Earth’s Critical Zone (CZ), the near-surface layer where rock is weathered and landscapes co-evolve with life, is profoundly influenced by the type of underlying bedrock. Previous studies employing the CZ framework have focused almost exclusively on landscapes dominated by silicate rocks. However, carbonate rocks crop out on approximately 15% of Earth’s ice-free continental surface and provide important water resources and ecosystem services to ~1.2 billion people. Unlike silicates, carbonate minerals weather congruently and have high solubilities and rapid dissolution kinetics, enabling the development of large, interconnected pore spaces and preferential flow paths that restructure the CZ. Here we review the state of knowledge of the carbonate CZ, exploring parameters that produce contrasts in the CZ in different carbonate settings and identifying important open questions about carbonate CZ processes. We introduce the concept of a carbonate-silicate CZ spectrum and examine whether current conceptual models of the CZ, such as the conveyor model, can be applied to carbonate landscapes.We argue that, to advance beyond site-specific understanding and develop a more general conceptual framework for the role of carbonates in the CZ, we need integrative studies spanning both the carbonate-silicate spectrum and a range of carbonate settings.

The El Niño Southern Oscillation (ENSO) modulates rainfall amount variability and, by extension, river discharge in the Philippines on seasonal to interannual temporal scales. The El Niño phase (ENP) of ENSO considerably decreases rainfall amounts on a seasonal scale in the western Pacific with varying degrees of heterogeneity expressed across the Philippines. Our understanding of the response in the hydroclimate to ENPs on interannual timescales is still relatively immature. As such, to investigate the hydroclimate response, a composite time series of 29 rainfall and 61 river discharge stations spanning 1901-2020 and 1908-2017 C.E., respectively, and covering the four major climate types in the Philippines were assessed. Our results suggest, regardless of climate type, that river discharge and rainfall data decrease following ENPs. The median response suggests that the decreasing trend can last up to seven years. Further, the hydroclimate response follows either a decreasing trend, if at conception of an ENP, or an increasing trend, if at the termination of an ENP. As water-scarcity becomes an area of immediate concern in an increasingly warming climate, our results have implications for interannual water resource management in this drought-prone tropical archipelago.