Crustal thickness along the western Galápagos Spreading Center and the compensation of the Galápagos hotspot swell

Wide-angle refraction and multichannel reflection seismic data show that oceanic crust along the Galápagos Spreading Center (GSC) between 97°W and 91°25′W thickens by 2.3 km as the Galápagos plume is approached from the west. This crustal thickening can account for ∼52% of the 700 m amplitude of the Galápagos swell. After correcting for changes in crustal thickness, the residual mantle Bouguer gravity anomaly associated with the Galápagos swell shows a minimum of −25 mGal near 92°15′W, the area where the GSC is intersected by the Wolf-Darwin volcanic lineament (WDL). The remaining depth and gravity anomalies indicate an eastward reduction of mantle density, estimated to be most prominent above a compensation depth of 50-100 km. Melting calculations assuming adiabatic, passive mantle upwelling predict the observed crustal thickening to arise from a small increase in mantle potential temperature of ∼30°C. The associated thermal expansion and increase in melt depletion reduce mantle densities, but to a degree that is insufficient to explain the geophysical observations. The largest density anomalies appear at the intersection of the GSC and the WDL. Our results therefore require the existence of compositionally buoyant mantle beneath the GSC near the Galápagos plume. Possible origins of this excess buoyancy include melt retained in the mantle as well as mantle depleted by melting in the upwelling plume beneath the Galápagos Islands that is later transported to the GSC. Our estimate for the buoyancy flux of the Galápagos plume (700 kg s⁻¹) is lower than previous estimates, while the total crustal production rate of the Galápagos plume (5.5 m³s⁻¹) is comparable to that of the Icelandic and Hawaiian plumes.     

Organic matter,sediment particle size and nutrient distributions in a sewage affected shallow channel

Sediment and seawater samples were taken in a sewage affected channel in Blanca Bay, Argentina. Protein content, ‘humic substances’ and silt-clay percentage were evaluated in the sediments; NH₄⁺, PO₄^3? and ‘dissolved organic matter’ in seawater. A highly significant correlation (r=0.747, n=59) was obtained for the relation between protein and % silt-clay. The ‘humic substances’ distribution depends more on the distance from the outfall than does the protein content, probably because of the important relation of the latter with the sediment particle size. The dissolved components showed a dilution pattern similar to that of a contaminant plume in a moving water mass, reaching normal values at 1700 m from the outfall.     

Modelling larval dispersal and settlement of the reef-building polychaete Sabellaria alveolata: Role of hydroclimatic processes on the sustainability of biogenic reefs

The honeycomb worm Sabellaria alveolata forms biogenic reefs which constitute diversity hotspots on tidal flats. The largest known reefs in Europe, located in the Bay of Mont-Saint-Michel (English Channel), are suffering increasing anthropogenic disturbances which raise the question of their sustainability. As the ability to recover depends partly on the recolonization of damaged reefs by larval supply, evaluating larval dispersal and the connectivity between distant reefs is a major challenge for their conservation. In the present study, we used a 3D biophysical model to simulate larval dispersal under realistic hydroclimatic conditions and estimate larval retention and exchanges among the two reefs of different sizes within the bay. The model takes into account fine-scale hydrodynamic circulation (800×800 m²), advection–diffusion larval transport, and gregarious settlement behaviour. According to the field data, larval dispersal was simulated for a minimal planktonic larval duration ranging from 4 to 8 weeks and the larval mortality was set to 0.09 d⁻¹. The results highlighted the role played by a coastal eddy on larval retention within the bay, as suggested by previous in situ observations. Very different dispersal patterns were revealed depending on the spawning reef location, although the two reefs were located only 15 km apart. The settlement success of the larvae released from the smallest reef was mainly related to tidal conditions at spawning, with the highest settlement success for releases at neap tide. The settlement success of the larvae from the biggest reef was more dependent on meteorological conditions: favourable W and SW winds may promote a ten-fold increase in settlement success. Strong year-to-year variability was observed in settlers’ numbers, with favourable environmental windows not always coinciding with the main reproductive periods of Sabellaria. Settlement kinetics indicated that the ability to delay metamorphosis could significantly improve the settlement success. Although bidirectional exchanges occurred between the two reefs, the highest settlers’ numbers originated from the biggest reef because of its stronger reproductive output. Because of the recent decline of this reef due to increasing anthropogenic disturbances larval supply in the bay may not be sufficient enough to ensure the sustainability of the remarkable habitat formed by Sabellaria alveolata reefs.     

