3.3: Ocean Acidification - Biology

3.3: Ocean Acidification - Biology

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Ocean acidification is simply the decrease in the pH of all of the oceans on Earth. The ocean absorbs about 25% of the atmosphere’s carbon dioxide or CO2, and as atmospheric CO2 levels increase, so does the amount of CO2 that the ocean absorbs. Therefore, as the amount of greenhouse gases increase, not only does the temperature of the ocean begin to rise, but the increase in CO2 levels causes the ocean’s pH levels to decrease. The rising acidic conditions cause a multitude of deleterious effects from limiting the formation of skeletons for marine organisms, to limiting coral growth, and corroding already existing coral skeletons.

While natural levels of carbon dioxide are fine, the excess CO2 that humans have managed to produce through burning fuels are the major problem. This is largely because when CO2 dissolves in the sea water, (CO2 + H2O-> H2CO3), it produces carbonic acid. While carbonic acid is not as strong of an acid, as say HCl, it still acts as an acid by donating protons, and interacting with surrounding molecules. Now, when excess acid is added to a solution, it causes the pH of that solution to drop, or become more acidic, and while H2CO3 is not considered a strong acid, it still has the potential to massively impact the entire chemical makeup of the ocean environment. The lower the pH of a solution gets, the higher the concentration of H+ ions in that solution. This has become a massive problem for many species.

Chemical reactions can be extremely sensitive to any fluctuation in pH levels, however, in the ocean, these pH changes can affect marine life through chemical communication, reproduction, as well as growth. In particular, the building of the skeletons in marine life is extremely sensitive to any change in pH. Thus, the current increase in CO2 levels that have caused a more acidic environment, have greatly and negatively impacted the growth of new shells.

“Nautilus pompilius” by Wikimedia [CC BY SA 2.0]

This is because Hydrogen ions easily bond to carbonate (CO3 2-) molecules to create carbonic acid, and a marine animal’s shell consists of Calcium Carbonate(CaCO3). In order for marine animals to build shells, they take Calcium ions (Ca2+) with a carbonate molecule from the seawater surrounding it, to form the Calcium Carbonate needed to build their shells. So, instead of the carbonate giving all of it’s attention to Calcium so that the marine animal can build it’s shell, it now pays more attention to the Hydrogen ion. In addition, Hydrogen ions have a greater attraction to carbonate, than a Calcium iondoes to carbonate, and when two Hydrogen ions bind to carbonate, itproduces a bicarbonate ion, and a marine animal does not have the capability to extract only the carbonate ion. Ultimately, this limits marine animals from building any new shells for themselves, and even if the marine animal has the ability to build a new shell, it takes a lot of energyto do so, essentially taking away from other important processes and activities.

“Impacts of Ocean Acidification” by Wikimedia [CC BY SA 2.0]

Not only can this affect the formation of new shells, but in the right conditions, it can corrode already existing shells. When there are too many Hydrogen ions floating around, and not enough molecules for them to bind to, they can actually start breaking the already existing Calcium Carbonate molecules apart, ultimately breaking down the marine animal’s shell that already exists.

Another organism that feels the effects of ocean acidification are corals. Similar to other marine animals that build their homes with calcium carbonate, reef-building corals also use calcium carbonate to build their own bodies and structures. These reef-building corals are also home to other coral animals and other organisms. As mentioned before, the increased acidification greatly limits any further growth of new coral, as well as corrodes any pre-existing coral reefs. Even if a coral reef has surpassed all the odds, and has been able to grow, it will be a weaker reef that is subject to natural erosion. It has been predicted that by the middle of the century, healthy coral reefs will be eroding more quickly than can be reproduced.

“Blue Starfish on Hard Coral” by Wikimedia [CC by 3.0]

This is bad news for the species that live in these coral reefs. If these species are not able to grow and develop in a safe settlement, such as the coral reef, these larvae will be unable to reach adulthood, thus being unable to reproduce. This will ultimately lead to a mass extinction in the future.

The information in this chapter in thanks to content contributions from Jaime Marsh and Morgan Tupper.

Effect of Ocean Acidification on Organic and Inorganic Speciation of Trace Metals

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FAQ 5.1: How is life in the sea affected by climate change?

