Measurements of Seasonal Rates and Annual Budgets of Organic Carbon Fluxes in an Antarctic Coastal Environment at Signy Island, South Orkney Islands, Suggest a Broad Balance between Production and Decomposition

We report here the first comprehensive seasonal study of benthic microbial activity in an Antarctic coastal environment. Measurements were made from December 1990 to February 1992 of oxygen uptake and sulfate reduction by inshore coastal sediments at Signy Island, South Orkney Islands, Antarctica. From these measurements the rate of benthic mineralization of organic matter was calculated. In addition, both the deposition rate of organic matter to the bottom sediment and the organic carbon content of the bottom sediment were measured during the same period. Organic matter input to the sediment was small under winter ice cover, and the benthic respiratory activity and the organic content of the surface sediment declined during this period as available organic matter was depleted. On an annual basis, about 32% of benthic organic matter mineralization was anoxic, but the proportion of anoxic compared with oxic mineralization increased during the winter as organic matter was increasingly buried by the amphipod infauna. Fresh organic input occurred as the sea ice melted and ice algae biomass sedimented onto the bottom, and input was sustained during the spring after ice breakup by continued primary production in the water column. The benthic respiratory rate and benthic organic matter content correspondingly increased towards the end of winter with the input of this fresh organic matter. The rates of oxygen uptake during the southern summer (80 to 90 mmol of O₂ m^-2 day^-1) were as high as those reported for other sediments at much higher environmental temperatures, and the annual mineralization of organic matter was equally high (12 mol of C m^-2 year^-1). Seasonal variations of benthic activity in this antarctic coastal sediment were regulated by the input and availability of organic matter and not by seasonal water temperature, which was relatively constant at between -1.8 and 0.5°C. We conclude that despite the low environmental temperature, organic matter degradation broadly balanced organic matter production, although there may be significant interrannual variations in the sources of the organic matter inputs.     

Benthic fauna bio-irrigation effects on nutrient regeneration in fish farm sediments

Impacts of organic enrichment and a modified benthic fauna community (caused by fish farming) on benthic mineralization rates and nutrient cycling were studied in sediments at one Danish and one Cypriote fish farm. Sediment organic matter concentration and macrofauna community composition were manipulated in microcosms and changes in total benthic metabolism (oxygen consumption, TCO₂ production), anaerobic metabolism (sulfate reduction rates), nutrient fluxes and sediment parameters were followed for a period of 3 weeks. Mineralization rates were found to be highly correlated with irrigation velocities and largest fauna effects were found in the Danish sediments with the large and active irrigating climax species (Nereis diversicolor and Macoma balthica). Eastern Mediterranean climax species (Glycera rouxii and Naineris laevigata) also stimulated mineralization rates but to a smaller extent due to lower irrigation, whereas the opportunistic species (Capitella in Danish sediment and Hermodice carunculata in Cypriote sediment) showed less effect on mineralization. Ammonium and phosphate release increased with increasing irrigation velocities, but much less in Cyprus indicating higher nutrient retention at the ultra-oligotrophic location compared to eutrophic Danish site. Irrigation velocities, and thus mineralization rates, increased by organic matter loading, indicating larger fauna-induced oxidation in enriched environments. The result implies that a change in fauna structure in fish farm sediment towards smaller opportunistic polychaete species with lower irrigation will result in slower mineralization rates and potentially increase accumulation of organic waste products.     

