Project Brief SGA - pace.oceansciences.org · SFB/D Chs. Bay BIS_0613 BIS_0813 BIS_1113 BIS_0114 Korea ki Decreasing Density e The spectral slope of backscatter measured in situ appears

PACE Applications to Case II Waters:Backscatter Response to Particle Composition and Morphology

Steven Ackleson & Wesley MosesNaval Research Laboratory, DC.

Korea(N = 56)

ChesapeakeBay

(N = 7)

(N = 277)Block Island

Sound

San FranciscoBay

(N = 68)

N = 408

Definitions

Particle Morphology (LISST 100X)Sauter Diameter:

Apparent Density:

Particle Backscatter Properties (ac and bb sensors)Backscatter Ratio:

Mass-Specific Backscatter:

Spectral Slope:

Particle Composition (water samples)Suspended Particulate Mass:

Particulate Organic Carbon:

SPM g m-3

POC g m-3

Ds = 6 * Vp Ap-1 µ

ra = SPM Vp-1 kg m-3

h = ln[bbp(l)/bbp(lo)]/(lo/l)

b*bp = bbp SPM-1 m2 g-1

b~bp = bbp bp

-1

Particle Size and Apparent DensitySFB/D Chs. Bay BIS_0613 BIS_0813 BIS_1113 BIS_0114 Korea

ra kg m-3

D sµ

Particle size and apparent density (and excess density) are inversely correlated.

Fettweis, 2008

North Sea

Europe and French Guyana

Neukermans et al., 2012

Case ICase II

Particle Apparent Density and Carbon Content

Reynolds et al., 2016

Arctic Ocean

Particle apparent density decreases with increasing POC content.

ra kg m-3

POC:

SPM

BIS_0613 BIS_0813 BIS_1113 Korea

SPM Versus Composition

Particulate organic carbon concentration is positively correlated with the concentration of suspended particulate mass.

BIS_0613 BIS_0813 BIS_1113 Korea

Ni et al., 2008

Pearl River Delta

Reynolds et al., 2016

Arctic Ocean

0.01 0.1 1 10 100

Fractional Backscatter, b~bp

POC:SPM

b~bp

(532

nm

)

10-3

10-2

10-1

10-2 10-1 10-010-4

Backscatter ratio is negatively correlated with the fraction of organic carbon.

BIS_0613 BIS_0813 BIS_1113 Korea

10-4

10-3

10-2

10-1 Europe and French Guyana

Neukermans et al., 2012

Case ICase II

Fractional Backscatter, b~bp

SFB/D Chs. Bay BIS_0613 BIS_0813 BIS_1113 BIS_0114 Korea

b~bp

(532

nm

)

10-3

10-2

10-1

10-0 101 102 103

Backscatter ratio is positively correlated with particle apparent density.

Neukermans et al., 2012

Europe and French Guyana

Case ICase II

POC:SPM

b*

bp

(55

5 n

m)

m2

g-1

Wozniak et al. (Accepted, 2018)

Baltic and North Sea

POC:SPM

b*bp

(53

2 n

m)

b*

bp

(53

2 n

m)

m2

g-1

Mass-Specific Backscatter

BIS_0613 BIS_0813 BIS_1113 Korea

The spectral slope of backscatter appears to increase with the

fraction of organic matter, contrary to previous reports.

Baltic Low OrganicBaltic High OrganicNorth Sea Stations

Mass-Specific BackscatterSFB/D Chs. Bay BIS_0613 BIS_0813 BIS_1113 BIS_0114 Korea

Mass-specific backscatter and apparent particle density appear poorly correlated.

Reynolds et al., 2016

Arctic Ocean

0 1000 2000

ra kg m-3

OrganicMixedMineral

BIS_0613 BIS_0813 BIS_1113 Korea

Spectral Slope of Backscatter, h

0 0.2 0.4 0.6 0.8

Reynolds et al., 2016

Arctic Ocean

POC:SPM

The spectral slope of backscatter appears to be highly variable at low fractions of particulate carbon, but converge to a stable, intermediate

value as the fraction of POC increases.

-h

Spectral Slope, hSFB/D Chs. Bay BIS_0613 BIS_0813 BIS_1113 BIS_0114 Korea

Stramski

Decreasing Density

Increasing Size

The spectral slope of backscatter measured in situ appears to increase with particle size, contrary to laboratory measurements of clay suspensions.

Stramski et al., 2007

Mixed ( ) and Single-Mineral ( ) Clay

SPM and BackscatterSFB/D Chs. Bay BIS_0613 BIS_0813 BIS_1113 BIS_0114 Korea

RATIO MASS-SPECIFIC SPECTRAL SLOPE

- Backscatter ratio tended to increase with increasing SPM- Mass-specific backscatter is highly variable- Spectral slope tended to decrease with increasing SPM

Summary

Results support current ideas about the relationships between marine particle composition, morphology, and backscatter.

In response to increasing SPM:- Backscatter ratio tends to increase (POC:SPM decreases)- Mass-specific backscatter is highly variable- Spectral slope tends to decrease (decreasing aggregate size?)

There remains a great deal of uncertainty in these and previously published results, but teasing apart sources from fiend measurements is difficult;

- Sampling methods- Sensor bias/error