Archive for February, 2020

Freshening of the western Arctic negates anthropogenic carbon uptake potential

As human activities increase the atmospheric concentration of carbon dioxide (CO2), the oceans are known to absorb a significant portion. The Arctic Ocean has long been considered to have enormous potential to sequester anthropogenic CO2, and mitigate emissions. The frigid waters make CO2 more soluble, and as sea ice melts, greater surface area is exposed to absorb CO2. However, sparse data have made quantifying the amount of anthropogenic CO2 in the Arctic difficult, stimulating much debate over the basin’s contribution to CO2 sequestration from the atmosphere. Using three separate cruises in 1994, 2005, and 2015 in the Canada and Makarov basins, we analyze the decadal variability in anthropogenic CO2 uptake in the central western Arctic. Here we show, from direct carbon system measurements spanning two decades, that despite increased atmospheric CO2, total dissolved inorganic carbon has actually decreased, with minimal anthropogenic CO2 uptake. The reduction in dissolved CO2 results from a dilution of total alkalinity by increased freshwater supply, particularly river water. Changes in the freshwater budget of the western Arctic override its uptake potential, resulting in a weak sink, or possibly source of CO2.

Continue reading ‘Freshening of the western Arctic negates anthropogenic carbon uptake potential’

The UN Convention on the Law of the Sea: a governing framework for ocean acidification?

Ocean acidification is a major emergent threat to the ocean, its wildlife and the goods and services they provide. While the international community has committed to ‘minimize and address’ ocean acidification as part of the Sustainable Development Goals, it is unclear how this is to be fulfilled, especially as there are no international agreements explicitly designed to tackle this issue. Ocean acidification is of relevance to the work of several global agreements and makes achieving their goals more difficult. Being largely sectoral, these agreements are restricted in their ability to address ocean acidification holistically, often unable to both minimize and address the issue. This has resulted in a very limited response to ocean acidification that is fragmented across a number of regimes. The 1982 United Nations Convention on the Law of the Sea (UNCLOS) has been identified as an agreement that could be used to regulate carbon dioxide emissions and thus mitigate ocean acidification. However, this article argues that a far more pivotal role can be played by UNCLOS, through its creation of a governing framework for ocean acidification. UNCLOS is the one Convention with a mandate broad enough to address ocean acidification in a direct, holistic manner. UNCLOS places a duty on States to both minimize and address ocean acidification through its various provisions that pertain to the protection and preservation of the marine environment and the conservation of marine living resources. The Convention establishes the framework through which ocean governance is to be implemented, which should be understood as extending to ocean acidification. Thus, UNCLOS is uniquely placed to guide a coherent international response.

Continue reading ‘The UN Convention on the Law of the Sea: a governing framework for ocean acidification?’

Southern oyster growers feeling impacts of climate change

Oyster growers say the delicate environment that shellfish need to thrive is being disrupted by climate change. (Adobe Stock)

Oyster growers say the delicate environment that shellfish need to thrive is being disrupted by climate change.

WILMINGTON, N.C. — Oyster farmers are grappling with rising seas, ocean acidification, and more severe storms. They met in Wilmington over the weekend to discuss how to address these growing challenges.

One of the goals at the Oyster South Symposium was to brainstorm ways to deal with the impacts of climate change. Andy DePaola is a small-scale oyster farmer in Mobile Bay, Alabama. He said more frequent, heavy rains are flushing pathogens and fertilizer into waterways flowing into the bay, contaminating oyster habitat.

“Right now, we’re closed on bacterial counts. And last year, I was only open about one week between the beginning of the year and say, May,” DePaola said. “So, it’s very hard, you know, to maintain an operation for your cash flow and everything when you’re closed for months at a time. It’s really challenging.”

