Warm, not cold temperatures contributed to a Late Miocene reef decline in the Coral Sea

Abstract

Evidence shows that in the modern ocean, coral reefs are disappearing, and these losses are tied to climate change. However, research also shows that coral reefs can adapt rapidly to changing conditions leading some researchers to suggest that some reef systems will survive future climate change through adaptation. It is known that there were changes in the area covered by coral reefs in the past. Therefore, it is important to investigate the long-term response of coral reefs to environmental changes and high sea-surface temperatures (SSTs). However, because of diagenetic issues with SST proxies in neritic, metastable carbonate-rich environments, there is an incomplete and sometimes even incorrect understanding of how changes in SSTs affect carbonate reef systems. A good example is the Queensland Plateau offshore northeast Australia next to the threatened Great Barrier Reef. In the Late Miocene, between 11 and 7 Ma, a partial drowning caused the reef area on the Queensland Plateau to decline by ~ 50% leading to a Late Miocene change in platform geometry from a reef rimmed platform to a carbonate ramp. This reef decline was interpreted to be the result of SSTs at the lower limit of the modern reef growth window (20–18 °C). This article presents a new Late Miocene—ased SST record from the Coral Sea based on the TEX86H molecular paleothermometer, challenging this long held view. Our new record indicates warm tropical SSTs (27–32 °C) at the upper end of the modern reef growth window. We suggest that the observed temperatures potentially exceeded the optimal calcification temperatures of corals. In combination with a low aragonite supersaturation in the ocean, this could have reduced coral growth rates and ultimately lowered the aggradation potential of the reef system. These sub-optimal growth rates could have made the coral reefs more susceptible to other stressors, such as relative sea-level rise and/or changes in currents leading to reef drowning. Given that these changes affected coral reefs that were likely adapted to high temperature/low aragonite saturation conditions suggests that reefs that have adapted to non-ideal conditions may still be susceptible to future climate changes due to the interaction of multiple stressors associated with climate change.

Comment on cp-2024-28

“…Ma (Petrick et al, 2023). The data both for this study and the previous Petrick et al (2023) study is found as supplemental data 1.…”

“…Ma (Petrick et al, 2023). The data both for this study and the previous Petrick et al (2023) study is found as supplemental data 1. The Methane Index (MI) excludes any data affected by gas-hydrate-related anaerobic oxidation of methane (Zhang et 125 al., 2011).…”

“…For this study, we follow the age model of Petrick et al (2023), which updated the original shipboard (Davies et al, 150 1991) and previously published age model (Isern et al, 1996(Isern et al, , 1993 for the entire ODP Site 811 record. A part of the record presented in this study (6-12 Ma) was previously published in Petrick et al (2023) (Fig. 2).…”

“…Most coral reefs that are present in the Coral Sea today are thought to have first developed during the Late Pliocene/Early Pleistocene (Droxler et al, 1993), while the Great Barrier Reef appears to have developed even later during the Mid Pleistocene (Dubois et al, 2008). However, research has shown that across the Central Indo-Pacific, including the 60 Coral Sea, more extensive coral reefs prevailed during the Mid-Miocene (Santodomingo et al, 2016;Harrison et al, 2023;Davies et al, 1989;Petrick et al, 2023;Renema et al, 2008). However, during the Late Miocene, most of these systems seemed to have collapsed (Isern et al, 1996), leading to what has been described as the "Pliocene Reef Gap" (Harrison et al, 2023;Isern et al, 1996) (Fig.…”

“…It was recently suggested that multiple stressors, including climate, might have led to coral reef collapse on the Queensland Plateau during the Late Miocene (Petrick et al, 2023). There is, however, a dearth of data to understand the 80 factors that led to the Pliocene reef gap because many SST records for the Central Indo-Pacific have not covered the LMC and early Pliocene.…”