Santa Barbara Channel LTER

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Santa Barbara Channel LTER Oceanographic data
from near-shore stations, 2001-2002, with
implications for nutrient delivery to kelp reefs
Erika McPhee-Shaw David Siegel Libe
Washburn Mark Brzezinski
University of California Santa Barbara Janice
Jones, David Salazar, Mike Anghera, Leah Ow,
Bryn Evans, Helene Scalliet, Chris Gottschalk
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• Santa Barbara Channel LTER (Long-Term Ecological
  Research) Study
• NSF-funded LTER Long-term interdisciplinary
  study of ecosystem (giant kelp forests) at
  the land/ocean interface.
• General LTER Objectives
• study spatial and temporal scales of terrestrial
  and oceanographic forcing
• determine the relative importance of terrestrial
  versus oceanic sources of nutrients and other
  constituents to kelp forests
• Santa Barbara Channel, just south of Point
  Conception, is characterized by an abrupt
  transition to low surface nutrient
  concentrations, so summer nitrate limitation
  can be important.

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• Measurements
• Time series from near-shore stations, Feb
  2001 June/Aug 2002
• Three Stations 10, 15 m water depth
• Continuous data
• - CTD, optical backscatter, fluorescence at 4
  m depth
• - bottom-mounted ADCP
• - Thermistors at three depths
• Six separate deployments (covering 23 of one
  year)
• - Nitrate auto-analyzer (W.S. Oceans Wet
  Chemical Analyzer)
• (moored at different locations and depths)
• Focus on mechanisms for nutrient delivery to
  kelp reefs
• Upwelling
• Internal waves

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Santa Barbara Channel near-shore stations
Sources of Nutrients SPATIAL GRADIENTS Vertical
gradient nutricline depth 30 to 50 m in
summer 0 to 10 m in winter
Geographic gradient Cold water, higher
nutrients, north of Point Conception (where
upwelling is common)
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(AVHRR composites from Mark Otero, UCSB)
Upwelling common north of Point
Conception Within channel, a cyclonic synoptic
state most common Hendershott and Winant, 1996
- Harms and
Winant, 1998
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Feb, 2001 to July, 2002
Winter
Upwelling
Summer
Upwelling
Summer
Naples Mooring
T
S
U alongshore velocity (East positive)
Carpinteria Mooring
One storm event
T
S
U alongshore velocity (East positive)
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Measured Nitrate, July 2001 to July 2002
Temp
Measured NO3
When Nitrate measurements not available, use
temperature as a proxy
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Estimated nitrate over one year, July 2001 to
July 2002
Temp
N from near-surface temp (blue) Measured N (green)
N from near-bottom temp (blue) Measured N (green)
upwelling
Internal waves
summer
advection
winter
Background States Winter NO3 1.5 to 2
mmol/L Summer NO3 0.1 to 0.5 mmol/L
Nitrate delivery mechanisms Upwelling Internal
waves Advection
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December, 2001, Advection from western channel
Temperature
Measured NO3
U along-isobath
m/s E
Measured W-E Nitrate Gradient (profiled on
December 5) 6 - 2mol/l / 15 km
Advect linear gradient alongshore
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Spring Upwelling Event April to May, 2002.
Temperature
Measured NO3
U along-isobath
m/s E
V cross-isobath
m/s N
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Summer high stratification, diurnal
oscillations in temperature and cross-slope flow
temperature depths 3m, 4 m, 9m, 14m
m/s onshore
Forcing? May not be tidal frequency 1 cpd,
lt f (1.13 cpd)) Cp-cross-isobath 0.1 m/s
(Cudaback and Washburn) U/Cp 1, instability
possible
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Nitrate deployments - estimating nitrate supply
rate from different mechanisms
N(t) No/T U N mmol/L/ day
Supply Mechanisms
Upwelling 0.69
(mmol/l/day)
Advection from west 0.44
Internal waves Summer 12- m depth
0.07
"Background Conditions" (no identified advective
fluxes, background sources approximately balance
sinks)
0.03
Winter
0.01
Summer
One storm event from 2001 - N
estimated from freshwater dilution and NO3
measured in local streams
0.13
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Annual Nitrate Delivery Budget July 2001 to
July 2002
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Conclusions

• Upwelling dominates nutrient supply, providing
  76 of total flux over 21 of time
• Advection from western Channel also important
• Internal waves important in summer
• - near surface NO3 lt 1 mmol/l - nitrate
  limiting for kelp
• - 12 - m depth NO3 attains 5 to 10 mmol/l in
  diurnal pulses
• Kelp Response????
• Zimmerman and Kremer (1984), Kopczak et al
  (1991) suggest this is how kelp beds survive
  summers near Catalina Island (also nutrient
  limited)
• Terrestrial input negligible in 2001, 2002
• Future Work
• Forcing ?
• - Flow reversals of 3-6 days leading to eastward
  near-shore advection
• - Diurnal internal waves

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EXTRAS FOLLOW
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Upwelling in the Santa Barbara Channel no
simple relationship with local winds
March - April 2001
Temperature
N-S Wind
E-W Wind
March 2002
Temperature
N-S Wind
E-W Wind
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Advection Events sustained eastward flow is rare
advection_upwelling.m
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TIDES
Barotropic tides mixed semidiurnal and diurnal
Summer baroclinic oscillation diurnal signal
dominates
1 cpd
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Santa Barbara Channel Synoptic States
AVHRR composites from Mark Otero, UCSB
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Vertical Gradients Nutrients at depth.
Depth of nutricline changes
seasonally.
oC
mmol/L
From Plumes and Blooms mid-channel station -
(plot from Olga Polyakov)
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Terrestrial Runoff Events
Hydrograph Winter Spring, 2001. Santa Barbara
Streams USGS gauges Mission Creek at Rocky Nook
and Mission St. Atascadero at Patterson San Jose
at Goleta
(data from Ed Beighly)
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March Storm event
(40-day period)
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Nutrient Concentrations in Santa Barbara
Streams, Storm of March 3 6, 2001.
Mean Nitrate Concentrations (mM/l) during the Mar
3 -6 storm Arroyo Burro 71.3 Atascadero 64.
6 Mission 52.2 Franklin 297 (?) Santa
Monica 50.4 Carpinteria 44.0 Rincon 55.6 Arroyo
Hondo 61.9 ------------------------------------- m
ean (without Franklin) 57 mM/L mean
(including Franklin) 87 mM/L
(From Lydecker data report, 2001)
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Use dilution by freshwater to estimate NO3
concentration Maximum freshwater dilution was
7.6 Seawater initial NO3 1
mM/L Freshwater initial NO3 40, 60 80, 100
mM/L
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Winds at West - Channel buoy, 2001
upwelling period
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Maximum NO3 concentration estimates from storm
event (for freshwater range of 40 to 80
mM/L) 3.8 to 8.3 mM/L at Carpinteria 3.1 to
6.3 mM/L at Naples
Ocean measurements from March 7, 2001
Carpinteria Offshore 1 m - 5.6 mM
5 m - 4.1 10 m - 2.4 Reef 1 m -
5.1 5 m - 3.6 Inshore 1 m -
5.5
Naples Offshore 1 m - 3.0 mM 5 m -
2.2 10 m - 2.1 Reef 1 m - 1.9
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WARM
Advection back and forth across shelf via
internal tides
COLD
Implications for nutrient delivery?
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