Climate change poses a serious threat to life in our seas, including coral reefs and fisheries, with impacts on marine ecosystems, economies and societies, especially those most dependent upon natural resources. The risk posed by climate change can be reduced by limiting global warming to no more than 1.5°C.

Life in most of the global ocean, from pole to pole and from sea surface to the abyssal depths, is already experiencing higher temperatures due to human-driven climate change. In many places, that increase may be barely measurable. In others, particularly in near-surface waters, warming has already had dramatic impacts on marine animals, plants and microbes. Due to closely linked changes in seawater chemistry, less oxygen remains available (in a process called ocean deoxygenation). Seawater contains more dissolved carbon dioxide, causing ocean acidification. Non-climatic effects of human activities are also ubiquitous, including over-fishing and pollution. Whilst these stressors and their combined effects are likely to be harmful to almost all marine organisms, food-webs and ecosystems, some are at greater risk (FAQ5.1, Figure 1). The consequences for human society can be serious unless sufficient action is taken to constrain future climate change.

Warm water coral reefs host a wide variety of marine life and are very important for tropical fisheries and other marine and human systems. They are particularly vulnerable, since they can suffer high mortalities when water temperatures persist above a threshold of between 1 ° C–2 ° C above the normal range. Such conditions occurred in many tropical seas between 2015 and 2017 and resulted in extensive coral bleaching, when the coral animal hosts ejected the algal partners upon which they depend. After mass coral mortalities due to bleaching, reef recovery typically takes at least 10–15 years. Other impacts of climate change include SLR, acidification and reef erosion. Whilst some coral species are more resilient than others, and impacts vary between regions, further reef degradation due to future climate change now seems inevitable, with serious consequences for other marine and coastal ecosystems, like loss of coastal protection for many islands and low-lying areas and loss of the high biodiversity these reefs host. Coral habitats can also occur in deeper waters and cooler seas, and more research is needed to understand impacts in these reefs. Although these cold water corals are not at risk from bleaching, due to their cooler environment, they may weaken or dissolve under ocean acidification, and other ocean changes.

Mobile species, such as fish, may respond to climate change by moving to more favorable regions, with populations shifting poleward or to deeper water, to find their preferred range of water temperatures or oxygen levels. As a result, projections of total future fishery yields under different climate change scenarios only show a moderate decrease of around 4% (

3.4 million tonnes) per degree Celsius warming. However, there are dramatic regional variations. With high levels of climate change, fisheries in tropical regions could lose up to half of their current catch levels by the end of this century. Polar catch levels may increase slightly, although the extent of such gains is uncertain, because fish populations that are currently depleted by overfishing and subject to other stressors may not be capable of migrating to polar regions, as assumed in models.

In polar seas, species adapted to life on or under sea ice are directly threatened by habitat loss due to climate change. The Arctic and Southern Oceans are home to a rich diversity of life, from tiny plankton to fish, krill and seafloor invertebrates to whales, seals, polar bears or penguins. Their complex interactions may be altered if new warmer-water species extend their ranges as sea temperatures rise. The effects of acidification on shelled organisms, as well as increased human activities (e.g., shipping) in ice-free waters, can amplify these disruptions.

Whilst some climate change impacts (like possible increased catch levels in polar regions) may benefit humans, most will be disruptive for ecosystems, economies and societies, especially those that are highly dependent upon natural resources. However, the impacts of climate change can be much reduced if the world as a whole, through inter-governmental interventions, manages to limit global warming to no more than 1.5°C.

34 Warming Waters and Souring Seas: Climate Change and Ocean Acidification

From: Oxford Public International Law ( (c) Oxford University Press, 2021. All Rights 01 July 2021

This chapter examines the impact of climate change and ocean acidification on the oceans and their implications for the international law of the sea. In particular, it assesses the implications of rising sea levels for territorial sea baselines, the seawards extent of maritime zones, and maritime boundaries. It also considers the restrictions placed by the UN Nations Convention on the Law of the Sea (LOSC) upon States in pursuing climate mitigation and adaptation policies, such as attempts to ‘engineer’ the global climate by artificially enhancing the capacity of the oceans to draw CO2 from the atmosphere. The chapter analyzes the role of the LOSC, alongside other treaty regimes, in addressing the serious threat of ocean acidification.

