Oxygen photolysis in the Mauritanian upwelling: Implications for net community production

We carried out 16 photochemical experiments of filtered surface water in a custom-built solar simulator and concomitant measurements of in vitro gross primary production (GPP) and respiration (R) in the Mauritanian upwelling during a Lagrangian study following three sulfur hexafluoride–labeled patches of upwelled water (P1 to P3). Oxygen photolysis rates were correlated with the absorbance of chromophoric dissolved organic matter (CDOM) at 300 nm, suggesting first-order kinetics with respect to CDOM. An exponential fit was used to calculate the apparent quantum yield (AQY) for oxygen photolysis, giving an average AQY of 0.00053 mmol O2 (mole photons m22 s21)21 at 280 nm and slope of 0.0012 nm21. Modeled photochemical oxygen demand (POD) at the surface (3–16 mmol m23 d21) occasionally exceeded R and was dominated by ultraviolet radiation (71– 79%). Euphotic-layer integrated GPP decreased with time during both P-1 and P-3, whereas R remained relatively constant and POD increased during P-1 and decreased during P-3. On Day 4 of P-3, GPP and POD maxima coincided with high CDOM absorbance, suggesting ‘‘new’’ CDOM production. Omitting POD may lead to an underestimation of net community production (NCP), both through in vitro and geochemical methods (here by 2–22%). We propose that oxygen-based NCP estimates should be revised upward. For the Mauritanian upwelling, the POD-corrected NCP was strongly correlated with standard NCP with a slope of 1.0066 6 0.0244 and intercept of 46.51 6 13.15 mmol m22 d21

Seasonal and spatial variability in plankton production and respiration in the Subtropical Gyres of the Atlantic Ocean

Euphotic zone plankton production (P) and respiration (R) were determined from the in vitro flux of dissolved oxygen during six latitudinal transects of the Atlantic Ocean, as part of the Atlantic Meridional Transect (AMT) programme. The transects traversed the North and South Atlantic Subtropical Gyres (N gyre, 18–38°N; S gyre, 11–35°S) in April–June and September–November 2003–2005. The route and timing of the cruises enabled the assessment of the seasonal variability of P, R and P/R in the N and S gyres, and the comparison of the previously unsampled N gyre centre with the more frequently sampled eastern edge of the gyre. Mean euphotic zone integrated rates (±SE) were P=63±23 (n=31), R=69±22 (n=30) mmol O2 m-2 d-1 in the N gyre; and P=58±26 (n=30), R=62±24 (n=30) mmol O2 m-2 d-1 in the S gyre. Overall, the N gyre was heterotrophic (R>P) and it was more heterotrophic than the S gyre, but the metabolic balance of both gyres changed with season. Both gyres were net heterotrophic in autumn, and balanced in spring. This seasonal contrast was most pronounced for the S gyre, because it was more autotrophic than the N gyre during spring. This may have arisen from differences in nitrate availability, because spring sampling in the S gyre coincided with periods of deep mixing to the nitracline, more frequently than spring sampling within the N gyre. Our results indicate that the N gyre is less heterotrophic than previous estimates suggested, and that there is an apparent decrease in R from the eastern edge to the centre of the N gyre, possibly indicative of an allochthonous organic carbon source to the east of the gyre

Predicting plankton net community production in the Atlantic Ocean

We present, test and implement two contrasting models to predict euphotic zone net community production (NCP), which are based on 14C primary production (PO14CP) to NCP relationships over two latitudinal (ca. 30°S–45°N) transects traversing highly productive and oligotrophic provinces of the Atlantic Ocean (NADR, CNRY, BENG, NAST-E, ETRA and SATL, Longhurst et al., 1995 [An estimation of global primary production in the ocean from satellite radiometer data. Journal of Plankton Research 17, 1245–1271]). The two models include similar ranges of PO14CP and community structure, but differ in the relative influence of allochthonous organic matter in the oligotrophic provinces. Both models were used to predict NCP from PO14CP measurements obtained during 11 local and three seasonal studies in the Atlantic, Pacific and Indian Oceans, and from satellite-derived estimates of PO14CP. Comparison of these NCP predictions with concurrent in situ measurements and geochemical estimates of NCP showed that geographic and annual patterns of NCP can only be predicted when the relative trophic importance of local vs. distant processes is similar in both modeled and predicted ecosystems. The system-dependent ability of our models to predict NCP seasonality suggests that trophic-level dynamics are stronger than differences in hydrodynamic regime, taxonomic composition and phytoplankton growth. The regional differences in the predictive power of both models confirm the existence of biogeographic differences in the scale of trophic dynamics, which impede the use of a single generalized equation to estimate global marine plankton NCP. This paper shows the potential of a systematic empirical approach to predict plankton NCP from local and satellite-derived P estimates

Contribution of bacterial respiration to plankton respiration from 50˚N to 44˚S in the Atlantic Ocean

