Post on 17-Dec-2015
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?
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]
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]
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]
QuickTime™ and a decompressor
are needed to see this picture.
Foley & Koch (in press)
QuickTime™ and a decompressor
are needed to see this picture.
Highly variable inputs seasonally
QuickTime™ and a decompressor
are needed to see this picture.
Foley & Koch (in prep)
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
[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
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
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
[Laws et al., 1995] [Popp et al., 1998]
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]
[Zeebe & Wolf-Gladrow, 2001]
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)
Newsome et al. (2007)
Newsome et al. (2007)