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Author information


Scottish Association for Marine Science, Scottish Marine Institute, Dunbeg, Oban, UK

Michael T. Burrows, Clive J. Fox & Benjamin L. Payne

Ocean and Earth Sciences, National Oceanography Centre Southampton, University of Southampton, Southampton, UK

Department of Ocean Sciences, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador, Canada

School of Environment, University of Auckland, Auckland, New Zealand

Sir Alister Hardy Foundation for Ocean Science, Citadel Hill Laboratory, Plymouth, UK

Marine Institute, Plymouth University, Plymouth, UK

Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia

Graham J. Edgar & Rick D. Stuart-Smith

Bren School of Environmental Science and Management, University of California, Santa Barbara, CA, USA

National Center for Ecological Analysis and Synthesis, University of California, Santa Barbara, CA, USA

School of Ocean Sciences Bangor University, Menai Bridge, UK

Department of Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ, USA

Malin L. Pinsky & Ryan D. Batt

Arctic Research Center, Hokkaido University, Sapporo, Japan

Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan

Global Station for Arctic Research, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan

Global Change Ecology Research Group, School of Science and Engineering, University of the Sunshine Coast, Maroochydore, Queensland, Australia

Centre for African Conservation Ecology, Department of Zoology, Nelson Mandela University, Port Elizabeth, South Africa

Division Biosciences/Integrative Ecophysiology, Helmholtz Centre for Polar and Marine Research, Alfred Wegener Institute, Bremerhaven, Germany

Global Change Institute, The University of Queensland, St Lucia, Queensland, Australia

Ocean acidification refers to the lowering of the ocean’s pH due to the uptake of anthropogenic CO2 from the atmosphere. Coral reef calcification is expected to decrease as the oceans become more acidic. Dissolving calcium carbonate (CaCO3) sands could greatly exacerbate reef loss associated with reduced calcification but is presently poorly constrained. Here we show that CaCO3 dissolution in reef sediments across five globally distributed sites is negatively correlated with the aragonite saturation state (Ωar) of overlying seawater and that CaCO3 sediment dissolution is 10-fold more sensitive to ocean acidification than coral calcification. Consequently, reef sediments globally will transition from net precipitation to net dissolution when seawater Ωar reaches 2.92 ± 0.16 (expected circa 2050 CE). Notably, some reefs are already experiencing net sediment dissolution.

Coral reef structures are the accumulation of calcium carbonate (CaCO3) from coral aragonite skeletons, red and green calcareous macroalgae, and other calcareous organisms such as bryozoans, echinoderms, and foraminifera. This structure provides the habitat for many species, promoting rich biological diversity and an associated myriad of ecosystem services to humans such as fisheries and tourism (1). There are two main pools of CaCO3 in coral reefs: the framework (e.g., deposited CaCO3 skeletons and living coral and other organisms) and permeable sediments (e.g., broken-down framework and any infaunal production) (2). For net accretion to occur at the whole-reef scale, CaCO3 production (plus any external sediment supply) must be greater than the loss through physical, chemical, and biological erosion and transport and dissolution as follows (2):

CaCO3 accretion = CaCO3 production – CaCO3 dissolution – physical loss of CaCO3 (1)

Net ecosystem calcification (NEC), which refers to the chemical balance of CaCO3 production and CaCO3 dissolution, is typically inferred from changes in total alkalinity and does not include physical loss of CaCO3.

Ocean acidification (OA) refers to the lowering of the ocean’s pH due to the uptake of anthropogenic CO2 from the atmosphere. When CO2 from the atmosphere dissolves in seawater, it decreases the pH, the CO3 2− concentration, and the CaCO3 saturation state (Ω = [Ca 2+ ] [CO3 2− ]/K*sp, where K*sp is the stoichiometric ion concentration product at equilibrium) (3). Although OA-associated changes are expected to negatively affect the accretion of coral reefs (4), these future predictions are mostly based on the relationship between Ω and calcification rates of individual corals or coral reef communities [e.g., (5, 6) table S3] and NEC [e.g., (7) table S2]. However, the impact of OA on net coral reef accretion is also dependent on the poorly known effects of OA on the dissolution of permeable coral reef CaCO3 sediments, which accumulate over thousands of years (8) and can be the major repository of CaCO3 in modern coral reefs (9). Numerical modeling, laboratory, field, and mesocosm studies have found an increase in CaCO3 sediment dissolution with decreasing Ω and pH (OA) (10, 11).

