Primary Production In Surface Waters Research Articles

Decadal-Scale Acidification Trends in Adjacent North Carolina Estuaries: Competing Role of Anthropogenic CO2 and Riverine Alkalinity Loads

Decadal-scale pH trends for the open ocean are largely monotonic and controlled by anthropogenic CO2 invasion. In estuaries, though, such long-term pH trends are often obscured by a variety of other factors, including changes in net metabolism, temperature, estuarine mixing, and riverine hydrogeochemistry. In this study, we mine an extensive biogeochemical database in two North Carolina estuaries, the Neuse River estuary (NeuseRE) and New River estuary (NewRE), in an effort to deconvolute decadal-scale trends in pH and associated processes. By applying a Generalized Additive Mixed Model (GAMM), we show that temporal changes in NewRE pH were insignificant, while pH decreased significantly throughout much of the NeuseRE. In both estuaries, variations in pH were accompanied by increasing river discharge, and were independent of rising temperature. Decreases in bottom-water pH in the NeuseRE coincided with elevated primary production in surface waters, highlighting the importance of eutrophication on long-term acidification trends. Next, we used a simple mixing model to illustrate the impact of changing river discharge on estuarine carbonate chemistry. We found that increased riverine alkalinity loads to the NewRE likely buffered the impact of CO2-intrusion-induced acidification. In the NeuseRE, however, elevated dissolved inorganic carbon loads further decreased the buffering capacity, exacerbating the effects of CO2-intrusion-driven acidification. Taken together, the findings of this study show that future trajectories in estuarine pH will be shaped by complex interactions among global-scale changes in climate, regional-scale changes in precipitation patterns, and local-scale changes in estuarine biogeochemistry.

Early Cretaceous ferruginous and its control on the lacustrine organic matter accumulation: Constrained by multiple proxies from the Bayingebi Formation in the Bayingebi Basin, inner Mongolia, NW China

The greenhouse climate in the Cretaceous period promoted widespread organic-rich marine/lacustrine black shales or mudrocks. Organic matter (OM) accumulation is generally affected by preservation conditions and surface water primary productivity. The detail of organic-rich mudrock formation in lacustrine system still remains enigmatic. The widespread OM-rich mudrocks in the Cretaceous period as petroleum source rocks in many large terrestrial petroliferous basins in China offer an opportunity to explore the mechanism of lacustrine OM accumulation. Fe speciation, CSFe system, pyrite morphology, pyrite-sulfur isotopic composition, elements, and biomarkers in the Bayingebi Formation from a drill core in the Bayingebi Basin, Inner Mongolia, NW China are used to constrain redox conditions, OM source and primary productivity in a lacustrine system. Our results show that the dark-gray mudrocks in the Bayingebi Formation were deposited in ferruginous and stratified water-column in the Bayingebi Basin. The biomarkers suggest a mixed organic matter source of algae, bacteria and high plant with a low algal contribution. The surface-water primary productivity during the deposition of the Bayingebi Formation was low and shows a weak correlation with total organic carbon (TOC) content. The OM accumulation in early Cretaceous lacustrine system was mainly controlled by redox conditions. Ferruginous anoxic conditions in lacustrine system may have high potential for hydrocarbon source rocks owing to the reduction of oxygen decomposition.

Carbonates dissolution and precipitation in hemipelagic sediments overlaid by supersaturated bottom-waters – Gulf of Aqaba, Red Sea

Abstract Whether CaCO3 dissolves within the top centimeters of marine sediments overlaid by deep, supersaturated bottom waters remains an area of debate in geochemistry. This uncertainty stems from the fact that different methods used to assess CaCO3 dissolution rates often provide what appear to be profoundly different results. Here we combine microelectrode and porewater chemistry profiles, core incubation experiments, mineral characterizations and observations of the state of preservation of coccolithophorid exoskeletons for a holistic view of carbonate reactions within the top 30 centimeters of hemipelagic sediments from the Gulf of Aqaba, Red Sea. Calculations based on pH and O2 microelectrode data suggest that rapid metabolic dissolution of carbonate minerals occurs in these sediments within the top two millimeters. Porewater chemistry supports these calculations. The porewater-based observations are further supported by sedimentological characteristics such as aragonite content, and dissolution pitting and fragmentation of coccoliths in sediment layers deposited over the last 200 y. Dissolution appears to be occurring today within surface sediments despite the bulk porewater solution being supersaturated with respect to aragonite and Mg-calcite. In spite of intense dissolution within the sediments, there is no evidence for significant alkalinity and/or calcium fluxes (transport) into bottom waters. It appears that the supersaturated bottom water promotes the removal of all excess alkalinity and calcium produced within the sediment, by CaCO3 precipitation at or above the sediment/bottom water interface. The precipitation mechanism may be by either benthic organisms (biogenic precipitation) or inorganically (direct precipitation on settling CaCO3 grains). We suggest that authigenic precipitation of (Ca,Mn)CO3 as it becomes supersaturated below 3 cm in the sediments can reconcile the evidence for carbonate dissolution in what appears to be supersaturated conditions. This means that MnCO3 replaces CaCO3 within the nanofossils below ∼3 cm, and that part of the manganese rich CaCO3 is bioturbated upwards into undersaturated conditions, facilitating dissolution of these fossils. Diminished calcite and aragonite concentrations in sediments deposited in recent decades are proposed to be a result of increased manganese cycling rates and greater rates of coupled dissolution within the interfacial sediments, possibly combined with diminished calcareous plankton productivity, in response to increased surface water primary productivity.

