Application of chemical tracers to an estimate of benthic denitrification in the Okhotsk Sea

Abstract

To estimate benthic denitrification in a marginal sea, we assessed the usefulness of ${\text{N}}_{2}^{*}$, a new tracer to measure the excess nitrogen gas (N₂) using dissolved N₂ and argon (Ar) with N* in the intermediate layer (26.6–27.4σ _θ ) of the Okhotsk Sea. The examined parameters capable of affecting ${\text{N}}_{2}^{*}$ are denitrification, air injection and rapid cooling. We investigated the relative proportions of these effects on ${\text{N}}_{2}^{*}$ using multiple linear regression analysis. The best model included two examined parameters of denitrification and air injection based on the Akaike information criterion as a measure of the model fit to data. More than 80 % of ${\text{N}}_{2}^{*}$ was derived from the denitrification, followed by air injection. Denitrification over the Okhotsk Sea shelf region was estimated to be 5.6 ± 2.4 μmol kg⁻¹. The distribution of ${\text{N}}_{2}^{*}$ was correlated with potential temperature (θ) between 26.6 and 27.4σ _θ (r = −0.55). Therefore, we concluded that ${\text{N}}_{2}^{*}$ and N* can act complementarily as a quasi-conservative tracer of benthic denitrification in the Okhotsk Sea. Our findings suggest that ${\text{N}}_{2}^{*}$ in combination with N* is a useful chemical tracer to estimate benthic denitrification in a marginal sea.