Glacially enhanced incongruent weathering in the Bering Sea recorded by hafnium-neodymium isotopes

Abstract

Glacial-interglacial cycles reorganized weathering regimes, leaving distinct geochemical imprints in marine sediments. Paired Hf-Nd isotopes (epsilon(Hf)-epsilon(Nd)) serve as a sensitive tracer of such variability, yet their behavior in multi-source sedimentary systems remains poorly constrained. To address this, we present a similar to 2.4 Ma epsilon(Hf) record from bulk detrital sediments at IODP Site U1343 in the Bering Sea, integrated with published epsilon(Nd) data. The combined epsilon(Hf)-epsilon(Nd) signatures indicate multiple sediment sources, whose relative contributions are largely insensitive to climate cycles. Deviations of epsilon(Hf) from the Terrestrial Array (Delta epsilon(Hf Terr.)), commonly used to track hydraulic sorting or weathering, show maxima during glacials and minima during interglacials. Comparison with grain size sensitive records indicates that these patterns mainly reflect climate-driven changes in chemical weathering, yet the mean Delta epsilon(Hf Terr.) remains relatively constant, highlighting the limitation of using Delta epsilon(Hf Terr.) alone to capture weathering regime dynamics in multi-source sediments. Applying a Delta epsilon(Hf Terr.)-epsilon(Nd) framework allows us to separate source effects from weathering signals, revealing that selective dissolution of labile minerals (i.e., incongruent weathering) was enhanced during source-area erosion and shelf-mediated modification in glacials. These results underscore the site-dependent nature of climate-weathering coupling in high-latitude marginal seas.