Abstract
Glacioeustacy, the waxing and waning of continental ice volume altering global sea level, tracks major climatic changes on Earth. Glacioeustatic magnitudes are typically constrained by oxygen isotopes, but this proxy may be confounded by local variations in seawater oxygen isotopic composition. Here we show freshwater influx to the Midcontinent Sea during the late Paleozoic Ice Age (LPIA) lowered the local seawater oxygen isotopic composition. Conodont oxygen and strontium isotope records from the Swope cyclothem of Kansas City, Missouri, USA, reveal episodic influxes of freshwater to the Midcontinent Sea during the Pennsylvanian. Organic matter C:N and carbon isotopes confirm these findings. Organic matter nitrogen isotopes suggest these freshwater influxes were associated with denitrification, likely caused by suboxic conditions. These freshwater influx events possibly resulted from increased tropical precipitation. The geochemical measurements inform an inverse model used to constrain the magnitude of the freshwater influx. The freshwater influx estimates, an approximated glacial to interglacial temperature curve, and published values for freshwater oxygen isotopic composition are used to isolate Midcontinent seawater oxygen isotopic composition. The resulting range suggests glacioeustatic magnitudes of 100 to 108 m during the Pennsylvanian. Multi-parameter geochemical analysis and inverse modeling thus enable separation of the influence of local precipitation and global glaciation.