Published by European Geosciences Union
Online ISSN: 1726-4189
Grasslands comprise natural tropical savannah over managed temperate fields to tundra and cover one quarter of the Earth's land surface. Plant growth, maintenance and decay result in volatile organic compound (VOCs) emissions to the atmosphere. Furthermore, biogenic VOCs (BVOCs) are emitted as a consequence of various environmental stresses including cutting and drying during harvesting. Fluxes of BVOCs were measured with a proton-transfer-reaction-mass-spectrometer (PTR-MS) over temperate mountain grassland in Stubai Valley (Tyrol, Austria) over one growing season (2008). VOC fluxes were calculated from the disjunct PTR-MS data using the virtual disjunct eddy covariance method and the gap filling method. Methanol fluxes obtained with the two independent flux calculation methods were highly correlated (y = 0.95×-0.12, R (2) = 0.92). Methanol showed strong daytime emissions throughout the growing season - with maximal values of 9.7 nmol m(-2) s(-1), methanol fluxes from the growing grassland were considerably higher at the beginning of the growing season in June compared to those measured during October (2.5 nmol m(-2) s(-1)). Methanol was the only component that exhibited consistent fluxes during the entire growing periods of the grass. The cutting and drying of the grass increased the emissions of methanol to up to 78.4 nmol m(-2) s(-1). In addition, emissions of acetaldehyde (up to 11.0 nmol m(-2) s(-1)), and hexenal (leaf aldehyde, up to 8.6 nmol m(-2) s(-1)) were detected during/after harvesting.
The ratio of mean annual soil respiration (mean SR annual , µmol m −2 s −1 ) over soil respiration at mean annual temperature (SR MAT , µmol m −2 s −1 ) as affected by the annual variation of soil temperature (T sd ) and Q 10 of the temperature-soil respiration relationship. Data points indicate values of the non water-limited sites for mean SR annual /SR MAT , T sd and Q 10 classes.
Soil respiration (SR) constitutes the largest flux of CO(2) from terrestrial ecosystems to the atmosphere. However, there still exist considerable uncertainties as to its actual magnitude, as well as its spatial and interannual variability. Based on a reanalysis and synthesis of 80 site-years for 57 forests, plantations, savannas, shrublands and grasslands from boreal to tropical climates we present evidence that total annual SR is closely related to SR at mean annual soil temperature (SR(MAT)), irrespective of the type of ecosystem and biome. This is theoretically expected for non water-limited ecosystems within most of the globally occurring range of annual temperature variability and sensitivity (Q(10)). We further show that for seasonally dry sites where annual precipitation (P) is lower than potential evapotranspiration (PET), annual SR can be predicted from wet season SR(MAT) corrected for a factor related to P/PET. Our finding indicates that it can be sufficient to measure SR(MAT) for obtaining a well constrained estimate of its annual total. This should substantially increase our capacity for assessing the spatial distribution of soil CO(2) emissions across ecosystems, landscapes and regions, and thereby contribute to improving the spatial resolution of a major component of the global carbon cycle.
Changes in land use and management have been strongly affecting mountain grassland, however, their effects on the net ecosystem exchange of CO(2) (NEE) and its components have not yet been well documented. We analysed chamber-based estimates of NEE, gross primary productivity (GPP), ecosystem respiration (R) and light use efficiency (LUE) of six mountain grasslands differing in land use and management, and thus site fertility, for the growing seasons of 2002 to 2008. The main findings of the study are that: (1) land use and management affected seasonal NEE, GPP and R, which all decreased from managed to unmanaged grasslands; (2) these changes were explained by differences in leaf area index (LAI), biomass and leaf-area-independent changes that were likely related to photosynthetic physiology; (3) diurnal variations of NEE were primarily controlled by photosynthetically active photon flux density and soil and air temperature; seasonal variations were associated with changes in LAI; (4) parameters of light response curves were generally closely related to each other, and the ratio of R at a reference temperature/ maximum GPP was nearly constant across the sites; (5) similarly to our study, maximum GPP and R for other grasslands on the globe decreased with decreasing land use intensity, while their ratio remained remarkably constant. We conclude that decreasing intensity of management and, in particular, abandonment of mountain grassland lead to a decrease in NEE and its component processes. While GPP and R are generally closely coupled during most of the growing season, GPP is more immediately and strongly affected by land management (mowing, grazing) and season. This suggests that management and growing season length, as well as their possible future changes, may play an important role for the annual C balance of mountain grassland.
The broad-band normalised difference vegetation index (NDVI) and the simple ratio (SR) were calculated from measurements of reflectance of photosynthetically active and short-wave radiation at two temperate mountain grasslands in Austria and related to the net ecosystem CO2 exchange (NEE) measured concurrently by means of the eddy covariance method. There was no significant statistical difference between the relationships of midday mean NEE with narrow- and broad-band NDVI and SR, measured during and calculated for that same time window, respectively. The skill of broad-band NDVI and SR in predicting CO2 fluxes was higher for metrics dominated by gross photosynthesis and lowest for ecosystem respiration, with NEE in between. A method based on a simple light response model whose parameters were parameterised based on broad-band NDVI allowed to improve predictions of daily NEE and is suggested to hold promise for filling gaps in the NEE time series. Relationships of CO2 flux metrics with broad-band NDVI and SR however generally differed between the two studied grassland sites indicting an influence of additional factors not yet accounted for.
Using a six year data set of eddy covariance flux measurements of sensible and latent heat, soil heat flux, net radiation, above-ground phytomass and meteorological driving forces energy partitioning was investigated at a temperate mountain grassland managed as a hay meadow in the Stubai Valley (Austria). The main findings of the study were: (i) Energy partitioning was dominated by latent heat, followed by sensible heat and the soil heat flux; (ii) When compared to standard environmental forcings, the amount of green plant matter, which due to three cuts varied considerably during the vegetation period, explained similar, and partially larger, fractions of the variability in energy partitioning; (iii) There were little, if any, indications of water stress effects on energy partitioning, despite reductions in soil water availability in combination with high evaporative demand, e.g. during the summer drought of 2003.
Half-hourly CO 2 , CH 4 and N 2 O fluxes over 2 years of 
Diurnal cycles of CH 4 and N 2 O fluxes during different time periods in 2010 and 2011. Whiskers to the right of each plot show the average standard deviation during the respective time period. Management data were excluded from the analysis.
N 2 O daily average fluxes (grey dots) versus soil water content and soil temperature. Blue circles in the upper two panels show bin averages (40 days per bin), with error bars representing the standard deviation within each bin. In the lower panel, fluxes < 0 ng m −2 s −1 are circled in blue, fluxes > 9 ng m −2 s −1 are circled in red. Management events were excluded from the analysis.
Cumulative GHG fluxes in 2011 expressed as CO 2 equivalents. The effect of the finite impulse response (FIR) filter with different time constants is shown for CH 4 and N 2 O budgets. Vertical lines show management dates, the numbers 1, 2 and 3 in green squares indicate the first, second and third cutting of the meadow, respectively, while M denotes manure spreading.
The methane (CH4) and nitrous oxide (N2O) exchange of a temperate mountain grassland near Neustift, Austria, was measured during 2010–2012 over a time period of 22 months using the eddy covariance method. Exchange rates of both compounds at the site were low, with 97% of all half-hourly CH4 and N2O fluxes ranging between ±200 and ±50 ng m−2 s−1, respectively. The meadow acted as a sink for both compounds during certain time periods, but was a clear source of CH4 and N2O on an annual timescale. Therefore, both gases contributed to an increase of the global warming potential (GWP), effectively reducing the sink strength in terms of CO2 equivalents of the investigated grassland site. In 2011, our best guess estimate showed a net greenhouse gas (GHG) sink of −32 g CO2 equ. m−2 yr−1 for the meadow, whereby 55% of the CO2 sink strength of −71 g CO2m−2 yr−1 was offset by CH4 (N2O) emissions of 7 (32) g CO2 equ. m−2 yr−1. When all data were pooled, the ancillary parameters explained 27 (42)% of observed CH4 (N2O) flux variability, and up to 62 (76)% on shorter timescales in-between management dates. In the case of N2O fluxes, we found the highest emissions at intermediate soil water contents and at soil temperatures close to 0 or above 14 °C. In comparison to CO2, H2O and energy fluxes, the interpretation of CH4 and N2O exchange was challenging due to footprint heterogeneity regarding their sources and sinks, uncertainties regarding post-processing and quality control. Our results emphasize that CH4 and N2O fluxes over supposedly well-aerated and moderately fertilized soils cannot be neglected when evaluating the GHG impact of temperate managed grasslands.
