Posts Tagged 'chemistry'

Pteropods make thinner shells in the upwelling region of the California Current ecosystem

Shelled pteropods are widely regarded as bioindicators for ocean acidification, because their fragile aragonite shells are susceptible to increasing ocean acidity. While short-term incubations have demonstrated that pteropod calcification is negatively impacted by ocean acidification, we know little about net calcification in response to varying ocean conditions in natural populations. Here, we examine in situ calcification of Limacina helicina pteropods collected from the California Current Ecosystem, a coastal upwelling system with strong spatial gradients in ocean carbonate chemistry, dissolved oxygen and temperature. Depth-averaged pH ranged from 8.03 in warmer offshore waters to 7.77 in cold CO2-rich waters nearshore. Based on high-resolution micro-CT technology, we showed that shell thickness declined by ~ 37% along the upwelling gradient from offshore to nearshore water. Dissolution marks covered only ~ 2% of the shell surface area and were not associated with the observed variation in shell thickness. We thus infer that pteropods make thinner shells where upwelling brings more acidified and colder waters to the surface. Probably the thinner shells do not result from enhanced dissolution, but are due to a decline in calcification. Reduced calcification of pteropods is likely to have major ecological and biogeochemical implications for the cycling of calcium carbonate in the oceans.

Continue reading ‘Pteropods make thinner shells in the upwelling region of the California Current ecosystem’

Stable Ca and Sr isotopes support volcanically triggered biocalcification crisis during Oceanic Anoxic Event 1a

Large igneous province (LIP) eruptions are hypothesized to trigger biocalcification crises. The Aptian nannoconid crisis, which correlates with emplacement of the Ontong Java Plateau and Oceanic Anoxic Event 1a (OAE 1a, ca. 120 Ma), represents one such example. The Ca isotope (δ44/40Ca) system offers potential to detect biocalcification fluctuations in the rock record because Ca isotope fractionation is sensitive to precipitation rate. However, other primary and secondary processes, such as input-output flux perturbations and early diagenesis, can produce similar signals. Here, we exploit emergent properties of the stable Sr isotope (δ88/86Sr) system to resolve the origin of δ44/40Ca variability during OAE 1a. This study reports high-precision thermal ionization mass spectrometry (TIMS) δ44/40Ca, δ88/86Sr, and 87Sr/86Sr records for Hole 866A of Ocean Drilling Program Leg 143 drilled in Resolution Guyot, mid-Pacific Ocean. The samples span ~27 m.y. from the Barremian (ca. 127 Ma) to the Albian (ca. 100 Ma). The δ44/40Ca and δ88/86Sr secular trends differ from the 87Sr/86Sr record but mimic each other. δ44/40Ca and [Sr], as well as δ44/40Ca and δ88/86Sr, strongly correlate and yield slopes predicted for kinetic control, which demonstrates that variable mass-dependent fractionation rather than end-member mixing dominated the isotopic relationship between carbonates and seawater. Positive δ44/40Ca and δ88/86Sr shifts that begin before OAE 1a and peak within the interval are consistent with reduced precipitation rates. All results combined point to a cascade of effects on rate-dependent Ca and Sr isotope fractionation, which derive from the dynamic interplay between LIP eruptions and biocalcification feedbacks.

Continue reading ‘Stable Ca and Sr isotopes support volcanically triggered biocalcification crisis during Oceanic Anoxic Event 1a’

Autonomous in situ calibration of ion‐sensitive field effect transistor pH sensors

Ion‐sensitive field effect transistor‐based pH sensors have been shown to perform well in high frequency and long‐term ocean sampling regimes. The Honeywell Durafet is widely used due to its stability, fast response, and characterization over a large range of oceanic conditions. However, potentiometric pH monitoring is inherently complicated by the fact that the sensors require careful calibration. Offsets in calibration coefficients have been observed when comparing laboratory to field‐based calibrations and prior work has led to the recommendation that an in situ calibration be performed based on comparison to discrete samples. Here, we describe our work toward a self‐calibration apparatus integrated into a SeapHOx pH, dissolved oxygen, and CTD sensor package. This Self‐Calibrating SeapHOx is capable of autonomously recording calibration values from a high quality, traceable, primary reference standard: equimolar tris buffer. The Self‐Calibrating SeapHOx’s functionality was demonstrated in a 6‐d test in a seawater tank at Scripps Institution of Oceanography (La Jolla, California, U.S.A.) and was successfully deployed for 2 weeks on a shallow, coral reef flat (Lizard Island, Australia). During the latter deployment, the tris‐based self‐calibration using 15 on‐board samples exhibited superior reproducibility to the standard spectrophotometric pH‐based calibration using > 100 discrete samples. Standard deviations of calibration pH using tris ranged from 0.002 to 0.005 whereas they ranged from 0.006 to 0.009 for the standard spectrophotometric pH‐based method; the two independent calibration methods resulted in a mean pH difference of 0.008. We anticipate that the Self‐Calibrating SeapHOx will be capable of autonomously providing climate quality pH data, directly linked to a primary seawater pH standard, and with improvements over standard calibration techniques.

