Reef core insights into mid‐Holocene water temperatures of the southern Great Barrier Reef. (18th October 2016)

• Record Type: Journal Article
• Authors: Sadler, James; Webb, Gregory E.; Leonard, Nicole D.; Nothdurft, Luke D.; Clark, Tara R.
• Is Part Of: Paleoceanography. Volume 31:Number 10(2016)
• Page Start: 1395
• Page End: 1408
• Publication Date: 2016-10-18
• Subjects: Sr/Ca -- Porites -- mid‐Holocene water temperatures -- Great Barrier Reef; Paleoceanography -- Periodicals; 551.46
• DOI: 10.1002/2016PA002943
• Languages: English
• ISSNs: 0883-8305

Abstract

Abstract: The tropical and subtropical oceans of the Southern Hemisphere are poorly represented in present‐day climate models, necessitating an increased number of paleoclimate records from this key region to both understand the Earth's climate system and help constrain model simulations. Here we present a site‐specific calibration of live collected massive Porites Sr/Ca records against concomitant in situ instrumental water temperature data from the fore‐reef slope of Heron Reef, southern Great Barrier Reef (GBR). The resultant calibration, and a previously published Acropora calibration from the same site, was applied to subfossil coral material to investigate Holocene water temperatures at Heron Reef. U‐Th‐dated samples of massive Porites suggest cooler water temperatures with reduced seasonal amplitude at ~5.2 ka (2.76–1.31°C cooler than present) and ~7 ka (1.26°C cooler than present) at Heron Reef. These results contrast the previous suggestion of a mid‐Holocene Thermal Maximum in the central GBR around 5.35 ka and 4.48 ka, yet may be explained by differences in temperature of the shallow ponded reef flat (central GBR) and the deeper reef slope waters (this study) and potential large reservoir correction errors associated with early radiocarbon dates. Combining coral‐based water temperature anomaly reconstructions from the tropical and subtropical western Pacific indicates a coherent temperature response across the meridional gradient from Indonesia and Papua New Guinea down to the southern GBR. This similarity in reconstructed temperature anomalies suggests a high probability of an earlier expression of a mid‐Holocene Thermal Maximum on the GBR between ~6.8 and 6.0 ka. Key Points: Expression of the mid‐Holocene Thermal Maximum in the GBR was likely between 6.8 and 6.0 ka, earlier than has been previously suggested The tropical and subtropical southwestern Pacific appears to display a similar magnitude of temperature changes through the mid‐Holocene Rotary coring techniques through the reef flat can provide well‐preserved subfossil coral cores for paleoclimate reconstruction