Biogeochemical patterns in the Atlantic Inflow through the Strait of Gibraltar
The effects of tidal forcing on the biogeochemical patterns of surface water masses flowing through the Strait of Gibraltar are studied by monitoring the Atlantic Inflow (AI) during both spring and neap tides. Three main phenomena were defined depending on the strength of the outflowing phase predic...
Published in: | Deep Sea Research Part I: Oceanographic Research Papers |
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Main Authors: | , , , |
Language: | English |
Published: |
PERGAMON-ELSEVIER SCIENCE LTD
2014
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Subjects: | |
Online Access: | https://publications.jrc.ec.europa.eu/repository/handle/JRC85744 http://www.sciencedirect.com/science/article/pii/S0967063713002434 https://doi.org/10.1016/j.dsr.2013.12.004 |
Summary: | The effects of tidal forcing on the biogeochemical patterns of surface water masses flowing through the Strait of Gibraltar are studied by monitoring the Atlantic Inflow (AI) during both spring and neap tides. Three main phenomena were defined depending on the strength of the outflowing phase predicted over the Camarinal Sill: non-wave events (a very frequent phenomenon during the whole year); type I Internal wave events (a very energetic event, occurring during spring tides); and type II Internal wave events (less intense, occurring during neap tides).During neap tides, a non-wave event comprising oligotrophic open-ocean water from the Gulf of Cádiz is the most frequent and clearly dominant flow through the Strait. In this tidal condition, the inflow of North Atlantic Central Water (NACW) provides the main nutrient input to the surface layer of the Alboran Sea, supplying almost 70% of total annual nitrate transport to the Mediterranean basin. A low percentage of active and large phytoplankton cells and low average concentrations of chlorophyll (0.3-0.4 mg m-3 ) were found in this tidal phase. Around 50% of total annual phytoplankton biomass transport into the Mediterranean Sea through the Strait presents these oligotrophic characteristics.In contrast, during spring tides, patches of water with high chlorophyll levels (0.7-1 mg m-3) arrive intermittently, and these are recorded concurrently with the passage of internal waves coming from the Camarinal Sill (type I internal wave events). When large internal waves are arrested over the Camarinal Sill this implies strong interfacial mixing and the probable concurrent injection of coastal waters into the main channel of the Strait. These processes result in a mixed water column in the AI and could account for around 30% of total annual nitrate transport into the Mediterranean basin. At least during some periods, phosphate injections to the inflow from coastal waters may also be associated mainly with internal wave events (of types I or II). Associated with type I internal wave events there is a regular inflow of large and active phytoplankton cells, transported in waters with relatively high nutrient concentrations, which constitutes a significant supply of planktonic resources to the pelagic ecosystem of the Alboran Sea (almost 30% of total annual phytoplankton biomass transport). This is the first study in which the presence of internal waves and the characteristics (percentage of active and large cells) of the accompanying chlorophyll patches are reported concurrently. JRC.H.1 - Water Resources |
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