Distribution of Pa in the Atlantic sector of the Southern Ocean: Tracking scavenging during water mass mixing along neutral density surfaces - Archive ouverte HAL Access content directly
Journal Articles Deep Sea Research Part I: Oceanographic Research Papers Year : 2023

Distribution of Pa in the Atlantic sector of the Southern Ocean: Tracking scavenging during water mass mixing along neutral density surfaces

Abstract

Dissolved and particulate Protactinium-231 ($^{231}$Pa) was analyzed for samples from the BONUS GoodHope (BGH) IPY-GEOTRACES cruise in the SE Atlantic sector of the Southern Ocean (36°S-13°E to 57°S-0°, Feb.–Mar. 2008). The inflowing waters from the Atlantic Ocean fuel the Antarctic Circumpolar Current in dissolved $^{231}$Pa which is mostly removed from seawater by the biogenic silica produced by diatoms in the Southern Ocean. This scavenging flux of the $^{231}$Pa induces a meridional gradient of the $^{231}$Pa concentration and of the Th–Pa fractionation factor (F$_{Th/Pa}$). We propose a first direct estimate of the $^{231}$Pa partition coefficient between suspended opal and seawater of about 1.42 ± 0.55 × 10$^6$ g/g. This partition coefficient could directly apply to simulate the particulate Pa concentration from the dissolved fraction and the opal concentration. We apply to $^{231}$Pa the isopycnal advection-diffusion-scavenging model built for Th isotopes across the ACC. This additional constraint on the model does not modify the isopycnal eddy diffusion estimate of about 1900 ± 180 m$^2$/s at different isopycnal surfaces but suggests a higher particle settling velocity, about 1000 m/y, in the northern part of the ACC than solely derived from Th isotopes. The most different feature is the reduction by half of the estimated uncertainties among the different transport parameters just by the addition of a new constraining parameter. Moreover, this study confirms that $^{231}$Pa budget of the Atlantic Sector of Southern Ocean cannot be balanced by considering meridional transport only, and need to consider eastward export to scavenge Pa in the whole area of the Opal Belt.

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Dates and versions

hal-04044045 , version 1 (27-11-2023)

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M. Levier, M. Roy-Barman, L. Foliot, A. Dapoigny, F. Lacan. Distribution of Pa in the Atlantic sector of the Southern Ocean: Tracking scavenging during water mass mixing along neutral density surfaces. Deep Sea Research Part I: Oceanographic Research Papers, 2023, 194, pp.103951. ⟨10.1016/j.dsr.2022.103951⟩. ⟨hal-04044045⟩
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