Millennial-scale trends in west Pacific warm pool hydrology since the Last Glacial Maximum

Abstract

Models and palaeoclimate data suggest that the tropical Pacific climate system plays a key part in the mechanisms underlying orbital-scale and abrupt climate change. Atmospheric convection over the western tropical Pacific is a major source of heat and moisture to extratropical regions, and may therefore influence the global climate response to a variety of forcing factors. The response of tropical Pacific convection to changes in global climate boundary conditions, abrupt climate changes and radiative forcing remains uncertain, however. Here we present three absolutely dated oxygen isotope records from stalagmites in northern Borneo that reflect changes in west Pacific warm pool hydrology over the past 27,000 years. Our results suggest that convection over the western tropical Pacific weakened 18,000-20,000 years ago, as tropical Pacific and Antarctic temperatures began to rise during the early stages of deglaciation. Convective activity, as inferred from oxygen isotopes, reached a minimum during Heinrich event 1 (ref. 10), when the Atlantic meridional overturning circulation was weak, pointing to feedbacks between the strength of the overturning circulation and tropical Pacific hydrology. There is no evidence of the Younger Dryas event in the stalagmite records, however, suggesting that different mechanisms operated during these two abrupt deglacial climate events. During the Holocene epoch, convective activity appears to track changes in spring and autumn insolation, highlighting the sensitivity of tropical Pacific convection to external radiative forcing. Together, these findings demonstrate that the tropical Pacific hydrological cycle is sensitive to high-latitude climate processes in both hemispheres, as well as to external radiative forcing, and that it may have a central role in abrupt climate change events.

Forest contraction in north equatorial Southeast Asia during the Last Glacial Period

“…A δ 18 O profile from Mulu cave speleothems, Sarawak, indicates a drier period centered at 13.0 ± 0.2 kyr ago coincident with the Antarctic Cold Reversal, which interrupted an increasing trend in precipitation (34). Such a decrease in rainfall could be responsible for a short phase of forest contraction at this time, as indicated in the guano record.…”

Southern Hemisphere control on Australian monsoon variability during the late deglaciation and Holocene

“…The weakest tropical convection, resulting in dry conditions, characterizes HS1 in Northern Hemisphere SE Asian records 15,16 . In contrast, there is evidence for sustained precipitation in the Flores Sea area during HS1 from speleothem d 18 O (ref.…”

Holocene and Eemian sea surface temperature trends as revealed by alkenone and Mg/Ca paleothermometry

“…Speleothem records from northern Borneo have revealed a mid-Holocene inflexion in precipitation trends with a comparable timing, likely reflecting a close relationship between Borneo precipitation and SST in adjacent seas (Partin et al, 2007). Possible is that alkenonederived SST and speleothem-based precipitation records, owing to concomitant phytoplankton productivity and regional precipitation, are both driven by spring/fall precessional forcing (Partin et al, 2007). This assumption is in line with studies demonstrating the importance of river discharge for seasonal dynamics of primary productivity in the South China Sea (Chen and Chen, 2006).…”