Beryllium isotope distribution in the western North Atlantic: a comparison to the Pacific

Abstract

The surface depletion/deep enrichment of the 10Be and 9Be distributions observed in the Pacific is not as conspicuous in the western North Atlantic Ocean between 33° and 42°N. In the case of 9Be, a surface excess sometimes even exists. While 10Be concentrations in the surface waters of the two oceans are comparable, 9Be concentrations in the surface North Atlantic are about five times those in the surface Pacific. Deep waters show an increase of concentrations from the Atlantic (via Antarctic) to the Pacific, but the degree of increase for the two isotopes is different: about 10% for 9Be and 2.5-fold for 10Be. Thus there is a systematic increasing trend in the ration 10Be/ 9Be ( atom/ atom × 10 −7) along the advective flow lines: surface North Atlantic (0.4)→ deep North Atlantic (0.6) → Circumpolar (1.0) → deep Pacific (1.2) → surface Pacific (1–3). These distributional patterns and contrasting North Atlantic-Pacific features can be explained in terms of: (a) a strong fluvial and continental dust input of 9Be to the North Atlantic and an ocean-wide, more-or-less uniform pluvial input of cosmogenically produced 10Be; (b) active participation of Be in the particle recycling involving surface uptake and deep water regeneration; and (c) mean removal time of Be from the ocean, which, based on the 10Be/ 230Th ratios in surface sediments of two deep-sea cores, are estimated as ∼1200 y in the open Pacific and ∼500 a in the open Atlantic, values that are close to water mixing times of the individual ocean basins.