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  • Wiley  (115)
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  • 1
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    Physical pathways for carbon transfers between the surface mixed-layer and the ocean interior (2013)
    Wiley
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    Publikationsdatum: 2013-09-15
    Beschreibung: [1]  Although they are key components of the surface ocean carbon budget, physical processes inducing carbon fluxes across the mixed-layer base, i.e. subduction and obduction, have received much less attention than biological processes. Using a global model analysis of the pre-industrial ocean, physical carbon fluxes are quantified and compared to the other carbon fluxes in and out of the surface mixed-layer, i.e. air-sea CO 2 gas exchange and sedimentation of biogenic material. Model-based carbon obduction and subduction are evaluated against independent data-based estimates to the extent that was possible. We find that climatological physical fluxes of DIC are two orders of magnitude larger than the other carbon fluxes and vary over the globe at smaller spatial scale. At temperate latitudes, the subduction of DIC and to a much lesser extent (〈10%) the sinking of particles maintain CO 2 undersaturation, whereas DIC is obducted back to the surface in the tropical band (75%) and Southern Ocean (25%).At the global scale, these two large counter-balancing fluxes of DIC amount to +275.5 PgC y -1 for the supply by obduction and -264.5 PgC y -1 for the removal by subduction which is ~ 3 to 5 times larger than previous estimates. Moreover, we find that subduction of organic carbon (dissolved and particulate) represents ~ 20% of the total export of organic carbon: at the global scale, we evaluate that, of the 11 PgC y–1 of organic material lost from the surface every year, 2.1 PgC y -1 are lost through subduction of organic carbon. Our results emphasis the strong sensitivity of the oceanic carbon cycle to changes in mixed-layer depth, ocean currents and wind.
    Print ISSN: 0886-6236
    Digitale ISSN: 1944-9224
    Thema: Biologie , Chemie und Pharmazie , Geographie , Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 2
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    Dynamic biogeochemical provinces in the global ocean (2013)
    Wiley
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    Publikationsdatum: 2013-09-21
    Beschreibung: [1]  In recent decades, it has been found useful to partition the pelagic environment using the concept of biogeochemical provinces, or BGCPs, within each of which it is assumed that environmental conditions are distinguishable and unique at global scale. The boundaries between provinces respond to features of physical oceanography and, ideally, should follow seasonal and inter-annual changes in ocean dynamics. But this ideal has not been fulfilled except for small regions of the oceans. Moreover, BGCPs have been used only as static entities having boundaries that were originally established to compute global primary production. In the present study, a new statistical methodology based on non-parametric procedures is implemented to capture the environmental characteristics within 56 BGCPs. Four main environmental parameters (bathymetry, chlorophyll-a concentration, surface temperature and salinity) are used to infer the spatial distribution of each BGCP over 1997–2007. The resulting dynamic partition allows us to integrate changes in the distribution of BGCPs at seasonal and inter-annual timescales, and so introduces the possibility of detecting spatial shifts in environmental conditions.
    Print ISSN: 0886-6236
    Digitale ISSN: 1944-9224
    Thema: Biologie , Chemie und Pharmazie , Geographie , Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 3
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    Eddy compensation and controls of the enhanced sea-to-air CO2 flux during positive phases of the southern annular mode (2013)
    Wiley
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    Publikationsdatum: 2013-09-13
    Beschreibung: [1]  The current positive trend in the Southern Annular Mode (SAM) is thought to reduce the growth rate of the Southern Ocean CO 2 sink because enhanced wind-driven upwelling of dissolved inorganic carbon (DIC) increases outgassing of natural CO 2 . However, no study to date has quantified the potentially large role of mesoscale eddies in compensating intensified upwelling, nor the mixed layer processes in terms of their effects on CO 2 fluxes. Here we report on results from two new simulations in a regional 0.5º eddying model of the Southern Ocean. The first simulation is forced with interannually varying atmospheric reanalysis and coupled to a biogeochemistry model run under constant preindustrial atmospheric CO 2 . The second simulation is like the first except that superimposed on the forcing is a poleward shifted and intensified westerlies wind anomaly consistent with the positive phase of the SAM. In response to the SAM, the Southern Ocean's sea-to-air CO 2 flux is enhanced by 0.1 Pg C yr -1 per standard deviation of the SAM, mostly from the Antarctic Zone (AZ), where enhanced surface DIC is only partly compensated by enhanced surface alkalinity. Increased mixed-layer DIC in the AZ results from a combination of increased upwelling below the mixed layer and increased vertical diffusion at the base of the mixed layer. Previous studies overlooked the latter. Thus upward supply of DIC and alkalinity depends on associated vertical gradients just below the mixed layer, which are affected by interior ocean transport. Our eddying model study suggests that about one-third of the SAM enhancement of the Ekman-induced northward DIC transport is compensated by southward transport from standing and transient eddies.
