Archive for February, 2013

Sea change: charting the course for biogeochemical ocean time-series research in a new millennium

Ocean time-series provide vital information needed for assessing ecosystem change. This paper summarizes the historical context, major program objectives, and future research priorities for three contemporary ocean time-series programs: The Hawaii Ocean Time-series (HOT), the Bermuda Atlantic Time-series Study (BATS), and the CARIACO Ocean Time-Series. These three programs operate in physically and biogeochemically distinct regions of the world’s oceans, with HOT and BATS located in the open-ocean waters of the subtropical North Pacific and North Atlantic, respectively, and CARIACO situated in the anoxic Cariaco Basin of the tropical Atlantic. All three programs sustain near-monthly shipboard occupations of their field sampling sites, with HOT and BATS beginning in 1988, and CARIACO initiated in 1996. The resulting data provide some of the only multi-disciplinary, decadal-scale determinations of time-varying ecosystem change in the global ocean. Facilitated by a scoping workshop (September 2010) sponsored by the Ocean Carbon Biogeochemistry (OCB) program, leaders of these time-series programs sought community input on existing program strengths and for future research directions. Themes that emerged from these discussions included:

1. Shipboard time-series programs are key to informing our understanding of the connectivity between changes in ocean-climate and biogeochemistry.

2. The scientific and logistical support provided by shipboard time-series programs forms the backbone for numerous research and education programs. Future studies should be encouraged that seek mechanistic understanding of ecological interactions underlying the biogeochemical dynamics at these sites.

3. Detecting time-varying trends in ocean properties and processes requires consistent, high-quality measurements. Time-series must carefully document analytical procedures and, where possible, trace the accuracy of analyses to certified standards and internal reference materials.

4. Leveraged implementation, testing, and validation of autonomous and remote observing technologies at time-series sites provide new insights into spatiotemporal variability underlying ecosystem changes.

5. The value of existing time-series data for formulating and validating ecosystem models should be promoted.

In summary, the scientific underpinnings of ocean time-series programs remain as strong and important today as when these programs were initiated. The emerging data inform our knowledge of the ocean’s biogeochemistry and ecology, and improve our predictive capacity about planetary change.

Continue reading ‘Sea change: charting the course for biogeochemical ocean time-series research in a new millennium’

Palaeontology: plankton in a greenhouse world

The Palaeocene–Eocene Thermal Maximum was marked by global warming and ocean acidification. Fossil and experimental analyses show that different species of marine calcifying algae responded very differently to the environmental upheavals.

Continue reading ‘Palaeontology: plankton in a greenhouse world’

Biological oceanography: plastic plankton prosper

Phytoplankton support most marine food webs, but little is known about their intraspecific diversity. Research shows the strains that are most responsive to changes in CO2 concentration may outcompete less flexible types in an acidifying ocean.

Continue reading ‘Biological oceanography: plastic plankton prosper’

Metabolic shifts in the Antarctic fish Notothenia rossii in response to rising temperature and PCO2

Introduction

Ongoing ocean warming and acidification increasingly affect marine ecosystems, in particular around the Antarctic Peninsula. Yet little is known about the capability of Antarctic notothenioid fish to cope with rising temperature in acidifying seawater. While the whole animal level is expected to be more sensitive towards hypercapnia and temperature, the basis of thermal tolerance is set at the cellular level, with a putative key role for mitochondria. This study therefore investigates the physiological responses of the Antarctic Notothenia rossii after long-term acclimation to increased temperatures (7°C) and elevated PCO2 (0.2 kPa CO2) at different levels of physiological organisation.

Results

For an integrated picture, we analysed the acclimation capacities of N. rossii by measuring routine metabolic rate (RMR), mitochondrial capacities (state III respiration) as well as intra- and extracellular acid–base status during acute thermal challenges and after long-term acclimation to changing temperature and hypercapnia. RMR was partially compensated during warm- acclimation (decreased below the rate observed after acute warming), while elevated PCO2 had no effect on cold or warm acclimated RMR. Mitochondrial state III respiration was unaffected by temperature acclimation but depressed in cold and warm hypercapnia-acclimated fish. In both cold- and warm-exposed N. rossii, hypercapnia acclimation resulted in a shift of extracellular pH (pHe) towards more alkaline values. A similar overcompensation was visible in muscle intracellular pH (pHi). pHi in liver displayed a slight acidosis after warm normo- or hypercapnia acclimation, nevertheless, long-term exposure to higher PCO2 was compensated for by intracellular bicarbonate accumulation.

