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<p>Submarine canyons are major topographic features that incise the continental shelf, modifying coastal ocean circulation and influencing the upwelling of subsurface slope waters onto the shelf. Interactions between Coastal Trapped Waves (CTWs) and tides at canyon heads can promote localized cooling events. Here, we evaluate how a negative-phase CTW interacts with the topography of the Biobio Canyon off central Chile, modulating cross-canyon circulation and the hydrographic structure at the canyon head. Our analysis is based on towed-ADCP observations collected along four transects, two moored ADCPs, a yo-yo CTD station, coastal tide gauges, and atmospheric and hydrological forcings (wind and Biobio River discharge). The towed-ADCP dataset was obtained on November 11–12, 2013, a few days after neap tide, during low upwelling-favorable winds (&lt; 0.03 N/m<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(^{2}\)</EquationSource> </InlineEquation>) and concurrent with the passage of a negative-phase CTW. We identified a mean asymmetric inflow–outflow circulation pattern in the zonal current, with a geostrophic northward flow confined near the coast. Most onshore flow occurred over the down-wave side (southern wall) of the canyon. Four cooling events were detected, each associated with coherent negative CTW signals. These events exhibited semidiurnal oscillations superimposed on diurnal variability and a pronounced subinertial band, particularly during events 2 and 4. The hydrographic response revealed the advection of cold, low-oxygen, nutrient-rich Equatorial Subsurface Water (ESSW) driven by the CTW passage and the accompanying semidiurnal oscillations, whose dominance varied across the events. Our results demonstrate that, even under weak wind conditions, CTWs and tidal forcing can enhance cross-shelf exchange, reinforcing the role of the Biobio Canyon in modulating cross-shore current variability and coastal ocean fertilization during local cooling events.</p>

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Coastal trapped wave and tidal modulation of cross-shore circulation and subsurface cooling at the head of the Biobio Canyon

  • 期刊论文

  • 发表日期：

    2026年7月10日

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  • Richard Muñoz,
  • Gonzalo S. Saldías,
  • Marcus Sobarzo,
  • Manuel I. Castillo

摘要

Submarine canyons are major topographic features that incise the continental shelf, modifying coastal ocean circulation and influencing the upwelling of subsurface slope waters onto the shelf. Interactions between Coastal Trapped Waves (CTWs) and tides at canyon heads can promote localized cooling events. Here, we evaluate how a negative-phase CTW interacts with the topography of the Biobio Canyon off central Chile, modulating cross-canyon circulation and the hydrographic structure at the canyon head. Our analysis is based on towed-ADCP observations collected along four transects, two moored ADCPs, a yo-yo CTD station, coastal tide gauges, and atmospheric and hydrological forcings (wind and Biobio River discharge). The towed-ADCP dataset was obtained on November 11–12, 2013, a few days after neap tide, during low upwelling-favorable winds (< 0.03 N/m \(^{2}\) ) and concurrent with the passage of a negative-phase CTW. We identified a mean asymmetric inflow–outflow circulation pattern in the zonal current, with a geostrophic northward flow confined near the coast. Most onshore flow occurred over the down-wave side (southern wall) of the canyon. Four cooling events were detected, each associated with coherent negative CTW signals. These events exhibited semidiurnal oscillations superimposed on diurnal variability and a pronounced subinertial band, particularly during events 2 and 4. The hydrographic response revealed the advection of cold, low-oxygen, nutrient-rich Equatorial Subsurface Water (ESSW) driven by the CTW passage and the accompanying semidiurnal oscillations, whose dominance varied across the events. Our results demonstrate that, even under weak wind conditions, CTWs and tidal forcing can enhance cross-shelf exchange, reinforcing the role of the Biobio Canyon in modulating cross-shore current variability and coastal ocean fertilization during local cooling events.