Relationship Between Light Attenuation and Suspended Particulate Material During Nearshore Coastal Upwelling

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Relationship Between Light Attenuation and
Suspended Particulate Material During Nearshore
Coastal Upwelling J.J. Grzymski1, J.T. Cullen1,
E.L. Peters2, S.M. Glenn1, R.M. Sherrell1, O.M.
Schofield1 1 Institute of Marine and Coastal
Sciences, Rutgers University 2 California
Polytechnic University, Biological Sciences
Department
2
Outline 1) Study site, sampling program and
scientific goals 2) Methods 3) Biogenic
particles (07/98 and 07/99)
Onshore-offshore POC gradients C/N
composition 4) Attenuation versus POC
regressions 5) Summary/Conclusions 6) Future
Research
3
Scientific Goals (07/98, 07/99)
1) determine the relationship between
in situ optics and particle concentration at
LEO-15
2) test/extend regression developed for study
site during 07/98 relating particulate organic
carbon (POC) to beam-c (c660nm) in coastal
surface waters by increasing a) spatial
resolution b) depth resolution
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Measurements (07/98 and 07/99)
Chemistry
POC and PN- on a nominal 0.8µm quartz fiber
filter (47mm). Measured with a Carlo-Erba
elemental analyzer
Optics
c660 (beam-c)- 10cm pathlength transmissometer
(SeaTech Inc.) integrated to a FSI Micro-CTD
Data Analysis
Type II linear regression according to Laws (1997)
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Onshore Offshore POC Gradients (samples collected
at 5m depth) 07/98
Distance Offshore (km)
- order of magnitude variation in POC
concentrations 30km length scale
- clearly defined front (chemical and optical
properties) migrates depending on upwelling
intensity
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Particulate C/N Ratios in Surface Waters (lt5 m)
07/98 and 07/99
35
J202
07/98
30
J203
J205
J207
25
J210
20
Particulate C/N (mol mol-1)
15
10
5
0
0
5
10
15
20
25
30
35
35
J184
07/99
J187
30
J188
J190
25
J201
J207
20
Particulate C/N (mol mol-1)
15
10
5
0
0
5
10
15
20
25
30
35
Distance Offshore (km)
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Particulate C/N Ratios in Surface and Bottom
Waters 07/99
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beam-c (660nm) vs POC (gt0.8µm) at 5m depth 07/98
n14
4
.
5
0
4
.
0
0
0-0.075 mg/L
0-0.144 mg/L
3
.
5
0
3
.
0
0
(m-1)
2
.
5
0
c
2
.
0
0
beam-
1
.
5
0
1
.
0
0
y 2.870.18x 0.600.12 r20.955
0
.
5
0
0
.
0
0
0
.
0
0
0
.
5
0
1
.
0
0
1
.
5
0
P
O
C

(
m
g
L-1)
------ EqPAC (Bishop 1999) y
5.280.025x 0.366 r20.970 ------ WCREBloom
(Bishop 1999) y 3.620.028x 0.372 r20.967
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beam-c (660nm) vs POC (gt0.8µm) for Surface and
Bottom Waters 07/99
3.5
3
2.5
2
beam c (m-1)
07/98
1.5
07/99
1
0.5
0
0
0.2
0.4
0.6
0.8
POC (mg L-1)
Surface y 3.670.28x 0.290.09 r20.743 n51
Bottom y 3.300.29x 0.400.09 r20.678 n48
Surface y 2.870.18x 0.600.12 r20.955 n14
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beam-c (660nm) vs POC (gt0.8µm) for Surface and
Bottom Waters 07/98 and 07/99 n113
4
3.5
3
2.5
beam c (m-1)
2
1.5
1
0.5
0
0
0.25
0.5
0.75
1
1.25
POC (mg L-1)
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Summary and Conclusions
1) POC concentrations and horizontal gradients
show interannual variability at LEO-15 2) C/N
composition of particles resembled marine
biogenic material in 07/98 while C/N ratios in
07/99 were higher on average and showed more
variability 3) differences in slopes and
intercepts of regressions relating beam-c to POC
concentrations in surface and bottom waters
during 07/99 were statistically insignificant 4)
in situ measurements of beam-c provide robust
estimates POC concentrations in optically complex
coastal surface and bottom waters despite
interannual differences in the physical and
chemical regime at LEO-15
In situ measurements of beam attenuation can be
used to construct temporal and spatial maps of
particle and POC distributions in the upwelling
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Future Research and Goals
1) test strength of regressions when
stratification is weak and inorganic/organic
particle ratio is at a maximum (during winter and
after high energy storm mixing events) 2)
stable isotope data to better determine nature of
biogenic material 3) ultimately develop a
framework for providing quantitative estimates of
POC from optical measurements to incorporate into
coastal circulation/sediment transport models