Regional patterns of hydroclimate variability in southeastern Australia
over the past 1200 years
Abstract
Long, continuous palaeoclimate records provide an opportunity to extend
knowledge of decadal to multi-decadal scale climate variability beyond
the limit of instrumental records. In this study, quality-controlled
proxy records from southeastern Australia are examined for coherent
variability during the Common Era, with age uncertainty for each record
estimated using iterative age modeling. Site-level empirical orthogonal
functions (EOFs) are derived from multivariate records for the purpose
of objective comparison of climate signals between sites without
selection bias. A regional Monte Carlo EOF (MCEOF) analysis is conducted
on combined time-uncertain single-proxy records and site-level EOFs. The
analysis identifies two robust vectors, which are inferred to represent
hydroclimate changes. The first regional MCEOF suggests an increase in
effective moisture between 900 – 1750 CE. Agreement between regional
MCEOF1 and Australian temperature reconstructions suggests suppressed
evaporation was a significant influence on regional effective moisture
during this time. Regional MCEOF2 exhibits shorter, centennial-scale
oscillations that show some similarity with rainfall reconstructions
based on remote high-resolution proxies. We interpret MCEOF2 to
represent regional-scale rainfall patterns driven by changes in seasonal
rainfall and the influence of the Southern Annular Mode over southern
Australian rainfall. This study presents the first quantitative regional
synthesis of southeastern Australian hydroclimate reconstructions from
multivariate sedimentary archives covering the last 1200 years. The
resulting MCEOFs demonstrate the utility of low-resolution climate
records from this region, but also highlight the limitations of the
existing data network, which must be resolved through the generation of
new records.