Stable isotopes of nitrate record effects of the 2015–2016 El Niño and diatom iron limitation on nitrogen cycling in the eastern North Pacific Ocean
Journal
Limnology and Oceanography
Journal Volume
67
Journal Issue
10
Start Page
2140
End Page
2156
ISSN
0024-3590
1939-5590
Date Issued
2022-10-01
Author(s)
White, Margot E.
Rafter, Patrick A.
Mazloff, Matthew R.
Wankel, Scott D.
Aluwihare, Lihini I.
Abstract
n eastern boundary current systems, strong coastal upwelling brings deep, nutrient-rich waters to the surface ocean, supporting a productive food web. The nitrate load in water masses that supply the region can be impacted by a variety of climate-related processes that subsequently modulate primary productivity. In this study, two coastal upwelling regimes along central and southern California were sampled seasonally for nitrogen and oxygen stable isotopes of nitrate (i.e., nitrate isotopes) over several years (2010–2016) on 14 California Cooperative Oceanic Fisheries Investigations (CalCOFI) cruises. Seasonal, interannual, and spatial variations in euphotic zone nitrate isotopes were largely driven by the extent of nitrate utilization, sometimes linked to iron limitation of diatom productivity. Pronounced isotopic enrichment developed with the El Niño conditions in late 2015 and early 2016 which likely resulted from increased nitrate utilization linked to reduced nitrate supply to the euphotic zone. Differential enrichment of nitrogen and oxygen isotopes was observed in the surface ocean, suggesting that phytoplankton increased their reliance on locally nitrified (recycled) nitrate during warmer and more stratified periods. Overall, nitrate isotopes effectively differentiated important euphotic zone processes such as nitrate assimilation and nitrification, while archiving the influence of disparate controls such as iron limitation and climatic events through their effects on nitrate utilization and isotopic fractionation.
Subjects
California
Pacific Ocean
Pacific Ocean (North)
United States
diatom
eastern boundary current
El Nino
euphotic zone
historical record
iron
nitrate
nitrogen cycle
nutrient limitation
phytoplankton
stable isotope
SDGs
Publisher
Wiley
Type
journal article