ALBERT

Description: Due to their large heat and moisture storage capabilities, the tropics are fundamental in modulating both regional and global climate. Furthermore, their thermal response during past extreme warming periods, such as super interglacials, is not fully resolved. In this regard, we present high-resolution (analytical) foraminiferal geochemical (δ18O and Mg/Ca) records for the last 1800 kyr from the shallow (487 m) Inner Sea drift deposits of the Maldives archipelago in the equatorial Indian Ocean. Considering the diagenetic susceptibility of these proxies, in carbonate-rich environments, we assess the integrity of a suite of commonly used planktonic and benthic foraminifera geochemical datasets (Globigerinoides ruber (white), Globigerinita glutinata (with bulla), Pulleniatina obliquiloculata (with cortex) and Cibicides mabahethi) and their use for future paleoceanographic reconstructions. Using a combination of spot Secondary Ion Mass Spectrometer, Electron Probe Micro-Analyzer and Scanning Electron Microscope image data, it is evident that authigenic overgrowths are present on both the external and internal test (shell) surfaces, yet the degree down-core as well as the associated bias is shown to be variable across the investigated species and proxies. Given the elevated authigenic overgrowth Mg/Ca (∼12–22 mmol/mol) and δ18O values (closer to the benthic isotopic compositions) the whole-test planktonic G. ruber (w) geochemical records are notably impacted beyond ∼627.4 ka (24.7 mcd). Yet, considering the setting (i.e. bottom water location) for overgrowth formation, the benthic foraminifera δ18O record is markedly less impacted with only minor diagenetic bias beyond ∼790.0 ka (28.7 mcd). Even though only the top of the G. ruber (w) and C. mabahethi records (whole-test data) would be suitable for paleo-reconstructions of absolute values (i.e. sea surface temperature, salinity, seawater δ18O), the long-term cycles, while dampened, appear to be preserved. Furthermore, planktonic species with thicker-tests (i.e. P. obliquiloculata (w/c)) might be better suited, in comparison to thinner-test counter-parts (i.e. G. glutinata (w/b), G. ruber (w)), for traditional whole-test geochemical studies in shallow, carbonate-rich environments. A thicker test equates to a smaller overall bias from the authigenic overgrowth. Overall, if the diagenetic impact is constrained, as done in this study, these types of diagenetically altered geochemical records can still significantly contribute to studies relating to past tropical seawater temperatures, latitudinal scale ocean current shifts and South Asian Monsoon dynamics

Description: The Maldivian archipelago, in the equatorial Indian Ocean, provides a unique location to assess long‐term basin‐wide South Asian Monsoon (SAM) processes as well as its response during climatic extremes. This insight is beneficial to better understand future SAM influences on the Maldives Inner Sea physicochemical characteristics and its diverse tropical ecosystems in a warming world. This study uses samples from International Ocean Discovery Program Expedition 359, drilled within the Inner Sea drift deposits. Multiple foraminiferal species ( n = 15) and proxies (δ 18 O, δ 13 C, and Mg/Ca) are used to assess glacial‐interglacial SAM dynamics influencing the Inner Sea conditions across Marine Isotope Stages (MIS) 1–2 and 10–13. The summer SAM is modulated by insolation and atmospheric CO 2 and has a predominant impact on the northern Indian Ocean surface salinity. As with present‐day observations, a strong summer monsoon resulted in large basin‐wide δ 18 O sw (salinity) gradients during the interglacials. Moreover, at the MIS11 minimum (MIS11c), a recognized analog for the present‐day, sea surface temperatures (SSTs) were warmer than the present with a stronger summer SAM. This led to an expanded surface mixed layer and strong thermocline, resulting in a highly stratified water column and prominent oxygen minimum zone in the Inner Sea during MIS11c. SSTs in the Maldives are projected to increase at the end of this century and based on the reality that current warming (anthropogenically driven) is much faster than seen during MIS11, the Maldivian tropical coral reef and benthic shoal ecosystems will be subject to increasing stress.