Posts Tagged 'regional'



Opposite latitudinal gradients in projected ocean acidification and bleaching impacts on coral reefs

Coral reefs and the services they provide are seriously threatened by ocean acidification and climate change impacts like coral bleaching. Here, we present updated global projections for these key threats to coral reefs based on ensembles of IPCC AR5 climate models using the new Representative Concentration Pathway (RCP) experiments. For all tropical reef locations, we project absolute and percentage changes in aragonite saturation state (Ωarag) for the period between 2006 and the onset of annual severe bleaching (thermal stress >8 degree heating weeks); a point at which it is difficult to believe reefs can persist as we know them. Severe annual bleaching is projected to start 10–15 years later at high-latitude reefs than for reefs in low latitudes under RCP8.5. In these 10–15 years, Ωarag keeps declining and thus any benefits for high-latitude reefs of later onset of annual bleaching may be negated by the effects of acidification. There are no long-term refugia from the effects of both acidification and bleaching. Of all reef locations, 90% are projected to experience severe bleaching annually by 2055. Furthermore, 5% declines in calcification are projected for all reef locations by 2034 under RCP8.5, assuming a 15% decline in calcification per unit of Ωarag. Drastic emissions cuts, such as those represented by RCP6.0, result in an average year for the onset of annual severe bleaching that is ~20 years later (2062 vs. 2044). However, global emissions are tracking above the current worst-case scenario devised by the scientific community, as has happened in previous generations of emission scenarios. The projections here for conditions on coral reefs are dire, but provide the most up-to-date assessment of what the changing climate and ocean acidification mean for the persistence of coral reefs.

Continue reading ‘Opposite latitudinal gradients in projected ocean acidification and bleaching impacts on coral reefs’

Carbonate mineral saturation states in the East China Sea: present conditions and future scenarios (update)

To assess the impact of rising atmospheric CO2 and eutrophication on the carbonate chemistry of the East China Sea shelf waters, saturation states (Ω) for two important biologically relevant carbonate minerals –calcite (Ωc) and aragonite (Ωa) – were calculated throughout the water column from dissolved inorganic carbon (DIC) and total alkalinity (TA) data collected in spring and summer of 2009. Results show that the highest Ωc (∼9.0) andΩa (∼5.8) values were found in surface water of the Changjiang plume area in summer, whereas the lowest values (Ωc = ∼2.7 and Ωa = ∼1.7) were concurrently observed in the bottom water of the same area. This divergent behavior of saturation states in surface and bottom waters was driven by intensive biological production and strong stratification of the water column. The high rate of phytoplankton production, stimulated by the enormous nutrient discharge from the Changjiang, acts to decrease the ratio of DIC to TA, and thereby increases Ω values. In contrast, remineralization of organic matter in the bottom water acts to increase the DIC to TA ratio, and thus decreases Ω values. The projected result shows that continued increases of atmospheric CO2 under the IS92a emission scenario will decrease Ω values by 40–50% by the end of this century, but both the surface and bottom waters will remain supersaturated with respect to calcite and aragonite. Nevertheless, superimposed on such Ω decrease is the increasing eutrophication, which would mitigate or enhance the Ωdecline caused by anthropogenic CO2 uptake in surface and bottom waters, respectively. Our simulation reveals that, under the combined impact of eutrophication and augmentation of atmospheric CO2, the bottom water of the Changjiang plume area will become undersaturated with respect to aragonite (Ωa =  ∼0.8) by the end of this century, which would threaten the health of the benthic ecosystem.

