Posts Tagged 'chemistry'

Dynamics of the carbonate system across the Peruvian oxygen minimum zone

The oxygen minimum zone (OMZ) of Peru is recognized as a source of CO2 to the atmosphere due to upwelling that brings water with high concentrations of dissolved inorganic carbon (DIC) to the surface. However, the influence of OMZ dynamics on the carbonate system remains poorly understood given a lack of direct observations. This study examines the influence of a coastal Eastern South Pacific OMZ on carbonate system dynamics based on a multidisciplinary cruise that took place in 2014. During the cruise, onboard DIC and pH measurements were used to estimate pCO2 and to calculate the calcium carbonate saturation state (Ω aragonite and calcite). South of Chimbote (9°S), water stratification decreased and both the oxycline and carbocline moved from 150 m depth to 20–50 m below the surface. The aragonite saturation depth was observed to be close to 50 m. However, values <1.2 were detected close to 20 m along with low pH (minimum of 7.5), high pCO2 (maximum 1,250 μatm), and high DIC concentrations (maximum 2,300 μmol kg−1). These chemical characteristics are shown to be associated with Equatorial Subsurface Water (ESSW). Large spatial variability in surface values was also found. Part of this variability can be attributed to the influence of mesoscale eddies, which can modify the distribution of biogeochemical variables, such as the aragonite saturation horizon, in response to shallower (cyclonic eddies) or deeper (anticyclonic eddies) thermoclines. The analysis of a 21-year (1993–2014) data set of mean sea surface level anomalies (SSHa) derived from altimetry data indicated that a large variance associated with interannual timescales was present near the coast. However, 2014 was characterized by weak Kelvin activity, and physical forcing was more associated with eddy activity. Mesoscale activity modulates the position of the upper boundary of ESSW, which is associated with high DIC and influences the carbocline and aragonite saturation depths. Weighing the relative importance of each individual signal results in a better understanding of the biogeochemical processes present in the area.

Continue reading ‘Dynamics of the carbonate system across the Peruvian oxygen minimum zone’

Upwelling amplifies ocean acidification on the East Australian shelf: implications for marine ecosystems

Frequent upwelling of deep, cold water, rich in dissolved inorganic nutrients and carbon dioxide but low in oxygen concentrations and pH, is well documented in eastern boundary systems. As a consequence, waters in vast areas of the continental shelf can turn corrosive to the mineral aragonite, vital to a number of marine organisms. This phenomenon is projected to become more severe with ongoing ocean acidification. Although upwelling is also known to occur in western boundary systems, the impact on present day aragonite saturation state (Ωarag) is virtually unknown, let alone for the decades to come. Here we identified 32 events during 18 weeks of continuous measurements in Cape Byron Marine Park, Australia, with prolonged drops in ocean temperature of up to 5°C, oxygen concentrations by 34%, pH by 0.12 and Ωarag by 0.9 in a matter of hours. Temperature, salinity and oxygen saturation during these events hint at a water mass from 200 to 250 m depth off the Central East Australian shelf. Extrapolating present day upwelling to a preindustrial setting shows that ongoing ocean acidification has already lead to the crossing of a number of biological and geochemical Ωarag thresholds. The future intensity of these events critically depends on carbon dioxide emission scenario, and might be even more pronounced in the Great Barrier Reef where current day shelf associated waters carry a stronger deep water signal (based on oxygen levels) than at the study location. Finally, the proposed use of artificially upwelled water to cool increasingly temperature-stressed coral reef communities will need to take its unique carbonate chemistry properties into account.

Continue reading ‘Upwelling amplifies ocean acidification on the East Australian shelf: implications for marine ecosystems’

Elevated trace elements in sediments and seagrasses at CO2 seeps

• Sandy CO2 seep sediments had higher concentration of trace elements.

• Metals can be more toxic in areas affected by CO2 acidification, with adverse effects on the sediment associated biota.

• Seagrasses element accumulation at CO2 seeps was highest in the roots.

