Temporal variations of C, N, δ13C, and δ15N in organic matter collected by a sediment trap at Cuenca Alfonso, Bahia de La Paz, SW Gulf of California

To monitor the composition and the vertical flux of particulate matter from the sea surface, a sediment trap was moored in Cuenca Alfonso, Bahia de La Paz, a zone of high productivity in the southwestern Gulf of California. Carbonate-free samples from 2002 to 2005 were analyzed for C-org, N, delta C-13, and delta N-15. The results show seasonal and interannual variability, with the delta C-13 and delta N-15 values larger in spring and summer than in fall and winter. The C:N ratio and delta C-13 increased by 1.5 units from 2002 to 2003-2005, suggesting a change in the supply of organic matter and-or the use or preferential degradation of No. There was no interannual variation in delta N-15. The occasional high delta N-15 values suggest that physical mechanisms, such as the shoaling and advection into the bay of N-15-rich subsurface equatorial water, occur over short time periods. The latter is presumed to be related to the periodic development of a significant cyclonic gyre in the southern Gulf. (C) 2010 Elsevier Ltd. All rights reserved.