New educational PDF – “Kongsfjord 2010: Exploring the future of the Arctic ocean”

Philippe Saugier has produced a new educational PDF, this time based on the experiments in Svalbard in the summer of 2010. You may find the 8-page PDF on the EPOCA Education web page (English and French versions).

Conditioning reefs for the future

In a world first, a new ‘state of the art’ climate change experimental facility has been completed at the University of Queensland’s (UQ) Heron Island Research Station.

The Climate Change Mesocosm (CCM) project led by Associate Professor Sophie Dove and Dr David Kline from the Global Change Institute’s (GCI) Coral Reef Ecosystems Laboratory is one of the largest and most accurately controlled ocean acidification and warming experimental systems in the world and simulates ocean temperatures and acidification levels predicted to occur on coral reefs in the next 50 to 100 years.

Able to regulate both temperature and CO2 levels prescribed by the 2100 Intergovernmental Panel on Climate Change (IPCC) scenarios in a highly controlled environment, the CCM system allows studies of climate change from the molecular to the ecosystem level.

“While similar to the “Free Ocean Carbon Enrichment” (FOCE) project, recently featured in Sir David Attenborough’s documentary “Death of the Oceans”, the CCM differs in that it regulates the temperature, in addition to, the acidification levels above and below the current ambient conditions of water on the reef,” Dr Dove said.

Effects of sediment acidification on the bioaccumulation of Zn in R. Philippinarum

Acidification resulting from the increase of carbon dioxide in the ocean is one of the main effects of global warming. Models predict that a decrease of pH in surface sediments results in higher mobility of metals in sediment pore water and overlying water. This hypothesis has been tested in an exposure sediment bioassay using the clam R. philippinarum. Different sediment samples (toxic mud from a mining spill; estuarine samples from the Ria de Huelva and Guadalquivir rivers, and sediments located in the Bay of Cadiz, all in Spain) were used to address the influence of pH values (6.5–8.5) in bioaccumulation of the metal Zn. Results show that there is a significant (p < 0.05) increase in bioaccumulation of this metal at lower values of pH (6.5 and 7.5) compared to the 8.5 value. These results indicate that modification of one unit in pH produces a significant effect in Zn bioavailability, which is also associated with adverse biological effects such us mortality. The results point out the importance of addressing the influence of sediment acidification and their implications in risk assessment in estuarine sediments or in special areas selected for carbon dioxide capture in marine environments.

pH decrease and effects on the chemistry of seawater

Variation in seawater pH is just one response to the increased CO₂concentration in the atmosphere due to anthropogenic activities. The decrease in pH has a significant effect on the carbonate chemistry of the ocean and causes a decrease in the calcium carbonate saturation state (Ω). Ten years of experimental pH measurements at the ESTOC station show a progressive reduction on pH in the ocean (-0.0017 ± 0.0002 year^–1) and its effects on its carbonate chemistry. The calcium carbonate saturation state decreases by 0.018 ± 0.006 unit year^–1for calcite and 0.012 ± 0.004 unit year^–1for aragonite. The direct consequences of the pH decrease are a decrease in the buffer capacity (-1.99 ± 0.25 µmol kg^–1year^–1) and an increase in the Revelle factor (0.02 ± 0.002 year^–1) of the surface seawater.

Aspects of phytoplankton communities response to climate changes

Climate changes concerning shifts in seasonal dominant winds and increases in atmospheric CO₂ are underway. Thus, changes are occurring in coastal upwelling regimes as well as increases in CO₂ absorption by the ocean/acidification impacting phytoplankton communities in terms of abundance and diversity. In order to illustrate these apparent changes we present results obtained from coastal waters adjacent to the Tagus estuary under different hydrological conditions. Upwelling events prevailed in winter 1994, were absent in winter 2001 and were present in summer 2002. Chemical and biological properties are examined: in March 1994, a strong bloom of phytoplankton developed (chlorophyll a up to 40 mg m^–3) which was attributed to the combined effect of intense freshwater runoff and upwelling, leading to the establishment of a strong frontal boundary and a supply of a considerable amount of nutrients. In March 2001, under an extremely intense river discharge and absence of upwelling, only values up to 1.5 mg m^–3 of chlorophyll a were measured. On the other hand, in June 2002, when Tagus river inflow was reduced and nutrient levels were quite low, chlorophyll a levels attained 5 mg m^–3 despite the occurrence of upwelling.