Notably, a number of studies have hypothesized that CaCO3 dissolution may respond more rapidly to OA than coral calcification [e.g., (2, 12, 13)]. Supporting this hypothesis, a recent in situ study found that CaCO3 sediment dissolution increased by an order of magnitude more than calcification decreased, per unit decrease in Ω (14). However, the in situ CaCO3 sediment dissolution measurements were only undertaken at one site on Heron Island, Australia, and it is unknown how applicable the findings are to coral reefs globally. For example, CaCO3 sediment dissolution of different coral reefs may respond differently to OA because of differences in the present-day saturation state of the water column and differences in sediment properties such as mineralogy, porosity, permeability, grain size, organic carbon concentration, and metabolism, which in turn are controlled by factors such as light, depth, and hydrodynamics.

We measured CaCO3 sediment dissolution using 57 individual in situ advective benthic chamber incubations at five reef locations in the Pacific and Atlantic Oceans (fig. S1). Incubations were undertaken over a diel light-dark cycle, and four of the reef incubations were run under control and end-of-century [high partial pressure of CO2 (pCO2), low pH] OA conditions. The five sites covered a range of initial water column CaCO3 saturation states and sediment properties such as mineralogy, grain size, organic carbon concentration, and metabolism (table S1).

Our results show that CaCO3 sediment dissolution across the five coral reefs is significantly and negatively correlated with average Ωar of the overlying seawater coefficient of determination [(r 2 ) = 0.49, P < 0.0001, n = 57] (fig. S2). The increase in CaCO3 sediment dissolution with decreasing seawater Ωar is consistent with other recent mesocosm and in situ studies from single locations (10, 11, 14). The seawater Ωar value of

2.92 ± 0.16 (x intercept) at which the sediments transition from net precipitating to net dissolving (Fig. 1) is well above the expected thermodynamic transition value for aragonite (Ωar = 1) and saturation state of the average bulk Mg-calcite (13 to 15 mol % MgCO3) found in most coral reefs (15). This can be explained by the interaction of bulk seawater saturation state and porewater metabolic processes (2). Much lower Ωar values are typically found in sediment porewater owing to the decomposition of organic matter and associated production of dissolved inorganic carbon (16). It has been hypothesized that organic matter decomposition decreases porewater Ω until it becomes undersaturated with respect to the most soluble bulk carbonate mineral phase present, which then starts to dissolve at a point called the carbonate critical threshold (CCT) (17). Further organic matter decomposition then drives carbonate sediment dissolution. However, in shallow carbonate sediments, there is a strong diel cycle in phytosynthesis and respiration, and the daily-integrated sediment productivity/respiration ratio can drive net dissolution or precipitation (2, 14). In our experiments, benthic chambers containing acidified seawater (with higher pCO2 and lower Ωar) (fig. S1) were placed over carbonate sands to mimic late–21st century seawater chemistry, and this seawater was advected into the permeable carbonate sands and became the starting composition of porewater (2). Under such conditions, less organic matter decomposition is required to reach the CCT, leaving more respiratory CO2 available to drive dissolution (17). That is, for the same amount of sediment respiration, more carbonate dissolution will occur when seawater with a lower Ωar is advected into the sediments. This hypothesis is supported by results of in situ sediment chamber incubations under controlled and elevated pCO2 conditions (10) but does not unequivocally demonstrate the underlying mechanism.

