Seasonal climatologies of nutrients and hydrographic properties on quasi-neutral surfaces for four coastal upwelling systems

Seasonal climatologies of upper-ocean hydrographic properties and nutrients are presented for four different major coastal upwelling centers: the California, Peru-Humboldt, Canary, and Benguela regions. The climatologies are built from historical hydrographic data primarily to serve as a tool for comparative studies of productivity variations and nutrient fluxes in the near-coastal zone. Care was taken to ensure that quantities were interpolated vertically to, and averaged horizontally on, approximately neutral surfaces to constrain averaging among only those water masses that would naturally mix easily. Rather than rely on potential density surfaces that are not coincident with neutral surfaces in regions with large vertical excursions of isopycnals, the neutral surfaces were properly approximated through the use of specific volume anomaly (δ) surfaces, and were spaced closely in the vertical (approximately 0.1 σ-unit apart). Horizontal averaging to a 1/6° spatial grid was accomplished via the application of bicubic splines under tension, and provided sufficient spatial resolution for resolving upwelling patterns near the coastline. Seasonal mean nutrient-to-nutrient relationships also were constructed as another diagnostic tool for inter-regional comparisons, and are consistent with expected Redfield ratios. A consistent, high-resolution climatology is now publicly available as a tool for local and comparative studies of four different upwelling zones.