Holocene El Niño–Southern Oscillation variability reflected in subtropical Australian precipitation

Abstract

The La Niña and El Niño phases of the El Niño-Southern Oscillation (ENSO) have major impacts on regional rainfall patterns around the globe, with substantial environmental, societal and economic implications. Long-term perspectives on ENSO behaviour, under changing background conditions, are essential to anticipating how ENSO phases may respond under future climate scenarios. Here, we derive a 7700-year, quantitative precipitation record using carbon isotope ratios from a single species of leaf preserved in lake sediments from subtropical eastern Australia. We find a generally wet (more La Niña-like) mid-Holocene that shifted towards drier and more variable climates after 3200 cal. yr BP, primarily driven by increasing frequency and strength of the El Niño phase. Climate model simulations implicate a progressive orbitally-driven weakening of the Pacific Walker Circulation as contributing to this change. At centennial scales, high rainfall characterised the Little Ice Age (~1450–1850 CE) in subtropical eastern Australia, contrasting with oceanic proxies that suggest El Niño-like conditions prevail during this period. Our data provide a new western Pacific perspective on Holocene ENSO variability and highlight the need to address ENSO reconstruction with a geographically diverse network of sites to characterise how both ENSO, and its impacts, vary in a changing climate.

Centennial-scale precipitation anomalies in the southern Altiplano (18° S) suggest an extratropical driver for the South American summer monsoon during the late Holocene

“…In the tropical Andes (5-13 • S) and the Altiplano (13-22 • S) regions of South America, a set of well-grounded paleoclimate reconstructions have revealed that significant precipitation changes occurred during the most recent millennia (Seltzer et al, 2000;Baker et al, 2005;Giralt et al, 2008;Bird et al, 2011a;Novello et al, 2016), reflecting decadal, centennial, and millennial changes in the mean strength of the South American summer monsoon (SASM). In addition, a composite tree ring chronology from the Altiplano showed that decadal anomalies in SASM-derived precipitation have been strongly modulated by the variability of the El Niño-Southern Oscillation (ENSO) over the last 700 years (Morales et al, 2012).…”

Groundwater mean residence times of a subtropical barrier sand island

“…Although barrier island hydrological systems are reasonable climate indicators, due to substantial variability in their short-and long-term climate patterns, the current understanding of these systems is generally poor, especially with respect to groundwater (Schneider and Kruse, 2003;Barr et al, 2013Barr et al, , 2019. In particular, due to recharge rates and residence times of water not being sufficiently investigated, the extent of connectivity between regional groundwater and perched aquifer systems is commonly not well understood.…”

“…The island is an important part of the coastal environment in south-east Queensland and provides a vital groundwater resource, recreational space for large urban areas and, most importantly, unique coastal ecosystems with many freshwater wetlands, lakes and marine coastal environments . The island also plays a major role in the palaeoclimate reconstructions for the east coast of Australia, as some of the longest sediment records have been extracted from the North Stradbroke Island wetlands (Barr et al, 2013(Barr et al, , 2019Tibby et al, 2016Tibby et al, , 2017. Apart from a small number of government reports (Leach, 2011), there are few studies on the groundwater resources of the island, and, to the best of our knowledge, there is no prior work on MRTs on large Early Quaternary subtropical islands.…”

“…The lower-permeability units of indurated sand, peat or sandrock/humicrete (locally known as coffee rock) as well as clay accumulations from the weathering of the small amounts of feldspar minerals form widely spread perched aquifer systems. The low-permeability layers of the perched systems are believed to originate from chemical leaching of older dune systems in the highlands as well as inclusions of marine muds and peats in the lowlands (Laycock, 1975;Thompson and Ward, 1975;Brooke et al, 2008). Some of the perched aquifers and wetland systems are disconnected from the regional aquifer and their locations; however, their extents and genesis are generally poorly understood, with only a few studies describing the governing processes (Leach, 2011;Barr et al, 2017;Cadd et al, 2018).…”

Groundwater mean residence time of a sub-tropical barrier sand island

“…The island is an important part of the coastal environment in South East Queensland and provides a vital groundwater resource, recreational space for the large urban areas and most importantly unique coastal ecosystems with many freshwater wetlands, lakes and marine coastal environments (Marshall et al, 2011). The island also plays a major role in the paleoclimate reconstructions for the east coast of Australia as some of the longest sediment records have been extracted from North Stradbroke Island wetlands (Barr et al, 2013;Tibby et al, 2016Tibby et al, , 2017Barr et al, 2019). Apart from a small number of government reports (Leach, 2011), there are few studies of the groundwater resource of the island and there is no prior work on residence times.…”