Characterization of sedimentary deposits at the confluence of two tributaries of the Pará River estuary (Guajará Bay,Amazon)

Guajará Bay, located at the right margin of the Pará River estuary (Amazon) is formed in the confluence of Guamá and Acará–Moju rivers. It has low-depth zones (∼5 m) and deep channels (∼25 m). The ebb channel is located in the west section, where there is intense erosion of the margin. The flood channels and intertidal mudflats, which stretch out from north to south along the shore of the city of Belém do Pará, are in the east section. There are sandy (northwest) and muddy sedimentary deposits (east–southeast). Some 70% of Guajará Bay's bottom is covered by mud. The depositation of such muddy sediments and the formation of a point bar in the south section (Guamá River mouth) happen due to a decrease in the intensity of tidal currents to the south and of fluvial currents to the north. However, the hydrodynamic regime is high, which is proved by the low clay amounts. The sand deposits in the northwest section indicate strong tidal currents. The vast area of the bottom that is covered by mud (∼90 km²) and the intertidal mudflats (∼150 m wide) in Guajará Bay hint the extent of the contribution and sediments flow from Guamá and Acará–Moju rivers (drainage basin total area of ∼87,400 km²) to the Pará River estuary. The regular rainfall regime, typical of the Amazon region, keeps the considerable discharges of such rivers and their high turbidity (Secchi depth ?0.5 m) in the investigation area. Generally speaking, the low topography, the great fluvial subsidy and the action of tidal currents are the main controlling elements of the depositation and dispersion of sediments in Guajará Bay.     

Space-time variability of the Amazon River plume based on satellite ocean color

Satellite ocean color images were used to determine the space-time variability of the Amazon River plume from 2000–2004. The relationship between sea-surface salinity (SSS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) absorption coefficient for dissolved and detrital material (a_dg) (r²=0.76, n=30, rmse=0.4) was used to identify the Amazon River plume low-salinity waters (<34 psu). The plume's spatial information was extracted from satellite bi-weekly time series using two metrics: plume area and plume shape. These metrics identified the seasonal variability of plume dimensions and dispersion patterns. During the study period, the plume showed the largest areas from July to August and the smallest from December to January. The mean annual amplitude and the mean, maximum and minimum plume areas were 1020×10³ km², 680×10³ km², 1506×10³ km² and 268×10³ km², respectively. Three main shapes and dispersion pattern periods were identified: (1) flow to the northeastern South American coast, in a narrow band adjacent to the continental shelf, from January to April; (2) flow to the Caribbean region, from April to July; and (3) flow to the Central Equatorial Atlantic Ocean, from August to December. Cross-correlation techniques were used to quantify the relationship between the plume's spatial variability and environmental forcing factors, including Amazon River discharge, wind field and ocean currents. The results showed that (1) river discharge is the main factor influencing plume area variability, (2) the wind field regulates the plume's northwestward flow velocity and residence time near the river mouth, and (3) surface currents have a strong influence over river plume dispersion patterns.     