Integrated Geochemical and Morphological Data Provide Insights into the Genesis of Ferromanganese Nodules

Ferromanganese nodules grow by precipitation of metals from seawater and/or sediment pore water. The formation of different genetic types depends on the composition and redox conditions of the water and upper sediment layers, water depth, and primary productivity in surface waters. Many characteristics of nodules have been used to investigate their genesis. In this paper, we compare nodules from different environments using Computed Tomography, Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy, and Micro X-ray Fluorescence data to better understand how geochemical differences are linked to different morphological features. We use representative samples of purely hydrogenetic nodules and mixed-type nodules with various proportions of hydrogenetic and diagenetic growth laminae. Our results show a micrometric alternation between high-absorbance massive Mn-enriched (Mn/Fe up to 40) laminae and low-absorbance dendritic Mn-depleted (Mn/Fe about 1) laminae in mixed-type nodules, suggesting the rhythmic alternation of hydrogenetic oxic conditions and suboxic diagenetic input. This micro-rhythmic alternation is absent in purely hydrogenetic nodules, which are homogenous both chemically and morphologically. A conceptual model is proposed to account for these geochemical and morphological differences in terms of the vertical migration of the oxic-suboxic front relative to the base of the nodules.

Distribution and Variability of the Meiobenthic Assemblages near the Korean Polymetallic Nodule Claim Area of the Clarion-Clipperton Fracture Zone (Subequatorial NE Pacific)

This study was carried out as part of a baseline long-term environmental project in the proposed mining areas for an environmental impact assessment of future mining in the Clarion-Clipperton Fracture Zone (CCFZ). The community structure and distributional pattern of meiobenthos were investigated in the deep-sea bottom of the Clarion-Clipperton Fracture Zone of the northeastern Pacific in July 1998, 1999, 2001, 2003 and August 2004, 2005. Twenty one meiobenthic groups were found at the stations in the study area. The most abundant meiobenthos comprised nematodes followed by benthic foraminiferans and harpacticoid copepods. The maximum density of meiobenthos was 306 ind/10 cm2 at the station located at 11°N (water depth, 4833 m), and the minimum density was 6 ind/10 cm2 at the station located at 14°N (water depth, 5037 m). Oligotrophic conditions in the CCFZ seem to directly reflect the lower standing stocks of meiobenthos in the CCFZ compared to other deep-sea plains of similar depth. The latitudinal distribution pattern of meiobenthos in the study area seemed to be related with surface water primary productivity, which was connected to the water circulation pattern of the Pacific Ocean near the Equator, diverging at 8oN latitude and converging at 5°N. The horizontal distribution of meiobenthic organisms in the study area showed high densities at the stations within 135–136°W. The densities of meiobenthic organismas within the CCFZ were high at stations with few manganese nodules on the sediment surface at low-latitude sites. In 1998, the observed relative high values of meiobenthic abundance were at stations from 5° to 6°N. Other stations from 7° to 10°N showed no significant fluctuations during the interannual sampling periods. It is considered that the inter-annual fluctuation of meiobenthos abundance is intimately related with a regime shift that may have occurred in the north Pacific between 1998 and 1999, the El Nino period. Vertical distribution of meiobenthic organisms showed the highest individual numbers in the surface sediment layers of 0∼2 cm depth and a steep decreasing trend as sediment becomes deeper at the stations of high latitude located in 16∼17°N. Size distribution analyses showed that organisms that fit into the sieve mesh size of 0.063 mm were abundant.

