scholarly journals Threshold of carbonate saturation state determined by CO<sub>2</sub> control experiment

2012 ◽  
Vol 9 (4) ◽  
pp. 1441-1450 ◽  
Author(s):  
S. Yamamoto ◽  
H. Kayanne ◽  
M. Terai ◽  
A. Watanabe ◽  
K. Kato ◽  
...  
Keyword(s):  
Coral Reef ◽  
Deep Sea ◽  
Control Experiment ◽  
Coralline Algae ◽  
Polar Regions ◽  
Carbonate Dissolution ◽  
Carbonate Sediments ◽  
Saturation State ◽  
Natural Coral ◽  
Seawater Pco2

Abstract. Acidification of the oceans by increasing anthropogenic CO2 emissions will cause a decrease in biogenic calcification and an increase in carbonate dissolution. Previous studies have suggested that carbonate dissolution will occur in polar regions and in the deep sea where saturation state with respect to carbonate minerals (Ω) will be <1 by 2100. Recent reports demonstrate nocturnal carbonate dissolution of reefs, despite a Ωa (aragonite saturation state) value of >1. This is probably related to the dissolution of reef carbonate (Mg-calcite), which is more soluble than aragonite. However, the threshold of Ω for the dissolution of natural sediments has not been clearly determined. We designed an experimental dissolution system with conditions mimicking those of a natural coral reef, and measured the dissolution rates of aragonite in corals, and of Mg-calcite excreted by other marine organisms, under conditions of Ωa > 1, with controlled seawater pCO2. The experimental data show that dissolution of bulk carbonate sediments sampled from a coral reef occurs at Ωa values of 3.7 to 3.8. Mg-calcite derived from foraminifera and coralline algae dissolves at Ωa values between 3.0 and 3.2, and coralline aragonite starts to dissolve when Ωa = 1.0. We show that nocturnal carbonate dissolution of coral reefs occurs mainly by the dissolution of foraminiferans and coralline algae in reef sediments.

scholarly journals Threshold of carbonate saturation state determined by a CO<sub>2</sub> control experiment

2011 ◽  
Vol 8 (4) ◽  
pp. 8619-8644 ◽  
Author(s):  
S. Yamamoto ◽  
H. Kayanne ◽  
M. Terai ◽  
A. Watanabe ◽  
K. Kato ◽  
...  
Keyword(s):  
Coral Reefs ◽  
Control Experiment ◽  
Coralline Algae ◽  
Polar Regions ◽  
Carbonate Dissolution ◽  
Carbonate Sediments ◽  
Natural Conditions ◽  
Dissolution Rates ◽  
Saturation State ◽  
Seawater Pco2

Abstract. Acidification of the oceans by increasing anthropogenic CO2 emissions will cause a decrease in biogenic calcification and an increase in carbonate dissolution. Previous studies suggest that carbonate dissolution will occur in polar regions and in the deep-sea oceans where saturation state with respect to carbonate minerals (Ω) will be <1 by 2100. However, carbonate in coral reefs distributed in tropical zones will not dissolve because the major carbonate in such reefs is aragonite, and the saturation state with respect to aragonite (Ω_a) is >1. Recent reports demonstrated nocturnal carbonate dissolution reefs, despite Ω_a > 1, probably relate to the dissolution of the minor reef carbonate (Mg-calcite), which is more soluble than aragonite. However, the threshold of Ω for the dissolution of natural sediments has not been clearly determined, and it is unknown whether these dissolution processes actually occur under natural conditions. This work describes the measurement of the dissolution rates of coral aragonite and Mg calcite excreted by marine organisms under conditions of Ω_a > 1 with controlled seawater pCO2. Laboratory experimental data of the present study show that bulk carbonate sediments sampled from a coral reef start to dissolve when Ω_a = 3.7, and dissolution rates increase with falling Ω_a. Mg-calcite derived from foraminifera and coralline algae dissolved when Ω_a reached 3.4, whereas coralline aragonite started to dissolve when Ω_a was almost 1.0. We show that nocturnal carbonate dissolution of coral reefs occurs mainly by the dissolution of foraminifera and coralline algae in reef sediment.

scholarly journals Net loss of CaCO<sub>3</sub> from coral reef communities due to human induced seawater acidification

2009 ◽  
Vol 6 (1) ◽  
pp. 2163-2182 ◽  
Author(s):  
A. J. Andersson ◽  
I. B. Kuffner ◽  
F. T. Mackenzie ◽  
P. L. Jokiel ◽  
K. S. Rodgers ◽  
...  
Keyword(s):  
Coral Reef ◽  
Continuous Flow ◽  
Fossil Fuels ◽  
Land Use Changes ◽  
Carbonate Dissolution ◽  
Ambient Seawater ◽  
Seawater Acidification ◽  
Reef Communities ◽  
Seawater Pco2 ◽  
Coral Reef Communities

