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Adopting a flexitarian diet could be a uniquely powerful way to help us keep warming levels below the 1.5C target of the Paris Agreement, finds new research. The gains from [...]

Byline: E. Comakli Keywords: Scots pine, afforestation, soil organic carbon stock, nitrogen stock, stratification ratio INTRODUCTION Forest ecosystems, covering nearly half of all terrestrial land, are the most important terrestrial [...]

Coasts are vast, ever-changing environments, with no two areas completely the same in their physical, chemical, or biological conditions. Over the years, sparse datasets have made it difficult for ocean-ographers [...]

Abstract Males and females often contribute differently to the ecosystem as a result of their different roles and labour responsibilities. This is especially true in remote areas like the Tibetan [...]

Agricultural practices, particularly land use, inputs and soil management, have a significant impact on the carbon cycle. Good management of agricultural practices may reduce carbon emissions and increase soil carbon sequestration. In this context, organic agricultural practices may have a positive role in mitigating environmental burden. Organic olive cultivation is increasing globally, particularly in Italy, which is ranked first worldwide for both organic olive production and cultivated area. The aim of the present study was to assess the effects of agricultural practices in organic and conventional olive systems on global warming potential (GWP) from a life cycle perspective and to identify the hot spots in each system. The impacts assessed were associated with the efficiency of both systems at sequestering soil in order to calculate the net carbon flux. There was a higher environmental impact on GWP in the organic system because of higher global greenhouse gas (GHG) emissions resulting from manure fertilisation rather than the synthetic foliar fertilisers used in the conventional system. However, manure was the main reason behind the higher soil organic carbon (SOC) content and soil carbon sequestration in the organic system. Fertilisation activity was the main contributor to carbon emissions, accounting for approximately 80% of total emissions in the organic system and 45% in the conventional system. Conversely, given the similarity of other factors (land use, residues management, soil cover) that may affect soil carbon content, manure was the primary contributor to increased SOC in the organic system, resulting in a higher efficiency of carbon sequestration in the soil following the addition of soil organic matter. The contribution of the manure to increased SOC compensated for the higher carbon emission from the organic system, resulting in higher negative net carbon flux in the organic versus the conventional system (-1.7 vs -0.52 t C [ha.sup.-1] [year.sup.-1], respectively) and higher efficiency of C[O.sub.2] mitigation in the organic system. Additional keywords: global warming potential, greenhouses gas emissions, net carbon flux, soil organic carbon., Introduction Atmospheric concentrations of C[O.sub.2] are increasing yearly at a rate of 0.5% (IPCC 1995) because of fossil fuel combustion, cement manufacturing and changes in carbon (C) sequestration caused by [...]

Our aim was to evaluate the long-term influences of urban organic amendments on the enzymes involved in the carbon cycle under semi-arid conditions, including changes in the biomass and structure of the microbial community. A soil was restored 24 years ago with an organic amendment based on domestic organic waste. Organic amendment was applied to soil in order to increase the content of total organic carbon (TOC) by 0.5% and 1.5% with respect to the original TOC content. Enzyme isoform composition was studied by using zymographic techniques based on protein extraction, separation by gel electrophoresis and further enzyme-specific, in-gel staining. Total cellulose and β-glucosidase activities, microbial biomass estimated by phospholipid-fatty acid analysis and the number of isoforms of each enzyme showed increases related to the initial amount of organic amendment and the consequent development of vegetation. The information obtained by enzyme activity assays may be improved by the use of zymographic techniques, which allow the investigation of the variety of isoforms of each enzyme. This information could improve the understanding of the relationship between the microbial community and carbon cycling in restored areas. Additional keywords: C cycling, isoform variety, microbial biomass and community, PFLA, semi-arid conditions, soil restoration, zymography., Introduction In semi-arid areas, soil degradation processes are mainly due to human activity (over-exploitation of soils, abandonment of soils from agriculture) and unfavourable environmental conditions. These factors arc linked to [...]

The observed stability of Earth's climate over millions of years is thought to depend on the rate of carbon dioxide (C[O.sub.2]) release from the solid Earth being balanced by the rate of C[O.sub.2] consumption by silicate weathering (1). During the Cenozoic era, spanning approximately the past 66 million years, the concurrent increases in the marine isotopic ratios of strontium, osmium and lithium (2-4) suggest that extensive uplift of mountain ranges may have stimulated C[O.sub.2] consumption by silicate weathering (5), but reconstructions of sea-floor spreading (6) do not indicate a corresponding increase in C[O.sub.2] inputs from volcanic degassing. The resulting imbalance would have depleted the atmosphere of all C[O.sub.2] within a few million years (7). As a result, reconciling Cenozoic isotopic records with the need for mass balance in the long-term carbon cycle has been a major and unresolved challenge in geochemistry and Earth history. Here we show that enhanced sulphide oxidation coupled to carbonate dissolution can provide a transient source of C[O.sub.2] to Earth's atmosphere that is relevant over geological timescales. Like drawdown by means of silicate weathering, this source is probably enhanced by tectonic uplift, and so may have contributed to the relative stability of the partial pressure of atmospheric C[O.sub.2] during the Cenozoic. A variety of other hypotheses (8-10) have been put forward to explain the 'Cenozoic isotope-weathering paradox', and the evolution of the carbon cycle probably depended on multiple processes. However, an important role for sulphide oxidation coupled to carbonate dissolution is consistent with records of radiogenic isotopes (2,3), atmospheric C[O.sub.2] partial pressure (11,12) and the evolution of the Cenozoic sulphur cycle, and could be accounted for by geologically reasonable changes in the global dioxygen cycle, suggesting that this C[O.sub.2] source should be considered a potentially important but as yet generally unrecognized component of the long-term carbon cycle., It has been proposed that excess C[O.sub.2] uptake from enhanced silicate weathering over the Cenozoic could be balanced by a net decrease in the size of the organic C reservoir [...]

