Radiocarbon Anomalies of Surface Waters in the Glacial-to-Deglacial Low-to-Mid-Latitude Atlantic

Abstract:

¹⁴C reservoir ages of surface waters are crucial for dating marine sediment records of the last 40,000 yr. In the low-latitude Atlantic, time series of ¹⁴C reservoir ages were reconstructed for five sites using the ¹⁴C plateau-tuning technique and supplemented by a reservoir age record from southern mid-latitudes (Skinner et al., 2010). Results suggest small-scale spatial and short-term (multi-centennial-scale) changes in reservoir age over last glacial-to-deglacial times, thus modify previously assigned calendar age chronologies by up to 500–2500 yr. During late peak glacial, enhanced summer winds off South Brazil and strengthened southerly trades off Namibia induced local reservoir ages of up to 900–1100 yr, whereas surface water ages in the Cariaco lagoon fell close to zero, a result of dominant CO₂ exchange with the atmosphere. Near 16.05 ka, reservoir ages dropped to a minimum of 170–420 yr all over the South Atlantic, possibly the response to an immediately preceding short-term major rise in atmospheric pCO₂ and East Antarctic temperatures. Our ¹⁴C reservoir ages provide a first basis for systematic data-model comparisons. They largely confirm model-based estimates for the LGM (Butzin et al., 2012) that have been derived from changes in both atmospheric ¹⁴C concentration and reductions in AMOC. Deviations are constrained to coastal upwelling zones in part insufficiently resolved by numerical models.