Nutrients,irradiance, and mixing as factors regulating primary production in coastal waters impacted by the Mississippi River plume

Relationships among primary production, chlorophyll, nutrients, irradiance and mixing processes were examined along the salinity gradient in the Mississippi River outflow region. A series of six cruises were conducted during 1988–1992 at various times of year and stages of river discharge. Maximum values of biomass and primary production were typically observed at intermediate salinities and coincided with non-conservative decreases in nutrients along the salinity gradient. Highest values of productivity (>10 gC m⁻² d⁻¹) and biomass (>30 mg chlorophyll a m⁻³) were observed in April 1988, July–August 1990 and April–May 1992; values were lower in March and September 1991. Rates of primary production were apparently constrained by low irradiance and mixing in the more turbid, low salinity regions of the plume, and by nutrient limitation outside the plume. Highest values of primary production occurred at stations where surface nutrient concentrations exhibited large deviations from conservative mixing relationships, indicating that depletion of nutrients was related to phytoplankton uptake. Mixing and advection were important in determining the location and magnitude of primary production maxima and nutrient depletion. In addition to growth within plume surface waters, enhanced growth and/or retention of biomass may have occurred in longer residence time waters at the plume edge and/or beneath the surface plume. Vertical structure of some plume stations revealed the presence of subsurface biomass maxima in intermediate salinity water that was depleted in nutrients presumably by uptake processes. Exchange between subsurface water and the surface plume apparently contributed to the reduction in nutrients at intermediate salinities in the surface layer. DIN (=nitrate+nitrite+ammonium) : PO₄ (=phosphate) ratios in river water varied seasonally, with high values in winter and spring and low values in late summer and fall. Periods of high DIN : PO₄ ratios in river nutrients coincided with cruises when surface nutrient concentrations and their ratios indicated a high probability for P limitation. N limitation was more likely to occur at high salinities and during late summer and fall. Evidence for Si limitation was also found, particularly in spring.     

Variability of the dissolved nutrient (N,P, Si) concentrations in the Bay of Annaba in relation to the inputs of the Seybouse and Mafragh estuaries

Dissolved inorganic nitrogen (DIN), phosphate (PO₄) and silicic acid (Si(OH)₄) loads from the Seybouse and the Mafragh estuaries into the Bay of Annaba, Algeria, were assessed at three stations of the Bay over three years. The Seybouse inputs had high levels of DIN and PO₄, in contrast to the Mafragh estuary’s near-pristine inputs; Si(OH)₄ levels were low in both estuaries. The DIN:PO₄ molar ratios were over 30 in most samples and the Si(OH)₄:DIN ratio was less than 0.5 in the Seybouse waters, but nearly balanced in the Mafragh. The specific fluxes of Si–Si(OH)₄ (400–540 kg Si km⁻² yr⁻¹) were comparable in the two catchments, but those of DIN were several-fold higher in the Seybouse (373 kg N km⁻² yr⁻¹). The inner Bay affected by the Seybouse inputs had high levels of all nutrients, while the Mafragh plume and the outer marine station were less enriched.     

Implementation of a wetting-and-drying model in simulating the Kennebec–Androscoggin plume and the circulation in Casco Bay

A high-resolution coastal ocean model was developed to simulate the temporal/spatial variability of the Kennebec–Androscoggin (K–A) river plume and the circulation in Casco Bay. The model results agree favorably with the moored and shipboard observations of velocity, temperature, and salinity. The surface salinity gradient was used to distinguish the plume from the ambient coastal water. The calculated plume thickness suggests that the K–A plume is surface trapped. Its horizontal scales correlate well with Q ^0.25, where Q is the volume discharge of the rivers. Directional spreading is affected by the wind with the upwelling favorable wind transporting the plume water offshore. Both the wind and the tide also enhance mixing in the plume. The inclusion of a wetting-and-drying (WAD) scheme appears to enhance the mixing and entrainment processes near the estuary. The plume becomes thicker near the mouth of the estuary, the outflow velocity of the plume is weaker, and the radius of the river plume shrinks. The flow field in the model run with the WAD is noisier, not only in shallow areas of Casco Bay but also in the plume and even on the shelf. We speculate that the WAD processes can affect much larger areas than the intertidal zones, especially via a river plume that feeds into a coastal current.     

