Carbon Production Rates Research Articles

FACIES PARTITIONING AND SEQUENCE STRATIGRAPHY OF A MIXED SILICICLASTIC-CARBONATE RAMP STACK IN THE GELASIAN OF SICILY (S ITALY): A POTENTIAL MODEL FOR ICEHOUSE, DISTALLY-STEEPENED HETEROZOAN RAMPS

The Gelasian succession of the Capodarso area (Enna-Caltanissetta basin, Sicily, Italy) consists of an offlapping stack of cycles composed of siliciclastic units passing to carbonate heterozoan, clino-stratified wedges, developed from a growing positive tectonic structure. Identification of a number of facies tracts, based on sedimentary facies, biofacies and taphofacies, provided important information about the differentiation and characterisation of systems tracts and key stratal surfaces of sequence stratigraphy. The bulk of carbonate wedges are interpreted as representing the rapid falling-stage progradation of distally steepened ramps. The inferred highest rate of carbonate production during forced regressions was concomitant with active downramp resedimentation by storm-driven downwelling flows, leading to storing of most carbonate sediment on the ramp slope as clino-beds of the prograding bodies. Comparison of the Capodarso ramps with other icehouse carbonate ramps, with particular regard to the Mediterranean Plio-Pleistocene, provides clues for defining some common features. These are inferred to include: (1) brief, rapid episodes of progradation concomitant with orbitally-forced sea-level changes, resulting in limited ramp width; (2) preferential fostering of growth and downramp resedimentation of heterozoan carbonates during glacial hemicycles marked by enhanced atmospheric and marine circulation; (3) building out from positive features of entirely submerged distally-steepened ramps with storm-wave-graded profile and distinctive clinoforms; (4) ramp stacks generally consisting of mixed clastic-carbonate sequences showing an ordered spectrum of distinct frequencies; (5) rapid, continuous changes in environmental parameters, leading to the short-lived persistence of faunal communities, climax communities generally having insufficient time to form.

Estimating rates of biologically driven coral reef framework production and erosion: a new census-based carbonate budget methodology and applications to the reefs of Bonaire

Census-based approaches can provide important measures of the ecological processes controlling reef carbonate production states. Here, we describe a rapid, non-destructive approach to carbonate budget assessments, termed ReefBudget that is census-based and which focuses on quantifying the relative contributions made by different biological carbonate producer/eroder groups to net reef framework carbonate production. The methodology is presently designed only for Caribbean sites, but has potential to be adapted for use in other regions. Rates are calculated using data on organism cover and abundance, combined with annual extension or production rate measures. Set against this are estimates of the rates at which bioeroding species of fish, urchins and internal substrate borers erode reef framework. Resultant data provide a measure of net rates of biologically driven carbonate production (kg CaCO3 m−2 year−1). These data have potential to be integrated into ecological assessments of reef state, to aid monitoring of temporal (same-site) changes in rates of biological carbonate production and to provide insights into the key ecological drivers of reef growth or erosion as a function of environmental change. Individual aspects of the budget methodology can also be used alongside other census approaches if deemed appropriate for specific study aims. Furthermore, the methodology spreadsheets are user-changeable, allowing local or new process/rate data to be integrated into calculations. Application of the methodology is considered at sites around Bonaire. Highest net rates of carbonate production, +9.52 to +2.30 kg CaCO3 m−2 year−1, were calculated at leeward sites, whilst lower rates, +0.98 to −0.98 kg CaCO3 m−2 year−1, were calculated at windward sites. Data are within the ranges calculated in previous budget studies and provide confidence in the production estimates the methodology generates.

