ALBERT

Description: Not all calcite ballast is created equal: differing effects of foraminiferan and coccolith calcite on the formation and sinking of aggregates Biogeosciences Discussions, 10, 14861-14885, 2013 Author(s): K. Schmidt, C. L. De La Rocha, M. Gallinari, and G. Cortese Correlation between particulate organic carbon (POC) and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium carbonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the different effects on the aggregation and sinking of POC of small, non-sinking calcite particles like coccoliths and large, rapidly sinking calcite like planktonic foraminiferan tests. We have done that here in a simple experiment carried out in roller tanks that allow particles to sink continuously without being impeded by container walls. Coccoliths were efficiently incorporated into aggregates that formed during the experiment, increasing their sinking speed compared to similarly sized aggregates lacking added calcite ballast. The foraminiferan tests, which sank as fast as 700 m d −1 , became associated with only very minor amounts of POC. In addition, when they collided with other, larger, foraminferan-less aggregates, they fragmented them into two smaller, more slowly sinking aggregates. While these effects were certainly exaggerated within the confines of the roller tanks, they clearly demonstrate that calcium carbonate ballast is not just calcium carbonate ballast- different forms of calcium carbonate ballast have notably different effects on POC aggregation, sinking, and export.

Description: Phenology as a strategy for carbon optimality: a global model Biogeosciences Discussions, 10, 15107-15152, 2013 Author(s): S. Caldararu, D. W. Purves, and P. I. Palmer Phenology is essential to our understanding of biogeochemical cycles and the climate system. We develop a global mechanistic model of leaf phenology based on the hypothesis that phenology is a strategy for optimal carbon gain at the canopy level so that trees adjust leaf gains and losses in response to environmental factors such as light, temperature and soil moisture, to achieve maximum carbon assimilation. We fit this model to five years of satellite observations of leaf area index (LAI) using a Bayesian fitting algorithm. We show that our model is able to reproduce phenological patterns for all vegetation types and use it to explore variations in growing season length and the climate factors that limit leaf growth for different biomes. Phenology in wet tropical areas is limited by leaf age physiological constraints while at higher latitude leaf seasonality is limited by low temperature and light availability. Leaf growth in grassland regions is limited by water availability but often in combination with other factors. This model will advance the current understanding of phenology for ecosystem carbon models and our ability to predict future phenological behaviour.

Description: Timing of sea ice retreat can alter phytoplankton community structure in the western Arctic Ocean Biogeosciences Discussions, 10, 15153-15180, 2013 Author(s): given_name prefix surname suffix, A. Fujiwara, T. Hirawake, K. Suzuki, I. Imai, and S.-I. Saitoh This study assesses the response of phytoplankton assemblages to recent climate change, especially with regard to the shrinking of sea ice in the northern Chukchi Sea of the western Arctic Ocean. Distribution patterns of phytoplankton groups in the late summers of 2008–2010 were analyzed based on HPLC pigment signatures and, the following four major algal groups were inferred via multiple regression and cluster analyses: prasinophytes, diatoms, haptophytes and dinoflagellates. A remarkable interannual difference in the distribution pattern of the groups was found in the northern basin area. Haptophytes dominated and dispersed widely in warm surface waters in 2008, whereas prasinophytes dominated in cold water in 2009 and 2010. A difference in the onset date of sea ice retreat was evident among years – the sea ice retreat in 2008 was 1–2 months earlier than in 2009 and 2010. The spatial distribution of early sea ice retreat matched the areas in which a shift in algal community composition was observed. Steel-Dwass's multiple comparison tests were used to assess the physical, chemical and biological parameters of the four clusters. We found a statistically significant difference in temperature between the haptophyte-dominated cluster and the other clusters, suggesting that the change in the phytoplankton communities was related to the earlier sea ice retreat in 2008 and the corollary increase in sea surface temperatures. Longer periods of open water during the summer, which are expected in the future, may affect food webs and biogeochemical cycles in the western Arctic due to shifts in phytoplankton community structure.

Description: Uptake of phytodetritus by benthic foraminifera under oxygen depletion at the Indian Margin (Arabian Sea) Biogeosciences Discussions, 10, 15305-15335, 2013 Author(s): A. J. Enge, U. Witte, M. Kucera, and P. Heinz Benthic foraminifera in sediments on the Indian margin of the Arabian Sea where the oxygen minimum zone (OMZ) impinges on the continental slope are exposed to particularly severe levels of oxygen depletion. Food supply for the benthic community is high but delivered in distinct pulses during upwelling and water mixing events associated with summer and winter monsoon periods. In order to investigate the response by benthic foraminifera to such pulsed food delivery under oxygen concentrations of less than 0.1 mL L −1 (4.5 μmol L −1 ), an in situ isotope labeling experiment ( 13 C, 15 N) was performed at the western continental slope of India at 540 m water depth (OMZ core region). The assemblage of living foraminifera (〉125 μm) in the uppermost centimeter at this depth is characterized by an unexpectedly high population density of 3982 ind. 10 cm −2 and a strong dominance by few calcareous species. For the experiment, we concentrated on the nine most abundant taxa, which constitute 93% of the entire foraminifera population at 0–1 cm sediment depth. Increased concentrations of 13 C and 15 N in the cytoplasm indicate that all investigated taxa took up the labeled phytodetritus during the 4 day experimental phase. In total, these nine species had assimilated 113.8 mg C m −2 (17.5% of the total added carbon). The uptake of nitrogen by the three most abundant taxa ( Bolivina aff. B. dilatata , Cassidulina sp., Bulimina gibba ) was 2.7 mg N m −2 (2% of the total added nitrogen) and showed the successful application of 15 N as tracer in foraminiferal studies. The short-term response to the offered phytodetritus varied largely among foraminiferal species with Uvigerina schwageri being by far the most important species in short-term processing whereas the most abundant taxa Bolivina aff. B. dilatata and Cassidulina sp. showed comparably low uptake of the offered food. We suggest that the observed species-specific differences are related to individual biomass of species and to specific feeding preferences. The high numbers of living foraminifera and their rapid response to deposited fresh phytodetritus demonstrate the importance of foraminifera in short-term carbon cycling under oxygen-depleted conditions. We propose that foraminifera at the studied site benefit from unique adaptations in their metabolisms to nearly anoxic conditions as well as from the exclusion of macrofauna and the resulting relaxation of competition for food and low predation pressure.

Description: Summertime canopy albedo is sensitive to forest thinning Biogeosciences Discussions, 10, 15373-15414, 2013 Author(s): J. Otto, D. Berveiller, F.-M. Bréon, N. Delpierre, G. Geppert, A. Granier, W. Jans, A. Knohl, A. Kuusk, B. Longdoz, E. Moors, M. Mund, B. Pinty, M.-J. Schelhaas, and S. Luyssaert Despite an emerging body of literature linking canopy albedo to forest management, understanding of the process is still fragmented. We combined a stand-level forest gap model with a canopy radiation transfer model and satellite-derived model parameters to quantify the effects of forest thinning, that is removing trees at a certain time during the forest rotation, on summertime canopy albedo. The effects of different forest species (pine, beech, oak) and four thinning strategies (light to intense thinning regimes) were examined. During stand establishment, summertime canopy albedo is driven by tree species. In the later stages of stand development, the effect of tree species on summertime canopy albedo decreases in favour of an increasing influence of forest thinning on summertime canopy albedo. These trends continue until the end of the rotation where thinning explains up to 50% of the variance in near-infrared canopy albedo and up to 70% of the variance in visible canopy albedo. More intense thinning lowers the summertime shortwave albedo in the canopy by as much as 0.02 compared to unthinned forest. The structural changes associated with forest thinning can be described by the change in LAI in combination with crown volume. However, forests with identical canopy structure can have different summertime albedo values due to their location: the further north a forest is situated, the more the solar zenith angle increases and thus the higher is the summertime canopy albedo, independent of the wavelength. Despite the increase of absolute summertime canopy albedo values with latitude, the difference in canopy albedo between managed and unmanaged forest decreases with increasing latitude. Forest management thus strongly altered summertime forest albedo.

Description: Oxygen minimum zone of the open Arabian Sea: variability of oxygen and nitrite from daily to decadal time scales Biogeosciences Discussions, 10, 15455-15517, 2013 Author(s): K. Banse, S. W. A. Naqvi, P. V. Narvekar, J. R. Postel, and D. A. Jayakumar The oxygen minimum zone (OMZ) of the Arabian Sea is the thickest of the three oceanic OMZs, which is of global biogeochemical significance because of denitrification in the upper part leading to N 2 and N 2 O production. The residence time of the OMZ water is believed to be less than a decade. The upper few hundred meters of this zone are nearly anoxic but non-sulfidic and still support animal (metazoan) pelagic life, possibly as a result of episodic injections of O 2 by physical processes. The very low O 2 values obtained with the new STOX sensor in the eastern tropical South Pacific probably also characterize the Arabian Sea OMZ, but there is no apparent reason as to why the temporal trends of the historic data should not hold. We report on discrete measurements of dissolved O 2 and NO 2 - , besides temperature and salinity, made between 1959 and 2004 well below the tops of the sharp pycno- and oxyclines near 150, 200, 300, 400, and 500 m depth. We assemble nearly all O 2 determinations (originally, 849 values, 695 in the OMZ) by the visual endpoint detection of the iodometric Winkler procedure, which in our data base yields about 0.04 mL L −1 (∼2 μM) O 2 above the endpoint from modern automated titration methods. We find 632 values acceptable (480 from 150 stations in the OMZ). The data are grouped in zonally-paired boxes of 1° lat. and 2° long. centered at 8°, 10°, 12°, 15°, 18°, 20°, and 21° N along 65° E and 67° E. The latitudes of 8–12° N, outside the OMZ, are only treated in passing. The principal results are as follows: (1) an O 2 climatology for the upper OMZ reveals a marked seasonality at 200 to 500 m depth with O 2 levels during the northeast monsoon and spring intermonsoon season elevated over those during the southwest monsoon season (median difference, 0.08 mL L −1 [3.5 μM]). The medians of the slopes of the seasonal regressions of O 2 on year for the NE and SW monsoon seasons are −0.0043 and −0.0019 mL L −1 a −1 , respectively (−0.19 and −0.08 μM a −1 ; n = 10 and 12, differing at p = 0.01); (2) four decades of statistically significant decreases of O 2 between 15° and 20° N but a trend to a similar increase near 21° N are observed. The balance of the mechanisms that more or less annually maintain the O 2 levels are still uncertain. At least between 300 and 500 m the annual reconstitution of the decrease is inferred to be due to lateral, isopycnal re-supply of O 2 , while at 200 (250?) m it is diapycnal, most likely by eddies. Similarly, recent models show large vertical advection of O 2 well below the pycno- cum -oxycline. The spatial (within drift stations) and temporal (daily) variability in hydrography and chemistry is large also below the principal pycnocline. The seasonal change of hydrography is considerable even at 500 m. There is no trend in the redox environment for a quarter of a century at a GEOSECS station near 20° N. In the entire OMZ the slopes on year within seasons for the quite variable NO 2 - (taken as an indicator of active denitrification) do not show a clear pattern. Also, future O 2 or nutrient budgets for the OMZ should not be based on single cruises or sections obtained during one season only. Steady state cannot be assumed any longer for the intermediate layers of the central Arabian Sea.

Description: Stable isotopes dissect food webs from top to the bottom Biogeosciences Discussions, 10, 14923-14952, 2013 Author(s): J. J. Middelburg Stable isotopes have been used extensively to study food web functioning, i.e. the flow of energy and matter among organisms. Traditional food-web studies are based on the natural variability of carbon and nitrogen isotopes and are limited to larger organisms that can be physically separated from their environment. Recent developments allow isotope ratio measurements of microbes and this in turn allows then measurement of entire food webs, i.e. from small producers at the bottom to large consumers at the top. Here, I provide a concise review on the use and potential of stable isotope to reconstruct end-to-end food webs. I will first discuss food web reconstruction based on natural abundances isotope data and will then show that the use of stable isotopes as deliberately added tracers provides complementary information. Finally, challenges and opportunities for end-to-end food web reconstructions in a changing world are discussed.

Description: Responses of carbon dioxide flux and plant biomass to drought in a treed peatland in northern Alberta: a climate change perspective Biogeosciences Discussions, 10, 14999-15031, 2013 Author(s): T. M. Munir, B. Xu, M. Perkins, and M. Strack Northern peatland ecosystems represent large carbon stocks that are susceptible to changes such as accelerated mineralization due to water table lowering expected under a climate change scenario. During the growing seasons of 2011 and 2012 we monitored CO 2 fluxes and plant biomass along a microtopographic gradient (hummocks-hollows) in an undisturbed dry continental boreal treed bog (control) and a nearby site that was drained (drained) in 2001. Ten years of drainage in the bog significantly increased coverage of shrubs at hummocks and lichens at hollows. Considering measured hummock coverage and including tree incremental growth, we estimate that the control site was a larger sink in 2011 of −40 than that of −13 g C m −2 in 2012 while the drained site was a source of 144 and 140 g C m −2 over the same years. We infer that, drainage induced changes in vegetation growth led to increased biomass to counteract a portion of soil carbon losses. These results suggest that spatial variability (microtopography) and changes in vegetation community in boreal peatlands will affect how these ecosystems respond to lowered water table potentially induced by climate change.

Description: The coccolithophores Emiliania huxleyi and Coccolithus pelagicus : extant populations from the Norwegian-Iceland Sea and Fram Strait Biogeosciences Discussions, 10, 15077-15106, 2013 Author(s): C. V. Dylmer, J. Giraudeau, V. Hanquiez, and K. Husum Extant coccolithophores and their relation to the governing oceanographic features in the northern North Atlantic were investigated along two zonal transects of surface water sampling, both conducted during summer 2011 and fall 2007. The northern transects crossed Fram Strait and its two opposing boundary currents (West Spitsbergen Current and East Greenland Current), while the southern transects sampled the Norwegian and Iceland Seas (passing the island Jan Mayen) from the Lofoten Islands to the continental margin off Eastern Greenland. The distribution of the dominant coccolithophore species Emiliania huxleyi and Coccolithus pelagicus is discussed in view of both the surface hydrology at the time of sampling and the structure of the surface mixed layer. Remote-sensing images as well as CTD and ARGO profiles are used to constrain the physico-chemical state of the surface water at the time of sampling. Both transects were characterized by strong seasonal differences in bulk coccolithophore standing stocks with maximum values of 53 × 10 3 cells L −1 for the northern transect and 72 × 10 3 cells L −1 for the southern transect in fall and summer, respectively. The highest recorded bulk cell densities are essentially explained by E. huxleyi . This species shows a zonal shift in peak abundance in the Norwegian-Iceland Seas from a summer maximum in the Lofoten gyre to peak cell densities around the island Jan Mayen in fall. Vertical mixing of Atlantic waters west of Lofoten Island, a phenomenom related to pervasive summer large scale atmospheric changes in the eastern Nordic Seas, on one hand, and strengthened influence of melt-water and related surface water stratification around the island Jan Mayen during fall, on the other hand, explains the observed seasonal migration of the E. huxleyi peak production area, as well as the seasonal change in dominating species within the Iceland Sea. In addition our datasets are indicative of a well-defined maximum boundary temperature of 6 °C for the production of C. pelagicus in the northern North Atlantic. The Fram Strait transects provides, to our knowledge, a first view of the zonal distribution of extant coccolithophores in this remote setting during summer and fall. Our datasets are indicative of a seasonal change in the species community from an E. huxleyi -dominated assemblage during summer to a C. pelagicus -rich population during fall. Here, higher irradiance and increased Atlantic water influence during summer favored the production of the opportunistic species E. huxleyi close to the Arctic Front, whereas the peak production area during fall, with high concentrations of C. pelagicus , lays in true Arctic/Polar waters.

Description: Anthropogenic and natural methane fluxes in Switzerland synthesized within a spatially-explicit inventory Biogeosciences Discussions, 10, 15181-15224, 2013 Author(s): R. V. Hiller, D. Bretscher, T. DelSontro, T. Diem, W. Eugster, R. Henneberger, S. Hobi, E. Hodson, D. Imer, M. Kreuzer, T. Künzle, L. Merbold, P. A. Niklaus, B. Rihm, A. Schellenberger, M. H. Schroth, C. J. Schubert, H. Siegrist, J. Stieger, N. Buchmann, and D. Brunner We present the first high-resolution (500 m × 500 m) gridded methane (CH 4 ) emission inventory for Switzerland, which integrates the national emission totals reported to the United Nations Framework Convention on Climate Change (UNFCCC) and recent CH 4 flux studies conducted by research groups across Switzerland. In addition to anthropogenic emissions, we also include natural and semi-natural CH 4 fluxes, i.e., emissions from lakes and reservoirs, wetlands, wild animals as well as uptake by forest soils. National CH 4 emissions were disaggregated using detailed geostatistical information on source locations and their spatial extent and process- or area-specific emission factors. In Switzerland, the highest CH 4 emissions in 2011 originated from the agricultural sector (150 Gg CH 4 yr −1 ), mainly produced by ruminants and manure management, followed by emissions from waste management (15 Gg CH 4 yr −1 ) mainly from landfills and the energy sector (12 Gg CH 4 yr −1 ), which was dominated by emissions from natural gas distribution. Compared to the anthropogenic sources, emissions from natural and semi-natural sources were relatively small (6 Gg CH 4 yr −1 ), making up only 3 % of the total emissions in Switzerland. CH 4 fluxes from agricultural soils were estimated to be not significantly different from zero (between −1.5 and 0 Gg CH 4 yr −1 ), while forest soils are a CH 4 sink (approx. −2.8 Gg CH 4 yr −1 ), partially offsetting other natural emissions. Estimates of uncertainties are provided for the different sources, including an estimate of spatial disaggregation errors deduced from a comparison with a global (EDGAR v4.2) and a European CH 4 inventory (TNO/MACC). This new spatially-explicit emission inventory for Switzerland will provide valuable input for regional scale atmospheric modeling and inverse source estimation.

Description: Seasonal trends of dry and bulk concentration of nitrogen compounds over a rain forest in Ghana Biogeosciences Discussions, 10, 15225-15255, 2013 Author(s): F. Fattore, T. Bertolini, S. Materia, S. Gualdi, A. Thongo M'Bou, G. Nicolini, R. Valentini, A. De Grandcourt, D. Tedesco, and S. Castaldi African tropical forests of the equatorial belt might receive significant input of extra nitrogen derived from biomass burning occurring in the north savanna belt and transported equator wards by NE winds. In order to test this hypothesis an experiment was set up in a tropical rain forest in the National park of Ankasa (Ghana) aiming at: quantifying magnitude and seasonal variability of concentrations of N compounds, present as gas and aerosol (dry nitrogen) or in the rainfall (bulk nitrogen), over the studied forest; relating their seasonal variability to trends of local and regional winds and rainfall and to variations of fire events in the region. Three Delta systems, implemented for monthly measurements of NO 2 , were mounted over a tower at 45 m height, 20 m above forest canopy to sample gas (NH 3 , NO 2 , HNO 3 , HCl, SO 2 ) and aerosol (NH 4 + , NO 3 − , and several ions), together with three tanks for bulk rainfall collection (to analyze NH 4 + , NO 3 − and ion concentration). The tower was provided with a sonic anemometer to estimate local wind data. The experiment started in October 2011 and data up to October 2012 are presented. To interpret the observed seasonal trends of measured compounds, local and regional meteo data and regional satellite fire data were analyzed. The concentration of N compounds significantly increased from December to April, during the drier period, peaking in December-February when North Eastern winds (Harmattan) were moving dry air masses over the West central African region and the inter tropical convergence zone (ITCZ) was at its minimum latitude over the equator. This period also coincided with peaks of fire in the whole region. On the contrary, N concentration in gas, aerosol and rain decreased from May to October when prevalent winds arrived from the sea (South-East), during the Monsoon period. Both ionic compositions of rain and analysis of local wind direction showed a significant and continuous presence of see-breeze at site. The ionic composition of rain water resulted much closer to see water and poorer in N compounds from May to October.

Description: Inferences from CO 2 and CH 4 concentration profiles at the Zotino Tall Tower Observatory (ZOTTO) on local summer-time ecosystem fluxes Biogeosciences Discussions, 10, 15337-15372, 2013 Author(s): J. Winderlich, C. Gerbig, O. Kolle, and M. Heimann The Siberian region is still sparsely covered by ecosystem observatories, which motivates to exploit existing datasets to gain spatially and temporally better-resolved carbon fluxes. The Zotino Tall Tower Observatory (ZOTTO, 60°48' N, 89°21' E) observations of CO 2 and CH 4 mole fractions as well as meteorological parameters from six different heights up to 301 m allow for an additional estimate of surface-atmosphere fluxes of CO 2 and CH 4 for the Middle-Siberian region since 2009. The total carbon flux is calculated from the storage and the turbulent flux component. The gradients between the different tower levels determine the storage flux component, which dominates the local fluxes, especially during night. As a correction term, the turbulent flux component was estimated by the modified Bowen ratio method based on the sensible heat flux measurements at the top of the tower. The gained average night time fluxes (23:00 to 04:00 local time) are 2.7 ± 1.1 μmol (m 2 s) −1 for CO 2 and 5.6 ± 4.5 nmol (m 2 s) −1 for CH 4 during the summer months June-September in 2009 and 2011. During day, the method is limited due to numeric instabilities from vanishing vertical gradients; however, the derived CO 2 fluxes exhibit reasonable diurnal shape and magnitude compared to the eddy covariance technique, which become available at the site in 2012. Therefore, the tall tower data facilitates the extension of the new eddy covariance flux dataset back in time. The diurnal signal of the CH 4 flux is predominantly characterized by a strong morning transition, which is explained by local topographic effects.

