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)