Distribución y composición de la materia orgánica en sedimentos de la zona de oxígeno mínimo del pacífico nororiental mexicano: Implicaciones paleoceanográfcas

Total organic carbon (TOC) content, total nitrogen (TN) content, elemental (C and N), and isotopic (d¹³C-TOC) composition of organic matter derived from both marine and terrestrial sources constrain the relative contributions from marine productivity, the mangroves, and the continental wind erosion of 36 carbonate-free surface sediments along the southwestern coast of the Baja California Peninsula. In general, the spatial patterns of TOC, TN, C:N ratio and d¹³C-TOC are similar. The maximum content of TOC (14.5%) and TN (1.6%) were measured inside the oxygen minimum zone (OMZ). The stable carbon isotopic compositions were enriched in ¹²C in surface sediments at suboxic sites within the OMZ. The C:N ratio and δ¹³C-TOC values indicated that the organic sediment material is predominantly of marine origin, with a minor contribution from the terrestrial source or mangroves. In the stations near to the coast, the high values of the C:N ratio and the depleted ¹³C values suggest a proportionally greater accumulation of terrestrial organic matter. The terrestrial-derived organic carbon content is <10% at the continental margin and >40% at the stations near to the coast, based on a Mixing Model of End Members. This work was funded by projects SIP-IPN (20110143 and 20120689), awarded to Alberto Sa ́nchez, CICI-MAR-IPN, and project EP2 coordinated by Eduardo F. Balart, CIBNOR. We thank the crew of R/V BIP XII- CIBNOR for their support during the sampling at sea. We are also grateful to Dr. John Armstrong for constructive comments on an earlier version of our paper. Thanks are due to Dr. Ellis Glazier for editing this English-language text.