Use of the bomb radiocarbon chronometer for age validation in the blue grenadier Macruronus novaezelandiae
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Accelerator mass-spectrometry was used to measure radiocarbon in the earliest formed portions of selected blue grenadier, Macruronus novaezelandiae, otoliths to provide a validation of fish-age estimates based on the quantification of opaque and translucent zones in otolith thin-sections. Δ14C data from blue grenadier otoliths were compared with previous estimates of Δ14C in seawater-dissolved inorganic carbon at similar latitutes, longitudes, and depths to link variation in otolith Δ14C to time. Minimum otolith Δ14C was −76.9 ± 7.7‰, indicative of pre-bomb radiocarbon levels below the surface mixed-layer at latitudes where juvenile blue grenadier are found. When plotted versus fish age estimated from otolith sections, the majority of the Δ14C data combined to define a curve reflecting the increase in bomb radiocarbon in temperate oceans of the Southern Hemisphere, indicating that age-estimation procedures based on otolith thin-sections are satisfactory for determining blue grenadier age. If otolith-section age estimates were correct, peak otolith Δ14C of 106.8 ± 7.9‰ occurred during the late 1960s, i.e. earlier than expected. This may be a manifestation of an increase in the mixed-layer depth associated with increased frequency of zonal westerly winds at this time.
KeywordsInorganic Carbon Westerly Wind Temperate Ocean Translucent Zone Otolith Section
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