Archive for December, 2016

Season’s greetings and all the best in the new year!


Will kelp forests provide refuges from ocean acidification?

Arctic kelp forests may provide safety from acidifying oceans during long summer days because of extended sunlight exposure.

Long periods of sunlight force big algae, like kelp, to trap more solar energy and absorb more carbon dioxide from the water through photosynthesis. This pushes pH levels upward and provides sea creatures with a less acidic environment.

According to an article in Science Advances, an international team of researchers observed an Arctic kelp patch in Greenland and discovered that the average pH rose from 8.09 to 8.24 in 10 days.

Continue reading ‘Will kelp forests provide refuges from ocean acidification?’

Nucleation and growth from a biomineralization perspective

Biomineralization processes occur ubiquitously through a heterogeneous nucleation process. This despite the fact that nucleation follows a classical or no classical, two-step, pathway. In addition, in mineralizing organisms, the growth process can also take place through a classical path wherein instead of addition of single ions to the growing crystal nuclei, amorphous nanoparticles that crystallize on the growing crystal nuclei are utilized. After many years of evolution, organisms have established diverse strategies that follow the above principles. The molecular and structural details of those processes are for many aspects still unknown. In this chapter, a few representative cases among the most studied biominerals are presented. The final section is devoted to a summary of selected recent studies on the effect of ocean acidification on the biomineral synthesis and features.

Continue reading ‘Nucleation and growth from a biomineralization perspective’

Sea surface pCO2 and O2 dynamics in the partially ice-covered Arctic Ocean

Understanding the physical and biogeochemical processes that control CO2 and dissolved oxygen (DO) dynamics in the Arctic Ocean (AO) is crucial for predicting future air-sea CO2 fluxes and ocean acidification. Past studies have primarily been conducted on the AO continental shelves during low-ice periods and we lack information on gas dynamics in the deep AO basins where ice typically inhibits contact with the atmosphere. To study these gas dynamics, in situ time-series data have been collected in the Canada Basin during late summer to autumn of 2012. Partial pressure of CO2 (pCO2), DO concentration, temperature, salinity, and chlorophyll-a fluorescence (Chl-a) were measured in the upper ocean in a range of sea ice states by two drifting instrument systems. Although the two systems were on average only 222 km apart, they experienced considerably different ice cover and external forcings during the 40-50 d periods when data were collected. The pCO2 levels at both locations were well below atmospheric saturation whereas DO was almost always slightly supersaturated. Modeling results suggest that air-sea gas exchange, net community production (NCP) and horizontal gradients were the main sources of pCO2 and DO variability in the sparsely ice-covered AO. In areas more densely covered by sea ice, horizontal gradients were the dominant source of variability, with no significant NCP in the surface mixed layer. If the AO reaches equilibrium with atmospheric CO2 as ice cover continues to decrease, aragonite saturation will drop from a present mean of 1.00 ± 0.02 to 0.86 ± 0.01.

Continue reading ‘Sea surface pCO2 and O2 dynamics in the partially ice-covered Arctic Ocean’

Diurnal fluctuations in acidification and hypoxia reduce the growth and survival of larval and juvenile bay scallops (Argopecten irradians) and hard clams (Mercenaria mercenaria)

Diurnal variations in pH and dissolved oxygen (DO) concentrations are common seasonal phenomena in many eutrophic estuaries, yet few studies have investigated the concurrent effects of low pH and low DO on marine organisms inhabiting these coastal systems. Here, we assess the effects of diurnal variations in pH and DO on the early-life history of two bivalve species native to Northeast US estuaries, the bay scallop (Argopecten irradians) and hard clam (Mercenaria mercenaria). In one set of experiments, larval- and juvenile-life stage bivalves were exposed to ambient conditions (pHT ~ 7.9), two continuously-low pH levels (pHT ~ 7.3 and 7.6), and diurnal fluctuations between the ambient and low conditions yielding mean pH levels equal to the intermediate pH levels. In a second set of experiments, larval bivalves were exposed to ambient conditions (pHT ~7.9, DO ~ 7 mg L-1), two levels of low pH and DO (pHT ~ 7.2, DO ~1 mg L-1; pHT ~7.4, DO ~ 4 mg L-1) and diurnal fluctuations of both pH and DO between the ambient and low pH/DO levels that resulted in mean pH and DO levels equal to the intermediate pH and DO levels. Diurnal acidification treatments with ambient DO levels yielded survival rates for both species at both life stages that were consistent with the survival of individuals exposed to the same mean level of chronic pH with juveniles being more resistant to acidification than larvae. In contrast, when both pH and DO varied diurnally, the survival rates of larval bivalves were significantly lower than the survival of individuals chronically exposed to the same mean levels of pH and DO, an indication that bivalves were physiologically more vulnerable to concurrent fluctuations of both parameters compared to acidification alone. While both species displayed sensitivities to diurnal fluctuations in pH and DO, scallops were relatively more susceptible than hard clams. Since many shallow eutrophic estuaries presently experience diurnal cycles of both pH and DO when early-life stages of bivalves are present in estuaries, the populations of the bivalves studied are likely impacted by these conditions which are likely to intensify with climate change.