Description: Live foraminiferal faunas (Rose Bengal stained) from the northern Arabian Sea: links with bottom-water oxygenation Biogeosciences Discussions, 10, 15257-15304, 2013 Author(s): C. Caulle, K. A. Koho, M. Mojtahid, G. J. Reichart, and F. J. Jorissen Live (Rose Bengal stained) benthic foraminifera from the Murray Ridge, within and below the northern Arabian Sea Oxygen Minimum Zone (OMZ), were studied in order to determine the relationship between faunal composition, bottom-water oxygenation (BWO), pore-water chemistry and organic matter (organic carbon and phytopigment) distribution. A series of multicores were recovered from a ten-station oxygen (BWO: 2–78 μM) and bathymetric (885–3010 m depth) transect during the winter monsoon in January 2009. Foraminifera were investigated from three different size fractions (63–125 μm, 125–150 μm and 〉 150 μm). The larger foraminifera (〉 125 μm) were strongly dominated by agglutinated species (e.g. Reophax spp.). In contrast, in the 63–125 μm fraction, calcareous taxa were more abundant, especially in the core of the OMZ, suggesting an opportunistic behaviour. On the basis of a Principal Component Analysis, three foraminiferal groups were identified, reflecting the environmental parameters along the study transect. The faunas from the shallowest stations, in the core of the OMZ (BWO: 2 μM), were composed of "low oxygen" species, typical of the Arabian Sea OMZ (e.g., Rotaliatinopsis semiinvoluta , Praeglobobulimina spp. , Bulimina exilis, Uvigerina peregrina type parva ). These taxa are adapted to the very low BWO conditions and to high phytodetritus supplies. The transitional group, typical for the lower part of the OMZ (BWO: 5–16 μM), is composed of more cosmopolitan taxa tolerant to low-oxygen concentrations ( Globocassidulina subglobosa , Ehrenbergina trigona ). Below the OMZ (BWO: 26–78 μM), where food availability is more limited and becomes increasingly restricted to surficial sediments, more cosmopolitan calcareous taxa were present, such as Bulimina aculeata, Melonis barleeanus, Uvigerina peregrina and Epistominella exigua . Miliolids were uniquely observed in this last group, reflecting the higher BWO. At these deeper sites, the faunas exhibit a clear depth succession of superficial, intermediate and deep-infaunal microhabitats, because of the deeper oxygen and nitrate penetration into the sediment.

Description: Landscape-scale changes in forest structure and functional traits along an Andes-to-Amazon elevation gradient Biogeosciences Discussions, 10, 15415-15454, 2013 Author(s): G. P. Asner, C. Anderson, R. E. Martin, D. E. Knapp, R. Tupayachi, T. Kennedy-Bowdoin, F. Sinca, and Y. Malhi Elevation gradients provide opportunities to explore environmental controls on forest structure and functioning, but plot-based studies have proven highly variable due to limited geographic scope. We used airborne imaging spectroscopy and LiDAR (light detection and ranging) to quantify changes in three-dimensional forest structure and canopy functional traits in a series of 25 ha landscapes distributed along a 3300 m elevation gradient from lowland Amazonia to treeline in the Peruvian Andes. Canopy greenness, photosynthetic fractional cover and exposed non-photosynthetic vegetation varied as much across lowland forests (100–200 m) as they did from the lowlands to the Andean treeline (3400 m). Elevation was positively correlated with canopy gap density and understory vegetation cover, and negatively related to canopy height and vertical profile. Increases in gap density were tightly linked to increases in understory plant cover, and larger gaps (20–200 m 2 produced 25–30 times the response in understory cover than did smaller gaps ( 〈 5 m 2 . Scaling of gap size to gap frequency was, however, relatively constant along the elevation gradient, which when combined with other canopy structural information, indicates equilibrium turnover patterns from the lowlands to treeline. Our results provide a first landscape-scale quantification of forest structure and canopy functional traits with changing elevation, thereby improving our understanding of disturbance, demography and ecosystem processes in the Andes-to-Amazon corridor.

Description: Springtime phytoplankton dynamics in the Arctic Krossfjorden and Kongsfjorden (Spitsbergen) as a function of glacier proximity Biogeosciences Discussions, 10, 15519-15557, 2013 Author(s): A. M.-T. Piquet, W. H. van de Poll, R. J. W. Visser, C. Wiencke, H. Bolhuis, and A. G. J. Buma The hydrographic properties of the Kongsfjorden – Krossfjorden system (79° N, Spitsbergen) are affected by Atlantic water incursions as well as glacier meltwater runoff. This results in strong physical gradients (temperature, salinity and irradiance) within the fjords. Here, we tested the hypothesis that glaciers affect phytoplankton dynamics as early as the productive spring bloom period. During two campaigns in 2007 (late spring) and 2008 (early spring) we studied hydrographic characteristics and phytoplankton variability along 2 transects in both fjords, using HPLC-CHEMTAX pigment fingerprinting, molecular fingerprinting (DGGE) and sequencing of 18S rRNA genes. The sheltered inner fjord locations remained colder during spring as opposed to the outer locations. Vertical light attenuation coefficients increased from early spring onwards, at all locations, but in particular at the inner locations. During the end of spring, meltwater input had stratified surface waters throughout the fjords. The inner fjord locations were characterized by overall lower phytoplankton biomass. Furthermore HPLC-CHEMTAX data revealed that diatoms and Phaeocystis sp. were replaced by small nano- and picophytoplankton during late spring, coinciding with low nutrient availability. The innermost stations showed higher relative abundances of nano- and picophytoplankton throughout, notably of cyanophytes and cryptophytes. Molecular fingerprinting revealed a high similarity between inner fjord samples from early spring and late spring samples from all locations, while outer samples from early spring clustered separately. We conclude that glacier influence, mediated by early meltwater input, modifies phytoplankton biomass and composition already during the spring bloom period, in favor of low biomass and small cell size communities. This may affect higher trophic levels especially when regional warming further increases the period and volume of meltwater.

Description: Simulating microbial degradation of organic matter in a simple porous system using the 3-D diffusion based model MOSAIC Biogeosciences Discussions, 10, 15613-15640, 2013 Author(s): O. Monga, P. Garnier, V. Pot, E. Coucheney, N. Nunan, W. Otten, and C. Chenu This paper deals with the simulation of microbial degradation in soil within pore space at microscopic scale. Pore space was described using sphere network coming from a geometrical modeling algorithm. The biological model was improved regarding previous work in order to include transformation of dissolved organic compounds and diffusion processes. Our model was tested using experimental results of a simple substrate decomposition (Fructose) within a simple media (the sand). Diverse microbial communities were inoculated. Separated incubations in microcosms were carried out using 5 different bacterial communities at 2 different water potentials of −10 cm and −100 cm of water. We calibrated the biological parameters by means of experimental data obtained at high water content and we tested the model without any parameters change at low water content. Same as for experimental data, our simulation results showed the decrease in water content involved the decrease of mineralisation. The model was able to simulate the decrease of connectivity between substrate and microorganism due the decrease of water content.

Description: Influence of temperature and CO 2 on the strontium and magnesium composition of coccolithophore calcite Biogeosciences Discussions, 10, 15559-15586, 2013 Author(s): M. N. Müller, M. Lebrato, U. Riebesell, J. Barcelos e Ramos, K. G. Schulz, S. Blanco-Ameijeiras, S. Sett, A. Eisenhauer, and H. M. Stoll Marine calcareous sediments provide a fundamental basis for paleoceanographic studies aiming to reconstruct past oceanic conditions and understand key biogeochemical element cycles. Calcifying unicellular phytoplankton (coccolithophores) are a major contributor to both carbon and calcium cycling by photosynthesis and the production of calcite (coccoliths) in the euphotic zone and the subsequent long-term deposition and burial into marine sediments. Here we present data from controlled laboratory experiments on four coccolithophore species and elucidate the relation between the divalent cation (Sr, Mg and Ca) partitioning in coccoliths and cellular physiology (growth, calcification and photosynthesis). Coccolithophores were cultured under different seawater temperature and carbonate chemistry conditions. The partition coefficient of strontium ( D Sr ) was positively correlated with both carbon dioxide ( p CO 2 ) and temperature but displayed no coherent relation to particulate organic and inorganic carbon production rates. Furthermore, D Sr correlated positively with cellular growth rates when driven by temperature but no correlation was present when changes in growth rates were p CO 2 -induced. The results demonstrate the complex interaction between environmental forcing and physiological control on the strontium partitioning in coccolithophore calcite. The partition coefficient of magnesium ( D Mg ) displayed species-specific differences and elevated values under nutrient limitation. No conclusive correlation between coccolith D Mg and temperature was observed but p CO 2 induced a rising trend in coccolith D Mg . Interestingly, the best correlation was found between coccolith D Mg and chlorophyll a production suggesting that chlorophyll a and calcite associated Mg originate from the same intracellular pool. These results give an extended insight into the driving factors that lead to variations in the coccolith Mg / Ca ratio and can be used for Sr / Ca and Mg / Ca paleoproxy calibration.

Description: Forest NEP is significantly driven by previous year's weather Biogeosciences Discussions, 10, 15587-15611, 2013 Author(s): S. Zielis, S. Etzold, R. Zweifel, W. Eugster, M. Haeni, and N. Buchmann Understanding the response of forest net ecosystem productivity (NEP) to environmental drivers under climate change is highly relevant for predictions of annual forest carbon (C) flux budgets. Modeling annual forest NEP with soil–vegetation–atmosphere transfer models (SVATs), however, remains challenging due to unknown responses of forests to weather of the previous year. In this study, we addressed the influence of previous year's weather on the inter-annual variability of NEP for a subalpine spruce forest in Switzerland. Analysis of long-term (1997–2011) eddy covariance measurements showed that the Norway spruce forest Davos Seehornwald was a consistent sink for atmospheric CO 2 , sequestering 210 ± 88 g C m −2 per year on average. Previous year's weather strongly affected inter-annual variability of NEP, increasing the explained variance in linear models to 53% compared to 20% without previous year's weather. Thus, our results highlight the need to consider previous year's weather in modeling annual C budgets of forests. Furthermore, soil temperature in the current year's spring played a major role controlling annual NEP, mainly by influencing gross primary productivity early in the year, with spring NEP accounting for 56% of annual NEP. Consequently, we expect an increase in net CO 2 uptake with future climate warming, as long as no other resources become limiting.

Description: Synoptic evaluation of carbon cycling in Beaufort Sea during summer: contrasting river inputs, ecosystem metabolism and air–sea CO 2 fluxes Biogeosciences Discussions, 10, 15641-15710, 2013 Author(s): A. Forest, P. Coupel, B. Else, S. Nahavandian, B. Lansard, P. Raimbault, T. Papakyriakou, Y. Gratton, L. Fortier, J.-É. Tremblay, and M. Babin The accelerated decline in Arctic sea ice combined with an ongoing trend toward a more dynamic atmosphere is modifying carbon cycling in the Arctic Ocean. A critical issue is to understand how net community production (NCP; the balance between gross primary production and community respiration) responds to changes and modulates air–sea CO 2 fluxes. Using data collected as part of the ArcticNet-Malina 2009 expedition in southeastern Beaufort Sea (Arctic Ocean), we synthesize information on sea ice, wind, river, water column properties, metabolism of the planktonic food web, organic carbon fluxes and pools, as well as air–sea CO 2 exchange, with the aim of identifying indices of ecosystem response to environmental changes. Data were analyzed to develop a non-steady-state carbon budget and an assessment of NCP against air–sea CO 2 fluxes. The mean atmospheric forcing was a mild upwelling-favorable wind (~5 km h −1 ) blowing from the N-E and a decaying ice cover ( 600 mg C m −2 d −1 ) over the shelf prior to our survey, (2) freshwater dilution by river runoff and ice melt, and (3) the presence of cold surface waters offshore. Only the Mackenzie River delta and localized shelf areas directly affected by upwelling were identified as substantial sources of CO 2 to the atmosphere (〉10mmol C m −2 d −1 ). Although generally

Description: Foraminiferal survival after long term experimentally induced anoxia Biogeosciences Discussions, 10, 9243-9284, 2013 Author(s): D. Langlet, E. Geslin, C. Baal, E. Metzger, F. Lejzerowicz, B. Riedel, M. Zuschin, J. Pawlowski, M. Stachowitsch, and F. J. Jorissen Anoxia has been successfully induced in four benthic chambers installed on the Northern Adriatic seafloor from 1 week to 10 months. To accurately determine whether benthic foraminifera can survive experimentally induced prolonged anoxia, the CellTrackerGreen method has been applied. Numerous individuals have been found living at all sampling times and at all sampling depths, showing that benthic foraminifera can survive up to 10 months of anoxia with co-occurring hydrogen sulphides. However, foraminiferal standing stocks decrease with sampling time in an irregular way. A large difference in standing stock between two cores samples in initial conditions indicates the presence of a large spatial heterogeneity of the foraminiferal faunas. An unexpected increase in standing stocks after 1 month is tentatively interpreted as a reaction to increased food availability due to the massive mortality of infaunal macrofaunal organisms. After this, standing stocks decrease again in a core sampled after 2 months of anoxia, to attain a minimum in the cores sampled after 10 months. We speculate that the trend of overall decrease of standing stocks is not due to the adverse effects of anoxia and hydrogen sulphides, but rather due to a continuous diminution of labile organic matter.

Description: Environmental controls on the Emiliania huxleyi calcite mass Biogeosciences Discussions, 10, 9285-9313, 2013 Author(s): M. T. Horigome, P. Ziveri, M. Grelaud, K.-H. Baumann, G. Marino, and P. G. Mortyn Although ocean acidification is expected to impact (bio)calcification by decreasing the seawater carbonate ion concentration, [CO 3 2− ], there exists evidence of non-uniform response of marine calcifying plankton to low seawater [CO 3 2− ]. This raises questions on the role of environmental factors other than acidification and on the complex physiological responses behind calcification. Here we investigate the synergistic effect of multiple environmental parameters, including temperature, nutrient (nitrate and phosphate) availability, and seawater carbonate chemistry on the coccolith calcite mass of the cosmopolitan coccolithophore Emiliania huxleyi , the most abundant species in the world ocean. We use a suite of surface (late Holocene) sediment samples from the South Atlantic and southwestern Indian Ocean taken from depths lying well above the modern lysocline. The coccolith calcite mass in our results presents a latitudinal distribution pattern that mimics the main oceanographic features, thereby pointing to the potential importance of phosphorus and temperature in determining coccolith mass by affecting primary calcification and possibly driving the E. huxleyi morphotype distribution. This evidence does not necessarily argue against the potentially important role of the rapidly changing seawater carbonate chemistry in the future, when unabated fossil fuel burning will likely perturb ocean chemistry beyond a critical point. Rather our study highlights the importance of evaluating the combined effect of several environmental stressors on calcifying organisms to project their physiological response(s) in a high CO 2 world and improve interpretation of paleorecords.

Description: UV-induced carbon monoxide emission from living vegetation Biogeosciences Discussions, 10, 9373-9388, 2013 Author(s): D. Bruhn, K. R. Albert, T. N. Mikkelsen, and P. Ambus The global burden of carbon monoxide (CO) is rather uncertain. In this paper we address the potential for UV-induced CO emission by living terrestrial vegetation surfaces. Real-time measurements of CO concentrations were made with a cavity enhanced laser spectrometer connected in closed loop to either an ecosystem chamber or a plant-leaf scale chamber. Leaves of all examined plant species exhibited emission of CO in response to artificial UV-radiation as well as the UV-component of natural solar radiation. The UV-induced rate of CO emission exhibited a rather low dependence on temperature, indicating an abiotic process. The emission of CO in response to the UV-component of natural solar radiation was also evident at the ecosystem scale.

Description: Nutrient dynamics in tropical rivers, estuarine-lagoons, and coastal ecosystems along the eastern Hainan Island Biogeosciences Discussions, 10, 9091-9147, 2013 Author(s): R. H. Li, S. M. Liu, Y. W. Li, G. L. Zhang, J. L. Ren, and J. Zhang Nutrient dynamics were studied along the eastern Hainan Island based on field observations during 2006–2009, to understand nutrient biogeochemical processes and to have an overview of human perturbations on coastal ecosystems in this tropical region. The concentrations of nutrients in the rivers had seasonal variations enriched with dissolved inorganic nitrogen (DIN). High riverine concentrations of nitrate were mainly originated from agricultural fertilizer input. The ratios of DIN : PO 4 3− ranged from 37 to 1063, suggesting preferential PO 4 3− relative to nitrogen in the rivers. The areal yields of dissolved silicate (DSi) varied from 76 to 448 × 10 3 mol km −2 yr −1 due to erosion over the drainage area, inducing high levels of DSi among worldwide tropical systems. Aquaculture ponds contained high concentrations of NH 4 + (up to 157 μM) and DON (up to 130 μM). Particulate phosphorus concentrations (0.5 ∼1.4 μM) were in lower level comparied with estuaries around the world. Particulate silicate levels in rivers and lagoons were lower than global average level. Nutrient biogeochemistry in coastal areas were affected by human activities (e.g. aquaculture, agriculture), as well as natural events such as typhoon. Nutrient concentrations were low because open sea water dispersed land-derived nutrients. Nutrient budgets were built based on a steady-state box model, which showed that riverine fluxes would be magnified by estuarine processes (e.g. regeneration, desorption) in the Wenchanghe/Wenjiaohe Estuary, Wanquan River estuary, and the Laoyehai Lagoon except in the Xiaohai Lagoon. Riverine and groundwater input were the major sources of nutrients to the Xiaohai Lagoon and the Laiyehai Lagoon, respectively. Riverine input and aquaculture effluent were the major sources of nutrients to the eastern coastal of Hainan Island. Nutrient inputs to the coastal ecosystem can be increased by typhoon-induced runoff of rainwater, and phytoplankton bloom in the sea would be caused.

Description: Southern Hemisphere imprint for Indo–Asian summer monsoons during the last glacial period as revealed by Arabian Sea productivity records Biogeosciences Discussions, 10, 9315-9343, 2013 Author(s): T. Caley, S. Zaragosi, J. Bourget, P. Martinez, B. Malaizé, F. Eynaud, L. Rossignol, T. Garlan, and N. Ellouz-Zimmermann The monsoon is one of the most important climatic phenomena: it promotes inter-hemispheric exchange of energy and affects the economical prosperity of several countries exposed to its seasonal seesaw. Previous studies in both the Indian and Asian monsoon systems have suggested a dominant north hemispheric (NH) control on summer monsoon dynamics at the scale of suborbital-millennial climatic changes, while the forcing/response of Indian and Asian monsoons at the orbital scale remains a matter of debate. Here nine marine sediment cores distributed across the whole Arabian Sea are used to build a regional surface marine productivity signal. The productivity signal is driven by the intensity of Indian summer monsoon winds. Results demonstrate the existence of an imprint of suborbital Southern Hemisphere (SH) temperature changes (i.e., Antarctica) on the Indian summer monsoon during the last glacial period, challenging the traditional and exclusive NH forcing hypothesis. Meanwhile, during the last deglaciation, the NH plays a more significant role. The δ 18 O signal recorded in the Asian monsoon speleothem records could be exported by winds from the Indian summer monsoon region, as recently proposed in modelling exercise, explaining the SH signature observed in Asian cave speleothems. Contrary to the view of a passive response of Indian and Asian monsoons to NH anomalies, the present results strongly suggest that the Indo–Asian summer monsoon plays an active role in amplifying millennial inter-hemispheric asymmetric patterns. Additionally, this study helps to decipher the observed differences between Indian and Asian-speleothem monsoonal records at the orbital-precession scale.

Description: Heterogeneity of impacts of high CO 2 on the North Western European Shelf Biogeosciences Discussions, 10, 9389-9413, 2013 Author(s): Y. Artioli, J. C. Blackford, G. Nondal, R. G. J. Bellerby, S. L. Wakelin, J.T. Holt, M. Butenschön, and J. I. Allen The increase in atmospheric CO 2 is a dual threat to the marine environment: from one side it drives climate change leading to changes in water temperature, circulation patterns and stratification intensity; on the other side it causes a decrease in pH (Ocean Acidification or OA) due to the increase in dissolved CO 2 . Assessing the combined impact of climate change and OA on marine ecosystems is a challenging task: the response of the ecosystem to a single driver is highly variable and still uncertain, as well as the interaction between these that could be either synergistic or antagonistic. In this work we use the coupled oceanographic-ecosystem model POLCOMS-ERSEM driven by climate forcing to study the interaction between climate change and OA. We focus in particular on primary production and nitrogen speciation. The model has been run in three different configurations in order to separate the impacts of ocean acidification from those due to climate change. The model shows significant interaction among the drivers and high variability in the spatial response of the ecosystem. Impacts of climate change and of OA on primary production have similar magnitude, compensating in some area and exacerbating in others. On the contrary, the direct impact of OA on nitrification is much lower than the one imposed by climate change.

Description: On the role of mesoscale eddies for the biological productivity and biogeochemistry in the eastern tropical Pacific Ocean off Peru Biogeosciences Discussions, 10, 9179-9211, 2013 Author(s): L. Stramma, H. W. Bange, R. Czeschel, A. Lorenzo, and M. Frank Mesoscale eddies seem to play an important role for both the hydrography and biogeochemistry of the eastern tropical Pacific Ocean (ETSP) off Peru. However, detailed surveys of these eddies are not available, which has so far hampered an in depth understanding of their implications for nutrient distribution and biological productivity. In this study three eddies along a section at 16°45' S have been surveyed intensively during R/V Meteor cruise M90 in November 2012. A coastal mode water eddy, an open ocean mode water eddy and an open ocean cyclonic eddy have been identified and sampled in order to determine both their hydrographic properties and their influence on the biogeochemical setting of the ETSP. In the thermocline the temperature of the coastal anticyclonic eddy was up to 2 °C warmer, 0.2 more saline and the swirl velocity was up to 35 cm s –1 . The observed temperature and salinity anomalies, as well as swirl velocities of both types of eddies were about twice as large as had been described for the mean eddies in the ETSP and the observed heat and salt anomalies (AHA, ASA) show a much larger variability than the mean AHA and ASA. We found that the eddies contributed significantly to productivity by maintaining pronounced subsurface maxima of chlorophyll. Based on a comparison of the coastal (young) mode water eddy and the open ocean (old) mode water eddy we conclude that the aging of eddies when they detach from the coast and move westward to the open ocean considerably influences the eddies' properties: chlorophyll maxima are weaker and nutrients are subducted. The coastal mode water eddy was found to be a hotspot of nitrogen loss in the OMZ, whereas, the open ocean cyclonic eddy was of negligible importance for nitrogen loss. Our results show that the important role the eddies play in the ETSP can only be fully deciphered and understood through dedicated high spatial and temporal resolution oceanographic/biogeochemical surveys.