The Life In The Atacama (LITA) project develops and field tests a long-range, solarpowered, automated rover platform (Zo ) and a science payload assembled to search for microbial life in the Atacama desert. Life is barely detectable over most of the driest desert on Earth. Its unique geological, climatic, and biological evolution have created a unique training site for designing and testing exploration strategies and life detection methods for the robotic search for life on Mars.
Solar-normalized fluxes (with respect to those of today) vs. stellar age for different wavelength bands for solar-type stars. Taken from Ribas et al. (2005). 
Molar extinction coefficients at maximum absorption of the nucleobases, aromatic amino acids, and organic heterocyclic and aromatic cofactors common to all three domains of life.
Timeline demonstrating the correlation between the prevailing surface solar spectrum and the appearance and distribution of organic pigments. Major milestones in the evolution of life are also noted in the figure.
The driving force behind the origin and evolution of life has been the thermodynamic imperative of increasing the entropy production of the biosphere through increasing the global solar photon dissipation rate. In the upper atmosphere of today, oxygen and ozone derived from life processes are performing the short-wavelength UV-C and UV-B dissipation. On Earth's surface, water and organic pigments in water facilitate the near-UV and visible photon dissipation. The first organic pigments probably formed, absorbed, and dissipated at those photochemically active wavelengths in the UV-C and UV-B that could have reached Earth's surface during the Archean. Proliferation of these pigments can be understood as an autocatalytic photochemical process obeying non-equilibrium thermodynamic directives related to increasing solar photon dissipation rate. Under these directives, organic pigments would have evolved over time to increase the global photon dissipation rate by (1) increasing the ratio of their effective photon cross sections to their physical size, (2) decreasing their electronic excited state lifetimes, (3) quenching radiative de-excitation channels (e.g., fluorescence), (4) covering ever more completely the prevailing solar spectrum, and (5) proliferating and dispersing to cover an ever greater surface area of Earth. From knowledge of the evolution of the spectrum of G-type stars, and considering the most probable history of the transparency of Earth's atmosphere, we construct the most probable Earth surface solar spectrum as a function of time and compare this with the history of molecular absorption maxima obtained from the available data in the literature. This comparison supports the conjecture that many fundamental molecules of life are pigments which arose, proliferated, and co-evolved as a response to dissipating the solar spectrum, supports the thermodynamic dissipation theory for the origin of life, constrains models for Earth's early atmosphere, and sheds some new light on the origin of photosynthesis.
Five week variations of total bacterial abundance (TBA) and total bacterial production (TBP) in the upper zone (0-150 m depth). Crosses indicate sampling times and depths.
Evolution of bacterial parameters integrated over the upper 0-150 m. TBB=total bacterial biomass; TBP=total bacterial production; HNA=relative abundance of cells with high nucleic acid content to the total bacterial abundance; TBB/AB=TBB to autotrophic biomass ratio.
Short time scale variability (dt=6 h) of 20-70 m depth integrated P index (a proxy of salinity anomalies), 5 m depth temperature, and 0-150 m depth integrated chlorophyll a, total bacterial biomass (TBB), relative abundance of cells with high nucleic acid content to the total bacterial abundance (HNA) and total bacterial production (TBP) within 2 periods (JD 268-273 and JD 284-289).
Vertical changes in the total bacteria abundance and total bacterial production in the 0-1000 m water column during night (•) and day (•). Agreement with Julian days is: 18/09=262; 19/09=263; 26/09=270; 04/10=279; 05/10=280; 12/10=286.
Vertical changes of the attached to total bacterial abundance ratio in the 0-1000 m water column during night () and day (). Agreement with Julian days is: 18/09=JD 262; 19/09=JD 263; 26/09=JD 270; 04/10=JD 279; 05/10=JD 280; 12/10=JD 286.
We present the vertical and temporal dynamics of total vs. particle-attached bacterial abundance and activity over a 5 week period under summer to autumn transition in NW Mediterranean Sea. At a weekly time scale, total bacterial biomass and production in the euphotic layers was significantly correlated with phytoplanktonic biomass. At an hourly time scale, total bacterial biomass responded very rapidly to chlorophyll a fluctuations, suggesting a tight coupling between phytoplankton and bacteria for resource partitioning during the summer-autumn transition. In contrast, no influence of diel changes on bacterial parameters was detected. Episodic events such as coastal water intrusions had a significant positive effect on total bacterial abundance and production, whereas we could not detect any influence of short wind events whatever the magnitude. Finally, we show that particle-attached bacteria can represent a large proportion (up to 49%) of the total bacterial activity in the euphotic layer but display rapid and sporadic changes at hourly time scales. In the mesopelagic layers, bacterial abundance and production linearly decreased with depth, except some production peaks at 400–750 m. This study underlines the value of large datasets covering different temporal scales to clarify the biogeochemical role of bacteria in the cycling of organic matter in open seawater.
This study reports carbon and water fluxes between the land surface and atmosphere in eleven different ecosystems types in Sub-Saharan Africa, as measured using eddy covariance (EC) technology in the first two years of the CarboAfrica network operation. The ecosystems for which data were available ranged in mean annual rainfall from 320 mm (Sudan) to 1150 mm (Republic of Congo) and include a spectrum of vegetation types (or land cover) (open savannas, woodlands, croplands and grasslands). Given the shortness of the record, the EC data were analysed across the network rather than longitudinally at sites, in order to understand the driving factors for ecosystem respiration and carbon assimilation, and to reveal the different water use strategies in these highly seasonal environments. Values for maximum net carbon assimilation rates (photosynthesis) ranged from −12.5 μmol CO<sub>2</sub> m<sup>−2</sup> s<sup>−1</sup> in a dry, open Millet cropland (C<sub>4</sub>-plants) up to −48 μmol CO<sub>2</sub> m<sup>−2</sup> s<sup>−1</sup> for a tropical moist grassland. Maximum carbon assimilation rates were highly correlated with mean annual rainfall ( r <sup>2</sup>=0.74). Maximum photosynthetic uptake rates ( Fp <sub>max</sub>) were positively related to satellite-derived f <sub>APAR</sub>. Ecosystem respiration was dependent on temperature at all sites, and was additionally dependent on soil water content at sites receiving less than 1000 mm of rain per year. All included ecosystems dominated by C<sub>3</sub>-plants, showed a strong decrease in 30-min assimilation rates with increasing water vapour pressure deficit above 2.0 kPa.
Copyright: Author(s) 2009. This work is distributed under the Creative Commons Attribution 3.0 License. This study reports carbon and water fluxes between the land surface and atmosphere in eleven different ecosystems types in Sub-Saharan Africa, as measured using eddy covariance (EC) technology in the first two years of the CarboAfrica network operation. The ecosystems for which data were available ranged in mean annual rainfall from 320mm (Sudan) to 1150mm (Republic of Congo) and include a spectrum of vegetation types (or land cover) (open savannas, woodlands, croplands and grasslands). Given the shortness of the record, the EC data were analysed across the network rather than longitudinally at sites, in order to understand the driving factors for ecosystem respiration and carbon assimilation, and to reveal the different water use strategies in these highly seasonal environments. Values for maximum net carbon assimilation rates (photosynthesis) ranged from -12.5µmolCO2 m-2 s-1 in a dry, open Millet cropland (C4-plants) up to -48µmolCO2 m-2 s-1 for a tropical moist grassland. Maximum carbon assimilation rates were highly correlated with mean annual rainfall (r2=0.74). Maximum photosynthetic uptake rates (Fpmax) were positively related to satellite-derived fAPAR. Ecosystem respiration was dependent on temperature at all sites, and was additionally dependent on soil water content at sites receiving less than 1000mm of rain per year. All included ecosystems dominated by C3-plants, showed a strong decrease in 30-min assimilation rates with increasing water vapour pressure deficit above 2.0 kPa.
Suzuki et al.,
129 I concentrations in surface seawater before and after the 1FNPP accident as a function of latitude. The dark green, light green, dark orange, and light orange symbols indicate cruises KT-11-06, BO-11-05, KH11-07, and KT-11-27, respectively, after the 1FNPP accident. The purple symbols were cited from Hou et al. (2013). The white symbols indicate a cruise before the Fukushima NPP accident.
Inventory of 129 I before and after the 1FNPP accident and its influence.