Abstract. Acidification of seawater owing to oceanic uptake of atmospheric CO2 originating from human activities such as burning of fossil fuels and land-use changes has raised serious concerns for its adverse effects on corals, coral reefs and carbonate communities in general. Here we demonstrate a transition from net accumulation towards net loss of calcium carbonate (CaCO3) material owing to decreased calcification and increased carbonate dissolution from replicated subtropical coral reef communities (n=3) incubated in continuous-flow mesocosms subject to present and future seawater conditions. The calcifying community was dominated by the coral Montipora capitata. Daily average community calcification or Net Ecosystem Calcification (NEC = CaCO3 production – dissolution) was positive at 4.5 mmol CaCO3 m−2 h−1 under ambient seawater pCO2 conditions as opposed to negative at −0.1 mmol CaCO3 m−2 h−1 under seawater conditions of double the ambient pCO2. These experimental results provide support for the conclusion that some net calcifying communities could become subject to net dissolution in response to anthropogenic ocean acidification within this century.

Influence of deep-sea benthic processes on atmospheric CO 2

1990 ◽  
Vol 331 (1616) ◽  
pp. 155-165 ◽  
Keyword(s):  
Carbon Cycle ◽  
Deep Sea ◽  
Response Times ◽  
Model Atmosphere ◽  
Carbonate Content ◽  
Carbonate Dissolution ◽  
Carbonate Sediments ◽  
Marine Carbonate ◽  
Ocean Sediment ◽  
Global Carbon

Understanding ocean—atmosphere carbon-cycle interactions requires attention to the potential importance of marine benthic processes, particularly deep-sea carbonate dissolution. However, because of the wide array of processes that control marine carbonate dissolution rates, it is difficult to identify which processes dominate rates of response to global carbon-cycle perturbations. This paper describes a model that simulates atmospheric CO 2 , ocean chemistry and sediment carbonate content in a time-dependent fashion. Response times are assessed through an analysis of a series of perturbation experiments in which a pulse of CO 2 is added to the model atmosphere. The results of these experiments suggest that the relatively rapid buffering of atmospheric CO 2 by seawater is controlled by the rate of ocean mixing and accounts for about 60 % of the total buffering by the ocean-sediment system. The more gradual buffering of atmospheric CO 2 and seawater by carbonate sediments is controlled by the rate of sedimentation of carbonate particles, but the rate of this buffering is slower than previously thought because the dissolution or precipitation of carbonates does not produce dissolved carbonate ions on a mole-for-mole basis.

scholarly journals Current CaCO3 dissolution at the seafloor caused by anthropogenic CO2

2018 ◽  
Vol 115 (46) ◽  
pp. 11700-11705 ◽  
Author(s):  
Olivier Sulpis ◽  
Bernard P. Boudreau ◽  
Alfonso Mucci ◽  
Chris Jenkins ◽  
David S. Trossman ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Sea ◽  
Hot Spots ◽  
Ion Concentration ◽  
Rate Model ◽  
Saturation State ◽  
Calcite Dissolution ◽  
Carbonate Ion ◽  
Anthropogenic Component ◽  
Compensation Depth

Oceanic uptake of anthropogenic CO2 leads to decreased pH, carbonate ion concentration, and saturation state with respect to CaCO3 minerals, causing increased dissolution of these minerals at the deep seafloor. This additional dissolution will figure prominently in the neutralization of man-made CO2. However, there has been no concerted assessment of the current extent of anthropogenic CaCO3 dissolution at the deep seafloor. Here, recent databases of bottom-water chemistry, benthic currents, and CaCO3 content of deep-sea sediments are combined with a rate model to derive the global distribution of benthic calcite dissolution rates and obtain primary confirmation of an anthropogenic component. By comparing preindustrial with present-day rates, we determine that significant anthropogenic dissolution now occurs in the western North Atlantic, amounting to 40–100% of the total seafloor dissolution at its most intense locations. At these locations, the calcite compensation depth has risen ∼300 m. Increased benthic dissolution was also revealed at various hot spots in the southern extent of the Atlantic, Indian, and Pacific Oceans. Our findings place constraints on future predictions of ocean acidification, are consequential to the fate of benthic calcifiers, and indicate that a by-product of human activities is currently altering the geological record of the deep sea.

The role of diagenesis in the development of physical properties of deep-sea carbonate sediments

1985 ◽  
Vol 69 (1-2) ◽  
pp. 69-91 ◽  
Author(s):  
Dae-Choul Kim ◽  
Murli H Manghnani ◽  
Seymour O Schlanger
Keyword(s):  
Physical Properties ◽  
Deep Sea ◽  
Carbonate Sediments

scholarly journals Mesophotic Ecosystems: The Link between Shallow and Deep-Sea Habitats

Diversity ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 411
Author(s):  
Gal Eyal ◽  
Hudson T. Pinheiro
Keyword(s):  
Coral Reef ◽  
Deep Sea ◽  
New Technologies ◽  
Mesophotic Coral Ecosystems ◽  
Tropical Regions ◽  
Biogeographic Patterns ◽  
Global Diversity ◽  
Coral Reef Ecosystems ◽  
Threatened Habitats ◽  
Management And Conservation

