Quantifying 210Po/210Pb Disequilibrium in Seawater: A Comparison of Two Precipitation Methods With Differing Results

The disequilibrium between lead-210 ( 210 Pb) and polonium-210 Po) is increasingly used in oceanography to quantify particulate organic carbon (POC) export from the upper ocean. This proxy based on deficits of Po typically observed water column due preferential removal relative Pb by sinking particles. Yet, a number studies have reported unexpected large deep ocean indicating scavenging despite its radioactive mean life ∼ 200 days. Two precipitation methods, Fe(OH) 3 Co-APDC, are concentrate seawater samples, raise question whether this feature biogeochemically consistent or there methodological issue. Here, we present compilation that suggests at depths >300 m more often where precipitate seawater, than those using Co-APDC (in 68 versus 33% profiles analyzed for each method, respectively). In order test Po/ can be partly related artifact, directly compared total activities four duplicate depth-profiles determined unfiltered samples. While both methods produced same activities, results method showed equilibrium below 100 m, whereas resulted significantly lower throughout entire column. These show waters, but also ocean, may greater when calculated commonly protocol. finding has potential implications use pair as tracer particle oceans because (and thus POC) fluxes samples overestimated. Recommendations future research provided possible reasons discrepancy analytical methods.