Potential Modulation of a Late Triassic Pangean Megamonsoon by Solar Cycles

Abstract The supercontinentPangeaattainedits maximumsize with land masses being equally distributed on both hemispheres during the Triassic. The peculiar configuration of continents gave rise to the largest monsoon system of Earth’s history, termed Pangean Megamonsoon (PMM). This monsoon system peaked around 234–232 Myr during the Carnian Pluvial Episode, a short-lived period of strongly increased precipitation. We present a section from the Reifling Basin in Austria (Northern Calcareous Alps, central Europe), which formed at that time along the northwestern margin of the Tethys Realm. The record documents a strong modulation of the PMM on millennial and centennial scales over ~215 kyr of early Carnian time. Precessional modulation is expressed in alternations between phases of predominant summer monsoon and phases of strong winter monsoon. Moist landward directed southerlies resulted in increased runoff and strengthened coastalupwelling during summer monsoon. Both mechanisms boosted primary productivity and caused severe bottom water anoxia. Dry northerlies forced downwelling and bottom water ventilation during winter monsoon. Monsoon intensity was also governed by solar cycles. These cycles were not strong enough to initiate downwelling but are expressed by strongly reduced terrestrial input during phases of predominating winter monsoon.