Copper isotope evidence of particulate shuttle dynamics in the Late Pennsylvanian North American Midcontinent Sea, with implications for glacio-eustatic magnitude

•Copper (Cu) isotopes provide new insights into watermass dynamics of NAMS seaway.•Authigenic δ65Cu was controlled neither by redox conditions nor freshwater Cu input.•High δ65Cuauth linked to low Sr/Ba (greater FW influx) and high Mo/U (Fe-Mn cycling)•Fe-Mn cycling triggered by freshwater influx due to sea-level drop or humid climate.•Fe-Mn shuttle controlled δ65Cuauth by fractionation during Cu adsorption onto particulates.