What Ends an Interglacial? Feedbacks Between Tropical Rainfall, Atlantic Climate and Ice Sheets During the Last Interglacial - Integrated Analysis of Interglacial Climate Dynamics (INTERDYNAMIC) - page 26

(a)

Insolation

480
440
400

JJA 12°N

DJF 5°S

1 σ

80

Andes

(b)

5°N
GeoB4411-2

70

% Amazonian Andes

Lowland

80

Andes

(c)

9°N
GeoB7011-1

70

Lowland

% Amazonian Andes

Amazon

% Amazon

80

(d)

12°N
GeoB3938-1

70

Orinoco

LIG

60

110 120 130

Age (ka)

Fig. 2 Paleoclimatic records across the last interglacial (LIG). a Austral summer (DJF at 5 ° S,
black line) and boreal summer (JJA at 12 ° N, grey dotted line) insolation, b proportion of
Amazonian Andean (vs. lowland) material within the terrigenous fraction of core GeoB4411-2
(5.4 ° N, 44.5 ° W, 3,295 m), c same as b for core GeoB7011-1 (8.5 ° N, 53.3 ° W, 1,910 m),
d proportion of Amazonian (vs. Orinoco) material within the terrigenous fraction of core
GeoB3938-1 (12.3 ° N, 58.3 ° W, 1,972 m). The black line above the X-axis highlights the LIG
period, as de ned by benthic foraminiferal δ

18

O values

austral summer insolation variations over the last 250 ka (Cheng et al. 2013 ).
Therefore, the increase in austral summer insolation throughout the LIG (Fig. 2 a)
enhanced the ocean-land temperature gradient and moisture transport, thereby
intensifying precipitation over the Amazon basin. Enhanced rainfall over South
America and the adjacent ocean led to the reduced sea-surface salinities (SSS) that are
observed close to the Amazon mouth and advected further northward at 115 ka BP
compared to 125 ka BP (Fig. 1 c). Strong strati cation of surface waters indicated by

18 O records at 5

planktic foraminiferal N (not shown) supports this result.

While model and proxy data suggest increasing Amazon precipitation and runoff
across the LIG, the core at 12

° N and 9 °

δ

N exhibits a decrease in the relative proportion of
Amazon (vs. Orinoco) material that is centered around

°

119 ka BP (Fig. 2 d). The
model also simulates reduced precipitation and runoff in the Orinoco basin at
115 ka BP compared to 125 ka BP (Fig. 1 a, b), which agrees with the decrease in
boreal summer insolation (Fig. 2 a) but seems to disagree with the relative increase
in Orinoco input at 12 ° N (Fig. 2 d). In order to reconcile these findings, we suggest
that surface ocean currents, which redistribute freshwater input from the Amazon

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