Obliquity forcing of continental aquifers during the late Paleozoic ice age

Groundwater-driven eustasy has been proposed to explain the million-year-scale third-order sea-level fluctuations in greenhouses. However, the contribution of continental groundwater storage to global water cycle during icehouse episodes remains unexplored. Here, we perform cyclostratigraphic analyses and sedimentary noise modelling for three lacustrine sedimentary sequences (i.e., Well Haslam-1 in the Cooper Basin, Well J10025 in the Junggar Basin, and Well LY-F in the Paris Basin) from the late Paleozoic ice age (LPIA), aiming at the reconstruction of high-resolution lake level changes during deep-time icehouse episodes. In addition, we conduct two idealized paleoclimate simulations at ∼290 Ma with obliquity minimum and obliquity maximum by using an Earth system model, CESM1.2.2. Our results show that paleo-lake levels exhibited long-period obliquity (s4-s3) cycles, i.e., groundwater aquifers involved in the global water cycle at the Myr-scale during the late Paleozoic ice age. The paleoclimate simulations show that fluctuations of continental aquifers were in antiphase with the long-period obliquity cycles in the northern hemisphere at middle-high latitudes. Comparatively, the southern hemisphere exhibits overall low continental aquifers at the obliquity minimum. The enhanced poleward flux of moisture at the obliquity minimum drives the expansion of ice sheets and the decline in sea levels, manifested by the loss of groundwater aquifers in the southern hemisphere and recharge of groundwater aquifers in the middle-high latitudes of the northern hemisphere. This study provides the first robust geological and climatic simulation evidence for the involvement of astronomically forced continental aquifers in global water cycle at the Myr-scale during icehouse episodes.