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 Freshwater benthic algae from lakes are more 13 C-enriched than benthic algae collected in rivers One possible mechanism: development of a "stagnant boundary layer" in less turbulent waters restricting the rate of CO 2 diffusion and requiring use of 13 C-enriched of CO 2 pool [France, 1995]

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

Food Sources for Coastal Marine Animals d 13 C 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]

Foley & Koch (in press)

Highly variable inputs seasonally

Foley & Koch (in prep)

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

[Schell, 2000] Composite record constructed using presumed winter  13 C 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  13 C phytoplankton from 1966 to 1997 [Schell, 2000] Assumes: 1) constant offsets b/w  13 C baleen,  13 C zoo, and  13 C phyto 2) No change in plankton species composition/ abundance 3) Constant surface  13 C DIC 4) Whales spent winter in roughly the same place every year

2.7‰ decrease in  13 C phytoplankton 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 [CO 2(aq )] and surface  13 C DIC ?  p dependent upon: - growth rate - [CO 2 (aq)] Cullen et al. [2000] suggest that  13 C phyto was decreased over the last 30 yrs due to a combination of: - increase in [CO 2(aq) ] (resulting in an increase in  p ) - decrease in  13 C DIC Both effects result from increased pCO 2 and invasion of anthropogenic CO 2 into surface waters [Cullen et al., 2001]

[Zeebe & Wolf-Gladrow, 2001]

Schell Responds [Schell, 2001] No evidence for decrease in  13 C DIC or increase in [CO 2(aq) ] in the north Pacific - Not enough time for atmospheric equilibration in regions of vigorous vertical mixing - Similar decline in  15 N baleen (however, note low  15 N values in the late '40s)

Newsome et al. (2007)