Organic Carbon Budget Research Articles

Historical storage budgets of organic carbon, nutrient and contaminant elements in saltmarsh sediments: Biogeochemical context for managed realignment, Humber Estuary, UK

Biogeochemical data from Welwick marsh (Humber Estuary, UK), an actively accreting saltmarsh, provides a decadal–centennial-scale natural analogue for likely future biogeochemical storage effects of managed realignment sites accreting either intertidal muds or saltmarsh. Marsh topographic profiles and progradation history from aerial photographs were combined with 137Cs and niobium contamination history to establish and verify chronology and sediment mass accumulation. These data, combined with down-core measurements of particulate organic carbon (C org), organic nitrogen (N org), particle reactive phosphorus and selected contaminant metal (Zn, Pb, Cu, As and Nb) contents were then used to calculate sediment and chemical storage terms and to quantify changes in these over time. These data are used to help predict likely future biogeochemical storage changes at managed realignment sites in the estuary. The net effect of returning some 26 km 2 of reclaimed land to intertidal environments now (about 25% of the maximum possible realignment storage identified for the estuary) could result in the storage of some 40,000 tonnes a − 1 of sediment which would also bury about 800 tonnes a − 1 of C org and 40 tonnes a − 1 of N org. Particulate contaminant P burial would be around 25 tonnes a − 1 along with ~ 6 tonnes a − 1 contaminant Zn, 3 tonnes a − 1 contaminant Pb, and ~ 1 tonnes a − 1 contaminant As and Cu. The study also shows that reclamation activities in the outer estuary since the mid-1700s has prevented, in total, the deposition of about 10 million tonnes of sediment, along with 320,000 tonnes of C org and 16,000 tonnes of N org. The study provides a mid-1990s baseline against which future measurements at the site can determine changes in burial fluxes and improvement or deterioration in contaminant metal contents of the sediments. The data are directly relevant for local managed realignment sites but also broadly indicative for sites generally on the European North Sea Coast.

Factors controlling the fluvial export of large woody debris, and its contribution to organic carbon budgets at watershed scales

The fluvial export of large woody debris (LWD) was monitored in 131 reservoirs throughout Japan. Published data on the fluvial export of dissolved and particulate organic carbon were used to estimate the contributions of LWD in carbon budgets. Of all variables tested, watershed area was most important in explaining LWD carbon (LWDC) export, followed by annual precipitation. LWDC export per unit area was relatively high in small watersheds, highest in intermediate‐sized watersheds, and decreased in large watersheds. In small watersheds, a large proportion of LWD retained on narrow valley floors may fragment or decay and eventually be exported in forms other than LWD. In intermediate‐sized watersheds, LWD supplied from upstream and recruited by bank erosion is consistently transported downstream. In large watersheds, LWD recruitment is limited and LWD transported from upstream is stored on large floodplains. These differences in LWD recruitment, retention and transport in watersheds of different sizes lead to the proportion of LWDC in organic carbon exports to be maximum in intermediate‐sized watersheds and decline rapidly in large watersheds.

Chlorophyll, primary production, and organic carbon fluxes in the Kara Sea

New maps of the mean monthly distribution of chlorophyll and the primary production in the Kara Sea were compiled using joint processing of CZCS (1978–1986), SeaWiFS (1998–2005), and MODIS (2002–2006) satellite data and field measurements. The annual primary production of phytoplankton is estimated at 22.3 × 106 t of C per year or 70 mg of C/m2 per day. The results of the calculations of the organic carbon budget in the Kara Sea are presented.

