The effect of environmental variables on C-13 discrimination by two marine phytoplankton

The effects that environmental variables, other than dissolved CO2, have on C-13 discrimination by marine phytoplankton were studied. Two selected species showed different responses. The delta(13)C values of the marine diatiom Phaeodactylum tricornutum grown in a range of temperatures with a constant dissolved [CO2] were more negative as the growth temperature decreased. delta(13)C values of P. tricornutum showed little response to changes in growth photon flux density (except at low PFD <10 mu mol m(-2) s(-1)) and growth pH. delta(13)C values of the prymnesiophyte Emiliania huxleyi were more negative with decreased growth temperature, more negative with decreased growth PFD and less negative with decreased growth pH. The distinct effects which environmental variables have on the delta(13)C values of 2 contrasting algal species suggest that species-specific responses to environmental change may be important in understanding the variability of delta(13)C values found in particulate organic carbon obtained from oceanic and coastal waters. The role of environmental variables in hindcasting dissolved [CO2] is discussed.