Tihomir Sabinov Kostadinov, David A. Siegel, Stéphane Maritorena, and Nathalie Guillocheau, "Optical assessment of particle size and composition in the Santa Barbara Channel, California," Appl. Opt. 51, 3171-3189 (2012)

The suspended particle assemblage in complex coastal waters is a mixture of living phytoplankton, other autochthonous matter, and materials of terrestrial origin. The characterization of suspended particles is important for understanding regional primary productivity and rates of carbon sequestration, the fate of anthropogenic materials released to the coastal environment, as well as its effects on bulk optical properties, which influence the passive optical remote sensing of the coastal ocean. Here, the extensive bio-optical Plumes and Blooms data set is used to characterize the surface particle assemblage in the Santa Barbara Channel, California, a highly productive, upwelling-dominated, coastal site affected by episodic sediment inputs. Available variables sensitive to characteristics of the particle assemblage include particle beam attenuation and backscattering coefficients, High Performance Liquid Chromatography (HPLC) pigment concentration observations, chlorophyll and particulate organic carbon concentration, particulate and phytoplankton absorption coefficients, and Laser In-situ Scattering and Transmissometry (LISST) 100-X particle sizer observations. Comparisons among these particle assemblage proxy variables indicate good agreement and internal consistency among the data set. Correlations among chlorophyll concentration, particulate organic carbon concentration (POC), HPLC pigments, and proxies sensitive to the entire particle assemblage such as backscattering and LISST data strongly indicate that in spite of its coastal character, variability in the particle assemblage in the Santa Barbara Channel is dominated by its marine biogenic component. Relatively high estimates of the bulk real index of refraction and its positive correlation with chlorophyll and lithogenic silica concentration tentatively indicate that there is minerogenic particle influence in the Santa Barbara Channel that tends to covary with the phytoplankton blooms. Limitations of each particle assemblage proxy and remote-sensing applications are discussed.

Wayne Homer Slade and Emmanuel Boss Appl. Opt. 54(24) 7264-7277 (2015)

References

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PFTs are related to size and can characterize the entire particle assemblage if it is of marine biogenic origin

Particulate backscattering probability

${\tilde{b}}_{\mathrm{bp}}$

Hydroscat-6 and AC-9 data

Function of the complex index of refraction (composition) and the PSD. Can be used to estimate the real index of refraction together with PSD slope data/estimates [30]

Ratio of phytoplankton absorption to total particulate absorption

%${a}_{\mathrm{ph}}$

Discrete hyperspectral spectrophotometric data of component IOPs. Calculated as ${a}_{\mathrm{ph}}(443)/{a}_{p}(443)$

Indicates particle composition, i.e., fraction of living phytoplankton cells in the total particle assemblage [38]

Data sources for calculation or modeling of the proxies are indicated, as well as significance of the proxy in terms of particle size and composition.

Table 2.

Table of ${R}^{2}$ Values of Regressions Between the Various Proxies of Particle Sizea

LISST-based

${\gamma}_{\mathrm{cp}}$-based (AC-9)

$\eta $-based (HS-6)

HPLC-based

${a}_{\mathrm{ph}}^{*}(\lambda )$-based

${\gamma}_{\mathrm{cp}}$-based (AC-9)

LISST $\xi $ vs. ${\gamma}_{\mathrm{cp}}+3$ Fig. 3(b)${R}^{2}=0.42$

$\eta $-based (HS-6)

$\eta $ versus LISST $\xi $ Fig. 3(d)${R}^{2}=0.09$

$\eta $ versus ${\gamma}_{\mathrm{cp}}+3$ Fig. 3(d)${R}^{2}=0.25$

The variables used in each regression are indicated, as well as the figure on which the regression is plotted, where more regression statistics can be found.

Table 3.

