Chlorophyll concentration and optical absorption spectra of particulate and dissolved material, collected at several depths on DEEPEND cruises DP05 from January-December 2017

The optical absorption spectra from seawater’s particulate and dissolved components can be used to compute the penetration of light to various depths, estimate the proportion of living to non-living particulate matter, assess photosynthetic light availability and the type of phytoplankton present, and to validate satellite or airborne ocean color measurements. Chlorophyll and phaeopigment concentrations are often used to estimate the amount of phytoplankton present, and to allow extrapolation of in situ fluorometric measurements. Water was collected using a CTD rosette near the surface and from several depths at each sampling station occupied by the DEEPEND cruise DP05 (see GRIIDC dataset R4.x257.226:0014). A variable amount (<1 to 5 l) of this water was filtered through glass-fiber filter pads. The filter pads were stored for subsequent analysis. Some of the filtrate was passed through an additional nylon membrane (0.2 µm) filter, and also retained for shore based analysis. Optical absorption of the particulate material on the filter pads was determined on shore, using the quantitative filter technique (Yentsch, 1962; Kiefer and SooHoo, 1982). The spectral transmission of light (400-800nm) passing through each filter pad was measured, both before and after the phytoplankton pigments are extracted from the particles retained on the filter pad using methanol (Kishino et al., 1985). These techniques allow the optical absorption spectra of the particles in the water to be determined, as well as the proportion of absorption due to pigmented or detrital material. The extraction of pigments allows the chlorophyll a and phaeopigment concentration to be determined fluorometrically using an acidification technique (Holm-Hansen et al., 1965; Holm-Hansen and Riemann, 1978). The filtrate from the at sea filtration is analyzed using a spectrophotometer to determine the absorption spectra (200-800nm) of the colored dissolved material (CDOM) in the water sample. This data was collected during the same cruise as GRIIDC CTD dataset R4.x257.230:0013.

海水颗粒物与溶解组分的光吸收光谱（optical absorption spectra）可用于计算光在不同深度的穿透情况、估算活体与非活体颗粒物的占比、评估光合有效光照条件及现存浮游植物（phytoplankton）类群，同时可用于验证卫星或机载海洋水色测量结果。叶绿素与脱镁叶绿素（phaeopigment）浓度常被用于估算现存浮游植物生物量，并可对原位荧光测量（in situ fluorometric measurements）结果进行外推校准。
研究人员采用温盐深采水器阵列（CTD rosette），在DEEPEND航次DP05的各采样站位分别采集近表层及多个深度层的海水样本（详见GRIIDC数据集R4.x257.226:0014）。取体积介于1升以下至5升的上述水样，经玻璃纤维滤垫（glass-fiber filter pads）过滤，过滤所得的滤垫将被留存以待后续分析。取部分滤液经孔径0.2微米的尼龙膜（nylon membrane）二次过滤，留存滤液以供岸基实验室分析。
采用定量滤膜技术（quantitative filter technique，Yentsch, 1962; Kiefer and SooHoo, 1982），在岸基实验室测定滤垫上留存颗粒物的光吸收特性：分别在利用甲醇萃取滤垫留存颗粒物中的浮游植物色素前后（Kishino等, 1985），测量波长范围400至800纳米的光透过各滤垫的光谱透射率。通过上述方法，可同时测定海水中颗粒物的光吸收光谱，以及色素类或碎屑类物质对总光吸收的贡献占比。
通过萃取浮游植物色素，可采用酸化荧光法（Holm-Hansen等, 1965; Holm-Hansen与Riemann, 1978）测定叶绿素a与脱镁叶绿素的浓度。现场过滤所得的滤液经分光光度计（spectrophotometer）分析，以测定水样中有色溶解物质（CDOM, colored dissolved material）的吸收光谱（波长范围200至800纳米）。本数据集与GRIIDC CTD数据集R4.x257.230:0013采集于同一航次。