Continue reading ‘Autonomous in situ calibration of ion‐sensitive field effect transistor pH sensors’

Abundances and morphotypes of the coccolithophore Emiliania huxleyi in southern Patagonia compared to neighboring oceans and northern-hemisphere fjords

Coccolithophores are potentially affected by ongoing ocean acidification, where rising CO2 lowers seawater pH and calcite saturation state (Ωcal). Southern Patagonian fjords and channels provide natural laboratories for studying these issues due to high variability in physical and chemical conditions. We surveyed coccolithophore assemblages in Patagonian fjords during late-spring 2015 and early-spring 2017. Surface Ωcal exhibited large variations driven mostly by freshwater inputs. High Ωcal conditions (max. 3.6) occurred in the Archipelago Madre de Dios. Ωcal ranged from 2.0–2.6 in the western Strait of Magellan, 1.5–2.2 in the Inner Channel, and was sub-saturating (0.5) in Skyring Sound. Emiliania huxleyi was the only coccolithophore widely distributed in Patagonian fjords (> 96 % of total coccolitophores), only disappearing in the Skyring Sound, a semi-closed mesohaline system. Correspondence analysis associated higher E. huxleyi biomasses with lower diatom biomasses. The highest E. huxleyi abundances in Patagonia were in the lower range of those reported in Norwegian fjords. Predominant morphotypes were distinct from those previously documented in nearby oceans but similar to those of Norwegian fjords. Moderate-calcified forms of E. huxleyi A morphotype were uniformly distributed throughout Patagonia fjords. The exceptional R/hyper-calcified coccoliths, associated with low Ωcal values in Chilean and Peruvian coastal upwellings, were a minor component associated with high Ωcal levels in Patagonia. Outlying mean index (OMI) niche analysis suggested that pH/Ωcal conditions explained most variation in the realized niches of E. huxleyi morphotypes. The moderate-calcified A morphotype exhibited the widest niche-breadth (generalist), while the R/hyper-calcified morphotype exhibited a more restricted realized niche (specialist). Nevertheless, when considering an expanded sampling domain, including nearby Southeast Pacific coastal and offshore waters, even the R/hyper-calcified morphotype exhibited a higher niche breadth than other closely phylogenetically-related coccolithophore species. The occurrence of E. huxleyi in naturally low pH/Ωcal environments indicates that its ecological response is plastic and capable of adaptation.

Continue reading ‘Abundances and morphotypes of the coccolithophore Emiliania huxleyi in southern Patagonia compared to neighboring oceans and northern-hemisphere fjords’

Projections of algae, eelgrass, and zooplankton ecological interactions in the inner Salish Sea – for future climate, and altered oceanic states

Highlights

  • Harmonized simulation of DO, pH, and Y2095 climate change impacts in the Salish Sea
  • A 52-fold increase in exposure and near-bed pelagic species to hypoxic waters in Y2095
  • Ocean acidification projections for Y2095 indicate ≈ 20 −114% increase in water column (ΩA) <1)
  • Primary productivity propagation to zooplankton projected for Y2095 with ≈ 13%−25% increases.
  • Eelgrass sensitive to stressors and potential for loss of eelgrass biomass in the future.