Quantification of the coralline carbonate from a Serravallian rhodolith bed of the Tertiary Piedmont Basin (Stazzano, Alessandria, NW Italy)

Digital photographs of the surface of Serravallian rhodolith-bearing strata from Stazzano (Tertiary Piedmont Basin) Italy have been elaborated by Image-J opensource software (U.S. National Institutes of Health — NIH), to obtain a map of the algal surface in each photograph. The 33 images in the 7 m-thick outcrop, covering a total of 11.53 m2, were complemented by data on rhodolith shape, structure, composition and taphonomy. The Serravallian rhodolith body was produced in a long-lasting infralittoral sedimentary environment and then transported into deeper water by slumping. Although biological and geological definitions of rhodolith-dominated facies are inconsistent in some respects, the image analysis described here allows direct comparison of percentages of rhodolith dominance in discrete fossil rhodolith facies and their living counterparts. The procedures involved are both rapid and inexpensive, so the method appears very useful for carbonate quantification. The calculated algal cover, based only on rhodoliths > 2 cm, ranges from 11.9 to 59.7% (mean 27.3%). The carbonate production rate of the Serravallian rhodolith bed was probably in the range 55 to 136.3 g CaCO3 m-2yr-1 as calculated for a Brazilian present-day analogue.

Indirect Estimation of CH4 from Livestock Feeds through TOCs Evaluation.

Thirty-five available feeds were fermented in vitro in order to investigate their soluble total organic carbon (TOCs) and methane (CH4) production rate. A fermentation reactor was designed to capture the CH4 gas emitted and to collect liquor from the reactor during in vitro fermentation. The results showed that CH4 production rate greatly varied among feeds with different ingredients. The lowest CH4-producing feeds were corn gluten feed, brewer’s grain, and orchard grass among the energy, protein, and forage feed groups, respectively. Significant differences (p<0.05) were found in digestibility, soluble total organic carbon (TOCs), and CH4 emissions among feeds, during 48 h of in vitro fermentation. Digestibility and TOCs was not found to be related due to different fermentation pattern of each but TOCs production was directly proportional to CH4 production (y = 0.0076x, r2 = 0.83). From this in vitro study, TOCs production could be used as an indirect index for estimation of CH4 emission from feed ingredients.

Sequence architecture and depositional evolution of theOrdovician carbonate platform margins in theTarimBasin and its response to tectonism and sea‐level change

AbstractThe sequence architecture and depositional evolution of theOrdovician carbonate platform margins in theTarimBasin,China, were formed in response to the interplay of tectonism and sea‐level change, their history being documented by the integrated analysis of many seismic lines, drilling and outcrop data. TheOrdovician carbonate system in the basin is divided into four composite sequences defined by major unconformities. Each sequence consists of a regional depositional cycle from transgression with an onlapping transgressive systems tract (TST) to regression with a prograding highstand systems tract (HST), and can be further subdivided into 10 third‐order sequences based on subordinate discontinuous boundaries at the carbonate platform marginal zones. Constrained by the marginal slope of the early‐riftedManjiaer aulacogen, the carbonate platform margins of the Lower and MiddleOrdovician that prograded eastward in an arcuate belt extending generally north‐south across the northern part of the basin. The development of theTazhong uplift due to compression resulted in an extensive paleokarst hiatus between the Middle and the UpperOrdovician in the south‐central basin, and subsequently constrained the formation of a peninsula‐shaped carbonate platform whose margins were controlled by marginal thrust‐fault belts of the paleo‐uplift during the LateOrdovician. In the northern basin, the LateOrdovician carbonate platform margin developed around the marginal slope of theTabei paleouplift. The transgressive–regressive cycles of the carbonate system are comparable and seem to have occurred simultaneously across the entire basin, suggesting that the cyclic sequence architecture was fundamentally controlled by eustatic fluctuations. Stacking patterns of the composite sequences varied due to the interplay between the accommodation produced by tectonism and sea‐level change, and the carbonate production rate. The reef–shoal facies complexes that developed along the platform margins, with paleokarst development at unconformities, constitute the major reservoir of large petroleum reserves in the basin.