Influence of crop rotation system on the spatial and temporal variation of the soil organic carbon budget in northern Kazakhstan

To optimize regional crop rotation systems to mitigate soil organic carbon (SOC) depletion, monitoring the spatial and temporal variation of the SOC budget is of major importance. This study evaluated the influence of crop rotation and topography on the spatial and temporal variation of the SOC budget under cereal cropping in northern Kazakhstan using a geostatistical method, predicted equations of CO2 emission and Moderate Resolution Imaging Spectroradiometer satellite images. The study was carried out in large-scale upland fields (7,915 ha) located in Shortandy, Aqmorinskaya Oblast, from 2001 to 2005. Under the assumption that all crop residue was incorporated into the soil, average annual C input as plant residues in cereal and abandoned fields ranged from 1.0 to 1.6 Mg C ha−1 year−1, with higher values in wet years. Average annual CO2 emission in the cereal fields and the fallow fields ranged from 1.0 to 1.2 Mg C ha−1 year−1 and from 0.7 to 0.8 Mg C ha−1 year−1, respectively. In relation to topography, CO2 emission was higher on the north-facing slope than the south-facing slope, with the highest values on the higher plateau, and the average annual carbon budget ranged from –0.1 to 0.3 Mg C ha−1 year−1. It should be noted that all fallow fields consistently had a negative carbon budget. The 5-year carbon budget for different crop rotation systems ranged from –0.5 (fallow-based rotation) to 0.6 (wheat-based 5-year continuous cereal cropped) Mg C ha−1. These results have some uncertainly because of the low predictive ability of the regression; however, the results indicated that fallow-based and barley-based crop rotation systems were depletive and conversion of the wheat-fallow system to continuous wheat cropping would sequestrate 0.1–0.3 Mg ha−1 year−1 of carbon into the soil.

Efficient organic carbon burial in the Bengal fan sustained by the Himalayan erosional system

Continental erosion controls atmospheric carbon dioxide levels on geological timescales through silicate weathering, riverine transport and subsequent burial of organic carbon in oceanic sediments. The efficiency of organic carbon deposition in sedimentary basins is however limited by the organic carbon load capacity of the sediments and organic carbon oxidation in continental margins. At the global scale, previous studies have suggested that about 70 per cent of riverine organic carbon is returned to the atmosphere, such as in the Amazon basin. Here we present a comprehensive organic carbon budget for the Himalayan erosional system, including source rocks, river sediments and marine sediments buried in the Bengal fan. We show that organic carbon export is controlled by sediment properties, and that oxidative loss is negligible during transport and deposition to the ocean. Our results indicate that 70 to 85 per cent of the organic carbon is recent organic matter captured during transport, which serves as a net sink for atmospheric carbon dioxide. The amount of organic carbon deposited in the Bengal basin represents about 10 to 20 per cent of the total terrestrial organic carbon buried in oceanic sediments. High erosion rates in the Himalayas generate high sedimentation rates and low oxygen availability in the Bay of Bengal that sustain the observed extreme organic carbon burial efficiency. Active orogenic systems generate enhanced physical erosion and the resulting organic carbon burial buffers atmospheric carbon dioxide levels, thereby exerting a negative feedback on climate over geological timescales.

Seasonal and interannual changes in particulate organic carbon export and deposition in the Chukchi Sea

Particulate organic carbon (POC) export fluxes were estimated in the shelf‐slope region of the Chukchi Sea using measurements of 234Th−238U disequilibria and the POC/234Th ratio in large (>53‐μm) particles. These export fluxes were used in conjunction with rates of primary productivity and benthic carbon respiration to construct a POC budget for this shelf‐slope region. Samples were collected along a series of shelf‐basin transects in the spring (May–June) and summer (July–August) of 2004. These stations were previously occupied during the ice covered (spring) and open water (summer) seasons of 2002, allowing for an interannual comparison of export flux. In contrast to 2002, when open water POC fluxes were significantly higher than in the ice‐covered period, POC export fluxes in 2004 were similar during the spring (average = 19.7 ± 24.8 mmol C m−2 d−1) and summer (average = 20.0 ± 14.5 mmol C m−2 d−1). The high POC fluxes measured during the spring are attributed to a plankton bloom, as evidenced by exceptionally high rates of primary productivity (average = 124.4 ± 88.1 mmol C m−2 d−1). The shelf‐slope budget of particulate organic carbon indicates that 10–20% of primary productivity was exported below 50 m but was not consumed during benthic carbon respiration or burial and oxidation in underlying sediments. Furthermore, a water column−sediment budget of 234Th indicates that particulate material is retained in shelf sediments on a seasonal basis.