Description: Soil moisture modifies the response of soil respiration to temperature in a desert shrub ecosystem Biogeosciences Discussions, 10, 9213-9242, 2013 Author(s): B. Wang, T. S. Zha, X. Jia, B. Wu, Y. Q. Zhang, and S. G. Qin The response of soil respiration (Rs) to soil temperature and moisture have been well documented in forests, but data and information from desert shrub ecosystems are limited. Soil CO 2 efflux from a desert shrub ecosystem was measured continuously with automated chambers in Ningxia, northwest China, from June to October 2012. The responses of Rs to Ts was strongly affected diurnally by soil moisture, with the diel variation in Rs being strongly related to 10 cm soil temperature (Ts) at moderate and high soil volumetric water content (VWC), but less related to Ts at low VWC. Ts typically lagged Rs by 3–4 h, however, the lag time varied in relation to VWC, with increased lag times at low VWC. Over the seasonal cycle, daily mean Rs was positively correlated with Ts when VWC exceeded 0.08 m 3 m −3 , but became decoupled from Ts when VWC dropped below this threshold. The annual temperature sensitivity of Rs ( Q 10 ) was 1.5. The short-term sensitivity of Rs to Ts, computed using three-day windows, varied significantly over the seasonal cycle; the short-term Q 10 was negatively correlated with Ts and positively correlated with VWC. These results suggest the potential for a negative feedback to climate warming in desert ecosystems, related to the impact of low soil moisture on Rs. The results highlight the biological causes of diel hysteresis between Rs and Ts and the need for carbon cycle models to account for the interacting effects of Ts and VWC as joint determinants of Rs in desert ecosystem.

Description: Do successive climate extremes weaken the resistance of plant communities? An experimental study using plant assemblages Biogeosciences Discussions, 10, 9149-9177, 2013 Author(s): F. E. Dreesen, H. J. De Boeck, I. A. Janssens, and I. Nijs The probability that plant communities undergo successive climate extremes increases under climate change. Exposure to an extreme event might elicit acclimatory responses and thereby greater resistance to a subsequent event, but might also reduce resistance if the recovery period is too short or resilience too low. Using experimental plant assemblages, we compared the effects of two successive extremes (either two drought extremes, two heat extremes or two drought + heat extremes) to those of assemblages being exposed only to the second extreme. Additionally, the recovery period between the successive extremes was varied (2, 3.5 or 6 weeks). Among the different types of climate extremes, combined drought + heat extremes induced substantial leaf and plant mortality, while the effects of drought and heat extremes were smaller. Preceding drought + heat extremes lowered the resistance in terms of leaf survival to a subsequent drought + heat extreme if the recovery period was 2 weeks, even though the leaves had completely recovered during that interval. No reduced resistance to subsequent extremes was recorded with longer recovery times or with drought or heat extremes. Despite mortality on the short term, the drought + heat and the heat extremes increased the end-of-season aboveground biomass, independent of the number of events or the recovery period. These results show that the effect of a preceding extreme event disappears quite quickly, but that recurrent climate extremes with short time intervals can weaken the resistance of herbaceous plant assemblages. This can however be compensated afterwards through rapid recovery and secondary, positive effects in the longer term.

Description: Climate and land use change impacts on global terrestrial ecosystems, fire, and river flows in the HadGEM2-ES Earth System Model using the Representative Concentration Pathways Biogeosciences Discussions, 10, 6171-6223, 2013 Author(s): R. A. Betts, N. Golding, P. Gonzalez, J. Gornall, R. Kahana, G. Kay, L. Mitchell, and A. Wiltshire A new generation of an Earth System Model now includes a number of land surface processes directly relevant to analyzing potential impacts of climate change. This model, HadGEM2-ES, allows us to assess the impacts of climate change, multiple interactions, and feedbacks as the model is run. This paper discusses the results of century-scale HadGEM2-ES simulations from an impacts perspective–specifically, terrestrial ecosystems and water resources–for four different scenarios following the Representative Concentration Pathways (RCPs), being used for next assessment report of the Intergovernmental Panel on Climate Change (IPCC). Over the 21st Century, simulated changes in global and continential-scale terrestrial ecosystems due to climate change appear to be very similar in all 4 RCPs, even though the level of global warming by the end of the 21st Century ranges from 2 °C in the lowest scenario to 5.5° in the highest. A warming climate generally favours broadleaf trees over needleleaf, needleleaf trees over shrubs, and shrubs over herbaceous vegetation, resulting in a poleward shift of temperate and boreal forests and woody tundra in all scenarios. Although climate related changes are slightly larger in scenarios of greater warming, the largest differences between scenarios arise at regional scales as a consequence of different patterns of anthropogenic land cover change. In the model, the scenario with the lowest global warming results in the most extensive decline in tropical forest cover due to a large expansion of agriculture. Under all four RCPs, fire potential could increase across extensive land areas, particularly tropical and sub-tropical latitudes. River outflows are simulated to increase with higher levels of CO 2 and global warming in all projections, with outflow increasing with mean temperature at the end of the 21st Century at the global scale and in North America, Asia, and Africa. In South America, Europe, and Australia, the relationship with climate warming and CO 2 rise is less clear, probably as a result of land cover change exerting a dominant effect in those regions.

Description: Horizontal distribution of Fukushima-derived radiocesium in zooplankton in the northwestern Pacific Ocean Biogeosciences Discussions, 10, 6143-6170, 2013 Author(s): M. Kitamura, Y. Kumamoto, H. Kawakami, E. C. Cruz, and K. Fujikura The magnitude of the 9.0 Tohoku earthquake and the ensuing tsunami on 11 March 2011, inflicted heavy damage on the Fukushima Dai-ichi nuclear power plant (FNPP1). Fission products were emitted, falling over a broad range in the northern hemisphere, and water contaminated with radionuclides leaked into the ocean. In this study, we described the horizontal distribution of the Fukushima-derived radiocesium in zooplankton and in seawater in the western North Pacific Ocean (500–2100 km from the FNPP1) 10 months after the accident. 134 Cs and 137 Cs were detected in zooplankton and seawater from all the stations. Because of its short half-lives, 134 Cs detected in our samples could only be derived from the FNPP1 accident. The highest 137 Cs activity in zooplankton was same order of magnitude as that one month after the accident, and average activity was one or two orders of magnitude higher than 137 Cs activities observed before the accident around Japan. Horizontally, the radiocesium activity concentrations in zooplankton were high at around 25° N while those in surface seawater were high at around the transition area between the Kuroshio and the Oyashio Currents (36–40° N). We observed subsurface radiocesium maxima in density range of the North Pacific Subtropical Mode Water and occurrence of many diel vertical migratory zooplanktons. These suggested that the high activity concentrations in the subtropical zooplankton at around 25° N were connected to the subsurface radiocesium and active vertical migration of zooplankton. However, the high activity concentrations of radiocesium in subsurface seawater did not necessarily follow the higher radiocesium activity in zooplankton. Biological characteristics of zooplankton community possibly influenced how large was contamination of radiocesium in the community but it is still unknown what kind of biological factors were important.

Description: Estimating carbonate parameters from hydrographic data for the intermediate and deep waters of the Southern Hemisphere Oceans Biogeosciences Discussions, 10, 6225-6257, 2013 Author(s): H. C. Bostock, S. E. Mikaloff Fletcher, and M. J. M. Williams Using GLODAP and CLIVAR ocean carbon data, we have developed several multiple linear regression (MLR) algorithms to estimate alkalinity and dissolved inorganic carbon (DIC) in the intermediate and deep waters of the Southern Hemisphere (south of 25° S) from only hydrographic data (temperature, salinity and dissolved oxygen). A Monte Carlo experiment was used to identify a potential density (σ θ ) of 27.5 as an optimal break point between the two regimes with different MLR algorithms. The algorithms provide a good estimate of DIC ( R 2 =0.98) and alkalinity ( R 2 =0.91), and excellent agreement for aragonite and calcite saturation states ( R 2 =0.99). Combining the algorithms with the CSIRO Atlas of Regional Seas (CARS), we have been able to map the calcite saturation horizon (CSH) and aragonite saturation horizon (ASH) for the Southern Ocean at a spatial resolution of 0.5°. These maps are more detailed and more consistent with oceanography than the gridded GLODAP data. The high resolution ASH map reveals a dramatic circumpolar shoaling at the Polar Front. North of 40° S the CSH is deepest in the Atlantic (~ 4000 m) and shallower in the Pacific Ocean (~ 2750 m), while the CSH sits between 3200 and 3400 m in the Indian Ocean.

Description: Productivity of aboveground coarse wood biomass and stand age related to soil hydrology of Amazonian forests in the Purus-Madeira interfluvial area Biogeosciences Discussions, 10, 6417-6459, 2013 Author(s): B. B. L. Cintra, J. Schietti, T. Emillio, D. Martins, G. Moulatlet, P. Souza, C. Levis, C. A. Quesada, and J. Schöngart The ongoing demand for information on forest productivity has increased the number of permanent monitoring plots across the Amazon. Those plots, however, do not comprise the whole diversity of forest types in the Amazon. The complex effects of soil, climate and hydrology on the productivity of seasonally waterlogged interfluvial wetland forests are still poorly understood. The presented study is the first field-based estimate for tree ages and wood biomass productivity in the vast interfluvial region between the Purus and Madeira rivers. We estimate stand age and wood biomass productivity by a combination of tree-ring data and allometric equations for biomass stocks of eight plots distributed along 600 km in the Purus-Madeira interfluvial area that is crossed by the BR-319 highway. We relate stand age and wood biomass productivity to hydrological and edaphic conditions. Mean productivity and stand age were 5.6 ± 1.1 Mg ha −1 yr −1 and 102 ± 18 yr, respectively. There is a strong relationship between tree age and diameter, as well as between mean diameter increment and mean wood density within a plot. Regarding the soil hydromorphic properties we find a positive correlation with wood biomass productivity and a negative relationship with stand age. Productivity also shows a positive correlation with the superficial phosphorus concentration. In addition, superficial phosphorus concentration increases with enhanced soil hydromorphic condition. We raise three hypotheses to explain these results: (1) the reduction of iron molecules on the saturated soils with plinthite layers close to the surface releases available phosphorous for the plants; (2) the poor structure of the saturated soils creates an environmental filter selecting tree species of faster growth rates and shorter life spans and (3) plant growth on saturated soil is favored during the dry season, since there should be low restrictions for soil water availability.

Description: Sources and fate of terrestrial dissolved organic carbon in lakes of a Boreal Plains region recently affected by wildfire Biogeosciences Discussions, 10, 6093-6141, 2013 Author(s): D. Olefeldt, K. J. Devito, and M. R. Turetsky Downstream mineralization and sedimentation of terrestrial dissolved organic carbon (DOC) render lakes important for landscape carbon cycling in the boreal region, with regulating processes potentially sensitive to perturbations associated with climate change including increased occurrence of wildfire. In this study we assessed chemical composition and reactivity (during both dark and UV incubations) of DOC from lakes and terrestrial sources within a peatland-rich western boreal plains region partially affected by a recent wildfire. While wildfire was found to increase aromaticity of DOC in peat pore-water above the water table, it had no effect on concentrations or composition of DOC from peatland wells and neither affected mineral well or lake DOC characteristics. Lake DOC composition reflected a mixing of peatland and mineral groundwater, with a greater influence of mineral sources to lakes in coarse- than fine-textured settings. Peatland DOC was less biodegradable than mineral DOC, but both mineralization and sedimentation of peatland DOC increased substantially during UV incubations through selective removal of aromatic humic and fulvic acids. DOC composition in lakes with longer residence times had characteristics consistent with increased UV-mediated processing. We estimate that about half of terrestrial DOC inputs had been lost within lakes, mostly due to UV-mediated processes. The importance of within-lake losses of aromatic DOC from peatland sources through UV-mediated processes indicate that terrestrial-aquatic C linkages in the study region are largely disconnected from recent terrestrial primary productivity. Together, our results suggest that characteristics of the study region (climate, surface geology and lake morphometry) render linkages between terrestrial and aquatic C cycling insensitive to the effects of wildfire by determining dominant terrestrial sources and within-lake processes of DOC removal.

Description: Solute specific scaling of inorganic nitrogen and phosphorus uptake in streams Biogeosciences Discussions, 10, 6671-6693, 2013 Author(s): R. O. Hall Jr., M. A. Baker, E. J. Rosi-Marshall, and J. L. Tank Stream ecosystem processes such as nutrient cycling may vary with stream position in the watershed. Using a scaling approach, we examined the relationship between stream size and nutrient uptake length, which represents the mean distance that a dissolved solute travels prior to removal from the water column. Ammonium uptake length increased proportionally with stream size measured as specific discharge (discharge/stream width) with a scaling exponent = 1.01. In contrast, the scaling exponent for nitrate (NO 3 − ) was 1.19 and for soluble reactive phosphorus (SRP) was 1.35, suggesting that uptake lengths for these nutrients increased more rapidly than increases in specific discharge. Additionally, the ratio of nitrogen (N) uptake length to SRP uptake length declined with stream size; there was lower demand for SRP relative to N as stream size increased. Ammonium and NO 3 − uptake velocity positively related with stream metabolism, while SRP did not. Finally, we related the scaling of uptake length and specific discharge to that of stream length using Hack's law and downstream hydraulic geometry. Ammonium uptake length increased less than proportionally with distance from the headwaters, suggesting a strong role for larger streams and rivers in regulating nutrient transport.

Description: Responses of lower trophic-level organisms to typhoon passage on the outer shelf of the East China Sea: an incubation experiment Biogeosciences Discussions, 10, 6605-6635, 2013 Author(s): N. Yasuki, K. Suzuki, and A. Tsuda Typhoons can induce vertical mixing, upwelling, or both in the water column due to strong wind stress. These events can induce phytoplankton blooms in the oligotrophic ocean after typhoon passage. However, little is known about the responses of lower trophic-level organisms or changes in the community structure following the passage of typhoons, particularly in offshore regions. Therefore, we evaluated community succession on the outer shelf of the East China Sea through on-deck bottle incubation experiments simulating hydrographic conditions after the passage of a typhoon. Under all of the experimental conditions we tested, chlorophyll a concentrations increased more than 9-fold within 6 days, and these algal cells were mainly composed of large diatoms (〉10 μm). Ciliates also increased along with the diatom bloom. These results suggest that increases in diatom and ciliate populations may enhance biogenic carbon export in the water column. Typhoons can affect not only phytoplankton productivity, but also the composition of lower trophic-level organisms and biogeochemical processes in oligotrophic offshore regions.

Description: Icehouse-greenhouse variations in marine denitrification Biogeosciences Discussions, 10, 14769-14813, 2013 Author(s): T. J. Algeo, P. A. Meyers, R. S. Robinson, H. Rowe, and G. Q. Jiang Long-term secular variation in the isotopic composition of seawater fixed nitrogen (N) is poorly known. Here, we document variation in the N-isotopic composition of marine sediments (δ 15 N sed ) since 660 Ma (million years ago) in order to understand major changes in the marine N cycle through time and their relationship to first-order climate variation. During the Phanerozoic, greenhouse climate modes were characterized by low δ 15 N sed (∼ −2 to +2‰) and icehouse climate modes by high δ 15 N sed (∼ +4 to +8‰). Shifts toward higher δ 15 N sed occurred rapidly during the early stages of icehouse modes, prior to the development of major continental glaciation, suggesting a potentially important role for the marine N cycle in long-term climate change. Reservoir box modeling of the marine N cycle demonstrates that secular variation in δ 15 N sed was likely due to changes in the dominant locus of denitrification, with a shift in favor of sedimentary denitrification during greenhouse modes owing to higher eustatic (global sea-level) elevations and greater on-shelf burial of organic matter, and a shift in favor of water-column denitrification during icehouse modes owing to lower eustatic elevations, enhanced organic carbon sinking fluxes, and expanded oceanic oxygen-minimum zones. The results of this study provide new insights into operation of the marine N cycle, its relationship to the global carbon cycle, and its potential role in modulating climate change at multimillion-year timescales.

Description: Technical Note: Disturbance of soil structure can lead to release of methane entrapped in glacier forefield soils Biogeosciences Discussions, 10, 14815-14834, 2013 Author(s): P. A. Nauer, E. Chiri, J. Zeyer, and M. H. Schroth Investigations of sources and sinks of atmospheric CH 4 are needed to understand the global CH 4 cycle and climate-change mitigation options. Glaciated environments might play a critical role due to potential feedbacks with global glacial meltdown. In an emerging glacier forefield, an ecological shift occurs from an anoxic, potentially methanogenic subglacial sediment to an oxic proglacial soil, in which soil-microbial consumption of atmospheric CH 4 is initiated. The development of this change in CH 4 turnover can be quantified by soil-gas profile analysis. We found evidence for CH 4 entrapped in glacier forefield soils when comparing two methods for the collection of soil-gas samples: a modified steel rod (SR) designed for one-time sampling and rapid screening (samples collected ~ 1 min after hammering the SR into the soil), and a novel multi-level sampler (MLS) for repetitive sampling through a previously installed access tube (samples collected weeks after access-tube installation). In glacier forefields on siliceous bedrock, sub-atmospheric CH 4 concentrations were observed with both methods. Conversely, elevated soil-CH 4 concentrations were observed in calcareous glacier forefields, but only in samples collected with the SR, while MLS samples all showed sub-atmospheric CH 4 concentrations. Time-series SR soil-gas sampling (additional samples collected 2, 3, 5, and 7 min after hammering) confirmed the transient nature of the elevated soil-CH 4 concentrations, which were decreasing from ~ 100 μL L −1 towards background levels within minutes. This hints towards the existence of entrapped CH 4 in calcareous glacier forefield soil that can be released when sampling soil-gas with the SR. Laboratory experiments with miniature soil cores collected from two glacier forefields confirmed CH 4 entrapment in these soils. Treatment by sonication and acidification resulted in a massive release of CH 4 from calcareous cores (on average 0.3–1.8 μg CH 4 (g d.w.) −1 ); release from siliceous cores was 1–2 orders of magnitude lower (0.02–0.03 μg CH 4 (g d.w.) −1 ). Clearly, some form of CH 4 entrapment exists in calcareous glacier forefield soils, and to a much lesser extent in siliceous glacier forefield soils. Its nature and origin remain unclear and will be subject of future investigations.

Description: Dynamics of particulate organic carbon flux in a global ocean model Biogeosciences Discussions, 10, 14715-14767, 2013 Author(s): I. D. Lima, P. J. Lam, and S. C. Doney The sinking of particulate organic carbon (POC) is a key component of the ocean carbon cycle and plays an important role in the global climate system. However, the processes controlling the fraction of primary production that is exported from the euphotic zone (export ratio) and how much of it survives respiration in the mesopelagic to be sequestered in the deep ocean (transfer efficiency) are not well understood. In this study, we use a three-dimensional, coupled physical-biogeochemical model (CCSM-BEC) to investigate the processes controlling the export of particulate organic matter from the euphotic zone and its flux to depth. We also compare model results with sediment trap data and other parameterizations of POC flux to depth to evaluate model skill and gain further insight into the causes of error and uncertainty in POC flux estimates. In the model, export ratios are mainly a function of diatom relative abundance and temperature while absolute fluxes and transfer efficiency are driven by mineral ballast composition of sinking material. The temperature dependence of the POC remineralization length scale is modulated by denitrification under low O 2 concentrations and lithogenic (dust) fluxes. Lithogenic material is an important control of transfer efficiency in the model, but its effect is restricted to regions of strong atmospheric dust deposition. In the remaining regions, CaCO 3 content of exported material is the main factor affecting transfer efficiency. The fact that mineral ballast composition is inextricably linked to plankton community structure results in correlations between export ratios and ballast minerals fluxes (opal and CaCO 3 ), and transfer efficiency and diatom relative abundance that do not necessarily reflect ballast or direct ecosystem effects, respectively. This suggests that it might be difficult to differentiate between ecosystem and ballast effects in observations. The model's skill at reproducing sediment trap observations is equal to or better than that of other parameterizations. However, the sparseness and relatively large uncertainties of sediment trap data makes it difficult to accurately evaluate the skill of the model and other parameterizations. More POC flux observations, over a wider range of ecological regimes, are necessary to thoroughly evaluate and test model results and better understand the processes controlling POC flux to depth in the ocean.

