Temporal and spatial distribution characteristics of nutrients in Clarion-Clipperton Fracture Zone in the Pacific in 2017
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Abstract: This research investigated eight stations in Clarion-Clipperton Fracture Zone (CCFZ) in the eastern tropical Pacific in 2017 to study the spatial distribution characteristics of nutrients and chlorophyll a (Chl a) concentration, and compared nutrient concentrations and molar ratios with those of other investigations 20 years ago in the same area. The study found that dissolved inorganic nutrient (N, P and Si) concentrations were lowest in the upper layer, and increased from surface to some depths, then they decreased a little to the bottom. N was the limited nutrient factor for the growth of phytoplankton community. Although nutrient concentrations and molar ratios have no obvious changes in 2017 comparing those in 1998−2003, supplemented from the equatorial Pacific, nutrient concentrations in the study area were higher than those in seamounts in the North Pacific and Station ALOHA. Furthermore, this study used Generalized Additive Models (GAMs) to infer the underlying bottom-up factors controlling phytoplankton abundance (Chl a concentration), showing that depth, salinity and
${\rm{PO}}_4^{3 - }{\text -}{\rm{ P}} $ concentration were major factors controlling the growth of phytoplankton community. Furthermore, this study can provide basic data and theoretical support for the development of polymetallic nodule area and its long-term impact assessment on the environment. -
Figure 7. Generalized Additive Models (GAMs) plots illustrate significant relationship (p<0.05) between the lgChl a and depth, salinity and
${\rm{PO}}_4^{3 - }{\text -}{\rm{P}} $ . The solid line is the fitted line, while the shaded areas represent 95% confidential intervals. The numbers in the labels of y-axis denote the effective degrees of freedom; the definition of the labels of y-axis refers to Table 8.Table 1. Location and water depth of sampling stations in 2017
Station Latitude Longitude Date Depth/m CC-S06 12°58.115 1' N 153°14.585 2' W Agu. 21 5 447 CC-S01 8°30.025 6' N 154°15.151 1' W Agu. 25 5 187 KW1-S37 9°30.103 0' N 154°14.884 1' W Spet. 4−5 5 133 KW1-S05 10°04.973 9' N 154°20.038 5' W Sept. 9−10 5 173 KW1-S01 11°00.011 8' N 154°15.006 0' W Sept. 17 5 240 KW1-S40 10°11.506 6' N 154°35.663 3' W Sept. 19 5 148 CC-S09 12°59.669 3' N 154°15.523 0' W Oct. 7 5 414 CC-S10 11°59.999 0' N 154°15.006 2' W Oct. 8 5 008 Table 2. Technical parameters of turbidity and Chl a by CTD (SeaBird, SBE 911plus CTD)
Parameters Wave length Sensitibity Resolution Range Turbidity 700 nm 0.01 NTU 0.007 NTU 0−25 NTU Chl a 470/695 nm 0.025 μg/L 0.013 μg/L 0−50 μg/L Table 3. Accuracy and precision of nutrient concentrations, DO and pH (General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China, Standardization Administration, 2008)
Parameters pH ${\rm{NO} }_3^ -\text{-} {\rm{N} }$
/(μmol·L−1)${\rm{NO}}_2^ -{\text -} {\rm{N}} $
/(μmol·L−1)${\rm{NH}}_4^+ {\text - }{\rm {N}} $
/(μmol·L−1)${\rm{SiO}}_3^{2 - } {\text -} {\rm{Si}}$
/(μmol·L−1)${\rm{PO}}_4^{3 - }{\text -}{\rm{P}} $
/(μmol·L−1)DO
/(μmol·L−1)Range − 0.05−16.0 0.02−4.00 0.03−8.00 0.10−25.0 0.02−4.80 5.3−1.0×103 Accuracy ±0.02 C=2.0,
RE=±7.0%;
C=10.0,
RE=±4.0%.C= 0.5,
RE=±5.0%;
C=1.00,
RE=±3.0%.C=1.0,
RE=±7.0%;
C=7.0,
RE=±4.0%.C=4.5,
RE=±5.0%.
−
−C=0.20,
RE=±10%;
C=2.0,
RE=±3.5%.−
−
−
−Precision ±0.01 C=5.0,
RSD=±4.0%;
C=10.0,
RSD=±3.0%.C=0.3,
RSD=±5.0%;
C=1.00,
RSD=±2.0%.C=1.00,
RSD=±7.0%;
C=7.00,
RSD=±3.0%.C=4.5,
RSD=±4.0%.
