Tropical Sand Cays as Natural Paleocyclone Archives

Abstract

Sand cays are valuable paleo‐archives that can significantly increase our understanding of Holocene tropical cyclone variability. Here we conducted detailed sedimentological and chronological analyses from a 195‐cm‐depth pit excavated on Guangjin Island (northern South China Sea), a cay influenced by frequent tropical cyclones. Radiometric dating of multiple deposits revealed that foraminifera, soft coral spicules, and gastropod shells yielded variable age distributions, while U/Th ages of pristine Acropora branches provided a clear record of deposition and cay formation. Based on this robust chronostratigraphy, the proportions of >2‐mm grain size fraction within the deposits corresponded with the frequency of paleotyphoons recorded by historical records in recent centuries. U/Th ages (CE 1687 ± 12, CE 1735 ± 6, and CE 1813 ± 5) of Acropora branches from the deposits matched with three known historical typhoon events. Our results highlight the potential of cyclone‐deposited sand cays as new archives for recording paleocyclones.

Increased typhoon activity in the Pacific deep tropics driven by Little Ice Age circulation changes

“…The presence of older, reworked material is common in carbonate environments, but is generally apparent as a wide distribution of inorganic carbonate dates at many depths, with no obvious trend in mean age with depth (e.g. Chen et al 64 ). In contrast, our inorganic carbonate dates lie close to a line of nearly constant slope, which would be improbable if they were reworked material.…”

Wave-driven geomorphology of Pacific carbonate coastlines: from landscape to wavelength scale

“…The presence of older, reworked material is common in carbonate environments, but is generally apparent as a wide distribution of inorganic carbonate dates at many depths, with no obvious trend in mean age with depth (e.g. Chen et al, 2019). In contrast, our inorganic carbonate dates lie close to a line of nearly constant slope, which would be improbable if they were reworked material.…”

Coral reef resilience persisted for a millennium but has declined rapidly in recent decades

“…In 2017, three cores (DM-1, collected from Dongmen Atoll; MJ-1 and MJ-2, collected from Meiji Atoll) were collected on the seaward margins (top of the front reef-slopes) of the two atolls (Figure 3), where the reef surfaces are always submerged, even during low tides, except for several large Porites blocks. Reef margins are ideal sites for coring because (1) fossil assemblages in cores can reflect the composition of the original coral assemblage of reef slopes (the main coral growing sites of an atoll) to the greatest extent; (2) reef flats and cays, in contrast, are largely composed of reworked and transported coral materials (e.g., Chen et al, 2019).…”

“…The northern South China Sea is among the most active areas of tropical cyclone activity globally (Chen et al, 2019). Although to a lesser extent than the reefs in the northern South China Sea, the southern Nansha atolls are still sporadically exposed to tropical cyclones (Figure 7A) that can transport coarse calcareous sand, coral rubble, and even large coral blocks from windward reef slopes to leeward reef flats and lagoons (Yu et al, 2009).…”