Interhemispheric anti-phasing of orbitally driven monsoon intensity: Implications for ice-volume forcing in the high latitudes

- Precession drives an interhemispheric anti-phasing of monsoon intensity.
- Maxima of boreal monsoon are opposed by minima of austral monsoon and vice versa.
- The anti-phasing of monsoon intensity influences low-to-high latitude climate gradients.
- These changes are superimposed on obliquityʼs influence on meridional climate gradients.
- Low-to-high latitude climate gradients drive ice-volume changes in the high latitudes.

The influence of precession on the redistribution of insolation on the top of the atmosphere predicts that climate change in the low latitudes is out of phase between the hemispheres. We test this prediction by the most direct approach, the analysis of terrestrial climate records, as they provide direct information on regional changes in the atmosphere. A review of evidence from absolutely-dated climate records shows that precession drives an interhemispheric anti-phasing of monsoon intensity. Maxima of boreal monsoon intensity are opposed by minima of austral monsoon intensity and vice versa.The interhemispheric anti-phasing of monsoon intensity implies that low-to-high latitude climate gradients are asymmetric between the hemispheres; periods with maximum boreal monsoon intensity steepen the gradient in the NH but flatten it in the SH and vice versa. These precession driven changes are superimposed on obliquityʼs influence on meridional climate gradients; high obliquity causes flat gradients and low obliquity steep gradients.We propose the hypothesis that orbitally driven changes of low-to-high latitude climate gradients drive ice-volume changes in the high latitudes. To test the hypothesis we quantify a proxy for the climate gradients and predict ice-volume forcing in the NH and SH during the last 120 ka. Then we use the contributions of both hemispheres to predict global ice-volume forcing. The comparison with records related to global ice volume verifies our ice-volume hypothesis. Therefore, ice-volume changes can be predicted for the NH and SH separately.