Continue reading ‘Southern oyster growers feeling impacts of climate change’

Elevated pCO2 and hypoxia alter the acid-base regulation of developing sheepshead minnows Cyprinodon variegatus

Lowered dissolved oxygen and pH levels are 2 environmental variables that concomitantly change in an estuarine environment and both are exacerbated by nutrient pollution and subsequent eutrophication. To better understand how estuarine residents compensate for daily fluctuations in these environmental variables, the interactive effects of elevated partial pressure of CO2 ( pCO2) and hypoxia were assessed in developing sheepshead minnows Cyprinodon variegatus using a 2 by 2 factorial design over a 42 d exposure. Embryos were exposed to either acidic ( pCO2: ~2000 µatm), hypoxic (reduced dissolved oxygen, ~2 mg l-1), or combined acidic and hypoxic conditions and monitored for development, hatch rate, and survival. Measurements of anaerobic pathway use, oxidative stress, and acid-base regulatory enzymes were evaluated at 3 life stages (embryo, larva, and juvenile) to discern if and how fish compensate for these stressors during development. The combination of elevated pCO2 and hypoxia delayed hatching in embryos but did not impact survival. Neither elevated pCO2, hypoxia, nor the combination of the stressors elicited an increase in anaerobic metabolic pathways or impacted oxidative stress of juvenile fish. Measurements of enzymes related to acid-base regulation were elevated in all 3 treatments in larval fish. Elevated carbonic anhydrase activity was observed in the multi-stress treatment in embryos and larval fish, but not in juvenile fish. These results show that developing sheepshead minnows can compensate for acidified and hypoxic waters.

Continue reading ‘Elevated pCO2 and hypoxia alter the acid-base regulation of developing sheepshead minnows Cyprinodon variegatus’

The challenge of scaling up from individual physiology to population level effects: using the Dynamic Energy Budget to describe and predict crustacean responses to climate variability

Predicting how marine communities will be affected by environmental change is one of the most significant challenges facing researchers today. In order to tackle this challenge, a mechanistic understanding of climate impacts at the individual level is necessary, as variations in species physiological responses are often reflected in patterns at higher organisational levels such as populations and communities. In order to explore the relationship between individual physiology and higher-level dynamics more fully, the swimming crab Liocarcinus depurator (Linnaeus, 1758) was selected as a model species for experimental work in which whole organism responses (growth, respiration and allocation to reproduction) to climate drivers were investigated using a bio-energetic modelling approach. This species was selected as a model organism after analysis of epibenthic time-series from the Western English Channel monitoring Station L4 revealed that decapod crustaceans played a key role in structuring the benthic community, and that L. depurator was one of the most dominant species in the area, in terms of both abundance and biomass. A bio-energetic approach was used as the same time-series analysis identified water temperature and seasonal phytodetrital input (e.g. food) as the predominant drivers of variation in benthic community wet biomass at L4, with the two drivers appearing to primarily influence community biomass at different times of the year. It is possible that warmer water temperatures in the autumn trigger gonad development and a consequent increase in reproductive biomass, while the sedimentation of the spring phytoplankton bloom drives an increase in somatic biomass. This time-series analysis clearly highlighted the role of organism energetics, and the environmental conditions that influence energy allocation, in structuring benthic communities. Further work elucidated the relationship between environmental variables and individual energy budgets. L. depurator responses to climate drivers (temperature, hypoxia and ocean acidification) were tested experimentally, and a mechanistic Dynamic Energy Budget (DEB) model was parameterised to describe the life history characteristics of crustaceans. At an individual level the model was able to accurately describe and predict observed responses to environmental drivers, both in isolation and in multiple stressor scenarios. Experimental results suggested that L. depurator was broadly tolerant of those climate drivers tested in the short term. Over the longer term however, model scenarios suggested that OA and the combined stressors may have an adverse effect on growth. When the multi-stressor model was forced with environmental projections from a coupled hydrodynamic-biogeochemical model (NEMO-ERSEM), it could be used to make predictions regarding ultimate carbon mass, age-at-maturity and cumulative allocation to reproduction, which were used to infer possible population level effects such as species distributions and population viability. Model scenarios suggested that, in the future, the optimum settlement time for juvenile L. depurator would shift forward across the north-west European shelf, and that this crustacean species may be able to expand its range further into the northern North Sea. The DEB model presented here can provide a mechanistic underpinning of observed species responses to climate drivers, and more broadly, the thesis demonstrates how multi-stressor models can be built from data collected in single stressor experiments, thereby providing a way of synthesising single stressor data into a modelling environment. This approach allows us to simulate more complex, ecologically relevant conditions. At a broader scale, the coupled DEB-ERSEM model showed that it can provide insight into why changes in species’ distributions are predicted, as these distributions are an emergent property of the processes being modelled.