Biogeochemical processes in the groundwater discharge zone of urban streams

The influence of biogeochemical processes on nitrogen and organic matter transformation and transport was investigated for two urban streams receiving groundwater discharge during the dry summer baseflow period. A multiple lines of evidence approach involving catchment-, and stream reach-scale investigations were undertaken to describe the factors that influence pore water biogeochemical processes. At the catchment-scale gaining stream reaches were identified from water table mapping and groundwater discharge estimated to be between 0.1 and 0.8 m³ m^?2 d^?1 from baseflow analysis. Sediment temperature profiles also suggested that the high groundwater discharge limited stream water infiltration into the sediments. At the stream reach-scale, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations were higher in stream water than in groundwater. However, DOC and DON concentrations were greatest in sediment pore water. This suggests that biodegradation of sediment organic matter contributes dissolved organic matter (DOM) to the streams along with that delivered with groundwater flow. Pore water ammonium (NH₄ ⁺) was closely associated with areas of high pore water DOM concentrations and evidence of sulfate (SO₄ ^2?) reduction (low concentration and SO₄:Cl ratio). This indicates that anoxic DOM mineralization was occurring associated with SO₄ ^2? reduction. However the distribution of anoxic mineralization was limited to the center of the streambed, and was not constrained by the distribution of sediment organic matter which was higher along the banks. Lower sediment temperatures measured along the banks compared to the center suggests, at least qualitatively, that groundwater discharge is higher along the banks. Based on this evidence anoxic mineralization is influenced by groundwater residence time, and is only measurable along the center of the stream where groundwater flux rates are lower. This study therefore shows that the distribution of biogeochemical processes in stream sediments, such as anoxic mineralization, is strongly influenced by both the biogeochemical conditions and pore water residence time.     

Effects of coral reef benthic primary producers on dissolved organic carbon and microbial activity

Benthic primary producers in marine ecosystems may significantly alter biogeochemical cycling and microbial processes in their surrounding environment. To examine these interactions, we studied dissolved organic matter release by dominant benthic taxa and subsequent microbial remineralization in the lagoonal reefs of Moorea, French Polynesia. Rates of photosynthesis, respiration, and dissolved organic carbon (DOC) release were assessed for several common benthic reef organisms from the backreef habitat. We assessed microbial community response to dissolved exudates of each benthic producer by measuring bacterioplankton growth, respiration, and DOC drawdown in two-day dark dilution culture incubations. Experiments were conducted for six benthic producers: three species of macroalgae (each representing a different algal phylum: Turbinaria ornata – Ochrophyta; Amansia rhodantha – Rhodophyta; Halimeda opuntia – Chlorophyta), a mixed assemblage of turf algae, a species of crustose coralline algae (Hydrolithon reinboldii) and a dominant hermatypic coral (Porites lobata). Our results show that all five types of algae, but not the coral, exuded significant amounts of labile DOC into their surrounding environment. In general, primary producers with the highest rates of photosynthesis released the most DOC and yielded the greatest bacterioplankton growth; turf algae produced nearly twice as much DOC per unit surface area than the other benthic producers (14.0±2.8 µmol h⁻¹ dm⁻²), stimulating rapid bacterioplankton growth (0.044±0.002 log10 cells h⁻¹) and concomitant oxygen drawdown (0.16±0.05 µmol L⁻¹ h⁻¹ dm⁻²). Our results demonstrate that benthic reef algae can release a significant fraction of their photosynthetically-fixed carbon as DOC, these release rates vary by species, and this DOC is available to and consumed by reef associated microbes. These data provide compelling evidence that benthic primary producers differentially influence reef microbial dynamics and biogeochemical parameters (i.e., DOC and oxygen availability, bacterial abundance and metabolism) in coral reef communities.     

Soil organic matter quality influences mineralization and GHG emissions in cryosols: a field‐based study of sub‐ to high Arctic

