The evolution of deep water in the Southwest Pacific Ocean since 30 ka BP

The Southern Ocean (SO) is a key area for global climate. It connects the deep water with the surface through upwelling. The deep SO, storing a large amount of carbon during the glacial period and releasing CO₂ during the deglacial period, is critical for the carbon cycle on orbital-millennial timescales.

In the Southwest Pacific (SWP), there are many reconstructions of deep water, however, these reconstructions primarily rely on carbon and oxygen isotopes, which cannot effectively distinguish the North Pacific Deep Water (NPDW) and the Circumpolar Deep Water (CDW). Neodymium isotopes (ε_Nd) of seawater is dominated by the crustal sources, which is spatial heterogeneous, enabling its wide application as water mass traces. However, the available data in the SWP is not enough to resolve spatial complexity and evolution mechanisms of water masses, especially at the depth of NPDW and UCDW (Upper CDW).

Here, ε_Nd on planktonic foraminifera are used to investigate the evolution of deep-water masses in SWP since 30 ka BP on core MD97-2115 (43° 6' 30" S, 171° 29' 7.8" W, 2160 m water depth), which is located on the east Chatham Rise.

The ε_Nd results show an increase from -4.5 to -3.8 between 30 ka BP and 21 ka BP, followed by a positive shift to -4.7 at 19 ka BP. After 19 ka BP, the values remain relatively stable around -5.

These values agree well with modern NPDW seawater ε_Nd value in Southwest Pacific Basin, ranging from -4 to -5. Comparison with nearby ε_Nd records suggests a persistent influence of NPDW in the eastern Chatham Drift since 30 ka BP. However, the mechanism of the shift around 19 ka BP needs further investigation.