Dynamics and controls of heterotrophic prokaryotic production in the western tropical South Pacific Ocean: links with diazotrophic and photosynthetic activity

Abstract. Heterotrophic prokaryotic production (BP) was studied in the western tropical South Pacific (WTSP) using the leucine technique, revealing spatial and temporal variability within the region. Integrated over the euphotic zone, BP ranged from 58 to 120 mg C m−2 d−1 within the Melanesian Archipelago, and from 31 to 50 mg C m−2 d−1 within the western subtropical gyre. The collapse of a bloom was followed during 6 days in the south of Vanuatu using a Lagrangian sampling strategy. During this period, rapid evolution was observed in the three main parameters influencing the metabolic state: BP, primary production (PP) and bacterial growth efficiency. With N2 fixation being one of the most important fluxes fueling new production, we explored relationships between BP, PP and N2 fixation rates over the WTSP. The contribution of N2 fixation rates to bacterial nitrogen demand ranged from 3 to 81 %. BP variability was better explained by the variability of N2 fixation rates than by that of PP in surface waters of the Melanesian Archipelago, which were characterized by N-depleted layers and low DIP turnover times (TDIP < 100 h). This is consistent with the fact that nitrogen was often one of the main factors controlling BP on short timescales, as shown using enrichment experiments, followed by dissolved inorganic phosphate (DIP) near the surface and labile organic carbon deeper in the euphotic zone. However, BP was more significantly correlated with PP, but not with N2 fixation rates where DIP was more available (TDIP > 100 h), deeper in the Melanesian Archipelago, or within the entire euphotic zone in the subtropical gyre. The bacterial carbon demand to gross primary production ratio ranged from 0.75 to 3.1. These values are discussed in the framework of various assumptions and conversion factors used to estimate this ratio, including the methodological errors, the daily variability of BP, the bacterial growth efficiency and one bias so far not considered: the ability for Prochlorococcus to assimilate leucine in the dark.

Atmospheric iron fluxes in the northern region of the Gulf of California: Implications for primary production and potential Fe limitation

To study the temporal variability of atmospheric mineral dust and Fe fluxes to the northern region of the Gulf of California, dust samples were collected at San Felipe, Baja California (Site 1) and Puerto Peñasco, Sonora (Site 2), from May 2010 to December 2011. Dust fluxes were partially associated with monsoon circulation, with highest (38 ± 20mgm−2 d−1) and lowest (8.8 ± 4.9mgm−2 d−1) fluxes linked to southwesterly winds (monsoon season) and north-northwesterly winds (non-monsoon season), respectively. Our analysis suggests that the surrounding deserts are the most probable source of dust arriving into the Gulf of California. However, analyses of Al and Fe concentrations in dusts showed no trends that could identify specific particulate Fe provenance. Average particulate Fe atmospheric fluxes (FeAtm) showed no clear temporal trends and their magnitudes (3.2 ± 3.4 and 6 ± 10µmolm−2 d−1 for sites 1 and 2, respectively) could be considered medium-to-low in magnitude within a global context. An Fe limitation index (FeLI), calculated as the ratio of phytoplankton Fe requirements to atmospheric and upwelling Fe fluxes, is proposed to estimate the impact of atmospheric mineral dust on phytoplankton primary production in surface waters of the Gulf of California. On a seasonal time scale, FeLI results suggest that under winter conditions, there is no evidence of Fe limitation because upwelling Fe contribution (FeUp) is high enough to support primary production. In contrast, during summer conditions, when FeUp is very low or negligible, high FeAtm combined with high particulate Fe dissolution factors could prevent the northern Gulf of California from becoming Fe-limited. Finally, we postulate that at an interannual scale, conditions prevailing during ENSO events could increase atmospheric Fe fluxes to the Gulf of California, further contributing to prevent Fe limitation in this marginal sea.