Continue reading ‘Diurnal fluctuations in acidification and hypoxia reduce the growth and survival of larval and juvenile bay scallops (Argopecten irradians) and hard clams (Mercenaria mercenaria)’

Climate sensitivity and the rate of ocean acidification: future impacts, and implications for experimental design

The global mean surface temperature and partial pressure of carbon dioxide (CO2) are increasing both in the atmosphere and ocean. Oceanic CO2 uptake causes a decline in pH called ocean acidification (OA), which also alters other biologically important carbonate system variables such as carbonate mineral saturation states. Here, we discuss how a “temperature buffering” effect chemically links the rates of warming and OA at a more fundamental level than is often appreciated, meaning that seawater warming could mitigate some of the adverse biological impacts of OA. In a global mean sense, the rate of warming relative to the CO2 increase can be quantified by the climate sensitivity (CS), the exact value of which is uncertain. It may initially appear that a greater CS would therefore reduce the negative influence of OA. However, the dependence of the rate of CO2 increase on the CS could enhance, nullify or even reverse the temperature buffering effect, depending upon the future trajectory of anthropogenic CO2 emissions. Regional deviations from the global mean seawater temperature and CO2 uptake trends could modulate local responses to OA. For example, mitigation of OA impacts through temperature buffering could be particularly effective in the Arctic Ocean, where the surface seawater warming rate is greater than the global mean, and the aqueous CO2 concentration might increase more slowly than elsewhere. Some carbonate system variables are more strongly affected than others, highlighting the need to develop a mechanistic understanding of precisely which variables are important to each biogeochemical process. Temperature buffering of the marine carbonate system should be taken into account when designing experiments to determine marine species and ecosystem responses to warming and OA, in order that their results accurately reflect future conditions, and therefore can generate realistic predictions when applied to Earth system models.

Continue reading ‘Climate sensitivity and the rate of ocean acidification: future impacts, and implications for experimental design’

Development of an equatorial carbonate platform across the Triassic-Jurassic boundary and links to global palaeoenvironmental changes (Musandam Peninsula, UAE/Oman)

The Triassic-Jurassic boundary is marked by one of the ‘big five’ mass extinctions of the Phanerozoic. This boundary event was accompanied by several carbon cycle perturbations, potentially induced by the opening of the Central Atlantic and associated volcanism, and accompanied by an ocean acidification event. Continuous carbonate successions covering this interval of environmental change are however rare. Here data from a shallow-marine equatorial mixed carbonate-siliciclastic succession is presented, that was studied on a regional scale. Four sections that are 48 km apart were examined on the Musandam Peninsula (United Arab Emirates and Sultanate of Oman). The system was analysed for its sedimentology, vertical and lateral facies changes, and stable carbon and oxygen isotopes. Strontium isotope analysis was used to determine the position of the Triassic-Jurassic boundary horizon. The studied ramp experienced an episode of demise during the Late Triassic, followed by a restricted microbialite dominated ramp, containing large amounts of siliciclastic facies. During the Latest Triassic the diverse carbonate factory revived and flourished across the Triassic-Jurassic boundary. No clear evidence for a biocalcification crisis or an ocean acidification event across the Triassic-Jurassic boundary is visible. Lateral facies heterogeneities can be observed across the studied interval, attributed to hydrodynamic activity, including tropical storms, crossing the extensive shelf area. Although evidence for synsedimentary tectonic activity is present, the vertical stacking pattern is largely controlled by changes in relative sea level. The refined chronostratigraphy accompanied by the detailed environment of deposition analysis allows for a refinement of the regional palaeogeography. The neritic equatorial carbonate ramp has archived a negative carbon isotope excursion preceding the Triassic-Jurassic boundary that has also been reported from other study sites. The lack of evidence for a biocalcification crisis across the equatorial Triassic-Jurassic boundary indicates that the Tethys did not experience a distinct global acidification event.

