Radiocarbon in Corals: Records of the Carbon Cycle, Surface Circulation and Climate

Ellen Druffel

doi:10.5670/oceanog.2002.43

Abstract

Author(s): Druffel, Ellen | Abstract: For more than two decades, coral skeletons have been used to reconstruct records of isotopic and chemical ratios in surface seawater (for reviews, see Druffel, 1997a; Gagan et al., 2000). Here I demonstrate how high precision 14C records (±3) reveal information regarding regional mixing of surface and subsurface waters. Climatic variability on many time scales (e.g. El Nino, Pacific Decadal Oscillation, and the North Atlantic Oscillation) are detected in the corals by small changes in Δ14C. Radiocarbon records in corals have also been used to reconstruct the input of fossil fuel CO2 into the subtropical and tropical regions of the Pacific and Atlantic Oceans.

Highlights

Time histories of A"C in corals vary on interannual to decade timescales because of changes in physical mechanisms such as vertical mixing and advection of (18°S; Druffel, 1981), Fiji (18°S) and Tarawa (l°N;Toggweiler et al, 1991)
Pre-bomb A14Cvalues were higher in the subtropiduring isolation from the atmosphere where 14Cis procal North (Hawaii) and South (Abraham Reef) Pacific duced
The Suess Effect is measurable and has grown to significant proportions during the 1980s and 1990s. Subtropical sites such as French Frigate Shoals display more rapid increases in A14Cthan those continually diluted by equatorial upwelling, such as Fanning, Tarawa and Galapagos

Summary

Introduction

Time histories of A"C (per mil, %o, deviation of the 14C/12Cratio between a sample and that of a 19~ century wood standard) in corals vary on interannual to decade timescales because of changes in physical mechanisms such as vertical mixing and advection of (18°S; Druffel, 1981), Fiji (18°S) and Tarawa (l°N;Toggweiler et al, 1991). The Suess Effect is measurable and has grown to significant proportions during the 1980s and 1990s Subtropical sites such as French Frigate Shoals display more rapid increases in A14Cthan those continually diluted by equatorial upwelling, such as Fanning, Tarawa and Galapagos. After 1974, AI'C values decrease noticeably at most subtropical regions and continue to rise at Fanning, Tarawa and Galapagos This is due to upwelling of bomb 14C-laden waters near the equator, which enter the subtropical gyres via downwelling and circulate toward the equator on the order of 6-10 years after the initial input of the bomb ~4Ctransient (Quay et al, 1983). The slopes of the postbomb Atlantic &14C records between 1962 and 1965, the most sensitive part of the ~4C rise, revealed that Porto de Galinhas (8°S) and Cape Verde Islands (17°N) appear to have been diluted the most by subsurface water due to upwelling in the South Equatorial Current and the North Equatorial Current (Druffel, 1996)

The Carbon Cycle

Findings

Climate Signals