Diversity and Transcriptional Levels of RuBisCO Form II of Sulfur-Oxidizing γ-Proteobacteria in Coastal-Upwelling Waters with Seasonal Anoxia

Seasonal wind-driven upwelling, high primary production in surface waters, and oxygen deficiency in subsurface waters characterize the coastal ecosystem of the subtropical eastern South Pacific (ESP), and shape the nature and dynamics of the microbial community structure and function. We investigated the diversity, abundance, and transcriptional levels of the gene encoding the large subunit form II of the RuBisCO enzyme (cbbM) in the pelagic microbial community at a continental-shelf site off central Chile over two years. We focused on cbbM genes affiliated with the sulfur-oxidizing -proteobacteria cluster, whose members are known to dominate in oxygen-deficient marine environments and are highly abundant in the study area. Phylogenetic analysis of cbbM sequences suggests the presence of a novel group of chemolithoautotrophs, closely related to the SUP05/ARCTIC96BD-19 clade. Through (RT)-qPCR, we studied the cbbM gene abundance and transcript dynamics over an annual cycle, finding a significantly higher number of cbbM copies per unit volume in months of active upwelling and at depths in which oxygen was scarce or absent. The same temporal pattern was observed at the transcriptional level. We also analyzed the relative expression of key genes for carbon, nitrogen and sulfur cycling in six metatranscriptomic datasets, for two characteristic periods within the annual cycle: the anoxic upwelling and the suboxic downwelling. Our results indicate that coastal waters of the subtropical ESP contain transcriptionally active populations of carbon fixing pelagic bacteria, whose dynamics is controlled, in large part, by fluctuations in oxygen levels. They also suggest that chemolithoautotrophic processes coupled to the sulfur and nitrogen cycles become increasingly important for the carbon economy of marine coastal waters as oxygen concentrations decline.

Millennial-scale changes of surface and bottom water conditions in the northwestern Pacific during the last deglaciation

Changes in water column conditions in the northwestern Pacific during the last 23ka were reconstructed using geochemical and isotope proxies and redox elemental compositions along with published data (alkenone sea surface temperature (SST) and benthic foraminiferal fauna) at core GH02-1030. Surface water primary productivity in terms of biogenic opal and TOC contents, which mainly represented export production of diatom, was closely related to alkenone (spring-summer) SST and the development of spring-summer mixed layer depth. The different variation patterns of nitrate and silicic acid utilization, estimated by bulk δ15N and δ30Sidiatom values, respectively, are most likely due to the water column denitrification influence on bulk δ15N. Dysoxic bottom water conditions occurred during the Bølling-Allerød (BA) and the Pre-Boreal (PB), which was evident by laminated sediments, abundant dysoxic benthic foraminifers, and increased redox elemental compositions. Although surface water productivity increased during the BA and PB, dysoxic bottom water conditions were caused by a combination of enhanced surface water productivity and reduced ventilation of North Pacific Intermediate Water (NPIW) in response to meltwater input from the high latitude areas. Based on records of core GH02-1030 and other cores in the northwestern Pacific, the Okhotsk Sea, and the Bering Sea, which are all proximal to the modern NPIW source region, dissolved oxygen concentrations of bottom water were more depleted during the BA than PB. Such difference was attributed to more sluggish NPIW ventilation due to more meltwater input during the BA than the PB. The opening or closure of the Bering Strait is critical to the direction of meltwater transport to the northwestern Pacific.

Effects of eutrophication and benthic respiration on water column carbonate chemistry in a traditional hypoxic zone in the Northern Gulf of Mexico

Abstract A simple river-ocean mixing approach has been frequently used to examine estuarine and coastal carbonate system speciation. Coastal areas receiving significant nutrient inputs, however, can have the carbonate chemistry greatly deviated from this mixing-only scheme because of disparate, but spatially coupled biogeochemical processes, i.e., intense primary production in surface waters and elevated respiration in bottom waters; the latter often leads to bottom-water hypoxia (dissolved oxygen or DO concentration − 1 ) and acidification. As a result of land use change, riverine TA input is known to enhance coastal water buffer capacity, although this effect in eutrophic coastal water has not been systematically studied. The physical disturbances of shallow coastal waters by storms can disrupt bottom hypoxia through overturning the water column. This overturn has been proposed to exacerbate bottom water acidification, because of the different exchange rates of oxygen and CO 2 , which could lead to a ‘reset’ of oxygen concentration but little change in the total dissolved inorganic carbon concentration. We used data from the summer 2010 hypoxia cruise in the northern Gulf of Mexico shelf, during which a tropical depression (Bonnie) perturbed the bottom water. Carbonate buffer capacity in both surface and subsurface waters along the salinity gradient suggested that eutrophication-induced surface production and bottom respiration far outweighed the influence of river TA variation and temperature changes in determining carbonate changes on centennial time scales. We propose, based on literature-based CO 2 flux reported in this area, that the benthic (both aerobic and anaerobic) respiration-produced CO 2 flux (with a lesser flux of alkalinity), instead of bottom water reset by storms, could be responsible for further acidifying hypoxic bottom water in addition to water column aerobic respiration.

