Posts Tagged 'sediment'

Extinction, dissolution, and possible ocean acidification prior to the Cretaceous/Paleogene (K/Pg) boundary in the tropical Pacific

Biotic perturbations and changes in ocean circulation during the Maastrichtian stage of the latest Cretaceous raise questions about whether the biosphere was preconditioned for the end-Cretaceous mass extinction of calcareous plankton. A brief acme of inoceramid clams at ~ 71 Ma on Shatsky Rise in the tropical North Pacific was followed by their extinction during the “mid-Maastrichtian event” at 70.1 Ma associated with an abrupt warming of deep waters. This was later followed by an interval of intense dissolution beginning ~ 67.8 Ma at ODP Site 1209 (2387 m). The late Maastrichtian dissolution interval was initially gradual, and is characterized by a low planktic/benthic (P/B) ratio, highly fragmented planktic foraminifera, mostly an absence of larger taxa, low abundances of smaller taxa, extremely low planktic foraminiferal numbers, and low planktic foraminiferal and nannofossil species richness. A partial recovery in carbonate preservation and calcareous plankton simple diversity began ~ 250 kyr prior to the K/Pg boundary associated with the incursion of a younger (more enriched δ13C) deep water mass, although total abundances of planktic foraminifera in the sediment remained a tiny fraction of their earlier Maastrichtian values. A second, brief dissolution event occurred ~ 200 kyr before the boundary evidenced by renewed increase in planktic fragmentation, but without a decrease in P/B ratio. Our data show that changing deep water masses, coupled with reduced productivity and associated decrease in pelagic carbonate flux was responsible for the first ~ 1.6-Myr dissolution interval, while Deccan Traps volcanism (?) may have caused surface ocean acidification ~ 200 kyr prior to the K/Pg mass extinction event.

Continue reading ‘Extinction, dissolution, and possible ocean acidification prior to the Cretaceous/Paleogene (K/Pg) boundary in the tropical Pacific’

Calcium carbonate (CaCO3) sediment dissolution under elevated concentrations of carbon dioxide (CO2) and nitrate (NO3−)

Ocean acidification (OA), attributed to the sequestration of atmospheric carbon dioxide (CO2) into the surface ocean, and coastal eutrophication, attributed in part to land-use change and terrestrial runoff of fertilizers, have received recent attention in an experimental framework examining the effects of each on coral reef net ecosystem calcification (Gnet). However, OA and eutrophication in conjunction have yet to receive attention from the perspective of coral reef sediment dissolution. To address this omission, CO2 and nitrate (NO3−) addition experiments were performed in Mo’orea, French Polynesia. Incubation chambers were used to measure sediment Gnet during the day and night under three different [NO3−] (0, 9.8, and 19.7 μM) that were nested within four separate constructed coral reef communities maintained at different PCO2 levels (417, 721, 1030, and 1333 μatm, respectively). PCO2 negatively affected sediment Gnetduring the day and night, resulting in a shift to diel net dissolution at a PCO2 of 1030 μatm. Elevated NO3− alone, and the combination of NO3− and PCO2, both negatively affected sediment Gnet at night. However, the response of Gnet to NO3− was less clear during the day, where diurnal sediment Gnet was enhanced under the combined treatment of elevated NO3− and PCO2, resulting in no net effect of NO3− on sediment Gnet on diel timescales. Overall, these results show that ocean acidification represents a greater threat to the balance of calcification and dissolution in Mo’orea’s back reef sediment communities than the potential impact of NO3− enrichment on relatively short timescales.

