Enduring questions remain regarding the transition from relatively warm and stable pre- and early-Pleistocene climate to that of the high amplitude glacial-interglacial cycles later in the Quaternary. The main shift in glacial intensity and periodicity around 1 Ma is known as the Mid Pleistocene Transition (MPT). Here we analyze detrital strontium (Sr) and neodymium (Nd) isotopes in a Western Arctic sediment core P23 previously investigated using several litho/biostratigraphic proxies. Based on an improved age framework combining lithostratigraphic cyclicity and Sr isotope stratigraphy, the P23 record extends to ~3.3 Ma, thus providing a rare insight into the Quaternary Arctic climate change. The distinct pre-MPT P23 record is dominated by Pacific-sourced sediment inputs, with little to no intra-Arctic glacial inputs except for a sandy interval around ~2.5 Ma. A consistent decrease of Nd isotopic values towards North American glacigenic signature started in both the Arctic and Bering Sea at ~1.5 Ma and led to a major threshold shift in P23 proxies at ~0.9 Ma. We argue that this threshold is associated with the first prolonged closure of the Bering Strait for an entire obliquity cycle. This shift marks the expansion of the North American ice sheets to the Arctic margin, with dramatic impacts on depositional and hydrographic environments in the Arctic Ocean. These impacts strengthened in the subsequent glacial intervals indicating further ice-sheet growth, probably fed back by continuing prolonged Bering Strait closures. Potential implications of these Arctic changes for the evolution of North Atlantic circulation require further investigation.