No high-pCO2 treatments were available for the Cook Islands. Error bars represent standard error. The sediments transition from net precipitating to net dissolving at a seawater Ωar value of

2.92 ± 0.16 (±95% confidence interval). Data are in table S5. [Top photo by K. Fabricius, Australian Institute of Marine Science, and bottom photo by A. Andersson, Scripps Institution of Oceanography]

Average CaCO3 sediment dissolution for each set of control and high-pCO2 treatments at each of the five reef locations is also significantly and negatively correlated with average Ωar (r 2 = 0.94, P < 0.001, n = 9) (Fig. 1). Notably, there is no significant difference (Student’s t test P < 0.01) in benthic metabolism (production/respiration) between control and pCO2 treatments at any of the reef sites (fig. S3), with increased dissolution only driven by changes in overlying seawater chemistry (i.e., OA conditions). Carbonate sediment dissolution at each of the four reefs has the same response to lowered seawater Ωar (increased seawater pCO2), but the impact of OA on each reef is different owing to different starting conditions (Fig. 1). For example, carbonate sediments in Hawaii are already net dissolving and will be strongly net dissolving by the end of the century. In contrast, carbonate sediments at Tetiaroa are strongly net precipitating and will remain net precipitating at the end of the century. Carbonate sediments at Heron Island and Bermuda will both transition from net precipitating to net dissolving by the end of the century.

The transition of coral reef sands from net precipitating to net dissolving occurs when the seawater Ωar reaches 2.92 ± 0.16 (Fig. 1 and fig. S1). Hence, current reef seawater conditions control the impact that OA will have on the net carbonate accretion of coral reefs. The current seawater carbonate chemistry (e.g., pH, Ωar) of coral reefs is controlled by a combination of the open ocean source water and biogeochemical and hydrodynamic processes on the reef. There are latitudinal and regional variations in the open ocean Ωar with, for example, tropical reefs bathed in higher-Ωar water than higher-latitude reefs (18). The open ocean seawater composition is then modified by net ecosystem production (NEP = photosynthesis minus autotrophic and heterotrophic respiration) and NEC (19). Globally, it has been proposed that the average pCO2 of coral reefs has increased 3.5 times faster than in the open ocean over the past 20 years, most likely due to increased terrestrial nutrient and organic matter inputs (20). For example, in Kaneohe Bay, Hawaii, the carbonate sediments are currently net dissolving because of low reef seawater Ωar (Fig. 1) associated with low-Ωar source water (7) and large inputs of terrestrial nutrients and organic matter (21, 22). In contrast, the carbonate sediments at Tetiaroa are strongly net precipitating because of high reef seawater Ωar (Fig. 1) associated with high-Ωar source water and most likely little to no terrestrial organic matter inputs. External inputs of organic matter are thus an important control on the dissolution and associated net accretion of coral reefs (2, 17).

CaCO3 sediment dissolution across the five reefs is clearly very sensitive to OA with a 170% change per unit change in seawater Ωar (Figs. 1 and 2). This is an order of magnitude greater than predicted changes in coral calcification due to OA. For example, a recent meta-analysis of biologically mediated coral calcification only showed a 15% reduction per unit change in seawater Ωar (Fig. 2), or as low as a 10% reduction if only studies integrating light and dark calcification rates were considered (23). The change in CaCO3 sediment dissolution per unit change in seawater Ωar across the individual reefs is also less variable than the response of coral calcification per unit change in seawater Ωar across the individual studies (Fig. 2). Differences in the response of carbonate sediment dissolution and coral calcification to OA most likely reflect differences in the biologically mediated process of calcification compared to the geochemically mediated process of dissolution.

The change is from a baseline Ωar of 3.5 and hence all lines intersect at Ωar = 3.5 (100%). The thin lines are the individual measurements, and the thick line is the average. The length of line is the Ωar range over which the study was done. Coral calcification data are from (23). NEC data are from table S2.

Coral calcification has shown taxa-specific responses to OA (24) most likely due to differences in characteristics such as the percentage of skeletal tissue cover and the ability to regulate pH of calcifying fluids (25, 26). Observations that both near-shore and deep-sea calcifiers can live and calcify under thermodynamically unfavorable conditions [Ωar < 1 (27, 28)] suggest that seawater chemistry is only part of the equation and that organisms may have mechanisms and/or strategies to deal with the predicted changes in seawater carbonate chemistry and could potentially adapt to OA (5, 29). For example, given a sufficient supply of nutrition and energy, many calcifiers are less negatively affected by OA (30). In contrast to biologically mediated calcification, increasing CaCO3 dissolution is mostly a geochemical response to changes in seawater chemistry and will increase according to thermodynamic and kinetic constraints (Fig. 3) (31, 32).