Abstract

Future projections based on the IPCC high emissions scenario RCP8.5 have previously shown that the Pacific Northwest coastal waters will be subjected to altered ocean states in the upwelled shelf waters, resulting in higher primary productivity and increased regions of hypoxia and acidification in the inner estuarine waters such as the Salish Sea. However, corresponding effects on the lower trophic levels and submerged aquatic vegetation have not yet been quantified. Supported by new synoptic field data, explicit coupled simulation of algae, zooplankton, and eelgrass biomass was accomplished for the first time in the Salish Sea. We re-applied the improved model to evaluate future ecological response and examined potential algal species shift, but with the effects of zooplankton production, metabolism, and predation-prey interactions included. We also evaluated the role of eelgrass with respect to potential for improvements to dissolved oxygen and pH levels and as a mitigation measure against hypoxia and ocean acidification. The results re-confirm the possibility that there could be a substantial area-days increase (≈52-fold) in exposure of benthic and near-bed pelagic species to hypoxic waters in 2095. The projections for ocean acidification similarly indicate ≈ 20 -114% increase in exposure to lower pH corrosive waters with aragonite saturation state ΩA <1. Importantly, projected increase in primary productivity was shown to propagate to higher trophic levels, with ≈ 13% and 25% increases in micro and mesozooplankton biomass levels. However, the preliminary results also point to sensitivity of the eelgrass model to environmental stressor and potential loss eelgrass biomass in the future.

Continue reading ‘Projections of algae, eelgrass, and zooplankton ecological interactions in the inner Salish Sea – for future climate, and altered oceanic states’

Ocean acidification locks algal communities in a species‐poor early successional stage

Long‐term exposure to CO2‐enriched waters can considerably alter marine biological community development, often resulting in simplified systems dominated by turf algae that possess reduced biodiversity and low ecological complexity. Current understanding of the underlying processes by which ocean acidification alters biological community development and stability remains limited, making the management of such shifts problematic. Here, we deployed recruitment tiles in reference (pHT 8.137 ± 0.056 SD) and CO2‐enriched conditions (pHT 7.788 ± 0.105 SD) at a volcanic CO2 seep in Japan to assess the underlying processes and patterns of algal community development. We assessed (i) algal community succession in two different seasons (Cooler months: January–July, and warmer months: July–January), (ii) the effects of initial community composition on subsequent community succession (by reciprocally transplanting preestablished communities for a further 6 months), and (iii) the community production of resulting communities, to assess how their functioning was altered (following 12 months recruitment). Settlement tiles became dominated by turf algae under CO2‐enrichment and had lower biomass, diversity and complexity, a pattern consistent across seasons. This locked the community in a species‐poor early successional stage. In terms of community functioning, the elevated pCO2 community had greater net community production, but this did not result in increased algal community cover, biomass, biodiversity or structural complexity. Taken together, this shows that both new and established communities become simplified by rising CO2 levels. Our transplant of preestablished communities from enriched CO2 to reference conditions demonstrated their high resilience, since they became indistinguishable from communities maintained entirely in reference conditions. This shows that meaningful reductions in pCO2 can enable the recovery of algal communities. By understanding the ecological processes responsible for driving shifts in community composition, we can better assess how communities are likely to be altered by ocean acidification.

Continue reading ‘Ocean acidification locks algal communities in a species‐poor early successional stage’

Ocean acidifcation may be increasing the intensity of lightning over the oceans

The anthropogenic increase in atmospheric CO2 is not only considered to drive global warming, but also ocean acidification. Previous studies have shown that acidification will affect many aspects of biogenic carbon uptake and release in the surface water of the oceans. In this report we present a potential novel impact of acidification on the flash intensity of lightning discharged into the oceans. Our experimental results show that a decrease in ocean pH corresponding to the predicted increase in atmospheric CO2 according to the IPCC RCP 8.5 worst case emission scenario, may increase the intensity of lightning discharged into seawater by approximately 30 ± 7% by the end of the twenty-first century relative to 2000.

