A Comparative High-Resolution Study of δ15N in Modern Sediments in the Gulf of California and the California Borderland, and the Miocene Monterey Formation: Interpreting Changes in the Intensity of the OMZ

Tems, Caitlin and Berelson, Will
[email protected]

The extent and severity of Oxygen Minimum Zones (OMZ) is increasing globally (Stramma et al., 2010) making it critical to understand the mechanisms driving this change. Reliable oxygen measurements are only available for the past ~70 years, therefore, it is necessary to use a geologic proxy to monitor the fluctuations in severity of OMZs in the recent past and geologic time. In an OMZ, low O2 content promotes water column denitrification, which enriches the residual nitrate pool in 15N. This 15N-enriched nitrate assimilated by primary producers imparts its isotopic signature on Particulate Organic Nitrogen (PON) exported from euphotic zone and buried in the sediments. Thus, the intensity of anoxia and associated denitrification is reflected in the degree of 15N enrichment in the sedimentary PON. Our high-resolution (1-3 mm) δ15N records obtained from laminated sediment cores from the Pescadero Slope (Gulf of California) and Santa Monica Basin (California Borderland) show distinct temporal fluctuations in the δ15-PON with a ~10 year frequency, likely driven by variability of water column O2 content. The techniques used on the modern, laminated sediment cores have been applied to laminated sections of the Monterey Formation to elucidate the application of this technique to the rock record and how the OMZ in the NE Pacific changed during the Miocene. We will discuss the history of OMZ intensity off of the Mexican Margin and California Borderland in modern sediments (back to ~200 ybp) and during the Miocene.

AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013