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Carbon Isotope Variations in Aquatic Plants: Applications

Carbon Isotope Variations in Aquatic Plants: Applications. Onshore-Offshore (Benthic vs. Pelagic?) Kelp forest ecology Decreased productivity in the Bering Sea? Phytoplankton  13 C from whale baleen and seal teeth?. Compilation of  13 C for Freshwater Algae.

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Carbon Isotope Variations in Aquatic Plants: Applications

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  1. 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?

  2. 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]

  3. Compilation of 13Cfor Marine Algae In coastal marine areas, 13C values of benthic algae are +5‰ higher than average planktonic 13Cvalues Planktonic 13C = -22 ± 4‰ Benthic 13C = -17 ± 3‰ [France, 1995]

  4. Food Sources for Coastal Marine Animals d13C values of consumers can be used to indicate food source Fish: Offshore = primarily planktonic food source Seagrass = some primarily planktonic, some primarily benthic Invertebrates: Offshore = primarily planktonic food source Seagrass = primarily benthic food source [France, 1995]

  5. Foley & Koch (in press)

  6. Highly variable inputs seasonally

  7. Foley & Koch (in prep)

  8. Carbon Isotope Record from Whale Baleen • Baleen plates contain a continuous record of dietary 13C/12C • Arctic bowhead whales - feed on zooplankton - migrate seasonally WINTER SUMMER [Kroopnick, 1985; Ravelo & Andreasen, 2000]

  9. 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 [Schell, 2000]

  10. Interpretation 2.7‰ decline in 13Cphytoplankton from 1966 to 1997 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 [Schell, 2000]

  11. 2.7‰ decrease in 13Cphytoplankton 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 http://visibleearth.nasa.gov/Regions/Bering_Sea/350.html

  12. [Popp et al., 1998] [Laws et al., 1995]

  13. 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]

  14. [Zeebe & Wolf-Gladrow, 2001]

  15. Schell Responds 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) [Schell, 2001]

  16. Newsome et al. (2007)

  17. Newsome et al. (2007)

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