A New Holocene Lake Sediment Archive from Samoa (Tropical South Pacific) Reveals Millennial Scale Changes in Hydroclimate.

Abstract:

El Niño-Southern Oscillation (ENSO) is the strongest source of interannual climate variability on the planet. Its behaviour leads to major hydro-climate impacts around the world, including flooding, drought, and altering cyclone frequency. Simulating ENSO behaviour is difficult using climate models, as it is a complex non-linear system, and hence predicting its future variability under changing climate is challenging. Using palaeoclimate data thus allows an insight into long-term ENSO behaviour against a range of different forcings throughout the Holocene. To date long, coherent, high resolution records from lake sediment archives have been limited to the Pacific Rim. We present new data from the closed crater Lake Lanoto’o, on Upolu Island, Samoa, located within the tropical South Pacific. The lake sediment record extends back into the early Holocene with an average sedimentation rate 0.4mm a^-1. We demonstrate a strong correspondence between precipitation at the study site and measures of the Southern Oscillation Index (SOI)¹. We compare geochemical proxies of precipitation to a long-term reconstruction of the SOI². The resulting proxy SOI record extends over the last 9000 years, revealing scales of change in ENSO that match those recorded from sites located on the Pacific rim^3,4. A major period of La-Nina dominance occurs around 4.5ka BP before abruptly switching to El-Nino dominance around 3.2ka. Thereafter, phases of El-Nino - La Nina dominance, alternate every c. 400yrs. The results point to prolonged phases of enhanced or reduced precipitation – conditions that may influence future population resilience to climate change, and may also have been triggers for the colonisation of more remote eastern Polynesia.

1. http://www.cgd.ucar.edu/cas/catalog/climind/SOI.signal.annstd.ascii.

2. Yan, H. et al. (2011) Nature Geoscience, 4, p.611.

3. Conroy J. L. et al. (2008) Quaternary Science Reviews, 27, p.1166

4. Moy, C. M. et al. (2002) Nature, 420, p.162