Diatom bloom‐derived bottom water hypoxia off the Changjiang estuary, with and without typhoon influence

AbstractDuring the summers of 2009 and 2013, seawater pH and concentrations of dissolved oxygen, inorganic carbon, and nutrients were measured off the Changjiang estuary in the East China Sea. The 2009 cruise captured the effects of Typhoon Morakot; the 2013 cruise sampled more typical conditions (no typhoon). Data from both years indicate a close correlation between high primary productivity in surface waters and hypoxia in bottom waters. Based on these observations, we developed a conceptual model to guide an exploration of processes contributing to the formation of summertime bottom hypoxia. A mixing‐model analysis of the 2009 data identified a surface diatom bloom as the major (70–80%) source of the organic carbon that decomposed and ultimately led to bottom water hypoxia. Within the Changjiang River plume, depth‐integrated net biological production in the water column was 1.8 g C m−2 d−1, indicating strong autotrophic production, which in turn led to a high respiration rate of 1.2 g C m−2 d−1 in the bottom water. During both cruises, strong surface‐to‐bottom physical and metabolic coupling was evident. In 2009, storm‐driven inputs of nutrients from elevated river discharge and strong vertical mixing helped to fuel the rapid development of a surface diatom bloom. Afterwards, stratified conditions re‐established, newly formed labile organic matter sank, and bottom water oxygen was quickly consumed to an extent that hypoxia and acidification developed. To our knowledge, the observed rate of hypoxia and acidification development (within 6 d) is the fastest yet reported for the Changjiang River plume.

The Coniacian–Santonian sedimentary record in southern Tanzania (Ruvuma Basin, East Africa): Planktonic foraminiferal evolutionary, geochemical and palaeoceanographic patterns

AbstractA 101 m thick stratigraphically complete late Coniacian–early Santonian (ca89 to 83 Ma) sedimentary sequence drilled in Tanzania (Tanzania Drilling Project Site 39) allows, for the first time, examination of the planktonic foraminiferal biostratigraphy and evolution, the depositional history, and geochemical patterns of the subtropical–tropical Indian Ocean region. The sedimentary succession corresponds to an outer shelf to upper slope setting and is dominated by calcareous clayey siltstones and mudstones. The occurrences of Tethyan marker species enable application of the tropical biozonation including identification of theDicarinella concavataandDicarinella asymetricaZones. In addition, Tanzania Drilling Project Site 39 is proposed as reference section for the Coniacian/Santonian boundary in the Indian Ocean with the boundary placed at the lowest occurrence ofGlobotruncana linneianain agreement with the Global Stratotype Section and Point (Spain). The record at Tanzania Drilling Project Site 39 provides a unique opportunity to document the planktonic foraminiferal evolution in a subtropical marginal sea environment during a key period in their evolutionary history characterized by a major radiation among the deep‐dwelling taxa. Combined documentation of lithological and geochemical changes (%CaCO3, %Corg,δ13Ccarbandδ18Ocarb) reveals a setting influenced by continental‐derived nutrients in theDicarinella concavataZone (Lindi Formation) with a change to higher carbonate production and reduced surface water primary productivity in the overlyingDicarinella asymetricaZone (Nangurukuru Formation). Planktonic foraminiferal assemblage changes mirror the depositional and geochemical trends and indicate a progressive shift from a more eutrophic to a more oligotrophic regime through time. At the local scale, this palaeoceanographic scenario is consistent with the deepening of coastal Tanzania in response to the Late Cretaceous marine transgression registered in south‐east Tanzania. Because the tectonic evolution and sea‐level rise along the East Africa continental margin is superimposed on the Coniacian–Campanian global long‐term sea‐level high, this study hypothesizes that the epicontinental invasion of blue waters may have favoured radiation among deep‐dwelling taxa.

Stable carbon isotope gradients in benthic foraminifera as proxy for organic carbon fluxes in the Mediterranean Sea