Distinguishing between the effects of ocean acidification and ocean carbonation in the coccolithophore Emiliania huxleyi

The coccolithophore Emiliania huxleyi was cultured under a broad range of carbonate chemistry conditions to distinguish the effects of individual carbonate system parameters on growth, primary production, and calcification. In the first experiment, alkalinity was kept constant and the fugacity of CO2 (fCO2) varied from 2 to 600 Pa (1 Pa ≈ 10 µatm). In the second experiment, pH was kept constant (pHfree = 8) with fCO2 varying from 4 to 370 Pa. Results of the constant‐alkalinity approach revealed physiological optima for growth, calcification, and organic carbon production at fCO2 values of ~ 20 Pa, ~ 40 Pa, and ~ 80 Pa, respectively. Comparing this with the constant‐pH approach showed that growth and organic carbon production increased similarly from low to intermediate CO2 levels but started to diverge towards higher CO2 levels. In the high CO2 range, growth rates and organic carbon production decreased steadily with declining pH at constant alkalinity while remaining consistently higher at constant pH. This suggests that growth and organic carbon production rates are directly related to CO2 at low (sub‐saturating) concentrations, whereas towards higher CO2 levels they are adversely affected by the associated decrease in pH. A pH dependence at high fCO2 is also indicated for calcification rates, while the key carbonate system parameter determining calcification at low fCO2 remains unclear. These results imply that key metabolic processes in coccolithophores have their optima at different carbonate chemistry conditions and are influenced by different parameters of the carbonate system at both sides of the optimum.

Patterns and Processes of Ancient Reef Crises

Reef crises need to be separated from mass extinctions because they are manifested in reductions of reefal carbonate production rather than elevated extinction rates. The volume of preserved fossil reefs per unit time is perhaps the best accessible metric to assess reefal carbonate production rates in the geologic record. Although this metric is prone to biases introduced by weathering, burial, and sampling, it offers the possibility to analyze general connections between reef crises and mass extinctions. The biases can be partially corrected by looking at short-term variations and by utilizing independent proxies of sampling. Using a comprehensive database of ancient reefs and considering the generally high volatility in reefal carbonate production, we can identify five significant metazoan reef crises in the post-Cambrian Phanerozoic, only three of which correspond to traditional mass extinctions. Ancient reefs crises appear to be due to episodes of rapid CO2release and warming, rather than cooling or meteorite impacts.

Sea urchin fecal production and accumulation in a rocky subtidal ecosystem

We used a spatial model of destructive grazing of kelp beds by dense aggregations (fronts) of sea urchins Strongylocentrotus droebachiensis, together with measures of sea urchin absorption efficiency and fecal degradation rate, to predict rates of fecal production and accumu- lation during the transition from a kelp bed to a barrens state in a rocky subtidal ecosystem of Nova Scotia, Canada. The rate of fecal production as dry mass reached 9.17 g m -2 d -1 at 10 yr after the formation of a grazing front, with associated rates of carbon and nitrogen production of 2.12 g C m -2 d -1 and 0.21 g N m -2 d -1 . Fecal production rate exceeded the rates of physical, chemical, and microbial degradation, such that up to 193.6 g of feces, 70.2 g of C, and 4.0 g of N accumulated per linear m of front after 10 yr. The extent of sea urchin grazing fronts along the Atlantic coast of Nova Scotia was estimated at 280 km in 2000, which translates to a total fecal production rate of 6423 kg of feces d -1 and an accumulation of 54 200 kg of feces after 10 yr of front formation, based on our model. This temporally variable flux of organic matter likely has a profound effect on adja- cent deeper-water macrobenthic communities utilizing the feces as a food source.

Fault-controlled stratigraphy of the Late Cretaceous Abiod Formation at Ain Medheker (Northeast Tunisia)

The palaeogeographic setting of the studied Ain Medheker section represents an Early Campanian to Early Maastrichtian moderately deep carbonate shelf to distal ramp position with high rates of hemipelagic carbonate production, periodically triggered by mass-flow processes. Syndepositional extensional tectonic processes are confirmed to the Early Campanian. Planktonic foraminifera identified in thin sections and calcareous nannofossils allow the identification of the following biozones: Globotruncanita elevata, Contusotruncana plummerae (replacing former Globotruncana ventricosa Zone), Radotruncana calcarata, Globotruncana falsostuarti, and Gansserina gansseri. The following stable C-isotope events were identified: the Santonian/Campanian boundary Event, the Mid-Campanian Event, and the Late Campanian Event. Together with further four minor isotopic events, they allow for correlation between the western and eastern realms of Tunisia. Frequently occurring turbidites were studied in detail and discussed in comparison with contourites.