−
−C=0.20,
RSD=±10%;
C=2.0,
RSD=±3.0%.C<160,
SD=±2.8;
C≥550,
SD=±4.0.Note: − repersents no data; C represents concentration; RSD, relative standard deviation; SD, standard deviation; RE, relative error. Table 4. Comparing nutrient concentrations and molar ratios in water columns in SWPO and CCFZ in 2017
Area DIN/(μmol·L−1) ${\rm{PO}}_4^{3 - }{\text -}{\rm{ P}} $/(μmol·L−1) ${\rm{SiO}}_3^{2 - } {\text -} {\rm{Si}} $/(μmol·L−1) N/P N/Si Si/P NA range nd−56.8 nd−2.91 0.29−208 1.21−2284 0.00−2.90 11.6−1372 average 18.1±20.8 1.08±1.27 50.0±63.5 151±392 0.73±0.73 405±419 NLG range nd−46.1 nd−2.93 0.36−145 0.94−1157 0.01−2.90 10.8−1784 average 17.3±18.6 1.20±1.27 50.4±59.5 83.4±182 0.73±0.76 285±433 MP4 range nd−46.3 nd−2.91 0.31−153 0.50−956 nd−3.00 8.57−1166 average 18.1±20.1 1.15±1.27 50.3±61.6 79.5±162 0.68±0.71 283±353 C1 range 0.02−42.8 nd−2.75 0.50−140 13.6−106 0.04−1.75 21.9−1114 average 18.6±19.5 1.19±1.25 52.4±60.4 46.1±25.3 0.66±0.57 288±385 CCFZ range nd−61.5 0.10−3.34 0.14−174 0.01−21.7 0.00−3.09 1.05−80.0 average 25.8±19.3 1.79±1.17 64.6±63.0 10.7±6.64 0.55±0.50 27.3±23.2 Note: nd represents under detection limit. Table 5. Comparing nutrient concentrations, nutrient molar ratios, and Chl a concentration in 0−100 m depth layer of SWPO and CCFZ in 2017
Area DIN/(μmol·L−1) ${\rm{PO}}_4^{3 - }{\text -}{\rm{ P}} $/(μmol·L−1) ${\rm{SiO}}_3^{2 - } {\text -} {\rm{Si}} $/(μmol·L−1) N/P N/Si Si/P Chl a/(μg·L−1) NA range nd−0.44 nd 0.29−1.01 0.54−442 0.00−0.89 286−1007 nd−0.17 average 0.06±0.11 nd±0.00 0.67±0.21 57.6±108 0.12±0.24 666±208 0.08±0.05 NLG range 0.01−0.52 nd−0.10 0.36−1.61 0.43−523 0.01−1.47 11.7−1611 nd−0.39 average 0.10±0.13 0.01±0.02 0.99±0.35 79.8±132 0.14±0.30 617±456 0.12±0.10 MP4 range nd−0.43 nd−0.05 0.36−0.87 0.54−432 0.00−0.54 10.9−867 nd−0.32 average 0.08±0.12 0.00±0.01 0.59±0.17 78.4±127 0.13±0.16 512±244 0.10±0.09 C1 range 0.02−0.05 nd 0.50−1.01 19.5−48.0 0.02−0.10 495−1007 0.05−0.19 average 0.03±0.01 nd±0.00 0.70±0.22 32.6±13.1 0.05±0.03 704±219 0.11±0.06 CCFZ range 0.00−12.4 0.10−1.11 0.14−8.73 0.00−29.3 0.00−9.10 1.05−40.4 0.01−1.02 average 1.34±2.75 0.27±0.24 1.99±2.16 5.79±7.61 1.19±2.22 7.36±6.98 0.28±0.30 Note: nd represents under detection limit. Table 6. Ranges of nutrient and DO concentrations (μmol/L) in CCFZ in 1998−2017 (Tu, 2006)
Sampling time ${\rm{PO}}_4^{3 - }{\text -}{\rm{ P}} $ ${\rm{SiO}}_3^{2 - } {\text -} {\rm{Si}} $ ${\rm{NO}}_3^ - {\text -} {\rm{N}} $ ${\rm{NO}}_2^ - {\text -} {\rm{N}} $ ${\rm{NH}}_4^+ {\text - }{\rm {N}} $ DO Aug. 1998 0.07−3.09 0.00−165.9 0.00−64.12 0.00−0.85 0.00−2.04 32.8−440.2 Oct. 1999 0.00−3.28 0.00−178.3 0.00−64.35 0.01−1.58 − 28.8−438.9 Oct. 2001 0.02−3.19 0.40−152.8 0.13−54.15 0.00−0.73 0.49−1.07 22.4−442.4 Sept. 2002 0.10−3.10 0.62−133.9 0.01−50.31 − − 44.5−426.3 Sept.−Oct. 2003 0.05−3.22 2.94−152.8 0.00−52.56 0.00−0.54 − 15.0−457.5 Aug.−Oct. 2017 0.11−3.34 0.14−172.0 0.00−49.77 0.00−0.99 0.00−1.05 16.9−424.6 Note: − represents no data. Table 7. Variance inflation factor (VIF) among parameters in CCFZ in 2017
Depth Temperature Salinity DO DIN ${\rm{PO}}_4^{3 - }{\text -}{\rm{ P}} $ ${\rm{SiO}}_3^{2 - } {\text -} {\rm{Si}} $ N/P N/Si Si/P Initial 6.59 10.18 2.63 9.38 31.88 35.45 64.36 14.58 4.53 13.42 Ultimate 6.51 9.32 2.61 7.54 − 8.48 − 7.84 3.68 1.16 Note: − represents no data. Table 8. Statistical results of GAMs in CCFZ in 2017
Model R2 GCV n lgChl a=s(depth)+s(salinity)+s(${\rm{PO}}_4^{3 - }{\text -}{\rm{P}} $)+b 0.863 0.280 41 Note: R2 represents the adjusted proportion of total variability explained by the model; GCV, generalized cross validation score; n, the total number of samples; s, thin plate regression spline; b, a mean constant. -
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