Macro‐scale exhaustion of surface phosphate by dinitrogen fixation in the western North Pacific

Abstract

In the subtropical oceans, nutrient concentrations are frequently below the detection limits of standard analytical methods. We applied a highly sensitive method to the surface water of the western and central Pacific between 42°N and 40°S and between 141°E and 158°W except in the equatorial zone, and detected overall depletion of nitrate + nitrite and an excess of SRP. However, a remarkable exception was found: an almost complete exhaustion of SRP (<10 nM) existed at a horizontal scale of >2000 km in the western subtropical North Pacific in both summer and winter. The SRP exhaustion was a consequence of an elevated dinitrogen fixation, which occurred in areas with high dust deposition from the Asian continent that likely enhanced SRP consumption. A coupling among nutrient dynamics, dinitrogen fixation and dust deposition produces the extremely low P availability spanning a large area, which appears to be unique to the western North Pacific.

Phosphate monoesterase and diesterase activities in the North and South Pacific Ocean

“…The values were within the range of the reported values from the western North Pacific (Suzumura et al, 2012) and lower than that from the central North and eastern South Pacific (Duhamel et al, 2011). The contrasting turnover times at the North and South Pacific subtropical gyres may reflect the differences in the SRP concentrations between the two gyres (Hashihama et al, 2009;. Actually, the slower turnover of phosphate monoesters at the higher concentration of SRP was observed when the scope was confined to the western North Pacific in the present study (Tables 2 and 3).…”

“…The present study is the first to reveal the extensive distribution of alkaline phosphatase activities of both monoesterase and diesterase in the Pacific Ocean, including the north western subtropical area depleted with SRP at a nanomolar level (Hashihama et al, 2009). Previous phosphatase studies of the Pacific Ocean (Koike and Nagata, 1997;Duhamel et al, 2010Duhamel et al, , 2011 were primarily focused on the central and eastern Pacific, where > 10 nM of SRP was detected.…”

“…In the western part of the North Pacific subtropical gyre, surface soluble reactive phosphorus (SRP), which consists mainly of inorganic phosphate, is exhausted down to < 3 nM (Hashihama et al, 2009), while its concentration in the South Pacific subtropical gyre is higher than 100 nM . Despite the importance of revealing biogeochemical phosphorus cycling across these contrasting phosphorus regimes, studies have generally been concentrated in the South Pacific Duhamel et al, 2011) and the central part of the North Pacific near Hawaii (Björkman et al, 2000;Brum, 2005).…”

“…The SRP concentration was determined by using a highly sensitive colorimeter equipped with a liquid waveguide capillary cell (LWCC) (Hashihama et al, 2009). Phosphate-free seawater, prepared by the MAGIC procedure (Karl and Tien, 1992), was used as the blank and standard matrix.…”

Improved Solid-phase Spectrometry for the Microdetermination of Total and Dissolved Phosphate

“…18 The surface water phosphate concentration in the western North Pacific was determined by continuous-flow analysis using a 1-m long liquid waveguide capillary cell. 19 The detection limit was 0.1 μg dm -3 . Because the corresponding solution molybdenum blue method can be easily expanded to the SPS method presented here, all determination procedures are relatively simple.…”