Posts Tagged 'chemistry'

Continuous monitoring and future projection of ocean warming, acidification, and deoxygenation on the subarctic coast of Hokkaido, Japan

As the ocean absorbs excessive anthropogenic CO2 and ocean acidification proceeds, it is thought to be harder for marine calcifying organisms, such as shellfish, to form their skeletons and shells made of calcium carbonate. Recent studies have suggested that various marine organisms, both calcifiers and non-calcifiers, will be affected adversely by ocean warming and deoxygenation. However, regardless of their effects on calcifiers, the spatiotemporal variability of parameters affecting ocean acidification and deoxygenation has not been elucidated in the subarctic coasts of Japan. This study conducted the first continuous monitoring and future projection of physical and biogeochemical parameters of the subarctic coast of Hokkaido, Japan. Our results show that the seasonal change in biogeochemical parameters, with higher pH and dissolved oxygen (DO) concentration in winter than in summer, was primarily regulated by water temperature. The daily fluctuations, which were higher in the daytime than at night, were mainly affected by daytime photosynthesis by primary producers and respiration by marine organisms at night. Our projected results suggest that, without ambitious commitment to reducing CO2 and other greenhouse gas emissions, such as by following the Paris Agreement, the impact of ocean warming and acidification on calcifiers along subarctic coasts will become serious, exceeding the critical level of high temperature for 3 months in summer and being close to the critical level of low saturation state of calcium carbonate for 2 months in mid-winter, respectively, by the end of this century. The impact of deoxygenation might often be prominent assuming that the daily fluctuation in DO concentration in the future is similar to that at present. The results also suggest the importance of adaptation strategies by local coastal industries, especially fisheries, such as modifying aquaculture styles.

Continue reading ‘Continuous monitoring and future projection of ocean warming, acidification, and deoxygenation on the subarctic coast of Hokkaido, Japan’

The variable circulation and carbonate chemistry of ocean upwelling systems

Ocean upwelling is a process in which winds drive deep waters to the surface ocean. The biogeochemical state of these waters causes upwelling regions to have some of the strongest air-sea fluxes of carbon dioxide (CO2) and most productive fisheries in the global oceans. In this dissertation, I use Earth System models to investigate the variability and projected impacts of climate change on upwelling systems. I first use the Community Earth System Model Large Ensemble (CESM-LE) to project the impacts of climate change on upwelling in the California Current. The CESM-LE provides an ensemble of potential trajectories of the climate system that differ due to internal climate variability. I find that upwelling is expected to weaken over the next century in the summer and intensify poleward in the spring due to anthropogenic climate change. Next, I use the CESM-LE to highlight the role of internal climate variability in modulating air-sea CO2 fluxes in the major Eastern Boundary Upwelling Systems (EBUS). I identify the major mode of internal variability that influences air-sea CO2 flux in each EBUS. I then quantify how the given mode of variability modifies local conditions, which in turn leads to the anomalous air-sea CO2 fluxes. Following this, I use a version of the CESM-LE that is configured for climate prediction to examine predictability of ocean acidification in the California Current. I find that our system makes skillful forecasts of surface pH out to fourteen months relative to observations and has a potential ceiling of skillful prediction out to five years in some regions. Finally, I use the Model for Prediction Across Scales Ocean (MPAS-O) to investigate the pathways over which carbon upwells in the Southern Ocean. I seed a high-resolution version of MPAS-O with 1,000,000 Lagrangian floats and find that regions with complex ocean topography have a disproportionate influence on bringing carbon-rich waters from the deep Southern Ocean to the surface. The results of this dissertation highlight the value of using ensemble methods and the Lagrangian perspective in Earth System models to better understand the dynamic and variable biogeochemistry in ocean upwelling systems.

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Two offshore coral species show greater acclimatization capacity to environmental variation than nearshore counterparts in southern Belize

Coral reefs are enduring decline due to the intensifying impacts of anthropogenic global change. This widespread decline has resulted in increased efforts to identify resilient coral populations and develop novel restoration strategies. Paramount in these efforts is the need to understand how environmental variation and thermal history affect coral physiology and resilience. Here, we assess the acclimatization capacity of Siderastrea siderea and Pseudodiploria strigosa corals via a 17-month reciprocal transplant experiment between nearshore and offshore reefs on the Belize Mesoamerican Barrier Reef System. These nearshore reefs are more turbid, eutrophic, warm, and thermally variable than offshore reefs. All corals exhibited some evidence of acclimatization after transplantation. Corals transplanted from nearshore to offshore calcified slower than in their native habitat, especially S. siderea corals which exhibited 60% mortality and little to no net growth over the duration of the 17-month study. Corals transplanted from offshore to nearshore calcified faster than in their native habitat with 96% survival. Higher host tissue δ15N in nearshore corals indicated that increased heterotrophic opportunity or nitrogen sources between nearshore and offshore reefs likely promoted elevated calcification rates nearshore and may facilitate adaptation in nearshore populations to such conditions over time. These results demonstrate that offshore populations of S. siderea and P. strigosa possess the acclimatization capacity to survive in warmer and more turbid nearshore conditions, but that local adaptation to native nearshore conditions may hinder the plasticity of nearshore populations, thereby limiting their utility in coral restoration activities outside of their native habitat in the short term.