Continue reading ‘Carbonate mineral saturation states in the East China Sea: present conditions and future scenarios (update)’

Estimating carbonate parameters from hydrographic data for the intermediate and deep waters of the Southern Hemisphere oceans (update)

Using ocean carbon data from global datasets, we have developed several multiple linear regression (MLR) algorithms to estimate alkalinity and dissolved inorganic carbon (DIC) in the intermediate and deep waters of the Southern Hemisphere (south of 25° S) from only hydrographic data (temperature, salinity and dissolved oxygen). A Monte Carlo experiment was used to identify a potential density (σθ) of 27.5 as an optimal break point between the two regimes with different MLR algorithms. The algorithms provide a good estimate of DIC (R2=0.98) and alkalinity (R2=0.91), and excellent agreement for aragonite and calcite saturation states (R2=0.99). Combining the algorithms with the CSIRO Atlas of Regional Seas (CARS), we have mapped the calcite saturation horizon (CSH) and aragonite saturation horizon (ASH) for the Southern Ocean at a spatial resolution of 0.5°. These maps are more detailed and more consistent with the oceanography than the previously gridded GLODAP data. The high-resolution ASH map reveals a dramatic circumpolar shoaling at the polar front. North of 40° S the CSH is deepest in the Atlantic (~ 4000 m) and shallower in the Pacific Ocean (~ 2750 m), while the CSH sits between 3200 and 3400 m in the Indian Ocean. The uptake of anthropogenic carbon by the ocean will alter the relationships between DIC and hydrographic data in the intermediate and deep waters over time. Thus continued sampling will be required, and the MLR algorithms will need to be adjusted in the future to account for these changes.

Continue reading ‘Estimating carbonate parameters from hydrographic data for the intermediate and deep waters of the Southern Hemisphere oceans (update)’

Estuarine acidification and minimum buffer zone – a conceptual study

This study uses a simulation method to explore how estuarine pH is affected by mixing between river water, anthropogenic CO2 enriched seawater, and by respiration. Three rivers with different levels of weathering products (Amazon, Mississippi, and St. Johns) are selected for this simulation. The results indicate that estuaries that receive low to moderate levels of weathering products (Amazon and St. Johns) exhibit a maximum pH decrease in the mid-salinity region as a result of anthropogenic CO2 intrusion. This maximum pH decrease coincides with a previously unrecognized mid-salinity minimum buffer zone (MBZ). In addition, water column oxygen consumption can further depress pH for all simulated estuaries. We suggest that recognition of the estuarine MBZs may be important for studying estuarine calcifying organisms and pH-sensitive biogeochemical processes.

Continue reading ‘Estuarine acidification and minimum buffer zone – a conceptual study’

Estimating carbonate parameters from hydrographic data for the intermediate and deep waters of the Southern Hemisphere Oceans

Using GLODAP and CLIVAR ocean carbon data, we have developed several multiple linear regression (MLR) algorithms to estimate alkalinity and dissolved inorganic carbon (DIC) in the intermediate and deep waters of the Southern Hemisphere (south of 25° S) from only hydrographic data (temperature, salinity and dissolved oxygen). A Monte Carlo experiment was used to identify a potential density (σθ) of 27.5 as an optimal break point between the two regimes with different MLR algorithms. The algorithms provide a good estimate of DIC (R2=0.98) and alkalinity (R2=0.91), and excellent agreement for aragonite and calcite saturation states (R2=0.99). Combining the algorithms with the CSIRO Atlas of Regional Seas (CARS), we have been able to map the calcite saturation horizon (CSH) and aragonite saturation horizon (ASH) for the Southern Ocean at a spatial resolution of 0.5°. These maps are more detailed and more consistent with oceanography than the gridded GLODAP data. The high resolution ASH map reveals a dramatic circumpolar shoaling at the Polar Front. North of 40° S the CSH is deepest in the Atlantic (~ 4000 m) and shallower in the Pacific Ocean (~ 2750 m), while the CSH sits between 3200 and 3400 m in the Indian Ocean.