Over the same study area, potential impacts of acidification on phytoplankton communities are discussed. Actually, blooms of calcifying organisms occur often in Iberian coastal waters linked to upwelling events. In June 2002, a bloom episode of the Coccolithophore, Coccolithus braarudii, developed attaining up to 60 cells mL^–1, being responsible for production of 11.2 mmol CaCO₃ m^–2 d^–1. In the context of actual lowering of seawater pH, the expected calcification slow-down as well as the reduction of buffering seawater ability, a shift of such a phytoplankton group to other groups is likely to be induced. Thus, the maintenance of biogeochemical time-series is crucial for the detection of future changes in the structure and functioning of this marine ecosystem.

Present day carbon dioxide fluxes in the coastal ocean and possible feedbacks under global change

The present day contemporary CO2 fluxes in shelf seas could be significant for the global carbon cycle, since available estimates converge to a sink of ∼0.3 PgC yr^-1 corresponding to 21% of most recent estimate of contemporary sink of atmospheric CO2 in open oceans of 1.4 PgC yr^-1. These estimates are prone to large uncertainty mainly due to inadequate representation of the spatial variability and need to be improved based on more data, requiring a concerted global observational effort. The potential feedbacks on increasing atmospheric CO2 from changes in carbon flows in the coastal ocean could be disproportionately higher than in the open ocean. The changes in carbon flows and related potential feedbacks in the coastal ocean could be driven by 3 main processes: i) changes in coastal physics; ii) changes in land-used, waste water inputs, agricultural fertilizers and changes in hydrological cycle; iii) changes in seawater carbonate chemistry (ocean acidification). These potential feedbacks remain largely unquantified due to a poor understanding of the underlying mechanisms, or lack of modelling to quantify them. Based on reported evaluations and back of the envelop calculations, it is suggested that changes of biological activity due the increased nutrientdelivery by rivers would provide by 2100 a negative feedback on increasing atmospheric CO2 of the order of magnitude of the present day sink for atmospheric CO2. This negative feedback on increasing atmospheric CO2 would be one order of magnitude higher than negative feedback due to the decrease of either pelagic or benthic calcification related to ocean acidification, and than the negative feedback related to dissolution of CaCO3 in sediments. The increase of export production could also provide a significant feedback to increasing atmospheric CO2, although based on the conclusions from a single perturbation experiment. Feedbacks on increasing atmospheric CO2 due to effects of C cycling in continental shelf seas related to changes in circulation or stratification could be important but remain to be quantified.

CO2-driven compromises to marine life along the Chilean coast

CO₂-driven compromises to marine life were examined along the Chilean sector of the Humboldt Current System, a particularly vulnerable hypoxic and upwelling area, applying the Respiration index (RI = log₁₀ pO₂pCO₂) and the pH-dependent aragonite saturation (Ω) to delineate the water masses where aerobic and calcifying organisms are stressed. There was a remarkable negative relationship between oxygen concentration and pH or pCO₂ in the studied area, with the subsurface hypoxic Equatorial Subsurface Waters extending from 100 m to about 300 m depth and supporting elevated pCO₂ values. The RI reached a minimum at about 200 m depth and decreased towards the Equator. Increased pCO₂ in the hypoxic water layer reduced the RI values by as much as 0.59 RI units, with the upper water layer that presents conditions suitable for aerobic life (RI>0.7) declining by half between 42° S and 28° S. The intermediate waters hardly reached those stations closer to the equator so that the increased pCO₂ lowered pH and the saturation of aragonite. A significant fraction of the water column along the Chilean sector of the Humboldt Current System suffers from CO₂–driven compromises to biota, including waters corrosive to calcifying organisms, stress to aerobic organisms or both. The habitat free of CO₂-driven stresses was restricted to the upper mixed layer and to small water parcels at about 1000 m depth. pCO₂ acts as a hinge connecting respiratory and calcification challenges expected to increase in the future, resulting in a spread of the challenges to aerobic organisms.