Land-based nutrient enrichment of the Buccoo Reef Complex and fringing coral reefs of Tobago, West Indies

Tobago’s fringing coral reefs (FR) and Buccoo Reef Complex (BRC) can be affected locally by wastewater and stormwater, and regionally by the Orinoco River. In 2001, seasonal effects of these inputs on water-column nutrients and phytoplankton (Chl a), macroalgal C:N:P and δ¹⁵N values, and biocover at FR and BRC sites were examined. Dissolved inorganic nitrogen (DIN, particularly ammonium) increased and soluble reactive phosphorus (SRP) decreased from the dry to wet season. Wet season satellite and Chl a data showed that Orinoco runoff reaching Tobago contained chromophoric dissolved organic matter (CDOM) but little Chl a, suggesting minimal riverine nutrient transport to Tobago. C:N ratios were lower (16 vs. 21) and macroalgal δ¹⁵N values higher (6.6‰ vs. 5.5‰) in the BRC vs. FR, indicating relatively more wastewater N in the BRC. High macroalgae and low coral cover in the BRC further indicated that better wastewater treatment could improve the health of Tobago’s coral reefs.     

Spatial variability in organic material sinking export in the Hudson Bay system,Canada, during fall

Spatial variations in the sinking export of organic material were assessed within the Hudson Bay system (i.e., Hudson Bay, Hudson Strait and Foxe Basin) during the second oceanographic expedition of ArcticNet, on board the CCGS Amundsen in early fall 2005. Sinking fluxes of particulate organic material were measured using short-term free-drifting particle interceptor traps deployed at 50, 100 and 150 m for 8–20 h at eight stations. Measurements of chlorophyll a (chl a), pheopigments (pheo), particulate organic carbon (POC), biogenic silica (BioSi), protists, fecal pellets and bacteria were performed on the collected material. In parallel, sea surface salinity and temperature were determined at 121 stations in the Hudson Bay system. Three hydrographic regions presenting different sedimentation patterns were identified based on average surface salinity and temperature. Hudson Strait was characterized by a marine signature, with high salinity (average=32.3) and low temperature (average=2.1 °C). Eastern Hudson Bay was strongly influenced by river runoff and showed the lowest average salinity (26.6) and highest average temperature (7.6 °C) of the three regions. Western Hudson Bay showed intermediate salinity (average=29.4) and temperature (average=4.4 °C). Sinking fluxes of total pigments (chl a+pheo: 3.37 mg m⁻² d⁻¹), diatom-associated carbon (19.8 mg m⁻² d⁻¹) and BioSi (50.2 mg m⁻² d⁻¹) at 50 m were highest in Hudson Strait. Eastern Hudson Bay showed higher sinking fluxes of total pigments (0.52 mg m⁻² d⁻¹), diatom-associated carbon (3.29 mg m⁻² d⁻¹) and BioSi (36.6 mg m⁻² d⁻¹) compared to western Hudson Bay (0.19, 0.05 and 7.76 mg m⁻² d⁻¹, respectively). POC sinking fluxes at 50 m were low and relatively uniform throughout the Hudson Bay system (50.0–76.8 mg C m⁻² d⁻¹), but spatial variations in the composition of the sinking organic material were observed. A large part (37–78%) of the total sinking POC was unidentifiable by microscopic observation and was qualified as amorphous detritus. Considering only the identifiable material, the major contributors to the POC sinking flux were intact protist cells in Hudson Strait (28%), fecal pellets in eastern Hudson Bay (52%) and bacteria in western Hudson Bay (17%). A significant depth-related attenuation of the POC sinking fluxes (average loss between 50 and 150 m=32%) and a significant increase in the BioSi:POC ratio (average increase between 50 and 150 m=76%) were observed in Hudson Strait and eastern Hudson Bay. For all other sinking fluxes and composition ratios, we found no statistically significant difference with depth. These results show that during fall, the sinking export of total POC from the euphotic zone remained fairly constant throughout the Hudson Bay system, whereas other components of the organic sinking material (e.g., chl a, BioSi, fecal pellets, protist cells) showed strong spatial variations.     

