The first detection of the Madden-Julian Oscillation signal in daily to hourly resolution proxy records derived from a natural archive of Giant Clam Shell (Tridacna spp.)

The Madden-Julian Oscillation (MJO) is the most prominent mode of intraseasonal variability in the tropics which is responsible for much of the observed intraseasonal climate variance not only there but also in higher latitudes. The short time-span of modern instrumental data limits our understanding of the MJO and obtaining MJO information from natural archives could extend this greatly. Here a Giant Clam shell (Tridacna spp.) with a life span about two years (from January 29, 2012 to December 9, 2013) was collected from the northern South China Sea, in the western Pacific. Several daily to hourly resolution biological and geochemical proxy records, including the daily growth rate, hourly Fe/Ca, Sr/Ca and fluorescence intensity, were developed to compare these with local weather/climate records. Spectral analyses suggested that these ultra-high resolution proxy records can clearly record MJO variability in the tropics. The substantial connection between the proxy records and MJO possibly linking through the local effective solar radiation, SST, precipitation and wind speeds. This is the first record of the MJO signal in a natural paleoclimate archive. Our findings provide new insights to study the MJO beyond the instrumental records, and since fossil Tridacna shells from different geological times can be used to investigate the MJO under various climate conditions. (C) 2020 Elsevier B.V. All rights reserved