CarboCAT: A cellular automata model of heterogeneous carbonate strata

CarboCAT is a new numerical model of carbonate deposystems that uses a cellular automata to calculate lithofacies spatial distributions and hence to calculate the accumulation of heterogeneous carbonate strata in three dimensions. CarboCAT includes various geological processes, including tectonic subsidence, eustatic sea-level oscillations, water depth-dependent carbonate production rates in multiple carbonate factories, lateral migration of carbonate lithofacies bodies, and a simple representation of sediment transport. Results from the model show stratigraphically interesting phenomena such as heterogeneous strata with complex stacking patterns, laterally discontinuous subaerial exposure surfaces, nonexponential lithofacies thickness distributions, and sensitive dependence on initial conditions whereby small changes in the model initial conditions have a large effect on the final model outcome. More work is required to fully assess CarboCAT, but these initial results suggest that a cellular automata approach to modeling carbonate strata is likely to be a useful tool for investigating the nature and origins of heterogeneity in carbonate strata.

Primary production and plankton carbon biomass in a river-influenced upwelling area off Concepción, Chile

The combined influence of freshwater inputs and wind-driven upwelling may generate contrasting environmental conditions over small spatial scales in the coastal ocean. Over two consecutive years (mid-2006 through to mid-2008), we compared the springtime and wintertime composition, biomass, and primary production of the main phytoplankton groups at two coastal stations (RV and UW) near the Itata River mouth in the upwelling area off central Chile. Hydrographic and nutrient profiles showed distinct seasonal features: a relatively weak surface thermocline and weak river influence at both stations in spring, and in winter a stronger surface halocline at station RV, located closer to the river mouth. At both stations, primary production (24–8000 mg C m −2 d −1) and chlorophyll-a concentrations (5–20 mg Chl-a m −3) were highest in the spring, with a dominance of microphytoplankton ( Chaetoceros spp., Thalassiosira spp.). Total primary production and chlorophyll-a in the winter corresponded mostly to smaller size fractions (pico- and nanoplankton), which dominated the phytoplankton community (>50%) in terms of carbon biomass at station RV. At this river-influenced station, small autotrophic and heterotrophic groups (<20 μm), including picophytoeukaryotes, photo- and heterotrophic nanoflagellates, and ciliates, were two to four times more abundant than at station UW. We conclude that most of the integrated carbon biomass and production rates during winter months are accounted for by small cells in the microbial food web. This component of the phytoplankton community may be enhanced in response to the additional surface input of nutrients by river discharges into the nearshore environment.

Quantifying the flux of CaCO3and organic carbon from the surface ocean using in situ measurements of O2, N2, pCO2, and pH

[1] Ocean acidification from anthropogenic CO2 has focused our attention on the importance of understanding the rates and mechanisms of CaCO3 formation so that changes can be monitored and feedbacks predicted. We present a method for determining the rate of CaCO3 production using in situ measureme nts of fCO2 and pH in surface waters of the eastern subarctic Pacific Ocean. These quantities were determined on a surface mooring every 3 h for a period of about 9 months in 2007 at Ocean Station Papa (50°N, 145°W). We use the data in a simple surface ocean, mass balance model of dissolved inorganic carbon (DIC) and alkalinity (Alk) to constrain the CaCO3: organic carbon (OC) production ratio to be approximately 0.5. A CaCO3 production rate of 8 mmol CaCO3 m−2 d−1 in the summer of 2007 (1.2 mol m−2 yr−1) is derived by combining the CaCO3: OC ratio with the a net organic carbon production rate (2.5 mol C m−2 yr−1) determined from in situ measurements of oxygen and nitrogen gas concentrations measured on the same mooring (Emerson and Stump, 2010). Carbonate chemistry data from a meridional hydrographic section in this area in 2008 indicate that isopycnal surfaces that outcrop in the winter in the subarctic Pacific and deepen southward into the subtropics are a much stronger source for alkalinity than vertical mixing. This pathway has a high enough Alk:DIC ratio to support the CaCO3:OC production rate implied by the fCO2 and pH data.