    Print ISSN: 0886-6236
    Digitale ISSN: 1944-9224
    Thema: Biologie , Chemie und Pharmazie , Geographie , Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 4
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    Hysteresis conditions the vertical position of deep chlorophyll maximum in the temperate ocean. (2013)
    Wiley
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    Publikationsdatum: 2013-10-05
    Beschreibung: [1]  Deep chlorophyll maxima (DCMs) are widespread features of oceans. In temperate regions, DCMs are commonly associated with isopycnal surfaces that frequently move over a wide vertical range. This general association between DCMs and isopycnals remains unexplained by present theories and we show here that it emerges from the seasonal history of the water column. Analysis of the formation of more than 9,000 seasonal DCMs throughout the world's oceans consistently locates the vertical position of spring/summer DCMs in temperate seas at the density of the previous winter mixed layer, independently of this density value and future depth. These results indicate that DCM formation cannot be understood without hysteresis by solely considering the instantaneous response of phytoplankton to vertical gradients in physical and chemical fields. Presents theories for DCM formation cannot explain why spring and summer DCMs are systematically found at a density equal to that of the previous mixed layer where a bloom has occurred. Rather than reacting to instantaneous physical forcing, the results indicate that DCMs operate as self-preserving biological structures that are associated with particular isopycnals because of their capacity to modify the physico-chemical environment. Combined with remote sensors to measure salinity and temperature in the surface ocean, this new understanding of DCM dynamics have the potential improve the quantification of three-dimensional primary production via satellites. This significant enhancement of the representation of oceanic biological processes can also allow increasingly realistic predictions of future biogeochemical scenarios in a warming ocean.
    Print ISSN: 0886-6236
    Digitale ISSN: 1944-9224
    Thema: Biologie , Chemie und Pharmazie , Geographie , Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 5
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    Future arctic ocean primary productivity from CMIP5 simulations: Uncertain outcome, but consistent mechanisms (2013)
    Wiley
    Details
    Publikationsdatum: 2013-06-09
    Beschreibung: [1]  Net Arctic Ocean primary production (PP) is expected to increase over this century, due to less perennial sea ice and more available light, but could decrease depending on changes in nitrate (NO 3 ) supply. Here, CMIP5 simulations performed with 11 Earth System Models are analyzed in terms of PP, surface NO 3 and sea ice coverage over 1900-2100. Whereas the mean model simulates reasonably well Arctic-integrated PP (511 TgC/yr, 1998-2005) and projects a mild 58 TgC/yr increase by 2080-2099 for the strongest climate change scenario, models do not agree on the sign of future PP change. However, similar mechanisms operate in all models. The perennial ice loss-driven increase in PP is in most models NO 3 -limited. The Arctic surface NO 3 is decreasing over the 21 st century (-2.3 ± 1 mmol/m 3 ), associated with shoaling mixed layer and with decreasing NO 3 in the nearby North Atlantic and Pacific waters. However, the inter-model spread in the degree of NO 3 limitation is initially high, resulting from 〉1000 yr spin-up simulations. This initial NO 3 spread, combined with the trend, causes a large variation in the timing of oligotrophy onset – which directly controls the sign of future PP change. Virtually all models agree in the open ocean zones on more spatially-integrated PP and less PP per unit area. The source of model uncertainty is located in the sea ice zone, where a subtle balance between light and nutrient limitations determines the PP change. Hence, it is argued that reducing uncertainty on present Arctic NO 3 in the sea ice zone would render Arctic PP projections much more consistent.