Reef bioerosion: agents and processes

Coral reef maintenance depends on the balance between constructive and destructive forces. Constructive forces are mainly calcification and growth of corals and encrusting coralline algae. Destructive forces comprise physical, chemical, and biological erosion. Bioerosion is considered as the main force of reef degradation because physical erosion (storms) is temporary and localized, and chemical erosion is considered as negligible due to the actual ocean chemistry (Scoffin et al. 1980). Reef bioerosion affects sedimentary and skeletal carbonate substrates. It plays an important role in reef sedimentation, diversity maintenance by creating habitats and by providing food resources, and in biogeochemical cycles (recycling of dissolved Ca²⁺ and C). Thus, bioerosion is an integral part of the coral reef carbonate balance. The concept of bioerosion was introduced by Neumann (1966). It includes biocorrosion, which refers to destruction of carbonates by chemical means, and bioabrasion which refers to mechanical removal of carbonates by organisms (Golubic and Schneider 1979; Schneider and Torunski 1983).

The impact of climate change on coral reef ecosystems

Human activities such as the burning of fossil fuels, deforestation and changing land use have dramatically altered the atmospheric concentration of greenhouse gases such as carbon dioxide and methane. These changes have resulted in global warming and ocean acidification, both of which pose serious threats to coral reef ecosystems through increased thermal stress and ocean acidity as well as declining carbonate ion concentrations. Observed impacts on coral reefs include increased mass coral bleaching, declining calcification rates, and a range of other changes to subtle yet fundamentally important physiological and ecological processes. There is little evidence that reef-building corals and other organisms will be able to adapt to these changes leading to the conclusion reef ecosystems will become rare globally by the middle of the current century. Constraining the growth of carbon dioxide in the atmosphere as well as reducing local stresses such as overfishing and declining water quality, however, holds considerable hope for avoiding this gloomy future for coral reefs. Given the importance of coral reefs to the livelihoods of millions of people, actions such as these must be pursued as a matter of extreme urgency.

Coral calcification under ocean acidification and global change

Coral reefs are unique marine ecosystems that form huge morphological structures (frameworks) in today’s oceans. These include coral islands (atolls), barrier reefs, and fringing reefs that form the most impressive products of CaCO₃ biomineralization. The framework builders are mainly hermatypic corals, calcareous algae, foraminifera, and mollusks that together are responsible for almost 50% of the net annual CaCO₃ precipitation in the oceans. The reef ecosystem acts as a huge filtration system that extracts plankton from the vast fluxes of ocean water that flow through the framework. The existence of these wave resistant structures in spite of chemical, biological, and physical erosion depends on their exceedingly high rates of calcification. Coral mortality due to bleaching (caused by global warming) and ocean acidification caused by atmospheric CO₂ increase are now the major threats to the existence of these unique ecosystems. When the rates of dissolution and erosion become higher than the rates of precipitation, the entire coral ecosystem starts to collapse and will eventually be reduced to piles of rubble while its magnificent and high diversity fauna will vanish. The loss to nature and to humanity would be unprecedented and it may occur within the next 50 years. In this chapter, we discuss the issue of ocean acidification and its major effects of corals from the cell level to the reef communities. Based on the recently published literature, it can be generalized that calcification in corals is strongly reduced when seawater become slightly acidified. Ocean acidification lowers both the pH and the CO₃²⁻ ion concentration in the surface ocean, but calcification at the organism level responds mainly to CO₃²⁻ and not to pH. Most reports show that the symbiotic algae are not sensitive to changes in the carbonate chemistry. The potential mechanisms responsible for coral sensitivity to acidification are either direct input of seawater to the biomineralization site or high sensitivity of the enzymes involved in calcification to pH and/or CO₂ concentrations. Increase in pH at the biomineralization site is most probably the most energy demanding process that is influenced by ocean acidification. While hermatypic corals and other calcifiers reduce their rates of calcification, chemical and biological dissolution increase and hence net calcification of the entire coral reef is decreasing dramatically. Community metabolism in several sites and in field enclosures show in some cases net dissolution. Using the relations between aragonite saturation (Ω_arag) and community calcification, it is possible to predict that coral reefs globally may start to dissolve when atmospheric CO₂ doubles.