Arctic soils store large amounts of labile soil organic matter (SOM) and several studies have suggested that SOM characteristics may explain variations in SOM cycling rates across Arctic landscapes and Arctic ecosystems. The objective of this study was to investigate the influence of routinely measured soil properties and SOM characteristics on soil gross N mineralization and soil GHG emissions at the landscape scale. This study was carried out in three Canadian Arctic ecosystems: Sub‐Arctic (Churchill, MB), Low‐Arctic (Daring Lake, NWT), and High‐Arctic (Truelove Lowlands, NU). The landscapes were divided into five landform units: (1) upper slope, (2) back slope, (3) lower slope, (4) hummock, and (5) interhummock, which represented a great diversity of Static and Turbic Cryosolic soils including Brunisolic, Gleysolic, and Organic subgroups. Soil gross N mineralization was measured using the ¹⁵N dilution technique, whereas soil GHG emissions (N₂O, CH₄, and CO₂) were measured using a multicomponent Fourier transform infrared gas analyzer. Soil organic matter characteristics were determined by (1) water‐extractable organic matter, (2) density fractionation of SOM, and (3) solid‐state CPMAS ¹³C nuclear magnetic resonance (NMR) spectroscopy. Results showed that gross N mineralization, N₂O, and CO₂ emissions were affected by SOM quantity and SOM characteristics. Soil moisture, soil organic carbon (SOC), light fraction (LF) of SOM, and O‐Alkyl‐C to Aromatic‐C ratio positively influenced gross N mineralization, N₂O and CO₂ emissions, whereas the relative proportion of Aromatic‐C negatively influenced those N and C cycling processes. Relationships between SOM characteristics and CH₄ emissions were not significant throughout all Arctic ecosystems. Furthermore, results showed that lower slope and interhummock areas store relatively more labile C than upper and back slope locations. These results are particularly important because they can be used to produce better models that evaluate SOM stocks and dynamics under several climate scenarios and across Arctic landscapes and ecosystems.     

Reassessing the nitrogen relations of Arctic plants: a mini-review

The Arctic is often assumed to be an NH₄⁺-dominated ecosystem. This review assesses the validity of this assumption. It also addresses the question of whether Arctic plant growth is limited by the ability to use the forms of nitrogen that are available. The review demonstrates that several sources of soil nitrogen are available to Arctic plants, including soluble organic nitrogen (e.g. glycine, aspartic acid and glutamic acid), NH₄⁺ and NO^?₃. In mesic Arctic soils, soluble organic nitrogen is potentially more important than either NH⁺₄ or NO^?₃. Many Arctic species are capable of taking up soluble organic nitrogen (either directly and/or in association with ectomycorrhizae), with the greatest potential for soluble organic nitrogen uptake being exhibited by deciduous species. The ability to take up soluble organic nitrogen may enable some Arctic plants to avoid nitrogen limitations imposed by the slow rate of organic matter decomposition. NO^?₃ is also present in many Arctic soils, especially calcareous soils and soils near flowing water, animal burrows and bird cliffs. Arctic species characteristic of mesic and xeric habitats are capable of taking up and assimilating NO^?₃. Even when present in lower concentrations in soils than NH⁺₄, NO^?₃ is still an important source of nitrogen for some Arctic plants. Arctic-plants therefore have a variety of nitrogen sources available to them, and are capable of using those nitrogen sources. Taken together, these findings demonstrate that the Arctic is not an NH⁺₄dominated ecosystem. Symbiotic fixation of atmospheric N₂ does not appear to be an important source of nitrogen for Arctic plants. The reliance of Arctic plants on internal recycling of nitrogen substantially reduces their dependence on soil nitrogen uptake (this is particularly the case for slow-growing evergreens). Despite the high level of internal nitrogen recycling, Arctic plant growth remains limited by the low levels of available soil nitrogen. However, Arctic plant growth is not limited by an inability to utilize any of the available forms of nitrogen. The potential effects of climatic warming on nitrogen availability and use are discussed. The question of whether the Arctic ecosystem is uniquely different from temperate nitrogen-deficient ecosystems is also assessed.     

