Taphonomic and early diagenetic effects on the C and N stable isotope composition of cladoceran remains : implications for paleoecological studies

International audienceI addressed the effects of taphonomic and early diagenetic processes on the isotope composition of cladoceran remains, using both experimental and field approaches. An experiment was designed to mimic the conditions encountered by cladoceran remains when they settle through the water column and are buried in the sediment. Cladoceran exoskeletons were incubated for 4 months in oxic or anoxic water, and in sediment. Changes in their carbon (C) and nitrogen (N) content and isotope compositions were measured. Most changes in isotope composition of exoskeletons took place when they settled through the water column. Once buried in the sediment, however, the δ13C and δ15N values of cladoceran exoskeletons did not undergo further change. Taphonomic processes resulted in an increase in δ13C and δ15N of the cladoceran remains and this was related to microbial degradation, which selectively removed isotopically light C and N compounds from the remains. For δ13C, changes were minimal (