On the radiocarbon record in banded corals: Exchange parameters and net transport of ¹⁴CO₂ between atmosphere and surface ocean

Abstract

We have made radiocarbon measurements of banded hermatypic corals from Florida, Belize, and the Galapagos Islands. Interpretation is presented here of these previously reported results. These measurements represent the 14C/12C ratios in dissolved inorganic carbon (DIOC) in the surface ocean waters of the Gulf Stream and the Peru Current at the time of coral ring formation. A depletion in radiocarbon concentration was observed in coral rings that grew from A.D. 1900–1952. It was caused by dilution of existing 14C levels with dead CO2 from fossil fuel burning (the Suess effect, or Se). The observed depletion of radiocarbon was greater in corals from the Gulf Stream (−11‰) than in corals from the Peru Current (−6‰). A similar trend was observed in the distribution of bomb‐produced 14C in corals that had grown during the years following A.D. 1952. The concentration of bomb‐produced radiocarbon was much higher in corals from temperate regions (Florida, Belize, Hawaiian Islands) than in corals from tropical regions (Galapagos Islands and Canton Island). A linear relationship appears to exist between the preanthropogenic Δ14C values and the Se values measured in the individual corals, because the 14C in corals is derived from two different carbon reservoirs: (1) the atmosphere and (2) the subsurface ocean. A linear relationship is also observed between the preanthropogenic Δ14C values and the concentration of bomb‐produced 14C in the individual corals during A.D. 1973. The apparent radiocarbon ages of the surface waters in temperate and tropical oceans during the preanthropogenic period range from about 280 to 520 years B.P. (−40 to −69‰). At all investigated locations, it is likely that waters at subsurface depths have the same apparent radiocarbon age of about 670 years B.P. From the change of oceanic Δ14C in the surface ocean during post‐bomb times, the approximate annual rate of net input of 14CO2 to the ocean waters is calculated to be about 8% of the prevailing 14C difference between atmosphere and ocean. From this input and from preanthropogenic Δ14C values found at each location, it can be seen that vertical mixing of water in the Peru Current is about 3 times greater than that in the Gulf Stream.

Post-Bomb Radiocarbon Records of Surface Corals from the Tropical Atlantic Ocean

“…Patterns reveal differences between the -se and previously published data sets from Florida (Druffel and Suess 1983) and Bermuda (Druffel 1989). Comparisons are resented betw observed and model-calculated e14C trends for the temperate and tropical North Atlantic.…”

“…The Florida coral record is also shown for comparison (Druffel and Suess 1983). Prior to the introduction of bomb-produced 14C to the oceans (-1956-1958), the average pre-bomb A14C value from six measurements of the large Abrolhos coral (CABO) was -57.9 ± 4.5%o (sd).…”

Bomb-produced radiocarbon in the shell of the chambered nautilus: rate of growth and age at maturity

“…Bomb-produced radiocarbon increased the A14C (per mil deviation with respect to the activity in 19th century wood) of the atmosphere to nearly 1000%o by 1964. In the surface ocean, the record of A14C is well documented in hermatypic corals [17][18][19][20][21] and exhibits an increase above the pre-bomb level starting in the late 1950's and continuing into the mid-1970's. This pattern of a4C variation with time has been used as a chronometer to determine the growth rate of the marine bivalve, Arctica islandica.…”

Growth rate and potential climate record from a rhodolith using 14C accelerator mass spectrometry

“…As they grow, these plants deposit calcium carbonate, which should contain chemical and isotopic records reflecting environmental conditions. Previous isotopic studies on coral and mollusks found that the amount of 14 C deposited as a part of the total carbon in biogenic carbonate records the 14 C concentration in the ocean water surrounding the organism (e.g., Druffel and Linick 1978;Nozaki et al 1978;Druffel and Suess 1983). This type of 14 C record should also be found in the carbonate of rhodoliths and can potentially be used as a record of climate variation.…”