The Marine Radiocarbon Bomb Pulse Across the Temperate North Atlantic: A Compilation of Δ14C Time Histories from Arctica Islandica Growth Increments

Abstract

ABSTRACT. Marine radiocarbon bomb-pulse time histories of annually resolved archives from temperate regions have been underexploited. We present here series of  14 C excess from known-age annual increments of the long-lived bivalve mollusk Arctica islandica from 4 sites across the coastal North Atlantic (German Bight, North Sea; Tromsø, north Norway; Siglufjordur, north Icelandic shelf; Grimsey, north Icelandic shelf) combined with published series from Georges Bank and Sable Bank (NW Atlantic) and the Oyster Ground (North Sea). The atmospheric bomb pulse is shown to be a step-function whose response in the marine environment is immediate but of smaller amplitude and which has a longer decay time as a result of the much larger marine carbon reservoir. Attenuation is determined by the regional hydrographic setting of the sites, vertical mixing, processes controlling the isotopic exchange of 14 C at the air-sea boundary, 14 C content of the freshwater flux, primary productivity, and the residence time of organic matter in the sediment mixed layer. The inventories form a sequence from high magnitude-early peak (German Bight) to low magnitude-late peak (Grimsey). All series show a rapid response to the increase in atmospheric  14 C excess but a slow response to the subsequent decline resulting from the succession of rapid isotopic airsea exchange followed by the more gradual isotopic equilibration in the mixed layer due to the variable marine carbon reservoir and incorporation of organic carbon from the sediment mixed layer. The data constitute calibration series for the use of the bomb pulse as a high-resolution dating tool in the marine environment and as a tracer of coastal ocean water masses.

Reply to Pearson and Nicholas, Stassen et al., and Zeebe et al.: Teasing out the missing piece of the PETM puzzle

“…Thus, any parameterization of the "surface mixed-layer" as a single box (e.g., LOSCAR) is inappropriate for simulating these conditions. This nonuniform response is expressed clearly in bomb radiocarbon records, which vary in magnitude and duration as a function of deep-water influence (2). Similar heterogeneity is preserved in the PETM, as evidenced by the differential response of shelf localities to an atmospheric perturbation (e.g., ∼−8‰ δ 13 C decrease at Medford vs. −3.5‰ decrease at Bass River).…”

“…Needed to Simulate an Instantaneous Release of CO 2 Zeebe et al (3) use results from two carboncycle models showing that a large instantaneous release of "light" carbon should produce a −20 to −22‰ δ 13 C excursion in surface water, compared with −3.5‰ recorded at Millville, thereby attempting to invalidate the rapid release hypothesis for the PETM (1). Zeebe (4) states that LOSCAR (Long-term Ocean-atmosphereSediment CArbon cycle Reservoir model) "is not designed to address carbon cycle problems on time scales much shorter than centuries," treating the surface ocean as one box.…”

“…This aspect is critical because the temporal/spatial scales of surface ocean carbon invasion from an instantaneous release vary significantly, and much of the excursion dissipates over decades to a century. Here An instantaneous, transient carbon perturbation produces nonuniform and spatially heterogeneous carbon isotope changes in the surface ocean (2,6). Thus, any parameterization of the "surface mixed-layer" as a single box (e.g., LOSCAR) is inappropriate for simulating these conditions.…”

“…1). Temporal differences are predicted by a rapid (instantaneous) release of light carbon, which would lower the surface ocean ½CO = 3 in a matter of months, in contrast to the carbon isotopic equilibrium exchange, which occurs on the scale of a decade (2) and can only be recorded in a core with a high sedimentation rates (1). Based on the rhythmic bedding in the Marlboro Clay, we argue that the drop in %CaCO 3 occurred in less than a year and the δ 13 C equilibrium was on the order of a decade.…”

Nuclear Weapons Tests and Environmental Consequences: A Global Perspective

“…One of the methods used in reconstructing its fluctuations in the ocean consists in measuring its concentration in aquatic organisms, reservoirs that store 14 C. One example is the Arctica islandica bivalves mollusk, which served in the reconstruction of fluctuations of the radionuclide 14 C in the marine environment in the temperate zone of the North Atlantic (Scourse et al 2012).…”