Continue reading ‘Development of an equatorial carbonate platform across the Triassic-Jurassic boundary and links to global palaeoenvironmental changes (Musandam Peninsula, UAE/Oman)’

Putting temperature and oxygen thresholds of marine animals in context of environmental change: a regional perspective for the Scotian Shelf and Gulf of St. Lawrence

We conducted a literature review of reported temperature, salinity, pH, depth and oxygen preferences and thresholds of important marine species found in the Gulf of St. Lawrence and Scotian Shelf region. We classified 54 identified fishes and macroinvertebrates as important either because they support a commercial fishery, have threatened or at risk status, or meet one of the following criteria: bycatch, baitfish, invasive, vagrant, important for ecosystem energy transfer, or predators or prey of the above species. The compiled data allow an assessment of species-level impacts including physiological stress and mortality given predictions of future ocean physical and biogeochemical conditions. If an observed, multi-decadal oxygen trend on the central Scotian Shelf continues, a number of species will lose favorable oxygen conditions, experience oxygen-stress, or disappear due to insufficient oxygen in the coming half-century. Projected regional trends and natural variability are both large, and natural variability will act to alternately amplify and dampen anthropogenic changes. When estimates of variability are included with the trend, species encounter unfavourable oxygen conditions decades sooner. Finally, temperature and oxygen thresholds of adult Atlantic wolffish (Anarhichas lupus) and adult Atlantic cod (Gadus morhua) are assessed in the context of a potential future scenario derived from high-resolution ocean models for the central Scotian Shelf.

Continue reading ‘Putting temperature and oxygen thresholds of marine animals in context of environmental change: a regional perspective for the Scotian Shelf and Gulf of St. Lawrence’

Seawater pH predicted for the year 2100 affects the metabolic response to feeding in copepodites of the Arctic copepod Calanus glacialis

Widespread ocean acidification (OA) is transforming the chemistry of the global ocean, and the Arctic is recognised as a region where the earliest and strongest impacts of OA are expected. In the present study, metabolic effects of OA and its interaction with food availability was investigated in Calanus glacialis from the Kongsfjord, West Spitsbergen. We measured metabolic rates and RNA/DNA ratios (an indicator of biosynthesis) concurrently in fed and unfed individuals of copepodite stages CII-CIII and CV subjected to two different pH levels representative of present day and the “business as usual” IPCC scenario (RCP8.5) prediction for the year 2100. The copepods responded more strongly to changes in food level than to decreasing pH, both with respect to metabolic rate and RNA/DNA ratio. However, significant interactions between effects of pH and food level showed that effects of pH and food level act in synergy in copepodites of C. glacialis. While metabolic rates in copepodites stage CII-CIII increased by 78% as a response to food under present day conditions (high pH), the increase was 195% in CII-CIIIs kept at low pH—a 2.5 times greater increase. This interaction was absent for RNA/DNA, so the increase in metabolic rates were clearly not a reaction to changing biosynthesis at low pH per se but rather a reaction to increased metabolic costs per unit of biosynthesis. Interestingly, we did not observe this difference in costs of growth in stage CV. A 2.5 times increase in metabolic costs of growth will leave the copepodites with much less energy for growth. This may infer significant changes to the C. glacialis population during future OA.

Continue reading ‘Seawater pH predicted for the year 2100 affects the metabolic response to feeding in copepodites of the Arctic copepod Calanus glacialis’

Coral responses to anthropogenic stress in the twenty-first century: an ecophysiological perspective

The number of ecophysiological studies involving reef corals has increased markedly over the last 20 years, driven primarily by the concern over the potential effects of anthropogenic change on coral communities. In particular, the evaluation of the effects of global climate change has prompted major research efforts into understanding the consequences of both rising seawater temperatures and ocean acidification on the physiology of corals.

Continue reading ‘Coral responses to anthropogenic stress in the twenty-first century: an ecophysiological perspective’

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Ocean acidification in the IPCC AR5 WG II

OUP book