Continue reading ‘The challenge of scaling up from individual physiology to population level effects: using the Dynamic Energy Budget to describe and predict crustacean responses to climate variability’

Climate science for the classroom: ocean acidification and oysters

This module provides a hands-on learning activity where students analyze real-world data to explain how ocean acidification is affecting the oyster aquaculture industry in the Pacific Northwest. Students learn how seawater chemistry affects organisms’ ability to build shells, as well as how short-term variability and long-term changes influence seawater chemistry. The module is designed so that it can be used as an extension to supplement existing ocean acidification teaching resources or as a stand-alone unit for students with no prior exposure to ocean acidification. The module is focused around the question of what is controlling the ability to successfully raise oyster larvae at the Whiskey Creek Hatchery in Netarts Bay, Oregon, which students investigate through guided analysis of real scientific data using Microsoft Excel.

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Recruits of the temperate coral Oculina arbuscula mimic adults in their resilience to ocean acidification

Ocean acidification has been investigated extensively in scleractinian corals, but studies on different life stages of the same species are lacking. We investigated the response of recruits of the temperate coral Oculina arbuscula to increased CO2 concentrations, a species whose adults show significant tolerance to elevated concentrations of CO2. Specifically, we exposed small colonies (5-12 mm diameter) to 475, 710, and 1261 ppm CO2 for 75 d in the laboratory to address the hypothesis that, like adults, the health of O. arbuscula recruits is not affected by increased CO2 concentrations. Calcification rates were monitored regularly during the experiment, while mortality, respiration rates, photosynthetic rates, algal symbiont densities, and soluble protein were quantified at the end. As predicted, CO2 concentration did not impact survival, algal densities, or soluble protein concentrations in O. arbuscula recruits. In contrast, both calcification rates and photosynthesis:respiration ratios tended to be lower at higher CO2. Comparing the results of this study on recruits with published studies on adults suggested that both life stages exhibit a similar non-linear response to CO2 concentration, whereby recruits may be unable to counter the increased energetic cost of calcification that occurs at the highest CO2. Based on these results and environmental monitoring showing that mean pCO2 is increasing by ~2.4% yr-1 in the waters off Georgia, USA, we conclude that O. arbuscula recruits may begin to exhibit depressed calcification rates within the current century if CO2 emissions are not reduced.

Continue reading ‘Recruits of the temperate coral Oculina arbuscula mimic adults in their resilience to ocean acidification’

Ocean acidification threatens livelihoods and lives. Can anyone be held accountable?

brown coral reef in the oceanNew research links carbon emissions from the major oil and gas producers to dangerous changes in the oceans’ chemistry

A change is brewing in our world’s oceans: waters are warming and becoming more acidic. The long-term effects of these changes could be ruinous for marine life worldwide, and for the people who depend on it for their food and income. The effects of warming and acidification—among other climate-related impacts on our oceans—are already being felt in some regions, as fish populations migrate, and corals die en masse. Who is responsible for these and future damages? And how can they pay for what they’ve done?

Continue reading ‘Ocean acidification threatens livelihoods and lives. Can anyone be held accountable?’

