Enhanced climate variability in the tropics: a 200 000 yr annual record of monsoon variability from Pangea's equator

A continuous series of 209 000 evaporite varves from the equator of arid western Pangea (age=-255 ma), as a proxy for surface temperature, has a complete suite of Milankovitch cycles and harmonics as expected for a rectified reaction to precession-modulated insolation at the equator. Included are modes of precession (23.4 kyr, 18.2 kyr), semi-precession (11.7 kyr, 9.4 kyr), and harmonics at similar to 7 kyr and 5.4 kyr. An oscillation of similar to 100 kyr, with 35% of total variance, originates as an amplitude modulation of precession cycles. An exceptionally strong 2.3 kyr quasi-bimillennial oscillation (QBMO) appears to have had its own source of forcing, possibly solar, with its amplitude enhanced at Milankovitch frequencies. Seasonal information in varves traces the rectifying process to asymmetrical distribution of Pangea relative to the equator, and its effect on monsoonal circulation and heat flow near the equator during summer solstices in the hemispheres.