    Print ISSN: 0886-6236
    Digitale ISSN: 1944-9224
    Thema: Biologie , Chemie und Pharmazie , Geographie , Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 6
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    On the variation of regional CO2 exchange over temperate and boreal North America (2013)
    Wiley
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    Publikationsdatum: 2013-09-17
    Beschreibung: [1]  Inverse-estimated net carbon exchange time series spanning two decades for six North American regions are analyzed to examine long-term trends and relationships to temperature and precipitation variations. Results reveal intensification of carbon uptake in eastern boreal North America (0.1 PgC/decade) and the Midwest United States (0.08 PgC/decade). Seasonal cross-correlation analysis shows a significant relationship between net carbon exchange and temperature/precipitation anomalies during the western United States growing season with warmer, dryer conditions leading reduced carbon uptake. This relationship is consistent with “global change-type drought” dynamics which drive increased vegetation mortality, increases in dry woody material, and increased wildfire occurrence. This finding supports the contention that future climate change may increase carbon loss in this region. Similarly, higher temperatures and reduced precipitation are accompanied by decreased net carbon uptake in the Midwestern United States towards the end of the growing season. Additionally, intensified net carbon uptake during the BE growing season is led by increased precipitation anomalies in the previous year, suggesting the influence of “climate memory” carried by regional snowmelt water. The two regions of boreal North America exhibit opposing seasonal carbon-temperature relationships with the eastern half experiencing a net carbon loss with near coincident increases in temperature and the western half showing increased net uptake. The carbon response in the boreal west region lags the temperature anomalies by roughly 6 months. This opposing carbon-temperature relationship in boreal North America may be a combination of different dominant vegetation types, the amount and timing of snowfall, and temperature anomaly differences across boreal North America.
    Print ISSN: 0886-6236
    Digitale ISSN: 1944-9224
    Thema: Biologie , Chemie und Pharmazie , Geographie , Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 7
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    Olivine thermometry and source constraints for mantle fragments in the Navajo Volcanic Field, Colorado Plateau, southwest United States: Implications for the mantle wedge (2013)
    Wiley
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    Publikationsdatum: 2013-01-17
    Beschreibung: [1]  The evolution of the mantle wedge below the Colorado Plateau during low-angle subduction has been investigated by analysis of fragments from the Navajo Volcanic Field (NVF), most from serpentinized ultramafic microbreccia (SUM) diatremes. In most SUM-hosted olivine, concentrations of Al and V are 〈 1 ppm, and Cr, Ca, and Na concentrations also are unusually low: most temperatures from three olivine thermometers (Al, Cr, and V-based) are in the range 530 °C to 650 °C. The temperatures are consistent with the presence of chlorite in some inclusions, and they support the utility of olivine thermometry for diverse mineral assemblages in cool peridotite. Most pressures calculated for discrete diopside grains in SUM correspond to depths in the range 80 to 120 km. Diopside is relatively high in Li (~3.5 ppm), and two of five diopside grains have high Sr/Nd. SUM diatreme sources are inferred to be serpentine-rich mélange tectonically eroded from the forearc, transported above the Farallon slab, and incorporated into the lithosphere of the Plateau. Garnet peridotite xenoliths from minettes of the NVF record deeper depths in the range 120 to 150 km. These garnet peridotites also may be from forearc mantle emplaced during Farallon subduction. Calculated temperatures preclude the possibility that asthenosphere was in contact with that lithosphere at or near 150 km depth for tens of m.y. before NVF formation. Structures observed in seismic images of mantle to depths of 150 km below the central Colorado Plateau may be related to Farallon subduction, not inherited from Proterozoic lithosphere.
