SURFACE OCEAN RADIOCARBON FROM A <i>PORITES</i> CORAL RECORD IN THE GREAT BARRIER REEF: 1945–2017
Yang Wu, Stewart Fallon, Neal E. Cantin, Janice Lough
Abstract
ABSTRACT We present a high-resolution seawater radiocarbon (Δ 14 C) record from a Porites coral collected from Masthead Island in the southern Great Barrier Reef (GBR) covering the years 1945–2017. The Δ 14 C values from 1945–1953 (pre-bomb era) averaged –49‰. As a result of bomb-produced 14 C in the atmosphere, Δ 14 C values started to rise rapidly from 1959, levelled off at ∼131‰ in the late 1970s and gradually decreased to ∼40.3‰ by 2017 due to the decrease in the air-sea 14 C gradient and the overturning of the 14 C ocean reservoir (i.e., surface ocean to subsurface ocean; atmosphere to surface ocean). The Masthead Island record is in agreement with previous 14 C coral records from the southern GBR. A comparison between surface ocean and atmospheric Δ 14 C suggests that, since 2010, the main reservoir of bomb-derived 14 C has shifted from the atmosphere to the surface ocean, potentially resulting in reversed 14 C flux in regions where the CO 2 gradient is favorable. The high-resolution Masthead coral Δ 14 C sheds light on long-term variability in air-sea exchange and GBR regional ocean dynamics associated with climate change and in conjunction with the previous records provides a robust seawater 14 C reference series to date other carbonate samples.