Biogeochemical controls on distributions and fluxes of dissolved and particulate organic carbon in the Northern South China Sea

Abstract Dissolved organic carbon (DOC) represented the major portion of total organic carbon (80–95% TOC) in the Northern South China Sea (NSCS) that was influenced significantly by the Kuroshio intrusion and continental fluxes. The concentration of DOC ranged from 70 to 85 μM in the mixed layer of studied areas excluding the coastal zone. The concentration of particulate organic carbon (POC) was relatively low, ranging from 1.6 to 4 μM in the mixed layer. Distributions of DOC (43±3 μM) and POC (1.1±02 μM) were uniform in deep and bottom layers (>1000 m) of the deep basin areas. However, elevated concentrations of DOC and POC up to 132 and 13 μM, respectively, were found in the Zhujiang (Pearl River) plume during summer with the highest river discharge. Both DOC and POC were generally higher in shelf zones than in deep basins, and also higher in summer than in other seasons particularly for coastal zones. Terrestrial inputs and mixing processes may primarily control the horizontal and vertical distributions of DOC and POC in the NSCS, as both correlate significantly with water density and temperature but less significantly with salinity. Biological effect on DOC and POC distributions also may be significant in the central basin, as both are correlated well with chlorophyll a . A portion of surface DOM with poor nitrogen and phosphorus contents appears to be released during C org syntheses inferred from stoichiometric patterns of DOM and POM in the euphotic zone. The degradation rate of DOC in the mixed layer is generally higher in the Zhujiang plume (decay coefficient: −0.045 d −1 ) than in the deep basin (−0.011 d −1 ). The labile and semi-labile fractions of DOC account for roughly 42–50% of total DOC in the mixed layer. The increase of DOM and POM stoichiometry (C/N or C/P ratio) with depth in deep-basin waters implies a preferential decay of phosphorus (nitrogen) over carbon. Contribution of DOC oxidation to apparent oxygen utilization (AOU) below the mixed layer is fairly low, ranging from 11% and 30% with an average of ∼19%, implying that DOC may be largely recycled in the upper layer. Although the downward flux of DOC is smaller than the sinking flux of C org , its magnitude (0.27–4.4 mmol C m −2 d −1 ) constitutes a significant flux of total organic carbon transported through the depth of 100 or 150 m in the NSCS basin. With the exception of fluxes through 100 m in summer, the downward fluxes of total C org are nearly balanced by new productivity derived from upward fluxes of nutrients by considering the estimate uncertainty. DOC appears to play an important role in organic carbon cycling and budgets in the upper layer of NSCS.

Particulate organic carbon budget in the open Algero-Balearic Basin (Western Mediterranean): Assessment from a one-year sediment trap experiment

With the aim of improving the knowledge of the open ocean carbon cycle, we present a budget of particulate organic carbon (POC) fluxes carried out in the deep central part of the Algero-Balearic Basin (ABB) at 2850 m water depth based on a single mooring equipped with five automated sediment traps deployed from April 2001 to May 2002 at depths of 250, 845, 1440, 2145 and 2820 m. Suspended particulate matter (SPM) and superficial sediments were also used as indicators of hydrodynamics and carbon burial, respectively. The data reveal that the fraction of primary production buried in the sediment, which finally leads to the sequestration of carbon dioxide from the atmosphere, is 0.16%, lower than the values found in the nearby continental margin regions such as the Alboran Sea (0.48–0.89%) but of the same order as recorded at other Mediterranean sites at similar depths, such as the Ionian Sea (0.11%). As they sink through the water column, the particles exhibit decreases in flux that are similar to those observed elsewhere, but also show variations that appear to correlate with hydrological features of the water masses present in the basin, as revealed by SPM concentrations and compositions. The input of the tyrrhenian deep water (TDW) into the ABB at 800–1500 m of water depth exhibits low suspended POC concentrations and low sinking POC fluxes were also observed in this depth range. Gulf of Lions water mass formation appears to also contribute to elevated suspended POC concentrations and perhaps POC accumulation in the traps and sediments by spreading of dense cold water along the whole ABB that supplied POC at depths higher than 2000 m.