Seagrasses often occur around shallow marine CO2 seeps, allowing assessment of trace metal accumulation. Here, we measured Cd, Cu, Hg, Ni, Pb and Zn levels at six CO2 seeps and six reference sites in the Mediterranean. Some seep sediments had elevated metal concentrations; an extreme example was Cd which was 43x more concentrated at a seep than its reference. Three seeps had metal levels that were predicted to adversely affect marine biota, namely Vulcano (for Hg), Ischia (for Cu) and Paleochori (for Cd and Ni). There were higher-than-sediment levels of Zn and Ni in Posidonia oceanica and of Zn in Cymodocea nodosa, particularly in roots. High levels of Cu were found in Ischia seep sediments, yet seagrass was abundant, and the plants contained low levels of Cu. Differences in bioavailability and toxicity of trace elements helps explain why seagrasses can be abundant at some CO2 seeps but not others.

Continue reading ‘Elevated trace elements in sediments and seagrasses at CO2 seeps’

Coastal dynamic, nitrate (NO3-) phosphate (PO4-) and phytoplankton abundance at Morodemak North Java Sea Indonesia

Coastal dynamic of North Java sea was the influence of the west and east monsoon as well as interseasonal effect during April-June and October-December. Espescialy to coastal current patern and to nitrate and phosphate variation and ultimately to phytoplankton. Study area focused at 110°52’03.72”E – 110°54’68” E and 06°80.4’75”S – 06°82’72.22”S. The study was conducted for 1 mont in September 2014. Location of this research at Morodemak waters of North Java Sea. Aim of study was to built current spatial model, measure insitu nitrate and phosphate variation and phytoplankton abundance. Coastal current spatial modelling was done using SMS-v8.1 and sampling site based to purposive sampling represetative to the estuary and coastal system. Spatial modelling using Arc.GIS 10 software. The study revealed that nitrate concentration ranged at 0.60 – 2.0 mg/l, phosphate 0.04 – 0.24 mg/l and current speed 0.0003 – 0.0033 m/sec to southeast direction. About 22 genera of phytoplankton were found, with moderate dominancy of Baccilariophyceae, Dinophyceae and most dominance of Rhizosolenia. Most abundance of phytoplankton was at the mouth of the river or the estuary with 28,090,000 cell/m3. Lowest abundance at offshore coastal site with 17,060,000 cell/m3. The highest diversity index (H’) was 1.606 at the estuary and the lowest was 0.8730 at coastal offshore.

Continue reading ‘Coastal dynamic, nitrate (NO3-) phosphate (PO4-) and phytoplankton abundance at Morodemak North Java Sea Indonesia’

In situ growth and bioerosion rates of Lophelia pertusa in a Norwegian fjord and open shelf cold-water coral habitat

Coral reef resilience depends on the balance between carbonate precipitation, leading to reef growth, and carbonate degradation, for example, through bioerosion. Changes in environmental conditions are likely to affect the two processes differently, thereby shifting the balance between reef growth and degradation. In cold-water corals estimates of accretion-erosion processes in their natural habitat are scarce and solely live coral growth rates were studied with regard to future environmental changes in the laboratory so far, limiting our ability to assess the potential of cold-water coral reef ecosystems to cope with environmental changes. In the present study, growth rates of the two predominant colour morphotypes of live Lophelia pertusa as well as bioerosion rates of dead coral framework were assessed in different environmental settings in Norwegian cold-water coral reefs in a 1-year in situ experiment. Net growth (in weight gain and linear extension) of live L. pertusa was in the lower range of previous estimates and did not significantly differ between inshore (fjord) and offshore (open shelf) habitats. However, slightly higher net growth rates were obtained inshore. Bioerosion rates were significantly higher on-reef in the fjord compared to off-reef deployments in- and offshore. Besides, on-reef coral fragments yielded a broader range of individual growth and bioerosion rates, indicating higher turnover in live reef structures than off-reef with regard to accretion-bioerosion processes. Moreover, if the higher variation in growth rates represents a greater variance in (genetic) adaptations to natural environmental variability in the fjord, inshore reefs could possibly benefit under future ocean change compared to offshore reefs. Although not significantly different due to high variances between replicates, growth rates of orange branches were consistently higher at all sites, while mortality was statistically significantly lower, potentially indicating higher stress-resistance than the less pigmented white phenotype. Comparing the here measured rates of net accretion of live corals (regardless of colour morphotype) with net erosion of dead coral framework gives a first estimate of the dimensions of both processes in natural cold-water coral habitats, indicating that calcium carbonate loss through bioerosion amounts to one fifth to one sixth of the production rates by coral calcification (disregarding accretion processes of other organisms and proportion of live and dead coral framework in a reef). With regard to likely accelerating bioerosion and diminishing growth rates of corals under ocean acidification, the balance of reef accretion and degradation may be shifted towards higher biogenic dissolution in the future.