Abstract. We have determined stable carbon isotope ratios of epifaunal and shallow infaunal benthic foraminifera in the Mediterranean Sea to relate the inferred gradient of pore water δ13CDIC to varying trophic conditions. This is a prerequisite for developing this difference into a potential transfer function for organic matter flux rates. The data set is based on samples retrieved from a well-defined bathymetric range (400–1500 m water depth) of sub-basins in the western, central, and eastern Mediterranean Sea. Regional contrasts in organic matter fluxes and associated δ13CDIC of pore water are recorded by the δ13C difference (Δδ13CUmed-Epi) between the shallow infaunal Uvigerina mediterranea and epifaunal species (Planulina ariminensis, Cibicidoides pachydermus, Cibicides lobatulus). Within epifaunal taxa, the highest δ13C values are recorded for P. ariminensis, providing the best indicator for bottom water δ13CDIC. In contrast, C. pachydermus reveals minor pore water effects at the more eutrophic sites. Because of ontogenetic trends in the δ13C signal of U. mediterranea of up to 1.04 ‰, only tests larger than 600 µm were used for the development of the transfer function. The recorded differences in the δ13C values of U. mediterranea and epifaunal taxa (Δδ13CUmed-Epi) range from −0.46 to −2.13 ‰, with generally higher offsets at more eutrophic sites. The measured δ13C differences are related to site-specific differences in microhabitat, depth of the principal sedimentary redox boundary, and TOC content of the ambient sediment. The Δδ13CUmed-Epi values reveal a consistent relation to Corg fluxes estimated from satellite-derived surface water primary production in open-marine settings of the Alboran Sea, Mallorca Channel, Strait of Sicily, and southern Aegean Sea. In contrast, Δδ13CUmed-Epi values in areas affected by intense resuspension and riverine organic matter sources of the northern to central Aegean Sea and the canyon systems of the Gulf of Lion suggest higher Corg fluxes compared to the values based on recent primary production. Taking regional biases and uncertainties into account, we establish a first Δδ13CUmed-Epi-based transfer function for Corg fluxes for the Mediterranean Sea.

The trophic structure of Spongosorites coralliophaga-coral rubble communities at two northeast Atlantic cold water coral reefs

ABSTRACTWe examined the isotopic signatures (δ13C, δ15N) of fauna living in association with the sponge Spongosorites coralliophaga colonizing coral rubble on cold-water coral reefs in the northeast Atlantic – the shallow inshore (122–131 m collection depth) Mingulay 01 area and the deep offshore (683–800 m) Logachev 02 mound. The δ15N signatures of suspended particulate organic matter and three primary consumers, i.e. Spongosorites coralliophaga, Reteporella beaniana and Parazoanthus anguicomus were used as trophic baselines and the resulting trophic structure was compared. In both regions four trophic levels were distinguished. However, the use of S. coralliophaga or R. beaniana as baselines resulted in a skewed trophic structure due to the enriched δ15Ν signatures of these two species on the Logachev 02 mound. Using suspended particulate organic matter and P. anguicomus as baselines, the Mingulay 01 area communities were characterized by elevated relative biomass of lower trophic levels compared to the Logachev 02 mound. Relative biomass of suspension/filter feeders was also higher at the Mingulay 01 area. The two regions differed significantly with regard to the prevailing environmental conditions: apart from the difference in depth and distance from shore, the Mingulay 01 area was characterized by higher primary production in surface waters, tight pelagic–benthic coupling and higher velocity of bottom currents, and it is hypothesized that these characteristics were the main drivers of the observed differences. This study highlighted that multiple trophic baselines can provide a better interpretation of food-web structure and that the use of sponges or bryozoans as baselines across bathymetric gradients should be avoided.

Geochemical paleoredox indicators in organic-rich shales of the Irati Formation, Permian of the Paraná Basin, southern Brazil

ABSTRACT: Paleoredox indicators were used to assess the depositional environment of the Permian Irati Formation, and discuss the controls on the accumulation of organic-rich sediments. Geochemical data were measured for 43 drill-core samples in southern Paraná Basin. We infer that redox boundary was located at the sediment-water interface during the accumulation of these sediments. Trace-element data demonstrate that Irati shales were similar to average shales, except during deposition of two organic-rich beds in which U and Mo are enriched, suggesting fully anoxic conditions. The variable degree of oxygenation of bottom waters is also attested by DOPT, FeT/Al, and sedimentological indicators of episodic ventilation. DOPT and Fe and S correlation points to an iron-limited environment, where the main sulfur sink is organic matter rather than pyrite. Cu and Cu/Mo ratio suggests bottom-water anoxia driven by increased organic flux. The Irati Formation was probably deposited in a salinity-stratified body of water, with positive water balance. The main control on the accumulation of the organic-rich sediments was the high organic carbon flux resultant from high primary productivity in surface waters. Anoxia arose as a consequence of increased productivity, not as the primary driver in the formation of these organic-rich rocks.