Preservation of Organic Matter in Marine Sediments: Controls, Mechanisms, and an Imbalance in Sediment Organic Carbon Budgets?

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Experiments on the operation of a combined aquaculture-algae system

A combined aquaculture-algae system was developed for the purification and reuse of effluent water from intensive fish production in a combination of a high-rate algal pond and extensive fishpond. The integrated system was operated as a closed system, thus the water demand was reduced through the recirculation of the treated water. The pilot-scale experimental system consisted of three different compartments: tanks for intensive fish production, an algal pond where the excess nutrients are removed by algae uptake and a fishpond where the produced algae biomass was consumed by fish. The objective of this study was to describe and evaluate the nutrient transformation efficiency of the combined system through the analysis of the organic carbon, nitrogen and phosphorus budgets.

Preservation of Organic Matter in Marine Sediments: Controls, Mechanisms, and an Imbalance in Sediment Organic Carbon Budgets?

Preservation of Organic Matter in Marine Sediments: Controls, Mechanisms, and an Imbalance in Sediment Organic Carbon Budgets?

Content and isotopic composition of organic carbon within a flood layer in the Po River prodelta (Adriatic Sea)

Thirty-three surface sediment samples from cross-shelf transects on the northern Adriatic shelf were collected in December 2000, soon after a 100-yr flood of the Po River, in order to determine the distribution of organic carbon (OC) along the main sediment dispersal system. To evaluate the temporal variability, stations were re-occupied eight times at seasonal intervals until June 2003. Downcore sediment profiles from two sites characterized by high flood deposit thicknesses were also examined to assess the OC variability within the flood layer. In December 2000, the highest contents of OC (up to 1.24 wt%) were measured in front of the main distributary mouths (Pila, Tolle and Gnocca-Goro) where the greatest thicknesses of the flood deposit were recorded. However, the influence of the Po di Gnocca-Goro sediment supply on the OC surface distribution declined after ∼1.5 years from the fall-2000 river flood, probably because these mouths are less active when the water discharge is lower. The δ 13C of organic matter was used to trace the dispersal of fluvial OC on the continental shelf. The δ 13C values ranged from −25.9‰ to −23.1‰. The fraction of fluvially derived organic particles decreased with increasing water depth according to a radial dispersal pattern around the Po River delta. This pattern persisted in all cruises. δ 13C values increased progressively until April 2002, suggesting an increasing marine contribution to the OC content but decreased again following a second minor flood event in November 2002. The molar C/N ratio was on average 10.0±1.6, with slightly lower values in southern and central areas. Assuming contributions from three OC end-members (terrestrial, riverine and marine), a mixing model based on δ 13C and the ratio of N to C (statistically more robust than C/N; Goñi, M.A., Teixeir, M.J., Perkley, D.W., 2003. Sources and distribution of organic matter in a river-dominated estuary (Winyah Bay, SC, USA). Estuarine, Coastal and Shelf Science 57, 1023–1048) was applied in order to quantitatively assess the OC sources for Po shelf sediments. δ 13C is significantly and positively correlated with the marine OC fraction. The terrestrial fraction is inversely correlated with N/C, while the riverine fraction is positively correlated with N/C. The terrestrial OC source was the most abundant end-member (>70%) showing only little temporal variability regardless of the Po River water discharge. Temporal and spatial changes in OC composition suggest that: (a) the Po River prodelta is always dominated from terrestrial OC input; (b) the Po della Pila supplies most terrestrial OC, whilst other tributaries (e.g., Po di Gnocca-Goro) are secondary sources. However, these mouths are as important as the Po della Pila in affecting the riverine OC signature; (c) offshore, biological primary production raises the marine OC contribution. At two sites on the Po River prodelta, the 2000-flood deposit shows slight but consistent compositional changes of organic matter (N/C and δ 13C) which can help to recognize other flood events in the sedimentary record. The OC budget for the 2000-flood deposit accounts for a terrestrial+riverine OC supply of 68–162 Gg (10 9 g) against an OC deposition of 106–162 Gg (excluding the marine fraction), which implies a rapid and efficient sedimentation of the flood material, and scarce or negligible export out the study area. Flood events may thus enhance terrestrial carbon burial, whereas marine carbon arrives more slowly and may be largely mineralized at the sediment–water interface.