A broad compilation of modern carbon isotope compositions in all C3 plant types shows a monotonic increase in [delta][sup.13]C with decreasing mean annual precipitation (MAP) that differs from previous models. Corrections for temperature, altitude, or latitude are smaller than previously estimated. As corrected for altitude, latitude, and the [delta][sup.13]C of atmospheric C[O.sub.2], these data permit refined interpretation of MAP, paleodiet, and paleoecology of ecosystems dominated by C3 plants, either prior to 7-8 million years ago (Ma), or more recently at mid- to high latitudes. Twenty-nine published paleontological studies suggest preservational or scientific bias toward dry ecosystems, although wet ecosystems are also represented. Unambiguous isotopic evidence for C4 plants is lacking prior to 7-8 Ma, and hominid ecosystems at 4.4 Ma show no isotopic evidence for dense forests. Consideration of global plant biomass indicates that average [delta][sup.13]C of C3 plants is commonly overestimated by approximately 2[per thousand] aridity | carbon cycle | closed canopy | paleoprecipitation doi/ 10.1073/pnas.1004933107

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2010.06.011 Byline: Victoria J. Hill, Richard C. Zimmerman Keywords: Arctic Ocean; Primary productivity; Remote sensing; LIDAR Abstract: The Arctic Ocean, including its regional shelf seas, is assumed to play an important role in the global carbon cycle. However, the true magnitude of annual production is unknown, as in situ data are sparse in time and space. Remote sensing technology has the potential to provide large scale estimates of phytoplankton biomass at much higher frequency and spatial coverage than shipboard observations in this remote region. Subsurface peaks in both biomass and primary production (PP), which are the characteristics of the Arctic, are shown to limit the reliability of ocean color based integrated PP (IPP) models in the Chukchi Sea. Here we report that the retrievals of IPP from remotely sensed ocean color data were accurate only when limited to 1.2 optical depths, which severely constrains the utility of ocean color remote sensing for the assessment of Arctic Ocean dynamics. Active sensors such as LIDAR, can, in combination with passive ocean color, dramatically improve our ability to estimate IPP for the Arctic. IPP retrievals were improved to within a factor of 2-3 of the measured values, when the vertical distribution of Chl a was determined to a resolution of 1m using modeled LIDAR retrievals of the beam attenuation coefficient. This was far better than models using only passive ocean color. The instrument specifications of the current NASA spaceborne LIDAR (CALIOP) allow for the retrieval of K.sub.d at a depth resolution of 23m. Even with this constraint, however, the accuracy of the modeled IPP was improved over passive ocean color retrievals to approximately a factor of 3. The Arctic is a perfect location to merge ocean color and LIDAR measurements as the polar orbit of CALIOP provides complete grid coverage of the area every 8 days, crossing the horizontal gradients in Chl a already known to exist from passive ocean color observations. Author Affiliation: Ocean, Earth and Atmospheric Sciences, 4600 Elkhorn Avenue, Old Dominion University, Norfolk, VA 23529, USA Article History: Received 16 December 2009; Revised 11 June 2010; Accepted 18 June 2010

