Glacial-driven sea-level changes in the Late Triassic

Projecting future anthropogenic sea-level rise requires a comprehensive understanding of the mechanistic links between climate and short-term sea-level changes under a warming climate. Two different hypotheses, glacioeustasy and groundwater aquifer eustasy, have been proposed to explain short-term, high amplitude sea-level oscillations during past greenhouse intervals. However, the aquifer eustasy hypothesis – supported by subjective evidence of sequence stratigraphy in the Late Triassic greenhouse, has never been rigorously tested. Here we test these competing hypotheses using a recently proposed, objective approach of sedimentary noise modeling for both sea- and lake-level reconstructions for the first time. Sedimentation rate estimates and astronomical calibration of multiple paleoclimate proxies from the lacustrine Newark Basin and the marine Austrian Alps enable the construction of a highly resolved astronomical time scale for the Late Triassic. Using this timescale, sedimentary noise modeling for both lacustrine and marine successions is carried out through the Late Triassic. Lake level fluctuations reconstructed by sedimentary noise modeling and principal component analysis revealed that million-year scale lake-level variations were linked to astronomical forcing with periods of ~3.3 Myr, ~1.8 Myr, and ~1.2 Myr. Our objective water-depth reconstructions demonstrate that lake-level variations in the Newark Basin correlate with sea-level changes in the Austrian Alps, rejecting the aquifer eustasy hypothesis and supporting glacioeustasy as the sea-level driver for the Late Triassic. This study thus emphasizes the importance of high-resolution, objective reconstruction of sea- and lake-levels and supports the hypothesis that fluctuations in continental ice mass drove sea-level changes during the Late Triassic greenhouse.