The annual organic carbon budget of Young Sound, NE Greenland

On the basis of data presented in the previous chapters a carbon budget for the respective compartments of the outer region of Young Sound (76 km2) was established. The average and maximum water depth of the region was 76 m and 177 m, respectively. Primary production was mainly related to the activity of phytoplankton (65%), benthic macrophytes (21%) and benthic microphytes (13%), while the contribution sea-ice algae and corallines was negligible (<1%). The pelagic grazing community was completely dominated by copepods, which were capable of consuming 87% of the pelagic primary production.
 The benthic carbon demand was almost balanced by the measured sedimentation of POC and the benthic primary production. The organic carbon collected in the sediment traps was estimated to consist of 40% terrestrial carbon, 20% fecal pellets, while the rest was poorly defined marine detritus. The benthic sink for settling organic material was dominated by microbial respiration (59%) and only to a minor extent related to macrofauna respiration (15%) and carbon preservation (26%).
 The total primary production in the region (1119 t C yr-1) only sustained c. 40% the estimated organic carbon demand (2850 t C yr-1). Thus, the independently determined input of TOC (990 t C yr-1) imported to Region 1 from land via freshwater runoff and the TOC import of 1446 t C yr-1 from the Greenland Sea are required to balance the carbon sinks of the net heterotrophic region. A complete balance between the respective compartments cannot be expected, as the various components of the carbon budget are determined independently. The microbial and viral loops remain poorly constrained, as does the carbon demand of the top predators. Only the importance of walrus was quantitatively assessed.

Soil organic carbon budget and fertility variation of black soils in Northeast China

AbstractBlack soils in Northeast China are characteristic of high soil organic carbon (SOC) density and were strongly influenced by human activities. Therefore, any change in SOC pool of these soils would not only impact the regional and global carbon cycle, but also affect the release and immobilization of nutrients. In this study, we reviewed the research progress on SOC storage, budget, variation, and fertility under different scenarios. The results showed that the organic carbon storage of black soils was 646.2 TgC and the most potential sequestration was 2887.8 g m−2. According to the SOC budget, the net carbon emission of black soils was 1.3 TgC year−1 under present soil management system. The simulation of CENTURY model showed that future climate change and elevated CO2 concentration, especially the increase of precipitation, would increase SOC content. Furthermore, fertilization and cropping sequence obviously influenced SOC content, composition, and allocation among different soil particles. Long‐term input of organic materials such as manure and straw renewed original SOC, improved soil structure and increased SOC accumulation. Besides, soil erosion preferred to transport soil particles with low density and fine size, decreased recalcitrant SOC fractions at erosion sites and increased activities of soil microorganism at deposition sites. After natural grasslands were converted into croplands, obvious variation of soil chemical nutrients, physical structure, and microbial activities had taken place in surface and subsurface soils, and represented a degrading trend to a certain degree. Our studies suggested that adopting optimal management such as conservation tillage in black soil region is an important approach to sequester atmospheric CO2 and to slow greenhouse effects.

Sunlight and tidal interaction as a mechanism of carbon transport in an ice-covered region: Results of a coupled ice–ocean ecosystem model

In order to clarify the mechanism of carbon transport in an ice-covered ecosystem in Lake Saroma ( 44 ∘ N , 143 ∘ E , Hokkaido, Japan), a three-dimensional numerical calculation using a coupled ice–ocean ecosystem model was conducted. This model comprises an ocean ecosystem model, an ice ecosystem model, and equations for the coupling between ice and ocean. Comparisons of calculated results with observational data confirm that the calculation well reproduced the in situ phenomena with respect to tides, tidal currents, concentrations of POC and chlorophyll a in ice and in water, and sinking fluxes beneath the ice. The analysis of the organic carbon budget based on the calculation reveals that tide-induced transport, the enhancement of biological production in a pelagic system, and the physical release of organic matter from ice associated with ice-melting are important factors affecting the carbon transport during the ice-melting season. The carbon transport has a one-day time cycle. This is because principal driving forces are sunlight, and diurnal tides. The described mechanism of “sunlight and tidal pumping” is one of the most important features of carbon transport in a coupled ice–water ecosystem.

