Re-evaluating paleocirculation changes from neodymium isotopes: can calcareous sediments provide a source of neodymium to the global ocean?

Australia's climate, economy, and habitability are strongly tied to the surrounding ocean and the warming, acidification, and deoxygenation associated with climate change present a triple threat. Any one of these changes may be amplified in both magnitude and rate by even small shifts in the strength or location of ocean currents. Accurate prediction of these changes requires our climate models to be informed by proxy records since the range of environmental variability captured by human observation, let along quantified by instrumentation, fails to capture the full spectrum of behavior exhibited by Earth's climate system. Marine neodymium isotope records are one such proxy, considered quasi-conservative and widely used for paleocirculation despite ambiguities in the modern oceanic budget. A sedimentary source has recently been proposed to resolve the budget, indicating non-conservative behavior. Shallow continental margins and non-calcareous sediments have been focused on as regions where the paleocirculation record may be compromised by sediment processes. However, new data from the Tasman Sea suggests that even regions dominated by calcareous sediments experience a significant benthic flux of neodymium. These findings suggest that the use of sedimentary neodymium isotope records as strictly a water mass tracer may not be viable.