Continue reading ‘Estimating carbonate parameters from hydrographic data for the intermediate and deep waters of the Southern Hemisphere Oceans’

Impact of ocean acidification on recruitment and yield of Bristol Bay red king crab

The excess of anthropogenic carbon dioxide (CO2) produced since the industrial revolution is being absorbed by the oceans through the carbon cycle. Atmospheric carbon dioxide has increased about 40% since the preindustrial era, and the oceans have absorbed more than a third of these emissions. This has led to the release of H+ ions via seawater carbonate chemistry, and hence to a reduction in ocean pH, that is, ocean acidification. Ocean pH has been reduced by roughly 0.1 units, which is equivalent to an increase in H+ of roughly 30%, and about a 16% decrease in . Corrosive waters, the waters below the CaCO3 saturation horizon, are predicted to reach shallower depths more in the Northeast Pacific Ocean than in any other ocean basin. The saturation horizon is projected to reach the surface of the North Pacific Ocean during this century, and some regions of the Bering Sea are predicted to become carbon shell corrosive seasonally by the middle of this century, which will expose a wide range of North Pacific species, including Bristol Bay Red king crab, to corrosive waters. Bristol Bay Red king crab has been one of the most valuable fished stocks in the US. It is managed by the State of Alaska under federal guidelines defined in the Fishery Management Plan (FMP) for crab in the Bering Sea and Aleutian Islands. Current management rules are designed to handle short-term fluctuations in stock abundance mainly due to exploitation. The impact of ocean acidification on red king crab is predicted to lead to long-term changes to stock abundance, and for which management is currently unprepared. This thesis explores the impact of ocean acidification on recruitment and yield of Bristol Bay red king crab under a range of ocean acidification scenarios and management strategies. The management strategies include setting the exploitation rate for the directed fishery to that under the overfishing limit (OFL) rule, applying constant exploitation rates, and setting exploitation rates that maximize catch and discounted profit. Trends in recruitment to the first size-class in the stock assessment model are estimated using a pre-recruit model in which survival is parameterized based on experimental results from the NMFS Kodiak laboratory. Exploitation rates are estimated, and time series (2000-2100) for MMB, catch, and discounted profit are projected, for each management strategy for three levels of variable fishery costs and for the economic discount factor. The catch, biomass, and discounted profit equilibrate at non-zero values for the no-OA scenario, but are driven to zero for all exploitation rates in the OA scenarios. Lower constant exploitation rates lead to a longer time before the biomass is driven close to zero, but the total discounted profit is highest at the highest exploitation rate for the three OA scenarios. The OFL control rule performs better than the constant exploitation rate strategies in terms of conserving the resource, because this rule closes the fishery at low biomass levels, which are also unprofitable. Estimated total discounted profits for the strategies which maximize catch and discounted profit are about the same for the base no-OA scenario, while the strategy that maximizes profit leads to slightly higher discounted profit and it depletes the stock below the biomass threshold sooner than the strategy which maximizes catch. Catches are the same for the strategies which maximize catch for no-OA scenario, and are higher for the strategy which maximizes catch for the OA scenarios. Higher discount rates lead to higher biomasses and catches, and the fishery is closed earlier for higher costs (food, fuel, and bait costs) for the OA scenarios when exploitation rates are selected to maximize profit.

Continue reading ‘Impact of ocean acidification on recruitment and yield of Bristol Bay red king crab’

Potential impacts of ocean acidification on the Puget Sound food web

Ecosystem impacts of ocean acidification (OA) were explored by imposing scenarios designed to mimic OA on a food web model of Puget Sound, a large estuary in northwestern USA. The productivity of functional groups containing mostly calcifiers was decreased while still allowing other species groups to respond to the scenarios in a dynamic way through indirect effects. Results focus on changes in ecosystem services and structure. Sometimes the direct and indirect effects of OA countered each other due to interactions between predators and prey within the food web, leading to little change in the food web. In other cases, direct and indirect effects caused greater change in the food web than anticipated from direct effects alone. Results were strongly affected by the group on which OA was directly imposed, with changes in copepod productivity being the most influential. While there is much uncertainty in our predictions, focusing on the complex interactions among species, and between species and their environment, will yield better understanding of how ecosystems may respond to OA.

Continue reading ‘Potential impacts of ocean acidification on the Puget Sound food web’


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Ocean acidification in the IPCC AR5 WG II

OUP book