DOI: 10.6084/m9.figshare.20486022
title: Seasonal distribution of particulate organic matters in the South Yellow Sea during late 2017 to 2019

description: This study focused on two subregions of the South Yellow Ses (SYS): the Subei coast region and the central basin. The Subei coast region is near the Subei Shoal with a hydrological regime driven by vertical mixing and costal currents. Its average depth is &lt;20 m, which means robust resuspension due to strong bottom stress and turbulent kinetic energy. The central basin has average depth of &gt;70 m. Its variability of biogeochemical dynamics is substantial with moderate mixing in winter, phytoplankton blooms in spring/autumn, and stratification in summer. <br> Four field surveys were conducted in the SYS between late 2017 and 2019, covering the four seasons. The winter, spring, and summer cruises were conducted by the R/V “<em>Dongfanghong</em> <em>2</em>” during 18 December 2017 to 18 January 2018, 28 March to 16 April 2018, and 24 July to 8 August 2018, respectively. The autumn survey was performed by the R/V “<em>Lanhai 101</em>” during 10–19 October 2019. Three water depth samples were collected at each station in the coastal region (surface layer: 2–4 m; middle layer: 7–10 m; bottom layer: 13–25 m), and three or four water depth samples were collected in the central region (surface layer: 2–5m; subsurface layer: 15–20 m; middle layer: 30–45 m; bottom layer: 55–75 m). Water samples were collected using an onboard Rosette sample system equipped with a conductivity–temperature–depth (CTD) instrument (Seabird 19 Plus). Additional hydrological parameters including temperature, salinity, turbidity, and depth were also measured simultaneously via the CTD sensors. The total number of samples obtained in this study were 108 (9 in the Subei coast region and 47 in the central basin), 84 (9 in the Subei coast region and 33 in the central basin), 116 (8 in the Subei coast region and 41 in the central basin), and 124 (9 in the Subei coast region and 39 in the central basin) in winter, spring, summer, and autumn, respectively. <br> A certain volume of each sample, extracted for particulate matter analysis (depending on the site: 0.5–2 L in the coastal region; 3–5 L in the central region), was filtered through glass fiber filters (GF/F, 47 mm diameter, Whatman). These filters were preweighed and precombusted in a muffle furnace at 450 °C for 5 h. After filtration, these filters were rinsed three times with ultrapure water. Subsequently, they were folded and wrapped in precombusted aluminum foil and then preserved at −20 °C until required for analysis in the laboratory. Prior to analysis, filters were fully dried in a vacuum freeze dryer for at least 24 h. Each dried filter was weighed and then quantitatively divided into two parts. The first part was used to determine particulate carbon and nitrogen; the second part was fumed with 15 mL of 36% HCl for removal of carbonate and then redried for POC measurement. Determination of these elements was performed using a Costech ECS4024 Elemental Analyzer following the standard CHN analysis method by combusting the filters at high temperature (Sharp, 1991). The standard curve was obtained using standard methionine (NC Technologies). The detection limit for carbon was 0.002 mg C (R<sup>2</sup> &gt; 0.99) and that for nitrogen was 0.005 mg N (R<sup>2</sup> &gt; 0.99). A methodological problem is that the protocol for removing carbonate is inefficient for the removal of inorganic N, which means that the residual N after fuming is actually the total nitrogen consisting of both organic and inorganic parts. Hence, the N composition of the suspended POM is hereafter represented by PN. The mass of TSM was taken as the dry weight difference of the filters before and after filtration. <br> Weidong Zhai designed the field surveys and supervised the research. Shu Yang maintained the operation of instrument. Congcong Guo finalized the data set. Jing Lang is appreciated for field sampling and most laboratory determination. Yao Niu contributed to the autumn data collection.