Tidal dynamics and mangrove carbon sequestration during the Oligo–Miocene in the South China Sea

Modern mangroves are among the most carbon-rich biomes on Earth, but their long-term (≥106 yr) impact on the global carbon cycle is unknown. The extent, productivity and preservation of mangroves are controlled by the interplay of tectonics, global sea level and sedimentation, including tide, wave and fluvial processes. The impact of these processes on mangrove-bearing successions in the Oligo–Miocene of the South China Sea (SCS) is evaluated herein. Palaeogeographic reconstructions, palaeotidal modelling, and facies analysis suggest that elevated tidal range and bed shear stress optimised mangrove development along tide-influenced tropical coastlines. Preservation of mangrove organic carbon (OC) was promoted by high tectonic subsidence and fluvial sediment supply. Lithospheric storage of OC in peripheral SCS basins potentially exceeded 4000 Gt (equivalent to 2000 ppm of atmospheric CO2). These results highlight the crucial impact of tectonic and oceanographic processes on mangrove OC sequestration within the global carbon cycle on geological timescales

The study of atmospheric ice-nucleating particles via microfluidically generated droplets

Ice-nucleating particles (INPs) play a significant role in the climate and hydrological cycle by triggering ice formation in supercooled clouds, thereby causing precipitation and affecting cloud lifetimes and their radiative properties. However, despite their importance, INP often comprise only 1 in 10³–10⁶ ambient particles, making it difficult to ascertain and predict their type, source, and concentration. The typical techniques for quantifying INP concentrations tend to be highly labour-intensive, suffer from poor time resolution, or are limited in sensitivity to low concentrations. Here, we present the application of microfluidic devices to the study of atmospheric INPs via the simple and rapid production of monodisperse droplets and their subsequent freezing on a cold stage. This device offers the potential for the testing of INP concentrations in aqueous samples with high sensitivity and high counting statistics. Various INPs were tested for validation of the platform, including mineral dust and biological species, with results compared to literature values. We also describe a methodology for sampling atmospheric aerosol in a manner that minimises sampling biases and which is compatible with the microfluidic device. We present results for INP concentrations in air sampled during two field campaigns: (1) from a rural location in the UK and (2) during the UK’s annual Bonfire Night festival. These initial results will provide a route for deployment of the microfluidic platform for the study and quantification of INPs in upcoming field campaigns around the globe, while providing a benchmark for future lab-on-a-chip-based INP studies

Mixed process, humid-tropical, shoreline-shelf deposition and preservation: middle Miocene-modern Baram Delta Province, Northwest Borneo

This evaluation of the Miocene–Modern Baram Delta Province (BDP) depositional system provides: (1) a rare case study of outcrop observations that can be directly compared with a closely comparable and geographically adjacent modern analogue; (2) new insights into how deposition and preservation occur across a range of process regimes in a highly aggradational tectono-stratigraphic setting; and (3) an example of a well-exposed mixed-influenced shoreline–shelf depositional system, displaying variable interaction of fluvial, wave, and tidal processes. The exceptionally close relationship between the present-day BDP source-to-sink system and its ancient (Miocene–Pliocene) counterpart is because the climatic (humid-tropical, ever-wet, monsoon-influenced), tectonic (active foreland margin), hydrological (multiple, relatively short rivers), and gross depositional (shoreline–shelf) settings have remained consistent over the past c. 15–20 Myr. This study compares exposure-based analyses of facies and stratigraphic architecture in the middle Miocene Belait Formation (eastern BDP) with process-based geomorphological and sedimentological analyses of coastal–deltaic depositional environments in the present-day BDP. The Belait Formation comprises three distinct types of vertical facies-succession sets: (1) aggradationally-stacked, upward-sanding units (10–50 m thick), dominated by erosionally based sandstone beds showing swaly cross-stratification and gutter casts, record deposition during simultaneously high storm-wave energy and storm-enhanced fluvial discharge (“storm floods”); these are interpreted as analogs for deposits along the present-day open coastline in the BDP (e.g., the present-day, open-shelf Baram delta and flanking strandplain); (2) aggradationally stacked, heterolithic, upward-sanding units characterized by interbedded swaly cross-stratified sandstone and combined-flow-rippled heterolithics, record deposition by time-varying storm and storm-flood processes under relatively high fluvial influence; these compare favorably with deposits along the present-day low-wave-energy, embayed deltaic coastlines in the BDP (e.g., Trusan delta and other bayhead deltas in eastern Brunei Bay); (3) heterogeneous successions comprising heterolithic, variably bioturbated and carbonaceous-rich, mudstone-dominated and muddier- to sandier-upwards units, document highly variable mixed-process deposition; these are similar to the present-day fluvio-tidal deposits along embayed deltaic coastlines in the BDP (e.g., northern Brunei Bay and Inner Brunei Bay in the southwest). The principal controls on large-scale (100–1000s m) ancient stratigraphic architecture and changes in process regime in the BDP were: (1) sediment-supply variation along the multiple river-sourced coastal plain, mainly caused by tectonically driven drainage-basin switching, and (2) formation of tectonically controlled embayments