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2010.03.008 Byline: Tsung-Hung Peng, Rik Wanninkhof Keywords: Global carbon cycle; Oceanic uptake of anthropogenic CO.sub.2; Decadal increase in DIC in the Atlantic Ocean Abstract: Data from the first systematic survey of inorganic carbon parameters on a global scale, the GEOSECS program, are compared with those collected during WOCE/JGOFS to study the changes in carbon and other geochemical properties, and anthropogenic CO.sub.2 increase in the Atlantic Ocean from the 1970s to the early 1990s. This first data-based estimate of CO.sub.2 increase over this period was accomplished by adjusting the GEOSECS data set to be consistent with recent high-quality carbon data. Multiple Linear Regression (MLR) and extended Multiple Linear Regression (eMLR) analyses to these carbon data are applied by regressing DIC with potential temperature, salinity, AOU, silica, and PO.sub.4 in three latitudinal regions for the western and eastern basins in the Atlantic Ocean. The results from MLR (and eMLR provided in parentheses) indicate that the mean anthropogenic CO.sub.2 uptake rate in the western basin is 0.70 (0.53)mol m.sup.-2 yr.sup.-1 for the region north of 15[degrees]N; 0.53 (0.36)mol m.sup.-2 yr.sup.-1 for the equatorial region between 15[degrees]N and 15[degrees]S; and 0.83 (0.35)mol m.sup.-2 yr.sup.-1 in the South Atlantic south of 15[degrees]S. For the eastern basin an estimate of 0.57 (0.45)molm.sup.-2 yr.sup.-1 is obtained for the equatorial region, and 0.28 (0.34)mol m.sup.-2 yr.sup.-1 for the South Atlantic south of 15[degrees]S. The results of using eMLR are systematically lower than those from MLR method in the western basin. The anthropogenic CO.sub.2 increase is also estimated in the upper thermocline from salinity normalized DIC after correction for AOU along the isopycnal surfaces. For these depths the results are consistent with the CO.sub.2 uptake rates derived from both MLR and eMLR methods. Author Affiliation: Ocean Chemistry Division, NOAA/AOML, Miami, FL 33149, USA Article History: Received 27 February 2009; Revised 5 March 2010; Accepted 24 March 2010