Depth profiles of 129 I before and after the 1FNPP accident. The dark green, dark orange, and light orange symbols indicate cruises KT-11-06, KH11-07, and KT-11-27, respectively, after the 1FNPP accident. The white symbols indicate a cruise before the 1FNPP accident.
Anthropogenic radionuclides were released into the environment in large quantities by the Fukushima Daiichi Nuclear Power Plant (1FNPP) accident. To evaluate accident-derived 129I, the 129I concentrations in seawater before and after the accident were compared. Before the accident (2008-2009), the 129I concentrations in the western margin of the North Pacific between 32° N and 44° N showed a latitudinal gradient that was expressed as a linear function of latitude. The highest and average 129I concentrations after the accident were 73 times and approximately 8 times, respectively, higher than those before the accident in this study area. Considering the distribution of 129I in surface seawater, the accident-derived 129I in the southern and northern stations of the 1FNPP was predominantly supplied by seawater advection and atmospheric deposition (including microbial volatilization), respectively. As of October 2011, depth profiles of 129I revealed that 129I originating from the 1FNPP existed mainly in the upper 100 m depth. From the depth profiles, the cumulative inventories of accident-derived 129I were estimated to be (1.6-9.6) × 1012 atoms m-2 in this study area. On the basis of the 129I data in the seawater near Fukushima, the effective dose of 129I from seafood ingestion was much smaller than the annual dose limit.
The impact of drought and rewetting on carbon cycling in peatland ecosystems is currently debated. We studied the impact of experimental drought and rewetting on intact monoliths from a temperate fen over a period of ~300 days, using a permanently wet treatment and two treatments undergoing drought for 50 days. In one of the mesocosms vegetation had been removed. Net production of CH<sub>4</sub> was calculated from mass balances in the peat and emission using static chamber measurements and results compared to <sup>13</sup>C isotope budgets of CO<sub>2</sub> and CH<sub>4</sub> and energy yields of acetoclastic and hydrogenotrophic methanogenesis. Drought retarded methane production after rewetting for days to weeks and promoted methanotrophic activity. Based on isotope and flux budgets, aerobic soil respiration contributed 32?96% in the wet and 86?99% in the other treatments. Drying and rewetting did not shift methanogenic pathways according to ? <sup>13</sup>C ratios of CH<sub>4</sub> and CO<sub>2</sub>. Although ?<sup>13</sup>C ratios indicated a prevalence of hydrogenotrophic methanogenesis, free energies of this process were small and often positive on the horizon scale, suggesting that methane was produced very locally. Fresh plant-derived carbon input apparently supported respiration in the rhizosphere and sustained methanogenesis in the unsaturated zone according to a <sup>13</sup>C-CO<sub>2</sub> labelling experiment. The study documents that drying and rewetting in a rich fen soil may have little effect on methanogenic pathways but result in rapid shifts between methanogenesis and methanotrophy. Such shifts may be promoted by roots and soil heterogeneity, as hydrogenotrophic methanogenesis occurred locally even when conditions were not conducive for this process in the bulk peat.
Schematic of the different approaches used to measure CO 2 efflux. The chamber collar is inserted into the soil surface. Mini-towers are place within the confines of the collar and after 2 min soil CO 2 is collected at multiple heights along the towers. The mini-towers are removed and then the chamber is then sealed and headspace is collected over a 21-min time interval. Finally a soil probe is inserted into predetermined depths for collecting soil CO 2 .
The 13 C of root free soil samples. The arrow on the x-axis indicates the mean (n=12) of the 13 C of soil CO 2 flux determined from the mini-tower intercepts.
Three approaches for determining the stable isotopic composition (?<sup>13</sup>C and ?<sup>18</sup>O) of soil CO efflux were compared. A new technique employed mini-towers, constructed of open-topped piping, that were placed on the soil surface to collect soil-emitted CO<sub>2</sub>. Samples were collected along a vertical gradient and analyzed for CO<sub>2</sub> concentration and isotopic composition. These data were then used to produce Keeling plots to determine the ?<sup>18</sup>O and ?<sup>13</sup>C of CO<sub>2</sub> emitted from the soil. These results were then compared to the ?<sup>18</sup>O and ?<sup>13</sup>C of soil-respired CO<sub>2</sub> measured with two other techniques: (1) flux chambers and (2) estimation from the application of the diffusional fractionation factor to measured values of below ground soil CO<sub>2</sub> and to CO<sub>2</sub> in equilibrium with soil water ?<sup>18</sup>O. Mini-tower ?<sup>18</sup>O Keeling plots were linear and highly significant (0.81< r <sup>2</sup> > 0.96), in contrast to chamber ?<sup>18</sup>O Keeling plots, which showed significant curvature, necessitating the use of a mass balance to calculate the ?<sup>18</sup>O of respired CO<sub>2</sub>. In the chambers, the values determined for the ?<sup>18</sup>O of soil respired CO<sub>2</sub> approached the value of CO<sub>2</sub> in equilibrium with surficial soil water, and the results were significantly ?<sup>18</sup>O enriched relative to the mini-tower results and the ?<sup>18</sup>O of soil CO<sub>2</sub> efflux determined from soil CO<sub>2</sub>. There were close agreements between the three methods for the determination of the ?<sup>13</sup>C of soil efflux CO<sub>2</sub>. Results suggest that the mini-towers can be effectively used in the field for determining the ?<sup>18</sup>O and the ?<sup>13</sup>C of soil-respired CO<sub>2</sub>.
The Keeling plot analysis is an interpretation method widely used in terrestrial carbon cycle research to quantify exchange processes of carbon between terrestrial reservoirs and the atmosphere. Here, we analyse measured data sets and artificial time series of the partial pressure of atmospheric carbon dioxide ( p CO<sub>2</sub>) and of ?<sup>13</sup>C of CO<sub>2</sub> over industrial and glacial/interglacial time scales and investigate to what extent the Keeling plot methodology can be applied to longer time scales. The artificial time series are simulation results of the global carbon cycle box model BICYCLE. The signals recorded in ice cores caused by abrupt terrestrial carbon uptake or release loose information due to air mixing in the firn before bubble enclosure and limited sampling frequency. Carbon uptake by the ocean cannot longer be neglected for less abrupt changes as occurring during glacial cycles. We introduce an equation for the calculation of long-term changes in the isotopic signature of atmospheric CO<sub>2</sub> caused by an injection of terrestrial carbon to the atmosphere, in which the ocean is introduced as third reservoir. This is a paleo extension of the two reservoir mass balance equations of the Keeling plot approach. It gives an explanation for the bias between the isotopic signature of the terrestrial release and the signature deduced with the Keeling plot approach for long-term processes, in which the oceanic reservoir cannot be neglected. These deduced isotopic signatures are similar (?8.6?) for steady state analyses of long-term changes in the terrestrial and marine biosphere which both perturb the atmospheric carbon reservoir. They are more positive than the ?<sup>13</sup>C signals of the sources, e.g. the terrestrial carbon pools themselves (?25?). A distinction of specific processes acting on the global carbon cycle from the Keeling plot approach is not straightforward. In general, processes related to biogenic fixation or release of carbon have lower y-intercepts in the Keeling plot than changes in physical processes, however in many case they are indistinguishable (e.g. ocean circulation from biogenic carbon fixation).
Map of the western North Pacific between Japan and Hawaii illustrating sampling locations. The red and blue filled symbols represent sampling in 2011 and 2012, respectively; empty symbols are used for stations where sampling was performed in both years (for details see Tables 1 and 2). The contours of an average ocean surface velocity > 0.4 m s −1 were calculated by the SCUD model for June 2011 (red) and June 2012 (blue) to visualize the major Kuroshio and Kuroshio extension currents (Maximenko and Hafner, 2010).  
Activities of 134 Cs (red pattern) and 137 Cs (blue solid) in transect surface seawater samples between Japan and Hawaii from June 2011 (a) and June 2012 (b). The estimated preexisting 137 Cs activities are drawn by the empty boxes. Activities are decaycorrected to 11 March 2011. Salinity of the samples is shown by triangles.  
137 Cs activities in surface seawater around the Hawaiian Islands (M1–M6), Guam (G1–G7), and time series for Station Aloha and Honolulu. The solid line is an average for Station Aloha, and dashed lines are ±2 standard deviations of the average.  
The activities of 134 Cs and 137 Cs in analyzed surface seawater from the North Pacific Ocean. The linear fit of the data is represented by straight line (solid) and 95 % confidence limits (dashed lines).  