Description: Thin terrestrial sediment deposits on intertidal sandflats: effects on pore water solutes and juvenile bivalve burial behaviour Biogeosciences Discussions, 10, 14835-14860, 2013 Author(s): A. Hohaia, K. Vopel, and C. A. Pilditch Changes in land use and climate increase the supply of terrestrial sediment (hereafter, TS) to coastal waters worldwide but the effects of these sediments on benthic ecosystem functioning are not well known. Past experiments with defaunated, intertidal sediment suggested a link between the de-oxygenation of sediments underlying a thin (mm) layer of TS and reduced burial rates of juvenile macrofaunal recruits. We examined this link predicting that surficial TS deposits will still negatively affect burial when applied to sediments that are initially well oxygenated due to bioturbation (C) or depleted of organic matter (D). We observed the behaviour of post-settlement juveniles of the tellinid bivalve \textit{Macomona liliana} on the surface of four treatments; C, D, and the same sediments to which we added a thin layer of TS (CTS, DTS). Pore water analyses confirmed that the diffusive impedance of the 1.7–1.9 mm TS deposit decreased the oxygenation of the underlying intertidal sediment (CTS) but not that of the depleted sediment (DTS). Unexpectedly, (1) the application of a TS deposit significantly increased but not decreased the probability of burial, irrespectively of treatment, and (2) juveniles more likely buried into C than into D. We attribute the failure to document a negative effect of TS on the recruits' burial to the activity of the resident macroinfauna (CTS) or the absence of organic matter (DTS). Our results underline the important role of the resident macrofauna in mediating the stress response of benthic ecosystems.

Description: Calcium carbonate corrosivity in an Alaskan inland sea Biogeosciences Discussions, 10, 14887-14922, 2013 Author(s): W. Evans, J. T. Mathis, and J. N. Cross Ocean acidification is the hydrogen ion increase caused by the oceanic uptake of anthropogenic CO 2 , and is a focal point in marine biogeochemistry, in part, because this chemical reaction reduces calcium carbonate (CaCO 3 ) saturation states (Ω) to levels that are corrosive (i.e. Ω ≤ 1) to shell-forming marine organisms. However, other processes can drive CaCO 3 corrosivity; specifically, the addition of tidewater glacial melt. Carbonate system data collected in May and September from 2009 through 2012 in Prince William Sound (PWS), a semi-enclosed inland sea located on the south-central coast of Alaska that is ringed with fjords containing tidewater glaciers, reveal the unique impact of glacial melt on CaCO 3 corrosivity. Initial limited sampling was expanded in September 2011 to span large portions of the western and central sound, and included two fjords proximal to tidewater glaciers: Icy Bay and Columbia Bay. The observed conditions in these fjords affected CaCO 3 corrosivity in the upper water column (

Description: Surface circulation and upwelling patterns around Sri Lanka Biogeosciences Discussions, 10, 14953-14998, 2013 Author(s): A. de Vos, C. B. Pattiaratchi, and E. M. S. Wijeratne Sri Lanka occupies a unique location within the equatorial belt in the northern Indian Ocean with the Arabian Sea on its western side and the Bay of Bengal on its eastern side. The region is characterised by bi-annually reversing monsoon winds resulting from seasonal differential heating and cooling of the continental land mass and the ocean. This study explored elements of the dynamics of the surface circulation and coastal upwelling in the waters around Sri Lanka using satellite imagery and the Regional Ocean Modelling System (ROMS) configured to the study region and forced with ECMWF interim data. The model was run for 2 yr to examine the seasonal and shorter term (∼10 days) variability. The results confirmed the presence of the reversing current system in response to the changing wind field: the eastward flowing Southwest Monsoon Current (SMC) during the Southwest (SW) monsoon transporting 11.5 Sv and the westward flowing Northeast Monsoon Current (NMC) transporting 9.5 Sv during the Northeast (NE) monsoon, respectively. A recirculation feature located to the east of Sri Lanka during the SW monsoon, the Sri Lanka Dome, is shown to result from the interaction between the SMC and the Island of Sri Lanka. Along the eastern and western coasts, during both monsoon periods, flow is southward converging along the south coast. During the SW monsoon the Island deflects the eastward flowing SMC southward whilst along the east coast the southward flow results from the Sri Lanka Dome recirculation. The major upwelling region, during both monsoon periods, is located along the south coast and is shown to be due to flow convergence and divergence associated with offshore transport of water. Higher surface chlorophyll concentrations were observed during the SW monsoon. The location of the flow convergence and hence the upwelling centre was dependent on the relative strengths of wind driven flow along the east and west coasts: during the SW (NE) monsoon the flow along the western (eastern) coast was stronger and hence the upwelling centre was shifted to the east (west). The presence of upwelling along the south coast during both monsoon periods may explain the blue whale ( Balaenoptera musculus ) aggregations in this region.

Description: Strong sensitivity of Southern Ocean carbon uptake and nutrient cycling to wind stirring Biogeosciences Discussions, 10, 15033-15076, 2013 Author(s): K. B. Rodgers, O. Aumont, S. E. Mikaloff Fletcher, Y. Plancherel, L. Bopp, C. de Boyer Montégut, D. Iudicone, R. F. Keeling, G. Madec, and R. Wanninkhof Here we test the hypothesis that winds have an important role in determining the rate of exchange of CO 2 between the atmosphere and ocean through wind stirring over the Southern Ocean. This is tested with a sensitivity study using an ad hoc parameterization of wind stirring in an ocean carbon cycle model. The objective is to identify the way in which perturbations to the vertical density structure of the planetary boundary in the ocean impacts the carbon cycle and ocean biogeochemistry. Wind stirring leads to reduced uptake of CO 2 by the Southern Ocean over the period 2000–2006, with differences of order 0.9 Pg C yr −1 over the region south of 45° S. Wind stirring impacts not only the mean carbon uptake, but also the phasing of the seasonal cycle of carbon and other species associated with ocean biogeochemistry. Enhanced wind stirring delays the seasonal onset of stratification, and this has large impacts on both entrainment and the biological pump. It is also found that there is a strong sensitivity of nutrient concentrations exported in Subantarctic Mode Water (SAMW) to wind stirring. This finds expression not only locally over the Southern Ocean, but also over larger scales through the impact on advected nutrients. In summary, the large sensitivity identified with the ad hoc wind stirring parameterization offers support for the importance of wind stirring for global ocean biogeochemistry, through its impact over the Southern Ocean.

Description: Hydrologic control of the oxygen isotope ratio of ecosystem respiration in a semi-arid woodland Biogeosciences Discussions, 10, 1-48, 2013 Author(s): J. H. Shim, H. H. Powers, C. W. Meyer, A. Knohl, T. E. Dawson, W. J. Riley, W. T. Pockman, and N. McDowell We conducted high frequency measurements of the δ 18 O value of atmospheric CO 2 from a juniper ( Juniperus monosperma ) woodland in New Mexico, USA, over a four-year period to investigate climatic and physiological regulation of the δ 18 O value of ecosystem respiration ( δ R ). Rain pulses reset δ R with the dominant water source isotope composition, followed by progressive enrichment of δ R . Transpiration ( E T ) was significantly related to post-pulse δ R enrichment because leaf water δ 18 O value showed strong enrichment with increasing vapor pressure deficit that occurs following rain. Post-pulse δ R enrichment was correlated with both E T and the ratio of E T to soil evaporation ( E T / E S ). In contrast, soil water δ 18 O value was relatively stable and δ R enrichment was not correlated with E S . Model simulations captured the large post-pulse δ R enrichments only when the offset between xylem and leaf water δ 18 O value was modeled explicitly and when a gross flux model for CO 2 retro-diffusion was included. Drought impacts δ R through the balance between evaporative demand, which enriches δ R , and low soil moisture availability, which attenuates δ R enrichment through reduced E T . The net result, observed throughout all four years of our study, was a negative correlation of post-precipitation δ R enrichment with increasing drought.

Description: Biological soil crusts on initial soils: organic carbon dynamics and chemistry under temperate climatic conditions Biogeosciences Discussions, 10, 851-894, 2013 Author(s): A. Dümig, M. Veste, F. Hagedorn, T. Fischer, P. Lange, R. Spröte, and I. Kögel-Knabner Numerous studies have been carried out on the community structure and diversity of biological soil crusts (BSCs) as well as their important functions on ecosystem processes. However, the amount of BSC-derived organic carbon (OC) input into soils and its chemical composition under natural conditions has rarely been investigated. In this study, different development stages of algae- and moss-dominated BSCs were investigated on a~natural (

Description: Incorporating genomic information and predicting gene expression patterns in a simplified biogeochemical model Biogeosciences Discussions, 10, 815-850, 2013 Author(s): P. Wang, A. B. Burd, M. A. Moran, R. R. Hood, V. J. Coles, and P. L. Yager We present results from a new marine plankton model that combines selective biogeochemical processes with genetic information. The model allows for phytoplankton to adapt to a changing environment by invoking different utilization pathways for acquisition of nutrients (nitrogen and phosphorus) in response to concentration changes. The simulations use simplified environmental conditions represented by a continuously stirred tank reactor, which is populated by 96 different types of phytoplankton that differ in their physiological characteristics and nutrient uptake/metabolism genes. The results show that the simulated phytoplankton community structure is conceptually consistent with observed regional and global phytoplankton biogeography, the genome content from the dominant types of phytoplankton reflects the imposed environmental constraints, and the transcription of the gene clusters is qualitatively simulated according to the environmental changes. The model shows the feasibility of including genomic knowledge into a biogeochemical model and is suited to understanding and predicting changes in marine microbial community structure and function, and to simulating the biological response to rapid environmental changes.

Description: A~model for variable phytoplankton stoichiometry based on cell protein regulation Biogeosciences Discussions, 10, 3241-3279, 2013 Author(s): J. A. Bonachela, S. D. Allison, A. C. Martiny, and S. A. Levin The elemental ratios of marine phytoplankton emerge from complex interactions between the biotic and abiotic components of the ocean, and reflect the plastic response of individuals to changes in their environment. The stoichiometry of phytoplankton is, thus, dynamic and dependent on the physiological state of the cell. We present a theoretical model for the dynamics of the carbon, nitrogen and phosphorus contents of a phytoplankton population. By representing the regulatory processes controlling nutrient uptake, and focusing on the relation between nutrient content and protein synthesis, our model qualitatively replicates existing experimental observations for nutrient content and ratios. The population described by our model takes up nutrients in proportions that match the input ratios for a broad range of growth conditions. In addition, there are two zones of single-nutrient limitation separated by a wide zone of co-limitation. Within the co-limitation zone, a single point can be identified where nutrients are supplied in an optimal ratio. The existence of a wide co-limitation zone affects the standard picture for species competing for nitrogen and phosphorus, which shows here a much richer pattern. However, additional comprehensive laboratory experiments are needed to test our predictions. Our model contributes to the understanding of the global cycles of oceanic nitrogen and phosphorus, as well as the elemental ratios of these nutrients in phytoplankton populations.

Description: Seasonal signatures in SFG vibrational spectra of the sea surface nanolayer at Boknis Eck Time Series Station (SW Baltic Sea) Biogeosciences Discussions, 10, 3177-3201, 2013 Author(s): K. Laß, H. W. Bange, and G. Friedrichs The very thin sea surface nanolayer on top of the sea surface microlayer, sometimes just one monomolecular layer thick, forms the interface between ocean and atmosphere. Due to the small dimension and tiny amount of substance, knowledge about the development of the layer in the course of the year is scarce. In this work, the sea surface nanolayer at Boknis Eck Time Series Station (BE), southwestern Baltic Sea, has been investigated over a period of three and a half years. Surface water samples were taken monthly by screen sampling and were analyzed in terms of organic content and composition by sum frequency generation spectroscopy, which is specifically sensitive to interfacial layers. A yearly periodicity has been observed with a pronounced abundance of sea surface nanolayer material (such as carbohydrate-rich material) during the summer months. On the basis of our results we conclude that the abundance of organic material in the nanolayer at Boknis Eck is not directly related to phytoplankton abundance. We suggest that indeed sloppy feeding of zooplankton together with photochemical and/or microbial processing of organic precursor compounds are responsible for the pronounced seasonality.

Description: Food quality regulates the metabolism and reproduction of Temora longicornis Biogeosciences Discussions, 10, 3203-3239, 2013 Author(s): R. Nobili, C. Robinson, E. Buitenhuis, and C. Castellani A laboratory study was undertaken to determine the effect of food quality on feeding, respiration, reproduction and the resulting carbon budget of Temora longicornis . The stoichiometric ratios N : P, C : N and C : P of Rhodomonas salina were used as indicators of food quality. R. salina was grown in media with different inorganic nutrient concentrations to produce food for T. longicornis with particulate organic N : P ratios ranging from 10 : 1 to 23 : 1. Feeding rate was not affected by food quality. Maximum respiration (R), egg production rate (EPR), assimilation efficiency (AE), gross growth efficiency (GGE) and metabolic increment (MI) occurred when T. longicornis was fed on phytoplankton with a food quality of 16N : 1P. EPR, GGE and AE also decreased with decreasing C : N ratio and the energy required to produce eggs (CoE) decreased with decreasing N : P ratio, indicative of nitrogen-dependent production. These data suggest that an algal composition of 16N : 1P defines the Threshold Elemental Ratio (TER) and is the optimum diet for T. longicornis . The variations in metabolic rates and the resulting carbon budget are proportional to the quality of food ingested. GGE was negatively affected at dietary ratios above and below 16N : 1P, which in the natural environment could lead to a decline in species biomass with detrimental consequences for fisheries and carbon export. Field data show that phytoplankton organic N : P ratios can change on decadal timescales, and that an increase in the food N : P ratio can co-occur with a shift to smaller sized zooplankton and a change in species abundance. Further research is required to assess how much of the change in zooplankton community structure and activity can be attributed to changes in food quality, rather than to changes in temperature and food quantity.

Description: Microhabitat and shrimp abundance within a Norwegian cold-water coral ecosystem Biogeosciences Discussions, 10, 3365-3396, 2013 Author(s): A. Purser, J. Ontrup, T. Schoening, L. Thomsen, R. Tong, V. Unnithan, and T. W. Nattkemper Cold-water coral reefs are highly heterogeneous ecosystems comprising of a range of diverse microhabitats. In a typical European cold-water coral reef various biogenic habitats (live colonies of locally common coral species such as Lophelia pertusa, Paragorgia arborea and Primnoa resedaeformis , dead coral structure, coral rubble) may be surrounded and intermixed with non-biogenic habitats (soft sediment, hardground, gravel/pebbles, steep walls). To date, studies of distribution of sessile fauna across these microhabitats have been more numerous than those investigating mobile fauna distribution. In this study we quantified shrimp densities associated with key CWC habitat categories at the Røst reef, Norway, by analysing image data collected by towed video sled. We also investigated shrimp distribution patterns on the local scale (

Description: Climate change and ocean acidification impacts on lower trophic levels and the export of organic carbon to the deep ocean Biogeosciences Discussions, 10, 3455-3522, 2013 Author(s): A. Yool, E. E. Popova, A. C. Coward, D. Bernie, and T. R. Anderson Most future projections forecast significant and ongoing climate change during the 21st century, but with the severity of impacts dependent on efforts to restrain or reorganise human activity to limit carbon dioxide (CO 2 ) emissions. A major sink for atmospheric CO 2 , and a key source of biological resources, the World Ocean is widely anticipated to undergo profound physical and – via ocean acidification – chemical changes as direct and indirect results of these emissions. Given strong biophysical coupling, the marine biota is also expected to experience strong changes in response to this anthropogenic forcing. Here we examine the large-scale response of ocean biogeochemistry to climate and acidification impacts during the 21st century for Representative Concentration Pathways (RCPs) 2.6 and 8.5 using an intermediate complexity global ecosystem model, Medusa–2.0. The primary impact of future change lies in stratification-led declines in the availability of key nutrients in surface waters, which in turn leads to a global decrease (1990s vs. 2090s) in ocean productivity (−6.3%). This impact has knock-on consequences for the abundances of the low trophic level biogeochemical actors modelled by Medusa–2.0 (−5.8%), and these would be expected to similarly impact higher trophic level elements such as fisheries. Related impacts are found in the flux of organic material to seafloor communities (−40.7% at 1000 m), and in the volume of ocean suboxic zones (+12.5%). A sensitivity analysis removing an acidification feedback on calcification finds that change in this process significantly impacts benthic communities, suggesting that a better understanding of the OA-sensitivity of calcifying organisms, and their role in ballasting sinking organic carbon, may significantly improve forecasting of these ecosystems. For all processes, there is geographical variability in change, and changes are much more pronounced under RCP 8.5 than the RCP 2.6 scenario.

Description: Controlled experimental aquarium system for multi-stressor investigation: carbonate chemistry, oxygen saturation, and temperature Biogeosciences Discussions, 10, 3431-3453, 2013 Author(s): E. E. Bockmon, C. A. Frieder, M. O. Navarro, L. A. White-Kershek, and A. G. Dickson As the field of ocean acidification has grown, researchers have increasingly turned to laboratory experiments to understand the impacts of increased CO 2 on marine organisms. However, other changes such as ocean warming and deoxygenation are occurring concurrently with the increasing CO 2 concentrations, complicating the anthropogenic impact on organisms. This experimental aquarium design allows for independent regulation of CO 2 concentration, O 2 levels, and temperature in a controlled environment to study the impacts of multiple stressors. The system has the flexibility for a wide range of treatment chemistry, seawater volumes, and study organisms. Control of the seawater chemistry is achieved by equilibration of a chosen gas mixture with seawater using a Liqui-Cel ® membrane contactor. Included as examples, two experiments performed using the system have shown control of CO 2 between approximately 500–1400 μatm and O 2 from 80–240 μmol kg −1 . Temperature has been maintained to 0.5 °C or better in the range of 10–17 °C. On a weeklong timescale, control results in variability in pH of less than 0.007 pH units and in oxygen concentration less than 3.5 μmol kg −1 . Longer experiments, over a month, have been completed with reasonable but lessened control, still better than 0.08 pH units and 13 μmol kg −1 O 2 . The ability to study the impacts of multiple stressors in the laboratory simultaneously, as well as independently, will be an important part of understanding the response of marine organisms to a high-CO 2 world.

Description: Mangroves facing climate change: landward migration potential in response to projected scenarios of sea level rise Biogeosciences Discussions, 10, 3523-3558, 2013 Author(s): D. Di Nitto, G. Neukermans, N. Koedam, H. Defever, F. Pattyn, J. G. Kairo, and F. Dahdouh-Guebas Mangrove forests prominently occupy an intertidal boundary position where the effects of sea level rise will be fast and well visible. This study in East Africa (Gazi Bay, Kenya) addresses the question whether mangroves can be resilient to a rise in sea level by focusing on their potential to migrate towards landwards areas. The combinatory analysis between remote sensing, DGPS-based ground truth and digital terrain models (DTM) unveils how real vegetation assemblages can shift under different projected (minimum (+9 cm), relative (+20 cm), average (+48 cm) and maximum (+88 cm)) scenarios of sea level rise (SLR). Under SLR scenarios up to 48 cm by the year 2100, the landward extension remarkably implies an area increase for each of the dominant mangrove assemblages, except for Avicennia marina and Ceriops tagal , both on the landward side. On one hand, the increase of most species in the first 3 scenarios, including the socio-economically most important species in this area, Rhizophora mucronata and C. tagal on the seaward side, strongly depends on the colonisation rate of these species. On the other hand, a SLR scenario of +88 cm by the year 2100 indicates that the area flooded only by equinoctial tides strongly decreases due to the topographical settings at the edge of the inhabited area. Consequently, the landward Avicennia -dominated assemblages will further decrease as a formation if they fail to adapt to a more frequent inundation. The topography is site-specific; however non-invadable areas can be typical for many mangrove settings.

Description: Continuing 137 Cs release to the sea from the Fukushima Dai-ichi Nuclear Power Plant through 2012 Biogeosciences Discussions, 10, 3577-3595, 2013 Author(s): J. Kanda Rate of cesium-137 ( 137 Cs) release to the sea from the Fukushima Dai-ichi Nuclear Power Plant was estimated until September 2012. Based on publicly released data of 137 Cs in seawater near the power plant by Tokyo Electric Power Company, a continuing release of radionuclides to the sea is strongly suggested. The plant has an artificial harbour facility, and the exchange rate of harbour water with surrounding seawater was estimated by decrease of radioactivity immediately after an intense event of radioactive water release. The estimated exchange rate of water in the harbour is 0.44 day −1 during the period from 6 to 19 April 2011. 137 Cs radioactivity of the harbour water is substantially higher than seawater outside and remained relatively stable after June 2011. A quasi-steady state was assumed with continuous water exchange, and an average release rate of 137 Cs was estimated to be 93 GBq day −1 in summer 2011 and 8.1 GBq day −1 in summer 2012.

Description: Upper Arctic Ocean water masses harbor distinct communities of heterotrophic flagellates Biogeosciences Discussions, 10, 3397-3430, 2013 Author(s): A. Monier, R. Terrado, M. Thaler, A. M. Comeau, E. Medrinal, and C. Lovejoy The ubiquity of heterotrophic flagellates (HFL) in marine waters has been recognized for several decades, but the phylogenetic diversity of these small (ca. 0.8–20 μm cell diameter), mostly phagotrophic protists in the pelagic zone of the ocean is underappreciated. Community composition of microbes, including HFL, is the result of past and current environmental selection, and different taxa may be indicative of food webs that cycle carbon and energy very differently. While all oceanic water columns can be density stratified due to the temperature and salinity characteristics of different water masses, the Arctic Ocean is particularly well stratified, with nutrients often limiting in surface waters and most photosynthetic biomass confined to a subsurface chlorophyll maximum (SCM) layer. This physically well-characterized system provided an opportunity to explore the community diversity of HFL across a wide region, and down the water column. We used high-throughput DNA sequencing techniques as a rapid means of surveying the diversity of HFL communities in the southern Beaufort Sea (Canada), targeting the surface, the SCM and just below the SCM. In addition to identifying major clades and their distribution, we explored the micro-diversity within the globally significant but uncultivated clade of marine stramenopiles (MAST-1) to examine the possibility of niche differentiation within the stratified water column. Our results strongly implied that HFL community composition was determined by water mass rather than geographical location across the Beaufort Sea. Future work should focus on the biogeochemical and ecological repercussions of different HFL communities in the face of climate driven changes to the physical structure of the Arctic Ocean.