Continue reading ‘Calcium carbonate (CaCO3) sediment dissolution under elevated concentrations of carbon dioxide (CO2) and nitrate (NO3−)’

Reef-building corals thrive within hot-acidified and deoxygenated waters

Coral reefs are deteriorating under climate change as oceans continue to warm and acidify and thermal anomalies grow in frequency and intensity. In vitro experiments are widely used to forecast reef-building coral health into the future, but often fail to account for the complex ecological and biogeochemical interactions that govern reefs. Consequently, observations from coral communities under naturally occurring extremes have become central for improved predictions of future reef form and function. Here, we present a semi-enclosed lagoon system in New Caledonia characterised by diel fluctuations of hot-deoxygenated water coupled with tidally driven persistently low pH, relative to neighbouring reefs. Coral communities within the lagoon system exhibited high richness (number of species = 20) and cover (24–35% across lagoon sites). Calcification rates for key species (Acropora formosa, Acropora pulchra, Coelastrea aspera and Porites lutea) for populations from the lagoon were equivalent to, or reduced by ca. 30–40% compared to those from the reef. Enhanced coral respiration, alongside high particulate organic content of the lagoon sediment, suggests acclimatisation to this trio of temperature, oxygen and pH changes through heterotrophic plasticity. This semi-enclosed lagoon therefore provides a novel system to understand coral acclimatisation to complex climatic scenarios and may serve as a reservoir of coral populations already resistant to extreme environmental conditions.

Continue reading ‘Reef-building corals thrive within hot-acidified and deoxygenated waters’

Estuarine sediment resuspension and acidification: Release behaviour of contaminants under different oxidation levels and acid sources

Carbon dioxide (CO2) Capture and Storage (CCS) is a technology to reduce the emissions of this gas to the atmosphere by sequestering it in geological formations. In the case of offshore storage, unexpected CO2 leakages will acidify the marine environment. Reductions of the pH might be also caused by anthropogenic activities or natural events such as acid spills and dredging operations or storms and floods. Changes in the pH of the marine environment will trigger the mobilisation of elements trapped in contaminated shallow sediments with unclear redox boundary. Trace element (As, Cd, Cr, Cu, Ni, Pb and Zn) release from anoxic and oxic estuarine sediment is analysed and modelled under different laboratory acidification conditions using HNO3 (l) and CO2 (g): acidification at pH = 6.5 as worst-case scenario in events of CO2 leakages and acid spills, and acidification at pH = 7.0 as a seawater scenario under CO2 leakages, acid spills, as well as sediment resuspension. The prediction of metal leaching behaviour appear to require sediment specific and site specific tools. In the present work it is demonstrated that the proposed three in-series reactions model predicts the process kinetics of the studied elements under different simulated environmental conditions (oxidation levels and acid sources). Differences between HNO3 and CO2 acidification are analysed through the influence of the CO2 gas on the ionic competition of the medium. The acidification with CO2 provokes higher released concentrations from the oxic sediment than from the anoxic sediment, except in the case of Zn, which influences the release of the other studied elements. Slight acidification can endanger the aquatic environment through an important mobilisation of contaminants. The obtained prediction of the contaminant release from sediment (kinetic parameters and maximum concentrations) can contribute to the exposure assessment stage for risk management and preincidental planning in accidental CO2 leakages and chemical spills scenarios.

Continue reading ‘Estuarine sediment resuspension and acidification: Release behaviour of contaminants under different oxidation levels and acid sources’

Deepwater carbonate ion concentrations in the western tropical Pacific since 250 ka: Evidence for oceanic carbon storage and global climate influence

We present new “size-normalized weight” (SNW)-Δ[CO32−] core-top calibrations for three planktonic foraminiferal species and assess their reliability as a paleo-alkalinity proxy. SNWs of Globigerina sacculifer and Neogloboquadrina dutertrei can be used to reconstruct past deep Pacific [CO32−], whereas SNWs of Pulleniatina obliquiloculata are controlled by additional environmental factors. Based on this methodological advance, we reconstruct SNW-based deepwater [CO32−] for core WP7 from the western tropical Pacific since 250 ka. Secular variation in the SNW proxy documents little change in deep Pacific [CO32−] between the Last Glacial Maximum and the Holocene. Further back in time, deepwater [CO32−] shows long-term increases from marine isotope stage (MIS) 5e to MIS 3 and from early MIS 7 to late MIS 6, consistent with the “coral reef hypothesis” that the deep Pacific Ocean carbonate system responded to declining shelf carbonate production during these two intervals. During deglaciations, we have evidence of [CO32−] peaks coincident with Terminations 2 and 3, which suggests that a breakdown of oceanic vertical stratification drove a net transfer of CO2 from the ocean to the atmosphere, causing spikes in carbonate preservation (i.e., the “deglacial ventilation hypothesis”). During MIS 4, a transient decline in SNW-based [CO32−], along with other reported [CO32−] and/or dissolution records, implies that increased deep-ocean carbon storage resulted in a global carbonate dissolution event. These findings provide new insights into the role of the deep Pacific in the global carbon cycle during the late Quaternary.

