Primary, new and export production in the NW Pacific subarctic gyre during the vertigo K2 experiments

Abstract

This paper presents results on tracer experiments using 13 C and 15 N to estimate uptake rates of dissolved inorganic carbon (DIC) and nitrogen (DIN).Experiments were carried out at station K2 (47°N, 161°E) in the NW Pacific subarctic gyre during July-August 2005. Our goal was to investigate relationships between new and export production. New production was inferred from the tracer experiments using the f ratio concept (0-50m); while export production was assessed with neutrally buoyant sediment traps (NBSTs) and the e ratio concept (at 150m). During trap deployments, K2 was characterized both by changes in primary production (523 to 404), new production (119 to 67 mg C m -2 d -1), export production (68 to 24 mg) and phytoplankton composition (high to low proportion of diatoms). The data indicate that 17 to 23% of primary production is exportable to deeper layers (f ratio) but 2 only 6 to 13% collected as a sinking particle flux at 150m (e ratio). Accordingly, > 80% of the carbon fixed by phytoplankton would be mineralized in the upper 50m (1 -f), while < 11% would be within 50-150m (f -e). DIN uptake flux amounted to 0.5 mM m -2 h -1, which was equivalent to about 95% particulate nitrogen (PN) remineralized and/or grazed within the upper 150 m. Most of the shallow PN remineralization occurred just above the depth of the deep chlorophyll maximum (DCM), where a net ammonium production was measured. Below the DCM, while nitrate uptake rates became negligible because of light limitation, ammonium uptake did continue to be significant. The uptake of ammonium by heterotrophic bacteria was estimated to be 14-17% of the DIN assimilation. Less clear are the consequences of this uptake on the phytoplankton community and biogeochemical processes, e.g. new production. It was suggested that competition for ammonium could select for small cells and may force large diatoms to use nitrate. This implies that under Fe stress as observed here, ammonium uptake is preferred and new production progressively suppressed despite the surplus of nitrate. .

New estimation of N2 fixation in the western and central Pacific Ocean and its marginal seas

“…The open square indicates that no N 2 fixation was detected. Data for N 2 fixation measurements at various stations are from Dore et al [2002], Montoya et al [2004], Voss et al [2006], Needoba et al [2007], Garcia et al [2007], White et al [2007], Chen et al [2008], Elskens et al [2008], Moutin et al [2008], Grabowski et al [2008], Church et al [2009], and Bonnet et al [2009]. Background contour indicates nitrate concentrations ( μM ) in the surface waters.…”

Export and remineralization of POM in the Southern Ocean and the South China Sea estimated from 210Po/210Pb disequilibria

“…Our result was coincident with that. Elskens et al [27] found 3.7-4.3 mmol C·m −2 ·d −1 of new production were remineralized from 50-150 m in the northern Pacific according to carbon mass balance. Dehairs et al [28] estimated that the POC remineralization fluxes varied between 1.0-8.8 mmol C·m −2 ·d −1 in the northern Pacific.…”

Shedding light on processes that control particle export and flux attenuation in the twilight zone of the open ocean

“…; Table 5). Furthermore, for K2, we chose to parameterize the model with an initial PT immediately below the euphotic zone, given the shallow euphotic zone and some evidence from 234 Th and nutrient budgets of significant remineralization between 50 and 150 m (Buesseler et al 2008b;in press;Elskens et al 2008). At depths below this initial PT, we used a longer PT length scale (150 m) due to the larger size of zooplankton fecal pellets at K2 relative to ALOHA, which, along with their higher mineral content, would increase sinking rates (Buesseler et al 2007b;Wilson et al 2008).…”