A new low-latitude, high-elevation cosmogenic beryllium-10 production rate from the Rwenzori Mountains, Uganda

Abstract

Cosmogenic nuclide surface-exposure dating has emerged as a key tool in glacial geomorphology. Accurate application of the technique relies first on establishing local nuclide production rates using independently dated calibration sites. Certain regions of the world, such as the low latitudes, host few existing calibration sites. Developing local production rate calibrations in the low-latitudes is therefore a crucial first step for robust application of surface-exposure dating in these regions, particularly as cosmogenic nuclide production is theoretically more sensitive to changes in Earth’s magnetic field in the low-latitudes. Here we present a new local cosmogenic beryllium-10 production rate from the equatorial Rwenzori Mountains of Uganda based on radiocarbon dating of basal sediments from the moraine-dammed Lake Mahoma (~21.3 kyr BP; ~2,900 m asl). We also present the results of a systematic investigation of the performance of different parameters used to scale production rates spatially and temporally (e.g., scaling frameworks, geomagnetic field reconstructions, atmospheric models) using two public online calculators and limiting radiocarbon age data from nearby Lake Kopello (~4,000 m asl) in the Rwenzori. Our results highlight the sensitivity of low-latitude, high-elevation cosmogenic nuclide production to discrete parameters and underline the need for additional low-latitude production rate calibration sites.