and ODP-999 discussed in the text are indicated. MR
Mississippi River, LC loop current, FS Florida straits, YC Yucatan channel, BOR Blake outer
ridge. d Time series of spatially averaged current speed (in m/s) at 200 m water depth averaged
across the region given by 22
b
-
W, i.e., northwest of the Yucatan Channel.
Black line present-day reference simulation. Red line experiment with sea level lowered by 67 m;
green line experiment with sea level lowered by 110 m, blue line experiment with sea level
lowered by 200 m. Black arrow marks the shedding period of an eddy (T
shed
). The sharp decreases
in speed correspond to eddy shedding from the LC. Note that for better visualization CONTROL-
67 was shifted by 0.2 m/s, CONTROL-110 by 0.4 m/s and CONTROL-200 by 0.6 m/s,
respectively
°
N
24
°
N and 87
°
W
84
°
-
-
XRF measurements on selected samples. Potassium is used to infer MR sediment
discharge (Kujau et al.
2010
).
Numeric modeling concentrated on the impact of sea level and wind stress
change on the LC and eddy shedding (Mildner
2013
). We re-con
gured an existing
eddy-permitting model of the North Atlantic for different sea levels and for different
wind forcing. The model realistically reproduces today
'
s circulation (Eden and
B
ning
2002
), in particular the LC and its eddy shedding (Mildner
2013
; see also
Fig.
1
a
ö
c). Sea level was lowered by 67 m (Younger Dryas), 110 m (LGM), and
200 m (sensitivity experiment), respectively. In addition, we applied wind forcing
appropriate to the LGM to our model by adding wind stress anomalies with respect
to recent climate from 6 different coupled LGM model simulations of the PMIP-II
effort
-
to the standard recent wind forcing of our model
(Braconnot et al.
2007
; Barnier et al.
1995
). We did not change the surface heat
flux and freshwater
forcing of the model in order to concentrate on the response to wind and sea level
changes only. We believe this modeling strategy is justi
ed, since there is evidence
for only small changes in the North Atlantic thermohaline circulation during the
LGM (Lippold et al.
2012
).
3 Key Findings
Our SST
Mg/Ca
and SSS records from the northeastern GoM (MD02-2575) re
ect
the temporal dynamics of the LC, its relationship to varying MR discharge, and the
evolution of the Atlantic Warmpool (N
rnberg et al.
2008
). SST
Mg/Ca
and SSS
records from the northern GoM reveal glacial/interglacial amplitudes signi
ü
cantly
larger than in the Caribbean (Fig.
2
). We hypothesize that the extreme cooling of
the northern GoM during the LGM by
C is a result of reduced LC eddy
shedding and sluggish heat transport into the GoM. Considerable sea-surface
freshening implies glacially enhanced river discharge.
6
°
*
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