Funds are provided for the PIs to reconstruct thermocline hydrography in the Western Pacific Warm Pool/Indonesian Seas spanning the lat 2000 years of the late Holocene. The existing sediment cores have high sedimentation rates and the proxy records can be compared to the instrumental record. The proposed work will involve stable-isotopic anlayses and Mg/Ca ratios on planktic foraminifera as well as benthic foraminifera H. balthica, for which the study will refine the existing Mg/Ca-temperature calibration. In addition, a Cd/Ca calibration for this benthic species will be established. The study, if it is able to better characterize the upper-ocean hydrography in the Indonesian Seas will lead to a greater understanding of late Holocene climate change in the Western Pacific warm pool. The work is considered to have a modest risk but a high return, if it succeeds in its objectives. Broader impacts include support of a female graduate student who will conduct 300 Mg/Ca analyses. Part time undergraduate student support is also included at SUNY Albany for basic lab tasks. Understanding of the long-term ENSO dynamics would be important for other workers and modelers alike.
Historical and proxy records from the Northern hemisphere document significant centennial climate variability during the past two millennia (aka the Common Era; CE), which at times had major implications for human populations and cultural evolution. For example, ~0.8°C cooler than present temperature during the Little Ice Age (LIA, 1450-1850 CE) is associated with adverse effects on northern European societies e.g., the abandonment of Viking colonies in Southern Greenland. In contrast, northern hemisphere climate was as warm as or warmer than the early 20th Century during the Medieval Warm Period (MWP 950-1250 CE). Such large natural variability in the pre-industrial period is surprising, given only small changes in external forcing (e.g., solar variability, volcanic activity). However, while we now have a large body of evidence to document these anomalies in the northern hemisphere, the global extent and magnitude elsewhere is not well constrained. In this project we have assessed surface and subsurface (0-1000 m water depth) temperature variability in the western Pacific warm pool during the Common Era (WPWP). Our records overlap the instrumental record of the past century from this region thus providing a rigorous text for the proxies fidelity. Given that the WPWP is the largest heat reservoir on the planet, sea surface and sub-surface temperature records from this region may be more representative of global climate change as they integrate seasonal and interannual variability. In this project we use the trace metal (Mg/Ca) and isotopic composition of the calcitic shells of foraminifera, unicellular marine organisms, to reconstruct seawater temperatures in the past. We use planktonic and benthic foraminifera species from cores collected in rapidly accumulating sediments in the Indonesian Seaways to reconstruct multi-decadal to centennial temperature history of surface, thermocline and intermediate depth water masses in the WPWP. Whereas the surface records largely reflect the regional climate, the subsurface records are linked to climate variability in mid-to-high latitudes where these water masses originate. A compilation of down-core sea surface temperature (SST) records from Makassar Strait (Indonesia), extending the CE, suggests a 0.60 ± 0.25 °C cooling during the LIA followed by ~1.0 °C warming to the present. The latter estimate is consistent with tropical coral records for the past 150 years. SST in this region was about as warm as the reference period (1860-1890 CE) for the Medieval Climate Anomaly (MCA, 900-1250 CE). This result is highly correlated to the NH temperature reconstruction (aka Mann’s "Hockey Stick") suggesting the trend is more global in scope. Bottom water temperature records at intermediate depths (450-600m) closely follow the pattern observed in the overlying surface. Within error, the LIA cooling observed at this depth interval in Indonesia is comparable to the cooling we see at the surface. The anomalies are not as significant in deeper waters (>600 m). Model simulation with forcing parameters held constant at preindustrial levels shows only ± 0.25 °C variability at the proxy-records location thereby suggesting that the observed SST variability in the proxy compilation is externally forced. Combined, our records suggest a substantial perturbation of the earth energy budget during and following the LIA, which seems at odds with the small known perturbations in radiative forcing. It thus calls for internal dynamic processes to amplify and propagate these small perturbations into substantial climate variability.
