Intraseasonal variability of nearshore productivity in the Northern Humboldt Current System: The role of coastal trapped waves

• Strong intraseasonal variability of near shore plankton in Peru upwelling system.
• Chlorophyll variability is driven by the intraseasonal coastally trapped waves.
• Chlorophyll anomalies propagate poleward at speed of high order CTW mode.
• Intraseasonal wind impacts mainly the northern shelf variability and at 20–30 days.

The impact of intraseasonal coastal-trapped waves on the nearshore Peru ecosystem is investigated using observations and a regional eddy-resolving physical-ecosystem coupled model. Model results show that intraseasonal variability over the period 2000–2006 represents about one fourth of the total surface chlorophyll variance and one third of the carbon export variance on the Peruvian shelf. Evidence is presented that subsurface nutrient and chlorophyll intraseasonal variability are mainly forced by the coastally trapped waves triggered by intraseasonal equatorial Kelvin waves reaching the South American coast, and propagate poleward along the Peru shore at a speed close to that of high order coastal trapped waves modes. The currents associated with the coastal waves induce an input of nutrients that triggers a subsequent phytoplankton bloom and carbon export. The impact of the local wind-forced intraseasonal variability on the ecosystem is of a similar order of magnitude to that remotely forced in the northern part of the Peru shelf on [50–90] day time scales and dominates over the entire shelf on [20–30] day time scales.