Evidence for a pan-Arctic sea-ice diatom diet in Strongylocentrotus spp

The Arctic marine food web is based on organic matter produced by both phytoplankton and sea-ice algae. With the decline of Arctic sea ice, the sustained availability of organic carbon of sea-ice origin is unclear. Recently, the detection of the sea-ice diatom biomarker IP₂₅ in a range of Arctic benthic macrofauna indicated that this is a highly suitable biomarker for the identification of organic carbon derived from sea-ice primary production in Arctic food webs. However, the data presented previously were restricted to a single geographical region in the Canadian Arctic. Here, we show that IP₂₅ is present in sea urchins of the genus Strongylocentrotus collected from ten locations with seasonal sea-ice cover from the Canadian Archipelago, Greenland and Spitsbergen. In contrast, IP₂₅ was not found in specimens of Echinus esculentus collected from the southwest UK, where sea ice is absent. Our findings provide evidence that the presence of IP₂₅ in macrobenthic organisms can be used across different Arctic regions as a versatile indicator of a diet containing carbon of sea-ice origin.     

Sensitivity of Heterogeneous Marine Benthic Habitats to Subtle Stressors

It is important to understand the consequences of low level disturbances on the functioning of ecological communities because of the pervasiveness and frequency of this type of environmental change. In this study we investigated the response of a heterogeneous, subtidal, soft-sediment habitat to small experimental additions of organic matter and calcium carbonate to examine the sensitivity of benthic ecosystem functioning to changes in sediment characteristics that relate to the environmental threats of coastal eutrophication and ocean acidification. Our results documented significant changes between key biogeochemical and sedimentary variables such as gross primary production, ammonium uptake and dissolved reactive phosphorus flux following treatment additions. Moreover, the application of treatments affected relationships between macrofauna communities, sediment characteristics (e.g., chlorophyll a content) and biogeochemical processes (oxygen and nutrient fluxes). In this experiment organic matter and calcium carbonate showed persistent opposing effects on sedimentary processes, and we demonstrated that highly heterogeneous sediment habitats can be surprisingly sensitive to subtle perturbations. Our results have important biological implications in a world with relentless anthropogenic inputs of atmospheric CO₂ and nutrients in coastal waters.     

Metazoan meiofauna dynamics and pelagic–benthic coupling in the Southeastern Beaufort Sea,Arctic Ocean

Pelagic–benthic coupling is relatively well studied in the marginal seas of the Arctic Ocean. Responses of meiofauna with regard to seasonal pulses of particulate organic matter are, however, rarely investigated. We examined the dynamics of metazoan meiofauna and assessed the strength of pelagic–benthic coupling in the Southeastern Beaufort Sea, during autumn 2003 and spring–summer 2004. Meiofauna abundance varied largely (range: 2.3 × 10⁵ to 5 × 10⁶ ind m⁻²), both spatially and temporally, and decreased with increasing depth (range: 24–549 m). Total meiofauna biomass exhibited similar temporal as well as spatial patterns as abundance and varied from 25 to 914 mg C m⁻². Significant relationships between sediment photopigments and various representatives of meiofauna in summer and autumn likely indicate the use of sediment phytodetritus as food source for meiofauna. A carbon-based grazing model provided estimates of potential daily ingestion rates ranging from 32 to 723 mg C m⁻². Estimated potential ingestion rates showed that meiofauna consumed from 11 to 477% of the sediment phytodetritus and that meiofauna were likely not food-restricted during spring and autumn. These results show that factors governing the distribution and abundance of metazoan meiofauna need to be better elucidated if we are to estimate the benthic carbon fluxes in marginal seas of the Arctic Ocean. This paper is dedicated to the memory of our dear friend and colleague Gaston Desrosiers who contributed so much to benthic ecology. We will continue in his spirit.     