The recent warming in the Arctic is affecting a broad spectrum of physical, ecological, and human/cultural systems that may be irreversible on century time scales and have the potential to cause rapid changes in the earth system. The response of the carbon cycle of the Arctic to changes in climate is a major issue of global concern, yet there has not been a comprehensive review of the status of the contemporary carbon cycle of the Arctic and its response to climate change. This review is designed to clarify key uncertainties and vulnerabilities in the response of the carbon cycle of the Arctic to ongoing climatic change. While it is clear that there are substantial stocks of carbon in the Arctic, there are also significant uncertainties associated with the magnitude of organic matter stocks contained in permafrost and the storage of methane hydrates beneath both subterranean and submerged permafrost of the Arctic. In the context of the global carbon cycle, this review demonstrates that the Arctic plays an important role in the global dynamics of both C[O.sub.2] and C[H.sub.4]. Studies suggest that the Arctic has been a sink for atmospheric C[O.sub.2] of between 0 and 0.8 Pg C/yr in recent decades, which is between 0% and 25% of the global net land/ocean flux during the 1990s. The Arctic is a substantial source of C[H.sub.4] to the atmosphere (between 32 and 112 Tg C[H.sub.4]/yr), primarily because of the large area of wetlands throughout the region. Analyses to date indicate that the sensitivity of the carbon cycle of the Arctic during the remainder of the 21st century is highly uncertain. To improve the capability to assess the sensitivity of the carbon cycle of the Arctic to projected climate change, we recommend that (1) integrated regional studies be conducted to link observations of carbon dynamics to the processes that are likely to influence those dynamics, and (2) the understanding gained from these integrated studies be incorporated into both uncoupled and fully coupled carbon-climate modeling efforts. Key words: Arctic; Arctic Ocean; boreal forest; carbon cycle; carbon dioxide; climate change; climate feedbacks; hydrates; methane; permafrost; review; tundra.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2009.04.008 Byline: Robert M. Moore (a), Stephen Punshon (a), Claire Mahaffey (b), David Karl (b) Keywords: Hydrogen; Nitrogen fixation Abstract: Fixed nitrogen is a key nutrient involved in regulating global marine productivity and hence the global oceanic carbon cycle. Oceanic nitrogen (N.sub.2) fixation is estimated to supply 8x10.sup.12 molesNy.sup.-1 to the ocean, approximately equal to current riverine and the atmospheric inputs of fixed N, and between 50 and 100% of current estimates of oceanic denitrification. However, the spatial and temporal variability of N.sub.2 fixation remains uncertain, mostly because of the normal low resolution sampling for diazotroph distribution and fixation rates. It is well established that N.sub.2 fixation, mediated by the enzyme nitrogenase, is a source of hydrogen (H.sub.2), but the extent to which it leads to supersaturation of H.sub.2 in oceanic waters is unresolved. Here, we present simultaneous measurements of upper ocean dissolved H.sub.2 concentration (nmolL.sup.-1), and rates of N.sub.2 fixation ([mu]molNm.sup.-3 d.sup.-1), determined using.sup.15N.sub.2 tracer techniques (at 7 or 15m), on a transect from Fiji to Hawaii. We find a significant correlation (r=0.98) between dissolved H.sub.2 and rates of N.sub.2 fixation, with the greatest supersaturation of H.sub.2 and highest rates of N.sub.2 fixation being observed in the subtropical gyres at the southern ([approximately equal to]18[degrees]S) and northern (18[degrees]N) reaches of the transect. The lowest H.sub.2 saturation and N.sub.2 fixation were observed in the equatorial region between 8[degrees]S and 14[degrees]N. We propose that an empirical relationship between H.sub.2 supersaturations and N.sub.2 fixation measurements could be used to guide sampling for.sup.15N fixation measurements or to aid the spatial interpolation of such measurements. Author Affiliation: (a) Department of Oceanography, Dalhousie University 1355 Oxford Street, Halifax, NS, Canada B3H 4J1 (b) Department of Oceanography, University of Hawaii, Honolulu, HI 96822, USA Article History: Received 22 September 2008; Revised 22 April 2009; Accepted 24 April 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2009.04.002 Byline: Kozo Takahashi (a), Jonaotaro Onodera (b), Yoichiro Katsurada (a) Keywords: Diatoms; Seasonal fluxes; El NiA[+ or -]o; La NiA[+ or -]a; The equatorial Pacific Abstract: The water masses of the central and western equatorial Pacific can be divided into two parts: the Western Pacific Warm Pool (WPWP) and the Equatorial Upwelling Region (EUR). The behavior of the WPWP plays a significant role in global climate changes such as the El NiA[+ or -]o-Southern Oscillation (ENSO), and it drastically modifies the oceanographic conditions in the area every few years. It is important to evaluate changes in time-series diatom fluxes during both the El NiA[+ or -]o and the La NiA[+ or -]a events. As a part of the Global Carbon Cycle and Related Mapping based on Satellite Imagery (GCMAPS) Program, time-series sediment trap moorings were deployed and recovered along the Equator at seven stations (Sites MT1-MT7) during five R/V Mirai cruises in the central and western Pacific during January 1999-January 2003. The entire length of this study is divided into two phases depending on the oceanographic conditions: the La NiA[+ or -]a event (1999 and 2000); and the El NiA[+ or -]o event (2002). Site MT3 was located in the WPWP and Sites MT5-MT7 were in the EUR. Annual means of total diatom fluxes increased towards the east in each year. The fluxes observed at Sites MT4-MT6 decreased from the La NiA[+ or -]a event to the El NiA[+ or -]o event. However, the fluxes observed at Site MT3 in 2001 and 2002 were higher than those in 2000. Total diatom fluxes showed different seasonal patterns at all sites. The diatom assemblages in the WPWP differed from those of the EUR. Pennate diatoms (e.g., Nitzschia bicapitata, Thalassionema nitzschioides) dominated in the WPWP, while the relative abundances of centric diatoms (e.g., Rhizosolenia bergonii, Azpeitia spp., Thalassiosira spp.) were higher than those of pennate diatoms in the EUR. The diatom fluxes during the La NiA[+ or -]a event reflected seasonal oscillation of the WPWP in spatial extent. At Site MT3 during El NiA[+ or -]o, terrestrial materials appeared to have been transported by subsurface currents, which might be a secondary influence on total diatom fluxes. The spatial extent of the WPWP reached Site MT7 in 2002, when total diatom fluxes decreased in the sediment traps located in the eastern region including Site MT7. Therefore, we conclude that the relationships between the ENSO and diatoms fluxes in the western and central equatorial Pacific can be explained by the geographic (west-east) expansion or contraction of the WPWP. Author Affiliation: (a) Department of Earth and Planetary Sciences, Graduate School of Sciences, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-8581, Japan (b) Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku 783-8502, Japan Article History: Received 27 December 2008; Revised 30 March 2009; Accepted 6 April 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2009.01.014 Byline: JerA[acute accent]me Harlay (a), Caroline De Bodt (a), Anja Engel (b), Sandra Jansen (b), Quentin d'Hoop (a), Judith Piontek (b), Nicolas Van Oostende (c), Steve Groom (d), Koen Sabbe (c), Lei Chou (a) Keywords: TEP; Carbon; Coccolithophores; North Atlantic Ocean Abstract: The distribution of transparent exopolymer particles (TEP) was investigated during a coccolithophorid bloom in the northern Bay of Biscay (North Atlantic Ocean) in early June 2006. MODIS chlorophyll-a (Chl-a) and reflectance images before and during the cruise were used to localize areas of important biological activity and high reflectance (HR). TEP profiles along the continental margin, determined using microscopic (TEP.sub.micro) and colorimetric (TEP.sub.color) methods, showed abundant (6.1x10.sup.6-4.4x10.sup.7 L.sup.-1) and relatively small (0.5-20[mu]m) particles, leading to a low total volume fraction (0.05-2.2ppm) of TEP.sub.micro and similar vertical profiles of TEP.sub.color. Estimates of carbon content in TEP (TEP-C) derived from the microscopic approach yielded surface concentration of 1.50[mu]molCL.sup.-1. The contribution of TEP-C to particulate organic carbon (POC) was estimated to be 12% (molar C ratio) during this survey. Our results suggest that TEP formation is a probable first step to rapid and efficient export of C during declining coccolithophorid blooms. Author Affiliation: (a) Laboratoire d'Oceanographie Chimique et Geochimie des Eaux -- Universite Libre de Bruxelles (ULB) -- Campus de la Plaine (Building B/C, 5th level), CP208, boulevard du Triomphe, B-1050 Brussels, Belgium (b) HGF Young Investigators Group, Global change and the future marine carbon cycle -- Alfred Wegener Institute (AWI) -- Am Handelshafen 12 -- D-27570 Bremerhaven, Germany (c) Protistology & Aquatic Ecology -- Ghent University (UGhent) -- Krijgslaan 281-S8, B-9000 Ghent, Belgium (d) Remote Sensing Group -- Plymouth Marine Laboratory (PML) -- Prospect Place, The Hoe, Plymouth PL1 3DH, UK Article History: Received 21 July 2008; Revised 13 January 2009; Accepted 22 January 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2009.03.004 Byline: M.W. Lomas (a), N. Roberts (b), F. Lipschultz (a), J.W. Krause (c), D.M. Nelson (c), N.R. Bates (a) Keywords: New production; Phytoplankton community composition; Diatoms; Picoeukaryotes; Nitrate uptake; Export production Abstract: In this paper, we present multi-parameter data on phytoplankton community composition, and its response to storm events in the Sargasso Sea in late February and early March of 2 years (2004 and 2005). Observed physical conditions spanned a continuum from pulsed destratification/stratification to continuous mixing, with a corresponding range of phytoplankton growth responses. The pulsed destratification/stratification condition resulted in a rapid (1-2d) doubling of euphotic zone chlorophyll (Chl-a) along with a rapid succession, days timescale, from diatoms to haptophytes and then to cyanobacteria. Deep (>300m) continuous mixing led to a slow (8-9d) doubling of autotrophic biomass with no observed succession in the phytoplankton community. These different temporal responses appear to be due to differences between nutrient-limited and light-limited phytoplankton growth, although differences in grazing rates or selective grazing cannot be ruled out. Unexpectedly, we found that flow cytometrically enumerated picoeukaryotes were not accounted for in HPLC-pigment derived phytoplankton classifications and did not covary with any of the pigments quantified. Yet, the picoeukaryotes were positively related to increases in total Chl-a and increased carbon export, suggesting an important but as yet unknown role in the Sargasso Sea carbon cycle. Author Affiliation: (a) Bermuda Institute of Ocean Sciences, St. George's, GE01, Bermuda (b) Department of Earth Sciences, University of Cambridge, Cambridge, UK (c) College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA Article History: Received 3 October 2007; Revised 6 March 2009; Accepted 11 March 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.earscirev.2006.07.005 Byline: D. Sebag (a), Y. Copard (a), Ch. Di-Giovanni (b), A. Durand (a), B. Laignel (a), S. Ogier (a), E. Lallier-Verges (b) Keywords: organic matter; optical marker; sedimentary load; surficial deposits; soil; carbon cycle Abstract: Palynofacies analysis is based on transmitted light microscope study of organic constituents isolated and concentrated by acid and basic digestions. Published results of studies of present-day terrestrial environments show that two complementary approaches successfully characterize particulate organic matter (OM) from palynofacies analyses. The first method is based on the identification and the quantification of some typical particles (optical markers) according to their origin (i.e. aquatic or terrestrial), their nature (i.e. biogenic, anthropogenic, fossil), and/or their formation (i.e. biodegradation, combustion, oxidation). The second approach is based on the use of binary or ternary diagrams in order to define petrographical signatures from the relative proportions of significant organic constituents. This approach can be used for tracking i) changes in OM composition during humification in soil profiles, ii) transport of reworked terrestrial particles, iii) diagenesis of peaty deposits, or iv) weathering of geological substratum. The more advanced approach is based on the use of some predefined optical markers and their optical signatures to establish the relation between the OM compositions (palynofacies) and their depositional environments. In addition, this kind of study aims to define a modern frame of reference that can be applied in paleoenvironmental reconstructions. This paper combines a bibliographic review with previously unpublished data from palynofacies analyses. The aim is to present some applied examples illustrating (1) the main approaches developed for characterization of the particulate OM in surficial deposits, and (2) the study of OM transfers in terrestrial geosystems. Author Affiliation: (a) UMR CNRS 6143, M2C, Departement de Geologie, Universite de Rouen, 76821 Mont-Saint-Aignan Cedex, France (b) UMR CNRS 6113, ISTO, BAcentstiment Geosciences, Universite d'Orleans, BP 6759, 45067 Orleans Cedex 2, France Article History: Received 27 February 2006; Accepted 21 July 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2006.08.005 Byline: E.A. Speicher (a), S.B. Moran (a), A.B. Burd (b), R. Delfanti (c), H. Kaberi (d), R.P. Kelly (a), C. Papucci (c), J.N. Smith (e), S. Stavrakakis (d), L. Torricelli (c), V. Zervakis (f) Keywords: Particulate organic carbon; Carbon cycle; Thorium; Mediterranean Sea Abstract: Measurements of.sup.234Th/.sup.238U disequilibria and particle size-fractionated (1, 10, 20, 53, 70, 100[mu]m) organic C and.sup.234Th were made to constrain estimates of the export flux of particulate organic C (POC) from the surface waters of the Ligurian, Tyrrhenian and Aegean Seas in March-June 2004. POC exported from the surface waters (75-100m depth) averaged 9.2mmolm.sup.-2 d.sup.-1 in the Ligurian and Tyrrhenian Seas (2.3[+ or -]0.5-14.9[+ or -]3.0mmolm.sup.-2 d.sup.-1) and 0.9mmolm.sup.-2 d.sup.-1 in the Aegean Sea. These results are comparable to previous measurements of.sup.234Th-derived and sediment-trap POC fluxes from the upper 200m in the Mediterranean Sea. Depth variations in the POC/.sup.234Th ratio suggest two possible controls. First, decreasing POC/.sup.234Th ratios with depth were attributed to preferential remineralization of organic C. Second, the occurrence of maxima or minima in the POC/.sup.234Th ratio near the DCM suggests influence by phytoplankton dynamics. To assess the accuracy of these data, the empirical.sup.234Th-method was evaluated by quantifying the extent to which the.sup.234Th-based estimate of POC flux, P.sub.POC, deviates from the true flux, F.sub.POC, defined as the p-ratio (p-ratio=P.sub.POC /F.sub.POC=S.sub.Th /S.sub.POC, where S=particle sinking rate). Estimates of the p-ratio made using Stokes' Law and the particle size distributions of organic C and.sup.234Th yield values ranging from 0.93-1.45. The proximity of the p-ratio to unity implies that differences in the sinking rates of POC- and.sup.234Th-carrying particles did not bias.sup.234Th-normalized POC fluxes by more than a factor of two. Author Affiliation: (a) Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882 1197, USA (b) Department of Marine Sciences, University of Georgia, Athens, GA 30602 3636, USA (c) ENEA, Marine Environment Research Centre, La Spezia 19100, Italy (d) Department of Oceanography, Hellenic Centre for Marine Research, Anavyssos GE 19013, Greece (e) Marine and Environmental Sciences Division, Bedford Institute of Oceanography, Dartmouth, N.S., Canada B2Y 4A2 (f) Department of Marine Sciences, University of the Aegean, Mytilene GR 81100, Greece Article History: Received 7 October 2005; Revised 12 August 2006; Accepted 18 August 2006