Description: Apparent optical properties of the Canadian Beaufort Sea – Part 1: Observational overview and water column relationships Biogeosciences Discussions, 10, 4025-4065, 2013 Author(s): D. Antoine, S. B. Hooker, S. Belanger, A. Matsuoka, and M. Babin A data set of radiometric measurements collected in the Beaufort Sea (Canadian Arctic) in August 2009 (MALINA project) is analysed in order to describe apparent optical properties (AOPs) in this sea, which is subject to dramatic environmental changes for several decades. The two properties derived from the measurements are the spectral diffuse attenuation coefficient for downward irradiance, K d , and the spectral remote sensing reflectance, R rs . The former controls light propagation in the upper water column. The latter determines how light is backscattered out of the water and becomes eventually observable from a satellite ocean colour sensor. The data set includes offshore clear waters of the Beaufort basin as well as highly turbid waters of the Mackenzie River plumes. In the clear waters, we show K d values that are much larger in the ultraviolet and blue parts of the spectrum than what could be anticipated considering the chlorophyll concentration. A larger contribution of absorption by coloured dissolved organic matter (CDOM) is responsible for this high K d values, as compared to other oligotrophic areas. In turbid waters, attenuation reaches extremely high values, driven by high loads of particulate materials and also by a large CDOM content. In these two extreme types of waters, current satellite chlorophyll algorithms fail. This is questioning the role of ocean colour remote sensing in the Arctic when R rs from only the blue and green bands are used. Therefore, other parts of the spectrum (e.g. the red) should be explored if one aims at quantifying interannual changes in chlorophyll in the Arctic from space. The very peculiar AOPs in the Beaufort Sea also advocate for developing specific light propagation models when attempting to predict light availability for photosynthesis at depth.

Description: Development of a regional-scale pollen emission and transport modeling framework for investigating the impact of climate change on allergic airway disease Biogeosciences Discussions, 10, 3977-4023, 2013 Author(s): R. Zhang, T. Duhl, M. T. Salam, J. M. House, R. C. Flagan, E. L. Avol, F. D. Gilliland, A. Guenther, S. H. Chung, B. K. Lamb, and T. M. VanReken Exposure to bioaerosol allergens such as pollen can cause exacerbations of allergenic airway disease (AAD) in sensitive populations, and thus cause serious public health problems. Assessing these health impacts by linking the airborne pollen levels, concentrations of respirable allergenic material, and human allergenic response under current and future climate conditions is a key step toward developing preventive and adaptive actions. To that end, a regional-scale pollen emission and transport modeling framework was developed that treats allergenic pollens as non-reactive tracers within the WRF/CMAQ air-quality modeling system. The Simulator of the Timing and Magnitude of Pollen Season (STaMPS) model was used to generate a daily pollen pool that can then be emitted into the atmosphere by wind. The STaMPS is driven by species-specific meteorological (temperature and/or precipitation) threshold conditions and is designed to be flexible with respect to its representation vegetation species and plant functional types (PFTs). The hourly pollen emission flux was parameterized by considering the pollen pool, friction velocity, and wind threshold values. The dry deposition velocity of each species of pollen was estimated based on pollen grain size and density. An evaluation of the pollen modeling framework was conducted for southern California for the period from March to June 2010. This period coincided with observations by the University of Southern California's Children's Health Study (CHS), which included O 3 , PM 2.5 , and pollen count, as well as measurements of exhaled nitric oxide in study participants. Two nesting domains with horizontal resolutions of 12 km and 4 km were constructed, and six representative allergenic pollen genera were included: birch tree, walnut tree, mulberry tree, olive tree, oak tree, and brome grasses. Under the current parameterization scheme, the modeling framework tends to underestimate walnut and peak oak pollen concentrations, and tends to overestimate grass pollen concentrations. The model shows reasonable agreement with observed birch, olive, and mulberry tree pollen concentrations. Sensitivity studies suggest that the estimation of the pollen pool is a major source of uncertainty for simulated pollen concentrations. Achieving agreement between emission modeling and observed pattern of pollen releases is the key for successful pollen concentration simulations.

Description: Carbon dioxide fluxes at an intensively cultivated temperate lowland peatland in the East Anglian Fens, UK Biogeosciences Discussions, 10, 4193-4223, 2013 Author(s): R. Morrison, A. M. J. Cumming, H. E. Taft, J. Kaduk, S. E. Page, D. L. Jones, R. J. Harding, and H. Balzter This study reports the first recorded CO 2 flux measurements of a drained and intensively cultivated lowland peatland in the East Anglian Fens (UK) using the eddy covariance technique. Measurements were made over a complete lettuce crop rotation and a subsequent fallow period. Maximum average daytime CO 2 uptake and nocturnal loss rates were −10.39 and 7.63 μmol CO 2 m −2 s −1 , respectively. Daily CO 2 budgets ranged from a net loss of 4.7 to a small net uptake of −1.23 g CO 2 -C m −2 d −1 . Total vertical land/atmosphere CO 2 losses were estimated at 227.11 ± 46.5 g CO 2 -C m −2 for a~120 day measurement period. Losses over a sixty day interval between field preparation and disking of the field at the end of the crop cycle were 74.22 ± 18.8 g CO 2 -C m −2 . The site lost 152.89 ± 30.6 g CO 2 -C m −2 d −1 during a sixty day fallow period. Net ecosystem production was estimated at 117.72 ± 18.8 g CO 2 -C m −2 during the crop cycle and 270.61 ± 46.49 g CO 2 -C m −2 for the entire measurement period when harvested crop exports were accounted for. These results represent the first micrometeorological measurements obtained over degraded lowland peatland in Britain, and illustrate the scale of CO 2 losses associated with agricultural production on temperate organic soils.

Description: DNA from lake sediments reveals the long-term dynamics and diversity of Synechococcus assemblages Biogeosciences Discussions, 10, 2515-2564, 2013 Author(s): I. Domaizon, O. Savichtcheva, D. Debroas, F. Arnaud, C. Villar, C. Pignol, B. Alric, and M. E. Perga While picocyanobacteria (PC) are important actors in carbon and nutrient cycles in aquatic systems, factors controlling their interannual dynamics and diversity are poorly known due to the general lack of long-term monitoring surveys. This study intended to fill this gap by applying a DNA-based paleolimnological approach to sediment records from a deep subalpine lake that has experienced dramatic changes in environmental conditions during the last century (eutrophication, re-oligotrophication and large-scale climate changes). We particularly investigated the long-term (100 yr) diversity and dynamics of Synechococcus , PC that have presumably been affected by both the lake trophic status changes and global warming. The lake's morphological and environmental conditions provided ideal conditions for DNA preservation in the sediment archives. Generalised additive models applied to quantitative PCR (qPCR) results highlighted that an increase in summer temperature could have a significant positive impact on the relative abundance of Synechococcus (fraction of Synechococcus in total cyanobacteria). The diversity of Synechococcus in Lake Bourget was studied by phylogenetic analyses of the 16S rRNA gene and internal transcribed spacer (ITS). Up to 23 different OTUs (based on 16S rRNA), which fell into various cosmopolitan or endemic clusters, were identified in samples from the past 100 yr. Moreover, study of the ITS revealed a higher diversity within the major 16S rRNA-defined OTUs. Changes in PC diversity were related to the lake's trophic status. Overall, qPCR and sequencing results showed that environmental changes (here, in temperature and phosphorus concentration) affected Synechococcus community dynamics and structure, translating into changes in genotype composition. These results also helped to re-evaluate the geographical distribution of some Synechococcus clusters. Providing such novel insights into the long-term history of an important group of primary producers, this study illustrates the promising approach that consists in coupling molecular tools and paleolimnology to reconstruct a lake's biodiversity history.

Description: Combined use of stable isotopes and fallout radionuclides as soil erosion indicators in a forested mountain site, South Korea Biogeosciences Discussions, 10, 2565-2589, 2013 Author(s): K. Meusburger, L. Mabit, J.-H. Park, T. Sandor, and C. Alewell The aim of this study is to assess and to validate the suitability of the stable nitrogen and carbon isotope signature as soil erosion indicators in a mountain forest site in South Korea. Our approach is based on the comparison of the isotope signature of "stable" landscape positions (reference sites), which are neither affected by erosion nor deposition, with eroding sites. For undisturbed soils we expect that the enrichment of δ 15 N and δ 13 C with soil depth, due to fractionation during decomposition, goes in parallel with a decrease in nitrogen and carbon content. Soil erosion processes potentially weaken this correlation. 137 Cs-method and the Revised Universal Soil Loss Equation are applied for the soil erosion quantification. The erosion rates obtained with the 137 Cs method range from 0.9 t ha −1 yr −1 to 7 t ha −1 yr −1 . Considering the steep slopes of up to 40° and the erosive monsoon events (R-factor of 6600 MJ mm ha −1 h −1 yr −1 ), the rates are plausible and within the magnitude of the RUSLE- modelled soil erosion rates, varying from 0.02 t ha −1 yr −1 to 5.1 t ha −1 yr −1 . The soil profiles of the reference sites showed significant ( p 〈 0.0001) correlations between nitrogen and carbon content and its corresponding δ 15 N and δ 13 C signatures. In contrast, for the eroding sites this relationship was weaker and for the carbon not significant. These results verify the usefulness of the stable carbon isotope signature as qualitative indicator for soil disturbance. We could show further that the δ 15 N isotope signature can be used similarly for uncultivated sites. We thus propose that the stable δ 15 N and δ 13 C signature of soil profiles could serve as a tool confirming the accurate choice of the reference site in soil erosion studies using the 137 Cs-method.

Description: Temporal and spatial variations of CO 2 , CH 4 and N 2 O fluxes at three differently managed grasslands Biogeosciences Discussions, 10, 2635-2673, 2013 Author(s): D. Imer, L. Merbold, W. Eugster, and N. Buchmann A profound understanding of temporal and spatial variabilities of CO 2 , CH 4 and N 2 O fluxes between terrestrial ecosystems and the atmosphere is needed to reliably quantify these fluxes and to develop future mitigation strategies. For managed grassland ecosystems, temporal and spatial variabilities of these three greenhouse gas (GHG) fluxes are due to environmental drivers as well as to fertilizer applications, grazing and cutting events. To assess how these affect GHG fluxes at Swiss grassland sites, we studied three sites along an altitudinal gradient that corresponds to a management gradient: from 400 m a.s.l. (intensively managed) to 1000 m a.s.l. (moderately intensive managed) to 2000 m a.s.l. (extensively managed). Temporal and spatial variabilities of GHG fluxes were quantified along small-scale transects of 16 static soil chambers at each site. We then established functional relationships between drivers and the observed fluxes on diel and annual time scales. Furthermore, spatial variabilities and their effect on representative site-specific mean chamber GHG fluxes were assessed using geostatistical semivariogram approaches. All three grasslands were N 2 O sources, with mean annual fluxes ranging from 0.15 to 1.28 nmol m −2 s −1 . Contrastingly, all sites were net CH 4 sinks, with uptake rates ranging from −0.56 to −0.15 nmol m −2 s −1 . Mean annual respiration losses of CO 2 , as measured with opaque chambers, ranged from 5.2 to 6.5 μmol m −2 s −1 . While the environmental drivers and their respective explanatory power for N 2 O emissions differed considerably among the three grasslands (adjusted r 2 ranging from 0.19 to 0.42), CH 4 and CO 2 fluxes were much better constrained (adjusted r 2 ranging from 0.41 to 0.83), in particular by soil water content and air temperature, respectively. Throughout the year, spatial heterogeneity was particularly high for N 2 O and CH 4 fluxes. We found permanent hot spots for N 2 O emissions and CH 4 uptake at the extensively managed site. Including these hot spots in calculating the mean chamber flux was essential to obtain a representative mean flux for this ecosystem. At the intensively managed grassland, management effects clearly dominated over effects of environmental drivers on N 2 O fluxes. For CO 2 and CH 4 , the importance of management effects did depend on the status of the vegetation.

Description: Finding immune gene expression differences induced by marine bacterial pathogens in the deep-sea hydrothermal vent mussel Bathymodiolus azoricus Biogeosciences Discussions, 10, 2675-2703, 2013 Author(s): E. Martins, A. Queiroz, R. Serrão Santos, and R. Bettencourt The deep-sea hydrothermal vent mussel Bathymodiolus azoricus lives in a natural environment characterized by extreme conditions of hydrostatic pressure, temperature, pH, high concentrations of heavy metals, methane and hydrogen sulphide. The deep-sea vent biological systems represent thus the opportunity to study and provide new insights into the basic physiological principles that govern the defense mechanisms in vent animals and to understand how they cope with microbial infections. Hence, the importance of understanding this animal's innate defense mechanisms, by examining its differential immune gene expressions toward different pathogenic agents. In the present study, B. azoricus mussels were infected with single suspensions of marine bacterial pathogens, consisting of Vibrio splendidus, Vibrio alginolyticus , or Vibrio anguillarum , and a pool of these Vibrio strains. Flavobacterium suspensions were also used as an irrelevant bacterium . Gene expression analyses were carried out using gill samples from animals dissected at 12 h and 24 h post-infection times by means of quantitative-Polymerase Chain Reaction aimed at targeting several immune genes. We also performed SDS-PAGE protein analyses from the same gill tissues. We concluded that there are different levels of immune gene expression between the 12 h and 24 h exposure times to various bacterial suspensions. Our results from qPCR demonstrated a general pattern of gene expression, decreasing from 12 h over 24 h post-infection. Among the bacteria tested, Flavobacterium is the microorganism species inducing the highest gene expression level in 12 h post-infections animals. The 24 h infected animals revealed, however, greater gene expression levels, using V. splendidus as the infectious agent. The SDS-PAGE analysis also pointed at protein profile differences between 12 h and 24 h, particularly around a protein area, of 18 KDa molecular mass, where most dissimilarities were found. Multivariate analyses demonstrated that immune genes, as well as experimental infections, clustered in discrete groups in accordance with the patterns observed in gene expression changes induced by bacterial pathogens.

Description: Technical Note: Comparison of storage strategies of sea surface microlayer samples Biogeosciences Discussions, 10, 2835-2855, 2013 Author(s): K. Schneider-Zapp, M. E. Salter, P. J. Mann, and R. C. Upstill-Goddard The sea surface microlayer (SML) is an important biogeochemical system whose physico-chemical analysis often necessitates some degree of sample storage. However, many SML components degrade with time so the development of optimal storage protocols is paramount. Using freshwater and saline SML samples from a river-estuary, we interrogated temporal changes in surfactant activity (SA) and the absorbance and fluorescence of chromophoric dissolved organic matter (CDOM) over four weeks, following selected sample treatment and storage protocols. Some variability in the effectiveness of individual protocols most likely reflects sample provenance. None of the various protocols examined performed any better than dark storage at 4 °C without pre-treatment. We thus recommend this as the optimal strategy, coupled with minimal storage times as far as practicable. Future studies of SML properties should validate their chosen storage protocols independently.

Description: Short and long-term thermo-erosion of ice-rich permafrost coasts in the Laptev Sea region Biogeosciences Discussions, 10, 2705-2765, 2013 Author(s): F. Günther, P. P. Overduin, A. V. Sandakov, G. Grosse, and M. N. Grigoriev Permafrost coasts in the Arctic are susceptible to a variety of changing environmental factors all of which currently point to increasing coastal erosion rates and mass fluxes of sediment and carbon to the shallow arctic shelf seas. Rapid erosion along high yedoma coasts composed of Ice Complex permafrost deposits creates impressive coastal ice cliffs and inspired research for designing and implementing change detection studies for a long time, but continuous quantitative monitoring and a qualitative inventory of coastal thermo-erosion for large coastline segments is still lacking. Our goal is to use observations of thermo-erosion along the mainland coast of the Laptev Sea in eastern Siberia to understand how erosion rates depend on coastal geomorphology and the relative contributions of waterline and atmospheric drivers to coastal thermo-erosion over the past 4 decades and in the past few years. We compared multitemporal sets of orthorectified satellite imagery from 1965 to 2011 for three segments of coastline with a length of 73 to 95 km each and analyzed thermo-denudation (TD) along cliff top and thermo-abrasion (TA) along cliff bottom for two nested time periods: long-term rates (the past 39–43 yr) and short term rates (the past 1–3 yr). The Normalized Difference Thermo-erosion Index (NDTI) was used as a proxy that qualitatively describes the relative proportions of TD and TA. Mean annual erosion rates at all three sites were higher in recent years (−5.3 ± 1.31 m a −1 ) than over the long term mean (−2.2 ± 0.13 m a −1 ). The Mamontov Klyk coast exhibit primarily spatial variations of thermo-erosion, while intrasite-specific variations were strongest at the Buor Khaya coast, where slowest long-term rates around −0.5 ± 0.08 m a −1 were observed. The Oyogos Yar coast showed continuously rapid erosion up to −6.5 ± 0.19 m a −1 . In general, variable characteristics of coastal thermo-erosion were observed not only between study sites and over time, but also within single coastal transects along the cliff profile. Varying intensities of cliff bottom and top retreat are leading to diverse qualities of coastal erosion that have different impacts on coastal mass fluxes. The different extents of Ice Complex permafrost degradation within our study sites turned out to influence not only the degree of coupling between TD and TA, and the magnitude of effectively eroded volumes, but also the quantity of organic carbon released to the shallow Laptev Sea from coastal erosion, which ranged on a long-term from 88 ± 21.0 to 800 ± 61.1 t per km coastline per year and will correspond to considerably higher amounts, if recently observed more rapid coastal erosion rates prove to be persistent.

Description: Export of 134 Cs and 137 Cs in the Fukushima river systems at heavy rains by Typhoon Roke in September 2011 Biogeosciences Discussions, 10, 2767-2790, 2013 Author(s): S. Nagao, M. Kanamori, S. Ochiai, S. Tomihara, K. Fukushi, and M. Yamamoto Effects of a heavy rain event on radiocesium export were studied at stations on the Natsui River and the Same River in Fukushima Prefecture, Japan after Typhoon Roke during 21–22 September 2011, six months after the Fukushima Daiichi Nuclear Power Plant accident. Radioactivity of 134 Cs and 137 Cs in river waters was 0.011–0.098 Bq L −1 at normal flow conditions during July–September in 2011, but it increased to 0.85 Bq L −1 in high flow conditions by heavy rains occurring with the typhoon. The particulate fractions of 134 Cs and 137 Cs were 21–56% in the normal flow condition, but were close to 100% after the typhoon. These results indicate that the pulse input of radiocesium associated with suspended particles from land to coastal ocean occurred by the heavy rain event. Export flux of 134 Cs and 137 Cs by the heavy rain accounts for 30–50% of annual radiocesium flux in 2011. Results show that rain events are one factor controlling the transport and dispersion of radiocesium in river watersheds and coastal marine environments.

Description: Microphytobenthos and benthic macroalgae determine sediment organic matter composition in shallow photic sediments Biogeosciences Discussions, 10, 2791-2834, 2013 Author(s): A. K. Hardison, E. A. Canuel, I. C. Anderson, C. R. Tobias, B. Veuger, and M. Waters Benthic macroalgae are a common symptom of eutrophication in shallow coastal bays as a result of increased nutrient loads. Microphytobenthos (MPB) and benthic macroalgae play an important role in system metabolism within shallow coastal bays. However, their independent and interactive influences on sediment organic matter (SOM) are not well understood. We investigated the influence of macroalgae and MPB on SOM quantity and quality in an experimental mesocosm system using bulk and molecular level (total hydrolyzable amino acids, THAA; phospholipid linked fatty acids, PLFA; pigment) analyses. Our experiment used an incomplete factorial design made up of two factors, each with two levels: (1) light (ambient vs. dark) and (2) macroalgae (presence vs. absence of live macroalgae). Over the course of the 42-day experiment, total organic carbon (TOC) and total nitrogen (TN) increased under ambient light by 173 ± 14 and 141 ± 7%, respectively, compared to in the dark (78 ± 29 and 39 ± 22%). THAA comprised a substantial fraction of SOM (∼16% of TOC, 35% of TN) and followed TOC and TN accumulation patterns. Mole percent composition of the THAA pool indicated that SOM was composed of more labile organic material (e.g. L-glutamic acid, phenylalanine) under ambient light conditions while SOM in dark treatments was more degraded, with higher proportions of glycine and D-alanine. PLFA content, which represents viable biomass, made up ∼1% of TOC and contained high levels of algal fatty acids in the light, particularly PLFA derived from diatoms. In the presence of MPB (i.e. light and macroalgae treatments), SOM lability increased, resulting in the observed increases in bacterial PLFA concentrations. Macroalgae, which were added to half of the light treatments, decreased SOM accumulation compared to light treatments without macroalgae, with TOC and TN increasing by only 130 ± 32 and 94 ± 24 %, respectively. This decrease likely resulted from shading by macroalgae, which reduced production of MPB. The presence of macroalgae decreased SOM lability as well, which resulted in diminished buildup of bacterial biomass. By the final day of the experiment, PCA analyses revealed that sediment composition in treatments with macroalgae were more similar to dark treatments and less similar to light treatments without macroalgae. Overall MPB and benthic macroalgae fundamentally altered SOM quality and quantity, which may have notable ecological consequences for shallow-water systems such as increased hypoxia/anoxia, sulfide accumulation, enhanced mineralization and/or stimulated denitrification.