Surface seawater 134Cs and 137Cs samples were collected in the central and western North Pacific Ocean during the 2 yr after the Fukushima Dai-ichi Nuclear Power Plant accident to monitor dispersion patterns of these radioisotopes towards the Hawaiian Islands. In the absence of other recent sources and due to its short half-life, only those parts of the Pacific Ocean would have detectable 134Cs values that were impacted by Fukushima releases. Between March and May 2011, 134Cs was not detected around the Hawaiian Islands and Guam. Here, most 137Cs activities (1.2–1.5 Bq m–3) were in the range of expected preexisting levels. Some samples north of the Hawaiian Islands (1.6–1.8 Bq m–3) were elevated above the 23-month baseline established in surface seawater in Hawaii indicating that those might carry atmospheric fallout. The 23-month time-series analysis of surface seawater from Hawaii did not reveal any seasonal variability or trends, with an average activity of 1.46 ± 0.06 Bq m–3 (Station Aloha, 18 values). In contrast, samples collected between Japan and Hawaii contained 134Cs activities in the range of 1–4 Bq m–3, and 137Cs levels were about 2–3 times above the preexisting activities. We found that the southern boundary of the Kuroshio and Kuroshio extension currents represented a boundary for radiation dispersion with higher activities detected within and north of the major currents. The radiation plume has not been detected over the past 2 yr at the main Hawaiian Islands due to the transport patterns across the Kuroshio and Kuroshio extension currents.
134 Cs and 137 Cs activity in the surface water in the North Pacific Ocean until March 2012. 
134 Cs (left) and 137 Cs (right) activity in the surface water during the period from 11 March 2011 (day 0) to 31 July 2011 (day 510) in the meridional zone of 38-42 • N. 
134Cs and 137Cs were released to the North Pacific Ocean by two major likely pathways, direct discharge from the Fukushima NPP1 accident site and atmospheric deposition off Honshu Islands of Japan, east and northeast of the site. High density observations of 134Cs and 137Cs in the surface water were carried out by 17 cruises of cargo ships and several research vessel cruises from March 2011 till March 2012. The main body of radioactive surface plume of which activity exceeded 10 Bq m-3 travelled along 40° N and reached the International Date Line on March 2012, one year after the accident. A distinct feature of the radioactive plume was that it stayed confined along 40° N when the plume reached the International Date Line. A zonal speed of the radioactive plume was estimated to be about 8 cm s-1 which was consistent with zonal speeds derived by Argo floats at the region.
The fate of photosynthetic products within the plant-soil continuum determines how long the reduced carbon resides within the ecosystem and when it returns back to the atmosphere in the form of respiratory CO2. We have tested the possibility of measuring natural variation in δ13C and δ18O to disentangle the potential times needed to transfer carbohydrates produced by photosynthesis down to trunk, roots and, in general, to belowground up to its further release in the form of soil respiration into the atmosphere in a beech (Fagus sylvatica) forest. We have measured the variation in stable carbon and oxygen isotope compositions in plant material and in soil respired CO2 every three hours for three consecutive days. Possible steps and different signs of post-photosynthetic fractionation during carbon translocation were also identified. A 12 h-periodicity was observed for variation in δ13C in soluble sugars in the top crown leaves and it can be explained by starch day/night dynamics in synthesis and breakdown and by stomatal limitations under elevated vapour pressure deficits. Photosynthetic products were transported down the trunk and mixed with older carbon pools, therefore causing the dampening of the δ13C signal variation. The strongest periodicity of 24 h was found in δ13C in soil respiration indicating changes in root contribution to the total CO2 efflux. Other non-biological causes like diffusion fractionation and advection induced by gas withdrawn from the measurement chamber complicate data interpretation on this step of C transfer path. Nevertheless, it was possible to identify the speed of carbohydrates' translocation from the point of assimilation to the trunk breast height because leaf-imprinted enrichment of δ18O in soluble sugars was less modified along the downward transport and was well related to environmental parameters potentially linked to stomatal conductance. The speed of carbohydrates translocation from the site of assimilation to the trunk at breast height was estimated to be in the range of 0.3-0.4 m h-1.
Variability in the δ 13 C of the soil CO 2 efflux (upper figures) and of the DOC leached from both the litter layer and the mineral soil at a depth of 5 cm. The values of the Rendzina and the Cambisol are combined. Each box shows the median value, the quartiles and the 2.5%-and 97.5%-quantiles of 50 single measurements for the CO 2 and of 30 measurements for the DOC in the cold (November 2007-April 2008) and in the warm season (April 2008-November 2008).
Contribution of litter-derived C to the heterotrophic soil respiration and to the DOC 2 leached from the litter layer and from the mineral soil at a depth of 5 cm. Means and standard 3 errors of five replicates in the Rendzina (solid line) and the Cambisol (dashed line). 4
Total recovery of the 13 C-labelled litter C in litterbags and in different C fluxes and C pools after 1 yr of decomposition. Means and standard errors of five replicates.
Very few field studies have quantified the different pathways of C loss from decomposing litter even though this is essential to better understand long-term dynamics of C stocks in soils. Using 13C-labelled leaf (isotope ratio (δ13C) = −40.8‰) and twig litter (δ13C = −38.4‰), we tracked down the litter-derived C in the soil respiration, in the dissolved organic C (DOC) and in the soil organic matter of a beech forest in the Swiss Jura. After one year of decomposition, mass loss in the litter layer was almost twice as great for leaves as it was for twigs (75% vs. 40%). This difference was not the result of a slow mineralisation of the woody litter, but primarily of the only slight incorporation of twig-derived C into mineral soils. The C mineralisation rates of the twig litter were only slightly lower than those of the leaf litter (10–35%), in particular after the loss of the readily available litter fraction. However, the leaching of DOC from twigs amounted only to half of that from leaves. Tracing the litter-derived DOC showed that DOC from both litter types was mostly retained (88–96%) and stabilised in the top centimetres of the mineral soil. In the soil organic C at 0–2 cm depth, we recovered 8% of the initial leaf C, but only 4% of the twig C. Moreover, the 13C mass balance suggested that a substantial fraction of the leaf material (~30%) was transported via soil fauna to soil depths below 2 cm, while the twig litter mainly decomposed in situ on the soil surface, probably due to its rigid structure and low nutritional value. In summary, our study shows that decaying twigs are rapidly mineralised, but seem to be clearly less important for the C storage in this beech forest soils than leaf litter.
Dates of sampling and agronomic management (N application and grazing) in North and South fields. Data provided by Centre for Ecology & Hydrology, Edinburgh, Scotland.
Seasonal variations in bulk tissue NH + 4 concentration (A), pH (B) and (C) in different tissues of ryegrass. Inserts in A and C show bulk tissue NH + 4 concentration and , respectively, in green leaves, stems and inflorescences at a different scaling in order to reveal the fluctuations. Arrows below the X-axis represent N application as NH 4 NO 3 ; the bar with solid circle represents N application as urea.
Seasonal changes in nitrogen (N) pools, carbon (C) content and natural abundance of 13C and 15N in different tissues of ryegrass plants were investigated in two intensively managed grassland fields in order to address their ammonia (NH3) exchange potential. Green leaves generally had the largest total N concentration followed by stems and inflorescences. Senescent leaves had the lowest N concentration, indicating N re-allocation. The seasonal pattern of the Γ value, i.e. the ratio between NH4+ and H+ concentrations, was similar for the various tissues of the ryegrass plants but the magnitude of Γ differed considerably among the different tissues. Green leaves and stems generally had substantially lower Γ values than senescent leaves and litter. Substantial peaks in Γ were observed during spring and summer in response to fertilization and grazing. These peaks were associated with high NH4+ rather than with low H+ concentrations. Peaks in Γ also appeared during the winter, coinciding with increasing δ15N values, indicating absorption of N derived from mineralization of soil organic matter. At the same time, δ13C values were declining, suggesting reduced photosynthesis and capacity for N assimilation. δ15N and δ13C values were more influenced by mean monthly temperature than by the accumulated monthly precipitation. In conclusion, ryegrass plants showed a clear seasonal pattern in N pools. Green leaves and stems of ryegrass plants generally seem to constitute a sink for NH3, while senescent leaves have a large potential for NH3 emission. However, management events such as fertilisation and grazing may create a high NH3 emission potential even in green plant parts. The obtained results provide input for future modelling of plant-atmosphere NH3 exchange.
