Limpets counteract ocean acidification induced shell corrosion by thickening of aragonitic shell layers
Summary: Specimens of the patellogastropod limpet Patella caerulea were collected within and outside a CO2 vent site at Ischia, Italy. The distribution of different crystal structures across shell sections was analysed. Patella caerulea counteracts shell dissolution in corrosive waters by enhanced production of aragonitic parts of the shell. We conclude that it is not possible to predict the dissolution behaviour of a composite biomineral on the basis of the properties of its constituent mineral.
Processes determining the marine alkalinity and calcium carbonate saturation state distributions
Summary: We examine and discuss the portion of ocean alkalinity that varies in response to carbonate cycling and riverine alkalinity inputs using a new tracer, Alk*. We use this tracer to quantify the controls on marine carbonate saturation: at depth, we find carbonate cycling to be a minor control relative to organic matter cycling and pressure changes. In well-equilibrated surface water, we find carbonate cycling to be less important than temperature changes and freshwater cycling.
Biomass burning fuel consumption rates: a field measurement database
T. T. van Leeuwen, G. R. van der Werf, A. A. Hoffmann, R. G. Detmers, G. Rücker, N. H. F. French, S. Archibald, J. A. Carvalho Jr., G. D. Cook, W. J. de Groot, C. Hély, E. S. Kasischke, S. Kloster, J. L. McCarty, M. L. Pettinari, P. Savadogo, E. C. Alvarado, L. Boschetti, S. Manuri, C. P. Meyer, F. Siegert, L. A. Trollope, and W. S. W. Trollope Biogeosciences, 11, 7305-7329, 2014 AbstractFinal Revised Paper (PDF, 722 KB)Discussion Paper (BGD)
19 Dec 2014
iMarNet: an ocean biogeochemistry model intercomparison project within a common physical ocean modelling framework
L. Kwiatkowski, A. Yool, J. I. Allen, T. R. Anderson, R. Barciela, E. T. Buitenhuis, M. Butenschön, C. Enright, P. R. Halloran, C. Le Quéré, L. de Mora, M.-F. Racault, B. Sinha, I. J. Totterdell, and P. M. Cox Biogeosciences, 11, 7291-7304, 2014 AbstractFinal Revised Paper (PDF, 5874 KB)Supplement (2134 KB)Discussion Paper (BGD)
19 Dec 2014
Spring bloom community change modifies carbon pathways and C : N : P : Chl a stoichiometry of coastal material fluxes
Summary: Recent evidence suggests that competition between phytoplankton groups is significantly affected by changing climatic factors. We investigated the effects of phytoplankton community composition on spring bloom carbon flows. The comparison of differing communities showed that community structure significantly affected C accumulation parameters. Climate-driven changes in phytoplankton dominance patterns will have far-reaching consequences for major biogeochemical cycles.
Biogeophysical impacts of peatland forestation on regional climate changes in Finland
Summary: This work studies the biogeophysical impacts of peatland forestation on regional climate conditions in Finland by a regional climate model with two land cover maps produced from Finnish national forest inventories. A warming in spring and a slight cooling in the growing season are found in peatland forestation area, which are mainly induced by the decreased surface albedo and increased ET, respectively. The snow clearance days are advanced. The results are also compared with observational data.
CO2 and nutrient-driven changes across multiple levels of organization in Zostera noltii ecosystems
Summary: We found that the multi-level meadow response to nutrient enrichment was faster and stronger than to CO2 enrichment, being both mediated by shifts in leaf epiphyte or sediment communities. Our findings highlight the relevance of integrative approaches considering not only species interactions and connections between organization levels, but also the effect of interactive stressors, to anticipate the evolution of seagrass meadows in the near future and to endorse conservation efforts.
Methane and nitrous oxide exchange over a managed hay meadow
Summary: 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. 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. Both gases contributed to an increase of the global warming potential (GWP), effectively reducing the sink strength in terms of CO2 equivalents.
Identifying vital effects in Halimeda algae with Ca isotopes
Summary: Halimeda algae were used as a test organism to untangle some of the specific factors that influence skeletal composition, in particular Ca-isotope composition. Algae were stimulated to precipitate both calcite and aragonite by growth in artificial Cretaceous seawater. Comparison of the skeletal Ca-isotope ratios with inorganic carbonate forms indicates the effects of mineralogy and Rayleigh distillation of Ca on the geochemistry of their carbonate skeletons.
