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Fueling plankton production by a meandering frontal jet: a case study for the Alboran Sea (Western Mediterranean).

Oguz T, Macias D, Garcia-Lafuente J, Pascual A, Tintore J - PLoS ONE (2014)

Bottom Line: Biological production is larger in the western part of the basin and decreases eastwards with the gradual weakening of the jet.The higher production at the subsurface levels suggests that the Alboran Sea is likely more productive than predicted by the satellite chlorophyll data.The Mediterranean water mass away from the jet and the interiors of the western and eastern anticyclonic gyres remain unproductive.

View Article: PubMed Central - PubMed

Affiliation: SOCIB, Balearic Islands Coastal Ocean Observing and Forecasting System, Palma de Mallorca, Spain; Institute of Marine Sciences, Middle East Technical University, Erdemli, Mersin, Turkey.

ABSTRACT
A three dimensional biophysical model was employed to illustrate the biological impacts of a meandering frontal jet, in terms of efficiency and persistency of the autotrophic frontal production, in marginal and semi-enclosed seas. We used the Alboran Sea of the Western Mediterranean as a case study. Here, a frontal jet with a width of 15-20 km, characterized by the relatively low density Atlantic water mass, flows eastward within the upper 100 m as a marked meandering current around the western and the eastern anticyclonic gyres prior to its attachment to the North African shelf/slope topography of the Algerian basin. Its inherent nonlinearity leads to the development of a strong ageostrophic cross-frontal circulation that supplies nutrients into the nutrient-starved euphotic layer and stimulates phytoplankton growth along the jet. Biological production is larger in the western part of the basin and decreases eastwards with the gradual weakening of the jet. The higher production at the subsurface levels suggests that the Alboran Sea is likely more productive than predicted by the satellite chlorophyll data. The Mediterranean water mass away from the jet and the interiors of the western and eastern anticyclonic gyres remain unproductive.

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Modeled plankton biomass.Horizontal distributions of (a) integrated plankton biomass (phytoplankton plus zooplankton) and (b) integrated nitrate concentration over the upper 75 m layer (mmol N m−2), The background color shows the trajectory of the Atlantic jet. The contour interval is 10 mmol N m−2 for both plankton biomass and nitrate concentration.
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pone-0111482-g006: Modeled plankton biomass.Horizontal distributions of (a) integrated plankton biomass (phytoplankton plus zooplankton) and (b) integrated nitrate concentration over the upper 75 m layer (mmol N m−2), The background color shows the trajectory of the Atlantic jet. The contour interval is 10 mmol N m−2 for both plankton biomass and nitrate concentration.

Mentions: Starting initially from nutrient-starved conditions and maintaining the absence of horizontal nutrient transport from the Gibraltar Strait, the euphotic layer-integrated nitrate distributions (shown in Fig. 5a–c) illustrated how the developing frontal jet-gyre circulation system built up nutrients within the upper 75 m layer (roughly representative of the winter euphotic zone). The region to the east of the Almeria-Oran front remained nutrient depleted. Nutrients first accumulated along the south coast (Fig. 5a) and then gradually spread over the basin by the meandering jet and, at the same time, by their recycling within the upper layer water column (Fig. 5c). The structural changes that took place in the nutrient distributions indicated the efficiency of the frontal dynamics for supporting enhanced biological production in the Alboran Sea, taking into account that the model excluded the lateral nutrient supply from the Gibraltar Strait. The corresponding depth integrated plankton (the sum of phytoplankton and zooplankton) biomass at day 120 indeed revealed relatively high values up to 100 mmol N m−2 inside the meandering jet around the WAG and roughly half of it around the EAG (Fig. 6a). They were well-correlated with the nutrient accumulation in excess of 100 mmol m−2 around the WAG and approximately 60–70 mmol m−2 around the EAG (Fig. 6b). Nutrient concentrations approximately 50 mmol m−2 within the central parts of the gyres should be related to their accumulation due to isopycnal subduction from the peripheries. Owing to the ageostrophic frontal dynamics, the coastal strip to the north of the Gibraltar junction region, as well as the northern coastal zone confined between the WAG and the Spanish coast, also acquired relatively high plankton biomass. On the contrary, the biomass within the central parts of the gyres and in the cyclonic region between the gyres and along the south coast remained below 30 mmol m−2 (Fig. 6a). The Algerian basin to the east of the Almeria-Oran front exhibited even more oligotrophic character. All of these regions involved relatively low integrated nitrate concentrations in response to the weaker vertical velocities on the order of only few m day−1 (Fig. 3d) associated with the quasigeostrophic motion.


