Nanomolar phosphate supply and its recycling drive net community production in the subtropical North Pacific

Hashihama, Fuminori; Yasuda, Ichiro; Kumabe, Aki; Sato, Minoru; Sasaoka, Hiroshi; Iida, Yosuke; Shiozaki, Takuhei; Saito, Hiroaki; Kanda, Jun; Furuya, Ken; Boyd, Philip W.; Ishii, Masao

doi:10.1038/s41467-021-23837-y

Cited by 13 publications

(15 citation statements)

References 65 publications

(101 reference statements)

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“…This trend is consistent with the overall pattern in climatological values from the WOA dataset (Fig. 1a) alongside other previous observations (Hashihama et al 2009(Hashihama et al , 2021Kitajima et al 2009;Shiozaki et al 2010;Martiny et al 2019). Surface N 2 fixation rates measured at the four stations demonstrated an opposite trend to that of surface DIP concentrations, with rates decreasing abruptly between the two northerly stations (1.46 and 1.15 nmol L À1 d À1 at Stas.…”

Section: Resultssupporting

confidence: 91%

“…Most evidence for DIP depletion has been provided from the (sub)tropical North Atlantic, where numerous studies have demonstrated that DIP concentrations can be depleted to < 10 nmol L À1 , levels leading to microbial phosphorus stress (Wu et al 2000;Mather et al 2008;Moore et al 2008Moore et al , 2009Van Mooy et al 2009;Mahaffey et al 2014;Browning et al 2017). However, evidence has also accumulated for low DIP concentrations over a broad extent of the (sub)tropical North Pacific (Hashihama et al 2009(Hashihama et al , 2021Kitajima et al 2009;Shiozaki et al 2010;Martiny et al 2019;Browning et al 2022). This has important implications for projecting future changes of the broad oligotrophic North Pacific ecosystems, given the fact that DIP concentrations have been suggested to be declining in recent decades in this region (Kim et al 2014).…”

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confidence: 99%

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Potential drivers and consequences of regional phosphate depletion in the western subtropical North Pacific

Yuan

Browning

Zhang

et al. 2023

Limnol Oceanogr Letters

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Concentrations of phosphate, an essential nutrient for phytoplankton growth, are depleted across a large extent of the western subtropical North Pacific. However, the drivers and consequences of this are still not well constrained. We investigated this with field and satellite observations, shipboard experiments, and model estimates of aerosol nutrient supply across a major phosphate gradient in this region. Collectively these data suggested that phosphate depletion was primarily driven by enhanced nitrogen fixation rates stimulated by aerosol iron, in turn supplying biologically available nitrogen without a corresponding supply of phosphate. The impact of observed phosphate depletion was enhanced microbial utilization of the more abundant dissolved organic phosphorus pool.

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Section: Resultssupporting

confidence: 91%

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confidence: 99%

Potential drivers and consequences of regional phosphate depletion in the western subtropical North Pacific

Yuan

Browning

Zhang

et al. 2023

Limnol Oceanogr Letters

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“…Despite the above-described uncertainties of our calculations, our estimates are in the lower range, but in the same order of magnitude, of the only reported diapycnal P fluxes to the upper euphotic zone based on simultaneous turbulence microstructure and high-resolution chemical measurements in the oligotrophic South China Sea (Du et al, 2017) and in the subtropical North Pacific (Hashihama et al, 2021). Thus, despite hydrological differences among these oceanic regions, we assume our estimates to be valid for the purpose of the following section of this work, i.e., to assess the relative contribution of external and internal sources of phosphate to the mixed layer.…”