Physical and biogeochemical controls on light attenuation in a eutrophic, back-barrier estuary
Summary: Light availability to seagrass is an important factor in their success. We deployed instrumentation to measure light in Barnegat Bay, New Jersey, and found lower availability in the southern bay due to high turbidity (suspended sediment), while the northern bay has higher availability. In the northern bay, dissolved organic material and chlorophyll are most responsible for blocking light to the seagrass canopy. We also found that boat wakes do not have a large effect on sediment resuspension.
Drivers of trophic amplification of ocean productivity trends in a changing climate
Summary: Climate change projections suggest large regional ocean productivity shifts for mesozooplankton, an important food resource for fish, which are amplified relative to changes in phytoplankton production. Amplification is attributed to changes in planktonic food web dynamics under global warming. Results have implications for regional economies and food security. Improved understanding of the response of plankton food webs to climate change is essential to refine amplification estimates.
Multi-factor controls on terrestrial carbon dynamics in urbanized areas
Summary: Based on a comprehensive analysis framework including 15 factors, a factorial analysis scheme was developed to quantify a relative contribution of individual factors to carbon dynamics induced by urbanization. A case study in the southern US showed that land conversion had larger impacts than other factors, causing C loss. Urban managements & the interactive effect among factors compensated for 42% of the C loss in LC. The altered disturbance regime after urbanization enhanced the urban C sink.
I/Ca ratios in benthic foraminifera from the Peruvian oxygen minimum zone: analytical methodology and evaluation as a proxy for redox conditions
Summary: Our study explores the correlation of I/Ca ratios in four benthic foraminiferal species (three calcitic, one aragonitic) from the Peruvian OMZ with bottom water oxygenation ([O2]BW), and evaluates foraminiferal I/Ca ratios as a possible redox proxy. All species have a positive trend in the I/Ca ratios as a function of [O2]BW. Only for the aragonitic species Hoeglundina elegans is this trend not significant. The highest significance has been found for Uvigerina striata.
Biogeochemistry and ecosystems of continental margins in the western North Pacific Ocean and their interactions and responses to external forcing – an overview and synthesis
Summary: This paper provides background info on the East China Sea, Japan/East Sea and South China Sea and highlights major findings in the special issue on their biogeochemical conditions and ecosystem functions. The three seas are subject to strong impacts from human activities and/or climate forcing. Because these continental margins sustain arguably some of the most productive marine ecosystems in the world, changes in these stressed ecosystems may threaten the livelihood of a large human population.
Biomarkers in the stratified water column of the Landsort Deep (Baltic Sea)
Summary: The water column of the Landsort Deep, central Baltic Sea, is stratified into an oxic, suboxic, and anoxic zone. This stratification controls the distributions of individual microbial communities and biogeochemical processes. Our study of in situ biomarkers in the Landsort Deep provides an integrated insight into the distribution of relevant compounds and describes useful tracers to reconstruct stratified water columns in the geological record.
Disentangling residence time and temperature sensitivity of microbial decomposition in a global soil carbon model
Summary: We use a reduced complexity soil organic carbon (SOC) model to address the influence of two parameters on the response of SOC stocks to climate change: baseline turnover time (k) and temperature sensitivity of decomposition (Q10). In our model, k determines SOC stocks and the magnitude of the response to climate change (from 1850 to 2100 under RCP 8.5) while Q10 drives its sign. We dismiss unlikely simulations using global SOC data to reduce the uncertainty in projections and parameter values.
Using atmospheric observations to evaluate the spatiotemporal variability of CO2 fluxes simulated by terrestrial biospheric models
Summary: Terrestrial biospheric models (TBMs) are used to assess carbon--climate interactions. We present a new and complementary approach for evaluating the spatiotemporal patterns, rather than magnitudes, of biosphere--atmosphere carbon exchange predicted by TBMs, based on atmospheric observations. Experiments demonstrate that the performance of TBMs varies substantially across seasons and biomes, with best performance during the growing season and more limited skill during transition seasons.