Fueling plankton production by a meandering frontal jet: a case study for the Alboran Sea (Western Mediterranean).

Oguz T, Macias D, Garcia-Lafuente J, Pascual A, Tintore J - PLoS ONE (2014)

Modeled plankton biomass.Horizontal distributions of (a) integrated plankton biomass (phytoplankton plus zooplankton) and (b) integrated nitrate concentration over the upper 75 m layer (mmol N m−2), The background color shows the trajectory of the Atlantic jet. The contour interval is 10 mmol N m−2 for both plankton biomass and nitrate concentration.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4221033&req=5

pone-0111482-g006: Modeled plankton biomass.Horizontal distributions of (a) integrated plankton biomass (phytoplankton plus zooplankton) and (b) integrated nitrate concentration over the upper 75 m layer (mmol N m−2), The background color shows the trajectory of the Atlantic jet. The contour interval is 10 mmol N m−2 for both plankton biomass and nitrate concentration.
Mentions: Starting initially from nutrient-starved conditions and maintaining the absence of horizontal nutrient transport from the Gibraltar Strait, the euphotic layer-integrated nitrate distributions (shown in Fig. 5a–c) illustrated how the developing frontal jet-gyre circulation system built up nutrients within the upper 75 m layer (roughly representative of the winter euphotic zone). The region to the east of the Almeria-Oran front remained nutrient depleted. Nutrients first accumulated along the south coast (Fig. 5a) and then gradually spread over the basin by the meandering jet and, at the same time, by their recycling within the upper layer water column (Fig. 5c). The structural changes that took place in the nutrient distributions indicated the efficiency of the frontal dynamics for supporting enhanced biological production in the Alboran Sea, taking into account that the model excluded the lateral nutrient supply from the Gibraltar Strait. The corresponding depth integrated plankton (the sum of phytoplankton and zooplankton) biomass at day 120 indeed revealed relatively high values up to 100 mmol N m−2 inside the meandering jet around the WAG and roughly half of it around the EAG (Fig. 6a). They were well-correlated with the nutrient accumulation in excess of 100 mmol m−2 around the WAG and approximately 60–70 mmol m−2 around the EAG (Fig. 6b). Nutrient concentrations approximately 50 mmol m−2 within the central parts of the gyres should be related to their accumulation due to isopycnal subduction from the peripheries. Owing to the ageostrophic frontal dynamics, the coastal strip to the north of the Gibraltar junction region, as well as the northern coastal zone confined between the WAG and the Spanish coast, also acquired relatively high plankton biomass. On the contrary, the biomass within the central parts of the gyres and in the cyclonic region between the gyres and along the south coast remained below 30 mmol m−2 (Fig. 6a). The Algerian basin to the east of the Almeria-Oran front exhibited even more oligotrophic character. All of these regions involved relatively low integrated nitrate concentrations in response to the weaker vertical velocities on the order of only few m day−1 (Fig. 3d) associated with the quasigeostrophic motion.

Bottom Line: Biological production is larger in the western part of the basin and decreases eastwards with the gradual weakening of the jet.The higher production at the subsurface levels suggests that the Alboran Sea is likely more productive than predicted by the satellite chlorophyll data.The Mediterranean water mass away from the jet and the interiors of the western and eastern anticyclonic gyres remain unproductive.

View Article: PubMed Central - PubMed

Affiliation: SOCIB, Balearic Islands Coastal Ocean Observing and Forecasting System, Palma de Mallorca, Spain; Institute of Marine Sciences, Middle East Technical University, Erdemli, Mersin, Turkey.

ABSTRACT
A three dimensional biophysical model was employed to illustrate the biological impacts of a meandering frontal jet, in terms of efficiency and persistency of the autotrophic frontal production, in marginal and semi-enclosed seas. We used the Alboran Sea of the Western Mediterranean as a case study. Here, a frontal jet with a width of 15-20 km, characterized by the relatively low density Atlantic water mass, flows eastward within the upper 100 m as a marked meandering current around the western and the eastern anticyclonic gyres prior to its attachment to the North African shelf/slope topography of the Algerian basin. Its inherent nonlinearity leads to the development of a strong ageostrophic cross-frontal circulation that supplies nutrients into the nutrient-starved euphotic layer and stimulates phytoplankton growth along the jet. Biological production is larger in the western part of the basin and decreases eastwards with the gradual weakening of the jet. The higher production at the subsurface levels suggests that the Alboran Sea is likely more productive than predicted by the satellite chlorophyll data. The Mediterranean water mass away from the jet and the interiors of the western and eastern anticyclonic gyres remain unproductive.

Show MeSH