An ammonia-oxidizing, carbon-fixing archaeon, Candidatus 'Nitrosopumilus maritimus,' recently was isolated from a salt-water aquarium, definitively confirming that chemoautotrophy exists among the marine archaea. However, in other incubation studies, pelagic archaea also were capable of using organic carbon. It has remained unknown what fraction of the total marine archaeal community is autotrophic in situ. If archaea live primarily as autotrophs in the natural environment, a large ammonia-oxidizing population would play a significant role in marine nitrification. Here we use the natural distribution of radiocarbon in archaeal membrane lipids to quantify the bulk carbon metabolism of archaea at two depths in the subtropical North Pacific gyre. Our compound-specific radiocarbon data show that the archaea in surface waters incorporate modern carbon into their membrane lipids, and archaea at 670 m incorporate carbon that is slightly more isotopically enriched than inorganic carbon at the same depth. An isotopic mass balance model shows that the dominant metabolism at depth indeed is autotrophy (83%), whereas heterotrophic consumption of modern organic carbon accounts for the remainder of archaeal biomass. These results reflect the in situ production of the total community that produces tetraether lipids and are not subject to biases associated with incubation and/or culture experiments. The data suggest either that the marine archaeal community includes both autotrophs and heterotrophs or is a single population with a uniformly mixotrophic metabolism. The metabolic and phylogenetic diversity of the marine archaea warrants further exploration; these organisms may play a major role in the marine cycles of nitrogen and carbon. biomarkers | carbon isotopes | microbial ecology | nitrogen cycle | oceanography