Mesophotic ecosystems (MEs) are characterized by the presence of light-dependent organisms, found at depths ranging from ~30 to 150 m in temperate, subtropical and tropical regions. These communities occasionally create massive reef structures with diverse but characteristic morphologies, which serve as the framework builders of those ecosystems. In many localities, MEs are physically linked with shallow and deep-sea habitats, and while taxa from both environments share this space, a unique and endemic biodiversity is also found. The main MEs studied to date are the mesophotic coral ecosystems (MCEs) and the temperate mesophotic ecosystems (TMEs), which have received increased attention during the last decade. As shallow coral reef ecosystems are among the most threatened habitats on Earth, the potential of MEs to act as refugia and contribute to the resilience of the whole ecosystem has been a subject of scrutiny. New technologies and methods have become more available to study these deeper parts of the reef ecosystems, yielding many new discoveries. However, basic gaps in knowledge remain in our scientific understanding of the global diversity of MEs, limiting our ability to recognize biogeographic patterns and to make educated decisions for the management and conservation of these ecosystems.

A Method for Quantitative Evaluation of Carbonate Dissolution in Deep-Sea Sediments and its Application to Paleoceanographic Reconstruction

1978 ◽  
Vol 10 (1) ◽  
pp. 112-129 ◽  
Author(s):  
Teh-Lung Ku ◽  
Tadamichi Oba
Keyword(s):  
Quantitative Evaluation ◽  
Deposition Rate ◽  
Deep Sea ◽  
Bottom Water ◽  
Carbonate Dissolution ◽  
Present Value ◽  
Dissolution Rates ◽  
Sea Floor ◽  
The Pacific ◽  
The Difference

A method is proposed by which the degree of attrition of the tests of certain foraminifera species, such as Globorotalia menardii and Globorotalia tumida, is used to “scale” the amount of CaCO3 that has been dissolved from sediment. The scale is calibrated experimentally in the laboratory. The method has been applied to three calcareous cores from the Pacific and the Indian Oceans. It is shown that the original CaCO3 contents in these cores were high (82–95%) and relatively uniform compared to the present down-core values. About 65 to 85% of the originally deposited CaCO3 has been dissolved, corresponding to dissolution rates on the order of 0.1-0.3 moles/cm2/yr. These results indicate that appreciable solution could have occurred on sea floor rich in calcareous sediments and that the variation in CaCO3 content in a core may have resulted largely from dissolution. The difference in the degree of solution between glacial and interglacial sediments in these cores is not so distinct, with ⋍ 10% less intense dissolution during glacial times on the average. However, the dissolution minimum occurring around the late Wisconsin glaciation (10,000–20,000 yr B.P.) previously noted in several cores elsewhere is confirmed. At that time, near the site of core M70 PC-20 in the southwest Pacific, the CO32− concentration of the bottom water is estimated to have been approximately 5% higher than the present value, and the calcite lysocline was about 300 m deeper. To evaluate possible variations in CaCO3 deposition rate across the glacial-interglacial transitions requires precise age control, which the present study lacks.

scholarly journals A hypothesis linking sub-optimal seawater <I>p</I>CO<sub>2</sub> conditions for cnidarian-<I>Symbiodinium</I> symbioses with the exceedence of the interglacial threshold (>260 ppmv)

2012 ◽  
Vol 9 (5) ◽  
pp. 1709-1723 ◽  
Author(s):  
S. A. Wooldridge
Keyword(s):  
Coral Reef ◽  
Elevated Temperatures ◽  
Evidence Base ◽  
Coral Reef Ecosystem ◽  
Coral Reef Ecosystems ◽  
Extinction Events ◽  
Response To Temperature ◽  
Host Metabolism ◽  
New Hypothesis ◽  
Seawater Pco2

Abstract. Most scleractinian corals and many other cnidarians host intracellular photosynthetic dinoflagellate symbionts ("zooxanthellae"). The zooxanthellae contribute to host metabolism and skeletogenesis to such an extent that this symbiosis is well recognised for its contribution in creating the coral reef ecosystem. The stable functioning of cnidarian symbioses is however dependent upon the host's ability to maintain demographic control of its algal partner. In this review, I explain how the modern envelope of seawater conditions found within many coral reef ecosystems (characterised by elevated temperatures, rising pCO2, and enriched nutrient levels) are antagonistic toward the dominant host processes that restrict excessive symbiont proliferation. Moreover, I outline a new hypothesis and initial evidence base, which support the suggestion that the additional "excess" zooxanthellae fraction permitted by seawater pCO2 levels beyond 260 ppmv significantly increases the propensity for symbiosis breakdown ("bleaching") in response to temperature and irradiance extremes. The relevance of this biological threshold is discussed in terms of historical reef extinction events, glacial-interglacial climate cycles and the modern decline of coral reef ecosystems.

Sign in / Sign up

Export Citation Format

Share Document