Identification of the sea ice diatom biomarker IP25 in Arctic benthic macrofauna: direct evidence for a sea ice diatom diet in Arctic heterotrophs

Currently, the impact of declining seasonal sea ice extent in the Arctic on polar food webs remains uncertain. Previously, a range of proxy techniques has been employed to determine links between sea ice or phytoplankton primary production and the Arctic marine food web, although it is accepted that such approaches have their limitations. Here, we propose a novel approach to tracing sea ice primary production through Arctic food webs using the sea ice diatom biomarker, IP₂₅. Various benthic macrofaunal specimens were collected between March and May 2008 from Franklin Bay in the Amundsen Gulf, Arctic Canada, as part of the International Polar Year–Circumpolar Flaw Lead system study. Each specimen was analysed for the presence of the sea ice diatom biomarker IP₂₅ in order to provide evidence for feeding by benthic organisms on sea ice algae. IP₂₅ was found in nineteen out of the twenty-one specimens analysed, often as the most abundant of the highly branched isoprenoid biomarkers detected. The stable isotope composition of IP₂₅ (δ¹³C = −17.1 ± 0.5‰) in the sea urchin (Strongylocentrotus sp.) specimens was similar to that reported previously for this biomarker in Arctic sea ice, sedimenting particles and sediments. It is concluded that detection of IP₂₅ in Arctic benthic macrofauna represents a novel approach to providing convincing evidence for feeding on sea ice algae. It is also proposed that analysis of IP₂₅ may be used to trace trophic transfer of sea ice algal-derived organic matter through Arctic food webs in the future.     

Oxygen respiration rates of benthic foraminifera as measured with oxygen microsensors

Oxygen respiration rates of benthic foraminifera are still badly known, mainly because they are difficult to measure. Oxygen respiration rates of seventeen species of benthic foraminifera were measured using microelectrodes and calculated on the basis of the oxygen fluxes measured in the vicinity of the foraminiferal specimens. The results show a wide range of oxygen respiration rates for the different species (from 0.09 to 5.27 nl cell⁻¹ h⁻¹) and a clear correlation with foraminiferal biovolume showed by the power law relationship: R = 3.98 10⁻³ BioVol^0.88 where the oxygen respiration rate (R) is expressed in nl O₂ h⁻¹ and in μm³ biovolume (BioVol) (n = 44, R² = 0.72, F = 114, p < 0.0001). The results expressed per biovolume unit (1.82 to 15.7 nl O₂ 10⁻⁸ μm⁻³ h⁻¹) allow us to compare our data with the previous published data showing similar ranges. A comparison with available data for other microbenthos groups (nematodes, copepods, ostracods, ciliates and flagellates) suggests that benthic foraminifera have a lower oxygen respiration rates per unit biovolume. The total contribution of benthic foraminifera to the aerobic mineralisation of organic matter is estimated for the studied areas. The results suggest that benthic foraminifera play only a minor role (0.5 to 2.5%) in continental shelf environments, which strongly contrasts with their strong contribution to anaerobic organic matter mineralisation, by denitrification, in the same areas.     

Ethological analysis of the trace fossil Zoophycos: hints from the Arctic Ocean

Löwemark, L. 2011: Ethological analysis of the trace fossil Zoophycos: Hints from the Arctic Ocean. Lethaia, Vol. 45, pp. 290–298. The distribution of the trace fossil Zoophycos in Quaternary marine sediments from the Arctic Ocean was studied in twelve piston and gravity cores retrieved during the Swedish icebreaker expeditions YMER80, Arctic Ocean‐96 and LOMROG I & II. The sampled cores span an area from the Makarov Basin to the Fram Strait. Zoophycos was only found in two cores taken at more than 2 km water depth on the slope of the Lomonosov Ridge, but was absent in cores obtained at shallower depth, confirming earlier observations of the trace maker’s bathymetric preferences. The two cores containing Zoophycos are characterized by quiet sedimentation and slightly enhanced food flux compared with the general Arctic. The occurrence of Zoophycos in these cores in a setting that is characterized by extreme seasonal variations in food flux due to the total ice coverage during winters and high primary productivity during the long summer days, is interpreted to be a cache‐behaviour response to pulsed flux of food to the benthic realm. □Arctic Ocean, ethology, Quaternary, spreiten, trace fossils, Zoophycos.     

