Fig. S3 . Elevation map showing variation of the minimum
BaMwidth (red line) under different sea-level scenarios.
Pink lines denote contours at specified elevation/bathymetry.
Once depth-width data had been collected, we used an ensemble of
polynomial fits to create a smooth model for width under different
sea-level conditions. The final polynomial model was selected based on
three criteria: 1) no width-depth inversions were detected (i.e., with
increased depth, BaMwidth must decrease); 2) a p-value
of <0.05 and R2 value >0.95 was
achieved; and 3) our current measured width of the Strait (25.6 ± 0.225
km) must fall within the 95% confidence intervals of the polynomial
model. We chose a 3-order polynomial fit. While 4-6 order fits provided
higher R2 values, these resulted in substantial
width-depth inversions (i.e., as sea-levels decreased, at points
BaMwidth increased) when combined with the RSL. The
resultant formula of the fit (Fig. S4A) was combined with the RSL
Probability Maximum curve and 95% confidence intervals (Grant et al.,
2012, 2014) to provide models for the minimum BaMwidthat 0.125 kyr intervals over the last 130 ka BP. Our modelled
BaMwidth at 0 ka BP (30.15 +4.88/-4.26 km) is slightly
greater than our measured width (25.6 ± 0.225 km). (fig. 4). We relate
this to two complications: 1) the complex elevation and bathymetry of
the Bab-al-Mandab area (sudden changes in elevation gradients) which the
smooth polynomial fit does not easily detect (Fig. S4A), and 2) the RSL
slightly overpredicts present sea-levels by ~1.7 m.
However, uncertainties of the measured width (25.6 ± 0.225 km) and
modelled width (30.15 +4.88/-4.26 km) overlap, and the measured width
falls within the 95% confidence intervals of the polynomial fit.
Additionally, the chosen polynomial fit slightly underestimates contour
distance at +10 m, meaning that the reconstructed
BaMwidth is slightly conservative to sea-level increases
during early MIS 5e.