Section: Vertical Variability Of Phosphate Inside the Phosphate-depleted Layersupporting

confidence: 42%

Phosphorus cycling in the upper waters of the Mediterranean Sea (PEACETIME cruise): relative contribution of external and internal sources

et al. 2021

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Abstract. The study of phosphorus cycling in phosphate-depleted oceanic regions, such as the Mediterranean Sea, has long suffered from methodological limitations, leading to a simplistic view of a homogeneous surface phosphate pool with concentrations below the detection limit of measurement above the phosphacline. During the PEACETIME (Process studies at the air-sea interface after dust deposition in the Mediterranean Sea) cruise, carried out from 10 May to 11 June 2017, we conducted co-located measurements of phosphate pools at the nanomolar level, alkaline phosphatase activities and atmospheric deposition of phosphorus, across a longitudinal gradient from the west to the central Mediterranean Sea. In the phosphate-depleted layer (PDL), between the surface and the phosphacline, nanomolar phosphate was low and showed little variability across the transect spanning from 6 ± 1 nmol L−1 in the Ionian basin to 15 ± 4 nmol L−1 in the westernmost station. The low variability in phosphate concentration contrasted with that of alkaline phosphatase activity, which varied over 1 order of magnitude across the transect. Nanomolar phosphate data revealed gradients of phosphate concentration over density inside the PDL ranging between 10.6 ± 2.2 µmol kg−1 in the westernmost station to values close to zero towards the east. Using the density gradients, we estimated diapycnal fluxes of phosphate to the PDL and compared them to atmospheric deposition, another external source of phosphate to the PDL. Phosphate supply to the PDL from dry deposition and diapycnal fluxes was comparable in the western part of the transect. This result contrasts with the longtime idea that, under stratification conditions, the upper waters of the Mediterranean Sea receive new P almost exclusively from the atmosphere. The contribution of atmospheric deposition to external P supply increased under the occurrence of rain and Saharan dust. Although this finding must be taken cautiously given the uncertainties in the estimation of diapycnal fluxes, it opens exciting questions on the biogeochemical response of the Mediterranean Sea, and more generally of marine oligotrophic regions, to expected changes in atmospheric inputs and stratification regimes. Taken together, external sources of phosphate to the PDL contributed little to total phosphate requirements which were mainly sustained by in situ hydrolysis of dissolved organic phosphorus. The results obtained in this study show a highly dynamic phosphorus pool in the upper layer of the euphotic zone, above the phosphacline, and highlight the convenience of combining highly sensitive measurements and high-resolution sampling to precisely depict the shape of phosphate profiles in the euphotic zone with still unexplored consequences on P fluxes supplying this crucial layer for biogeochemical cycles.

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“…The limitations of iron and phosphate were confirmed during both seasons. The surface phosphate level in the western NPSG was <15 nmol l −1 , regardless of the season (Hashihama et al., 2009, 2019, 2021; Kodama et al., 2011). Similarly, low levels were observed in the North Atlantic subtropical gyre (Mather et al., 2008), where diazotrophs are under phosphate limitation and colimitation of iron and phosphate (Langlois et al., 2012; Mills et al., 2004; Sañudo‐Wilhelmy et al., 2001; Turk‐Kubo et al., 2012).…”

Section: Discussionmentioning

confidence: 99%

Regionally Variable Responses of Nitrogen Fixation to Iron and Phosphorus Enrichment in the Pacific Ocean

et al. 2021

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Nitrogen fixation is a major source of new nitrogen in the ocean, where nitrogen limits primary production and drives carbon flux from the surface water to the ocean interior (Gruber & Galloway, 2008). Iron and phosphorus are well-known key factors for marine nitrogen fixation (Sohm, Webb, & Capone, 2011;Zehr & Capone, 2020). Iron is contained in the reaction center of nitrogenase, the key enzyme for nitrogen fixation, and is essential to the dimeric protein of nitrogenase that donates electrons to the catalytic sites (Dixon & Kahn, 2004). Since diazotrophs require a substantial amount of iron (Kustka et al., 2003), iron availability controls the distribution of nitrogen fixation in the ocean (Falkowski, 1997). Nitrogen fixation

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Nanomolar phosphate supply and its recycling drive net community production in the subtropical North Pacific

Cited by 13 publications

References 65 publications

Potential drivers and consequences of regional phosphate depletion in the western subtropical North Pacific

Potential drivers and consequences of regional phosphate depletion in the western subtropical North Pacific

Phosphorus cycling in the upper waters of the Mediterranean Sea (PEACETIME cruise): relative contribution of external and internal sources

Regionally Variable Responses of Nitrogen Fixation to Iron and Phosphorus Enrichment in the Pacific Ocean

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