Linear Correlation Coefficients Between PnB Variables Relevant to Particle Assemblage Compositionab

POC

0.78

${\tilde{b}}_{\mathrm{bp}}$

0.20

0.18

$\eta $

$-\mathbf{0.39}$

$-\mathbf{0.38}$

$-\mathbf{0.25}$

$\xi $

$-\mathbf{0.46}$

$-\mathbf{0.47}$

$-\mathbf{0.48}$

0.31

LISST V

0.60

0.37

0.17

$-\mathbf{0.33}$

$-\mathbf{0.63}$

% pico

$-\mathbf{0.74}$

$-\mathbf{0.47}$

$-\mathbf{0.44}$

0.47

0.70

$-\mathbf{0.75}$

LSi

0.39

0.32

0.47

$-\mathbf{0.06}$

$-\mathbf{0.51}$

0.39

$-\mathbf{0.45}$

${n}_{p}$

0.44

0.35

—

$-\mathbf{0.45}$

$-\mathbf{0.67}$

0.50

$-\mathbf{0.73}$

0.38

${\gamma}_{\mathrm{cp}}$

$-\mathbf{0.58}$

$-\mathbf{0.44}$

$-\mathbf{0.27}$

0.50

0.65

$-\mathbf{0.64}$

0.74

$-\mathbf{0.13}$

—

% ${a}_{\mathrm{ph}}$

0.18

0.16

$-0.09$

0.06

$-\mathbf{0.24}$

0.03

0.00

$-\mathbf{0.37}$

0.03

$-\mathbf{0.16}$

Chl

POC

${\tilde{b}}_{\mathrm{bp}}$

$\eta $

$\xi $

LISST V

% pico

LSi

${n}_{p}$

${\gamma}_{\mathrm{cp}}$

Variable symbols and units are as follows: Chl—chlorophyll-$a$ concentration in $\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{-3}$ (here in log10-space); POC—particulate organic carbon in $\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{-3}$; ${\tilde{b}}_{\mathrm{bp}}$—probability of particle backscattering (spectral average); $\eta $—slope of ${b}_{\mathrm{bp}}(\lambda )$, $\xi $—PSD slope; LISST V—total particle volume from the LISST, ${\mathrm{m}}^{3}/{\mathrm{m}}^{3}$ in log10-space; % pico—HPLC-based percent picoplankton; and LSi—lithogenic silica concentration in $\mathrm{\mu mol}/\mathrm{L}$ in log10-space; ${n}_{p}$—real index of refraction; ${\gamma}_{\mathrm{cp}}$—slope of the particle beam attenuation coefficient; % ${a}_{\mathrm{ph}}$—percent of particulate absorption due to phytoplankton particles at 443 nm. The correlation coefficients of ${n}_{p}$ with ${\tilde{b}}_{\mathrm{bp}}$ and ${\gamma}_{\mathrm{cp}}$ are not included, because ${n}_{p}$ is modeled from these variables; see Fig. 5(a) and [30].
Significant correlations at the 95% confidence level are indicated in bold.

Tables (3)

Table 1.

Table of Particle Size and Composition Proxies Used in the Presented Analysesa

Particle Size/Composition Parameter or Proxy

Symbol

Calculated from

Notes

Slope of the particle size distribution

$\xi $

PSD data (LISST 100-X)

A fit of the actual PSD to a power law over a certain size range [Eq. (1)]. Can also be modeled from ${\gamma}_{\mathrm{cp}}$ and $\eta $ (see below)

Number concentration at reference diameter

${N}_{o}$

PSD data (LISST 100-X)

See [Eq. (1)]; here 2 μm is used as reference diameter. Can also be modeled from $\eta $ and ${b}_{\mathrm{bp}}(440)$ (see below)

Real index of refraction relative to seawater

${n}_{p}$

N/A

Modeled from PSD slope $\xi $ and particle backscattering probability ${\tilde{b}}_{\mathrm{bp}}$ [30]

Slope of the particle beam attenuation spectrum, ${c}_{p}(\lambda )$

${\gamma}_{\mathrm{cp}}$

AC-9 beam attenuation data and CDOM absorption data, ${c}_{p}(\lambda )=c(\lambda )-{a}_{g}(\lambda )$.

Related to $\xi $ via $\xi ={\gamma}_{\mathrm{cp}}+3$ [29]

Slope of the particle backscattering spectrum, ${b}_{\mathrm{bp}}(\lambda )$

PFTs are related to size and can characterize the entire particle assemblage if it is of marine biogenic origin

Particulate backscattering probability

${\tilde{b}}_{\mathrm{bp}}$

Hydroscat-6 and AC-9 data

Function of the complex index of refraction (composition) and the PSD. Can be used to estimate the real index of refraction together with PSD slope data/estimates [30]

Ratio of phytoplankton absorption to total particulate absorption

%${a}_{\mathrm{ph}}$

Discrete hyperspectral spectrophotometric data of component IOPs. Calculated as ${a}_{\mathrm{ph}}(443)/{a}_{p}(443)$

Indicates particle composition, i.e., fraction of living phytoplankton cells in the total particle assemblage [38]

Data sources for calculation or modeling of the proxies are indicated, as well as significance of the proxy in terms of particle size and composition.

