Posts Tagged 'chemistry'



Features of the regional balance of inorganic carbon of marine ecosystems under anthropogenic pressure (in Russian)

The global changes in the biogeochemical structure of the oceans, which are most pronounced on a regional scale, caused by an increase in the flow of carbon into aquatic ecosystems as a result of increased releases from the atmosphere, coastal sources, primary production and destruction processes in the marine environment, make the issues of sharing the influence of the natural climatic and anthropogenic factors. For a quantitative assessment and analysis of the degree of influence of factors leading to the transformation of the natural carbon cycle, it is necessary to restore its budget, which is determined by the intake and removal of carbon, as well as the processes that result in its redistribution between different forms. The paper estimates the carbon budget for the ecosystem of the Sevastopol Bay (Black Sea), as well as analyzes the contribution of the anthropogenic component according to many years of research (2007–2018) of hydrochemical and geochemical characteristics. The results of studying the carbonate system of bottom sediments are presented: the vertical profile of the total dissolved inorganic carbon, alkalinity and pH, as well as the ratio between dissolved inorganic carbon and alkalinity. It has been established that the oxidation of organic matter occurs predominantly under anaerobic conditions. The values ​​of the flux of total dissolved inorganic carbon ( J TCO2 ) at the water-bottom boundary are directed from the bottom sediments to the bottom layer of water and are J T CO2 = 0.42 … 0.61 mol / (m 2 ∙ year). An analysis of the various components of the inorganic carbon budget showed that the largest role is played by anthropogenic sources, whose contribution is at least 75% of the total inorganic carbon supply. By the value of the total stock of dissolved inorganic carbon and its removal to the open sea, it was suggested that the time for the complete renewal of the waters of the Sevastopol Bay is 2 years 4 months.

Continue reading ‘Features of the regional balance of inorganic carbon of marine ecosystems under anthropogenic pressure (in Russian)’

Mangrove lagoons of the Great Barrier Reef support coral populations persisting under extreme environmental conditions

Global degradation of coral reefs has increased the urgency of identifying stress-tolerant coral populations, to enhance understanding of the biology driving stress tolerance, as well as identifying stocks of stress-hardened populations to aid reef rehabilitation. Surprisingly, scientists are continually discovering that naturally extreme environments house established coral populations adapted to grow within extreme abiotic conditions comparable to seawater conditions predicted over the coming century. Such environments include inshore mangrove lagoons that carry previously unrecognised ecosystem service value for corals, spanning from refuge to stress preconditioning. However, the existence of such hot-spots of resilience on the Great Barrier Reef (GBR) remains entirely unknown. Here we describe, for the first time, 2 extreme GBR mangrove lagoons (Woody Isles and Howick Island), exposing taxonomically diverse coral communities (34 species, 7 growth morphologies) to regular extreme low pH (<7.6), low oxygen (7°C) conditions. Coral cover was typically low (0.5 m diameter), with net photosynthesis and calcification rates of 2 dominant coral species (Acropora millepora, Porites lutea) reduced (20-30%), and respiration enhanced (11-35%), in the mangrove lagoon relative to adjacent reefs. Further analysis revealed that physiological plasticity (photosynthetic ‘strategy’) and flexibility of Symbiodiniaceae taxa associations appear crucial in supporting coral capacity to thrive from reef to lagoon. Prevalence of corals within these extreme conditions on the GBR (and elsewhere) increasingly challenge our understanding of coral resilience to stressors, and highlight the need to study unfavourable coral environments to better resolve mechanisms of stress tolerance.

Continue reading ‘Mangrove lagoons of the Great Barrier Reef support coral populations persisting under extreme environmental conditions’

Deconvolving the long-term impacts of ocean acidification and warming on coral biomineralisation

Highlights

• Evaluation of temperature and pH effects in coral carbonate chemistry over 1939-2013.

• Coral calcifying fluid pH influenced by both, seawater pH and temperature.

• Temperature principal influence on calcifying fluid pH on seasonal scales.

• Long-term changes in calcifying fluid pH mainly influenced by seawater pH.

• Decline in carbonate ion and calcification consistent with ocean acidification.

Abstract

Identifying the long-term effects of ocean acidification (OA) and global warming on coral calcification has proven elusive yet has major implications for the continuing viability of coral reefs in the face of climate change. Here we address this question using seasonally and annually resolved boron proxies (11B/10B and B/Ca) of calcifying fluid (cf) pHcf and carbonate ion concentrations ([CO]cf) preserved in a long-lived Porites coral from the Great Barrier Reef (GBR). From 1939 to 2013 we find that the coral pHcf closely followed the decline in seawater pH of ∼0.1 units, but at a reduced rate of ∼60%, indicative of biological buffering. Of the decline in pHcf ∼82% is attributed to OA and ∼17% to the ∼0.5 °C long-term warming observed over this period. This long-term warming induced change in pHcf is consistent with the much larger seasonally modulated changes in pHcf where ∼4 to 6 °C seasonal changes in temperatures are accompanied by relatively large antithetic ∼0.1 changes in pHcf. Furthermore, we find that although the supply of dissolved inorganic carbon (DIC) of the coral cf has remained at constant elevated levels of ∼1.5 × seawater, there has been a significant long-term decline (4 to 11%) in the [CO]cf, due primarily to the OA-induced change in pHcf. This decline in [CO]cf, a critical parameter controlling calcification, is thus likely responsible for the ∼15% decline in coral calcification observed since 1939 and across the GBR generally.