Experimental calibration equations of temperature versus δ 18 O f − δ 18 O w of cultured specimens of B. marginata. Averages and standard deviations are presented separately for the ≤150 µm (a), 150-200 µm (b), 200-250 µm (c), and > 250 µm (d) shell size fractions. The number of measurements for each average value is indicated in parenthesis. Different symbols correspond to the three systems: PD (diamonds), CS I (squares) and CS II (crosses). The calibration equations summarised in (e) are based on all data from each size fractions (for all equations p < 0.001).
Shell size effect on the oxygen isotopic composition (δ 18 O f − δ 18 O w ) of B. marginata calcified in culture at 10.2 (triangles), 12.7 (squares) and 14.7 • C (diamonds). The number of measurements for each average value is indicated in parenthesis. The linear regressions are: y = 0.0012 x + 0.9745 (R 2 = 0.40; p = 0.003; gray dashed line) at 10.2 • C; y = 0.0022 x + 0.2655 (R 2 = 0.71; p = 0.001; black dashed line) at 12.7 • C; and y = 0.0017 x + 0.0588 (R 2 = 0.57; p = 0.005; black line) at 14.7 • C.
The geochemical composition of deep-sea benthic foraminiferal calcite is widely used to reconstruct sea floor paleoenvironments. The calibration of the applied proxy methods has until now been based on field observations in complex natural ecosystems where multiple factors are interfering. However, laboratory experiments with stable physico-chemical conditions appear to be the ideal way to evaluate the influence of a single parameter. In this paper, we present the oxygen isotopic composition of deep-sea benthic foraminiferal shells entirely calcified under controlled experimental conditions over a large temperature range (4 to 19 °C). The new laboratory protocols developed for this study allowed us to produce large quantities of shells in stable conditions, so that also the shell size effect could be investigated. It appears that when considering a narrow test size range, the curve describing the temperature dependency of δ<sup>18</sup>O in Bulimina marginata is parallel to the thermodynamically determined curve observed in inorganically precipitated calcite (−0.22‰ °C<sup>−1</sup>). This observation validates the use of δ<sup>18</sup>O of this benthic species in paleoceanographical studies. Over the studied size range (50 to 300 μm), the effect of test size was 0.0014‰ μm<sup>−1</sup>, confirming previous suggestions of a substantial test size effect on δ<sup>18</sup>O of benthic foraminifera. This study opens new perspectives for future proxy calibrations in laboratory set-ups with deep-sea benthic foraminifera (e.g. quantification of the influence of the carbonate chemistry).
In spite of the many factors that are occurring and known for positively affecting the growth of forests, some boreal forests across North America have recently felt the adverse impacts of environmental changes. Knowledge of causes for productivity declines in North American boreal forests remains limited, and this is owed to the large spatial and temporal scales involved, and the many plant processes affected. Here, the response of pristine eastern boreal North American (PEBNA) forests to ongoing climatic changes is examined using in situ data, community ecology statistics, and species-specific model simulations of carbon exchanges forced by contemporary climatic data. To examine trends in forest growth, we used a recently acquired collection of tree-ring width data from 252 sample plots distributed in PEBNA forests dominated by black spruce (Picea mariana [Mill.] B.S.P.) and jack pine (Pinus banksiana Lamb.). Results of linear trend analysis on the tree growth data highlight a dominating forest growth decline in overmature forests (age > 120 years) from 1950 to 2005. In contrast, improving growth conditions are seen in jack pine and mature (70-120 years) black spruce stands. Multivariate analysis of climate and growth relationships suggests that responses of PEBNA forests to climate are dependent on demographic and species traits via their mediation of temperature and water stress constraints. In support of this hypothesis, the simulation experiment suggests that in old-growth black spruce stands the benefit to growth brought on by a longer growing season may have been low in comparison with the increasing moisture stress and respiration losses caused by warmer summer temperatures. Predicted increases in wildfire frequency in PEBNA forests will likely enhance the positive response of landscape-level forest growth to climate change by shifting the forest distribution to younger age classes while also enhancing the jack pine component.
Examples of the relationships between the components of net primary production (NPP) and aboveground net primary production (ANPP). (a) The relationship between total net primary production (TNPP) and ANPP for C. japonica forests. (b) The relationship between stem net primary production (NPP S ) and ANPP for evergreen broadleaf forests. (c) The relationship between leaf net primary production (NPP L ) and ANPP for needle-leaf and broadleaf mixed forests. The relationships between these NPP components and ANPP for other forest types are shown in Table 1.  
Recent studies based on remote sensing and carbon process models have revealed that terrestrial net primary production (NPP) in the middle and high latitudes of the Northern Hemisphere has increased significantly; this is crucial for explaining the increased terrestrial carbon sink in the past several decades. Regional NPP estimation based on significant field data, however, has been rare. In this study, we estimated the long-term changes in aboveground NPP (ANPP) for Japan&apos;s forests from 1980 to 2005, using forest inventory data, direct field measurements, and an allometric method. The overall ANPP for all forest types averaged 10.5 Mg ha−1 yr−1, with a range of 9.6 to 11.5 Mg ha−1 yr−1, and ANPP for the whole country totaled 249.1 Tg yr−1 (range: 230.0 to 271.4 Tg yr−1) during the study period. Over the 25 years, the net effect of increased ANPP in needle-leaf forests and decreased ANPP in broadleaf forests has led to an increase of 1.9 Mg ha−1 yr−1 (i.e., 0.79% yr−1). This increase may be mainly due to the establishment of plantations and the rapid early growth of these planted forests.
Global Ocean Biogeochemistry General Circulation Models are useful tools to study biogeochemical processes at global and large scales under current climate and future scenario conditions. The credibility of future estimates is however dependent on the model skill in capturing the observed multi-annual variability of firstly the mean bulk biogeochemical properties, and secondly the rates at which organic matter is processed within the food web. For this double purpose, the results of a multi-annual simulation of the global ocean biogeochemical model PELAGOS have been objectively compared with multi-variate observations from the last 20 years of the 20th century, both considering bulk variables and carbon production/consumption rates. Simulated net primary production (NPP) is comparable with satellite-derived estimates at the global scale and when compared with an independent data-set of in situ observations in the equatorial Pacific. The usage of objective skill indicators allowed us to demonstrate the importance of comparing like with like when considering carbon transformation processes. NPP scores improve substantially when in situ data are compared with modeled NPP which takes into account the excretion of freshly-produced dissolved organic carbon (DOC). It is thus recommended that DOC measurements be performed during in situ NPP measurements to quantify the actual production of organic carbon in the surface ocean. The chlorophyll bias in the Southern Ocean that affects this model as well as several others is linked to the inadequate representation of the mixed layer seasonal cycle in the region. A sensitivity experiment confirms that the artificial increase of mixed layer depths towards the observed values substantially reduces the bias. Our assessment results qualify the model for studies of carbon transformation in the surface ocean and metabolic balances. Within the limits of the model assumption and known biases, PELAGOS indicates a net heterotrophic balance especially in the more oligotrophic regions of the Atlantic during the boreal winter period. However, at the annual time scale and over the global ocean, the model suggests that the surface ocean is close to a weakly positive autotrophic balance in accordance with recent experimental findings and geochemical considerations.
Global Ocean Biogeochemistry General Circulation models are useful tools to study biogeochemical processes at gobal and large scales under current climate and future scenario conditions. The accuracy of the future estimate is however dependent on the adequate representation of the current ocean biogeochemical features. To this purpose, the results of an interannual simulation of the global ocean biogeochemical model PELAGOS have been objectively compared with multi-variate observations from the last 20 years of the XX century. The model was assessed in terms of spatial and temporal variability of chlorophyll and primary production derived from satellite sensors, with a specific focus on the simulation of carbon production/consumption rates observed in the equatorial Pacific ocean and at the long-term JGOFS stations. The predicted chlorophyll is acceptable in the northern mid-latitude regions and equatorial Pacific, but is underestimated in the upwelling regions of the Atlantic and Indian Oceans and markedly overestimated in the Southern Ocean. This latter bias is linked to the inadequate representation of the mixed layer seasonal cycle in the region, which favours primary production during austral spring. Simulated primary production is comparable with satellite estimates both at the global scale and when compared with an independent data-set in the equatorial Pacific. A comparison with other models showed that PELAGOS results are as good as the estimates from state-of-the-art diagnostic models based on satellite data. The skill in reproducing the interannual varibility was assessed in the equatorial Pacific and against the decadal JGOFS timeseries BATS and HOT. In the tropical Pacific our analysis suggests that interannual variability of primary production is related to the climate variability both in the observations and in the model. At the JGOFS stations PELAGOS has skill to simulate the observed bacterial biomass and shows realistic means of primary and bacterial production at BATS. These results have been further strenghtened with an analysis of spatial variability of microbial carbon production/consumption and comparison with observations along a transect in the Atlantic ocean. Within the limits of the model assumption and known biases, PELAGOS predicts that the system is net heterotrophic if the boreal winter period only is considered and especially in the more oligotrophic regions. However, at the annual time scale and over the global ocean, the model suggests that surface ocean is close to a slightly positive autotrophic balance in accordance with recent experimental findings and geochemical evidences.