Organic carbon budget for the Gulf of Bothnia

We calculated input of organic carbon to the unproductive, brackish water basin of the Gulf of Bothnia from rivers, point sources and the atmosphere. We also calculated the net exchange of organic carbon between the Gulf of Bothnia and the adjacent marine system, the Baltic Proper. We compared the input with sinks for organic carbon; permanent incorporation in sediments and mineralization and subsequent evasion of CO 2 to the atmosphere. The major fluxes were riverine input (1500 Gg C year − 1 ), exchange with the Baltic Proper (depending on which of several possible DOC concentration differences between the basins that was used in the calculation, the flux varied between an outflow of 466 and an input of 950 Gg C year − 1), sediment burial (1100 Gg C year − 1 ) and evasion to the atmosphere (3610 Gg C year − 1 ). The largest single net flux was the emission of CO 2 to the atmosphere, mainly caused by bacterial mineralization of organic carbon. Input and output did not match in our budget which we ascribe uncertainties in the calculation of the exchange of organic carbon between the Gulf of Bothnia and the Baltic Proper, and the fact that CO 2 emission, which in our calculation represented 1 year (2002) may have been overestimated in comparison with long-term means. We conclude that net heterotrophy of the Gulf of Bothnia was due to input of organic carbon from both the catchment and from the Baltic Proper and that the future degree of net heterotrophy will be sensible to both catchment export of organic carbon and to the ongoing eutrophication of the Baltic Proper.

An organic carbon budget for the Mississippi River turbidity plume and plume contributions to air-sea CO2 fluxes and bottom water hypoxia

We investigated seasonal variability in organic carbon (OC) budgets using a physical-biological model for the Mississippi River turbidity plume. Plume volume was calculated from mixed layer depth and area in each of four salinity subregions based on an extensive set of cruise data and satellite-derived suspended sediment distributions. These physical measurements were coupled with an existing food web model to determine seasonally dependent budgets for labile (reactive on time scales of days to weeks) OC in each salinity subregion. Autochthonous gross primary production (GPP) equaled 1.3×1012 g C yr−1 and dominated labile OC inputs (88% of the budget) because riverine OC was assumed mostly refractory (nonreactive). For perspective, riverine OC inputs amounted to 3.9×1012 g C yr−1, such that physical inputs were 3 times greater than biological inputs to the plume. Annually, microbial respiration (R) accounted for 65% of labile OC losses and net metabolism (GPP—R) for the entire plume was, autotrophic, equaling 5.1×1011 g C yr−1. Smaller losses of labile OC occurred via sedimentation (20%), advection (10%), and export to higher trophic levels (5%). In our present model, annual losses of labile OC are 10% higher than inputs, indicating future improvements are required. Application of our model to estimate air-sea carbon dioxide (CO2) fluxes indicated the plume was a net sink of 2.0×109 mol CO2 yr−1, of which 90% of the total drawdown was from biotic factors. In all seasons, low salinity waters were a source of CO2 (pCO2=560–890 μatm), and intermediate to high salinity waters were a sink of CO2 (pCO2=200–370 μatm). Our model was also used to calculate O2 demand for the development, of regional hypoxia, and our spring and early summer budgets indicated that sedimentation of autochthonous OC from the immediate plume contributed 23% of the O2 demand necessary for establishment of hypoxia in the region.

Fluxes and sources of particulate organic carbon in the Ganga‐Brahmaputra river system