The application of lead isotope ratios in the Antarctic macroalga Iridaea cordata as a contaminant monitoring tool

Lead (Pb) isotope ratios were measured in the marine macroalga Iridaea cordata collected from four locations in the Windmill Islands, East Antarctica. Based on the masses of thalli collected, samples analysed in this study were likely to be a mixture of one and two year old thalli. For a sample of thalli of various ages (<12 months to 2 years old) from the same site there was no apparent variation in Pb concentration or Pb isotope ratio with thallus mass/age, indicating that contaminant sources had been constant over the lifetime of the thalli sampled. I.cordata samples close to the Thala Valley waste disposal site (Brown Bay Inner) near the Australian Station, Casey, displayed isotopic signatures (²⁰⁸Pb/²⁰⁴Pb 35.99; ²⁰⁶Pb/²⁰⁷Pb 1.066; n = 3; average values shown) trending towards that possessed by major Australian Pb sources (Broken Hill and Mt Isa, ²⁰⁸Pb/²⁰⁴Pb 35.60; ²⁰⁶Pb/²⁰⁷Pb 1.041) suggesting that these samples had been exposed to anthropogenic Pb originating from the Thala Valley waste disposal site. Material collected hundreds of metres from the tip location at Brown Bay Outer had isotopic values (²⁰⁸Pb/²⁰⁴Pb 36.32; ²⁰⁶Pb/²⁰⁷Pb 1.088; n = 10) intermediate between Brown Bay Inner and sites further from the contaminant source at Sparkes Bay and Wilkes (²⁰⁸Pb/²⁰⁴Pb 36.46; ²⁰⁶Pb/²⁰⁷Pb 1.094; n = 4) showing that contaminant transport was predominantly restricted to Brown Bay Inner. This study demonstrates that the isotope ratios of Pb in marine macroalgae can provide valuable information as to the origin and extent of heavy metal flux in a marine environment.     

The effects of alteration and the interpretation of heat flow and radioactivity data—a reply to R.U.M. Rao

The first²²⁴Ra (t_1/2 = 3.64days) measurements from mixing zones of estuarine systems are presented for the Pee Dee River-Winyah Bay and Delaware Bay Estuaries. High-resolution gamma-ray spectrometry was used to determine²²⁴Ra,²²⁸Ra (t_1/2 = 5.7years), and²²⁶Ra (t_1/2 = 1622years) activity ratios. Desorption and diffusion from suspended and bottom sediments contributes to the non-conservative increases of the three isotopes in each systems. In Delaware Bay²²⁴Ra concentrations were nearly constant over the 2.5‰ to 15‰ salinity range where two turbidity maximum zones are located.²²⁸Th scavenging onto the suspended particles in the turbid zones may supply a regenerative source of²²⁴Ra in this system. Samples collected on the ebb and flood tide from a salt marsh along Delaware Bay have a 5-fold increase in²²⁴Ra from flood to ebb and 3- and 2-fold increases for²²⁸Ra and²²⁶Ra respectively, indicating salt marshes are another source of radium to estuarine waters.     

Primitive neon and helium isotopic compositions of high-MgO basalts from the Kerguelen Archipelago,Indian Ocean

