Abstract
The margin of the western North Pacific Ocean releases redox-active elements like Mn, Co, and Ce into the water column to undergo further transformation through oxide formation, scavenging, and reductive dissolution. Near the margin, the upper ocean waters enriched in these elements are characterized by high dissolved oxygen, low salinity, and low temperature, and are a source of the North Pacific Intermediate Water. High dissolved concentrations are observed across the Western Subarctic Gyre, with a rapid decrease in concentrations away from the margin and across the subarctic-subtropical front. The particulate concentrations of Mn, Co, and Ce are also high in the subarctic surface ocean and enriched relative to Ti and trivalent rare earth elements. Furthermore, the particles enriched in Mn, Co, and Ce coincide at the same depth range, suggesting that these elemental cycles are coupled through microbial oxidation in the subarctic gyre as the waters travel along the margin before being subducted at the subarctic-subtropical front. Away from the margin, the Mn, Co, and Ce cycles decouple, as Mn and Ce settle out as particles while dissolved Co is preserved and transported within the North Pacific Intermediate Water into the central North Pacific Ocean.
Highlights
The lateral transport of material from continental margins can provide essential trace metals to the ocean (Westerlund et al, 1986; Elrod et al, 2004; Lam et al, 2006; Lam and Bishop, 2008; AguilarIslas et al, 2013; Noble et al, 2017; Tagliabue et al, 2017)
While surface maxima of manganese (Mn) may result from atmospheric deposition or freshwater inputs (Shiller, 1997; van Hulten et al, 2016), numerous studies have established the importance of Mn as a tracer of redox mobilized sediment inputs from continental margins in the upper ocean
The North Pacific Ocean can be divided into three general hydrographic regions (Figure 1): the Western Subarctic Gyre (WSG) in the north, the Subtropical Gyre (STG) in the south, and the Mixed Water Region (MWR) between the two gyres
Summary
The lateral transport of material from continental margins can provide essential trace metals to the ocean (Westerlund et al, 1986; Elrod et al, 2004; Lam et al, 2006; Lam and Bishop, 2008; AguilarIslas et al, 2013; Noble et al, 2017; Tagliabue et al, 2017). In addition to Mn, other trace elements can be released from margin sediments via redox mobilization, including Co (Noble et al, 2012, 2017; Hawco et al, 2016; Tagliabue et al, 2018) and Ce (Zhang and Nozaki, 1998; Obata et al, 2007; Zheng et al, 2016). While the reduced forms of Mn and Ce are generally found in the aqueous phase, the oxidized forms are found in the particulate phase (Stumm and Morgan, 1995; Moffett and Ho, 1996; Nozaki, 2001)
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