Drivers of the carbonate system seasonal variations in a Mediterranean gulf

The effects of different physical and biogeochemical drivers on the carbonate system were investigated in a semi-enclosed coastal area characterized by high alkalinity riverine discharge (Gulf of Trieste, Northern Adriatic Sea, Mediterranean Sea). Our 2-year time-series showed that a large part of the seasonal carbonate chemistry variation was controlled by the large seasonal change of seawater temperature, though air-sea CO2 exchange, biological activity (primary production-respiration), and riverine inputs also exerted a significant influence.With the exception of summer, the Gulf of Trieste was a sink of atmospheric carbon dioxide, showing a very strong CO2 fluxes from atmosphere into the sea (−16.10 mmol m−2 day−1) during high wind speed event of north easterly Bora wind. The CO2 influx was particularly evident in winter, when the biological activity was at minimum and the low seawater temperature enhanced CO2 solubility. During spring, the drawdown of CO2 by primary production overwhelmed the CO2 physical pump, driving a significant decrease of dissolved inorganic carbon (DIC), [CO2], and increase of pHT25 °C. In summer the primary production in surface waters occurred with the same intensity as respiration in the bottom layer, so the net biological effect on the carbonate system was very low and the further reduction of seawater CO2 concentration observed was mainly due to carbon dioxide degassing induced by high seawater temperature. Finally, during autumn the respiration was the predominant process, which determined an overall increase of DIC, [CO2], and decrease of pHT25 °C. This was particularly evident when the breakdown of summer stratification occurred and a large amount of CO2, generated by respiration and segregated below the pycnocline, was released back to the whole water column. Local rivers also significantly affected the carbonate system by direct input of total alkalinity (AT) coming from the chemical weathering of carbonate rocks, which dominate the river watershed. Our finding clearly demonstrates a high AT concentration in low salinity surface waters (AT max = 2742.8 μmol kg−1) and a negative AT-salinity correlation. As a result the Gulf of Trieste revealed a low Revelle factor (10.1) and one of the highest buffer capacities of the Mediterranean Sea (ßDIC = 0.31 mmol kg−1), which allows the system to store a significant amount of atmospheric CO2 with a small decrease of seawater pH.

High resolution dinoflagellate cyst record of environmental change in Effingham Inlet (British Columbia, Canada) over the last millennium

We present a high resolution sedimentary record of dinoflagellate cysts spanning the last ~900years recovered from Effingham Inlet, a glacial fjord on the west coast of Vancouver Island, Canada. The combination of seasonal coastal upwelling supporting high levels of marine primary productivity in surface waters, together with restricted bottom water circulation in the silled fjord, fosters the preservation of laminated sediments in the inner basin of Effingham Inlet. Geochemical data are used to assess the sedimentary facies of the core, which is composed primarily of laminated units (50.2%) occasionally interrupted by “seismites” (39.5%) and homogenous units (10.2%). The chronology of the ~2m-long core is based on varve counting and fifteen 14C dates, and is anchored by a seismite previously dated at AD 1946.The dinoflagellate cyst assemblages are diverse (total of 47 taxa), abundant (average concentrations of 102,900cystg−1 of dry sediment), and characterized by a proportionally equal contribution of autotrophic and heterotrophic cyst taxa in most samples. Overall, cyst assemblages are characterized by Operculodinium centrocarpum (36.2%) accompanied by Brigantedinium spp. (18.0%) and Dubridinium spp. (6.6%). Multivariate analyses are used to extract the dominant patterns of variability in autotrophic and heterotrophic dinoflagellate cyst assemblages separately, and help in identifying the temperature and primary productivity gradients encoded in the cyst sedimentary record in this particular estuary.Specific intervals identified in the dinoflagellate cyst record are interpreted to represent the local expression of the “Medieval Climate Anomaly” (from the base of the record, ~AD 1090 to 1230), the “Little Ice Age” (~AD 1230 to late 19th century) and warming in the second half of the 20th century. The timing of these intervals are consistent with the regional paleoclimate and help constrain past climatic and oceanographic variability on the west coast of Vancouver Island. The origin of homogenous units in the sedimentary record of Effingham Inlet and paleoseismicity in the region are also discussed.

