Quaternary record of terrestrial environmental change in response to climatic forcing and anthropogenic perturbations, in Puerto Rico

We present cospatial, contemporary archival records of biotic and abiotic terrestrial processes operating over the past similar to 25 ky within the Rio Fajardo watershed, in northeastern Puerto Rico. The proxy records were derived from a 5-m-thick stratigraphic section exposed by cut bank incision. We interpreted ecosystem dynamics from changes in the stable carbon isotopic ratio of sedimentary organic material compared to delta C-13 ratios of contemporary carbon sources. Sedimentary organic material had delta C-13 values ranging from -29.715 to -15.291. We derived a record of paleo-erosion rates in the catchment from the concentration of meteoric Be-10 in layers of the floodplain sediments. Paleo-erosion rates ranged from 13 to 356 mm ky(-1). The chronology of the sediments was constrained with the radiocarbon ages of organic deposits, the oldest age was calibrated to similar to 22.4 ky BP (thousand years before present) and retrieved at 440 cm depth. We collected grain size data, clay mineralogies, and analyzed geochemical indices including the chemical weathering index, salinization, and base cation loss down profile. This stratigraphic sequence captures major shifts in the Caribbean climate, the intensification of the El Nino-Southern Oscillation, and the arrival of humans on the island. During the last glacial and early Holocene epochs both biotic (delta C-13) and abiotic proxies (Be-10(met) and geochemical data) indicated dynamic equilibrium with climate. The past five thousand years (ky) of record are characterized instead by pulsed responses to disturbances in both systems. Colonial-era land use drove changes that significantly exceeded natural variability in any proxy over the period of record. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This study presents cospatial archival records of biotic and abiotic terrestrial processes in the Rio Fajardo watershed in northeastern Puerto Rico over the past 25 ky. The findings reveal dynamic ecosystem changes, paleo-erosion rates, and major climate shifts in the Caribbean region. The past five thousand years show pulsed responses to disturbances, with colonial-era land use driving changes beyond natural variability.