Posts Tagged 'chemistry'

Evidence for shelf acidification during the onset of the Paleocene‐Eocene Thermal Maximum

A transect of paleoshelf cores from Maryland and New Jersey contains an ~0.19 m to 1.61 m thick interval with reduced percentages of carbonate during the onset of the Paleocene‐Eocene Thermal Maximum (PETM). Outer paleoshelf cores are barren of nannofossils and correspond to two minor disconformities. Middle paleoshelf cores contain a mixture of samples devoid of nannofossils and those with rare specimens characterized by significant dissolution (i.e., etching). The magnitude of the decrease in carbonate cannot be explained by dilution by clastic material or dissolution resulting from the oxidation of organic matter during early diagenesis. The observed preservation pattern implies a shoaling of the calcite compensation depth (CCD) and lysocline to the middle shelf. This reduced carbonate interval is observed during the onset of the PETM on other continental margins raising the possibility that extreme shoaling of the CCD and lysocline was a global signal, which is more significant than in previous estimates for the PETM. An alternative scenario is that shoaling was restricted to the northwest Atlantic, enhanced by regional and local factors (eutrophication from rivers, microbial activity associated with warming) that exacerbated the impact of acidification on the shelf.
Continue reading ‘Evidence for shelf acidification during the onset of the Paleocene‐Eocene Thermal Maximum’

Rapid warming and salinity changes in the Gulf of Maine alter surface ocean carbonate parameters and hide ocean acidification

A profound warming event in the Gulf of Maine during the last decade has caused sea surface temperatures to rise to levels exceeding any earlier observations recorded in the region over the last 150 years. This event dramatically affected CO2 solubility and, in turn, the status of the sea surface carbonate system. When combined with the concomitant increase in sea surface salinity and assumed rapid equilibration of carbon dioxide across the air sea interface, thermodynamic forcing partially mitigated the effects of ocean acidification for pH, while raising the saturation index of aragonite (ΩARΩAR ) by an average of 0.14 U. Although the recent event is categorically extreme, we find that carbonate system parameters also respond to interannual and decadal variability in temperature and salinity, and that such phenomena can mask the expression of ocean acidification caused by increasing atmospheric carbon dioxide. An analysis of a 34-year salinity and SST time series (1981–2014) shows instances of 5–10 years anomalies in temperature and salinity that perturb the carbonate system to an extent greater than that expected from ocean acidification. Because such conditions are not uncommon in our time series, it is critical to understand processes controlling the carbonate system and how ecosystems with calcifying organisms respond to its rapidly changing conditions. It is also imperative that regional and global models used to estimate carbonate system trends carefully resolve variations in the physical processes that control CO2 concentrations in the surface ocean on timescales from episodic events to decades and longer.

Continue reading ‘Rapid warming and salinity changes in the Gulf of Maine alter surface ocean carbonate parameters and hide ocean acidification’

Seagrass and macrophyte mediated CO2 and CH4 dynamics in shallow coastal waters

Seagrass meadows are among the most important coastal/ marine ecosystems for long-term carbon storage and conditioning of coastal waters. A combined air-water flux of CO2 and CH4 from the seagrass meadows was studied for the first time from Asia’s largest brackish–water lagoon, Chilika, India. Ecosystem-based comparisons were carried out during two hydrologically different conditions of dry and wet seasons in the seagrass dominated southern sector (SS); macrophyte-dominated northern sector (NS); the largely un-vegetated central sector (CS) and the tidally active outer channel (OC) of the lagoon. The mean fluxes of CO2 from SS, NS, CS and OC were 9.8, 146.6, 48.4 and 33.0mM m-2d-1, and that of CH4 were 0.12, 0.11, 0.05 and 0.07mM m-2d-1, respectively. The net emissions (in terms of CO2 equivalents), considering the global warming potential of CO2 (GWP: 1) and CH4 (GWP: 28) from seagrass meadows were over 14 times lower compared to the macrophyte-dominated sector of the lagoon. Contrasting emissivity characteristics of CO2 and CH4 were observed between macrophytes and seagrass, with the former being a persistent source of CO2. It is inferred that although seagrass meadows act as a weak source of CH4, they could be effective sinks of CO2 if land-based pollution sources are minimized.

Continue reading ‘Seagrass and macrophyte mediated CO2 and CH4 dynamics in shallow coastal waters’

Energy metabolism and survival of the juvenile recruits of the American lobster (Homarus americanus) exposed to a gradient of elevated seawater pCO2

Highlights

• Responses were largely linear, traits being predictable across the pCO2 gradient.
• Oxygen consumption rates was not affected by elevated pCO2 levels.
• Exposure to elevated pCO2 increased mortality and intermoult period.
• Reduced aerobic capacity at high pCO2 suggested energy metabolism reorganisation.