The response of deep-water benthic foraminiferal assemblages to changes in paleoproductivity during the Pleistocene (last 769.2 kyr), western South Atlantic Ocean

Benthic foraminiferal assemblages and δ18O records in a core from Santos Basin (western South Atlantic, 2220m water depth) were analyzed to investigate productivity changes during the Pleistocene. The sediment core recorded the last 770kyr, including Marine Isotope Stages (MIS) 19 to 1. The four dominant benthic foraminiferal assemblages were identified using Q-mode Varimax Factor Analysis, and are represented by Globocassidulina crassa, Bolivina spp., Epistominella exigua and Alabaminella weddellensis. From 769.2kyr (MIS 19) to ~300kyr (MIS 8), the highest values of factor 2 (Bolivina spp. assemblage) indicate increased influx of organic matter to the seafloor and a slight decrease in the oxygen concentration at the sediment–water interface. This condition began to change in the stage 8 (~288.9kyr to ~268.3kyr), and it is characterized by high values of factor 1, when the G. crassa assemblage became dominant, indicating an increase in oxygen concentrations and a decrease in the influx of organic matter. Seasonally-pulsed organic matter resulting in a distinct phytodetritus layer accumulated mostly during the glacial MIS 14, 10, 8, 6, and 5.2–5.1, and in the interglacial stage 11 and the end of 9, as indicated by factor 3 (E. exigua assemblage) and factor 4 (A. weddellensis assemblage). The highest peak of the A. weddellensis assemblage during MIS 11 (~401.4kyr) coincides with the Mid-Brunhes Event. The highest benthic foraminiferal accumulation rates occurred during mostly glacial stages, indicating delivery of more organic matter to the seafloor. The changes in benthic foraminifera assemblages in the glacial stages during the Pleistocene indicate changes in primary productivity in surface waters. Increasing the amount of organic matter delivered to the seafloor amplified the benthic foraminiferal response.

Zonation of bacterioplankton communities along aging upwelled water in the northern Benguela upwelling.

Upwelling areas are shaped by enhanced primary production in surface waters, accompanied by a well-investigated planktonic succession. Although bacteria play an important role in biogeochemical cycles of upwelling systems, little is known about bacterial community composition and its development during upwelling events. The aim of this study was to investigate the succession of bacterial assemblages in aging upwelled water of the Benguela upwelling from coastal to offshore sites. Water from the upper mixed layer at 12 stations was sampled along two transects from the origin of the upwelling to a distance of 220 km. 16S rRNA gene amplicon sequencing was then used in a bacterial diversity analysis and major bacterial taxa were quantified by catalyzed reporter deposition-fluorescence in situ hybridization. Additionally, bacterial cell numbers and bacterial production were assessed. Community statistical analysis revealed a reproducible zonation along the two transects, with four clusters of significantly different microbial assemblages. Clustering was mainly driven by phytoplankton composition and abundance. Similar to the temporal succession that occurs during phytoplankton blooms in temperate coastal waters, operational taxonomic units (OTUs) affiliated with Bacteroidetes and Gammaproteobacteria were dominant during algal blooming whereas “Pelagibacterales” were highly abundant in regions with low algal abundance. The most dominant heterotrophic OTU (9% of all reads) was affiliated with “Pelagibacterales” and showed a strong negative correlation with phytoplankton. By contrast, the second most abundant heterotrophic OTU (6% of all reads) was affiliated with the phylum Verrucomicrobia and correlated positively with phytoplankton. Together with the close relation of bacterial production and phytoplankton abundance, our results showed that bacterial community dynamics is strongly driven by the development and composition of the phytoplankton community.

Temporal and spatial variability of particle transport in the deep Arctic Canada Basin

AbstractTo better understand the current carbon cycle and potentially detect its change in the rapidly changing Arctic Ocean, we examined sinking particles collected quasi‐continuously over a period of 7 years (2004–2011) by bottom‐tethered sediment trap moorings in the central Canada Basin. Total mass flux was very low (<100 mg m−2 d−1) at all sites and was temporally decoupled from the cycle of primary production in surface waters. Extremely low radiocarbon contents of particulate organic carbon and high aluminum contents in sinking particles reveal high contributions of resuspended sediment to total sinking particle flux in the deep Canada Basin. Station A (75°N, 150°W) in the southwest quadrant of the Canada Basin is most strongly influenced while Station C (77°N, 140°W) in the northeast quadrant is least influenced by lateral particle supply based on radiocarbon content and Al concentration. The results at Station A, where three sediment traps were deployed at different depths, imply that the most likely mode of lateral particle transport was as thick clouds of enhanced particle concentration extending well above the seafloor. At present, only 1%–2% of the low levels of new production in Canada Basin surface waters reaches the interior basin. Lateral POC supply therefore appears to be the major source of organic matter to the interior basin. However, ongoing changes to surface ocean boundary conditions may influence both lateral and vertical supply of particulate material to the deep Canada Basin.