Continue reading ‘In situ growth and bioerosion rates of Lophelia pertusa in a Norwegian fjord and open shelf cold-water coral habitat’

Assessing annual variability in the shell thickness of the pteropod Heliconoides inflatus in the Cariaco Basin using micro-CT scanning

Pteropods have been nicknamed the canary in the coal mine for ocean acidification because they are predicted to be among the first organisms to be affected by future changes in ocean chemistry. This is due to their fragile, aragonitic shells and high abundances in polar and sub-polar regions where the impacts of ocean acidification will manifest first. For pteropods to be used most effectively as indicators of ocean acidification, their natural variability in the modern ocean needs to be quantified and understood. Here, we measured the shell condition (i.e., the degree to which a shell has dissolved) and shell characteristics, including size, number of whorls, shell thickness, and shell volume (i.e., amount of shell material) of nearly fifty specimens of the pteropod species Heliconoides inflatus from a sediment trap in the Cariaco Basin, Venezuela sampled over an 11-month period. The water in the Cariaco Basin is supersaturated with respect to aragonite year-round, and hydrographic and chemical properties vary seasonally due to the movement of the Inter Tropical Convergence Zone (ITCZ). Shell condition was assessed using with two methods: the Limacina Dissolution Index (LDX) and the opacity method. The opacity method captured changes in shell condition only in the early stages of dissolution, whereas the LDX recorded dissolution changes over a much larger range. Shell condition did not deteriorate with the length of time in the sediment trap. Instead, the most altered shells occurred in samples collected in September and October when water temperatures were warmest, and the amount of organic matter degradation in the water column was likely to have been the greatest. Shells of H. inflatus varied in size, number of whorls, and thickness throughout the year. The number of whorls did not correlate with shell diameter, suggesting that shell growth is plastic. H. inflatus formed shells that were 40 % thicker and 20 % larger in diameter when nutrient concentrations were high during times of upwelling, compared to specimens sampled from the oligotrophic rainy season. This study produces a baseline dataset of the variability in shell characteristics of H. inflatus in the Cariaco Basin and establishes a methodology for generating similar baseline records for pteropod populations globally.

Continue reading ‘Assessing annual variability in the shell thickness of the pteropod Heliconoides inflatus in the Cariaco Basin using micro-CT scanning’

Reduced continental weathering and marine calcification linked to late Neogene decline in atmospheric CO2

The globally averaged calcite compensation depth has deepened by several hundred metres in the past 15 Myr. This deepening has previously been interpreted to reflect increased alkalinity supply to the ocean driven by enhanced continental weathering due to the Himalayan orogeny during the late Neogene period. Here we examine mass accumulation rates of the main marine calcifying groups and show that global accumulation of pelagic carbonates has decreased from the late Miocene epoch to the late Pleistocene epoch even though CaCO3 preservation has improved, suggesting a decrease in weathering alkalinity input to the ocean, thus opposing expectations from the Himalayan uplift hypothesis. Instead, changes in relative contributions of coccoliths and planktonic foraminifera to the pelagic carbonates in relative shallow sites, where dissolution has not taken its toll, suggest that coccolith production in the euphotic zone decreased concomitantly with the reduction in weathering alkalinity inputs as registered by the decline in pelagic carbonate accumulation. Our work highlights a mechanism whereby, in addition to deep-sea dissolution, changes in marine calcification acted to modulate carbonate compensation in response to reduced weathering linked to the late Neogene cooling and decline in atmospheric partial pressure of carbon dioxide.

Continue reading ‘Reduced continental weathering and marine calcification linked to late Neogene decline in atmospheric CO2’

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Ocean acidification in the IPCC AR5 WG II

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