| Abstrakt: |
The international GEOTRACES program has been instrumental in demonstrating how marine sediments are a critical source of dissolved Fe to the world's oceans. Here, we present dissolved iron (dFe) from the GEOTRACES North Pacific GP15 section, which, alongside other sediment‐source tracers (including dissolved δ56Fe, Mn, 228Ra, and particulate Fe), allows for identification of the dFe provenance of three distinct dFe depth maxima at the Alaskan margin. Two of these (shelf and abyssal depths) are of local Alaskan sedimentary origin. The third, a mid‐depth dFe maximum with an absence of 228Ra, is an advected signal that, based on tracer data from Western Pacific GEOTRACES transects and circulation models, must be advected from sedimentary sources on the Asian margin, ∼5,000 km away. This study illustrates the importance of measuring diagnostic sedimentary tracers like radium when assigning local margins as sedimentary sources of marine trace metal budgets. Plain Language Summary: Iron is an essential, yet limiting, micronutrient for marine primary producers, and thus influences patterns of global oceanic primary productivity and carbon exchange. In recent years, the International GEOTRACES program has highlighted that marine sediments, hydrothermal vents, and atmospheric dust all supply dissolved iron to the oceans. Here, we investigated the sources of dissolved iron to the Eastern North Pacific Ocean, using samples collected on the U.S. GEOTRACES GP15 Pacific Meridional Cruise that sailed from Alaska to Tahiti in 2018. We identified three elevated dissolved iron features close to the Alaskan continental margin, with two originating from local sedimentary sources (shelf and abyss). The third, an intermediate depth dissolved iron plume that extends south into the gyre, is not of local sedimentary origin, but instead results from long‐distance transport of dissolved iron from Asian marginal sediment sources. A critical aspect of this study is the use of multiple chemical tracers such as radium, iron, and manganese, coupled with ocean circulation models, to correctly attribute the sources of trace metals to the ocean. Key Points: Three distinct dFe maxima were identified close to the Alaskan margin at different depths. Two are of local origin (shelf and abyssal)An intermediate depth dFe plume with an absence of Mn and Ra, is a distal advected signal from Asian margin sedimentary sources (5,000 km away)A multiple tracer approach of Fe, Mn, and Ra was necessary to rule out what appeared to be a local margin source [ABSTRACT FROM AUTHOR] |
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