Fast production of monolithic carbide-derived carbons with secondary porosity produced by chlorination of carbides containing a free metal phase

Hierarchical structured carbide-derived carbons (CDC) are produced by high temperature chlorination of silicon carbides containing free silicon (Si/SiC). The influence of free silicon in the precursor carbide on the resulting pore and carbon structure and production rate is studied. The two phases – free silicon and silicon carbide – of Si/SiC gives the possibility to synthesize a monolithic carbon with the typical microporous character and narrow pore size distribution combined with larger voids in the micrometer range, while the carbon structure itself stays unchanged. The study revealed that using Si/SiC material increases the production rate for carbide-derived carbons dramatically, due to higher reactive surface area and lower mass transfer limitations, which allows for the time effective production of larger monoliths.

Coupled organic and inorganic carbon cycling in the deep subseafloor sediment of the northeastern Bering Sea Slope (IODP Exp. 323)

We studied microbially mediated diagenetic processes driven by carbon mineralization in subseafloor sediment of the northeastern Bering Sea Slope to a depth of 745 meters below seafloor (mbsf). Sites U1343, U1344 and U1345 were drilled during Integrated Ocean Drilling Program (IODP) Expedition 323 at water depths of 1008 to 3172 m. They are situated in the high productivity “Green Belt” region, with organic carbon burial rates typical of the high-productivity upwelling domains on western continental margins. The three sites show strong geochemical similarities. The downward sequence of microbially mediated processes in the sediment encompasses (1) organoclastic sulfate reduction, (2) anaerobic oxidation of methane (AOM) coupled to sulfate reduction, and (3) methanogenesis. The sediment contains two distinct zones of diagenetic carbonate formation, located at the sulfate–methane transition zone (SMTZ) and between 300 and 400 mbsf. The SMTZ at the three sites is located between 6 and 9 mbsf. The upward methane fluxes into the SMTZ are similar to fluxes in SMTZs underlying high-productivity surface waters off Chile and Namibia. Our Bering Sea results show that intense organic carbon mineralization drives high ammonium and dissolved inorganic carbon (DIC) production rates (> 4.2 mmol m − 3 y − 1 ) in the uppermost 10 mbsf and strongly imprints on the stable carbon isotope composition of DIC, driving it to a minimum value of − 27‰ (VPDB) at the SMTZ. Pore-water calcium and magnesium profiles demonstrate formation of diagenetic Mg-rich calcite in the SMTZ. Below the SMTZ, methanogenesis results in 13C-enrichment of pore-water DIC, with a maximum value of + 11.9‰. The imprint of methanogenesis on the DIC carbon isotope composition is evident down to a depth of 150 mbsf. Below this depth, slow or absent microbially mediated carbon mineralization leaves DIC isotope composition unaffected. Ongoing carbonate formation between 300 and 400 mbsf strongly influences pore-water DIC and magnesium concentration profiles. The linked succession of organic carbon mineralization and carbonate dissolution and precipitation patterns that we observe in the Bering Sea Slope sediment may be representative of passive continental margin settings in high-productivity areas of the world's ocean.

Response of the microbial community to coral spawning in lagoon and reef flat environments of Hawaii, USA

The response of the microbial community to coral spawning was investigated over a period of 18 mo, from January 2006 to July 2007, in reef flat and lagoon environments of a sub- tropical embayment (Kaneohe Bay, Oahu, Hawaii, USA). The composition of the bacterioplankton community was characterized using terminal restriction fragment length polymorphism (T-RFLP) analysis of bacterial small-subunit (SSU) ribosomal RNA genes in parallel with measurements of microbial cell abundances, bacterial production via 3 H-leucine incorporation, and seawater bio- chemical parameters. We observed a variable bacterioplankton community structure and 2- to 3-fold changes in the cellular abundance of microorganisms, concentrations of chlorophyll a, and rates of bacterial carbon production at both sites during non-spawning conditions. While shifts in the structure of the bacterioplankton community were evident for both environments following coral spawning, microbial abundances and rates of bacterial production remained largely unchanged from pre-spawning levels. Thus, it appeared that only a small fraction of the microbial community responded to the presence of coral-produced organic matter. Differences in the composition of the bacterioplankton community, cellular abundances of microorganisms, and rates of bacterial produc- tion were evident between the lagoon and reef flat sites during non-spawning conditions, probably signifying the importance of the surface flow regime for coastal reef microbial communities. Our observations indicate that the Kaneohe Bay microbial community may be more significantly affected by physical mixing processes than by organic matter loading from coral spawning.