The current (2010) global average Ωar of ocean water around reefs was set at 3.3 (37), and the average annual change in Ωar was set at –0.01 (18). Theoretical reefs with coral:sand covers of 80:20, 60:40, 40:60, 20:80, and 5:95% were also modeled (dashed lines). The red symbols are global estimates of NEC for full coral reefs (109.6 mmol CaCO3 m −2 day −1 ) (circle), an average of coral reefs and coral reef lagoons (41.1 mmol CaCO3 m −2 day −1 ) (triangle), and coral reef lagoons (21.9 mmol CaCO3 m −2 day −1 ) (square) (40).

Future predictions of OA effects on coral reefs are often based on the relationship between average Ωar and NEC (see table S2). On average, there is a 102% change in NEC per unit change in seawater Ωar (Fig. 2), which is more sensitive than coral calcification (10 to 15%) but less sensitive than carbonate sediment dissolution (170%). The order-of-magnitude greater response of NEC compared to coral calcification could in part be due to sediment dissolution being more sensitive to decreasing Ωar and therefore making an increasingly greater contribution to the decrease in NEC. In addition, other components of the coral reef benthic community such as crustose coralline algae and calcareous benthic macroalgae, which are also more sensitive to changes in Ωar than corals (33, 34), could also contribute to the greater response of NEC. Consistent with this is the stronger response and sensitivity of whole coral reef community calcification to changes in Ωar than that observed in studies of individual organisms [e.g., (12, 35, 36)]. The highly variable response of the NEC of individual reefs to changes in Ωar probably reflects variations in composition of benthic communities, combined with the variable response of individual benthic communities (i.e., sediments, corals, crustose coralline algae).

An understanding of the absolute changes in CaCO3 production and dissolution (and physical loss) as the ocean acidifies is required to be able to predict the future evolution of coral reefs (see Eq. 1). We developed a simple model based on empirical relationships between average Ωar and NEC, coral calcification, and sediment dissolution from reefs around the globe (Fig. 1 and tables S2 and S3) and predicted future changes in the open ocean Ωar (18) to quantify changes in the CaCO3 production of coral reefs (see materials and methods for a detailed description of the model). Under present-day average tropical ocean Ωar (3.3), coral reef sediments are net precipitating and coral calcification and NEC are positive (Fig. 3). However, the model shows there has already been on average a reduction in coral reef sediment precipitation from 18.1 to 4.3 mmol m −2 day −1 , a reduction in NEC from 210.7 to 78.5 mmol m −2 day −1 , and a reduction in coral calcification of 111.4 to 92.8 mmol m −2 day −1 since pre-industrial time when the average tropical ocean Ωar was

4.5 (37). When the average tropical ocean Ωar reaches

2048, coral reef sediments will become net dissolving (Fig. 3). By 2082, global average coral reef NEC will become negative (i.e., net dissolving Fig. 3). By 2078 (Ωar = 2.62), sediment dissolution will exceed the global average coral reef NEC (Fig. 3). For coral reefs with 5% coral cover and 95% sediment cover, probably a common future scenario with increasing coral cover loss, this transition to net dissolution will also occur in 2085 (Ωar = 2.55) (Fig. 3).

The above model scenarios assumed a current average open ocean Ωar of 3.3 for coral reefs. However, an analysis of 22 coral reefs (see also table S1) shows a wide range of Ωar values, and therefore the timing of the transition to net dissolving will vary for individual reefs (Fig. 4). On average, four reefs already experience conditions that would promote net sediment dissolution, and by the end of the century, all but two reefs across the three ocean basins would on average experience sediment dissolution. The above model scenarios also assumed open ocean changes in Ωar, but the average seawater carbonate chemistry conditions of coral reefs may be appreciably different because of changes in reef biogeochemical processes and inputs of terrestrial nutrient and organic matter (19, 20). One study suggests that the seawater pCO2 on some reefs has increased up to 3.5 times faster than in the open ocean (20). Under this more rapid acidification scenario, coral reefs on average could transition to net sediment dissolution by the end of the decade (2020) (Ωar = 2.92), and NEC will become negative by 2031 (Ωar = 2.58). This study also has not included the effect of sea surface temperature increases on CaCO3 sediment dissolution. Although initial studies show a nonadditive effect of increased temperature and lowered Ωar on CaCO3 sediment dissolution (38), little is known about these combined stressors. Bleaching and coral mortality will also most likely accelerate the breakdown of coral reefs (39), making more sediment and organic matter available for dissolution.

