Understanding groundwater recharge is a key challenge for arid and semi-arid regions as water stress and population growth increases in the 21 st century. Geochemical variations encoded in speleothem layers may provide records of recharge when and where no instrumental data exist. In particular, transition metal concentrations have been developed as a proxy for hydrological dynamics (here, recharge episodes) in speleothems, in modern cave calcite, and in cave drip water. However, a mechanistic understanding of sub-annual transition metal variability as a proxy for recharge, which requires a comparative investigation of speleothems that grew at least partly during the instrumental period, has not yet been well developed. We present here sub-annually resolved trace element concentration time series from two stalagmite cores that grew near the entrance of a shallow cave over the 20th century in semi-arid southeastern New Mexico, a region that is impacted by climate systems that includes the North American Monsoon (NAM) and El-Nino Southern Oscillation (ENSO). Alkalineearth metal concentrations in both cores vary quasi-sinusoidally, whereas transition metal concentration variability is characterized by aperiodic spikes. Multivariate statistical tests indicate that the alkaline-earth metal time series are sensitive to changes in epikarst processes (including flow paths) and seasonal temperature changes, whereas the transition metal time series are sensitive to periods of recharge. Using the variability in alkaline-earth metal concentrations, we develop a depth-age model using dimensionality reduction (Principal Component Analyses; PCA) and Fast Fourier Transform (FFT). The derived growth rates are used in a novel peak counting model to calculate the number of growth years to construct a robust agemodel. Results from the depth-age model are independently checked against radiometric (U-series and radiocarbon) dates and band counting derived from reflected light and Confocal Laser Fluorescent Microscopy. The results of cross wavelet analysis applied to our time-resolved speleothem records suggest that the leading Principal Component for transition metals (PC1tm) is sensitive to the rainfall periodicity associated with NAM and ENSO. Our annually resolved stalagmite records that span the instrumental period uniquely facilitate an analysis of how recharge events in semi-arid regions relate to stalagmite transition metal incorporation. The sensitivity of transition metals to recharge episodes in semi-arid New Mexico on a sub-annual to sub-decadal temporal scale supports the use of transition metal concentrations as proxies of paleo-recharge in semi-arid and arid regions elsewhere. Modern speleothems that grew over the instrumental period are typically difficult to date via radiometric methods such as Uranium-series and radiocarbon dating. We demonstrate that our peak counting algorithm developed using cyclicity observed in alkaline-earth metal concentrations can be used to build chronologies for stalagmites that grew during into the instrumental period.