PYROLYSIS-MASS SPECTROMETRY OF SEDIMENT TRAP ORGANIC-MATTER FROM LAKE-MICHIGAN

The composition of total organic matter associated with sinking partic les collected by sediment traps moored at five depths in Lake Michigan has been characterized by pyrolysis-chemical ionization mass spectrom etry. Concentrations of organic carbon decrease dramatically in the up per part of the water column as organic matter is remineralized. Remin eralization changes the character of organic matter associated with pa rticles as they settle, and different pyrolysate distributions are con sequently obtained. Nitrogen-containing compounds are more abundant in trap contents from the epilimnion and metalimnion, whereas saccharide s and humic acids are more abundant in particles settling within the n ear-bottom nepheloid layer. Comparison of extractable n-alkane distrib utions to the pyrolysates of bulk organic matter indicates preferentia l degradation of algal components during sinking of sediment particles .