Continue reading ‘Two offshore coral species show greater acclimatization capacity to environmental variation than nearshore counterparts in southern Belize’

A pronounced spike in ocean productivity triggered by the Chicxulub impact

Abstract

There is increasing evidence linking the mass-extinction event at the Cretaceous-Paleogene boundary to an asteroid impact near Chicxulub, Mexico. Here we use model simulations to explore the combined effect of sulfate aerosols, carbon dioxide and dust from the impact on the oceans and the marine biosphere in the immediate aftermath of the impact. We find a strong temperature decrease, a brief algal bloom caused by nutrients from both the deep ocean and the projectile, and moderate surface ocean acidification. Comparing the modeled longer-term post-impact warming and changes in carbon isotopes with empirical evidence points to a substantial release of carbon from the terrestrial biosphere. Overall, our results shed light on the decades to centuries after the Chicxulub impact which are difficult to resolve with proxy data.

Plain Language Summary

The sudden disappearance of the dinosaurs and many other species during the end-Cretaceous mass extinction 66 million years ago marks one of the most profound events in the history of life on Earth. The impact of a large asteroid near Chicxulub, Mexico, is increasingly recognised as the trigger of this extinction, causing global darkness and a pronounced cooling. However, the links between the impact and the changes in the biosphere are not fully understood. Here, we investigate how life in the ocean reacts to the perturbations in the decades and centuries after the impact. We find a short-lived algal bloom caused by the upwelling of nutrients from the deep ocean and nutrient input from the impactor.

Continue reading ‘A pronounced spike in ocean productivity triggered by the Chicxulub impact’

Planktic foraminiferal and pteropod contributions to carbon dynamics in the Arctic Ocean (North Svalbard Margin)

Planktic foraminifera and shelled pteropods are some of the major producers of calcium carbonate (CaCO3) in the ocean. Their calcitic (foraminifera) and aragonitic (pteropods) shells are particularly sensitive to changes in the carbonate chemistry and play an important role for the inorganic and organic carbon pump of the ocean. Here, we have studied the abundance distribution of planktic foraminifera and pteropods (individuals m–3) and their contribution to the inorganic and organic carbon standing stocks (μg m–3) and export production (mg m–2 day–1) along a longitudinal transect north of Svalbard at 81° N, 22–32° E, in the Arctic Ocean. This transect, sampled in September 2018 consists of seven stations covering different oceanographic regimes, from the shelf to the slope and into the deep Nansen Basin. The sea surface temperature ranged between 1 and 5°C in the upper 300 m. Conditions were supersaturated with respect to CaCO3 (Ω > 1 for both calcite and aragonite). The abundance of planktic foraminifera ranged from 2.3 to 52.6 ind m–3 and pteropods from 0.1 to 21.3 ind m–3. The planktic foraminiferal population was composed mainly of the polar species Neogloboquadrina pachyderma (55.9%) and the subpolar species Turborotalita quinqueloba (21.7%), Neogloboquadrina incompta (13.5%) and Globigerina bulloides (5.2%). The pteropod population was dominated by the polar species Limacina helicina (99.6%). The rather high abundance of subpolar foraminiferal species is likely connected to the West Spitsbergen Current bringing warm Atlantic water to the study area. Pteropods dominated at the surface and subsurface. Below 100 m water depth, foraminifera predominated. Pteropods contribute 66–96% to the inorganic carbon standing stocks compared to 4–34% by the planktic foraminifera. The inorganic export production of planktic foraminifera and pteropods together exceeds their organic contribution by a factor of 3. The overall predominance of pteropods over foraminifera in this high Arctic region during the sampling period suggest that inorganic standing stocks and export production of biogenic carbonate would be reduced under the effects of ocean acidification.

