North American glaciations and Pacific inputs in the Nd and Sr isotope
Pleistocene record from the western Arctic Ocean
Abstract
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.