Combined effects of temperature, irradiance and pH on Teleaulax amphioxeia (Cryptophyceae) physiology and feeding ratio for its predator Mesodinium rubrum (Ciliophora)

The cryptophyte Teleaulax amphioxeia is a source of plastids for the ciliate Mesodinium rubrum and both organisms are members of the trophic chain of several species of Dinophysis. It is important to better understand the ecology of organisms at the first trophic levels before assessing the impact of principal factors of global change on Dinophysis spp. Therefore, combined effects of temperature, irradiance and pH on growth rate, photosynthetic activity and pigment content of a temperate strain of T. amphioxeia were studied using a full factorial design (central composite design 23*) in 17 individually controlled bioreactors. The derived model predicted an optimal growth rate of T. amphioxeia at a light intensity of 400 µmol photons · m‐2 · s‐1, more acidic pH (7.6) than the current average and a temperature of 17.6°C. An interaction between temperature and irradiance on growth was also found, while pH did not have any significant effect. Subsequently, to investigate potential impacts of prey quality and quantity on the physiology of the predator, M. rubrum was fed two separate prey: predator ratios with cultures of T. amphioxeia previously acclimated at two different light intensities (100 and 400 µmol photons · m‐2 · s‐1). M. rubrum growth appeared to be significantly dependant on prey quantity while effect of prey quality was not observed. This multi‐parametric study indicated a high potential for a significant increase of T. amphioxeia in future climate conditions but to what extent this would lead to increased occurrences of Mesodinium spp. and Dinophysis spp. should be further investigated.

Continue reading ‘Combined effects of temperature, irradiance and pH on Teleaulax amphioxeia (Cryptophyceae) physiology and feeding ratio for its predator Mesodinium rubrum (Ciliophora)’

An important biogeochemical link between organic and inorganic carbon cycling: effects of organic alkalinity on carbonate chemistry in coastal waters influenced by intertidal salt marshes

Dissolved organic carbon (DOC) contains organic acid charge groups that contribute organic alkalinity (OrgAlk) to total alkalinity (TA). These effects are often ignored or treated as a calculation uncertainty in many aquatic CO2 studies. This study evaluated OrgAlk variability, sources, and characteristics in estuarine waters exchanged tidally with a groundwater-influenced salt marsh in the northeast USA. OrgAlk provided a biogeochemical link between organic and inorganic carbon cycling through its direct effects on pH, and thus CO2 system speciation and buffer capacity. Two main charge groups were identified including carboxylic and phenolic or amine groups. Terrestrial groundwater and in-situ production within salt marsh peat contributed OrgAlk to the tidal creek, with the former being a more significant source. Groundwater entering the marsh complex contained exceptionally high OrgAlk (> 150 µmol kg-1), and these compounds were preferentially preserved within the DOC pool during groundwater transport and mixing with coastal water. OrgAlk:DOC ratios in groundwater and marsh-influenced water varied across space and time. This highlights the insufficiency of using a fixed proportion of DOC to account for organic acid charge groups. Accounting for OrgAlk altered H+ concentrations by ∼ 1 – 41 nmol kg-1 (equivalent to a pH change of ∼ 0.03 – 0.26), pCO2 by ∼ 30 – 1600 μatm and buffer capacity by ∼ 0.00 – 0.14 mmol kg-1 at the relative OrgAlk contributions of 0.9 – 4.3% of TA observed in the marsh-influenced tidal water. Thus, OrgAlk may have a significant influence on coastal inorganic carbon cycling. Further theoretical calculations confirm that these concentrations of OrgAlk would have sizable impacts on both carbonate speciation and, ultimately, air-sea CO2 fluxes in different coastal environments, ranging from estuarine to shelf waters. A new conceptual model linking organic and inorganic carbon cycling for coastal waters is proposed to highlight the sources and sinks of organic acid charge groups, as well as their biogeochemical behaviors and mechanistic control on the CO2 system.

Continue reading ‘An important biogeochemical link between organic and inorganic carbon cycling: effects of organic alkalinity on carbonate chemistry in coastal waters influenced by intertidal salt marshes’

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Ocean acidification in the IPCC AR5 WG II

OUP book