10 Be in late deglacial climate simulated by ECHAM5-HAM - Part 2: Isolating the solar signal from 10 Be deposition

• Published in: Climate of the Past
• Main Authors: Heikkila, U, Shi, X, Phipps, SJ, Smith, AM
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus GmbH 2014
• Subjects: Earth Sciences; Physical Geography and Environmental Geoscience; Palaeoclimatology; Greenland; Law Dome; GRIP; Sea ice
• Online Access: https://doi.org/10.5194/cp-10-687-2014; http://ecite.utas.edu.au/104732

This study investigates the effect of deglacial climate on the deposition ofthe solar proxy 10 Be globally, and at two specific locations, the GRIPsite at Summit, Central Greenland, and the Law Dome site in coastalAntarctica. The deglacial climate is represented by three 30 year time slicesimulations of 10 000 BP (years before present = 1950 CE), 11 000 and12 000 BP, compared with a preindustrial control simulation. The model usedis the ECHAM5-HAM atmospheric aerosolclimate model, driven with sea-surfacetemperatures and sea ice cover simulated using the CSIRO Mk3L coupled climatesystem model. The focus is on isolating the 10 Be production signal,driven by solar variability, from the weather- or climate-driven noise in the 10 Be deposition flux during different stages of climate. The productionsignal varies at lower frequencies, dominated by the 11 year solar cyclewithin the 30 year timescale of these experiments. The climatic noise is ofhigher frequencies than 11 years during the 30 year period studied. Wefirst apply empirical orthogonal function (EOF) analysis to global 10 Bedeposition on the annual scale and find that the first principal component,consisting of the spatial pattern of mean 10 Be deposition and thetemporally varying solar signal, explains 64% of the variability. Thefollowing principal components are closely related to those of precipitation.Then, we apply ensemble empirical decomposition (EEMD) analysis to the timeseries of 10 Be deposition at GRIP and at Law Dome, which is an effectivemethod for adaptively decomposing the time series into different frequencycomponents. The low-frequency components and the long-term trend representproduction and have reduced noise compared to the entire frequency spectrumof the deposition. The high-frequency components represent climate-drivennoise related to the seasonal cycle of e.g. precipitation and are closelyconnected to high frequencies of precipitation. These results firstly showthat the 10 Be atmospheric production signal is preserved in thedeposition flux to surface even during climates very different from today'sboth in global data and at two specific locations. Secondly, noise can beeffectively reduced from 10 Be deposition data by simply applying the EOFanalysis in the case of a reasonably large number of available data sets, orby decomposing the individual data sets to filter out high-frequency fluctuations.