Marine bacteria play an important role in the global cycling of carbon and therefore in climate regulation. However, the paucity of direct measurements means that our understanding of the magnitude and variability of bacterial respiration in the ocean is poor. Estimations of respiration in the 0.2-0.8 µm size-fraction (considered as bacterial respiration), total plankton community respiration, and the contribution of bacterial respiration to total plankton community respiration were made along two latitudinal transects in the Atlantic Ocean (ca. 50 ºN – 44 ºS) during 2010 and 2011. Two different methodologies were used: determination of changes in dissolved O2 concentration after standard 24 h dark bottle incubations, and measurements of in vivo reduction of 2-(ρ-iodophenyl)-3- (ρ-nitrophenyl)-5phenyl tetrazolium salt (INT). There was an overall significant correlation (r = 0.44, p <0.0001, n = 90) between the rates of community respiration estimated by both methods. Depth-integrated community respiration varied as much as three-fold between regions. Maximum rates occurred in waters of the western European shelf and Patagonian shelf, and minimum rates in the North and South oligotrophic gyres. Depth-integrated bacterial respiration followed the same pattern as community respiration. There was a significantly higher cell-specific bacterial respiration in the northern subtropical gyre than in the southern subtropical gyre which suggests that bacterial carbon turnover is faster in the northern gyre. The relationships between plankton respiration and physicochemical and biological variables were different in different years. In general, INTT was correlated to both chlorophyll-a and bacterial abundance, while INT0.2-0.8 was only correlated with bacterial abundance. However, in 2010 INTT and INT0.2-0.8 were also correlated with temperature and primary production while in 2011 they were correlated with nitrate + nitrite concentration. The bacterial contribution to depth integrated community respiration was highly variable within provinces (4 - 77 %). Results from this study suggest that the proportion of total community respiration attributable to bacteria is similar between the 6 oceanographic regions studied

Both respiration and photosynthesis determine the scaling of plankton metabolism in the oligotrophic ocean

Despite its importance to ocean–climate interactions, the metabolic state of the oligotrophic ocean has remained controversial for >15 years. Positions in the debate are that it is either hetero- or autotrophic, which suggests either substantial unaccounted for organic matter inputs, or that all available photosynthesis (P) estimations (including 14C) are biased. Here we show the existence of systematic differences in the metabolic state of the North (heterotrophic) and South (autotrophic) Atlantic oligotrophic gyres, resulting from differences in both P and respiration (R). The oligotrophic ocean is neither auto- nor heterotrophic, but functionally diverse. Our results show that the scaling of plankton metabolism by generalized P:R relationships that has sustained the debate is biased, and indicate that the variability of R, and not only of P, needs to be considered in regional estimations of the ocean’s metabolic state

Impact of atmospheric deposition on the metabolism of coastal microbial communities

11 páginas, 3 tablas, 5 figurasThe impact of rain water collected at marine, urban and rural sites on coastal phytoplankton biomass, primary production and community composition as well as the effect on microbial plankton metabolism was studied in 3 microcosm experiments conducted under contrasting spring, autumn and winter conditions. The measured responses were highly variable. Rainwater additions increased chlorophyll a (Chl a) concentration (5–68% difference between rainwater treatments relative to the control) in all experiments and reduced or stimulated primary production (PP) depending on the treatment and the experiment (from −10 to +169% relative to the control). Autotrophic stimulation was highest in spring, probably related to the low initial natural nutrient concentrations. Under winter nutrient replete conditions, rainwater inputs changed the phytoplankton community although this change did not promote increases in primary production. Enhancement of net autotrophy (increase of net oxygen production up to 227%) after rainwater inputs were only found during the period of low nutrient availability. Inputs of dissolved organic nitrogen (DON) explained a large fraction of the variability in the response of PP, Chl a, community respiration (CR) and net community production (NCP). Our results suggest that differences in the initial environmental conditions (i.e. nutrient availability), rainwater composition and the ability of the present autotrophic communities to utilize the new nutrients result in substantial changes in the microbial responses and associated biologically-mediated carbon fluxes. As atmospheric nutrient inputs into coastal oceans are increasing rapidly, our results help to understand the effects of different inputs on the metabolism of distinct microbial communitiesThis research was supported by the Galician Government (Xunta de Galicia) through the grants 07MMA002402PR (IMAN) and PGIDIT06PXIB312222PR (AddEx). S.M-G. and E.E.G-M. were funded by F.P.U. fellowships and E.T. by a Ramón y Cajal contract of the Spanish Ministry of Science and InnovationPeer reviewe

Both respiration and photosynthesis determine the scaling of plankton metabolism in the oligotrophic ocean

Despite its importance to ocean–climate interactions, the metabolic state of the oligotrophic ocean has remained controversial for >15 years. Positions in the debate are that it is either hetero- or autotrophic, which suggests either substantial unaccounted for organic matter inputs, or that all available photosynthesis (P) estimations (including 14 C) are biased. Here we show the existence of systematic differences in the metabolic state of the North (heterotrophic) and South (autotrophic) Atlantic oligotrophic gyres, resulting from differences in both P and respiration (R). The oligotrophic ocean is neither auto- nor heterotrophic, but functionally diverse. Our results show that the scaling of plankton metabolism by generalized P:R relationships that has sustained the debate is biased, and indicate that the variability of R, and not only of P, needs to be considered in regional estimations of the ocean’s metabolic state.Ministerio de Ciencia e Innovación | Ref. CTM2009-0S069-E/MARMinisterio de Ciencia e Innovación | Ref. CTM2011-2961

