Science - USA (2020-03-13)

for each one to run to completion ( 18 ). We find
that duration is significantly correlated with
caloric summer half-year energy (approximately
equal contributions from obliquity and preces-
sion), integrated summer energy, and NH sum-
mer insolation intensity (all at 65°N) (Fig. 3F)
at the commencement of a termination; the
correlation with the precession index is much
weaker but remains significant for tilt. This
reinforces the strong role of obliquity in post-
MPT terminations.

The radiometrically constrained ensemble

of 11 terminations allows us to evaluate the

findings of a recent study implicating a combi-

nation of obliquity and precession in control-

ling termination timing over the past 1 million

years ( 13 ). In this study, an approximate age

of each termination midpoint was estimated

using the rate of change in benthicd^18 Oon

the basis of a stack of benthicd^18 Orecords

tied to a depth-derived (rather than orbitally

tuned) age model ( 13 , 14 ). This study suggested

that the ~100-kyr G-IG spacing consists of

clusters of two (80-kyr) or three (~120-kyr)

tilt cycles ( 13 , 14 ), with the interval between

each termination controlled by obliquity, but

the exact timing within a given cycle occur-

ring when Earth is at perihelion during the

NH summer solstice (i.e., maximum preces-

sion) ( 13 ). Our results show that the spacing

of termination midpoints is consistent with

obliquity forcing (Figs. 3B and 4A), and that

the midpoints are most consistently aligned

Bajoet al.,Science 367 , 1235–1239 (2020) 13 March 2020 4of5

Fig. 3. Radiometric-based timing and
duration of 11 terminations (TI to TVII, TX,
and TXII) compared with astronomical
and insolation parameters.(A) Polar plots
showing phasing in degrees for both obliquity
(solid circles) and precession (open circles)
at the start (green), midpoint (orange), and
end (red) of each termination. The black
dots in each series highlight the phasings
for TX and TXII. (BtoE) Phasing between
the timing of the start (green), midpoint
(orange), and end (red) of each termination
and (B) obliquity ( 1 ), (C) climatic precession
( 1 ), (D) integrated summer energy (>275 W/m^2 )
at 65°N ( 16 ), and (E) insolation intensity for
July at 65°N ( 1 ). (F) Scatterplots and Pearson
rcorrelation coefficients for the duration of
11 terminations ( 18 ) (tables S3 and S4) versus
orbital and insolation metrics at the start
of each termination [left to right: obliquity ( 1 ),
climatic precession ( 1 ), integrated summer
energy (>275 W/m^2 )at65°N( 16 ),
July insolation intensity at 65°N ( 1 ), and
caloric summer half-year energy at 65°N ( 9 )].
The blue squares highlight the data for
TX and TXII. Underlinedrvalues are
statistically significant (P< 0.05; degrees
of freedom = 9).

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