We discuss the spatial and temporal resolution of monthly carbon flux estimates for the period 1983?2002 using a fixed-lag Kalman Smoother technique with a global chemical transport model, and the GLOBALVIEW data product. The observational network has expanded substantially over this period, and we the improvement in the constraints provided flux estimates by observations for the 1990's in comparison to the 1980's. The estimated uncertainties also decrease as observational coverage expands. In this study, we use the Globalview data product for a network that changes every 5 y, rather than using a small number of continually-operating sites (fewer observational constraints) or a large number of sites, some of which may consist almost entirely of extrapolated data. We show that the discontinuities resulting from network changes reflect uncertainty due to a sparse and variable network. This uncertainty effectively limits the resolution of trends in carbon fluxes. The ability of the inversion to distinguish, or resolve, carbon fluxes at various spatial scales is examined using a diagnostic known as the resolution kernel. We find that the global partition between land and ocean fluxes is well-resolved even for the very sparse network of the 1980's, although prior information makes a significant contribution to the resolution. The ability to distinguish zonal average fluxes has improved significantly since the 1980's, especially for the tropics, where the zonal ocean and land biosphere fluxes can be distinguished. Care must be taken when interpreting zonal average fluxes, however, since the lack of air samples for some regions in a zone may result in a large influence from prior flux estimates for these regions. We show that many of the TransCom 3 source regions are distinguishable throughout the period over which estimates are produced. Examples are Boreal and Temperate North America. The resolution of fluxes from Europe and Australia has greatly improved since the 1990's. Other regions, notably Tropical South America and the Equatorial Atlantic remain practically unresolved. Comparisons of the average seasonal cycle of the estimated carbon fluxes with the seasonal cycle of the prior flux estimates reveals a large adjustment of the summertime uptake of carbon for Boreal Eurasia, and an earlier onset of springtime uptake for Temperate North America. In addition, significantly larger seasonal cycles are obtained for some ocean regions, such as the Northern Ocean, North Pacific, North Atlantic and Western Equatorial Pacific, regions that appear to be well-resolved by the inversion.
This paper presents a long-term time series (1986?2005) of hydrological and biogeochemical data, both published and unpublished. Data were collected in the north-western area of the Adriatic Sea, at two stations that are considered hydrodynamically and trophically different. The time series have been statistically and graphically analysed on a monthly scale in order to study the annual climatologies, links between the concentrations of chlorophyll- a and the variability in the environment, trophic differences between the two areas and chlorophyll- a trends over time. Basically, the two areas have similar hydrological features, yet they present significant differences in the amount of nutrient inputs: these are in fact higher at the coastal site, which is characterized by a prevalence of surface blooms, while they are lower at the offshore station, which is mainly affected by blooms at intermediate depths. Nonetheless, throughout the whole water column, chlorophyll- a concentrations are only slightly different. Both areas are affected by riverine discharge, though chlorophyll- a concentrations are also driven strongly by the seasonal cycle at the station closer to the coast. Results show that the two stations are not trophically different, although some controlling factors, such as zooplankton grazing in one case and light attenuation in the other, may further regulate the growth of phytoplankton. In both cases no significant trends are detected in either the average chlorophyll- a values or in dispersion of the data, in contrast with significant trends in temperature and salinity.
Data obtained during the monthly cruises of the DYFAMED time-series study (northwestern Mediterranean Sea) in the period 1995–2007 were compiled to examine the hydrological changes and the linked variation of some biogeochemical characteristics (nutrients and pigments). A regular increase of temperature and salinity (0.005 °C y−1, 0.0022 psu y−1) was recorded in deep waters of the NW Mediterranean Sea (2000 m depth) during 1995–2005. In February 2006 an abrupt increase in T (+0.1 °C) and S (+0.03 psu) was measured at 2000 m depth as the result of successive intense winter mixing events during the 3 previous years. The February 2006 event led to the mixing of the whole water column (0 to >2000 m) and increased salt and heat content of the Western Mediterranean Deep Water by mixing with saltier and warmer Levantine Intermediate Water. The deficit in fresh water inputs to the western Mediterranean basin in three successive years (2003–2005) was suspected to be the major cause of this event since an increase of salinity in surface waters was monitored during these years. The measured phytoplankton biomass was specifically high after the periods of intense mixing. Chlorophyll a integrated biomass reached 230 mg m−2 in 1999, 175 mg m−2 in 2003, and 206 mg m−2 in 2006. The high levels of biomass were related to the particularly high increases in nutrients content in surface layers following the intense water column mixing and the subsequent development of a diatom bloom (as seen by fucoxanthin content). The occurrence of extreme events (high mixing, high nutrients, and high biomass) increased in recent drought years (2003 to 2006). Our results indicated that the NW Mediterranean Sea productivity is increasing.
Location of the sampling site (Pt. B) in the Ligurian Sea and the meteorological station S ´ emaphore (S ´ em.) situated in Cap Ferrat 1.2 km from Point B. The cyclonic circulation of the Ligurian Sea with the Liguro-Provençal Current, the Western Corsican Current and the Eastern Corsican Current are also shown on this map. The central zone of the Ligurian Sea is separated from more coastal areas by the frontal zone.
Dynamic of nitrates (NO 3 ) in µmol L −1 and chlorophyll-a in µg L −1. (A) annual anomalies of NO 3 ; (B) annual anomalies of chlorophyll-a; (C) monthly values of NO 3 ; (D) monthly values of chlorophyll-a.
An integrated analysis of the pelagic ecosystems of the Ligurian Sea is performed combining time series (1995-2005) of several zooplankton groups (one group for copepods smaller than 0.724mm(3) and nine groups for individuals larger than 0.724mm(3), i.e. large copepods, decapod larvae other crustaceans, chaetognaths, appendicularians, pteropods, thaliaceans, gelatinous predators and other zooplankton), chlorophyll-a, nutrients, salinity, temperature, density, and local weather at Point B coastal station (Northern Ligurian Sea). From 1995 to 2000 winters were wet and mild resulting in lower winter sea surface density. These years showed lower than average nutrients and zooplankton concentrations while chlorophyll-a biomass was high. After 2000, winters were colder and dryer resulting in higher sea surface density. Nutrients and zooplankton showed higher concentrations while chlorophyll-a was lower than average. The ca. 2000 change was observed for most zooplankton groups with a one-year delay for some groups. Inter-annual variability within each period was also observed. The observed patterns suggest that the pelagic ecosystem trophic state at the studied point is mostly set by the winter forcing on the vertical mixing that upwells nutrients to the surface sustaining primary production. Surprisingly, low chlorophyll-a biomass in high nitrate and zooplankton conditions during the well mixed years suggest that phytoplankton biomass is controlled by grazers. The proposed mechanisms of stronger winter vertical mixing hold for most of the time series, but specific years with contradicting patterns suggest also the possible influence of the summer climate. A review of recent literature suggests that changes in the pelagic ecosystem are not limited to the studied site but concern also the central Ligurian Sea.
