Termination 1 Millennial‐Scale Rainfall Events Over the Sunda Shelf

• Published in: Geophysical research letters Vol. 49; no. 5
• Main Authors: Buckingham, F. L., Carolin, S. A., Partin, J. W., Adkins, J. F., Cobb, K. M., Day, C. C., Ding, Q., He, C., Liu, Z., Otto‐Bliesner, B., Roberts, W. H. G., Lejau, S., Malang, J.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.03.2022
• Subjects: Anticyclones; Circulation; Climate; Climate change; Climate models; Convection; Convergence zones; Deglaciation; El Nino; El Nino events; El Nino phenomena; Global climate; Ice ages; indo‐pacific warm pool; Intertropical convergence zone; Meltwater; Meridional overturning circulation; model data comparison; Modelling; Ocean circulation; Ocean currents; Oceans; Oxygen; Oxygen isotopes; Paleoclimate; Rain; Rainfall; Rainfall simulators; speleothem; stable isotopes; termination 1; Tropical climate; Tropical convection; Water circulation; Winter; Younger Dryas; United States > US; Borneo; Atlantic Ocean
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL096937

Recent paleoclimate reconstructions have suggested millennial‐scale variability in the Indo‐Pacific Warm Pool region coincident with events of the last deglaciation. Here, we present a new stalagmite oxygen isotope record from northern Borneo, which today is located near the center of the region's mean annual intertropical convergence zone. The record spans the full deglaciation, and reveals for the first time distinct oxygen isotope variations at this location connected with the Bølling‐Allerød onset and the Younger Dryas event. The full deglaciation in the Borneo stalagmite proxy reconstruction appears remarkably similar to a 20–11 ka transient simulation of rainfall over the area produced using the isotope‐enabled Community Earth System Model. In this model, periods of weakened Atlantic Ocean meridional overturning circulation are associated with an anomalous Western North Pacific anticyclone, which is produced in boreal autumn and shifts south over Borneo during boreal winter, causing dry conditions. Plain Language Summary Here, we aim to resolve conflicting evidence of how tropical convection in Borneo in the Indo‐Pacific oceanic region, a critical region associated with El Niño events and the Asian and Australian‐Indonesian monsoon systems, was affected by past changes in the strength of Atlantic Ocean circulation. Analyzing a 20,000+ year old Borneo cave stalagmite along its growth axis, we find large oxygen isotope shifts coincident with two prominent millennial‐scale periods of reduced Atlantic Ocean overturning circulation strength. The isotope record is similar to a neighboring southwestern Philippine stalagmite record, and we interpret the signal as drier mean annual conditions over the region during these events compared to the background state; an interpretation supported by simulations in three independent state‐of‐the‐art climate models. One model suggests that these conditions in Borneo were driven by the southward shift of an anomalous anticyclone in the boreal winter season. By combining geochemical and model evidence, this study has shown that rainfall decreased for millennial periods during the end of the ice age, when the Atlantic Ocean overturning circulation weakened. In doing so, we have elucidated further how this region responds to major changes in global climate and ocean conditions. Key Points A new stalagmite record reveals for the first time distinct Bølling‐Allerød and Younger Dryas oxygen isotope variations in northern Borneo The stalagmite oxygen isotope pattern strongly resembles the recent iCESM transient annual rainfall simulation from 20 to 11 ka Borneo drying during Heinrich 1 and the Younger Dryas may be attributed to an anomalous boreal winter Western North Pacific anticyclone