Publication Date:
2024-03-21
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
Type:
Article
,
PeerReviewed
Format:
text
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