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2005.08.004 Byline: C.H. Pilskaln (a), T.A. Villareal (b), M. Dennett (c), C. Darkangelo-Wood (d), G. Meadows (e) Keywords: Biogeochemical cycles; Carbon cycle; Nitrogen cycle; Particle flux; North Pacific Subtropical Gyre; 24-32[degrees]N; 168-123[degrees]W Abstract: A video plankton recorder (VPR) and a remotely operated vehicle (ROV) were utilized on three cruises in the oligotrophic North Pacific Subtropical Gyre (NPSG) between 1995 and 2002 to quantify the size and abundance of marine snow and Rhizosolenia diatom mats within the upper 305m of the water column. Quantitative image analysis of video collected by the VPR and an ROV-mounted particle imaging system provides the first transect of marine snow size and abundance across the central North Pacific Gyre extending from 920km NW of Oahu to 555km off Southern California. Snow abundance in the upper 55m was surprisingly high for this oligotrophic region, with peak values of 6.0-13.0x10.sup.3 aggregatesm.sup.-3 at the western- and easternmost stations. At stations located in the middle of the transect (farthest from HI and CA), upper water column snow abundance displayed values of [approximately equal to]0.5-1.0x10.sup.3 aggregatesm.sup.-3. VPR and ROV imagery also provided in situ documentation of the presence of nitrogen-transporting, vertically migrating Rhizosolenia mats from the surface to >300m with mat abundances ranging from 0 to 10matsm.sup.-3. There was clear evidence that Rhizosolenia mats commonly reach sub-nutricline depths. The mats were noted to be a common feature in the North Pacific Gyre, with the lower salinity edge of the California Current appearing to be the easternmost extent of their oceanic distribution. Based on ROV observations at depth, flux by large ([greater than or equal to]1.5cm) mats is revised upward 4.5-fold, yielding an average value of 40[mu]molNm.sup.-2 d.sup.-1, a value equaling previous estimates that included much smaller mats visible only to towed optical systems. Our results suggest that the occurrence across a broad region of the NPSG of particulate organic matter production events represented by high concentrations of Rhizosolenia mats, associated mesozooplankton, and abundant detrital marine aggregates may represent significant stochastic components in the overall carbon, nitrogen, and silica budgets of the oligotrophic subtropical gyre. Likewise, their presence has important implications for the proposed climate-driven, ecosystem reorganization or domain shift occurring in the NPSG. Author Affiliation: (a) Bigelow Laboratory for Ocean Sciences, 180 McKown Point Road, West Boothbay Harbor, ME 04575, USA (b) Marine Science Institute, University of Texas at Austin, 750 Channel View Drive, Port Aransas, TX 78373, USA (c) Department of Biology, Woods Hole Oceanographic Inst., Woods Hole, MA 02543, USA (d) University of Maine, School of Marine Sciences, Orono, ME 04473, USA (e) School of Naval Architecture and Marine Engineering, College of Engineering, University of Michigan, Ann Arbor, MI 48109, USA Article History: Received 18 January 2005; Revised 13 July 2005; Accepted 2 August 2005

