Reef Carbonate Productivity During Quaternary Sea Level Oscillations

Abstract

Global variations in reef productivity during the Quaternary depend on external parameters that may alter the global chemical balance in the oceans and atmosphere. We designed a numerical model that simulates reef growth, erosion, and sedimentation on coastlines undergoing sea level oscillations, and uplift or subsidence. We further develop a probabilistic evaluation that accounts for variable vertical ground motion, erosion, and foundation morphologies. Absolute sea level change appears primordial, as productivity must have increased by an order of magnitude since the onset of the glacial cycles, ∼2.6 Ma. But most important is relative sea level change, i.e., eustasy modulated by uplift or subsidence, that rejuvenates the accommodation space and exposes pristine domains of the shore to active reefs at each cycle. Integrated over the long‐term, vertical land motion sets the pace of reef growth: productivity in tectonically unstable domains is thus expected to be up to 10 times higher than in stable regions, if any. We quantify the global length of reef coasts and the probability density functions for slopes and uplift rates. Productivity waxes during transgressions to reach 2–8 Gt CaCO3/yr and wanes during highstands, which may contribute to increase atmospheric pCO2 by several tens of ppm during deglaciations. Over the last 1.5 Ma, reefs precipitated ∼0.8 × 106 Gt CaCO3 (∼500 × 103 km3), the equivalent of a 1 m‐thick layer spread over the entire surface of the Earth. This production modulates the calcium budget, for it represents some 30% of the modern Ca flux in the ocean.

TerraceM-2: A Matlab® Interface for Mapping and Modeling Marine and Lacustrine Terraces

“…The application of LEMs in wave-dominated coastal systems have allowed studying diverse processes shaping the landscape, such as relative sea-level variations, vertical deformation, coral reef growth rates, sediment transport and deposition, cliff retreat and diffusion, eolian transport, and river erosion among others (e.g., Hanks et al, 1984;Anderson et al, 1999;Storms and Swift, 2003;Nakamura and Nakamori, 2007;Refice et al, 2012;Thébaudeau et al, 2013;Kline et al, 2014;Shikakura, 2014;Melnick, 2016;Husson et al, 2018;Limber and Barnard, 2018). The application of LEMs for modeling the development of sequences of coastal terraces sequences can provide valuable chronological information in the absence of terrace ages (e.g., Jara-Muñoz et al, 2017; Bilbao-Lasa et al, 2019).…”

How do sea-level curves influence modeled marine terrace sequences?

“…Usage of the 3-Ma SL curve of Bintanja and Van der Wal (2008) resulted in similar conclusions, highlighting that the~100-ky,~120 m amplitude SL cycles since~1 Ma lead to relatively more cliff erosion (Trenhaile, 2014). Similar tests for coral reef terraces by Husson et al (2018) accentuated that SL noise is an influential factor in reef building, and infrequent, relatively long SL transgressions are important to the geometry of a sequence.…”

“…UR ¼ uplift rate. Profiles are based on Authemayou et al, 2017;Merritts and Bull, 1989;Pedoja et al, 2006Pedoja et al, , 2018Ward, 1988 (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) mechanism driving SL changes (Bloom, 1971).…”

“…The amplitude and period of SL cycles have a distinct influence on the geometry of a modeled marine terrace sequence. Using synthetic SL curves, both Trenhaile (2002) and Husson et al (2018) show that short-period, low amplitude SL oscillations before the MPT result in narrower terraces with smaller paleocliffs, compared to longer-period, higher amplitude SL swings after the MPT. Usage of the 3-Ma SL curve of Bintanja and Van der Wal (2008) resulted in similar conclusions, highlighting that the~100-ky,~120 m amplitude SL cycles since~1 Ma lead to relatively more cliff erosion (Trenhaile, 2014).…”

Subsiding Sundaland: REPLY

“…Sea-level curves are, in principle, more insightful in uplifting regions, for multiple fingerprints (typically, in Southeast Asia, flights of uplifted coral reefs) are often present, at a range of elevations, and can be dated. But even these more-favorable settings are often difficult to interpret in tropical environments, because of the uncertainty of sea-level curves (e.g., Pedoja et al, 2018), but also from the complexity inherent to reef constructions (e.g., Husson et al, 2018). These complexities become even more striking when attempting to interpret the geological record in subsiding or submerged regions, in the absence of radiometric dates ( 14 C, U/Th), offshore morphologies, and quantitative (numerical) models.…”