Table 2.

Table of ${R}^{2}$ Values of Regressions Between the Various Proxies of Particle Sizea

LISST-based

${\gamma}_{\mathrm{cp}}$-based (AC-9)

$\eta $-based (HS-6)

HPLC-based

${a}_{\mathrm{ph}}^{*}(\lambda )$-based

${\gamma}_{\mathrm{cp}}$-based (AC-9)

LISST $\xi $ vs. ${\gamma}_{\mathrm{cp}}+3$ Fig. 3(b)${R}^{2}=0.42$

$\eta $-based (HS-6)

$\eta $ versus LISST $\xi $ Fig. 3(d)${R}^{2}=0.09$

$\eta $ versus ${\gamma}_{\mathrm{cp}}+3$ Fig. 3(d)${R}^{2}=0.25$

The variables used in each regression are indicated, as well as the figure on which the regression is plotted, where more regression statistics can be found.

Table 3.

Linear Correlation Coefficients Between PnB Variables Relevant to Particle Assemblage Compositionab

POC

0.78

${\tilde{b}}_{\mathrm{bp}}$

0.20

0.18

$\eta $

$-\mathbf{0.39}$

$-\mathbf{0.38}$

$-\mathbf{0.25}$

$\xi $

$-\mathbf{0.46}$

$-\mathbf{0.47}$

$-\mathbf{0.48}$

0.31

LISST V

0.60

0.37

0.17

$-\mathbf{0.33}$

$-\mathbf{0.63}$

% pico

$-\mathbf{0.74}$

$-\mathbf{0.47}$

$-\mathbf{0.44}$

0.47

0.70

$-\mathbf{0.75}$

LSi

0.39

0.32

0.47

$-\mathbf{0.06}$

$-\mathbf{0.51}$

0.39

$-\mathbf{0.45}$

${n}_{p}$

0.44

0.35

—

$-\mathbf{0.45}$

$-\mathbf{0.67}$

0.50

$-\mathbf{0.73}$

0.38

${\gamma}_{\mathrm{cp}}$

$-\mathbf{0.58}$

$-\mathbf{0.44}$

$-\mathbf{0.27}$

0.50

0.65

$-\mathbf{0.64}$

0.74

$-\mathbf{0.13}$

—

% ${a}_{\mathrm{ph}}$

0.18

0.16

$-0.09$

0.06

$-\mathbf{0.24}$

0.03

0.00

$-\mathbf{0.37}$

0.03

$-\mathbf{0.16}$

Chl

POC

${\tilde{b}}_{\mathrm{bp}}$

$\eta $

$\xi $

LISST V

% pico

LSi

${n}_{p}$

${\gamma}_{\mathrm{cp}}$

Variable symbols and units are as follows: Chl—chlorophyll-$a$ concentration in $\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{-3}$ (here in log10-space); POC—particulate organic carbon in $\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{-3}$; ${\tilde{b}}_{\mathrm{bp}}$—probability of particle backscattering (spectral average); $\eta $—slope of ${b}_{\mathrm{bp}}(\lambda )$, $\xi $—PSD slope; LISST V—total particle volume from the LISST, ${\mathrm{m}}^{3}/{\mathrm{m}}^{3}$ in log10-space; % pico—HPLC-based percent picoplankton; and LSi—lithogenic silica concentration in $\mathrm{\mu mol}/\mathrm{L}$ in log10-space; ${n}_{p}$—real index of refraction; ${\gamma}_{\mathrm{cp}}$—slope of the particle beam attenuation coefficient; % ${a}_{\mathrm{ph}}$—percent of particulate absorption due to phytoplankton particles at 443 nm. The correlation coefficients of ${n}_{p}$ with ${\tilde{b}}_{\mathrm{bp}}$ and ${\gamma}_{\mathrm{cp}}$ are not included, because ${n}_{p}$ is modeled from these variables; see Fig. 5(a) and [30].
Significant correlations at the 95% confidence level are indicated in bold.