Balanced plankton net community metabolism in the oligotrophic North Atlantic subtropical gyre from Lagrangian observations

Characterization of the microbial plankton metabolism in oligotrophic oceans is of relevance for the quantification of the global carbon balance; however whether the plankton community metabolism in oligotrophic gyres is net autotrophic or heterotrophic is still under debate. Discrepancies have been in part attributed to the difficulties of the standard snapshot estimations, based on in vitro measurements, to adequately represent the temporal scale of trophic processes. This work presents concurrent measurements of gross primary production and community respiration carried out in the North Atlantic Oligotrophic Gyre throughout two 7-day Lagrangian experiments that allowed us to investigate the effect of short term (daily) variability on the microbial metabolism quantification. Physicochemical and biological variables showed a low variability in each Lagrangian experiment and a balanced net plankton metabolism was found in 83% of the sampling days.Ministerio de Educación y Ciencia | Ref. REN2003-09532-C03-0

Satellite estimates of net community production indicate predominance of net autotrophy in the Atlantic Ocean

There is ongoing debate as to whether the oligotrophic ocean is predominantly net autotrophic and acts as a CO2 sink, or net heterotrophic and therefore acts as a CO2 source to the atmosphere. This quantification is challenging, both spatially and temporally, due to the sparseness of measurements. There has been a concerted effort to derive accurate estimates of phytoplankton photosynthesis and primary production from satellite data to fill these gaps; however there have been few satellite estimates of net community production (NCP). In this paper, we compare a number of empirical approaches to estimate NCP from satellite data with in vitro measurements of changes in dissolved O2 concentration at 295 stations in the N and S Atlantic Ocean (including the Antarctic), Greenland and Mediterranean Seas. Algorithms based on power laws between NCP and particulate organic carbon production (POC) derived from 14C uptake tend to overestimate NCP at negative values and underestimate at positive values. An algorithm that includes sea surface temperature (SST) in the power function of NCP and 14C POC has the lowest bias and root-mean square error compared with in vitro measured NCP and is the most accurate algorithm for the Atlantic Ocean. Nearly a 13 year time series of NCP was generated using this algorithm with SeaWiFS data to assess changes over time in different regions and in relation to climate variability. The North Atlantic subtropical and tropical Gyres (NATL) were predominantly net autotrophic from 1998 to 2010 except for boreal autumn/winter, suggesting that the northern hemisphere has remained a net sink for CO2 during this period. The South Atlantic sub-tropical Gyre (SATL) fluctuated from being net autotrophic in austral spring-summer, to net heterotrophic in austral autumn–winter. Recent decadal trends suggest that the SATL is becoming more of a CO2 source. Over the Atlantic basin, the percentage of satellite pixels with negative NCP was 27%, with the largest contributions from the NATL and SATL during boreal and austral autumn–winter, respectively. Variations in NCP in the northern and southern hemispheres were correlated with climate indices. Negative correlations between NCP and the multivariate ENSO index (MEI) occurred in the SATL, which explained up to 60% of the variability in NCP. Similarly there was a negative correlation between NCP and the North Atlantic Oscillation (NAO) in the Southern Sub-Tropical Convergence Zone (SSTC), which explained 90% of the variability. There were also positive correlations with NAO in the Canary Current Coastal Upwelling (CNRY) and Western Tropical Atlantic (WTRA) which explained 80% and 60% of the variability in each province, respectively. MEI and NAO seem to play a role in modifying phases of net autotrophy and heterotrophy in the Atlantic Ocean.Chinese State Scholarship Fund | Ref. 201206310058Ministerio de Ciencia e Innovación | Ref. CTM2011-2961

Activation of the Integrated Stress Response and ER Stress Protect from Fluorizoline-Induced Apoptosis in HEK293T and U2OS Cell Lines

The prohibitin (PHB)-binding compound fluorizoline as well as PHB-downregulation activate the integrated stress response (ISR) in HEK293T and U2OS human cell lines. This activation is denoted by phosphorylation of eIF2 alpha and increases in ATF4, ATF3, and CHOP protein levels. The blockage of the activation of the ISR by overexpression of GRP78, as well as an increase in IRE1 activity, indicate the presence of ER stress after fluorizoline treatment. The inhibition of the ER stress response in HEK293T and U2OS led to increased sensitivity to fluorizoline-induced apoptosis, indicating a pro-survival role of this pathway after fluorizoline treatment in these cell lines. Fluorizoline induced an increase in calcium concentration in the cytosol and the mitochondria. Finally, two different calcium chelators reduced fluorizoline-induced apoptosis in U2OS cells. Thus, we have found that fluorizoline causes increased ER stress and activation of the integrated stress response, which in HEK293T and U2OS cells are protective against fluorizoline-induced apoptosis