Benthic infaunal community variability on the northern Svalbard shelf

Marine benthic communities are effective indicators of environmental change. Yet in the Arctic, there are few empirical tests of how sustained climatic change may influence community structure. Northern Svalbard is influenced by both warm Atlantic and cold Arctic water masses, providing an opportunity to assess potential effects of long-term environmental changes by examining spatial variation in community structure. We examined benthic macroinfaunal communities and sediment pigments under Atlantic and Arctic water masses on the northern shelf and fjords of Svalbard. We report on infaunal biomass, abundance, species composition, and diversity at 10 stations spanning 79°–81°N and ranging in depth from 200 to 500?m. Benthic biomass averaged 128?g?WW?m^?2 (48–253?g?WW?m^?2), mean density was 3,635?ind.?m^?2 (780–7,660?ind.?m^?2), and species richness varied from 45 to 136?taxa?stn.^?1. Abundance-based community structure clustered stations in groups related to water mass characteristics, with Atlantic and Arctic shelf stations being well distinguished from each other. Dominant taxa were different in Atlantic- and Arctic-influenced locations. Faunal biomass was highest in the Atlantic-influenced fjords, followed by Arctic fjords and Arctic shelf stations, with Atlantic shelf stations having the lowest biomass. Species richness and diversity were inversely related to biomass. Patterns in faunal biomass were strongly correlated with sedimentary pigments (R ²?=?0.74 for chl a and R ²?=?0.77 for phaeopigments), with large differences in sedimentary pigment concentration among stations. These relationships suggest that benthic fauna on the northern Svalbard shelf are food limited and dependent on predictable, albeit episodic, delivery of organic matter from the water column.     

Deposit-Feeding Sea Cucumbers Enhance Mineralization and Nutrient Cycling in Organically-Enriched Coastal Sediments

Background

Bioturbators affect multiple biogeochemical interactions and have been suggested as suitable candidates to mitigate organic matter loading in marine sediments. However, predicting the effects of bioturbators at an ecosystem level can be difficult due to their complex positive and negative interactions with the microbial community.

Methodology/Principal Findings

We quantified the effects of deposit-feeding sea cucumbers on benthic algal biomass (microphytobenthos, MPB), bacterial abundance, and the sediment–seawater exchange of dissolved oxygen and nutrients. The sea cucumbers increased the efflux of inorganic nitrogen (ammonium, NH₄ ⁺) from organically enriched sediments, which stimulated algal productivity. Grazing by the sea cucumbers on MPB (evidenced by pheopigments), however, caused a net negative effect on primary producer biomass and total oxygen production. Further, there was an increased abundance of bacteria in sediment with sea cucumbers, suggesting facilitation. The sea cucumbers increased the ratio of oxygen consumption to production in surface sediment by shifting the microbial balance from producers to decomposers. This shift explains the increased efflux of inorganic nitrogen and concordant reduction in organic matter content in sediment with bioturbators.

Conclusions/Significance

Our study demonstrates the functional role and potential of sea cucumbers to ameliorate some of the adverse effects of organic matter enrichment in coastal ecosystems.     

The barnacles (Cirripedia: Thoracica) collected by the Viking expedition in chemobiotic benthic communities of the Norwegian and Barents Seas

The barnacles (Cirripedia Thoracica) collected by the Viking expedition in chemobiotic benthic communities of Arctic Ocean-Nyegga area in Norwegian Sea and Håkon Mosby Mud Volcano area in the Barents Sea are investigated. The species (Weltnerium nymphocola in Håkon Mosby Mud Volcano area and Hamatoscalpellum hamatum in Nyegga area) that were found are common inhabitants of the Barents and Norwegian sea benthic communities. The absence of obligatory barnacle fauna that was revealed in investigated chemobiotic benthic communities of the Arctic Ocean shows they are similar to corresponding communities of the Atlantic Ocean, while the specific obligatory barnacle fauna is noted for chemobiotic benthic communities of the Pacific and Indian oceans.     

