Variability in the tropical ocean-atmospheric system causes global scale climate anomalies, most evident in the El Niño-Southern Oscillation’s coupled climate
feedbacks. Despite being an area of high interest, many questions still remain regarding the west Pacific warm pool’s response to external forcing, particularly its
response to increases in anthropogenic greenhouse gases. Paleoclimate reconstructions coupled with model simulations provide insight into the tropical Pacific’s role
in past climate variability necessary to the development of robust climate projections. Most paleoclimate records, however, still lack the resolution, length, and
chronological control to resolve rapid variability against a background of orbital-scale variations. Here we present stalagmite oxygen isotope (δ18O) reconstructions
from Gunung Mulu National Park (4oN, 115oE ), in northern Borneo, that provide reproducible centennial-scale records of western Pacific hydrologic variability that
are precisely U/Th-dated and continuous throughout most of the late Pleistocene (0-160 thousand years ago, kybp). The record comprises an entire glacial-interglacial
cycle, which allows us to investigate orbital-scale climate forcings and compare two well-dated glacial terminations in the western tropical Pacific. The ice-
volume-corrected δ18O records suggest that glacial boundary condtions, which include significantly lower atmospheric carbon dioxide levels, did not drive significant
changes in Mulu rainfall δ18O. Similarly, Borneo stalagmite δ18O is poorly correlated to either global sea level shifts or Sunda Shelf areal exposure is not evident.
The Borneo record does vary in phase with local mid-fall equatorial insolation, suggesting that precessional forcing may impart a strong influence on hydroclimate
variability in the warm pool. This is best illustrated across Glacial Termination II, when the oscillation of equatorial fall insolation is large and out of phase
with ice sheet decay. We also use a subset of well-dated, high-resolution stalagmite δ18O records from Mulu to investigate millennial-scale climate variability
during Marine Isotope Stages 3-5 (30-100kybp). We find that regional convection likely decreased during the six massive iceberg discharges defined in the North
Atlantic sediment records (“Heinrich events”). The inferred drying (increased stalagmite δ18O) during Heinrich events is consistent with a southward shift of the
Intertropical Convergence Zone – the dominant paradigm to explain global climate anomalies originating in the north Atlantic (ref). However, any hydrologic
variability related to Dansgaad-Oeschgar (D/O) events, millennial-scale sawtooth temperature anomalies of the last glacial period first evident in the Greenland ice
records, is notably absent in the stalagmite records. . The Mulu stalagmite record’s absence of D/O signal, however, is in marked contrast to the regional west
Pacific marine records and suggests D/O events and Heinrich events may be characterized by fundamentally different climate mechanisms and feedbacks.
| Identifer | oai:union.ndltd.org:GATECH/oai:smartech.gatech.edu:1853/52277 |
| Date | 27 August 2014 |
| Creators | Carolin, Stacy Anne |
| Contributors | Cobb, Kim M. |
| Publisher | Georgia Institute of Technology |
| Source Sets | Georgia Tech Electronic Thesis and Dissertation Archive |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
| Format | application/pdf |
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