Projected pH reductions by 2100 might put deep North Atlantic biodiversity at risk
Summary: This study evaluates potential impacts of pH reductions on North Atlantic deep-sea ecosystems in response to latest IPCC scenarios.Multi-model projections of pH changes over the seafloor are analysed with reference to a critical threshold based on palaeo-oceanographic studies, contemporary observations and model results. By 2100 under the most severe IPCC CO2 scenario, pH reductions occur over ~23% of deep-sea canyons and ~8% of seamounts – including seamounts proposed as marine protected areas.
M. Gehlen, R. Séférian, D. O. B. Jones, T. Roy, R. Roth, J. Barry, L. Bopp, S. C. Doney, J. P. Dunne, C. Heinze, F. Joos, J. C. Orr, L. Resplandy, J. Segschneider, and J. Tjiputra Biogeosciences, 11, 6955-6967, 2014 AbstractFinal Revised Paper (PDF, 2189 KB)Supplement (660 KB)Discussion Paper (BGD)
11 Dec 2014
Continental-scale impacts of intra-seasonal rainfall variability on simulated ecosystem responses in Africa
Summary: Climate change is expected to modify the way that rainfall arrives, namely the frequency and intensity of rainfall events and rainy season length. Yet, the quantification of the impact of these possible rainfall changes across large biomes is lacking. Our study fills this gap by developing a new modeling framework, applying it to continental Africa. We show that African ecosystems are highly sensitive to these rainfall variabilities, with esp. large sensitivity to changes in rainy season length.
Transfer of organic carbon through marine water columns to sediments – insights from stable and radiocarbon isotopes of lipid biomarkers
Summary: Compound-specific δ13C and Δ14C of lipids show that marine organic carbon (OC) in Black and Arabian Sea sediment trap material accounted for 66-100% of OC, with lower terrigenous (3-8%) and relict (4-16%) contributions. Marine OC in sediments was lower (66-90%), but terrigenous and relict OC were higher (3-17% and 7-13%). Sinking OC is overwhelmingly marine, but pre-aged terrigenous and relict OC are better preserved during delivery to the sediments.
Insights into biogeochemical cycling from a soil evolution model and long-term chronosequences
Summary: We present a soil evolution model which incorporates the major processes of pedogenesis: mineral weathering, leaching, erosion, bioturbation, nutrient cycling and organic carbon inputs. We compare the modelled soil properties with soil chronosequences from Hawaii and demonstrate that the model captures well the key components of soil development. The model also highlights the important role that vegetation plays in accelerating the weathering and the release of globally important nutrients.
Corrigendum to "Impacts of freezing and thawing dynamics on foliar litter carbon release in alpine/subalpine forests along an altitudinal gradient in the eastern Tibetan Plateau" published in Biogeosciences, 11, 6471–6481, 2014
How drought severity constrains gross primary production(GPP) and its partitioning among carbon pools in a Quercus ilex coppice?
Summary: The partitioning of carbon input in biomass has a key role in the sink function of forests. We analyzed how carbon is allocated in relation to drought in an evergreen Mediterranean forest. Carbon exchanges were drastically affected by drought. Partitioning was impacted with a hierarchy of responses going from the most affected, the stem, to the least one, the leaves. 40% of carbon input is allocated in biomass and this proportion tended to decrease with drought due to acclimation of respiration.
Local spatial structure of forest biomass and its consequences for remote sensing of carbon stocks
Summary: Forest carbon mapping may greatly reduce uncertainties in the global carbon budget. Accuracy of such maps depends however on the quality of field measurements. Using 30 large forest plots, we found large local spatial variability in biomass. When field calibration plots are smaller than the remote sensing pixels, this high local spatial variability results in an underestimation of the variance in biomass.
