Anthropogenic Iron Invasion into the Ocean: Results from the East Sea (Japan Sea)

Abstract

Iron (Fe) is an essential micronutrient for phytoplankton growth, and its availability limits primary production in half of the global ocean. Traditionally, atmospheric input of natural mineral dust has been considered as a main source of Fe in the surface ocean. However, here we show that about 45% of the water-soluble Fe in aerosols collected over the East Sea (Japan Sea) is anthropogenic, which originates mainly from heavy fuel oil combustion, based on the analyses of various chemical tracers (Al, K, V, Ni, Pb, and 210 Pb). It is striking that a tiny quantity of oil, less than 1% of the aerosols in mass, can constitute the majority of water-soluble Fe in aerosols due to its high Fe solubility. Furthermore, we show that a quarter of dissolved Fe in the East Sea is anthropogenic using a 210 Pb-based scavenging model. Since this sea is almost fully enclosed (200−3000 m) and located at the forefront of the Asian human footprint, our results provide an insight that the marine Fe cycle may be already perturbed by human activities.

Representation of iron aerosol size distributions is critical in evaluating atmospheric soluble iron input to the ocean

“…over all ocean basins compared to Hamilon2019 and Wang2015 cases. In particular, the cases with a more uniformly distributed particle size distribution across modes captures the high concentration (>1 ng m -3 ) in North Pacific, which can be linked to atmospheric plumes transported from East Asia with intensive emission rates [Moteki et al, 2017;Seo and Kim, 2023]. Some underestimations still exist in near-surface or high altitudes.…”

“…Dust storms, which frequently occur in arid or semiarid regions of the world, such as North Africa and East Asia, provide an abundant iron source to the ocean and support primary production [Mahowald et al, 2009;Westberry et al, 2023]. In addition, a growing body of evidence is showing that pyrogenic iron, with higher fractional solubility than dust [Ito et al, 2019], is a large source of atmospheric soluble iron deposition to many ocean basins, including the Southern Ocean, Northern Pacific Ocean, and Northern Atlantic Ocean [Conway et al, 2019;Matsui et al, 2018;Seo and Kim, 2023]. Because the strength of each source could be affected by future climate change and/or human activities, their contributions to bioavailable iron input to the ocean may vary regionally and temporally by the end of the century [Bergas-Massó et al, 2023].…”

New Insight Into the Source and Sink of 227Ac in the Ocean

“…The water exchange between the East Sea and the northwestern Pacific Ocean is limited to several sills (Tsugaru, Soya, and Korea Straits), which are shallower than 130 m (Chang et al., 2004). In the surface layer, a considerable amount of material is transported from the Asian continent to the East Sea through the atmosphere and ECSYS shelf water (Mukai & Suzuki, 1996; Seo et al., 2022; Seo & Kim, 2023), including the Tsushima Warm Current and Changjiang Diluted Water. Furthermore, the East Sea has its own deep thermohaline circulation, with a turnover time of approximately 100 years (Kumamoto et al., 1998; Tsunogai et al., 1993; Watanabe et al., 1991).…”