The visible-near infrared (Vis-NIR) electronic absorption spectrum of neptunium(V) (NpO2+) comprises numerous f-f electronic transitions with mostly undocumented temperature dependencies. The effect of temperature on the absorption spectrum of the pentavalent neptunyl dioxocation (NpO2+) is an important factor to consider with spectrophotometric applications but has often been overlooked. Optical Vis-NIR absorption spectra (400–1700 nm) of Np(V) (0.017–0.89 M) in 1 M nitric acid were evaluated with varying temperatures (T = 10–80 °C). The intensity, position, and overall shape of the bands were sensitive to interactions with the solvent and coordination environment. Numerous temperature-induced isosbestic points were identified resulting from dynamic, overlapping peak shifts. Spectral variations were characterized using principal component analysis (PCA) and 2D correlation spectroscopy (COS). 2D-COS revealed that the absorption band near 1095 nm likely consists of two bands centered near 1087 and 1096 nm, which cannot be explained by current computational methods. 2D-COS analysis also provided an unambiguous assignment of unresolved peaks in the visible region for comparison with computational predictions. PCA was used to identify nonlinearity in the spectral response at elevated Np(V) concentrations ≥ 0.5 M. This unique experimental data and interpretation will foster a deeper understanding of the absorption spectra for complex actinyl ions.

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<p>In the context of warming climate and rising sea level, records from the early-to-mid Holocene provide important analogues to investigate how the environment responds to such changes. The Sunda shelf provides favourable conditions to reconstruct past environmental change as the presence of numerous large paleo-valley systems and high sedimentation rates allow transgressive deposits from the early-mid Holocene sea-level rise to accumulate continuously in topographic depressions.  To this end, we analysed the sedimentological, geochemical and micropaleontological characteristics of a sediment core (GRBH03) to investigate early-to-mid Holocene environmental changes in southern Singapore. We constrained the chronology with ten radiocarbon dates that were placed in <em>Bchron </em>age-depth model. Using a multi-proxy approach (e.g., grain size distribution, loss on ignition and XRF core-scanning), supported by benthic foraminifera, three sedimentary units were identified in GRBH03. Sedimentary unit I was found at the base of the core. This unit was characterised by a dark grey sandy silt unit deposited from about 9.0 to 8.9 cal ka BP. Few or no foraminifera were found in this unit, likely due to degradation of organic material. Sedimentary unit II was a blue-grey marine mud that was deposited between 8.8 and 5.8 cal ka BP. Within the marine mud unit, foraminiferal assemblages show a transition to shallow marine environment from about 8.8 to 6.4 cal ka BP as open marine species (e.g., <em>Murrayinella murrayi </em>and <em>Bulimina </em>sp. cf. <em>B. marginata</em>) become more abundant up-core. Subsequently, brackish species such as <em>Muyrrayinella globosa </em>and <em>Ammonia veneta </em>started to dominate mud unit assemblages, reflecting a transition from shallow marine to brackish environments, likely associated with decelerating sea level rise. The marine unit is then overlain by the sedimentary unit III, which is a shelly-silt unit deposited after 5.9 cal ka BP. This unit was mostly barren of foraminifera, which may be attributed to a high-energy marginal marine environment where conditions were unfavourable for foraminiferal preservation. Our study show that changes in sedimentary units and foraminiferal assemblages present in GRBH03 are linked to varying rate of relative sea-level rise during the early-to-mid Holocene. </p>