M. Réjou-Méchain, H. C. Muller-Landau, M. Detto, S. C. Thomas, T. Le Toan, S. S. Saatchi, J. S. Barreto-Silva, N. A. Bourg, S. Bunyavejchewin, N. Butt, W. Y. Brockelman, M. Cao, D. Cárdenas, J.-M. Chiang, G. B. Chuyong, K. Clay, R. Condit, H. S. Dattaraja, S. J. Davies, A. Duque, S. Esufali, C. Ewango, R. H. S. Fernando, C. D. Fletcher, I. A. U. N. Gunatilleke, Z. Hao, K. E. Harms, T. B. Hart, B. Hérault, R. W. Howe, S. P. Hubbell, D. J. Johnson, D. Kenfack, A. J. Larson, L. Lin, Y. Lin, J. A. Lutz, J.-R. Makana, Y. Malhi, T. R. Marthews, R. W. McEwan, S. M. McMahon, W. J. McShea, R. Muscarella, A. Nathalang, N. S. M. Noor, C. J. Nytch, A. A. Oliveira, R. P. Phillips, N. Pongpattananurak, R. Punchi-Manage, R. Salim, J. Schurman, R. Sukumar, H. S. Suresh, U. Suwanvecho, D. W. Thomas, J. Thompson, M. Uríarte, R. Valencia, A. Vicentini, A. T. Wolf, S. Yap, Z. Yuan, C. E. Zartman, J. K. Zimmerman, and J. Chave Biogeosciences, 11, 6827-6840, 2014 AbstractFinal Revised Paper (PDF, 481 KB)Supplement (702 KB)Discussion Paper (BGD)
08 Dec 2014
Seasonal distributions and fluxes of 210Pb and 210Po in the northern South China Sea
Modeling the impediment of methane ebullition bubbles by seasonal lake ice
Summary: Methane (CH4) bubbles emitted from the anoxic sediments of northern lakes constitute a significant methane flux to the atmosphere, but entrapment by seasonal lake ice impedes bubble release to the atmosphere. Using numerical modeling and field measurement of a lake in Alaska, we found that 80% of CH4 in ice-trapped bubbles dissolves into the water column. Microbes consume half of that CH4. Emission by bubbling is greatest in summer but continues in winter through some open holes in lake ice.
Sea-ice melt CO2–carbonate chemistry in the western Arctic Ocean: meltwater contributions to air–sea CO2 gas exchange, mixed-layer properties and rates of net community production under sea ice
Summary: In a era or rapid warming and sea-ice loss in the Arctic Ocean, the paper describes the variability of seawater carbon dioxide (CO2) in summertime sea-ice melt pond water in the Pacific Arctic region, and the impact of melt pond chemistry upon the underlying upper ocean.
Dependence of the cyclization of branched tetraethers on soil moisture in alkaline soils from arid–subhumid China: implications for palaeorainfall reconstructions on the Chinese Loess Plateau
Summary: The relationships between environmental variables and the cyclization of branched tetraethers (CBT) were investigated in surface soils in the Chinese Loess Plateau (CLP) and its vicinity. We find that CBT is not sensitive to soil pH but correlates best with soil moisture in these alkaline soils from arid-subhumid regions. Therefore, we suggest that CBT can potentially be used as a palaeorainfall proxy on the CLP and applied it to three loess-paleosol sequences published before.
Microbial food web dynamics during spring phytoplankton blooms in the naturally iron-fertilized Kerguelen area (Southern Ocean)
Summary: The concurrent investigation of several parameters has provided insight into two key roles of heterotrophic bacteria, and the microbial food web functioning, at the onset and late phase of the spring phytoplankton bloom induced by natural iron fertilization in the Southern Ocean.
Pasture degradation modifies the water and carbon cycles of the Tibetan highlands
W. Babel, T. Biermann, H. Coners, E. Falge, E. Seeber, J. Ingrisch, P.-M. Schleuß, T. Gerken, J. Leonbacher, T. Leipold, S. Willinghöfer, K. Schützenmeister, O. Shibistova, L. Becker, S. Hafner, S. Spielvogel, X. Li, X. Xu, Y. Sun, L. Zhang, Y. Yang, Y. Ma, K. Wesche, H.-F. Graf, C. Leuschner, G. Guggenberger, Y. Kuzyakov, G. Miehe, and T. Foken Biogeosciences, 11, 6633-6656, 2014 AbstractFinal Revised Paper (PDF, 3397 KB)Supplement (65 KB)Discussion Paper (BGD)
02 Dec 2014
Quantification of iron-rich volcanogenic dust emissions and deposition over the ocean from Icelandic dust sources
Summary: Iceland is one of the largest dust sources on Earth. Based on two separate methods, we estimate dust emissions to range between 30 and 40 million tons annually. Ocean deposition ranges between 5.5 and 13.8 million tons. Calculated iron deposition in oceans around Iceland ranges between 0.56 to 1.4 million tons, which are distributed over wide areas. Iron is a limiting nutrient for primary production in these waters, and dust is likely to affect oceanic Fe levels around Iceland.