5:15 PM - 6:30 PM
[MIS16-P14] Millennial variability in precipitation in Papua New Guinea during the last deglaciation
Keywords:ITCZ, Bismarck Sea, Last deglaciation
Millennial climate changes during the last deglaciation is attributed to changes in the Atlantic Meridional Overturning Circulation (AMOC). Although the millennial climate changes have been observed worldwide, the mechanism by which the AMOC change is transmitted is not clear. One plausible hypothesis is that the AMOC variability changes the heat balance in the northern and southern hemispheres, which in turn changes the mean position of the Intertropical Convergence Zone (ITCZ), which in turn changes global temperature and precipitation. Indeed, it has been reported that when the AMOC weakened the ITCZ shifted southward in the Atlantic and eastern Pacific regions. However, there is no conclusive evidence in the regions away from the Atlantic Ocean.
In this study, to test this hypothesis, we reconstructed the variability of the ITCZ in the western Pacific Ocean over the past 25,000 years by analyzing GDGT and long-chain fatty acid isotopes in marine sediments from IODP site U1485 in the Bismarck Sea off the northern coast of Papua New Guinea (PNG). In PNG, orogenic precipitation caused by the northwest monsoon increase when the ITCZ is located south of PNG. The detrital matter is delivered via the Sepik and Ramu rivers to the study site. Thus, the study site is ideal to capture ITCZ variability.
The CBT and BIT, which reflect river discharge, were higher during Bølling-Allerød (BA) period and lower in the Younger-dryas (YD) period. Stable hydrogen isotope ratios (δD) of long-chain fatty acid, which reflect atmospheric convective activity (and thus precipitation), were lower in the BA period and higher in the YD period. These results indicate that precipitation in PNG was higher in the BA period and lower in the YD period. This is contrary to the results predicted by the above hypothesis, and suggests that the AMOC weakening did not cause the ITCZ to move southward in the western Pacific.
In this study, to test this hypothesis, we reconstructed the variability of the ITCZ in the western Pacific Ocean over the past 25,000 years by analyzing GDGT and long-chain fatty acid isotopes in marine sediments from IODP site U1485 in the Bismarck Sea off the northern coast of Papua New Guinea (PNG). In PNG, orogenic precipitation caused by the northwest monsoon increase when the ITCZ is located south of PNG. The detrital matter is delivered via the Sepik and Ramu rivers to the study site. Thus, the study site is ideal to capture ITCZ variability.
The CBT and BIT, which reflect river discharge, were higher during Bølling-Allerød (BA) period and lower in the Younger-dryas (YD) period. Stable hydrogen isotope ratios (δD) of long-chain fatty acid, which reflect atmospheric convective activity (and thus precipitation), were lower in the BA period and higher in the YD period. These results indicate that precipitation in PNG was higher in the BA period and lower in the YD period. This is contrary to the results predicted by the above hypothesis, and suggests that the AMOC weakening did not cause the ITCZ to move southward in the western Pacific.