Sea-level and monsoonal control on the Maldives carbonate platform (Indian Ocean) over the last 1.3 million years

Abstract

Abstract. The Maldives Archipelago (Indian Ocean), composed of two rows of atolls that enclose an inner sea, offers an excellent study site to explore the forcings of carbonate production at platforms. Glacial–interglacial sea-level changes have been claimed to be the main factor controlling the carbonate platform factories; however, climatic factors may also have an impact. In this work we used geochemical compositional records, obtained by X-ray fluorescence (XRF) core-scanning from the International Ocean Discovery Program (IODP) Site U1467 in the Maldives Inner Sea, to analyze the orbitally driven fluctuations on the carbonate production and export from the neritic environment into the Maldives Inner Sea over the last 1.3 million years. High Sr aragonite-rich carbonates (HSAC) from neritic settings were deposited in the Maldives Inner Sea during sea-level highstand intervals, increasing the Sr/Ca values. In contrast, low Sr/Ca values are observed coincident with sea-level lowstand periods, suggesting that large areas of the atolls were exposed or unable to grow, and therefore, there was a demise in the carbonate production and sediment export to the Maldives Inner Sea. However, comparison of the Sr/Ca values and the sea-level reconstructions for different interglacial periods before and after the mid-Brunhes event (MBE, ∼ 430 ka) indicates that sea level is not the only factor controlling the production of HSAC during sea-level highstands. The study of monsoon and primary productivity proxies (Fe-normalized, Fe/K, and Br-normalized records) from the same site suggests that the intensity of the summer monsoon and the Indian Ocean dipole probably modulated the carbonate production at the atolls. Moreover, Marine Isotope Stage 11 stands out as a period with high sea level and extraordinary carbonate production in the Maldives platform. This outstanding carbonate production in the Maldives atolls (and in other low-latitude carbonate platforms) probably contributed to the mid-Brunhes dissolution event through a strong shelf-to-basin fractionation of carbonate deposition.

Changes in mesophotic carbonate‐platform export across the end of the last glacial cycle (Saya de Malha Bank, western Indian Ocean)

“…Consequently, these two intervals likely mark the low sea-level state (lowstand). In core GC59, this assumption matches the Sr/Ca trend, which in the Indian Ocean has been shown to correlate with sea level (Alonso-Garcia et al, 2024;Bialik, Reolid, et al, 2020;Counts et al, 2019). The record in core GC63 is likely younger than 20 kyr BP (see correlation and ages in Figure 6).…”

“…Export of HSA and HMC has been demonstrated in many modern active carbonate platforms with a wide active euphotic production area (Alonso-Garcia et al, 2024;Counts et al, 2019;Dunbar & Dickens, 2003;Eberli et al, 1997;Lantzsch et al, 2007;Rendle et al, 2000;Slowey et al, 2002). But less is known about this response on the margins of drowned platforms, that is, carbonate platforms with a top located predominately below the euphotic depth.…”