Description: Trace metal distribution in pristine permafrost-affected soils of the Lena River Delta and its Hinterland, Northern Siberia, Russia Biogeosciences Discussions, 10, 2205-2244, 2013 Author(s): I. Antcibor, S. Zubrzycki, A. Eschenbach, L. Kutzbach, D. Bol'shiyanov, and E.-M. Pfeiffer Soils are an important compartment of ecosystems and have the ability to immobilize chemicals preventing their movement to other environment compartments. Predicted climatic changes together with other anthropogenic influences on Arctic terrestrial environments may affect biogeochemical processes enhancing leaching and migration of trace elements in permafrost-affected soils. This is especially important since the Arctic ecosystems are considered to be very sensitive to climatic changes as well as to chemical contamination. This study characterizes background levels of trace metals in permafrost-affected soils of the Lena River Delta and its hinterland in northern Siberia (73.5° N–69.5° N) representing a remote region far from evident anthropogenic trace metal sources. Investigations on total element contents of iron (Fe), arsenic (As), manganese (Mn), zinc (Zn), nickel (Ni), copper (Cu), lead (Pb), cadmium (Cd), cobalt (Co) and mercury (Hg) in different soil types developed in different geological parent materials have been carried out. The highest concentrations of the majority of the measured elements were observed in soils belonging to ice-rich permafrost sediments formed during the Pleistocene (ice-complex) in the Lena River Delta region. Correlation analyses of trace metal concentrations and soil chemical and physical properties at a Holocene estuarine terrace and two modern floodplain levels in the southern-central Lena River Delta (Samoylov Island) showed that the main factors controlling the trace metal distribution in these soils are organic matter content, soil texture and contents of iron and manganese-oxides. Principal Component Analysis (PCA) revealed that soil oxides play a significant role in trace metal distribution in both top and bottom horizons. Occurrence of organic matter contributes to Cd binding in top soils and Cu binding in bottom horizons. Observed ranges of the background concentrations of the majority of trace elements were similar to background levels reported for other pristine arctic areas and did not exceed mean global background concentrations examined for the continental crust as well as for the world's soils.

Description: Space-time dynamics of carbon stocks and environmental parameters related to carbon dioxide emissions in the Buor-Khaya Bay of the Laptev Sea Biogeosciences Discussions, 10, 2159-2204, 2013 Author(s): I. P. Semiletov, N. E. Shakhova, I. I. Pipko, S. P. Pugach, A. N. Charkin, O. V. Dudarev, D. A. Kosmach, and S. Nishino This study aims to improve understanding of carbon cycling in the Buor-Khaya Bay (BKB) by studying the inter-annual, seasonal, and meso-scale variability of carbon stocks and related hydrological and biogeochemical parameters in the water, as well as factors controlling carbon dioxide (CO 2 ) emission. Here we present data sets obtained on summer cruises and winter expeditions during 12 yr of investigation. Based on data analysis, we suggest that in the heterotrophic BKB area, coastal erosion and river discharge serve as predominant drivers of the organic carbon (OC) cycle, determining OC input and transformation, dynamics of nutrients, carbon stocks in the water column, and atmospheric emissions of CO 2 .

Description: Arctic Gypsum Endoliths: a biogeochemical characterization of a viable and active microbial community Biogeosciences Discussions, 10, 2269-2304, 2013 Author(s): L. A. Ziolkowski, N. C. S. Mykytczuk, C. R. Omelon, H. Johnson, L. G. Whyte, and G. F. Slater Extreme environmental conditions such as those found in the polar regions on Earth are thought to test the limits of life. Microorganisms living in these environments often seek protection from environmental stresses such as high UV exposure, desiccation and rapid temperature fluctuations, with one protective habitat found within rocks. Such endolithic microbial communities, which often consist of bacteria, fungi, algae and lichens, are small-scale ecosystems comprised of both producers and consumers. However, the harsh environmental conditions experienced by polar endolithic communities are thought to limit microbial diversity and the rate at which they cycle carbon. In this study, we characterized the microbial community diversity, turnover, and microbe-mineral interactions of a gypsum-based endolithic community in the polar desert of the Canadian high Arctic. 16S/18S rRNA pyrotag sequencing demonstrated the presence of a diverse community of phototrophic and heterotrophic bacteria, algae and fungi. Stable carbon isotope analysis of the viable microbial membranes, as phospholipid fatty acids and glycolipid fatty acids, confirmed the diversity observed by molecular techniques and indicated that atmospheric carbon is assimilated into the microbial community biomass. Uptake of radiocarbon from atmospheric radioweapons testing during the 1960s into microbial lipids was used as a pulse label to determine that the microbial community turns over carbon on the order of 10 yr, equivalent to 4.4 g C m −2 yr −1 gross primary productivity. SEM micrographs indicated that mechanical weathering of gypsum by freeze-thaw cycles leads to increased porosity, which ultimately increases the habitability of the rock. In addition, while bacteria were adhered to these mineral surfaces there was little evidence for microbial alteration of minerals, which contrasts with other gypsum endolithic habitats. While it is possible that these communities turn over carbon quickly and leave little evidence of microbial-mineral interaction, an alternative hypothesis is that the soluble and friable nature of the gypsum and harsh conditions lead to elevated erosion rates, limiting microbial residence times in this habitat. Regardless, this endolithic community represents a microbial system that does not rely on a nutrient pool from the host gypsum cap rock, instead receiving these elements from allochthonous debris to maintain a more diverse and active community than might have been predicted in the polar desert of the Canadian high Arctic.

Description: A new estimate of ocean oxygen utilization points to a reduced rate of respiration in the ocean interior Biogeosciences Discussions, 10, 2245-2267, 2013 Author(s): O. Duteil, W. Koeve, A. Oschlies, D. Bianchi, I. Kriest, E. Galbraith, and R. Matear The Apparent Oxygen Utilization (AOU) is a classical measure of the amount of oxygen respired by biological processes in the ocean interior. We show that the AOU systematically overestimates the True Oxygen Utilization (TOU) in 6 coupled circulation-biogeochemical ocean models, due to atmosphere–ocean oxygen disequilibrium in the subduction regions, consistent with prior work. We develop a new approach that we call Evaluated Oxygen Utilization (EOU), which approximates the TOU at least twice as well as AOU in all 6 models, despite large differences in the physical and biological components of the models. Applying the EOU approach to a global observational dataset leads to an estimated biological oxygen consumption rate that is by 25 percent lower than that derived from AOU-based estimates.

Description: Origin of the Hawaiian rainforest ecosystem and its evolution in long-term primary succession Biogeosciences Discussions, 10, 2415-2453, 2013 Author(s): D. Mueller-Dombois and H. J. Boehmer Born among volcanoes in the north central Pacific about 4 million years ago, the Hawaiian rainforest became assembled from spores of algae, fungi, lichens, bryophytes, ferns and from seeds of about 275 flowering plants that over the millenia evolved into ca. 1000 endemic species. Outstanding among the forest builders were the tree ferns ( Cibotium spp.) and the 'Ōhi'a lehua trees ( Metrosideros spp.), which still dominate the Hawaiian rainforest ecosystem today. The structure of this forest is simple. The canopy in closed mature rainforests is dominated by cohorts of Metrosideros polymorpha and the undergrowth by tree fern species of Cibotium . When a new lava flow cuts through this forest, kipuka are formed, i.e. islands of remnant vegetation. On the new volcanic substrate, the assemblage of plant life-forms is similar as during the evolution of this system. In open juvenile forests, a mat-forming fern, the uluhe fern ( Dicranopteris lineraris ) becomes established. It inhibits further regeneration of the dominant 'Ōhi'a tree, thereby reinforcing the cohort structure of the canopy guild. In the later part of its life cycle, the canopy guild breaks down often in synchrony. The trigger is hypothesized to be a climatic perturbation. After that disturbance the forest becomes reestablished in about 30–40 yr. As the volcanic surfaces age, they go from a mesotrophic to a eutrophic phase, reaching a biophilic nutrient climax by about 1–25 K yr. Thereafter, a regressive oligotrophic phase follows; the soils become exhausted of nutrients. The shield volcanoes break down. Marginally, forest habitats change into bogs and stream ecosystems. The broader 'Ōhi'a rainforest redeveloping in the more dissected landscapes of the older islands looses stature, often forming large gaps that are invaded by the aluminum tolerant uluhe fern. The 'Ōhi'a trees still thrive on soils rejuvenated from landslides and from Asian dust on the oldest (5 million year old) island Kaua'i but their stature and living biomass is greatly diminished.

Description: Taking nature into lab: biomineralization by heavy metal resistant streptomycetes in soil Biogeosciences Discussions, 10, 2345-2375, 2013 Author(s): E. Schütze, A. Weist, M. Klose, T. Wach, M. Schumann, S. Nietzsche, D. Merten, J. Baumert, J. Majzlan, and E. Kothe Biomineralization by heavy metal resistant streptomycetes was tested to evaluate the potential influence on metal mobilities in soil. Thus, we designed an experiment adopting conditions from classical laboratory methods to natural conditions prevailing in metal-rich soils with media spiked with heavy metals, soil agar, and nutrient enriched or unamended soil incubated with the bacteria. As a result, all strains were able to form struvite minerals on tryptic soy broth (TSB) media supplemented with AlCl 2 , MnCl 2 and CuSO 4 , as well as on soil agar. Some strains additionally formed struvite on nutrient enriched contaminated and control soil, as well as on metal contaminated soil without addition of media components. In contrast, switzerite was exclusively formed on minimal media spiked with MnCl 2 by four heavy metal resistant strains, and on nutrient enriched control soil by one strain. Hydrated nickel hydrogen phosphate was only crystallized on complex media supplemented with NiSO 4 by most strains. Thus, mineralization is a~dominant property of streptomycetes, with different processes likely to occur under laboratory conditions and sub-natural to natural conditions. This new understanding may be transferred to formation of minerals in rock and sediment evolution, to ore deposit formation, and also might have implications for our understanding of biological metal resistance mechanisms. We assume that biogeochemical cycles, nutrient storage and metal resistance might be affected by formation and re-solubilization of minerals like struvite in soil at microscale.

Description: Seasonal dissolved inorganic nitrogen and phosphorus budgets for two sub-tropical estuaries in south Florida, USA Biogeosciences Discussions, 10, 2377-2413, 2013 Author(s): C. Buzzelli, Y. Wan, P. H. Doering, and J. N. Boyer Interactions among watershed nutrient loading, circulation, and biogeochemical cycling determine the capacity of estuaries to accommodate introduced nutrients. Baseline quantification of loading, flushing time, export, and internal processes is essential to understand responses of sub-tropical estuaries to variable climate and nutrient loading. The goal of this study was to develop seasonal dissolved inorganic nitrogen (DIN) and phosphorus (DIP) budgets for the two estuaries in south Florida, the Caloosahatchee River Estuary (CRE) and the St. Lucie Estuary (SLE), from 2002–2008 spanning various climatic conditions. The Land Ocean Interactions in the Coastal Zone (LOICZ) Biogeochemical Model was used to generate water, salt, and (DIN and DIP) budgets. The predicted increase in internal DIN production for the CRE vs. the SLE was associated with increased external DIN loading. Water column DIN concentrations decreased and stabilized in both estuaries as flushing time increased to 〉 10 d. The CRE demonstrated heterotrophy or balanced metabolism across all seasonal budgets. Although the SLE was also sensitive to DIN loading, system autotrophy and net ecosystem metabolism increased with DIP loading to this estuary. This included a huge DIP consumption and bloom of a cyanobacterium ( Microcystis aeruginosa ) following hurricane-induced discharge in 2005. Additionally, while denitrification offered a loss pathway for inorganic nitrogen in the CRE, this potential was not evident for the smaller and more anthropogenically altered St. Lucie Estuary. Disparities between total and inorganic loading ratios suggested that management actions should examine the role of dissolved organic nitrogen (DON) in attempts to reduce both nitrogen and phosphorus inputs to the SLE. Establishment of quantitative loading limits for anthropogenically impacted estuaries requires an understanding of the inter-seasonal and inter-annual relationships for both N and P, circulation and flushing, variability in plankton community composition, and the dynamics of DON.

Description: Structural and functional responses of harpacticoid copepods to anoxia in the Northern Adriatic: an experimental approach Biogeosciences Discussions, 10, 2479-2514, 2013 Author(s): M. De Troch, M. Roelofs, B. Riedel, and M. Grego Combined in situ and laboratory studies were conducted to document the effects of anoxia on the structure and functioning of meiobenthic communities, with special focus on harpacticoid copepods. In a first step, anoxia was created artificially by means of an underwater chamber at 24 m depth in the Northern Adriatic, Gulf of Trieste (Mediterranean). Nematodes were found as most abundant taxon, followed by harpacticoid copepods. While nematode densities were not affected by treatment (anoxia/normoxia) or sediment depth, these factors had a significant impact on copepod abundances. Harpacticoid copepod family diversity, in contrast, was not affected by anoxic conditions, only by depth. Ectinosomatidae and Cletodidae were most abundant in both normoxic and anoxic samples. The functional response of harpacticoid copepods to anoxia was studied in a laboratory tracer experiment by adding 13 C pre-labelled diatoms to sediment cores in order to test (1) if there is a difference in food uptake by copepods under normoxic and anoxic conditions and (2) whether initial (normoxia) feeding of harpacticoid copepods on diatoms results in a better survival of copepods in subsequent anoxic conditions. Independent of the addition of diatoms, there was a higher survival rate in normoxia than anoxia. The supply of additional food did not result in a higher survival rate of copepods in anoxia, which might be explained by the presence of a nutritionally better food source and/or a lack of starvation before adding the diatoms. However, there was a reduced grazing pressure by copepods on diatoms in anoxic conditions. This resulted in a modified fatty acid composition of the sediment. We concluded that anoxia not only impacts the survival of consumers (direct effect) but also of primary producers (indirect effect), with important implications for the recovery phase.

Description: Natural and Fukushima-derived radioactivity in macroalgae and mussels along the Japanese shoreline Biogeosciences Discussions, 10, 2617-2633, 2013 Author(s): Z. Baumann, N. Casacuberta, H. Baumann, P. Masqué, and N. S. Fisher Following the failure of the nuclear power plant in Fukushima Prefecture in March 2011, peer-reviewed publications describing radioactivity levels in organisms inhabiting coastal environments are scarce. This paper reports on elevated levels of 134 Cs and 137 Cs in macroalgae and mussels (up to ~ 800 Bq kg −1 dry wt.) in June 2011. Cs concentrations in biota sampled in early June 2011 were higher in areas south of Fukushima than sampled in the last third of the month north of Fukushima. Radioactivity from 134+137 Cs in organisms south of Fukushima were comparable to or lower than that from the naturally occuring 40 K in the same samples. While 210 Pb and 210 Po concentrations were generally lower than these other radionuclides, 210 Po as an α-emitter is more significant from a radiological viewpoint than γ-emitters as it can inflict greater biological damage. By applying known bioconcentration factors of Cs in biota, measured biota concentrations of Cs were also used to estimate Cs concentraitons in coastal seawater to be in the range of 10 2 –10 3 Bq m −3 . These estimates show that 3 months after the accident and maximal release of radioactive Cs, levels of Cs persisted in coastal waters, although at levels that were two orders of magnitude lower than at the time of release. These June coastal seawater Cs levels were four orders of magnitude above Cs concentrations off Japan prior to the Fukushima disaster.

Description: Spatial heterogeneity in mangroves assessed by GeoEye-1 satellite data: a case-study in Zhanjiang Mangrove National Nature Reserve (ZMNNR), China Biogeosciences Discussions, 10, 2591-2615, 2013 Author(s): K. Leempoel, C. Bourgeois, J. Zhang, J. Wang, M. Chen, B. Satyaranayana, J. Bogaert, and F. Dahdouh-Guebas Mangrove forests, which are declining across the globe mainly because of human intervention, require an evaluation of their past and present status (e.g. areal extent, species-level distribution, etc.) to better implement conservation and management strategies. In this paper, mangrove cover dynamics at Gaoqiao (under the jurisdiction of Zhanjiang Mangrove National Nature Reserve – ZMNNR, P. R. China) were assessed through time using 1967 (Corona KH-4B), 2000 (Landsat ETM+), and 2009 (GeoEye-1) satellite imagery. An important decline in mangrove cover (−36%) was observed between 1967 and 2009 due to dike construction for agriculture (paddy) and aquaculture practices. Moreover, dike construction prevented mangroves from expanding landward. Although a small increase of mangrove area was observed between 2000 and 2009 (+24%), the ratio mangrove/aquaculture kept decreasing due to increased aquaculture at the expense of rice culture. In the land-use/cover map based on ground-truth data (5 m × 5 m plot-based tree measurements) (August–September, 2009) and spectral reflectance values (obtained from pansharpened GeoEye-1), both Bruguiera gymnorrhiza and small Aegiceras corniculatum are distinguishable at 73–100% accuracy, whereas tall A. corniculatum is identifiable at only 53% due to its mixed vegetation stands close to B. gymnorrhiza (classification accuracy: 85%). Sand proportion in the sediment showed significant differences (Kruskal-Wallis/ANOVA, P 〈 0.05) between the three mangrove classes ( B. gymnorrhiza and small and tall A. corniculatum ). Distribution of tall A. corniculatum on the convex side of creeks and small A.corniculatum on the concave side (with sand) show intriguing patterns of watercourse changes. Overall, the advantage of very high resolution satellite images like GeoEye-1 for mangrove spatial heterogeneity assessment and/or species-level discrimination is well demonstrated, along with the complexity to provide a precise classification for non-dominant species (e.g. Kandelia obovata ) at Gaoqiao. Despite the limitations such as geometric distortion and single band information, the 42-yr old Corona declassified images are invaluable for land-use/cover change detections when compared to recent satellite data sets.

Description: Natural variability in hard bottom communities and possible drivers assessed by a time-series study in the SW Baltic Sea: know the noise to detect the change Biogeosciences Discussions, 10, 2967-3007, 2013 Author(s): M. Wahl, H.-H. Hinrichsen, A. Lehmann, and M. Lenz In order to detect shifts in community structure and function associated with global change, the natural background fluctuation in these traits must be known. In a 6-yr study we quantified year to year variability of taxonomic and functional composition of benthic hard bottom communities in the Western Baltic. While taxonomic fluctuations were substantial, functionality of the communities seems preserved in most cases. Environmental conditions potentially driving these fluctuations are winter temperatures and current regimes. We tentatively define a confidence range of natural variability in productivity, composition and diversity a departure from which might help identifying an ongoing regime shift driven by global change. In addition, we propose a statistical procedure distinguishing directional shifts ("signal") from natural fluctuations ("noise").

Description: Regional variability of acidification in the Arctic: a sea of contrasts Biogeosciences Discussions, 10, 2937-2965, 2013 Author(s): E. E. Popova, A. Yool, A. C. Coward, and T. R. Anderson The Arctic Ocean is a region that is particularly vulnerable to the impact of ocean acidification driven by rising atmospheric CO 2 , negatively impacting calcifying organisms such as coccolithophorids and foraminiferans. In this study, we use an ocean general circulation model, with embedded biogeochemistry and a full description of the carbon cycle, to study the response of pH and saturation states of calcite and aragonite to changing climate in the Arctic Ocean. Particular attention is paid to the strong regional variability within the Arctic and, for comparison, simulation results are contrasted with those for the global ocean. Simulations were run to year 2099 using the RCP 8.5 (the highest IPCC AR5 CO 2 emission scenario). The separate impacts of the direct increase in atmospheric CO 2 and indirect effects via climate feedbacks (changing temperature, stratification, primary production and fresh water fluxes) were examined by undertaking two simulations, one with the full system and the other in which ocean-atmosphera exchange of CO 2 was prevented from increasing beyond the flux calculated for year 2000. Results indicate that climate feedbacks, and spatial heterogeneity thereof, play a strong role in the declines in pH and carbonate saturation (Ω) seen in the Arctic. The central Arctic, Canadian Arctic Archipelago and Baffin Bay show greatest rates of acidification and Ω decline as a result of melting sea ice. In contrast, areas affected by Atlantic inflow including the Greenland Sea and outer shelves of the Barents, Kara and Laptev seas, had minimal decreases in pH and Ω because weakening stratification associated with diminishing ice cover led to greater mixing and primary production. As a consequence, the predicted onset of undersaturation is highly variable regionally within the Arctic, occurring during the decade of 2000–2010 in the Siberian shelves and Canadian Arctic Archipelago, but as late as the 2080s in the Barents and Norwegian Seas. We conclude that, in order to make future projections of acidification and carbon saturation state in the Arctic, regional variability needs to be adequately resolved, with particular emphasis on reliable predictions of the rates of retreat of the sea-ice which are a major source of uncertainty.

Description: Influence of physical and biological processes on the seasonal cycle of biogenic flux in the equatorial Indian Ocean Biogeosciences Discussions, 10, 2889-2936, 2013 Author(s): P. J. Vidya, S. Prasanna Kumar, M. Gauns, A. Verenkar, D. Unger, and V. Ramaswamy Seasonal cycle of biogenic fluxes obtained from sediment trap at two locations 5° 24′ N, 86° 46′ E (SBBT) and 3° 34′ N, 77° 46′ E (EIOT) within the equatorial Indian Ocean (EIO) were examined to understand the factors that control them. The sediment trap data at SBBT were collected for ten years from November 1987 while that at EIOT was for one year period from January 1996. The characteristic of biogenic flux at SBBT was the strong seasonality with peak flux in August, while lack of seasonality characterized the flux at EIOT. At the SBBT and EIOT, the higher chlorophyll biomass during summer monsoon was supported by wind-mixing, which supplied new nitrogen to the upper ocean. The stronger winds at SBBT compared to EIOT resulted in greater entrainment of nutrients to the euphotic zone, which supported higher chlorophyll biomass. High cell counts of phytoplankton (〉 5 μm) at SBBT dominated by diatoms suggest the operation of classical food web and high carbon export. On the contrary, one-and-half time higher magnitude of micro-zooplankton biomass dominated by picophytoplankton along with 2-fold lesser meso-zooplankton at EIOT indicated the importance of microbial loop. The substantial decrease in the carbon export at EIOT indicated faster remineralization of photosynthetically produced organic matter. We see a striking similarity between the biological process that operates in the SBBT with that of the equatorial Atlantic and EIOT with that of the equatorial Pacific, though the physical forcing in these three regions, namely EIO, the equatorial Atlantic and the equatorial Pacific, are very different.

