Publication
On the effect of internal tidal waves on near-surface chlorophyll concentration and productivity around Nazaré Canyon and in the central region of the Bay of Biscay
| Summary: | The present study describes the effect of large-amplitude internal tidal waves on near-surface chlorophyll concentration in the central region of Bay of Biscay and around the Nazaré Canyon (western Portugal), and investigates its ecological impact. Internal wave propagation introduces vertical motions within the water column, especially near the thermocline, forcing water particles to undergo upward and downward motions. Since neutrally buoyant phytoplankton cells are usually passive, these cells can be significantly displaced in the vertical. Because light intensity decreases exponentially with depth, internal waves will expose phytoplankton cells to a larger light intensity on average. The main objective of this study was to investigate if this light enhancement in the euphotic zone can induce a biomass increase and affect positively primary production in the two regions of interest. SAR data was used to characterize the signatures of internal solitary waves in the central Bay of Biscay, which are locally generated by internal tidal beams, which first propagate downwards from the shelf break and reflect from the sea floor. Two similar episodes of internal wave propagation in the Bay of Biscay were investigated and it was shown the existence of two different axes of wave beam propagation, which result in internal solitary wave generation and propagation in two distinct directions. SAR and Ocean Colour satellite synergy support the occurrence of enhanced levels of chlorophyll spatially correlated with internal solitary waves observed around the Nazaré Canyon (generated by the barotropic tides at the Estremadura Promontory). In addition, the results from the central Bay of Biscay (near 46° N, 7° W) show evidence of the confluence of internal tidal waves, which produce chlorophyll patterns visible in ocean colour images. The results derived from satellite climatological chlorophyll concentrations (2002-2011) and from a productivity model, suggest that high internal wave activity is an important mechanism playing a significant role on biomass growth, and thus have a relevant regional ecological impact. |
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| Main Authors: | Alves, Sérgio Muacho, 1977- |
| Subject: | Ondas oceânicas Clorofila Cor oceânica Radar de abertura sintética (SAR) Produtividade primária Canhão da Nazaré (Portugal) Centro do Golfo da Biscaia Teses de doutoramento - 2013 |
| Year: | 2013 |
| Country: | Portugal |
| Document type: | doctoral thesis |
| Access type: | open access |
| Associated institution: | Universidade de Lisboa |
| Language: | English |
| Origin: | Repositório da Universidade de Lisboa |
| Summary: | The present study describes the effect of large-amplitude internal tidal waves on near-surface chlorophyll concentration in the central region of Bay of Biscay and around the Nazaré Canyon (western Portugal), and investigates its ecological impact. Internal wave propagation introduces vertical motions within the water column, especially near the thermocline, forcing water particles to undergo upward and downward motions. Since neutrally buoyant phytoplankton cells are usually passive, these cells can be significantly displaced in the vertical. Because light intensity decreases exponentially with depth, internal waves will expose phytoplankton cells to a larger light intensity on average. The main objective of this study was to investigate if this light enhancement in the euphotic zone can induce a biomass increase and affect positively primary production in the two regions of interest. SAR data was used to characterize the signatures of internal solitary waves in the central Bay of Biscay, which are locally generated by internal tidal beams, which first propagate downwards from the shelf break and reflect from the sea floor. Two similar episodes of internal wave propagation in the Bay of Biscay were investigated and it was shown the existence of two different axes of wave beam propagation, which result in internal solitary wave generation and propagation in two distinct directions. SAR and Ocean Colour satellite synergy support the occurrence of enhanced levels of chlorophyll spatially correlated with internal solitary waves observed around the Nazaré Canyon (generated by the barotropic tides at the Estremadura Promontory). In addition, the results from the central Bay of Biscay (near 46° N, 7° W) show evidence of the confluence of internal tidal waves, which produce chlorophyll patterns visible in ocean colour images. The results derived from satellite climatological chlorophyll concentrations (2002-2011) and from a productivity model, suggest that high internal wave activity is an important mechanism playing a significant role on biomass growth, and thus have a relevant regional ecological impact. |
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