Contributions of fungi to carbon flow and nutrient cycling from standing dead Typha angustifolia leaf litter in a temperate freshwater marsh

Standing dead plant litter often constitutes a large fraction of the detritus in many freshwater marshes and lake littoral habitats. Despite this evidence, microbial decay processes in standing litter and its contribution to wetland carbon and nutrient cycling have rarely been quantified. We examined the contribution of fungi to carbon flow and nutrient cycling from Typha angustifolia during senescence and standing litter decomposition. Naturally standing Typha leaves were collected in August and then periodically over 1 yr. We quantified losses in leaf carbon (C), fungal biomass, and fungal production rates and constructed a partial budget estimating C flow into fungal decomposers. Additionally, we determined leaf litter N and P concentrations to assess the effect of fungi on detrital nutrient dynamics. Significant losses in leaf C occurred during plant senescence and standing litter decay (∼ 55%). Fungal biomass increased during litter decay, reaching a maximum of 106 ± 7 mg C g−1 detrital C. Cumulative fungal production totaled 123 mg C g−1 initial detrital C, indicating that 22% of the Typha leaf C lost was assimilated into fungal biomass. Fungi also transformed and immobilized nutrients within Typha leaves, with fungal N and P accounting for &gt; 50% of the total detrital N and P during later stages of leaf decay. Significant transformation and decomposition of emergent macrophyte litter occurs during the standing dead phase, and a large portion of the plant C and nutrients are channeled into and through fungal decomposers.

Response of the coccolithophores Emiliania huxleyi and Coccolithus braarudii to changing seawater Mg 2+ and Ca 2+ concentrations: Mg/Ca, Sr/Ca ratios and δ 44/40Ca, δ 26/24Mg of coccolith calcite

Calcium and magnesium concentrations in seawater have varied over geological time scales. On short time scales, variations in the major ion composition of seawater influences coccolithophorid physiology and the chemistry of biogenically produced coccoliths. Validation of those changes via controlled laboratory experiments is a crucial step in applying coccolithophorid based paleoproxies for the reconstruction of past environmental conditions. Therefore, we examined the response of two species of coccolithophores, Emiliania huxleyi and Coccolithus braarudii, to changes in the seawater Mg/Ca ratio (≈0.5 to 10 mol/mol) by either manipulating the magnesium or calcium concentration under controlled laboratory conditions. Concurrently, seawater Sr/Ca ratios were also modified (≈2 to 40 mmol/mol), while keeping salinity constant at 35. The physiological response was monitored by measurements of the cell growth rate as well as the production rates of particulate inorganic and organic carbon, and chlorophyll a. Additionally, coccolithophorid calcite was analyzed for its elemental composition (Sr/Ca and Mg/Ca) as well as isotope fractionation of calcium and magnesium (Δ 44/40Ca and Δ 26/24Mg). Our results reveal that physiological rates were substantially influenced by changes in seawater calcium rather than magnesium concentration within the range estimated to have occurred over the past 250 million years when coccolithophores appear in the fossil record. All physiological rates of E. huxleyi decreased at a calcium concentration above 25 mmol L −1, whereas C. braarudii displayed a higher tolerance to increased seawater calcium concentrations. Partition coefficient of Sr was calculated as 0.36 ± 0.04 (±2 σ) independent of species. Partition coefficient of Mg 2+ increased with increasing seawater Ca 2+ concentrations in both coccolithophore species. Calcium isotope fractionation was constant at 1.1 ± 0.1‰ (±2 σ) and not altered by changes in seawater Mg/Ca ratio. There is a well-defined inverse linear relationship between calcium isotope fractionation and partition coefficient of Sr 2+ in all experiments, suggesting similar controls on both proxies in the investigated species. Magnesium isotope ratios were relatively stable for seawater Mg/Ca ratios ranging from 1 to 5, with a higher degree of fractionation in Emiliania huxleyi (by ≈0.2‰ in Δ 26/24Mg). Although Mg/Ca ratios in the calcite of coccolithophores and foraminifera are similar, the former have considerably higher Δ 26/24Mg (by >+3‰), presumably due to differences in calcification mechanisms between the two taxa. These observations suggest, a physiological control over magnesium elemental and isotopic fractionation during the process of calcification in coccolithophores.