Description: CellTracker Green labelling vs. Rose Bengal staining: CTG wins by points in distinguishing living from dead anoxia-impacted copepods and nematodes Biogeosciences Discussions, 10, 2857-2887, 2013 Author(s): M. Grego, M. Stachowitsch, M. De Troch, and B. Riedel Hypoxia and anoxia have become a key threat to shallow coastal seas. Much is known about their impact on macrofauna, less on meiofauna. In an attempt to shed more light on the latter group, in particular from a process-oriented view, we experimentally induced short-term anoxia (1 week) in the Northern Adriatic Sea, Mediterranean, and examined the two most abundant meiofauna taxa – harpacticoid copepods and nematodes. Both taxa also represent different ends of the tolerance spectrum, with copepods being the most sensitive and nematodes among the most tolerant. We compared two methods: CellTracker Green (CTG) – new labelling approach for meiofauna – with the traditional Rose Bengal (RB) staining method. CTG binds to active enzymes and therefore colours live organisms only. The two methods show considerable differences in the number of living and dead individuals of both meiofauna taxa. Generally, RB will stain dead but not yet decomposed copepods and nematodes equally as live ones. Specifically, RB significantly overestimated the number of living copepods in all sediment layers in anoxic samples, but not in any normoxic samples. In contrast, for nematodes, the methods did not show such a clear difference between anoxia and normoxia. Surprisingly, RB overestimated the number of living nematodes in the top sediment layer of normoxic samples, which implies an overestimation of the overall live nematofauna. For monitoring and biodiversity studies, the RB method might be sufficient, but for more fine-scaled (days, hours, tipping points) studies, especially on hypoxia and anoxia where it is necessary to resolve the course of events, CTG labelling is a better tool. Moreover, it clearly highlights the surviving species within the copepod or nematode community. As already accepted for foraminiferal research, we demonstrate that the CTG labelling is also valid for other meiofauna groups.

Description: Isotopic constraints on the pre-industrial oceanic nitrogen budget Biogeosciences Discussions, 10, 3121-3175, 2013 Author(s): C. J. Somes, A. Oschlies, and A. Schmittner The size of the bio-available (i.e. "fixed") nitrogen inventory in the ocean influences global marine productivity and the biological carbon pump. Despite its importance, the pre-industrial rates for the major source and sink terms of the oceanic fixed nitrogen budget, N 2 fixation and denitrification, respectively, are not well known. However, these processes leave distinguishable imprints on the ratio of stable nitrogen isotopes, δ 15 N, which can therefore help to infer their patterns and rates. Here we use δ 15 N observations from the water column and a new database of seafloor measurements to constrain rates of N 2 fixation and denitrification predicted by a global three-dimensional Model of Ocean Biogeochemistry and Isotopes (MOBI). Sensitivity experiments were performed to quantify uncertainties associated with the isotope effect of denitrification in the water column and sediments. They show that the level of nitrate utilization in suboxic zones, that is the balance between nitrate consumption by denitrification and nitrate replenishment by mixing (dilution effect), significantly affects the isotope effect of water column denitrification and thus global mean δ 15 NO 3 − . Experiments with lower levels of nitrate utilization within the suboxic zone (i.e. higher residual water column nitrate concentrations, ranging from 20–32 μM) require higher ratios of benthic to water column denitrification (BD:WCD = 0.75–1.4, respectively), to satisfy the global mean NO 3 − and δ 15 NO 3 − constraints in the modern ocean. This suggests that nitrate utilization in suboxic zones play an important role in global nitrogen isotope cycling. Increasing the net fractionation factor for benthic denitrification (ϵ BD = 0–4‰) requires even higher ratios of benthic to water column denitrification (BD:WCD = 1.4–3.5, respectively). The model experiments that best reproduce observed seafloor δ 15 N support the middle to high-end estimates for the net fractionation factor of benthic denitrification (ϵ BD = 2–4‰). Assuming a balanced fixed nitrogen budget, we estimate that pre-industrial rates of N 2 fixation, water column denitrification, and benthic denitrification were approximately 195–345, 65–75, and 130–270 Tg N yr −1 , respectively. Although uncertainties still exist, these results suggest that previous estimates of N 2 fixation have been significantly underestimated and the residence time for oceanic fixed nitrogen is between ~ 1500–3000 yr.

Description: Subsurface low pH and carbonate saturation state of aragonite on China side of the North Yellow Sea: combined effects of global atmospheric CO 2 increase, regional environmental changes, and local biogeochemical processes Biogeosciences Discussions, 10, 3079-3120, 2013 Author(s): W.-D. Zhai, N. Zheng, C. Huo, Y. Xu, H.-D. Zhao, Y.-W. Li, K.-P. Zang, J.-Y. Wang, and X.-M. Xu Based upon seven field surveys conducted between May 2011 and January 2012, we investigated pH, carbonate saturation state of aragonite (Ω arag ), and ancillary parameters on the Chinese side of the North Yellow Sea, a western North Pacific continental margin of major economic importance. Subsurface waters were nearly in equilibrium with air in May and June. From July to October, the fugacity of CO 2 ( f CO 2 ) of bottom water gradually increased to 697 ± 103 μatm and pH decreased to 7.83 ± 0.07 due to respiration/remineralization processes of primary production induced biogenic particles. In November and January, bottom water f CO 2 decreased and pH gradually returned to an air-equilibrated level due to cooling enhanced vertical mixing. The corresponding bottom water Ω arag was 1.74 ± 0.17 (May), 1.77 ± 0.26 (June), 1.70 ± 0.26 (July), 1.72 ± 0.33 (August), 1.32 ± 0.31 (October), 1.50 ± 0.28 (November), and 1.41 ± 0.12 (January). Critically low Ω arag values of 1.0 to 1.2 were mainly observed in subsurface waters in a salinity range of 31.5–32.5 psu in October and November, accounting for ~ 10% of the North Yellow Sea area. Water mass derived from the adjacent Bohai Sea had a typical water salinity of 30.5–31.5 psu, and bottom water Ω arag values ranged mostly between 1.6 and 2.4. This study showed that the carbonate system in the North Yellow Sea was substantially influenced by global atmospheric CO 2 increase. The community respiration/remineralization rates in typical North Yellow Sea bottom water mass were estimated at 0.55–1.0 μmol O 2 kg −1 d −1 in warm seasons, leading to seasonal drops in subsurface pH and Ω arag . Outflow of the Bohai Sea water mass counteracted the subsurface Ω arag reduction in the North Yellow Sea.

Description: Erosion control blankets, organic amendments and site variability influenced the initial plant community at a limestone quarry in the Canadian Rocky Mountains Biogeosciences Discussions, 10, 3009-3037, 2013 Author(s): A. C. Cohen-Fernández and M. A. Naeth Season of seeding and soil amendment with manure mix, wood shavings and erosion control blankets were evaluated over two growing seasons to determine their effect on soil properties and native grass establishment at a Canadian limestone quarry and lime processing plant. Season (fall, spring) of soil amending and seeding did not significantly affect revegetation or soil properties. Site characteristics such as slope, aspect, initial soil nutrients and surrounding plant communities influenced early plant community development and overall effects of soil treatments. Erosion control blankets resulted in the highest seeded plant cover and the lowest non seeded plant cover despite not significantly changing soil chemical properties. Total nitrogen and carbon significantly increased establishment of seeded grasses and non seeded species. Increased nitrogen and carbon in the constructed soils were best achieved through addition of manure. Wood shavings did not favour establishment of vegetation and resulted in similar, and in some cases less, vegetation than controls. Assisted revegetation increased plant cover from 〈 6 to 50% and reduced cover of non seeded species. Amendments that modified both chemical and physical soil conditions were best to increase vegetation establishment in the harsh conditions of the quarry.

Description: Evaluating the agreement between measurements and models of net ecosystem exchange at different times and time scales using wavelet coherence: an example using data from the North American Carbon Program Site-Level Interim Synthesis Biogeosciences Discussions, 10, 3039-3077, 2013 Author(s): P. C. Stoy, M. Dietze, A. D. Richardson, R. Vargas, A. G. Barr, R. S. Anderson, M. A. Arain, I. T. Baker, T. A. Black, J. M. Chen, R. B. Cook, C. M. Gough, R. F. Grant, D. Y. Hollinger, R. C. Izaurralde, C. J. Kucharik, P. Lafleur, B. E. Law, S. Liu, E. Lokupitiya, Y. Luo, J. W. Munger, C. Peng, B. Poulter, D. T. Price, D. M. Ricciuto, W. J. Riley, A. K. Sahoo, K. Schaefer, C. R. Schwalm, H. Tian, H. Verbeeck, and E. Weng Earth system processes exhibit complex patterns across time, as do the models that seek to replicate these processes. Model output may or may not be significantly related to observations at different times and on different frequencies. Conventional model diagnostics provide an aggregate view of model-data agreement, but usually do not identify the time and frequency patterns of model misfit, leaving unclear the steps required to improve model response to environmental drivers that vary on characteristic frequencies. Wavelet coherence can quantify the times and frequencies at which models and measurements are significantly different. We applied wavelet coherence to interpret the predictions of twenty ecosystem models from the North American Carbon Program (NACP) Site-Level Interim Synthesis when confronted with eddy covariance-measured net ecosystem exchange (NEE) from ten ecosystems with multiple years of available data. Models were grouped into classes with similar approaches for incorporating phenology, the calculation of NEE, and the inclusion of foliar nitrogen (N). Models with prescribed, rather than prognostic, phenology often fit NEE observations better on annual to interannual time scales in grassland, wetland and agricultural ecosystems. Models that calculate NEE as net primary productivity (NPP) minus heterotrophic respiration (HR) rather than gross ecosystem productivity (GPP) minus ecosystem respiration (ER) fit better on annual time scales in grassland and wetland ecosystems, but models that calculate NEE as GPP – ER were superior on monthly to seasonal time scales in two coniferous forests. Models that incorporated foliar nitrogen (N) data were successful at capturing NEE variability on interannual (multiple year) time scales at Howland Forest, Maine. Combined with previous findings, our results suggest that the mechanisms driving daily and annual NEE variability tend to be correctly simulated, but the magnitude of these fluxes is often erroneous, suggesting that model parameterization must be improved. Few NACP models correctly predicted fluxes on seasonal and interannual time scales where spectral energy in NEE observations tends to be low, but where phenological events, multi-year oscillations in climatological drivers, and ecosystem succession are known to be important for determining ecosystem function. Mechanistic improvements to models must be made to replicate observed NEE variability on seasonal and interannual time scales.

Description: Photooxidation of dimethylsulfide (DMS) in the Canadian Arctic Biogeosciences Discussions, 10, 2093-2126, 2013 Author(s): A. Taalba, H. Xie, M. G. Scarratt, S. Bélanger, and M. Levasseur Photolysis of dimethylsulfide (DMS), a secondary photochemical process mediated by chromophoric dissolved organic matter (CDOM), has previously been demonstrated to be an important loss term of DMS in the surface layer of warm seas and the Southern Ocean. The role of photolysis in regulating the DMS dynamics in the Arctic Ocean, however, remains obscure. This study for the first time determined the apparent quantum yield (AQY) spectra of DMS photooxidation in northern polar marine milieus covering the Baffin Bay in the eastern Canadian Arctic and the Mackenzie River estuary, Mackenzie Shelf and Canada Basin in the western Canadian Arctic. The DMS AQY was fairly invariant at salinities 〈 25 but rose rapidly with further increasing salinity, which is well defined by a three-parameter exponential decay equation with a constant intercept. Salinity can therefore be used as a quantitative indicator of the DMS AQY. The DMS AQY in the ultraviolet (UV) wavelengths was linearly and positively correlated with the spectral slope coefficient (275–295 nm) of the CDOM absorption spectrum, suggesting that marine CDOM photosensitizes the degradation of DMS more efficiently than does terrestrial CDOM. High concentrations of nitrate (~12 μmol L −1 ) in deep water samples boosted DMS photooxidation by 70–80%, due likely to radical chemistry of nitrate photolysis. Coupled optical-photochemical modeling, based on the obtained DMS AQY spectra, shows that UV-A (320–400 nm) accounted for 60–75% of the DMS photolysis in the sunlit surface layer and that photochemistry degraded DMS on an e -folding time from 9 to 100 d (mean: 29 d). The photooxidation term on average accounted for 21% of the DMS gross loss rate and was comparable to the atmospheric DMS ventilation rate estimated for the same geographic regions.

Description: Monthly measured primary and new productivities in the Ulleung Basin as a biological "hot spot" in the East/Japan Sea Biogeosciences Discussions, 10, 2127-2158, 2013 Author(s): J. H. Kwak, S. H. Lee, H. J. Park, E. J. Choy, H. D. Jeong, K. R. Kim, and C. K. Kang The Ulleung Basin (UB), located in the southwestern part of the East/Japan Sea (EJS), is considered having an unusually high productivity for a~deep basin. Recently changes have been reported in physical, chemical, and in biological properties. Here we measured the primary and new productivities in the UB using a 13 C- 15 N dual isotope tracer technique. Measurements took place every month for the first time throughout a year for a~better estimate of the annual primary production in the EJS. Temporal variations of temperature, salinity and density (σ t ) in the study area were highly seasonal as expected for an ocean in the temperate zone. Nutrient distributions reflected these seasonal fluctuations in the vertical structure of the water column. Diatoms were in general the most dominant phytoplankton ranging from 15.5 to 82.2% with an average of 42.0% (S.D. = ± 9.9%). Based on those average daily productivities from our monthly measurements, the annual primary, new, and regenerated production in the UB were 273.0 g C m −2 yr −1 , 62.6 g N m −2 yr −1 , and 48.7 g N m −2 yr −1 , respectively. Our estimated high f -ratio (0.59) in the UB, indicated that the predominant nitrogen source for primary production was nitrate. This is comparable with the nitrogen source in a productive coastal-upwelling region. New carbon production by phytoplankton is estimated as 212.8 g C m −2 yr −1 (S.D. = ± 9.7 g C m −2 yr −1 ) which indicates that a large portion (78%) of total annual primary production might potentially be exported from the diatom-dominated euphotic zone to a deeper zone in the UB. Further intense integrated field observations will be necessary to improve our understanding of the current marine ecosystem in the UB as an important biological production area in the EJS.

Description: Fukushima-derived radiocesium in western North Pacific sediment traps Biogeosciences Discussions, 10, 2455-2477, 2013 Author(s): M. C. Honda, H. Kawakami, S. Watanabe, and T. Saino At two stations in the western North Pacific, K2 in the subarctic gyre and S1 in the subtropical gyre, time-series sediment traps were collecting sinking particles when the Fukushima Daiichi Nuclear Power Plant (FNPP1) accident occurred on 11 March 2011. Radiocesium ( 134 Cs and 137 Cs) derived from FNPP1 accident was detected in sinking particles collected at 500 m by late March 2011 and at 4810 m by early April 2011 at both stations. The sinking velocity of 134 Cs and 137 Cs was estimated to be 8 to 36 m day −1 between the surface and 500 m and 〉 180 m day −1 between 500 m and 4810 m. 137 Cs specific activity varied from 0.14 to 0.25 Bq g −1 dry weight. These values are higher than those of surface seawater, suspended particles, and zooplankton collected in April 2011. Although the radiocesium may have been adsorbed onto or incorporated into clay minerals, correlations between 134 Cs and lithogenic material were not always significant; therefore, the form of the cesium associated with the sinking particles is still an open question. The total 137 Cs flux by late June at K2 and by late July at S1 was 0.5 to 1.7 Bq m −2 at both depths. Compared with 137 Cs input to both stations by April 2011, estimated from the surface 137 Cs activity and mixed layer depth and by assuming that the observed 137 Cs flux was constant throughout the year, the estimated removal rate of 137 Cs from the upper layer (residence time in the upper layer) was 0.3 to 1.5% (68 to 312 yr). The estimated removal rates and residence times are comparable to previously reported values.

Description: Phytoplankton community structure in the Lena Delta (Siberia, Russia) in relation to hydrography Biogeosciences Discussions, 10, 2305-2344, 2013 Author(s): A. C. Kraberg, E. Druzhkova, B. Heim, M. J. G. Loeder, and K. H. Wiltshire The Lena Delta in Northern Siberia is one of the largest river deltas in the world. During peak discharge, after the ice melt in spring, it delivers between 60–8000 m 3 s −1 of water and sediment into the Arctic Ocean. The Lena Delta and the Laptev Sea coast also constitute a~continuous permafrost region. Ongoing climate change, which is particularly pronounced in the Arctic, is leading to increased rates of permafrost thaw. This is likely to profoundly change the discharge rates of the Lena River and the chemistry of the river waters which are discharged into the coastal Laptev Sea, e.g. by increasing concentrations of inorganic nutrients, DOC and importantly methane. These physical and chemical changes will also affect the composition of and interactions between phytoplankton and zooplankton communities, forming the basis of the food web. However, before potential consequences of climate change for coastal arctic plankton communities can be judged, the inherent status of the diversity and linked foodweb interactions within the delta need to be established. As part of the AWI Lena Delta Programme in 2010 the phyto- and microzooplankton community in three river channels as well as four coastal transects were investigated to capture the typical river phytoplankton communities and the transitional zone of brackish/marine conditions. Most CTD profiles from 23 coastal stations showed very strong stratification. The only exception to this was a small a shallow and mixed area running from the outflow of Bykovskaya channel in a northerly direction parallel to the shore (transect 3). Of the five stations in this area three had a salinity of close to zero. Two further stations had salinities of around 2 and 5 throughout the water column. In the remaining transects on the other hand salinities varied between 5–30 with depth. Phytoplankton counts from the outflow from the Lena were dominated by diatoms ( Aulacoseira species) cyanobacteria ( Aphanizomenon , Pseudanabaena ) and chlorophytes, in those stations characterized by river outflow (stations in the Lena itself and in coastal transect 3). In contrast in the stratified stations the plankton was mostly dominated by dinoflagellates, ciliates and nanoflagellates, with only an insignificant diatom component from the genera Chaetoceros and Thalassiosira (brackish as opposed to freshwater species). Ciliate abundance was significantly coupled with the abundance of total flagellates. A pronounced partitioning in the phytoplankton community was also discernible with depth, with a different community composition and abundance above and below the thermocline in the stratified sites. This work represents the first attempt at analyzing the phytoplankton structure of the region of freshwater influence at confluence Lena–Laptev sea.

Description: The submarine groundwater discharge as a carbon source to the Baltic Sea Biogeosciences Discussions, 10, 2069-2091, 2013 Author(s): B. Szymczycha, A. Maciejewska, A. Szczepanska, and J. Pempkowiak Submarine Groundwater Discharge (SGD) is an important, yet poorly recognized pathway of material transport to the marine environment. This work reports on the results of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) concentrations in the groundwater seeping to the Bay of Puck. The loads of carbon via SGD were quantified for the Baltic Sea sub-basins and the entire Baltic Sea. The annual averages of DIC and DOC concentrations in the groundwater were equal to 64.5 ± 10.0 mg C L −1 and 5.8 ± 0.9 mg C L −1 . The DIC and DOC fluxes via SGD to the Baltic Sea were estimated at 283.6 ± 66.7 kt yr −1 and 25.5 ± 4.2 kt yr −1 . The SGD derived carbon load to the Baltic Sea is an important component of carbon budget, which turns the status of the sea into firmly heterotrophic. The carbon load to the World Ocean, which was calculated basing on few reports on groundwater discharges and the measured carbon concentrations, amounts to- (142–155) × 10 3 kt yr −1 (DIC), and (13–14) × 10 3 kt yr −1 (DOC). The carbon flux via SGD amounts to some 25% of the riverine carbon load, and should be included into the World Ocean carbon budget.

Description: 90 Sr and 89 Sr in seawater off Japan as a consequence of the Fukushima Dai-ichi nuclear accident Biogeosciences Discussions, 10, 2039-2067, 2013 Author(s): N. Casacuberta, P. Masqué, J. Garcia-Orellana, R. Garcia-Tenorio, and K. O. Buesseler The impact of the earthquake and tsunami in the east coast of Japan in 11 March 2011 caused a loss of power at the Fukushima Dai-ichi Nuclear Power Plant (NPP) that resulted in one of the most important releases of artificial radioactivity to the environment. Although several works were devoted to evaluate the atmospheric dispersion of radionuclides, the impact of the discharges to the ocean has been less investigated. Here we evaluate the distribution of Fukushima-derived 90 Sr and 89 Sr throughout waters 30–600 km offshore in June 2011. Concentrations of 90 Sr and 89 Sr in both surface waters and shallow profiles ranged from 0.8 ± 0.2 to 85 ± 3 Bq m −3 and from 19 ± 6 to 265 ± 74 Bq m −3 , respectively. Because of its short half-life, all measured 89 Sr was due to the accident, while the 90 Sr concentrations can be compared to the background levels in the Pacific Ocean of about 1.2 Bq m −3 . Fukushima-derived radiostrontium was mainly detected north of Kuroshio Current, as this was acting as a southern boundary for transport. The highest activities were associated with near-shore eddies, and larger inventories were found in the closest stations to Fukushima NPP. The data evidences a major influence of direct liquid discharges of radiostrontium compared to the atmospheric deposition. Existing 137 Cs data reported from the same samples allowed us establishing a 90 Sr/ 137 Cs ratio of 0.0256 ± 0.0006 in seawater off Fukushima, being significantly different than that of the global atmospheric fallout (i.e. 0.63) and may be used in future studies to track waters coming from the east coast of Japan. Liquid discharges of 90 Sr to the ocean were estimated, resulting in an inventory of 53 ± 1 TBq of 90 Sr in the inshore study area in June 2011 and total releases of 90 Sr ranging from 90 to 900 TBq, depending upon the reported estimates of 137 Cs releases that are considered.

