Data from: Defining isoscapes in the Northeast Pacific as an index of ocean productivity

Aim: We modeled isoscapes in the Northeast Pacific using satellite-based
data with the main objective of testing if isoscapes defined by a few key
parameters can be used as a proxy for secondary productivity. Location:
Northeast (NE) Pacific; 46 – 60⁰N and 125 – 165⁰W. Time period: From 1998
to 2017 (ongoing). Major taxa studied: Zooplankton with a focus on large
herbivores. Methods: Approximately 280 summer zooplankton samples were
analyzed for Carbon (δ13C) and Nitrogen (δ15N) stable isotope (SI) ratios.
Environmental conditions experienced by zooplankton organisms were
extracted from satellite, in situ sensor and model databases. A
generalized additive model approach was used to explain the spatial
variability of δ13C and δ15N values and predict isoscapes. Results: Sea
surface temperature (SST), sea level anomaly (SLA) and chlorophyll-a
concentration emerged as the significant SI predictors. Modelled isoscapes
reproduced patterns observed in δ13C and δ15N value distribution, such as
a decrease from the coast to offshore. The contribution of eddies in
enhancing local production in the open ocean was also well captured by the
models. In the central part of the NE Pacific higher SI values were
correlated with higher large copepod biomass measured by the North Pacific
Continuous Plankton Recorder (CPR) survey. However, in the area off the
coast of British Columbia (BC) high δ15N variability appeared to be
associated with episodic intrusions of coastal waters demonstrating that
caution is needed when interpreting sharp changes in SI ratios. Main
conclusions: While the mechanisms driving SI ratio variability are
complex, we demonstrated that a few parameters used as a proxy for some of
these major mechanisms are able to successfully produce isoscape models.
This approach was proven useful to provide a qualitative estimate of the
secondary production, which can be particularly valuable in a region where
few data are available.