The dashed line at Ωar 2.92 shows when the reef sediments will transition to net dissolving. The 2010, 2050, and 2100 predictions were calculated with the average annual open ocean change in Ωar of –0.01, but with average actual Ωar starting values for each reef for the year the data were collected. These calculations ignore the minor nonlinear behavior of Ωar in response to rising CO2 over the range modeled. The box plot red square is the mean the horizontal line in the box is the median the upper and lower box are the 75 and 25 percentiles, respectively and the top and bottom whiskers are the 90 and 10 percentiles, respectively.

A transition to net sediment dissolution will result in loss of material for building shallow reef habitats such as reef flats and lagoons and associated coral cays (2). However, it is unknown if the whole reef will erode once the sediments become net dissolving, as the corals will still calcify (Fig. 3), and the framework may still accrete. It is also unknown if reefs will experience catastrophic destruction once they become net eroding, or if they will slowly erode, driven by organic matter input and OA (17).

Saving the Oceans Through Law: The International Legal Framework for the Protection of the Marine Environment

The oceans provide many vital ecosystem services for humankind, but the health of the world’s seas is in serious decline. The protection of the marine environment has emerged as one of the most pressing challenges for the international community. An effective solution depends upon the cooperation of all states towards achieving agreed objectives. International law plays a vital role in this process. This book provides a critical assessment of the international legal instruments that have been negotiated for the protection of the marine environment and identifies key trends in global ocean governance. Starting with a detailed analysis of the United Nations Convention on the Law of the Sea, the book explains and evaluates the main global and regional treaties and related instruments that seek to prevent, reduce, and control damage to the marine environment caused by navigation, seabed exploitation, fishing, dumping, geo-engineering, and land-based activities, as well as emerging pressures such as ocean noise, ocean acidification, and climate change. The book demonstrates how international institutions have expanded their mandates to address a broader range of marine environmental issues and to promote an ecosystems approach to regulation. It also discusses the development of diverse regulatory tools to address anthropogenic impacts on the marine environment and the extent to which States have adopted a precautionary approach in different maritime sectors. Whilst many advances have been made, the book highlights the need for greater coordination between international institutions, as well as the desirability of developing stronger enforcement mechanisms for international environmental rules.

SIXTH EXTINCTION: Present and Future?

In the 1990s, paleontologist and famed conservationist Richard Leakey warned that human activity was causing a “sixth extinction.” In the decades since Leakey’s observation, with piles of new supporting evidence, many more researchers have signed on to the idea.

Across time and around the planet, extinctions of one or another individual species are always occurring. Known as the “background rate” and documented both historically and in the fossil record, these extinctions are like low-volume static compared with the sudden cymbal crash of a mass die-off. Determining extinction rates as they are unfolding is difficult, but a 2015 Science Advances study, using a range of conservative estimates, placed the current pace at up to 100 times the normal background rate.

Human activities are to blame, including population growth, increased resource consumption and climate change spurred by fossil fuel burning and the release of greenhouse gases.

In the journal PNAS in 2017, scientists concluded that focusing on species extinction may actually underrepresent the severity of what one team called “biological annihilation.” The global extinction of a species is, after all, just the final nail in the coffin.

The downward spiral begins with the destruction and fragmentation of habitat, and the introduction of invasive species and pathogens. The killing of individual members of a species through overhunting or poaching also takes its toll. Just ask any rhino, if you can find one. All of these activities can result, over time, in local extinctions known as extirpations. Even before global extinction of a species occurs, these extirpations reduce biodiversity and can destabilize ecosystems, leading to more extinctions.

As Leakey observed in his landmark 1995 book on the topic: “ Homo sapiens might not only be the agent of the sixth extinction, but also risks being one of its victims.”

Watch the video: Ocean Acidification by the Alliance for Climate Education - With Captions (September 2022).


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