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Seasonal changes in carbonate saturation state and air‐sea CO2 fluxes during an annual cycle in a stratified‐temperate fjord (Reloncaví Fjord, Chilean Patagonia)

Changes may be occurring in the carbonate chemistry of fjords due to natural and anthropogenic disturbance of major freshwater sources. We present a high frequency time series study of seasonal pH and CO2 partial pressure (pCO2) in a north Patagonian fjord with a focus on changes in freshwater inflows and biological processes. To do this, we monitored pH and pCO2 in situ, along with river streamflow, salinity, temperature, and dissolved oxygen (DO) in the Reloncaví Fjord (41.5°S) for a full year (January to December 2015). Strong seasonal variability was observed in the pCO2, pH and DO of the fjord’s surface waters. During the summer, pCO2 reached its annual minimum (range: 187‐571 μatm) and pH its maximum (range: 7.98‐8.24), coinciding with lower freshwater inflows (204‐307 m3 s‐1) and high DO (280‐378 μmol kg‐1), as well as aragonite saturation states (ΩArag) higher than 1. In contrast, in winter, pCO2 ranged from 461‐1008 μatm and pH from 7.57‐8.03, coinciding with high freshwater inflows (1049‐1402 m3 s‐1), lower oxygen (216‐348 μmol kg‐1) and constant under‐saturation of ΩArag. Reloncaví Fjord had an annual air‐water CO2 flux of 0.716 ± 2.54 mol m‐2 yr‐1 during 2015, and thus acted as a low emission system. The annual cycle was mainly governed by seasonal changes in biological processes that enhanced the shift from a CO2 sink in late spring and summer, caused by high primary production rates, to a CO2 source during the rest of the year caused by high community respiration due to allochthonous organic carbon inputs.

Continue reading ‘Seasonal changes in carbonate saturation state and air‐sea CO2 fluxes during an annual cycle in a stratified‐temperate fjord (Reloncaví Fjord, Chilean Patagonia)’

Heterotrophy of oceanic particulate organic matter elevates net ecosystem calcification

Coral reef calcification is expected to decline due to climate change stressors such as ocean acidification and warming. Projections of future coral reef health are based on our understanding of the environmental drivers that affect calcification and dissolution. One such driver that may impact coral reef health is heterotrophy of oceanic‐sourced particulate organic matter, but its link to calcification has not been directly investigated in the field. In this study, we estimated net ecosystem calcification (NEC) and oceanic particulate organic carbon (POCoc) uptake across the Kāneʻohe Bay barrier reef in Hawai‘i. We show that higher rates of POCoc uptake correspond to greater NEC rates, even under low aragonite saturation states (Ωar). Hence, reductions in offshore productivity may negatively impact coral reefs by decreasing the food supply required to sustain calcification. Alternatively, coral reefs that receive ample inputs of POCoc may maintain higher calcification rates, despite a global decline in Ωar.

Continue reading ‘Heterotrophy of oceanic particulate organic matter elevates net ecosystem calcification’

Factors regulating nitrification in the Arctic Ocean: potential impact of sea ice reduction and ocean acidification

Nitrification is susceptible to changes in light and pH and, thus, could be influenced by recent sea ice reductions and acidification in the Arctic Ocean. We investigated the sensitivity of nitrification to light, pH, and substrate availability in a natural nitrifier community of the Arctic Ocean. Nitrification was active near the bottom of the shelf region (250 m). In pH control experiments, nitrification rates significantly declined when the pH was manipulated to be 0.22 lower than the controls. However, nitrification was relatively insensitive to changes in pH compared to changes in light. Light control experiments showed that nitrification was inhibited by a light intensity above 0.11 mol photons m−2 day−1, which was presumably the light threshold. A light intensity greater than the light threshold extended to the shelf bottom and upper halocline layer, limiting nitrification in these waters. Satellite data analyses indicated that the area where light levels inhibit nitrification has increased throughout the Arctic Ocean due to the recent sea ice reduction, which may lead to a declining trend in nitrification. Our results suggest that stronger light levels in the future Arctic Ocean could further suppress nitrification and alter the composition of inorganic nitrogen, with implications for the structure of ecosystems.

Continue reading ‘Factors regulating nitrification in the Arctic Ocean: potential impact of sea ice reduction and ocean acidification’

Simulating and quantifying multiple natural subsea CO2 seeps at Panarea Island (Aeolian Islands, Italy) as a proxy for potential leakage from subseabed carbon storage sites

Carbon dioxide (CO2) capture and storage (CCS) has been discussed as a potentially significant mitigation option for the ongoing climate warming. Natural CO2 release sites serve as natural laboratories to study subsea CO2 leakage in order to identify suitable analytical methods and numerical models to develop best-practice procedures for the monitoring of subseabed storage sites. We present a new model of bubble (plume) dynamics, advection-dispersion of dissolved CO2, and carbonate chemistry. The focus is on a medium-sized CO2 release from 294 identified small point sources around Panarea Island (South-East Tyrrhenian Sea, Aeolian Islands, Italy) in water depths of about 40–50 m. This study evaluates how multiple CO2 seep sites generate a temporally variable plume of dissolved CO2. The model also allows the overall flow rate of CO2 to be estimated based on field measurements of pH. Simulations indicate a release of ∼6900 t y–1 of CO2 for the investigated area and highlight an important role of seeps located at >20 m water depth in the carbon budget of the Panarea offshore gas release system. This new transport-reaction model provides a framework for understanding potential future leaks from CO2 storage sites.

Continue reading ‘Simulating and quantifying multiple natural subsea CO2 seeps at Panarea Island (Aeolian Islands, Italy) as a proxy for potential leakage from subseabed carbon storage sites’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book