Conclusion

The partial warm compensation in whole animal metabolic rate indicates beginning limitations in tissue oxygen supply after warm-acclimation of N. rossii. Compensatory mechanisms of the reduced mitochondrial capacities under chronic hypercapnia may include a new metabolic equilibrium to meet the elevated energy demand for acid–base regulation. New set points of acid–base regulation under hypercapnia, visible at the systemic and intracellular level, indicate that N. rossii can at least in part acclimate to ocean warming and acidification. It remains open whether the reduced capacities of mitochondrial energy metabolism are adaptive or would impair population fitness over longer timescales under chronically elevated temperature and PCO2.

Continue reading ‘Metabolic shifts in the Antarctic fish Notothenia rossii in response to rising temperature and PCO2’

Functional diversity and climate change: effects on the invasibility of macroalgal assemblages

Climate-driven and biodiversity effects on the structure and functioning of ecosystems are increasingly studied as multiple stressors, which subsequently may influence species invasions. We used a mesocosm experiment to test how increases in temperature and CO2 partial pressure (pCO2) interact with functional diversity of resident macroalgal assemblages and affect the invasion success of the non-indigenous macroalga Sargassum muticum. Early settlement of S. muticum germlings was assessed in the laboratory under common environmental conditions across three monocultures and a polyculture of functional groups of native macroalgae, which had previously grown for 3 weeks under crossed treatments of temperature and pCO2. Functional diversity was a key driver shaping early settlement of the invader, with significant identity and richness effects: higher settlement occurred in low-diversity and low-stature assemblages, even after accounting for treatment biomass. Overall, early survivorship of settled germlings responded to an interaction of temperature and pCO2 treatments, with survivorship enhanced in one treatment (high pCO2 at ambient Temperature) after 3 days, and reduced in another (ambient pCO2 at high Temperature) after 10 days, although size was enhanced in this same treatment. After 6 months in the field, legacy effects of laboratory treatments remained, with S. muticum reaching higher cover in most assemblages previously subjected to ambient pCO2, but ephemeral green algae appearing disproportionately after elevated-pCO2 treatment. These results caution that invasion outcomes may change at multiple points in the life cycle under higher-CO2, higher-temperature conditions, in addition to supporting a role for intact, functionally diverse assemblages in limiting invader colonization.

Continue reading ‘Functional diversity and climate change: effects on the invasibility of macroalgal assemblages’

Aquatic life in a warmer and higher CO2 world – session at SEB Valencia 2013

Dates: 4 July (all day)
Organised by: Rod Wilson (University of Exeter), Fredrik Jutfelt (University of Gothenburg)
Confirmed Speakers: Phil Munday (James Cook University, Australia), Goran Nilsson (University of Oslo), Hans Otto Poertner (Alfred Wegener Institute), Frank Melzner (GEOMAR Helmholtz Centre for Ocean Research Kiel)

Continue reading ‘Aquatic life in a warmer and higher CO2 world – session at SEB Valencia 2013’

The Paul G. Allen Ocean Challenge: mitigating acidification impacts

Submission deadline: 31 July 2013

The problem Over the last 150 years, atmospheric carbon dioxide has increased from 290 ppm to 395 ppm, primarily due to the burning of fossil fuels. Ocean acidification is occurring because the world’s oceans, as a primary sink for atmospheric carbon dioxide, are absorbing increasing amounts of CO2, resulting in a lower pH. Ocean acidification, together with changes in ocean temperature, salinity, and stratification, is altering the fundamental chemical balance of ocean and coastal waters, impacting the global ocean ecosystem, and potentially threatening marine food supplies.

The challenge The Paul G. Allen Family Foundation, as part of a larger ocean health initiative, and in collaboration with The Oceanography Society, is offering a $10,000 prize for the most promising new science-based concept for mitigating environmental and/or societal impacts of ocean acidification.

