Chlorophyll distribution throughout the southeastern Mediterranean in relation to the physical structure of the water mass

The spatial distribution of chlorophyll was recorded throughout the southern part of the Levantine Basin of the eastern Mediterranean and was related to patterns of the physical structure and nutrient concentrations. Chlorophyll a concentration in the upper 200 m of the water column ranged from 9.2 to 423 ng l−1, with an overall mean of 126 ± 85.6 (SD) ng l−1. The pattern of vertical distribution of chlorophyll was close to uniform throughout the basin, with a prominent deep chlorophyll maximum (DCM) of ca. 250 ng l−1 at 90–110 m. The values we report fall at the lower end of ranges reported from other oligotrophic seas, in accordance with the ultra-oligotrophic nature of the eastern Mediterranean. Throughout the basin more than 90% of the chlorophyll at the surface was confined to particles < 10 μ in diameter and more than 60% was found in particles < 2 μ. The proportion of chlorophyll in < 2 μ particles increased with depth between the surface and the DCM, as was also confirmed by flow cytometric analysis. Discontinuities of physical and chemical features were mostly confined to depths greater than 200 m, and had little impact on the distribution of chlorophyll. An exception was an anti cyclonic eddy south of Crete, within which chlorophyll (mostly > 100 μg l−1) was more evenly distributed with depth over the upper 200 m.