실내 자외선 노출 실험을 통한 극지 식물플랑크톤(Phaeocystis pouchetii, Porosira glacialis)의 자외선 흡수물질 생성 연구

Herein, we compared the production rate of UV-absorbing compounds (mycosporine-like amino acids) and carotenoids in two phytoplankton species--Phaeocystis pouchetii and Porosira glacialis--which are the dominant species in Polar Regions under artificial UV radiation conditions. P. pouchetii exposed to UVR and PAR evidenced reductions in the carbon fixation rate, and was not significantly influenced by differing light conditions. However, the concentrations of UV-absorbing compounds and photo-protective pigments of P. pouchetii were increased with increasing exposure time, but P. glacialis maintained constant levels during the UVR exposure experiment. The production rates of MAAs showed a reverse phase between the two phytoplankton species. The carbon fixation rate of P. pouchetii cells was inhibited by exposure to UV radiation, but the production rates of MAAs in P. pouchetii were increased under UV radiation exposure. The carbon fixation rate and production rate of MAAs in P. glacialis were simultaneously inhibited under UV radiation exposure conditions. These results provide us with new information regarding the processes involved in the production of UV-absorbing compounds and photoprotective pigments in two phytoplankton species.

Short-term coherency between gross primary production and community respiration in an algal-dominated reef flat

Rates of net community carbon production (mmol C m−2 h−1) were measured continuously in an algal-dominated reef flat community on the Kaneohe Bay barrier reef, Hawaii, for 12 days at the end of October 2006. The weather became increasingly cloudy during the last 5 days of measurements, resulting in a sevenfold decline in daily incident light (28–4 Ein m−2 d−1). In response, gross primary production (P) for the reef flat community also decreased sevenfold, varying linearly with light (r2 = 0.92, n = 12). Community respiration (R) decreased fivefold over this same period and was highly correlated with changes in P (r2 = 0.84, n = 12). We reason that this short-term coherence between P and R indicates that most of the carbon fixed during this period was rapidly metabolized via plant respiration. We further conclude that the dominance of autotrophic respiration under general conditions of nutrient-limited growth can explain much of the balance between P and R that is commonly observed in shallow reef communities.

Controls on authigenic carbonate precipitation at cold seeps along the convergent margin off Costa Rica

Five sediment cores from cold seeps at the forearc off Costa Rica were used to explore the relationship between fluid advection, dissolved Ca concentrations in upward migrating fluids, and authigenic CaCO3 precipitation. A numerical transport‐reaction model was used to determine rates of anaerobic oxidation of methane (AOM), CaCO3 precipitation, and benthic fluxes of solutes. Production of carbonate alkalinity and formation of authigenic carbonates is most intense at intermediate flow rates (3–40 cm a−1) and reduced under low and high flux conditions (0.1 and 200 cm a−1). Dissolved Ca concentrations observed in the vent fluids off Costa Rica cover a wide range between 4 and 31 mM, clearly exceeding seawater concentrations at two locations. Systematic model runs showed that high Ca concentrations in ascending fluids enhance the rate of authigenic carbonate production at moderate flow rates leading to an almost quantitative fixation of deeply derived Ca in authigenic carbonates. Hence, CaCO3 precipitation is not only controlled by Ca diffusing into the sediment from bottom water, but also by the Ca concentration in ascending fluids. Thus, Ca enriched fluids offer a reason for enhanced subsurface CaCO3 precipitation and the occurrence of carbonate caps on dewatering structures in the Central American fore‐arc. Based on average precipitation rates deduced from the systematic model runs it is possible to give a rough estimate of the global Ca‐fixation at cold seeps (∼2·1010 mol Ca a−1), which suggests that cold seeps are most likely not of key importance with respect to Ca cycling in the ocean.