The TP concentrations in diatomaceous oozes at stations BC1604 and BC1605 were lower than those in pelagic clays (
Table 1). This is similar to the spatial variation of the total sedimentary P in the central Indian Ocean, where higher TP concentrations were detected in the pelagic clay area (
Linsy et al., 2018). The high particle reactivity of P likely promotes its adsorption onto the surfaces of fine-grained particles, such as clays and oxides/hydroxides (
Lin et al., 2016;
Linsy et al., 2018). Compared with pelagic clays, diatomaceous ooze typically contains coarser grains, which may be responsible for low concentration of Ex-P and Fe-P compared with that of stations in vicinity with pelagic clay (
Garrison and Ellis, 2015;
Fig. 2). Due to higher sedimentation rates of diatomaceous ooze compared with pelagic clay (
Seibold and Berger, 2017), the accumulation time of Det-P is shorter in diatomaceous ooze station as we taken the same top 2 cm of box-corer for sample analysis. By the same token, the time either the formation
in situ or settlement of Auth-P is shorter. Thus, the concentrations of Det-P and Auth-P in diatomaceous ooze station was lower than pelagic clay. The relative proportion of different P phases in the BMW sediment follow the order of Det-P>Auth-P>Org-P>Fe-P>Ex-P (
Fig. 2). Det-P is the largest P pool in the BMW sediment, exceeding 50% of the TP, with an average of 58.9% (
Fig. 2). These results differ from those determined for sediments around the equatorial Pacific Ocean (
Filippelli and Delaney, 1996). Generally, P predominantly enters the ocean via rivers and atmospheric transport, with the atmospheric/aerosol input prevailing in open ocean environments, especially within the northern hemisphere “dust belt” between ~10°N and ~60°N (
Prospero et al., 2002;
Maher et al., 2010).
Kyte et al. (1993) reported that bulk surface sediments at site LL44-GC3 in the north central Pacific contained 95% eolian dust. Previous studies also described a large proportion of Det-P related to terrigenous input in the central Pacific Ocean and the Bering Sea (
März et al., 2014;
Ni et al., 2015;
Zhang et al., 2010). Earlier studies revealed the combined effects of the Asian winter monsoon and the westerly jet stream, which delivered terrigenous materials originating from the Taklimakan Desert, Loess Plateau, and south Mongolian Gobi Desert to the north Pacific Ocean, where the terrigenous input is the dominant component of pelagic sediments (
Chen et al., 2006;
Jones et al., 2000;
Miyazaki et al., 2016;
Yasukawa et al., 2019;
Zhao et al., 2015) (
Fig. 1).
Hashihama et al. (2009)’s research, based on the model stimulation, showed the area (20°–30°N, 150°–160°E) existed the spike of dust deposition which contributed to elevated N
2-fixed as the result of iron supply in the region. Given the source of P in aerosols varied highly, solubility of P from different sources is greatly difference. Generally, solubility of P from mineral source is lower than particles form anthropogenic sources (
Herut et al., 2002;
Anderson et al., 2010;
Shi et al., 2019;
Herbert et al., 2018). The solubility of P in aerosols also may be related to specific P phases which have different susceptibility to dissolution (
Anderson et al., 2010).
Shi et al. (2019) studied phosphorus solubility in aerosol particles from westerly wind in China, and found total dissolved P constitute 21.3%±9.8% of TP in spring, the season particles mainly influenced by mineral dust form the arid and semiarid areas. And the part of soluble P may connect with anthropogenic sources (
Anderson et al., 2010).
Nenes et al. (2011) proposed solubility of P in aerosols increased with enhanced acidification intensity which correlated to
${\rm{SO}}_4^{2-} $ and
${\rm{NO}}_3^- $. And pH may be seldom above 4 in aerosols only when aerosol particles were to reside in clouds and were activated into cloud droplets. Thus, Det-P may be more resistant to experience transformation than Auth-P in aerosols, due to pre-extraction step using acetate buffer (pH=4, step 3) for Auth-P before Det-P extraction in SEDEX procedure.
Flaum (2008) and
Guo et al. (2011) found that Det-P and Auth-P were the dominant P species in the dust from the Loess Plateau and Gobi Desert, accounting for approximately 42.5% and 41.9% of the TP, respectively. They determined that the higher concentration of Det-P was associated with finer grain size, which was easily transported by wind to the ocean. The percentage of Det-P in the sedimentary TP of the BMW (on average 59.0%) was comparable to that of the Asian eolian dust, indicating that Det-P in the study area was mainly derived from the eolian input.