A 5.3‐Million‐Year History of Monsoonal Precipitation in Northwestern Australia

Abstract

New proxy records from deep‐sea sediment cores from the northwestern continental margin of Western Australian reveal a 5.3 million year (Ma) history of aridity and tropical monsoon activity in northwestern Australia. Following the warm and dry early Pliocene (~5.3 Ma), the northwestern Australian continent experienced a gradual increase in humidity peaking at about 3.8 Ma with higher than present‐day rainfall. Between 3.8 and about 2.8 Ma, climate became progressively more arid with more rainfall variability. Coinciding with the onset of the Northern Hemisphere glaciations and the intensification of the Northern Hemisphere monsoon, aridity continued to increase overall from 2.8 Ma until today, with greater variance in precipitation and an increased frequency of large rainfall events. We associate the observed large‐scale fluctuations in Australian aridity with variations in Indian Ocean sea surface temperatures, which largely control the monsoonal precipitation in northwestern Australia.

Toward a Robust Plio‐Pleistocene Chronostratigraphy for ODP Site 762

“…The authors ascribe the difference to insufficient time resolution at Site 763 (Andrae et al, ) or to the fact that the Site U1463 records (Auer et al, ) do not extend far enough back in time. Finally, Stuut et al () argue that the smoothed wireline K wt.% long‐term Pliocene record at Site U1463 (Christensen et al, ) may be too imprecise to pinpoint this shift.…”

“…This commentary resulted in four significant outcomes: (1) a bundling of all chronostratigraphic constraints currently available for Site 762; (2) an alternative age model that integrates different chronostratigraphic approaches; (3) a demonstration that while precise and of high‐resolution, the Stuut et al () age‐depth model does not allow for unequivocal intersite comparison; and (4) a reminder of the importance of “integrated stratigraphy” for the interpretation of paleoclimatological time series and age‐model verification.…”

“…Site 762 consists of Lower Cretaceous to Holocene sediments. The early Pliocene to recent interval is subject to study in Stuut et al (2019). The authors present a comparison of their ODP Hole 762B proxy record with other records in the eastern Indian Ocean, including sea surface temperature (SST) at ODP Hole 763A (Karas et al, 2011;O'Brien et al, 2014) and natural gamma radiation-based terrigenous influx proxies from International Ocean Discovery Project (IODP) Site U1463 (Christensen et al, 2017).…”

“…Three hypotheses can be formulated why Site 762 and other records in the region diverge: (1) unique local conditions, (2) methodological differences, and (3) differences in age-depth modeling. Below we outline three aspects of the Site 762 age-depth model (Stuut et al, 2019) that potentially contribute to the observed differences:…”

“…In summary, the Stuut et al (2019) age-depth conversion potentially limits the utility of the Hole Site 762B proxy records in regional correlations (Table 1 and Figure 1a). In a next step, we explore to what extent O stack (Lisiecki & Raymo, 2005).…”