The geochemical characteristics of mildly alkalic basalts (24–25 Ma) erupted in the southeastern Kerguelen Archipelago are considered to represent the best estimate for the composition of the enriched Kerguelen plume end-member. A recent study of picrites and high-MgO basalts from this part of the archipelago highlighted the Pb and Hf isotopic variations and suggested the presence of mantle heterogeneities within the Kerguelen plume itself. We present new helium and neon isotopic compositions for olivines from these picrites and high-MgO basalts (6–17 wt.% MgO) both to constrain the enriched composition of the Kerguelen plume and to determine the origin of isotopic heterogeneities involved in the genesis of Kerguelen plume-related basalts. The olivine phenocrysts have extremely variable ⁴He / ³He compositions between MORB and primitive values observed in OIB (∼90,000 to 40,000; i.e., R / R_a ∼8 to 18) and they show primitive neon isotopic ratios (average ²¹Ne / ²¹Ne_ext ∼0.044). The neon isotopic systematics and the ⁴He / ³He ratios that are lower than MORB values for the Kerguelen basalts clearly suggest that the Kerguelen hotspot belongs to the family of primitive hotspots, such as Iceland and Hawaii. The rare gas signature for the Kerguelen samples, intermediate between MORB and solar, is apparently inconsistent with mixing of a primitive component with a MORB-like source, but may result from sampling a heterogeneous part of the mantle with solar ³He / ²²Ne and with a higher (U, Th) / ³He ratio compared to typically high R / R_a hotspot basalts such as those from Iceland and Hawaii.     

Evidence from isotopic geochemistry as an indicator of eutrophication of Meiliang Bay in Lake Taihu,China

In this paper, Lake Taihu, a large shallow freshwater lake in China, is chosen as an example of reconstruction of eutrophication through the comparison between stable isotopes from dissolved nutrients and plants and water column nutrient parameters and integration of multiple proxies in a sediment core from Meiliang Bay including TN, TP, TOC, C/N, δ ¹⁵N, δ ¹³C, etc. Differences in aquatic plant species and trophic status between East Taihu Bay and Meiliang Bay are indicated by their variations in δ ¹³C and δ ¹⁵N of aquatic plants and δ ¹⁵N of NH₄ ⁺. A significant influence of external nutrient inputs on Meiliang Bay is reflected in temporal changes in δ ¹⁵N of NH₄ ⁺ and hydro-environmental parameters. The synchronous change between δ ¹³C and δ ¹⁵N values of sedimented organic matter (OM) has been attributed to elevated primary production at the beginning of eutrophication between 1950 and 1990, then recent inverse correlation between them has been caused by the uptake of ¹⁵N-enriched inorganic nitrogen by phytoplankton grown under eutrophication and subsequent OM decomposition and denitrification in surface sediments, indicating that the lake has suffered from progressive eutrophication since 1990. Based on the use of a combination of stable isotopes and elemental geochemistry, the eutrophication of Meiliang Bay in Lake Taihu could be better traced. These transitions of the lake eutrophication respectively occurring in the 1950s and 1990s have been suggested as a reflection of growing impacts of human activities, which is coincident with the instrumental data.     

Physical and dynamical oceanography of Liverpool Bay

The UK National Oceanography Centre has maintained an observatory in Liverpool Bay since August 2002. Over 8 years of observational measurements are used in conjunction with regional ocean modelling data to describe the physical and dynamical oceanography of Liverpool Bay and to validate the regional model, POLCOMS. Tidal dynamics and plume buoyancy govern the fate of the fresh water as it enters the sea, as well as the fate of its sediment, contaminants and nutrient loads. In this context, an overview and summary of Liverpool Bay tidal dynamics are presented. Freshwater forcing statistics are presented showing that on average the bay receives 233 m³ s^− 1. Though the region is salinity controlled, river input temperature is shown to significantly modulate the plume buoyancy with a seasonal cycle. Stratification strongly influences the region’s dynamics. Data from long-term moored instrumentation are used to analyse the stratification statistics that are representative of the region. It is shown that for 65% of tidal cycles, the region alternates between being vertically mixed and stratified. Plume dynamics are diagnosed from the model and are presented for the region. The spring–neap modulation of the plume’s westward extent, between 3.5 °W and 4°W, is highlighted. The rapid eastward erosion of the plume during spring tides is identified as a potentially important freshwater mixing mechanism. Novel climatological maps of temperature, salinity and density from the CTD surveys are presented and used to validate numerical simulations. The model is found to be sensitive to the freshwater forcing rates, temperature and salinities. The existing CTD survey grid is shown to not extend sufficiently near the coast to capture the near coastal and vertically mixed component the plume. Instead the survey grid captures the westward spreading, shallow and transient, portion of the plume. This transient plume feature is shown in both the long-term averaged model and observational data as a band of stratified fluid stretching between the mouth of the Mersey towards the Isle of Man. Finally the residual circulation is discussed. Long-term moored ADCP data are favourably compared with model data, showing the general northward flow of surface water and southward trajectory of bottom water.     

