Patterns of climate variability in the Western Equatorial Pacific during the Common Era

• Main Author: Esswein, Katherine Lee
• Format: Text
• Language: unknown
• Published: No Publisher Supplied 2012
• Subjects: Pacific; Planktonic foraminifera
• Online Access: https://dx.doi.org/10.7282/t30r9n6n; https://rucore.libraries.rutgers.edu/rutgers-lib/38759/

Paleoclimate records suggest significant multi-centennial climate variability during the past two millennia, the Common Era (CE), despite the apparently small changes in external forcings. Proxy records suggest that the Northern hemisphere (NH) was about 0.8 °C cooler during the Little Ice Age (LIA, 1450-1850 CE) relative to the Medieval Climate Anomaly (MCA 950-1250 CE) and the last century. The majority of these anomaly reconstructions are from terrestrial records in the NH while information from the Indo-Pacific Warm pool (IPWP) are limited. As the latter exert strong influence on atmospheric convection and thus global climate and rainfall studying the climate of IPWP during the CE can help discern natural variability as well as anthropogenically forced alterations. Here I use planktonic foraminifera in rapidly accumulating sediments to reconstruct sea surface temperature (SST) and salinity in the Indonesian Seas to investigate changes in tropical temperature anomalies and monsoon strength throughout the CE. I have studied two sediment cores, one in the northern Makassar Strait, and the other in the Java Sea. The reconstruction of climate parameters is obtained by measuring magnesium/calcium ratios (Mg/Ca) and the oxygen isotopic (δ18O) composition in the tests of a surface dwelling foraminifer, Globigerinoides ruber (sensu stricto). The combined multi and gravity cores exhibit a significant trend in SST from northern to southern Makassar strait, suggesting significant local variability superimposed on the regional and global signals. A compilation of my Makassar Strait records with previously published records shows a 0.60 ± 0.25 °C cooling in the LIA and temperatures about as warm as the reference period (1860-1890 CE) during the MCA which is highly correlated with the NH temperature reconstruction. Model output showing the SST variability with forcing parameters held constant in the same region show ± 0.25 °C unforced variability leaving evidence that the SST variability in the proxy compilation could be externally forced. Paired measurements of Mg/Ca-SST and δ18Ocalicte data are used to derive the δ18Osw, a proxy for salinity which shows more depleted values in sites south of the equator during the LIA, interpreted as fresher conditions. This apparent freshening of the surface water suggests enhanced precipitation associated with the Indonesian boreal winter monsoon.