[1] Standard metabolic theory predicts that both respiration and photosynthesis should increase with increasing temperature, albeit at different rates. However, test of this prediction for ocean planktonic communities is limited, despite the broad consequences of this prediction in the present context of global ocean warming. We compiled a large data set on volumetric planktonic metabolism in the open ocean and tested the relationship between specific metabolic rates and water temperature. The relationships derived are consistent with predictions derived from metabolic theory of ecology, yielding activation energy for planktonic metabolism consistent with predictions from the metabolic theory. These relationships can be used to predict the effect of warming on ocean metabolism and, thus, the role of planktonic communities in the flow of carbon in the global ocean.Citation: Regaudie-de-Gioux, A., and C. M. Duarte (2012), Temperature dependence of planktonic metabolism in the ocean, Global Biogeochem. Cycles, 26, GB1015,

Incubation (in vitro) and incubation-free (in situ) methods, each with their own advantages and limitations, have been used to derive estimates of net community metabolism in the oligotrophic subtropical gyres of the open ocean. The hypothesis that heterotrophic communities are prevalent in most oligotrophic regions is consistent with the available evidence and supported by scaling relationships showing that heterotrophic communities prevail in areas of low gross primary production, low chlorophyll a, and warm water, conditions found in the oligotrophic ocean. Heterotrophic metabolism can prevail where heterotrophic activity is subsidized by organic carbon inputs from the continental shelf or the atmosphere and from nonphotosynthetic autotrophic and mixotrophic metabolic pathways. The growth of the oligotrophic regions is likely to be tilting the metabolic balance of the ocean toward a greater prevalence of heterotrophic communities.

The Arctic Ocean is warming at two to three times the global rate 1 and is perceived to be a bellwether for ocean acidification 2,3 . Increased CO 2 concentrations are expected to have a fertilization e ect on marine autotrophs 4 , and higher temperatures should lead to increased rates of planktonic primary production 5 . Yet, simultaneous assessment of warming and increased CO 2 on primary production in the Arctic has not been conducted. Here we test the expectation that CO 2 -enhanced gross primary production (GPP) may be temperature dependent, using data from several oceanographic cruises and experiments from both spring and summer in the European sector of the Arctic Ocean. Results confirm that CO 2 enhances GPP (by a factor of up to ten) over a range of 145-2,099 µatm; however, the greatest e ects are observed only at lower temperatures and are constrained by nutrient and light availability to the spring period. The temperature dependence of CO 2 -enhanced primary production has significant implications for metabolic balance in a warmer, CO 2 -enriched Arctic Ocean in the future. In particular, it indicates that a twofold increase in primary production during the spring is likely in the Arctic.Primary production in the Arctic Ocean supports significant fisheries 6 and renders it an important sink for anthropogenic carbon 2 ; however, climate change has the potential to alter these capacities. Accelerated ice loss is opening surface area across the Arctic, resulting in observations of increased rates of primary production 7 . The reduced salinity caused by melting ice, combined with increasing temperatures, however, increases stratification, restricting turbulent nutrient supply to surface layers 8 . Ice loss also increases surface area for air-sea CO 2 exchange, causing an uptake from the atmosphere into surface waters with already low p CO 2 (ref. 9), and ice melt introduces freshwater with low alkalinity and dissolved inorganic carbon, further lowering the carbon content of surface waters 10 . The surface waters of the Arctic Ocean are largely undersaturated with respect to CO 2 throughout spring and summer 2 . In the European sector of the Arctic Ocean (BarentsGreenland Sea/Fram Strait), p CO 2 varies seasonally by more than 200 µatm, with values as low as 100 µatm in spring months 11 owing to strong net community production associated with the spring bloom of ice algae followed by that of planktonic algae