Description: Differential gene expression in the mussel Bathymodiolus azoricus from the Menez Gwen and Lucky Strike deep-sea hydrothermal vent sites Biogeosciences Discussions, 10, 2013-2038, 2013 Author(s): R. Bettencourt, M. I. Rodrigues, I. Barros, T. Cerqueira, C. Freitas, V. Costa, M. Pinheiro, C. Egas, and R. S. Santos The deep-sea hydrothermal vent mussel Bathymodiolus azoricus is a symbiont bearing bivalve that is found in great abundance at the Menez Gwen and Lucky Strike vent sites and in close vicinity off the Azores region near the Mid-Atlantic Ridge (MAR). The distinct relationships that vent mussels have developed with their physical and chemical environments are likely reflected in global gene expression profiles providing thus a means to distinguish geographically distinct vent mussels on the basis of gene expression studies, fluorescence in situ hybridization (FISH) experiments and 16S rRNA amplicon sequencing, to assess the natural expression of bacterial genes and vent mussel immune genes and the constitutive distribution and relative abundance of endosymbiotic bacteria within gill tissues. Our results confirmed the presence of methanotroph-related endosymbionts in Menez Gwen vent mussels whereas Lucky Strike specimens seem to harbor a different bacterial morphotype when a methane monooxygenase gene specific probe was used. No qualitative differences could be visualized between Menez Gwen and Lucky Strike individuals when tested with sulfur-oxidizing-related nucleic-acid probe. Quantitative PCR (qPCR) studies revealed varied gene expression profiles in both Menez Gwen and Lucky Strike mussel gill tissues for the immune genes selected. Genes encoding transcription factors presented noticeably low levels of fold expression whether in MG or LS animals whereas the genes encoding effector molecules appeared to have higher levels expression in MG gill tissues. The peptidoglycan recognition molecule, encoding gene, PGRP presented the highest level of transcriptional activity among the genes analyzed in MG gill tissues, seconded by carcinolectin and thus denoting the relevance of immune recognition molecules in early stage of the immune responses onset. Genes regarded as encoding molecules involved in signaling pathways were consistently expressed in both MG and LS gill tissues. Remarkably, the immunity-related GTPase encoding gene demonstrated in LS samples, the highest level of expression among the signaling molecule encoding genes tested when expressions levels were compared between MG and LG animals. A differential expression analysis of bacterial genes between MG and LS indicated a clear expression signature in LS gill tissues. The bacterial community structure ensued from the 16S rRNA sequencing analyses pointed at a unpredicted conservation of endosymbiont bacterial loads between MG and LS samples. Taken together, our results support the premise that Bathymodiolus azoricus exhibits different transcriptional statuses depending on which hydrothermal vent site it is collected from and within the same collection site while exhibiting differential levels of expression of genes corresponding to different immune functional categories. The present study represents a first attempt to characterize gene expression signatures in hydrothermal vent animals issued from distinct deep-sea environmental sites based on immune and bacterial genes expressions.

Description: Initial Spread of 137 Cs over the shelf of Japan: a study using the high-resolution global-coastal nesting ocean model Biogeosciences Discussions, 10, 1929-1955, 2013 Author(s): Z. Lai, C. Chen, R. Beardsley, H. Lin, R. Ji, J. Sasaki, and J. Lin The 2011 Tohoku earthquake caused radionuclide 137 Cs be directly released into the ocean from the Fukushima Dai-ichi nuclear power plants. A high-resolution global-coastal nesting ocean model was established to simulate the initial spread of 137 Cs as conservative tracer over the shelf of Japan after the accident. The major advantage in the current model system is to use unstructured grids to resolve the power plant and the coastal geometry with a grid resolution much higher than that used in previous modeling experiments. Therefore, it gives us an opportunity to examine the necessity whether the detailed structure of the Power plant should be considered for numerical experiment of 137 Cs dispersion or not. This could provide us an alternative insight into the physical processes that lead to its spread of 137 Cs over the shelf of Japan. Our results suggested that to resolve the dispersion process from the source point to the south and north discharging canal is critical for an accurate prediction of the spread of 137 Cs to the 30 km sites off the coast. Moreover, a 2 km grid resolution along Japan coast is probably not high enough to resolve the plume correctly. Finally, the model-data comparison suggested that the physical process associated with the transfer of dissolved 137 Cs into the sediment phase could potentially be important and should be considered in the future tracer modeling.

Description: Direct observation of 134 Cs and 137 Cs in surface seawater in the western and central North Pacific after the Fukushima Dai-ichi nuclear power plant accident Biogeosciences Discussions, 10, 1993-2012, 2013 Author(s): H. Kaeriyama, D. Ambe, Y. Shimizu, K. Fujimoto, T. Ono, S. Yonezaki, Y. Kato, H. Matsunaga, H. Minami, S. Nakatsuka, and T. Watanabe The horizontal distribution of radioactive cesium (Cs) derived from the Fukushima Dai-ichi Nuclear Power Plant (FNPP) in the North Pacific is still unclear due to the limitation of direct measurement of the seawater in the open ocean. We present the result of direct observation of radioactive Cs in surface seawater collected from broad area in the western and central North Pacific in July, October 2011 and July 2012. We also conducted a simple particle tracking experiment to estimate the qualitative spatial distribution of radioactive Cs in the North Pacific. 134 Cs were detected at 94 stations out of 123 stations and 137 Cs was detected at all stations. The high 134 Cs and 137 Cs concentrations more than 10 mBq kg −1 were observed in the area where the northern part of Kuroshio extension at 144° E and 155° E in July 2011, in the area 147° E–175° E around 40° N in October 2011, and the northern part of Kuroshio extension at 155° E and 175° 30´ E in July 2012. Combining the result of direct observations and particle tracking experiment, the radioactive Cs derived from FNPP had been dispersed eastward to the central North Pacific during 2011. It was considered from the horizontal distribution that radioactive Cs was dispersed not only eastward but also north- and southward in the central North Pacific. Pronounced dilution process of radioactive Cs from FNPP during study period is suggested from temporal change in the activity ratio of 134 Cs/ 137 Cs which was decay corrected at 6 April 2011, and relationships between radioactive Cs and temperature.

Description: Detecting tropical forest biomass dynamics from repeated airborne Lidar measurements Biogeosciences Discussions, 10, 1957-1992, 2013 Author(s): V. Meyer, S. S. Saatchi, J. Chave, J. Dalling, S. Bohlman, G. A. Fricker, C. Robinson, and M. Neumann Reducing uncertainty of terrestrial carbon cycle depends strongly on the accurate estimation of changes of global forest carbon stock. However, this is a challenging problem from either ground surveys or remote sensing techniques in tropical forests. Here, we examine the feasibility of estimating changes of tropical forest biomass from two airborne Lidar measurements acquired about 10 yr apart over Barro Colorado Island (BCI), Panama from high and medium resolution airborne sensors. The estimation is calibrated with the forest inventory data over 50 ha that was surveyed every 5 yr during the study period. We estimated the aboveground forest biomass and its uncertainty for each time period at different spatial scales (0.04, 0.25, 1.0 ha) and developed a linear regression model between four Lidar height metrics and the aboveground biomass. The uncertainty associated with estimating biomass changes from both ground and Lidar data was quantified by propagating measurement and prediction errors across spatial scales. Errors associated with both the mean biomass stock and mean biomass change declined with increasing spatial scales. Biomass changes derived from Lidar and ground estimates were largely (36 out 50 plots) in the same direction at the spatial scale of 1 ha. Lidar estimation of biomass was accurate at the 1 ha scale ( R 2 = 0.7 and RMSE mean = 28.6 Mg ha −1 ). However, to predict biomass changes, errors became comparable to ground estimates only at about 10-ha or more. Our results indicate that the 50-ha BCI plot lost a~significant amount of biomass (−0.8 ± 2.2 Mg ha −1 yr −1 ) over the past decade (2000–2010). Over the entire island and during the same period, mean AGB change is −0.4 ± 3.7 Mg ha −1 yr −1 . Old growth forests lost biomass (−0.7 ± 3.5 Mg ha −1 yr −1 ), whereas the secondary forests gained biomass (+0.4 ± 3.4 Mg ha −1 yr −1 ). Our analysis demonstrates that repeated Lidar surveys, even with two different sensors, is able to estimate biomass changes in old-growth tropical forests at landscape scales (〉10 ha).

Description: The role of microorganisms and plants at different stages of ecosystem development for soil formation Biogeosciences Discussions, 10, 1867-1898, 2013 Author(s): S. Schulz, R. Brankatschk, A. Dümig, I. Kögel-Knabner, M. Schloter, and J. Zeyer Soil formation is the result of a complex network of biological as well as chemical and physical processes. Mainly the role of soil microbes is of high interest in this respect, as they are responsible for most transformations and drive the development of stable and labile carbon and nutrient pools in soil, which facilitate the basis for the subsequent establishment of plant communities. Glacier forefields, which provide a chronosequence of soils of different age due to the continuous retreat of the ice layer as a consequence of the increasing annual temperature since the last centuries, are a nice play ground to study the interaction of bacteria, fungi and archaea with their abiotic environment at different stages of soil formation. In this review we give insights into the role of microbes for soil development on the basis of investigations which have been performed at the Damma glacier in Switzerland in the frame of two international network projects Big Link ( http://www.cces.ethz.ch/projects/clench/BigLink/ ) and DFG SFB/TRR 38 ( http://www.tu-cottbus.de/ecosystem/ ). The review focusses on the microbiology of three major steps of soil formation including weathering of the parental material, the development of basic nutrient cycles, the formation of soil crusts and biofilms as initial microbial network structures and the occurrence of plants respectively the setup of plant communities.

Description: Benthic buffers and boosters of ocean acidification on coral reefs Biogeosciences Discussions, 10, 1831-1865, 2013 Author(s): K. R. N. Anthony, G. Diaz-Pulido, N. Verlinden, B. Tilbrook, and A. J. Andersson Ocean acidification is a threat to marine ecosystems globally. In shallow-water systems, however, ocean acidification can be masked by benthic carbon fluxes, depending on community composition, seawater residence time, and the magnitude and balance of net community production ( p n ) and calcification ( g n ). Here, we examine how six benthic groups from a coral reef environment on Heron Reef (Great Barrier Reef, Australia) contribute to changes in seawater aragonite saturation state (Ω a ). Results of flume studies showed a hierarchy of responses across groups, depending on CO 2 level, time of day and water flow. At low CO 2 (350–450 μatm), macroalgae ( Chnoospora implexa ), turfs and sand elevated Ω a of the flume water by around 0.10 to 1.20 h −1 – normalised to contributions from 1 m 2 of benthos to a 1 m deep water column. The rate of Ω a increase in these groups was doubled under acidification (560–700 μatm) and high flow (35 compared to 8 cm s −1 ). In contrast, branching corals ( Acropora aspera ) increased Ω a by 0.25 h −1 at ambient CO 2 (350–450 μatm) during the day, but reduced Ω a under acidification and high flow. Nighttime changes in Ω a by corals were highly negative (0.6–0.8 h −1 ) and exacerbated by acidification. Calcifying macroalgae ( Halimeda spp.) raised Ω a by day (by around 0.13 h −1 ), but lowered Ω a by a similar or higher amount at night. Analyses of carbon flux contributions from four different benthic compositions to the reef water carbon chemistry across Heron Reef flat and lagoon indicated that the net lowering of Ω a by coral-dominated areas can to some extent be countered by long water residence times in neighbouring areas dominated by turfs, macroalgae and potentially sand.

Description: Multiyear precipitation reduction strongly decrease carbon uptake over North China Biogeosciences Discussions, 10, 1605-1634, 2013 Author(s): W. P. Yuan, D. Liu, W. J. Dong, S. G. Liu, G. S. Zhou, G. R. Yu, T. B. Zhao, J. M. Feng, Z. G. Ma, J. Q. Chen, Y. Chen, S. P. Chen, S. J. Han, J. P. Huang, L. H. Li, H. Z. Liu, S. M. Liu, M. G. Ma, Y. F. Wang, J. Z. Xia, W. F. Xu, Q. Zhang, X. Q. Zhao, and L. Zhao Drought has been a concern of global and regional water, carbon and energy cycles. From 1999 to 2011, North China experienced a multiyear precipitation reduction, which decreased significantly water availability as indicated by decreased soil moisture and Palmer Drought Severity Index. In this study, three light use efficiency models (CASA, MODIS-GPP and EC-LUE) and one dynamic vegetation model (IBIS) were used to characterize the impacts of long-term drought on terrestrial carbon fluxes over the North China. All of four models showed the reduction in averaged GPP of 0.026–0.047 Pg C yr −1 from 1999 to 2011 compared to 1982–2011. Based on IBIS model, simulated ecosystem respiration fell from 1999 to 2011 by 0.016 Pg C yr −1 . Multiple precipitation reduction changed the regional carbon uptake of 0.0014 Pg C yr −1 from 1982 to 1998 to a~net source of 0.018 Pg C yr −1 . Moreover, a pronounced decrease of maize yield was found ranging from 1999 to 2011 versus the average of 1978–2011 at almost all provinces over the study region. The largest reduction of maize yield occurred in the Beijing (2499 kg ha −1 yr −1 ), Jilin (2180 kg ha −1 yr −1 ), Tianjing (1923 kg ha −1 yr −1 ) and Heilongjiang (1791 kg ha −1 yr −1 ), and maize yield anomaly was significantly correlated with the precipitation through May and September over the entire study area. Our results revealed that recent climate change, and especially drought-induced water stress, is the dominant cause of the reduction in the terrestrial carbon sink.

Description: Ecosystem-specific selection of microbial ammonia oxidizers in an acid soil Biogeosciences Discussions, 10, 1717-1746, 2013 Author(s): M. Saiful Alam, G. Ren, L. Lu, Y. Zheng, X. Peng, and Z. Jia The function of ammonia-oxidizing archaea (AOA) and bacteria (AOB) depends on the availability of ammonia substrate and the supply of oxygen. The interactions and evolutions of AOA and AOB communities along ecological gradients of substrate availability in complex environment have been much debated, but rarely tested. In this study, two ecosystems of maize and rice crops under different fertilization regimes were selected to investigate the community diversification of soil AOA and AOB in response to long-term field fertilization and flooding management in an acid soil. Real-time quantitative PCR of amoA genes demonstrated that the abundance of AOA was significantly stimulated after conversion of upland to paddy soils, while slight decline of AOB populations was observed. DGGE fingerprints of amoA genes further revealed remarkable changes in community compositions of AOA in paddy soil when compared to upland soil. Sequencing analysis revealed that upland soil was dominated by AOA within the soil group 1.1b lineage, while the marine group 1.1a lineage predominated AOA communities in paddy soils. Irrespective of upland and paddy soils, long-term field fertilizations led to higher abundance of amoA genes of AOA and AOB than control treatment that received no fertilization, whereas archaeal amoA gene abundances outnumbered their bacterial counterpart in all samples. Phylogenetic analyses of amoA genes showed that Nitrosospira cluster 3-like AOB dominated bacterial ammonia oxidizers in both paddy and upland soils, regardless of fertilization treatments. The results of this study suggest that the marine group 1.1a AOA could be better adapted to low-oxygen environment than AOA ecotypes of the soil group 1.1b lineage, and implicate that long-term flooding as the dominant selective force driving the community diversification of AOA populations in the acid soil tested.

Description: Phytoplankton biomass, composition, and productivity along a temperature and stratification gradient in the Northeast Atlantic Ocean Biogeosciences Discussions, 10, 1793-1829, 2013 Author(s): W. H. van de Poll, G. Kulk, K. R. Timmermans, C. P. D. Brussaard, H. J. van der Woerd, M. J. Kehoe, K. D. A. Mojica, R. J. W. Visser, and A. G. J. Buma The North Atlantic Ocean experiences considerable variability in sea surface temperature (SST, 〉10 m) on seasonal and inter-annual time-scales. Relationships between SST and vertical density stratification, nutrient concentrations, and phytoplankton biomass, composition, and absorption were assessed in spring and summer from latitudes 30–62° N. Furthermore, a bio-optical model was used to estimate productivity for five phytoplankton groups. Nutrient concentration (integrated from 0–125 m) was inversely correlated with SST in spring and summer. SST was also inversely correlated with near surface (0–50 m) Chl a and productivity for stratified stations. However, near surface Chl a showed an exponential relationship with SST, whereas a linear relationship was found for productivity and SST. The response of phytoplankton to changes in SST is therefore most likely to be observed by changes in Chl a rather than productivity. The discrepancy between relationships of Chl a and productivity were probably related to changes in phytoplankton cell size. The contribution of cyanobacteria to water column productivity correlated positively with SST and inversely with nutrient concentration. This suggests that a rise in SST (over a 13–23 °C range) stimulates productivity by cyanobacteria at the expense of haptophytes, which showed an inverse relationship to SST. At higher latitudes, where rising SST may prolong the stratified season, haptophyte productivity may expand at the expense of diatom productivity. Depth integrated Chl a (0–410 m) was greatest in the spring at higher latitudes, where stratification in the upper 200 m was weakest. This suggests that stronger stratification does not necessarily result in higher phytoplankton biomass standing stock in this region.

Description: Saturated CO 2 inhibits microbial processes in CO 2 -vented deep-sea sediments Biogeosciences Discussions, 10, 1899-1927, 2013 Author(s): D. de Beer, M. Haeckel, J. Neumann, G. Wegener, F. Inagaki, and A. Boetius This study focused on biogeochemical processes and microbial activity in sediments of a natural deep-sea CO 2 seepage area (Yonaguni Knoll IV hydrothermal system, Japan). The aim was to assess the influence of the geochemical conditions occurring in highly acidic and CO 2 saturated sediments on sulphate reduction (SR) and anaerobic methane oxidation (AOM). Porewater chemistry was investigated from retrieved sediment cores and in situ by microsensor profiling. The sites sampled around a sediment-hosted hydrothermal CO 2 vent were very heterogeneous in porewater chemistry, indicating a complex leakage pattern. Near the vents, droplets of liquid CO 2 were observed to emanate from the sediments, and the pH reached approximately 4.5 in a sediment depth 〉6 cm, as determined in situ by microsensors. Methane and sulphate co-occurred in most sediment samples from the vicinity of the vents down to a depth of at least 3 m. However, SR and AOM were restricted to the upper 7–15 cm below seafloor, although neither temperature, low pH, nor the availability of methane and sulphate could be limiting microbial activity. We argue that the extremely high subsurface concentrations of dissolved CO 2 (1000–1700 mM), through the ensuing high H 2 CO 3 levels (approx. 1–2 mM) uncouples the proton-motive-force (PMF) and thus inhibits biological energy conservation by ATPase-driven phosphorylation. This limits life to the surface sediment horizons above the liquid CO 2 phase, where less extreme conditions prevail. Our results may have to be taken into consideration in assessing the consequences of deep-sea CO 2 sequestration on benthic element cycling and on the local ecosystem state.

Description: Absorption and fluorescence properties of the eastern Bering Sea in the summer with special reference to the influence of a Cold Pool Biogeosciences Discussions, 10, 19109-19154, 2013 Author(s): E. J. D'Sa, J. I. Goes, H. Gomes, and C. Mouw The absorption and fluorescence properties of chromophoric dissolved organic matter (CDOM) are reported for the inner shelf, slope waters and outer shelf regions of the eastern Bering Sea during the summer of 2008, when a warm, thermally stratified surface mixed layer lay over a Cold Pool ( 〈 2 °C) that occupied the entire middle shelf. CDOM absorption at 355 nm ( a g 355) and its spectral slope ( S ) in conjunction with excitation emission matrix (EEM) fluorescence and parallel factor analysis (PARAFAC) revealed large variability in the characteristics of CDOM in different regions of the Bering Sea. PARAFAC analysis aided in the identification of three humic-like (components 1, 2 and 5) and two protein-like (a tyrosine-like component 3, and a tryptophan-like component 4) components. In the extensive shelf region, average absorption coefficients at 355 nm ( a g 355 m –1 ) and DOC concentrations (μM) were highest in the inner shelf (0.342 ± 0.11 m –1 , 92.67 ± 14.60 μM) and lower in the middle (0.226 ± 0.05 m –1 , 78.38 ± 10.64 μM) and outer (0.176 ± 0.05 m –1 , 80.73 ± 18.11 μM) shelves, respectively. Mean spectral slopes S were elevated in the middle shelf (24.38 ± 2.25 μm –1 ) especially in the surface waters (26.87 ± 2.39 μm –1 ) indicating high rates of photodegradation in the highly stratified surface mixed layer, which intensified northwards in the northern middle shelf likely contributing to greater light penetration and to phytoplankton blooms at deeper depths. The fluorescent humic-like components 1, 2, and 5 were most elevated in the inner shelf most likely from riverine inputs. Measurements at depth in slope waters (〉 250 m) revealed low values of a g 355 (0.155 ± 0.03 m –1 ) and S (15.45 ± 1.78 μm –1 ) indicative of microbial degradation of CDOM in deep waters. DOC concentrations, however were not significantly different suggesting CDOM sources and sinks to be uncoupled from DOC. Along the productive "green belt" in the outer shelf/slope region, absorption and fluorescence properties indicated the presence of fresh and degraded autochthonous DOM. Near the Unimak Pass region of the Aleutian Islands, low DOC and a g 355 (mean 66.99 ± 7.94 μM; 0.182 ± 0.05 m –1 ) and a high S (mean 25.95 ± 1.58 μm –1 ) suggested substantial photobleaching of the Alaska Coastal Waters, but high intensities of humic-like and protein-like fluorescence suggested sources of fluorescent DOM from coastal runoff and glacier melt waters during the summer. Although our data show that the CDOM photochemical environment of the Bering Sea is complex, our current information on its optical properties will aid in better understanding of the biogeochemical role of CDOM in carbon budgets in relation to the annual sea ice and phytoplankton dynamics, and to improved algorithms of ocean color remote sensing for this region.