Glacial Holocene environment of the southeastern Okhotsk Sea: evidence from geochemical and palaeontological data

Environmental conditions and productivity changes in the southeastern Okhotsk Sea have been reconstructed for the last 20 ka using planktonic and benthic foraminiferal oxygen isotope records and calcium carbonate, organic carbon and opal content data from two sediment cores. Species variability in benthic foraminiferal and diatom assemblages provides additional palaeoceanographic evidence. AMS radiocarbon dating of the sediments and oxygen isotope stratigraphy serve as the basis for the age models of the cores for the last 20 ¹⁴C kyr and for correlation between environmental variations in the Okhotsk Sea, and regional and global climate changes. Benthic foraminiferal assemblages in the two cores (depth 1590 and 1175 m) varied with time, so that we could recognise seven zones with different species composition. Changes in the benthic foraminiferal assemblages parallel major environmental and productivity variations. During the last glaciation, fluxes of organic matter to the sea floor showed strong seasonal variations, indicated by the presence of abundant A. weddellensis and infaunal Uvigerina spp. Benthic foraminiferal assemblages changed with warming at 12.5–11 and 10–8 ¹⁴C kyr BP, when productivity blooms and high organic fluxes were coeval with global meltwater pulses 1A and 1B. Younger Dryas cooling caused a decline in productivity (11–10 kyr BP) affecting the benthic faunal community. Subsequent warming triggered intensive diatom production, opal accumulation and a strong oxygen deficiency, causing significant changes in benthic fauna assemblages from 5.26–4.4 kyr BP to present time.     

The impact of ice melting on bacterioplankton in the Arctic Ocean

Global warming and the associated ice melt are leading to an increase in the organic carbon in the Arctic Ocean. We evaluated the effects of ice melt on bacterioplankton at 21 stations in the Greenland Sea and Arctic Ocean in the summer of 2007, when a historical minimum of Arctic ice coverage was measured. Polar Surface Waters, which have a low temperature and low salinity and originate mainly from melted ice, contained a very low abundance of bacteria (7.01 × 10⁵ ± 2.20 × 10⁵ cells ml⁻¹); however, these bacteria had high specific bacterial production (2.40 ± 1.61 fmol C bac⁻¹ d⁻¹) compared to those in Atlantic Waters. Specifically, bacterioplankton in Polar Surface Waters showed a preference for utilizing carbohydrates and had significantly higher specific activities of the glycosidases assayed, i.e. β-glucosidase, xylosidase, arabinosidase and cellobiosidase. Furthermore, bacterioplankton in Polar Sea Waters showed preferential growth on some of the carbohydrates in the Biolog Ecoplate, such as d-cellobiose and N-acetyl-d-glucosamine. Our results suggest that climate change and the associated melting of Arctic ice might induce changes in bacterioplankton functional diversity by enhancing the turnover of carbohydrates. Since organic aggregates are largely composed of polysaccharides, higher solubilization of aggregates might modify the carbon cycle, weaken the biological pump and have biogeochemical and ecological implications for the future Arctic Ocean.     

Predicting long‐term carbon mineralization and trace gas production from thawing permafrost of Northeast Siberia