Continue reading ‘Deepwater carbonate ion concentrations in the western tropical Pacific since 250 ka: Evidence for oceanic carbon storage and global climate influence’

Benthic pH gradients across a range of shelf sea sediment types linked to sediment characteristics and seasonal variability

This study used microelectrodes to record pH profiles in fresh shelf sea sediment cores collected across a range of different sediment types within the Celtic Sea. Spatial and temporal variability was captured during repeated measurements in 2014 and 2015. Concurrently recorded oxygen microelectrode profiles and other sedimentary parameters provide a detailed context for interpretation of the pH data. Clear differences in profiles were observed between sediment type, location and season. Notably, very steep pH gradients exist within the surface sediments (10–20 mm), where decreases greater than 0.5 pH units were observed. Steep gradients were particularly apparent in fine cohesive sediments, less so in permeable sandier matrices. We hypothesise that the gradients are likely caused by aerobic organic matter respiration close to the sediment–water interface or oxidation of reduced species at the base of the oxic zone (NH4+, Mn2+, Fe2+, S−). Statistical analysis suggests the variability in the depth of the pH minima is controlled spatially by the oxygen penetration depth, and seasonally by the input and remineralisation of deposited organic phytodetritus. Below the pH minima the observed pH remained consistently low to maximum electrode penetration (ca. 60 mm), indicating an absence of sub-oxic processes generating H+ or balanced removal processes within this layer. Thus, a climatology of sediment surface porewater pH is provided against which to examine biogeochemical processes. This enhances our understanding of benthic pH processes, particularly in the context of human impacts, seabed integrity, and future climate changes, providing vital information for modelling benthic response under future climate scenarios.

Continue reading ‘Benthic pH gradients across a range of shelf sea sediment types linked to sediment characteristics and seasonal variability’

Elevated temperature has adverse effects on GABA-mediated avoidance behaviour to sediment acidification in a wide-ranging marine bivalve

Sediment acidification is known to influence the burrowing behaviour of juvenile marine bivalves. Unlike the alteration of behaviour by ocean acidification (OA) observed in many marine organisms, this burrowing response to present-day variation in sediment pH is likely adaptive in that it allows these organisms to avoid shell dissolution and mortality. However, the consequences of global climate stressors on these burrowing responses have yet to be tested. Further, while neurotransmitter interference appears to be linked to the alteration of behaviour by OA in marine vertebrates, the mechanism(s) controlling the burrowing responses of juvenile bivalves in response to present-day variation in sediment acidification remain unknown. We tested the interactive effects of elevated seawater temperature and sediment acidification on juvenile soft-shell clam burrowing behaviour (measured as the proportion of clams burrowed into sediment) to test for effects of elevated temperature on bivalve burrowing responses to sediment acidification. We also examined whether GABAA-like receptor interference could act as a potential biological mechanism underpinning the burrowing responses of these clams to present-day variation in sediment acidification. Results showed that both elevated temperature and gabazine administration reduced the proportion of clams that avoided burrowing into low pH sediment. These results suggest that CO2 effects on neurophysiology (GABAA receptors) can act to mediate adaptive behaviours in juvenile marine bivalves to elevated CO2, but that these behaviours may be adversely affected by elevated temperature.

Continue reading ‘Elevated temperature has adverse effects on GABA-mediated avoidance behaviour to sediment acidification in a wide-ranging marine bivalve’

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Ocean acidification in the IPCC AR5 WG II

OUP book