Northern Borneo stalagmite records reveal West Pacific hydroclimate across MIS 5 and 6

- N. Borneo rainfall response to glacial conditions differs from regional SST response.
- Mulu δO18 has a significant 23 ky signal in phase with boreal fall insolation.
- Terminations 1-5 are marked by extreme δO18 enrichments in Mulu stalagmite records.
- N. Borneo convection responds to combined NH and SH forcing across deglaciations.

Over the past decades, tropical stalagmite δO18 records have provided valuable insight on glacial and interglacial hydrological variability and its relationship to a variety of natural climate forcings. The transition out of the penultimate glaciation (MIS 6) represents an important target for tropical hydroclimate reconstructions, yet relatively few such reconstructions resolve this transition. Particularly, comparisons between Termination 1 and 2 provide critical insight on the extent and influence of proposed climate mechanisms determined from paleorecords and model experiments spanning the recent deglaciation. Here we present a new compilation of western tropical Pacific hydrology spanning 0-160 ky BP, constructed from eleven different U/Th-dated stalagmite δO18 records from Gunung Mulu National Park in northern Borneo. The reconstruction exhibits significant precessional power in phase with boreal fall insolation strength over the 0-160 ky BP period, identifying precessional insolation forcing as the dominant driver of hydroclimate variability in northern Borneo on orbital timescales. A comparison with a network of paleoclimate records from the circum-Pacific suggests the insolation sensitivity may arise from changes in the Walker circulation system. Distinct millennial-scale increases in stalagmite δO18, indicative of reduced regional convection, occur within glacial terminations and may reflect a response to shifts in inter-hemispheric temperature gradients. Our results imply that hydroclimate in this region is sensitive to external forcing, with a response dominated by large-scale temperature gradients.