Planktic Foram Dates from the Indonesian Arc: Marine 14C Reservoir Ages and a Mythical AD 535 Volcanic Eruption

Abstract

ABSTRACT. The Indonesian Arc represents the subduction of the Indian-Australian plate beneath Asia. It has been the scene of catastrophic tectonic activity, including the recent 2004 M=9.1 Aceh earthquake and resulting Indian Ocean tsunami. We have dated planktonic forams associated with historic tephras (Tambora, 1815 and Krakatau, 1883) in marine sediment cores to determine radiocarbon reservoir ages for 2 locations along the arc. Our best estimates for 19th century regional reservoir corrections (R) are +90 ± 40 yr for surface-dwelling species and +220 ± 40 yr for mixed planktic assemblages containing some upper thermocline species, but scatter in the data suggests that past surface reservoir ages may have varied by about ±100 yr. We used the results of this study to investigate a proposed very large AD 535 eruption at or near Krakatau. We find no evidence for ash from such an eruption, and although this is negative evidence, we consider it sufficiently strong to rule out any possibility that one took place.

The consequences of opening the Sunda Strait on the hydrography of the eastern tropical Indian Ocean

“…The age models for sediment cores GeoB 10042–1 and GeoB 10043–3 are based on 18 and 16 calibrated radiocarbon dates, respectively, measured on the mixed layer dwelling planktic foraminifera species G. ruber and/or Globigerinoides sacculifer (Table ; Figure ). The upper 50 cm of both cores spans the last 5.2 kyr (GeoB 10042–1) and 2.3 kyr (GeoB 10043–3) have previously been studied by Southon et al []. In this study we provide 11 (GeoB 10042–1) and 8 (GeoB 10043–3) new radiocarbon dates.…”

“…The resulting age‐depth models suggest that cores GeoB 10042–1 and GeoB 10043–3 cover the past 39.4 and 34.4 kyr and indicate that the average sedimentation rates of cores GeoB 10042–1 and GeoB 10043–3 are 23.4 cm kyr −1 and 16.4 cm kyr −1 . Both sediment cores have a distinct ash layer (GeoB 10043–3: 13–18 cm; GeoB 10042–1: 6–8 cm core depth) that has been linked to the Krakatau eruption in 1883 [ Southon et al , ]. In addition, another ash layer is observed in core GeoB 10043–3 at a depth between 370 and 382 cm and in core GeoB 10042–1 at 470 cm (Figure ).…”

“…Samples were then measured at the Keck Carbon Cycle Accelerator Mass Spectrometry Laboratory, University of California, Irvine. Raw 14 C ages were converted to 2σ calendar ages with the CALIB 7.0 software using the Marine13 calibration data set [ Reimer et al , ] (Table ) with a regional reservoir correction of 100 years [ Southon et al , ].…”