The 4.2 ka event, ENSO, and coral reef development

Abstract

Abstract. Variability of sea-surface temperature related to shifts in the mode of the El Niño–Southern Oscillation (ENSO) has been implicated as a possible forcing mechanism for the global-scale changes in tropical and subtropical precipitation known as the 4.2 ka event. We review records of coral reef development and paleoceanography from the tropical eastern Pacific (TEP) to evaluate the potential impact of the 4.2 ka event on coral reefs. Our goal is to identify the regional climatic and oceanographic drivers of a 2500-year shutdown of vertical reef accretion in the TEP after 4.2 ka. The 2500-year hiatus represents ∼40 % of the Holocene history of reefs in the TEP and appears to have been tied to increased variability of ENSO. When ENSO variability abated approximately 1.7–1.6 ka, coral populations recovered and vertical accretion of reef framework resumed apace. There is some evidence that the 4.2 ka event suppressed coral growth and reef accretion elsewhere in the Pacific Ocean as well. Although the ultimate causality behind the global 4.2 ka event remains elusive, correlations between shifts in ENSO variability and the impacts of the 4.2 ka event suggest that ENSO could have played a role in climatic changes at that time, at least in the tropical and subtropical Pacific. We outline a framework for testing hypotheses of where and under what conditions ENSO may be expected to have impacted coral reef environments around 4.2 ka. Although most studies of the 4.2 ka event have focused on terrestrial environments, we suggest that understanding the event in marine systems may prove to be the key to deciphering its ultimate cause.

Upwelling buffers climate change impacts on coral reefs of the eastern tropical Pacific

“…Climatic variability has been a primary driver of centennial-to millennial-scale ecological change on coral reefs in the ETP (Glynn and Colgan 1992, Toth et al 2012, 2015b, Toth and Aronson 2019. Looking forward, increasing climatic variability will be an important component of climatology under anthropogenic climate change (Kim et al 2014, Cai et al 2018.…”

“…How the dynamics of living coral assemblages respond to climate change over the next years to decades will determine their prospects for continued construction of reef framework. Indeed, the millennial-scale history of reef development in Pacific Panam a demonstrates that intense climatic variability has the potential to stall reef development for thousands of years (Toth et al 2012, 2015b, Toth and Aronson 2019. Upwelling may confer a degree of localized protection on coral assemblages in the face of climate change.…”

How to Deal With Multi-Proxy Data for Paleoenvironmental Reconstructions: Applications to a Holocene Lake Sediment Record From the Tian Shan, Central Asia

“…a BP have been globally documented and identified as the 4.2 ka BP event (Booth et al, 2005;Staubwasser and Weiss, 2006;Walker et al, 2012). The causes and forcing mechanisms behind the 4.2 ka BP event are still not well understood, but potential explanations include, amongst others, a southward shift of the ITCZ (Mayewski et al, 2004), cooler conditions in the North Atlantic (Bond et al, 1997) and a strengthening of the El Niño Southern Oscillation (Walker et al, 2012;Toth and Aronson, 2019). Recently, Perşoiu et al (2019) hypothesized that the cold and arid conditions, which prevailed on the Eurasian landmass during the 4.2 ka BP event, resulted from a strengthening and expansion of the Siberian High, which hindered the transport of moisture by blocking the Westerlies.…”

Possible expression of the 4.2 kyr event in Madagascar and the south-east African monsoon

“…This paper does not mention the 4.2 kyr event once, instead referring to a series of climatic changes around 4.0 kyr event, potentially associated with changing tropical sea-surface temperatures. This 4 kyr BP shift in tropical climate is now widely documented in the literature and likely related to changes in the mean state of ENSO (Denniston et al, 2013;Gagan et al, 2004;Giosan et al, 2018;Li et al, 2018;MacDonald, 2011;Toth and Aronson, 2019). No causal relationship between the 4.0 kyr BP tropical climate shift and the 4.2kyr event has been established.…”