[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

Numerous studies have compared the rates of primary production using various techniques at specific locations and times. However, these comparisons are local and cannot be used to compare or scale rates of primary production using different methods across ocean basins or seasonal time scales. Here, we quantify the range in rates of primary production derived using different techniques and provide equations that allow conversions of estimates between different methods. We do so on the basis of a compilation of data on volumetric estimates of primary production rates concurrently estimated with at least two different methods. We observed that the comparison of estimates of marine phytoplankton primary production derived from different methods reveals very large variations between methods. The highest primary production estimates are derived using the 18 O method, which may provide the best and more generally applicable estimate of gross primary production (GPP). The regression equations presented in this work provide the best available approach to convert data across methods and therefore integrate and synthesize available and future data derived using different methods.

The metabolism of the Arctic Ocean is marked by extremely pronounced seasonality and spatial heterogeneity associated with light conditions, ice cover, water masses and nutrient availability. Here we report the marine planktonic metabolic rates (net community production, gross primary production and community respiration) along three different seasons of the year, for a total of eight cruises along the western sector of the European Arctic (Fram Strait – Svalbard region) in the Arctic Ocean margin: one at the end of 2006 (fall/winter), two in 2007 (early spring and summer), two in 2008 (early spring and summer), one in 2009 (late spring–early summer), one in 2010 (spring) and one in 2011 (spring). The results show that the metabolism of the western sector of the European Arctic varies throughout the year, depending mostly on the stage of bloom and water temperature. Here we report metabolic rates for the different periods, including the spring bloom, summer and the dark period, increasing considerably the empirical basis of metabolic rates in the Arctic Ocean, and especially in the European Arctic corridor. Additionally, a rough annual metabolic estimate for this area of the Arctic Ocean was calculated, resulting in a net community production of 108 g C m⁻² yr⁻¹

Rates of gross primary production (GPP) and respiration (CR) of plankton communities in the upper ocean were evaluated on the basis of a data set comprising 3149 paired light and dark bottle measurements of volumetric GPP‐CR of euphotic zone plankton communities. The data were from 72 published and unpublished reports of measurements made between 1981 and 2011 from the open ocean and the Mediterranean Sea. The data set is dominated by measurements in chlorophyll a (Chl a)‐rich oceans and North Atlantic waters, with a paucity of measurements in the Indian Ocean and South Pacific Ocean. CR scaled as the 3/4 power of GPP with a power slope of 0.79 ± 0.01, implying that the threshold GPP separating heterotrophic from autotrophic plankton communities is 1.26 mmol O2 m−3 d−1. Plankton communities with Chl a < 0.35 mg m−3 tend to be heterotrophic. Both GPP and CR declined exponentially with depth, but the GPP declined faster, at 42% ± 7% m−1, than CR (29% ± 8% m−1), so that CR increases relative to GPP with depth.

The notion that less productive marine planktonic communities tend to be heterotrophic was tested by synthesizing reported estimates of the relationships between the net community production or community respiration and gross primary production (GPP), allowing calculation of the threshold GPP separating less productive, heterotrophic communities from more productive, autotrophic ones. A total of 35 estimates of the threshold GPP were assembled, derived from reports of comparative analyses of individual regions (Mediterranean Sea, Atlantic Ocean, Southern Ocean, Pacific Ocean, and Indian Ocean) and global comparative analyses for open-ocean and coastal environments, time-series analyses of changes in planktonic metabolism at individual locations, experimental manipulations in mesocosms, and a semi-empirical modeling exercise. , with a general consistency across approaches for a given ecosystem. Plankton community respiration in the absence of or under low primary production is not negligible and is supported by semi-labile dissolved organic carbon. The analysis of GPP thresholds suggests that allochthonous organic inputs to the less productive regions of the ocean must be in the order of 5-6 mmol C m 22 d 21 , consistent with recent estimates of allochthonous inputs of organic carbon to the ocean.

The net community production (NCP) of plankton communities affects their role as sources or sinks of atmospheric CO 2 . Most estimates of NCP have been made by enclosing communities in bottles, generally glass borosilicate, that remove ultraviolet (UV)B and part of UVA wavelengths. A series of experiments were conducted to test whether NCP values from communities incubated excluding UVB (+ part of UVA) radiation (i.e., in glass borosilicate) differ from those of communities receiving the full solar radiation spectrum (i.e., incubated with quartz bottles) and to explore the effect of UV radiation on the respiration rates and bacterial production in these communities. Plankton NCP tended to be 43% lower, on average, when the rates were measured under full solar radiation than when UVB (+ part of UVA) was removed. Dark respiration was significantly enhanced after exposure to the full solar spectrum for most communities, showing lower values when previously incubated in a light environment free of UVB (250%) or in the dark (262%). Bacterial production was inhibited by natural sunlight but increased, as observed for community respiration, when transferred to the dark. Communities previously exposed to full solar spectrum showed the greatest increase in bacterial production when allowed to recover in the dark. The net result of these responses were an increase in community respiration and decline in net community production over 24 h, indicating that UVB radiation plays a major role in the metabolic balance of the ocean's surface ecosystem.