Continue reading ‘Planktic foraminiferal and pteropod contributions to carbon dynamics in the Arctic Ocean (North Svalbard Margin)’

Reversing ocean acidification along the Great Barrier Reef using alkalinity injection

The Great Barrier Reef (GBR) is a globally significant coral reef system supporting productive and diverse ecosystems. The GBR is under increasing threat from climate change and local anthropogenic stressors, with its general condition degrading over recent decades. In response to this, a number of techniques have been proposed to offset or ameliorate environmental changes. In this study, we use a coupled hydrodynamic-biogeochemical model of the GBR and surrounding ocean to simulate artificial ocean alkalinisation (AOA) as a means to reverse the impact of global ocean acidification on GBR reefs. Our results demonstrate that a continuous release of 90 000 t of alkalinity every 3 d over one year along the entire length of the GBR, following the Gladstone-Weipa bulk carrier route, increases the mean aragonite saturation state (Ωar) across the GBR’s 3860 reefs by 0.05. This change offsets just over 4 years (∼4.2) of ocean acidification under the present rate of anthropogenic carbon emissions. The injection raises Ωar in the 250 reefs closest to the route by ⩾0.15, reversing further projected Ocean Acidification. Following cessation of alkalinity injection Ωar returns to the value of the waters in the absence of AOA over a 6 month period, primarily due to transport of additional alkalinity into the Coral Sea. Significantly, our study provides for the first time a model of AOA applied along existing shipping infrastructure that has been used to investigate shelf scale impacts. Thus, amelioration of decades of OA on the GBR is feasible using existing infrastructure, but is likely to be extremely expensive, include as yet unquantified risks, and would need to be undertaken continuously until such time, probably centuries in the future, when atmospheric CO2 concentrations have returned to today’s values.

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The CO2 system dynamics in the vicinity of the vistula river mouth (the southern Baltic Sea): a baseline investigation

Highlights

  • The CO2 system in the Vistula River plume was investigated for the first time.
  • Vistula River as an important TA source to the Baltic Sea.
  • OM production and remineralization affect the CO2 system in the Vistula River plume.
  • The variability of pH and Ω in the Vistula River plume were significant.
  • Vistula River is a source of PIC to the Gdańsk Bay.

Abstract

The CO2 system dynamics in coastal areas strongly controlled by river outflow is largely understudied. In this study, the influence of a large, continental, carbonate-rich river on the carbonate system was seasonally examined in the vicinity of the Vistula River Mouth. Three parameters describing the CO2 system were investigated: the partial pressure of carbon dioxide (pCO2), total alkalinity (TA), and pH, together with salinity, temperature, oxygen concentration, calcium cation (Ca2+), particulate inorganic carbon (PIC), and inorganic carbon (IC) in sediments. TA varied from 1700 μmol kg−1 in the brackish water of the Gdańsk Bay to 3475 μmol kg−1 in the Vistula River plume, highlighting the difference between the two end-members. Highest pCO2 was observed in October (855 μatm) and lowest in May (148 μatm). Oxygen concentration was negatively correlated to pCO2 in all seasons, suggesting that both were inversely controlled by the net ecosystem production (NEP). The pH seasonal variation was significant with a range of 0.72 unit. The calcium carbonate saturation (Ω) varied from 0.8 to 8.5 for calcite and from 0.5 to 8.5 for aragonite, both displaying Ω < 1 in February 2018.

This study shows the importance of ecosystem metabolism and TA end-member variability (3138–3631 μmol kg−1), for controlling pH in the vicinity of the Vistula River Mouth. In addition, we present data on PIC, supporting possible deposition of inorganic forms of carbon to the sediments near the Vistula River Mouth.

Continue reading ‘The CO2 system dynamics in the vicinity of the vistula river mouth (the southern Baltic Sea): a baseline investigation’

Projecting ocean acidification impacts for the Gulf of Maine to 2050: new tools and expectations

Ocean acidification (OA) is increasing predictably in the global ocean as rising levels of atmospheric carbon dioxide lead to higher oceanic concentrations of inorganic carbon. The Gulf of Maine (GOM) is a seasonally varying region of confluence for many processes that further affect the carbonate system including freshwater influences and high productivity, particularly near the coast where local processes impart a strong influence. Two main regions within the GOM currently experience carbonate conditions that are suboptimal for many organisms—the nearshore and subsurface deep shelf. OA trends over the past 15 years have been masked in the GOM by recent warming and changes to the regional circulation that locally supply more Gulf Stream waters. The region is home to many commercially important shellfish that are vulnerable to OA conditions, as well as to the human populations whose dependence on shellfish species in the fishery has continued to increase over the past decade. Through a review of the sensitivity of the regional marine ecosystem inhabitants, we identified a critical threshold of 1.5 for the aragonite saturation state (Ωa). A combination of regional high-resolution simulations that include coastal processes were used to project OA conditions for the GOM into 2050. By 2050, the Ωa declines everywhere in the GOM with most pronounced impacts near the coast, in subsurface waters, and associated with freshening. Under the RCP 8.5 projected climate scenario, the entire GOM will experience conditions below the critical Ωa threshold of 1.5 for most of the year by 2050. Despite these declines, the projected warming in the GOM imparts a partial compensatory effect to Ωa by elevating saturation states considerably above what would result from acidification alone and preserving some important fisheries locations, including much of Georges Bank, above the critical threshold.