The accelerated rate of increase in atmospheric carbon dioxide and the substantial fraction of anthropogenic CO2 emissions absorbed by the oceans are affecting the anthropocenic signatures of seawater. Long-term time series are a powerful tool for investigating any change in ocean bio-geochemistry and its effects on the carbon cycle. We have evaluated the ESTOC (European Station for Time series in the Ocean at the Canary islands) observations of measured pH (total scale at 25 °C) and total alkalinity plus computed total dissolved inorganic carbon concentration (CT) from 1995 to 2004 for surface and deep waters, by following all changes in response to increasing atmospheric carbon dioxide. The observed values for the surface partial pressure of CO2 from 1995 to 2008 were also taken into consideration. The data were treated to better understand the fundamental processes controlling vertical distributions in the Eastern North Atlantic Ocean and the accumulation of anthropogenic CO2, C ANT. C T at constant salinity, NC T, increased at a rate of 0.85 μmol kg−1 yr−1 in the mixed layer, linked to an f CO2 increase of 1.7±0.7 μatm yr−1 in both the atmosphere and the ocean. Consequently, the mixed layer at ESTOC site has also become more acidic, −0.0017±0.0003 units yr−1, whereas the carbonate ion concentrations and CaCO3 saturation states have also decreased over time. NCT increases at a rate of 0.53, 0.49 and 0.40 μmol kg−1 yr−1 at 300, 600, and 1000 m, respectively. The general processes controlling the vertical variations of alkalinity and the inorganic carbon distribution were computed by considering the pre-formed values, the production/decomposition of organic matter and the formation/dissolution of carbonates. At 3000 m, 30% of the inorganic carbon production is related to the dissolution of calcium carbonate, increasing to 35% at 3685 m. The total column inventory of anthropogenic CO2 for the decade was 66±3 mol m−2. A model fitting indicated that the column inventory of C ANT increased from 61.7 mol m−2 in the year 1994 to 70.2 mol m−2 in 2004. The ESTOC site is presented as a reference site to follow C ANT changes in the Northeast Atlantic Sub-tropical gyre.
Prior error standard deviations, in g.m −2 per day, for the eight-day mean grid point CO surface emissions in 2004.
The space-time variations of the carbon budget at the Earth surface are highly variable and quantifying them represents a major scientific challenge. One strategy consists in inferring the carbon surface fluxes from the atmospheric concentrations. A variational scheme for the hydrocarbon oxidation chain, that includes CO and CH4, is presented here with a focus on the African continent. The multi-tracer system has been built as an extension of a system initially developed for CO2 and includes a new simplified non-linear chemistry module. Individual in situ measurements of methyl-chloroform and individual retrievals of CO concentrations from the Measurements Of Pollution In The Troposphere (MOPITT) space-born instrument have been processed by the new system for the period 2000–2006 to infer the time series of CO emissions at the resolution of 2.5°×3.75° (latitude, longitude). It is shown that the analysed concentrations improve the fit to five independent surface measurements located in or near Africa by up to 28% compared to standard inventories, which confirms that quantitative information about CO emissions can be obtained from MOPITT data. In practice, the inversion reduces the amplitude and the interannual variability of the seasonal cycle in the northern part of Africa, with a longer burning season. In the southern part, the inversion mainly shifts the emission peak by one month later in the season, consistent with previously-published inversion results.
Northern Eurasia experienced anomalous weather conditions in the 2003 summer. We examined how forest ecosystems responded to the meteorological anomalies during the period using the dataset collected at flux monitoring sites in Asia, including a boreal forest in Mongolia, temperate forests in China and Japan, and a sub-tropical forest in China, as well as the dataset from satellite remote sensing. From July to August 2003, an active rain band stayed in the mid-latitude in East Asia for an unusually long period. Under the influence of the rain band, the gross primary production (GPP) of temperate forests was 20–30% lower in the 2003 summer than in other years due to significant reduction in the photosynthetic photon flux density (PPFD). The GPP of a cool-temperate forest in the north of the rain band was slightly enhanced by the higher PPFD; however, the GPP of a sub-tropical forest located in the south of the rain band was reduced by drought stress due to extremely hot and dry conditions. The correlation coefficients for the year-to-year changes in the PPFD and GPP during mid-summer were calculated, and the spatial distribution was examined. The spatial pattern of the PPFD was calculated by satellite data, and that of the GPP was estimated by a regression-type model, which was trained and tested by ground observation data. The correlation was positive in the mid- and high-latitudes since light was an essential factor of the summer GPP. On the other hand, a negative correlation appeared in the lower latitudes, suggesting that the water limitation was much more important than the PPFD in the region. Our study illustrated that the integration of flux data from wide areas by combining satellite remote sensing data can help us gain an understanding of the ecosystem responses to large-scale meteorological phenomena.
Globally, the year 2003 is associated with one of the largest atmospheric CO<sub>2</sub> rises on record. In the same year, Europe experienced an anomalously strong flux of CO<sub>2</sub> from the land to the atmosphere associated with an exceptionally dry and hot summer in Western and Central Europe. In this study we analyze the magnitude of this carbon flux anomaly and key driving ecosystem processes using simulations of seven terrestrial ecosystem models of different complexity and types (process-oriented and diagnostic). We address the following questions: (1) how large were deviations in the net European carbon flux in 2003 relative to a short-term baseline (1998–2002) and to longer-term variations in annual fluxes (1980 to 2005), (2) which European regions exhibited the largest changes in carbon fluxes during the growing season 2003, and (3) which ecosystem processes controlled the carbon balance anomaly . In most models the prominence of 2003 anomaly in carbon fluxes declined with lengthening of the reference period from one year to 16 years. The 2003 anomaly for annual net carbon fluxes ranged between 0.35 and –0.63 Pg C for a reference period of one year and between 0.17 and –0.37 Pg C for a reference period of 16 years for the whole Europe. In Western and Central Europe, the anomaly in simulated net ecosystem productivity (NEP) over the growing season in 2003 was outside the 1s variance bound of the carbon flux anomalies for 1980–2005 in all models. The estimated anomaly in net carbon flux ranged between –42 and –158 Tg C for Western Europe and between 24 and –129 Tg C for Central Europe depending on the model used. All models responded to a dipole pattern of the climate anomaly in 2003. In Western and Central Europe NEP was reduced due to heat and drought. In contrast, lower than normal temperatures and higher air humidity decreased NEP over Northeastern Europe. While models agree on the sign of changes in simulated NEP and gross primary productivity in 2003 over Western and Central Europe, models diverge in the estimates of anomalies in ecosystem respiration. Except for two process models which simulate respiration increase, most models simulated a decrease in ecosystem respiration in 2003. The diagnostic models showed a weaker decrease in ecosystem respiration than the process-oriented models. Based on the multi-model simulations we estimated the total carbon flux anomaly over the 2003 growing season in Europe to range between –0.02 and –0.27 Pg C relative to the net carbon flux in 1998–2002.
The eastern equatorial Pacific plays a~great role in the global carbon budget due to its enhanced biological productivity linked to the equatorial upwelling. However, as confirmed by the Equatorial Biocomplexity cruises in 2004 and 2005, nutrient upwelling supply varies strongly, partly due to the tropical instability waves (TIWs). The aim of this study was to examine patterns of spatial and temporal variability in the biological uptake of NO3, Si(OH)4 and carbon in this region, and to evaluate the role of biological and physical interactions controlling this variability over seasonal and intraseasonal time scales. Here, high resolution Pacific ROMS-CoSiNE (Regional Ocean Modeling System-Carbon, Silicon, Nitrogen Ecosystem) model results were evaluated with in situ and remote sensing data. The results of model-data comparison revealed a good agreement in domain-average hydrographic and biological rate estimates, and patterns of spatio-temporal variability in primary productivity. We confirmed that TIWs have the potential to enhance phytoplankton biomass through an increased supply of nutrients and elevated local and instantaneous phytoplankton nutrient uptake as opposed to only advecting biomass. Furthermore, we concluded that initial biological conditions (e.g., zooplankton biomass) may play an important additional constraint on biological responses, in particular of large phytoplankton such as diatoms, to TIW-induced perturbations in the physical and biogeochemical fields and fluxes. In order to fully resolve the complexity of biological and physical interactions in the eastern equatorial Pacific, we recommended improving CoSiNE and other models by introducing more phytoplankton groups, variable Redfield and carbon to chlorophyll ratios, as well as resolving the Fe-Si co-limitation of phytoplankton growth.
The objectives of the BIOSOPE (BIogeochemistry and Optics SOuth Pacific Experiment) project was to study, during the austral summer, the biological, biogeochemical and bio-optical properties of different trophic regimes in the South East Pacific: the eutrophic zone associated with the upwelling regime off the Chilean coast, the mesotrophic area associated with the plume of the Marquises Islands in the HNLC (High Nutrient Low Chlorophyll) waters of this subequatorial area, and the extremely oligotrophic area associated with the central part of the South Pacific Gyre (SPG). At the end of 2004, a 55-day international cruise with 32 scientists on board took place between Tahiti and Chile, crossing the SPG along a North-West South-East transect. This paper describes in detail the objectives of the BIOSOPE project, the implementation plan of the cruise, the main hydrological entities encountered along the ~8000 km South East Pacific transect, and ends with a general overview of the 32 other papers published in this special issue.