Continue reading ‘The Paul G. Allen Ocean Challenge: mitigating acidification impacts’

Multiple stressors of ocean ecosystems in the 21st century: projections with CMIP5 models

Ocean ecosystems are increasingly stressed by human-induced changes of their physical, chemical and biological environment. Among these changes, warming, acidification, deoxygenation and changes in primary productivity by marine phytoplankton can be considered as four of the major stressors of open ocean ecosystems. Due to rising atmospheric CO2 in the coming decades, these changes will be amplified. Here, we use the most recent simulations performed in the framework of the Coupled Model Intercomparison Project 5 to assess how these stressors may evolve over the course of the 21st century. The 10 Earth System Models used here project similar trends in ocean warming, acidification, deoxygenation and reduced primary productivity for each of the IPCC’s representative concentration parthways (RCP) over the 21st century. For the “business-as-usual” scenario RCP8.5, the model-mean changes in 2090s (compared to 1990s) for sea surface temperature, sea surface pH, global O2 content and integrated primary productivity amount to +2.73 °C, −0.33 pH unit, −3.45% and −8.6%, respectively. For the high mitigation scenario RCP2.6, corresponding changes are +0.71 °C, −0.07 pH unit, −1.81% and −2.0% respectively, illustrating the effectiveness of extreme mitigation strategies. Although these stressors operate globally, they display distinct regional patterns. Large decreases in O2 and in pH are simulated in global ocean intermediate and mode waters, whereas large reductions in primary production are simulated in the tropics and in the North Atlantic. Although temperature and pH projections are robust across models, the same does not hold for projections of sub-surface O2 concentrations in the tropics and global and regional changes in net primary productivity.

Continue reading ‘Multiple stressors of ocean ecosystems in the 21st century: projections with CMIP5 models’

Light availability determines susceptibility of reef building corals to ocean acidification

Elevated seawater pCO2, and in turn ocean acidification (OA), is now widely acknowledged to reduce calcification and growth of reef building corals. As with other environmental factors (e.g., temperature and nutrients), light availability fundamentally regulates calcification and is predicted to change for future reef environments alongside elevated pCO2 via altered physical processes (e.g., sea level rise and turbidity); however, any potential role of light in regulating the OA-induced reduction of calcification is still unknown. We employed a multifactorial growth experiment to determine how light intensity and pCO2 together modify calcification for model coral species from two key genera, Acropora horrida and Porites cylindrica, occupying similar ecological niches but with different physiologies. We show that elevated pCO2 (OA)-induced losses of calcification in the light (G L) but not darkness (G D) were greatest under low-light growth conditions, in particular for A. horrida. High-light growth conditions therefore dampened the impact of OA upon G L but not G D. Gross photosynthesis (P G) responded in a reciprocal manner to G L suggesting OA-relieved pCO2 limitation of P G under high-light growth conditions to effectively enhance G L. A multivariate analysis of past OA experiments was used to evaluate whether our test species responses were more widely applicable across their respective genera. Indeed, the light intensity for growth was identified as a significant factor influencing the OA-induced decline of calcification for species of Acropora but not Porites. Whereas low-light conditions can provide a refuge for hard corals from thermal and light stress, our study suggests that lower light availability will potentially increase the susceptibility of key coral species to OA.

Continue reading ‘Light availability determines susceptibility of reef building corals to ocean acidification’

Ocean acidification

The oceans play a central role in the maintenance of life on Earth. Oceans provide extensive ecosystems for marine animals and plants covering two-thirds of the Earth’s surface, are essential sources of food, economic activity, and biodiversity, and are central to the global biogeochemical cycles. The oceans are the largest reservoir of carbon in the Planet, and absorb approximately one-third of the carbon emissions that are released to the Earth’s atmosphere as a result of human activities. Since the beginning of industrialization, humans have been responsible for the increase in one greenhouse gas, carbon dioxide (CO2), from approximately 280 parts per million (ppm) at the end of the nineteenth century to the current levels of 390ppm. As well as affecting the surface ocean pH, and the organisms living at the ocean surface, these increases in CO2 are causing global mean surface temperatures to rise.

Continue reading ‘Ocean acidification’


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