Abstract

The transition from the last pelagic larval stage to the first benthic juvenile stage in the complex life cycle of marine invertebrates, such as the American lobster Homarus americanus, a species of high economic importance, represents a delicate phase in these species development. Under future elevated pCO2 conditions, ocean acidification and other elevated pCO2 events can negatively affect crustaceans. This said their effects on the benthic settlement phase are virtually unknown. This study aimed to identify the effects of elevated seawater pCO2 on stage V American lobsters exposed to seven pCO2 levels. The survival, development time, metabolic and feeding rates, carapace composition, and mitochondrial function were investigated. Results suggested an increase in mortality, slower development and a reduction in aerobic capacity with increasing pCO2. Our study points to potential reduction in juvenile recruitment success as seawater pCO2 increases, thus foreshadowing important socio-economic repercussions for the lobster fisheries and industry.

Continue reading ‘Energy metabolism and survival of the juvenile recruits of the American lobster (Homarus americanus) exposed to a gradient of elevated seawater pCO2’

Seasonal net ecosystem metabolism of the near-shore reef system in La Parguera, Puerto Rico

Changes in ocean chemistry as a direct response to rising atmospheric carbon dioxide (CO2) concentrations is causing a reduction of pH in the surface ocean. While the dynamics and trends in carbonate chemistry are reasonably constrained for open ocean waters, the ways in which ocean acidification (OA) manifests within the shallow near-shore waters, where coral reefs reside, is less understood. Constraining near-reef variability in carbonate chemistry and net ecosystem metabolic processes across diel, seasonal, and annual scales is important in evaluating potential biogeochemical thresholds of OA that could result in ecological community changes. The OA Test-Bed at La Parguera Marine Reserve in Puerto Rico provides long-term carbonate chemistry observations at high-temporal resolution within a Caribbean near-shore coral reef ecosystem. A 1-D model was developed using the carbon mass balance approach to yield information about net ecosystem production and calcification processes occurring in the water column adjacent to the reef. We present results of nine years of sustained monitoring at the Enrique mid-shelf forereef, which provides for the characterization of temporal dynamics in carbonate chemistry and net ecosystem metabolic processes encompassing near-shore and upstream locations. Results indicate that net heterotrophy and net dissolution dominate over most of the year, while net autotrophic conditions coupled with calcification dominated from only January to mid-April. The average carbonate dissolution rate observed during summer is estimated at −2.19g CaCO3m−2 day−1 and net community dissolution persists 76% of the seasonal year despite the water column remaining super-saturated with respect to aragonite. This corresponds to −0.62 kg CaCO3m−2 year−1, classifying the Enrique fore-reef and off-reef areas in a net dissolutional state. The combination of thermodynamically-driven depressed aragonite saturation state and high rates of respiration during the summer cause conditions that jeopardize the most soluble carbonate minerals and the free energy in the system for calcification. These data suggest that the reef area and associated ecosystems upstream of the sampling location are experiencing a net loss of CaCO3, possibly compromising coral ecosystem health and reef accretion processes necessary for maintenance as sea level increases. Resiliency from other climate-scale stressors including rising sea surface temperatures and coral bleaching is likely to be compromised in a system exhibiting net carbonate loss.

Continue reading ‘Seasonal net ecosystem metabolism of the near-shore reef system in La Parguera, Puerto Rico’

The carbonate system in coastal waters off the northern region of the Baja California Peninsula under La Niña conditions

In the North Pacific, variations in isopycnal depth influence the biogeochemical characteristics of the water column and the aragonite saturation horizon (ZΩa) during interannual events. The objective of this study was to assess the effect of the 2011 La Niña conditions on ZΩa in Todos Santos Bay (Baja California, Mexico) and surrounding waters. The results showed that ZΩa variability was modulated by the intensity of interannual conditions and by the water masses that were present in the region. Subarctic Water predominated in the upper 200 m with anomalous characteristics, such as low temperature and low salinity. Also, isopycnals shoaled toward the coast and ZΩa was thus ~30 min the nearshore area, in contrast with the oceanic region, where ZΩa was ~150 m. Prior to this study, there were no records of ZΩa in Todos Santos Bay, nor were there any records of its shallowness.

Continue reading ‘The carbonate system in coastal waters off the northern region of the Baja California Peninsula under La Niña conditions’

Primary production and calcification rates of algae‐dominated reef flat and seagrass communities

Monitoring variability in coral reef primary production and calcification is needed to understand changes over time and between reef systems, which helps separate differences due to natural and/or anthropogenic factors happening now and in the future. This study measured net productivity and calcification for two reef systems at Shark Bay, Heron Reef in the southern Great Barrier Reef and Saipan Lagoon, Commonwealth of the Northern Mariana Islands. Net primary productivity and calcification were strongly correlated for reef flats with an adjusted R2 = 0.66. Night time dissolution occurred at Shark Bay reef flat with an average of −12.66  mmol  CaCO3 · m−2 · hr−1, while calcification increased at night for the Saipan reef flat. For both reef flat sites, net productivity from oxygen flux was much lower than rates calculated from change in dissolved inorganic carbon. This study provided the first baseline estimates of net productivity and calcification for a reef flat and seagrass community in Saipan Lagoon. The seagrass community had the lowest productivity of all sites. However, the high presence of calcareous algae at the site highlights the need for more research on the carbonate chemistry of these habitats. All sites had high net productivity that was most likely associated with the dominant presence of algae. Continue reading ‘Primary production and calcification rates of algae‐dominated reef flat and seagrass communities’


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Ocean acidification in the IPCC AR5 WG II

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