The late stage of the North East Atlantic (NEA) spring bloom was investigated during June 2005 along a transect section from 45 to 66° N between 15 and 20° W in order to characterize the contribution of siliceous and calcareous phytoplankton groups and describe their distribution in relation to environmental factors. We measured several biogeochemical parameters such as nutrients, surface trace metals, algal pigments, biogenic silica (BSi), particulate inorganic carbon (PIC) or calcium carbonate, particulate organic carbon, nitrogen and phosphorus (POC, PON and POP, respectively), as well as transparent exopolymer particles (TEP). Results were compared with other studies undertaken in this area since the JGOFS NABE program. Characteristics of the spring bloom generally agreed well with the accepted scenario for the development of the autotrophic community. The NEA seasonal diatom bloom was in the late stages when we sampled the area and diatoms were constrained to the northern part of our transect, over the Icelandic Basin (IB) and Icelandic Shelf (IS). Coccolithophores dominated the phytoplankton community, with a large distribution over the Rockall-Hatton Plateau (RHP) and IB. The Porcupine Abyssal Plain (PAP) region at the southern end of our transect was the region with the lowest biomass, as demonstrated by very low chl-a concentrations and a community dominated by picophytoplankton. Early depletion of dissolved silicic acid (DSi) and increased stratification of the surface layer most likely triggered the end of the diatom bloom, leading to coccolithophore dominance. The chronic Si deficiency observed in the NEA could be linked to moderate Fe limitation, which increases the efficiency of the Si pump. TEP closely mirrored the distribution of both biogenic silica at depth and prymnesiophytes in the surface layer suggesting the sedimentation of the diatom bloom in the form of aggregates, but the relative contribution of diatoms and coccolithophores to carbon export in this area still needs to be resolved.
This paper describes a numerical interpretation of the April 2007, CarboEurope Regional Experiment Strategy (CERES) campaign, devoted to the study of the CO2 cycle at the regional scale. Four consecutive clear sky days with intensive observations of CO2 concentration, fluxes at the surface and in the boundary layer have been simulated with the Meso-NH mesoscale model, coupled to ISBA-A-gs land surface model. The main result of this paper is to show how aircraft observations of CO2 concentration have been used to identify surface model errors and to calibrate the CO2 driving component of the surface model. In fact, the comparisons between modelled and observed CO2 concentrations within the Atmospheric Boundary Layer (ABL) allow to calibrate and correct not only the parameterization of respired CO2 fluxes by the ecosystem but also the Leaf Area Index (LAI) of the dominating land cover. After this calibration, the paper describes systematic comparisons of the model outputs with numerous data collected during the CERES campaign, in April 2007. For instance, the originality of this paper is the spatial integration of the comparisons. In fact, the aircraft observations of CO2 concentration and fluxes and energy fluxes are used for the model validation from the local to the regional scale. As a conclusion, the CO2 budgeting approach from the mesoscale model shows that the winter croplands are assimilating more CO2 than the pine forest, at this stage of the year and this case study.
A total of 8459 larval fish were collected from the southern East China Sea during the winter northeasterly monsoon season and the summer southwesterly monsoon season of 2008. The larvae comprised 184 species belonging to 105 families and 162 genera. The abundance in terms of CPUE (number of individuals/1000m3) of the larvae was approximately 6 times higher during the southwesterly monsoon season than it was during the northeasterly monsoon season. The primary environmental factors affecting the larval abundance were water temperature during the northeasterly monsoon season, and food availability during the southwesterly monsoon season. Three larval fish assemblages were recognized: inshore assemblage, offshore assemblage, and summer coastal assemblage. The distribution and species composition of the larvae in the assemblages reflected the hydrographic conditions and water currents resulting from the seasonal monsoons.
Surface waters from the Beaufort Sea in the Arctic Ocean were evaluated for dissolved organic carbon (DOC), and optical characteristics including UV (ultraviolet) radiation and PAR (photosynthetically active radiation) diffuse attenuation (Kd), and chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) as part of the MALINA field campaign (30 July to 27 August). Spectral absorption coefficients (aCDOM (350 nm) (m-1)) were significantly correlated to both diffuse attenuation coefficients (Kd) in the UV-A and UV-B and to DOC concentrations. This indicates CDOM as the dominant attenuator of both UV and PAR solar radiation and suggests its use as an optical proxy for DOC concentrations in this region. While the Mackenzie input is the main driver of CDOM dynamics in low salinity waters, locally, primary production can create significant increases in CDOM. Extrapolating CDOM to DOC relationships, we estimate that ∼16% of the DOC in the Mackenzie River does not absorb radiation at 350 nm. The discharges of DOC and its chromophoric subset (CDOM) by the Mackenzie River during the MALINA cruise are estimated as ∼0.22 TgC and 0.18 TgC, respectively. Three dissolved fluorescent components (C1-C3) were identified by fluorescence excitation/emission matrix spectroscopy (EEMS) and parallel factor (PARAFAC) analysis. Our results showed an aquatic dissolved organic matter (DOM) component (C1), probably produced in the numerous lakes of the watershed, that co-dominated with a terrestrial humic-like component (C2) in the Mackenzie Delta Sector. This aquatic DOM could partially explain the high CDOM spectral slopes observed in the Beaufort Sea.
The potential impact of rising carbon dioxide (CO2) on carbon transfer from phytoplankton to bacteria was investigated during the 2005 PeECE III mesocosm study in Bergen, Norway. Sets of mesocosms, in which a phytoplankton bloom was induced by nutrient addition, were incubated under 1x (~350 µatm), 2x (~700 µatm), and 3x present day CO2 (~1050 µatm) initial seawater and sustained atmospheric CO2 levels for 3 weeks. 13C labelled bicarbonate was added to all mesocosms to follow the transfer of carbon from dissolved inorganic carbon (DIC) into phytoplankton and subsequently heterotrophic bacteria, and settling particles. Isotope ratios of polar-lipid-derived fatty acids (PLFA) were used to infer the biomass and production of phytoplankton and bacteria. Phytoplankton PLFA were enriched within one day after label addition, whilst it took another 3 days before bacteria showed substantial enrichment. Group-specific primary production measurements revealed that coccolithophores showed higher primary production than green algae and diatoms. Elevated CO2 had a significant positive effect on post-bloom biomass of green algae, diatoms, and bacteria. A simple model based on measured isotope ratios of phytoplankton and bacteria revealed that CO2 had no significant effect on the carbon transfer efficiency from phytoplankton to bacteria during the bloom. There was no indication of CO2 effects on enhanced settling based on isotope mixing models during the phytoplankton bloom, but this could not be determined in the post-bloom phase. Our results suggest that CO2effects are most pronounced in the post-bloom phase, under nutrient limitation.
Populations can respond to environmental change over tens or hundreds of generations by shifts in phenotype that can be the result of a sustained physiological response, evolutionary (genetic) change, shifts in community composition, or some combination of these factors. Microbes evolve on human timescales, and evolution may contribute to marine phytoplankton responses to global change over the coming decades. However, it is still unknown whether evolutionary responses are likely to contribute significantly to phenotypic change in marine microbial communities under high p CO<sub>2</sub> regimes or other aspects of global change. Recent work by Müller et al. (2010) highlights that long-term responses of marine microbes to global change must be empirically measured and the underlying cause of changes in phenotype explained. Here, I briefly discuss how tools from experimental microbial evolution may be used to detect and measure evolutionary responses in marine phytoplankton grown in high CO<sub>2</sub> environments and other environments of interest. I outline why the particular biology of marine microbes makes conventional experimental evolution challenging right now and make a case that marine microbes are good candidates for the development of new model systems in experimental evolution. I suggest that "black box" frameworks that focus on partitioning phenotypic change, such as the Price equation, may be useful in cases where direct measurements of evolutionary responses alone are difficult, and that such approaches could be used to test hypotheses about the underlying causes of phenotypic shifts in marine microbe communities responding to global change.
Top-cited authors
Markus Reichstein
  • Max Planck Institute for Biogeochemistry Jena
Philippe Ciais
  • Laboratoire des Sciences du Climat et l'Environnement
Laurent Bopp
  • Ecole Normale Supérieure de Paris
Scott C. Doney
  • University of Virginia
Dario Papale
  • Tuscia University