Continue reading ‘Ocean acidifcation may be increasing the intensity of lightning over the oceans’

Seasonal variability of net sea-air CO2 fluxes in a coastal region of the northern Antarctic Peninsula

We show an annual overview of the sea-air CO2 exchanges and primary drivers in the Gerlache Strait, a hotspot for climate change that is ecologically important in the northern Antarctic Peninsula. In autumn and winter, episodic upwelling events increase the remineralized carbon in the sea surface, leading the region to act as a moderate or strong CO2 source to the atmosphere of up to 40 mmol m–2 day–1. During summer and late spring, photosynthesis decreases the CO2 partial pressure in the surface seawater, enhancing ocean CO2 uptake, which reaches values higher than − 40 mmol m–2 day–1. Thus, autumn/winter CO2 outgassing is nearly balanced by an only 4-month period of intense ocean CO2 ingassing during summer/spring. Hence, the estimated annual net sea-air CO2 flux from 2002 to 2017 was 1.24 ± 4.33 mmol m–2 day–1, opposing the common CO2 sink behaviour observed in other coastal regions around Antarctica. The main drivers of changes in the surface CO2 system in this region were total dissolved inorganic carbon and total alkalinity, revealing dominant influences of both physical and biological processes. These findings demonstrate the importance of Antarctica coastal zones as summer carbon sinks and emphasize the need to better understand local/regional seasonal sensitivity to the net CO2 flux effect on the Southern Ocean carbon cycle, especially considering the impacts caused by climate change.

Continue reading ‘Seasonal variability of net sea-air CO2 fluxes in a coastal region of the northern Antarctic Peninsula’

Animal size and sea water temperature, but not pH, influence a repeatable startle response behavior in a wide-ranging marine mollusc

Highlights

  • We measured startle response (time to open) in mussels following a predator cue.
  • We tested effects of temperature, pH and size and measured repeatability.
  • Larger mussels opened faster; repeatable startle response; evidence of habituation.
  • High temperature increased time to open; no effect of pH.
  • Blue mussels are sensitive to temperature and vulnerable to climate change.

Abstracts

Startle response behaviours are important in predator avoidance and escape for a wide array of animals. For many marine invertebrates, however, startle response behaviours are understudied, and the effects of global change stressors on these responses are unknown. We exposed two size classes of blue mussels (Mytilus edulis × trossulus) to different combinations of temperature (15 and 19 °C) and pH (8.2 and 7.5 pHT) for 3 months and subsequently measured individual time to open following a tactile predator cue (i.e. startle response time) over a series of four consecutive trials. Time to open was highly repeatable in the short term and decreased linearly across the four trials. Individuals from the larger size class had a shorter time to open than their smaller-sized counterparts. High temperature increased time to open compared to low temperature, while pH had no effect. These results suggest that bivalve time to open is repeatable, related to relative vulnerability to predation and affected by temperature. Given that increased closure times impact feeding and respiration, the effect of temperature on closure duration may play a role in the sensitivity to ocean warming in this species and contribute to ecosystem level effects.

Continue reading ‘Animal size and sea water temperature, but not pH, influence a repeatable startle response behavior in a wide-ranging marine mollusc’

Conodont calcium isotopic evidence for multiple shelf acidification events during the early Triassic

Highlights

  • Conodont δ44/40Ca curve is established for the latest Permian to Middle Triassic.
  • Three episodes of decreasing δ44/40Ca (0.16–0.23‰) occurred in the Early Triassic.
  • Negative δ44/40Ca shift in the PTB suggests a CO2-driven ocean acidification event.
  • Negative δ44/40Ca shifts in SSB & OAB suggest upwelling-driven shelf acidification.

Abstract

The marine calcium (Ca) cycle is controlled by rates of continental weathering, seawater pH, and carbonate deposition on the seafloor and is linked to atmospheric CO2, climate change, and marine biotic evolution. Here, we provide the first continuous seawater Ca isotope profile from conodont apatite in South China for the latest Permian to early Middle Triassic, revealing major fluctuations in the Early Triassic calcium cycle. Three episodes of decreasing conodont δ44/40Ca (by 0.16–0.23‰) occurred around the Permian-Triassic, Smithian-Spathian, and Olenekian-Anisian boundaries. The first episode, coincident with a negative excursion of carbonate carbon isotopes, global warming, oceanic anoxia, enhanced weathering, and sea-level fall, was likely caused by a combination of volcanic CO2 release, ocean acidification, a reduced skeletal carbonate sink, and enhanced weathering of shelf carbonates. The latter two episodes, coincident with positive excursions of carbon isotopes, global cooling, and oceanic anoxia, possibly resulted from upwelling-driven shelf acidification and reduced skeletal carbonate burial. All three events were associated with marine biotic diversity losses, demonstrating a link between the calcium cycle and mass extinctions.

Continue reading ‘Conodont calcium isotopic evidence for multiple shelf acidification events during the early Triassic’

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