Abstract
Here we provide compelling evidence that deep particle export enhanced dissolved organic carbon (DOC) concentrations beneath the Pacific’s Subarctic Front (SA, ∼42°N) and Northern Subtropical Front (NST, ∼34°N). We report three main findings: First, deep export of subjectively small particles (128–512 μm) was apparent throughout the frontal zone in which the SA resides. However, export of large particles was specifically associated with the SA, rather than the entire frontal zone, and appeared to exclusively transfer DOC into the bathypelagic water column. Second, a similar DOC enrichment existed beneath the NST, though this signal was curiously not accompanied by observable particles (>128 μm). We conclude that export occurring previously in winter left this DOC behind as a residue, though the associated particles were no longer present by spring. Third, the presence of strong hydrographic fronts was not the only control on export that resulted in these unique DOC distributions. Deep export and DOC enrichment was also controlled by latitude-specific biogeochemical and hydrographic conditions, such as depth of the nutricline and seasonal mixed layer shoaling. Given these observations, the fronts within the transitional region of the North Pacific are clearly special locations for deep carbon sequestration and for providing uncommon DOC enrichment that ultimately supports the deep microbial community.
Highlights
Hydrographic frontal zones, given their complex physical dynamics, stimulate biological growth and particle export to the interior ocean (Roden, 1991; D’Asaro et al, 2011; Guidi et al, 2012; Juranek et al, 2012; Ohman et al, 2012)
Hydrographic fronts within the transitional zone between the subarctic and subtropical gyres of the North Pacific appear to be unique drivers for the introduction of dissolved organic carbon (DOC) to great depths via deep-sinking particles
By analyzing DOC distributions below important hydrographic frontal zones, in combination with nutrient distributions, particle abundances, and satellite chlorophyll imagery, we conclude: (1) Dissolved organic carbon introduction via particle export into the bathypelagic occurred at the Northern Subtropical Front (NST) and Subarctic Front (SA)
Summary
Hydrographic frontal zones, given their complex physical dynamics, stimulate biological growth and particle export to the interior ocean (Roden, 1991; D’Asaro et al, 2011; Guidi et al, 2012; Juranek et al, 2012; Ohman et al, 2012). Bathypelagic bacterioplankton are abundant where overlying waters are most productive (Nagata et al, 2000; Hansell and Ducklow, 2003) and intrinsically where export is highest Through respiration, these microbes convert DOC to inorganic forms, effectively sequestering carbon until. In environments where export is minimal, DOC released at depth is likely rapidly consumed and an enrichment of DOC above typical background concentrations would unlikely be detected. Given that enhancement of export has been associated with fronts (Ohman et al, 2012; Stukel et al, 2017), DOC surplus may be found in the bathypelagic waters beneath them as well To explore this possibility, we present novel observations beneath well-defined, productive frontal zones in the central North Pacific.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