Stable and radiogenic isotopes as tracers for the origin,mixing and subsurface history of fluids in submarine shallow-water hydrothermal systems

The shallow-water hydrothermal system in Tutum Bay on the west side of Ambitle Island, Papua New Guinea provides us with an exceptional opportunity to study isotope systematics in a near shore setting. Compared to seawater, the hydrothermal fluids in Tutum Bay have lower values for δD, δ¹⁸O, δ¹³C, and ⁸⁷Sr and higher values for ³H, δ³⁴S(SO₄) and δ¹⁸O(SO₄). The δ¹⁸O and δD records for vents 1 and 4 indicate that fluid compositions remained stable over an extended period. Interpretation of isotope data clearly demonstrates the predominantly meteoric origin of Tutum Bay hydrothermal fluids, despite their location in a marine environment. δ¹⁸O and δD values are identical to mean average annual precipitation in eastern Papua New Guinea. The hypothesis that these fluids are a simple product of mixing between seawater and onshore hydrothermal fluids from the Waramung (W-1) and Kapkai (W-2) thermal areas has been rejected, because the observed δ³⁷Cl, ³H, δ³⁴S(SO₄) and δ¹⁸O(SO₄) values cannot be explained by a simple mixing model. The application of δ¹⁸O(SO₄) and δ¹³C thermometers in combination with ³H values corroborates the three-step model of Pichler et al. [Pichler, T., Veizer, J., Hall, G.E.M., 1999. The chemical composition of shallow-water hydrothermal fluids in Tutum Bay, Ambitle Island, Papua New Guinea and their effect on ambient seawater. Marine Chemistry 64 (3) 229–252], where (1) phase separation in the deep reservoir beneath Ambitle Island produces a high temperature vapor that rises upward and subsequently reacts with cooler ground water to form a low pH, CO₂-rich water of approximately 150–160 °C, (2) caused by the steep topography, this CO₂-rich fluid moves laterally towards the margin of the hydrothermal system where it mixes with the marginal upflow of the deep reservoir fluid. This produces a dilute chloride water of approximately 165 °C, and (3) possibly the entrainment of minor amounts of ground or seawater during its final ascent.     

Fumarole/plume and diffuse CO2 emission from Sierra Negra caldera, Galapagos archipelago

Measurements of visible and diffuse gas emission were conducted in 2006 at the summit of Sierra Negra volcano, Galapagos, with the aim to better characterize degassing after the 2005 eruption. A total SO₂ emission of 11?±?2?t day^?1 was derived from miniature differential optical absorption spectrometer (mini-DOAS) ground-based measurements of the plume emanating from the Mini Azufral fumarolic area, the most important site of visible degassing at Sierra Negra volcano. Using a portable multigas system, the H₂S/SO₂, CO₂/SO₂, and H₂O/SO₂ molar ratios in the Mina Azufral plume emissions were found to be 0.41, 52.2, and 867.9, respectively. The corresponding H₂O, CO₂, and H₂S emission rates were 562, 394, and 3?t day^?1, respectively. The total output of diffuse CO₂ emissions from the summit of Sierra Negra volcano was 990?±?85?t day^?1, with 605?t day^?1 being released by a deep source. The diffuse-to-plume CO₂ emission ratio was about 1.5. Mina Azufral fumaroles released gasses containing 73.6?mol% of H₂O; the main noncondensable components amounted to 97.4?mol% CO₂, 1.5?mol% SO₂, 0.6?mol% H₂S, and 0.35?mol%?N₂. The higher H₂S/SO₂ ratio values found in 2006 as compared to those reported before the 2005 eruption reveal a significant hydrothermal contribution to the fumarolic emissions. ³He/⁴He ratios measured at Mina Azufral fumarolic discharges showed values of 17.88?±?0.25?R _A , indicating a mid-ocean ridge basalts (MORB) and a Galapagos plume contribution of 53 and 47?%, respectively.     