Sources and fluxes of particulate organic carbon (OC) in the Ganga‐Brahmaputra river system were estimated from 13C/12C ratios of bedrocks, soils, bank and suspended river sediments from a Himalayan watershed (Narayani, Nepal), and the Bangladesh floodplain. In the watershed of the Narayani, OC δ13C values for bank and suspended sediments have similar values and narrow ranges, with a mean of about −24.2‰ at the base of the Himalayas. On the Bangladesh floodplain, bank and suspended sediments are enriched in 13C (δ13C about −22.5‰) relative to those collected at the base of the Himalayas. The OC exported at the base of the Himalayan range is estimated to include about 15% from the 13C enriched C4 biomass while the C4 contribution is about 25% of the OC exported by the Ganga and Brahmaputra. A calculated total OC flux of 0.65 × 1012 molC yr−1 is exported to the ocean or trapped in the plain. In sediments of the Ganga and Brahmaputra, the clay‐size fraction is depleted in 13C (<2.6‰) relative to the bulk sediment. Possible explanations are that either the organic matter associated with clays is largely inherited from the Himalayan watersheds, or, and considered more likely, the clays and coarser sediments sample different OC pools, possibly with different ages (the growth of C4 crops has dramatically increased since the mid twentieth century), on the floodplain. The OC budget of the actual Ganga‐Brahmaputra system is broadly comparable to that derived from the Quaternary sediments of the Bengal fan that represents about 10% of the global OC contribution to the continental margins.

Budget of organic carbon in a polluted atmosphere: Results from the New England Air Quality Study in 2002

An extensive set of volatile organic compounds (VOCs) and particulate organic matter (POM) was measured in polluted air during the New England Air Quality Study in 2002. Using VOC ratios, the photochemical age of the sampled air masses was estimated. This approach was validated (1) by comparing the observed rates at which VOCs were removed from the atmosphere with the rates expected from OH oxidation, (2) by comparing the VOC emission ratios inferred from the data with the average composition of urban air, and (3) by the ability to describe the increase of an alkyl nitrate with time in terms of the chemical kinetics. A large part of the variability observed for oxygenated VOCs (OVOCs) and POM could be explained by a description that includes the removal of the primary anthropogenic emissions, the formation and removal of secondary anthropogenic species, and a biogenic contribution parameterized by the emissions of isoprene. The OVOC sources determined from the data are compared with the available literature, and a satisfactory agreement is obtained. The observed sub‐μm POM was highly correlated with secondary anthropogenic gas‐phase species, strongly suggesting that the POM was from secondary anthropogenic sources. The results are used to describe the speciation and total mass of gas‐ and particle‐phase organic carbon as a function of the photochemical age of an urban air mass. Shortly after emission the organic carbon mass is dominated by primary VOCs, while after two days the dominant contribution is from OVOCs and sub‐μm POM. The total measured organic carbon mass decreased by about 40% over the course of two days. The increase in sub‐μm POM could not be explained by the removal of aromatic precursors alone, suggesting that other species must have contributed and/or that the mechanism for POM formation is more efficient than previously assumed.

A contemporary sediment and organic carbon budget for the Kara Sea shelf (Siberia)

It has recently been realized that the Arctic undergoes drastic changes, probably resulting from global change induced processes. This acts on the cycling of matter and on biogenic elements in the Arctic Ocean having feedback mechanisms with the global climate, for example by interacting with atmospheric trace gas concentration. A contemporary budget for biogenic elements as well as suspended matter for the Arctic Ocean as a baseline for comparison with effects of further global change is, thus, needed. Available budgets are based on the late Holocene sedimentary record and are therefore quiet different from the present which has already been affected by the intense anthropogenic activity of the last centuries. We calculated a contemporary suspended matter and organic carbon budget for the Kara Sea utilizing the numerous available data from the recent literature as well as our own data from Russian-German SIRRO (Siberian River Run-off) expeditions. For calculation of the budgets we used a multi-box model to simplify the Kara Sea shelf and estuary system: input was assumed to comprise riverine and eolian input as well as coastal erosion, output was assumed to consist of sedimentation and export to the Arctic Ocean. Exchange with the adjacent seas was considered in our budget, and primary production as well as recycling of organic material was taken into account. According to our calculations, about 18.5 × 10 6 t yr − 1 of sediments and 0.37 × 10 6 t yr − 1 of organic carbon are buried in the estuaries, whereas 20.9 × 10 6 t yr − 1 sediment and 0.31 × 10 6 t yr − 1 organic carbon are buried on the shelf. Most sources and sinks of our organic carbon budget of the Kara Sea are in the same order of magnitude, making it a region very sensitive to further changes.