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2005.06.010 Byline: William T. Hiscock, Frank J. Millero Keywords: Southern Ocean; Pacific sector; Subpolar regime; Subantarctic zone; Fe; Macronutrients; Marine carbon cycle; Biogeochemical cycle Abstract: During the 2002 austral summer, two in situ mesoscale iron fertilization experiments were conducted in two distinct silicic acid regimes of the Southern Ocean (SOFeX). The iron was added to the low Si(OH).sub.4 waters of the Subantarctic ( Author Affiliation: Rosenstiel School of Marine and Atmospheric Science, University of Miami, Department MAC, 4600 Rickenbacker Cswy, Miami, FL 33149, USA Article History: Received 12 July 2004; Revised 25 January 2005; Accepted 6 June 2005

Northern peatlands are substantial sinks of carbon (C), yet the sources of carbon dioxide (C[O.sub.2]) emitted from peatlands are largely unknown. Since the relationship between roots and peat in C cycling is important, vascular plants growing on the surface of peat deposits should influence C[O.sub.2] efflux from the peat surface and the overall C balance in peatlands. In our study, 30-cm peat cores were removed from an ombrotrophic bog in boreal,' continental western Canada. Surface vegetation in the cores remained intact and included a continuous bryophyte cover dominated by Sphagnum fuscum. In addition, some cores were collected such that either ericaceous shrubs (Ledum groenlandicum) or sedges (Eriophorum vaginatum) were present. We investigated how the presence of each vegetation type influenced soil respiration and the microbial mineralization of root exudates using a pulse [sup.14]C labeling of vegetation in the intact peat cores. The role of root biomass and root respiration in C[O.sub.2] emission and C allocation was quantified for each type of vegetation and compared through both measurement and modeling. Our results show that vascular plants contributed 35-57% of total C[O.sub.2] efflux from the peat surface, primarily derived from rhizosphere processes, including root respiration as well as microbial mineralization of root exudates. The mineralization of root exudates contributed 14-53 [micro]mol C-C[O.sub.2]*[m.sup.-2]*[d.sup.-1] (17-24% of total) to C[O.sub.2] efflux, depending on vegetation type and moisture conditions. The type of vegetation present did not influence the total amount of photosynthetic fixation over the course of the study, but did affect how C was allocated within and between both the aboveground and belowground components of the peat column. Key words: boreal; Canada; carbon balance; Eriophorum vaginatum; Ledum groenlandicum; ombrotrophic bog; peatlands; root exudation; Sphagnum fuscum.

