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 13C
for 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 13C
for 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 source
Seagrass = some primarily
planktonic, some primarily
benthic
Invertebrates:
Offshore = primarily
planktonic 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
Baleen plates contain a continuous record of dietary 13C/12C
Arctic bowhead whales
- feed on zooplankton
- migrate seasonally
WINTER
[Kroopnick, 1985; Ravelo & Andreasen, 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
[Schell, 2000]
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]
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
[Laws et al., 1995]
[Popp et al., 1998]
What about changes in [CO2(aq)] and
surface 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
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]
Newsome et al. (2007)
Newsome et al. (2007)