    Print ISSN: 0886-6236
    Digitale ISSN: 1944-9224
    Thema: Biologie , Chemie und Pharmazie , Geographie , Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 8
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    Seasonal variability in concentration, composition, age and fluxes of particulate organic carbon exchanged between the floodplain and Amazon River (2013)
    Wiley
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    Publikationsdatum: 2013-01-17
    Beschreibung: [1]  The composition, sources and age of particulate organic matter were determined in an Amazonian river-floodplain system during rising, high, falling and low water periods over seven years (1999-2006), and a mass balance for total organic carbon (dissolved and particulate) was estimated. The Curuai floodplain, comprised of several temporally interconnected lakes, is permanently connected to the Amazon River via channels. Organic matter (OM) is imported to the floodplain from the Amazon River mainly during the rising water period and produced in the floodplain and exported to the river during high and falling water periods. No significant exchanges occurred during low water periods. The OM produced in the floodplain is characterized by low C/N ratios and by high chlorophyll a concentrations (Chl-a). The δ 13 C signature has a seasonal trend, with more negative δ 13 C values during the high water period than other periods. Δ 14 C results indicate that the bulk OM present in floodplain lakes is predominantly post-bomb (i.e., post-1950). Particulate organic carbon (POC) and dissolved organic carbon (DOC) fluxes exported by the Curuai floodplain represent 1.3 % and 0.1 %, respectively, of the POC and DOC annual fluxes in the mainstem Amazon River at Óbidos but may reach up to 3.3 % and 0.8 % during falling water. Based on Δ 14 C, δ 13 C, Chl-a and elemental analysis of the particulate organic matter, we demonstrate that floodplain lakes have intense phytoplankton and macrophyte primary production, which is partly exported to the main river channel. Floodplains are thus a significant source of modern and labile organic carbon to the river mainstem, where it can be rapidly degraded and recycled back to the atmosphere.
    Print ISSN: 0886-6236
    Digitale ISSN: 1944-9224
    Thema: Biologie , Chemie und Pharmazie , Geographie , Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 9
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    Spatiotemporal variations of pCO2 and δ13C-DIC in subarctic streams in northern Sweden (2013)
    Wiley
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    Publikationsdatum: 2013-01-18
    Beschreibung: [1]  Current predictions of climate-related changes in high-latitude environments suggest major effects on the C export in streams and rivers. To what extent this will also affect the stream water CO 2 concentrations is poorly understood. In this study we examined the spatiotemporal variation in partial pressure of CO 2 ( p CO 2 ) and in stable isotopic composition of dissolved inorganic carbon (δ 13 C-DIC) in sub-arctic streams in northern Sweden. The selected watersheds are characterized by large variations in high-latitude boreal forest, tundra and differences in bedrock. We found that all streams generally were supersaturated in p CO 2 with an average concentration of 850 µatm. The variability in p CO 2 across streams was poorly related to vegetation cover and carbonaceous bedrock influence was manifested in high DIC concentrations but not reflected in either stream p CO 2 or δ 13 C-DIC. Stream water p CO 2 values were highest during winter baseflow when we also observed the lowest δ 13 C-DIC values and this pattern are interpreted as a high contribution from CO 2 from soil respiration. Summer base flow δ 13 C-DIC values probably are more affected by in-situ stream processes such as aquatic production/respiration and degassing. A challenge for further studies will be to disentangle the origin of stream water CO 2 and quantify their relative importance.
    Print ISSN: 0886-6236
    Digitale ISSN: 1944-9224
    Thema: Biologie , Chemie und Pharmazie , Geographie , Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 10
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    Evidence for elevated emissions from high-latitude wetlands contributing to high atmospheric CH4 concentration in the early Holocene (2013)
    Wiley
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    Publikationsdatum: 2013-01-19
    Beschreibung: [1]  The major increase in atmospheric methane (CH 4 ) concentration during the last glacial-interglacial transition provides a useful example for understanding the interactions and feedbacks among Earth's climate, biosphere carbon cycling, and atmospheric chemistry. However, the causes of CH 4 doubling during the last deglaciation are still uncertain and debated. Although the ice-core data consistently suggest a dominant contribution from northern high-latitude wetlands in the early Holocene, identifying the actual sources from the ground-based data has been elusive. Here we present data syntheses and a case study from Alaska to demonstrate the importance of northern wetlands in contributing to high atmospheric CH 4 concentration in the early Holocene. Our data indicate that new peatland formation as well as peat accumulation in northern high-latitude regions increased more than threefold in the early Holocene in response to climate warming and the availability of new habitat as a result of deglaciation. Furthermore, we show that marshes and wet fens that represent early stages of wetland succession were likely more widespread in the early Holocene. These wetlands are associated with high CH 4 emissions due to high primary productivity and the presence of emergent plant species that facilitate CH 4 transport to the atmosphere. We argue that early wetland succession and rapid peat accumulation and expansion (not simply initiation) contributed to high CH 4 emissions from northern regions, potentially contributing to the sharp rise in atmospheric CH 4 at the onset of the Holocene.
    Print ISSN: 0886-6236
    Digitale ISSN: 1944-9224
    Thema: Biologie , Chemie und Pharmazie , Geographie , Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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