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STABLE ISOTOPE-BASED NITROGEN BUDGET FOR THE CALIFORNIA CURRENT ECOSYSTEM DOMAIN DURING THE 2014 BLOB AND 2015-2016 EL NINO: FROM SOURCE NUTRIENTS TO FOOD WEBS (E)

Time series studies and regional models of the California Current Ecosystem (CCE) suggest that the euphotic zone nitrate inventory is reduced during strong El Nino events. Climate-driven nutrient supply can impact higher trophic levels as demonstrated using the stable nitrogen isotope (15N) signature of Calanus pacificus (Cp) zooplankton, where the 15N of Cp was enriched during strong Nino events coupled with reduced nitrate (Ohman et al., 2012). In this study, a nitrogen isotope budget approach was adopted to examine the impact of both the recent 2015-2016 ENSO event and the preceding 2014 Blob warming event on nitrogen cycling in the euphotic zone of the CCE. The 15N of Cp during the summer of 2014 was enriched similarly to previous strong Nino events yet had returned to Nino neutral 15N values during the spring of 2016. In addition to Cp, we report here some of the first nitrate isotope measurements made in this region during an ENSO event and include sinking and suspended particulate organic matter to balance the N budget of the euphotic zone. Nitrogen isotope mass balances enable us to estimate the potential contribution of euphotic zone nitrification to the nitrate inventory, which can be as significant as 30%. Accounting for nitrification, estimates of new production nearly balance N-based carbon export. Across the CCE region, the 15N budget approach presented here supports the hypothesis that nitrate availability impacts can be observed throughout the food web but not all warm events (i.e., Blob vs. El Nino) behave in the same manner.

Authors

Stephens, B. M., Scripps Institution of Oceanography, USA, bmstephe@ucsd.edu

Aluwihare, L. I., Scripps Institution of Oceanography, USA, laluwihare@ucsd.edu

Wankel, S. D., Woods Hole Oceanographic Institution, USA, sdwankel@whoi.edu

White, M. E., Scripps Institution of Oceanography, USA, mew070@ucsd.edu

Valencia, B., Scripps Institution of Oceanography, USA, bellival@ucsd.edu

Details

Oral presentation

Session #:059
Date: 03/03/2017
Time: 10:45
Location: 313 A

Presentation is given by student: Yes