Validation of Arenicola marina in field toxicity bioassays using benthic cages: biomarkers as tools for assessing sediment quality

Sediment toxicity assessments using caged organisms present advantages over using laboratory and native community studies. The use of caged Arenicola marina in sediment toxicity assessments was evaluated. Lugworms were exposed in situ to sediments from coastal and port areas in Spain for seven days, and the activities of the biotransformation enzymes ethoxyresorufin O-deethylase, dibenzylfluorescein dealkylase and glutathione S-transferase, the activities of the antioxidant enzymes glutathione reductase and glutathione peroxidase and lipid peroxidation were then analyzed as biomarkers. Biomarker results and sediment physicochemical data were integrated. Cádiz Bay (SW Spain) sediments presented metal contamination that was not linked to a biochemical response. In LPGC Port (SW Spain), Pb contamination exhibited a moderate toxic potential, while PAHs, and presumably pharmaceuticals, provoked biochemical responses that efficiently prevented lipid peroxidation. In Santander Bay (N Spain), exposure to PAHs and, presumably, pharmaceuticals induced biomarker responses, but lipid peroxidation occurred nevertheless. These results indicated that caged A. marina were effective for the assessment of sediment quality and that the selected biomarkers were sufficiently sensitive to identify chemical exposure and toxicity.     

Biochemical and microbial features of shallow marine sediments along the Terra Nova Bay (Ross Sea,Antarctica)

Shallow marine sediments were collected from seven stations (three of which located at Gerlache Inlet, two at Tethys Bay, one at Adelie Cove and one just beneath the Italian Research Base) along the Terra Nova Bay coast (Ross Sea, Antarctica). Their chemical, biochemical and microbiological properties were studied in order to provide further insights in the knowledge of this Antarctic benthic ecosystem. Overall, the organic carbon (OC) represented the major fraction of total carbon (TC) and displayed concentrations similar to or slightly lower than those previously measured in Antarctic bottom sediments. The biopolymeric carbon within OC ranged from 4.1% to 19.9% and showed a wide trophic range (65–834 μg g⁻¹ d.w.). Proteins (PRT) represented on average the main biochemical class contributing to labile organic carbon, followed by lipids (LIP) and carbohydrates (CHO). The activity of aminopeptidase, β-d-glucosidase, alkaline phosphatase and esterase was checked, giving the highest values at Tethys Bay and at the deepest water sediments. The principal component analysis, which was computed considering physical, chemical (elemental and biochemical sedimentary composition) and microbiological parameters (including bacterial abundance, ectoenzymatic activities, T-RFs richness and diversity indices), allowed to obtain two main clusters (“Tethys Bay” and “other stations”). Based on data obtained, two representative 16S rRNA clone libraries using samples from Tethys Bay and Gerlache Inlet were constructed. The sequences of 171 clones were compared to those available in public databases to determine their approximate phylogenetic affiliations. Both aerobic and anaerobic bacteria were disclosed, with the majority of them affiliated with the Gamma- and Deltaproteobacteria, Bacteroidetes and Acidobacteria. The occurrence of strictly anaerobic bacteria suggests that sediments might also undergo anoxic conditions that, in turn, could favor the accumulation of PRT in respect to CHO, assuming that fermentation of amino acids is slower than that of sugars from decomposing polysaccharides.