It is generally assumed that oceanic gas hydrates contain a huge volume of natural gases, mainly methane. The most widely cited estimate of global hydrate-bound gas is 21 x [10.sup.15] [m.sup.3] of methane at STP (or ~ 10,000 Gt of methane carbon), which is proposed as a 'consensus value' from several independent estimations. This large gas hydrate reservoir is further suggested as an important component of the global carbon cycle and as a future energy source. Here, I present a revised and updated set of well-justified global estimates and discuss how and why they changed over time. It appears that the global estimates of hydratebound gas decreased by at least one order of magnitude from 1970s--early 1980s (estimates on the order of [10.sup.17]- [10.sup.18] [m.sup.3) to late 1980s--early 1990s ([10.sup.16] [m.sup.3]) to late 1990s--present ([10.sup.14]-[10.sup.15] [m.sup.3]). The decrease of estimates is a result of growing knowledge of the distribution and concentration of gas hydrates in marine sediments and ongoing efforts to better constrain the volume of hydrate-bearing sediments and their gas yield. These parameters appear to be relatively well constrained at present through DSDP/ODP drilling and direct measurements of gas concentrations in sediments. The global estimate of hydrate-bound gas that best reflects the current knowledge of submarine gas hydrate is in the range (1-5) x [10.sup.15] [m.sup.3] (~ 500-2500 Gt of methane carbon). A significantly smaller global gas hydrate inventory implies that the role of gas hydrates in the global carbon cycle may not be as significant as speculated previously. Gas hydrate may be considered a future energy source not because the global volume of hydrate-bound gas is large, but because some individual gas hydrate accumulations may contain significant and concentrated resources that may be profitably recovered in the future. Keywords: Gas hydrate; Methane; Global estimates; Carbon cycle; Energy source

Keywords: coccolithophores, diatoms, dinoflagellates, phylogenetic trees, carbon cycle Abstract The evolutionary succession of marine photoautotrophs began with the origin of photosynthesis in the Archean Eon, perhaps as early as 3.8 billion years ago. Since that time, Earth's atmosphere, continents, and oceans have undergone substantial cyclic and secular physical, chemical, and biological changes that selected for different phytoplankton taxa. Early in the history of eukaryotic algae, between 1.6 and 1.2 billion years ago, an evolutionary schism gave rise to 'green' (chlorophyll b-containing) and 'red' (chlorophyll c-containing) plastid groups. Members of the 'green' plastid line were important constituents of Neoproterozoic and Paleozoic oceans, and, ultimately, one green clade colonized land. By the mid-Mesozoic, the green line had become ecologically less important in the oceans. In its place, three groups of chlorophyll c-containing eukaryotes, the dinoflagellates, coccolithophorids, and diatoms, began evolutionary trajectories that have culminated in ecological dominance in the contemporary oceans. Breakup of the supercontinent Pangea, continental shelf flooding, and changes in ocean redox chemistry may all have contributed to this evolutionary transition. At the same time, the evolution of these modern eukaryotic taxa has influenced both the structure of marine food webs and global biogeochemical cycles.

Water-column methane oxidation can represent a substantial carbon transformation pathway in lakes, and circumstantial evidence indicates that methane may be a potentially important source of carbon for pelagic food webs. We estimated methanotrophic bacterial production (MBP), methanotrophic bacterial growth efficiency (MBGE), heterotrophic bacterial production (HBP), primary production (PP), and the relative contribution of methanotrophic bacteria to overall bacterial biomass in three very different lakes during summer and winter. In addition, we measured stable carbon isotope ratios in particulate organic matter (POM), surface sediments, zooplankton, and methane. MBP corresponded to 0.3-7% of the organic C production by primary producers, and 0.5-17% of HBP during summer. During winter, MBP was 3-120% of HBP. MBP generally dominated the heterotrophic bacterial production at greater depths. Methanotrophic biomass was 3-11% of total bacterial biomass on a depth-integrated basis. Zooplankton were generally more depleted in [sup.13]C than POM. If phytoplankton [delta][sup.13]C signatures were -35 to -30[per thousand], such as the POM signals, observed zooplankton signatures could be explained by a fraction of 5-15% methanotrophic bacteria in their diet. The results indicate that methanotrophic bacteria can provide a significant food source for zooplankton, and that methane oxidation represents a potentially important benthic--pelagic carbon and energy link in many lakes, particularly during winter. Key words: aquatic food webs; bacterial growth efficiency; carbon cycling; methane, as source of C and energy in lake food webs; methane oxidation; methanotrophic bacteria; stable isotopes; Swedish lakes; zooplankton.

Forty-one diamonds sourced from the Juina-5 kimberlite pipe in Southern Brazil, which contain optically identifiable inclusions, have been studied using an integrated approach. The diamonds contain Keywords Diamonds * Sub-lithospheric mantle * Carbon cycle * Subduction, Introduction Diamond is thought of as a rare mineral that usually forms in the lithospheric mantle between depths of 140 and 220 km. However, a small proportion ( Diamonds that [...]

To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2009.01545.x Byline: Richard D. Bardgett (1), Gerlinde B. De Deyn (1), Nicholas J. Ostle (2) Author Affiliation: (1)Soil and Ecosystem Ecology Laboratory, Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK (2)Centre for Ecology and Hydrology, Lancaster Environment Centre, Lancaster LA1 4AP, UK Article note: (*) Correspondence author. E-mail: r.bardgett@lancaster.ac.uk

The burning of fossil fuels, which releases carbon dioxide into the atmosphere and the implications for global climate have highlighted the carbon cycle, including where carbon is store and for how long. New research indicates that much of the new carbon entering the forests rapidly leaks out through rivers and back into the atmosphere.