The currently observed Arctic warming will increase permafrost degradation followed by mineralization of formerly frozen organic matter to carbon dioxide (CO₂) and methane (CH₄). Despite increasing awareness of permafrost carbon vulnerability, the potential long‐term formation of trace gases from thawing permafrost remains unclear. The objective of the current study is to quantify the potential long‐term release of trace gases from permafrost organic matter. Therefore, Holocene and Pleistocene permafrost deposits were sampled in the Lena River Delta, Northeast Siberia. The sampled permafrost contained between 0.6% and 12.4% organic carbon. CO₂ and CH₄ production was measured for 1200 days in aerobic and anaerobic incubations at 4 °C. The derived fluxes were used to estimate parameters of a two pool carbon degradation model. Total CO₂ production was similar in Holocene permafrost (1.3 ± 0.8 mg CO₂‐C gdw^?1 aerobically, 0.25 ± 0.13 mg CO₂‐C gdw^?1 anaerobically) as in 34 000–42 000‐year‐old Pleistocene permafrost (1.6 ± 1.2 mg CO₂‐C gdw^?1 aerobically, 0.26 ± 0.10 mg CO₂‐C gdw^?1 anaerobically). The main predictor for carbon mineralization was the content of organic matter. Anaerobic conditions strongly reduced carbon mineralization since only 25% of aerobically mineralized carbon was released as CO₂ and CH₄ in the absence of oxygen. CH₄ production was low or absent in most of the Pleistocene permafrost and always started after a significant delay. After 1200 days on average 3.1% of initial carbon was mineralized to CO₂ under aerobic conditions while without oxygen 0.55% were released as CO₂ and 0.28% as CH₄. The calibrated carbon degradation model predicted cumulative CO₂ production over a period of 100 years accounting for 15.1% (aerobic) and 1.8% (anaerobic) of initial organic carbon, which is significantly less than recent estimates. The multiyear time series from the incubation experiments helps to more reliably constrain projections of future trace gas fluxes from thawing permafrost landscapes.     

Contribution of the polychaete,Neanthes japonica (Izuka), to the oxygen uptake and carbon dioxide production of an intertidal mud-flat of the Nanakita River estuary,Japan

The benthic oxygen consumption and carbon dioxide production of undisturbed and sieved sediment cores with various values for the biomass of polychaetes collected from the intertidal mud-flat of Nanakita River estuary of Japan were measured simultaneously. The benthic oxygen consumption and carbon dioxide production increased in proportion to the biomass of a dominant polychaete species Neanthes japonica (Izuka). This increase was not explained by the respiration of the animals alone. The residual increase in benthic O₂ and CO₂ fluxes may be due to mineralization processes in the burrow wall and enhanced diffusion caused by the pumping activity of the worms. From the average biomass of polychaetes at the study site, total benthic O₂ and CO₂ fluxes were estimated to be 5.2 mmol·m⁻²·h⁻¹ and 7.3 mmol·m⁻²·h⁻¹, respectively, at 20 ° C. The worms were responsible for 79% of the total O₂ flux and 73% of the total CO₂ flux but the respiration of the worms accounted for only 53% of the total O₂ flux and 36% of the total CO₂ flux. The residual enhanced fluxes were 26% and 37% for the total O₂ and CO₂ fluxes, respectively.     

Annual cycles of benthic community oxygen uptake in a deep oligotrophic lake (Attersee,Austria)

Benthic community oxygen uptake of Lake Attersee sediments was measured between 1976 and 1979, along two profiles at 25, 50 and 100 m depth. Profile I was situated in the bay of Unterach into which the main tributary, Mondsee-Ache, discharges a high load of organic matter. Profile II was chosen at Weyregg to avoid the eutrophying effect of Mondsee-Ache. Oxygen uptake rates of Unterach sediments at 25 and 50 m depth were found to be higher when compared to the other sites (mean rates: Unterach 25 m = 15.56, 50 m = 11.05 mg O₂ · m⁻² · h⁻¹; Weyregg 25 m = 6.43, 50 m = 5.14 mg O₂ · m⁻² · h⁻¹). Organic content of the uppermost sediment layer was also higher in the bay of Unterach than at Weyregg. Oxygen uptake rates of undisturbed sediment cores vary considerably throughout the year, but no simple correlation existed with variations in organic content of the sediments. Peaks of organic matter were found to concur with following peaks of oxygen uptake rates, which implies that a certain time span is necessary for transforming freshly sedimented organic matter into a state digestable for the benthic community. The retardation between increasing organic matter of the sediment and the corresponding increase of benthic oxygen uptake was different at Unterach and Weyregg respectively, which is explained by the different quality of sedimenting material.