Continue reading ‘Projecting ocean acidification impacts for the Gulf of Maine to 2050: new tools and expectations’

Coral bleaching response is unaltered following acclimatization to reefs with distinct environmental conditions

Significance

Ocean warming has caused catastrophic losses of corals on reefs worldwide and is intensifying faster than the adaptive rate of most coral populations that remain. Human interventions, such as propagation of heat-resistant corals, may help maintain reef function and delay further devastation of these valuable ecosystems as society confronts the climate crisis. However, exposing adult corals to a complex suite of new environmental conditions could lead to tradeoffs that alter their heat stress responses, and empirical data are needed to test the utility of this approach. Here, we show that corals transplanted to novel reef conditions did not exhibit changes in their heat stress response or negative fitness tradeoffs, supporting the inclusion of this approach in our management arsenal.

Abstract

Urgent action is needed to prevent the demise of coral reefs as the climate crisis leads to an increasingly warmer and more acidic ocean. Propagating climate change–resistant corals to restore degraded reefs is one promising strategy; however, empirical evidence is needed to determine whether stress resistance is affected by transplantation beyond a coral’s native reef. Here, we assessed the performance of bleaching-resistant individuals of two coral species following reciprocal transplantation between reefs with distinct pH, salinity, dissolved oxygen, sedimentation, and flow dynamics to determine whether heat stress response is altered following coral exposure to novel physicochemical conditions in situ. Critically, transplantation had no influence on coral heat stress responses, indicating that this trait was relatively fixed. In contrast, growth was highly plastic, and native performance was not predictive of performance in the novel environment. Coral metabolic rates and overall fitness were higher at the reef with higher flow, salinity, sedimentation, and diel fluctuations of pH and dissolved oxygen, and did not differ between native and cross-transplanted corals, indicating acclimatization via plasticity within just 3 mo. Conversely, cross-transplants at the second reef had higher fitness than native corals, thus increasing the fitness potential of the recipient population. This experiment was conducted during a nonbleaching year, so the potential benefits to recipient population fitness are likely enhanced during bleaching years. In summary, this study demonstrates that outplanting bleaching-resistant corals is a promising tool for elevating the resistance of coral populations to ocean warming.

Continue reading ‘Coral bleaching response is unaltered following acclimatization to reefs with distinct environmental conditions’

Reviews and syntheses: spatial and temporal patterns in metabolic fluxes inform potential for seagrass to locally mitigate ocean acidification

As global change continues to progress, there is a growing interest in assessing any local levers that could be used to manage the social and ecological impacts of rising CO2 concentrations. While habitat conservation and restoration have been widely recognized for their role in carbon storage and sequestration at a global scale, the potential for managers to use vegetated habitats to mitigate CO2 concentrations at local scales in marine ecosystems facing the accelerating threat of ocean acidification (OA) has only recently garnered attention. Early studies have shown that submerged aquatic vegetation, such as seagrass beds, can locally draw down CO2 and raise seawater pH in the water column through photosynthesis, but empirical studies of local OA mitigation are still quite limited. Here, we leverage the extensive body of literature on seagrass community metabolism to highlight key considerations for local OA management through seagrass conservation or restoration. In particular, we synthesize the results from 62 studies reporting in situ rates of seagrass gross primary productivity, respiration, and/or net community productivity to highlight spatial and temporal variability in carbon fluxes. We illustrate that daytime net community production is positive overall, and similar across seasons and geographies. Full-day net community production rates, which illustrate the potential cumulative effect of seagrass beds on seawater biogeochemistry integrated over day and night, were also positive overall, but were higher in summer months in both tropical and temperate ecosystems. Although our analyses suggest seagrass meadows are generally autotrophic, the modeled effects on seawater pH are relatively small in magnitude. In addition, we illustrate that periods when full-day net community production is highest could be associated with lower nighttime pH and increased diurnal variability in seawater pCO2/pH. Finally, we highlight important areas for future research to inform the next steps for assessing the utility of this approach for management.

Continue reading ‘Reviews and syntheses: spatial and temporal patterns in metabolic fluxes inform potential for seagrass to locally mitigate ocean acidification’

				
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Ocean acidification in the IPCC AR5 WG II

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