carbon isotope variations in aquatic plants: applications onshore-offshore (benthic vs. pelagic?)...
TRANSCRIPT
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Carbon Isotope Variations in Aquatic Plants: Applications
Onshore-Offshore (Benthic vs. Pelagic?)
Kelp forest ecology
Decreased productivity in the Bering Sea?
Phytoplankton 13C from whale baleen and seal teeth?
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Compilation of 13Cfor Freshwater Algae
Freshwater benthic algae from lakes are more 13C-enriched than benthic algae collected in rivers
One possible mechanism: development of a "stagnant boundary layer" in less turbulent waters restricting the rate of CO2 diffusion and requiring use of 13C-enriched of CO2 pool
[France, 1995]
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Compilation of 13Cfor Marine Algae
In coastal marine areas, 13C
values of benthic algae are
+5‰ higher than average
planktonic 13C values
Planktonic 13C = -22 ± 4‰
Benthic 13C = -17 ± 3‰
[France, 1995]
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Food Sources for Coastal Marine Animals
d13C values of consumers can be used to indicate food source
Fish:Offshore = primarily planktonic food sourceSeagrass = some primarily planktonic, some primarily benthic
Invertebrates:Offshore = primarily planktonic food sourceSeagrass = primarily benthic food source
[France, 1995]
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Foley & Koch (in press)
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Highly variable inputs seasonally
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Foley & Koch (in prep)
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Carbon Isotope Record from Whale Baleen
[Kroopnick, 1985; Ravelo & Andreasen, 2000]
Baleen plates contain a continuous record of dietary 13C/12C
Arctic bowhead whales
- feed on zooplankton
- migrate seasonally
WINTER
SUMMER
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[Schell, 2000]
Composite record constructed using presumed winter 13C values (most positive in cycle) from many baleen plates (n = 37)
Whale got these values while occupying the Bering Sea
"Summer" values not used because of apparent disagreement between different specimens
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Interpretation
2.7‰ decline in 13Cphytoplankton from 1966 to 1997
[Schell, 2000]
Assumes:
1) constant offsets b/w 13Cbaleen, 13Czoo, and 13Cphyto
2) No change in plankton species composition/ abundance
3) Constant surface 13CDIC
4) Whales spent winter in roughly the same place every year
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2.7‰ decrease in 13Cphytoplankton
http://visibleearth.nasa.gov/Regions/Bering_Sea/350.html
What does it mean?
Schell [2000] interprets an increase in p related to a decrease in phytoplankton growth rates ()
Infers a 30-40% decrease in productivity between 1966 and 1997 in the Bering Sea
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[Laws et al., 1995] [Popp et al., 1998]
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What about changes in [CO2(aq)] andsurface 13CDIC ?
p dependent upon:
- growth rate
- [CO2(aq)]
Cullen et al. [2000] suggest that 13Cphyto was decreased over the last 30 yrs due to a combination of:
- increase in [CO2(aq)] (resulting in an increase in p)
- decrease in 13CDIC
Both effects result from increased pCO2 and invasion of anthropogenic CO2 into surface waters
[Cullen et al., 2001]
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[Zeebe & Wolf-Gladrow, 2001]
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Schell Responds
[Schell, 2001]
No evidence for decrease in 13CDIC or increase in [CO2(aq)] in the north Pacific
- Not enough time for atmospheric equilibration in regions of vigorous vertical mixing
- Similar decline in 15Nbaleen (however, note low 15N values in the late '40s)
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Newsome et al. (2007)
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Newsome et al. (2007)