Abstract
Abstract. Planktonic gross community production (GPP), net community production (NCP) and community respiration (CR) across the Mediterranean Sea was examined in two cruises, Thresholds 2006 and 2007, each crossing the Mediterranean from West to East to test for consistent variation along this longitudinal gradient in late spring to early summer. GPP averaged 2.4±0.4 mmol O2 m−3 d−1, CR averaged 3.8±0.5 mmol O2 m−3 d−1, and NCP averaged – 0.8±0.6 mmol O2 m−3 d−1 across the studied sections, indicative of a tendency for a net heterotrophic metabolism in late spring to early summer, prevalent across studied sections of the Mediterranean Sea as reflected in 70% of negative NCP estimates. The median P/R ratio was 0.6, also indicating a strong prevalence of heterotrophic communities (P/R<1) along the studied sections of the Mediterranean Sea. The communities tended to be net heterotrophic (i.e. P/R<1) at GPP less than 2.8 mmol O2 m−3 d−1. The Western Mediterranean tended to support a higher gross primary production and community respiration than the Eastern basin did, but these differences were not statistically significant (t-test, p>0.05). The net heterotrophy of the studied sections of the Mediterranean Sea indicates that allochthonous carbon should be important to subsidise planktonic metabolism during the late spring.
Highlights
The Mediterranean Sea represents an anomaly in the world ocean because it ranks amongst the most oligotrophic areas of the world while receiving significant land-derived inputs of both natural and anthropogenic materials
Planktonic gross community production (GPP), net community production (NCP) and community respiration (CR) across the Mediterranean Sea was examined in two cruises, THRESHOLDS 2006 and 2007, each crossing the Mediterranean from West to East to test for consistent variation along this longitudinal gradient in late spring to early summer
Dissolved organic carbon ranged two fold within basins (Table 1), with dissolved organic carbon (DOC) concentrations generally declining with depth
Summary
The Mediterranean Sea represents an anomaly in the world ocean because it ranks amongst the most oligotrophic areas of the world while receiving significant land-derived inputs of both natural and anthropogenic materials. Whether a West-East gradient in net community production exists in the Mediterranean Sea has not yet been resolved, due to a paucity of reports on planktonic metabolism in the Mediterranean Sea, on the Eastern basin, as the bulk of the data available derive from the Western basin, with a dominance of studies in coastal waters (Gulf of Lions, Gonzalez et al, 2008; Lefevre et al, 1997; Bay of Blanes, Duarte et al, 2004; Lucea et al, 2005; Alboran Sea, Van Wambeke et al, 2004; Majorca Island, Gonzalez et al, 2008; Gazeau et al, 2005; Navarro et al, 2004). The metabolic balance of planktonic communities is a key determinant of their role in biogeochemical cycle and, the role of planktonic communities as CO2 sinks or sources affecting the atmospheresea CO2 transfer (Duarte and Prairie, 2005)
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