Archive for the 'Science' Category

OA-ICC bibliographic database now available on Zotero

The OA-ICC bibliographic database currently contains more than 5,520 references related to ocean acidification, and includes citations, abstracts and assigned keywords. In addition to being available in Mendeley, this bibliographic database is now freely available on the platform Zotero.

In order to access this database, go to the Zotero homepage and create a free account. Click on the Groups tab, search for the group “OA-ICC”, and join this group. For more information how to access the database and its functions, please see the “User instructions“.

Continue reading ‘OA-ICC bibliographic database now available on Zotero’

The pH dependency of the boron isotopic composition of diatom opal (Thalassiosira weissflogii)

The high latitude oceans are key areas of carbon and heat exchange between the atmosphere and the ocean. As such, they are a focus of both modern oceanographic and palaeoclimate research. However, most palaeoclimate proxies that could provide a long-term perspective are based on calcareous organisms, such as foraminifera, that are scarce or entirely absent in deep-sea sediments south of 50° latitude in the Southern Ocean and north of 40° in the North Pacific. As a result, proxies need to be developed for the opal-based organisms (e.g. diatoms) that are found at these high latitudes, and which dominate the biogenic sediments that are recovered from these regions. Here we present a method for the analysis of the boron (B) content and isotopic composition (δ11B) of diatom opal. We also apply it for the first time to evaluate the relationship between seawater pH and δ11B and B concentration ([B]) in the frustules of the diatom Thalassiosira weissflogii, cultured at a range of pCO2/pH. In agreement with existing data, we find that the [B] of the cultured diatom frustules increases with increasing pH (Mejia et al., 2013). δ11B shows a relatively well-defined negative trend with increasing pH; a completely distinct relationship from any other biomineral previously measured. This relationship not only has implications for the magnitude of the isotopic fractionation that occurs during boron incorporation into opal, but also allows us to explore the potential of the boron-based proxies for palaeo-pH and palaeo-CO2 reconstruction in high latitude marine sediments that have, up until now, eluded study due to the lack of suitable carbonate material.

Continue reading ‘The pH dependency of the boron isotopic composition of diatom opal (Thalassiosira weissflogii)’

Isotopic fractionation of carbon during uptake by phytoplankton across the South Atlantic subtropical convergence

The stable isotopic composition of particulate organic carbon (δ13CPOC) in the surface waters of the global ocean can vary with the aqueous CO2 concentration ([CO2(aq)]) and affects the trophic transfer of carbon isotopes in the marine food web. Other factors such as cell size, growth rate and carbon concentrating mechanisms decouple this observed correlation. Here, the variability in δ13CPOC is investigated in surface waters across the south subtropical convergence (SSTC) in the Atlantic Ocean, to determine carbon isotope fractionation (εp) by phytoplankton and the contrasting mechanisms of carbon uptake in the subantarctic and subtropical water masses. Our results indicate that cell size is the primary determinant of δ13CPOC across the Atlantic SSTC in summer. Combining cell size estimates with CO2 concentrations, we can accurately estimate εp within the varying surface water masses in this region. We further utilize these results to investigate future changes in εp with increased anthropogenic carbon availability. Our results suggest that smaller cells, which are prevalent in the subtropical ocean, will respond less to increased [CO2(aq)] than the larger cells found south of the SSTC and in the wider Southern Ocean. In the subantarctic water masses, isotopic fractionation during carbon uptake will likely increase, both with increasing CO2 availability to the cell, but also if increased stratification leads to decreases in average community cell size. Coupled with decreasing δ13C of [CO2(aq)] due to anthropogenic CO2 emissions, this change in isotopic fractionation and lowering of δ13CPOC may propagate through the marine food web, with implications for the use of δ13CPOC as a tracer of dietary sources in the marine environment.

Continue reading ‘Isotopic fractionation of carbon during uptake by phytoplankton across the South Atlantic subtropical convergence’

Ocean acidification post-Paris: Gauging law and policy responses in light of evolving scientific knowledge

On 12 December 2015, 195 States agreed on the text of the Paris Agreement, opening a new phase in the global response to the threat of climate change. The Agreement has been lauded as an “historic breakthrough in that it seems to have broken a decade long impasse” in the climate change negotiations. The impressive number of ratifications to date and its quick entry into force are indicators of this diplomatic success.

The Agreement achieved this remarkable feat by fundamentally changing the approach to the climate change cooperation. The Kyoto Protocol, generally considered unsuccessful to the influence States’ action, was drafted on the premise of jointly negotiated (i.e. top-down) and binding emission targets with strong consequences in case on non-compliance and rigid differentiation between developed and developing countries. The Paris Agreement, in contract, is a universal agreement that adopts a managerial approach to climate change cooperation under the premise that “self-imposed, voluntary commitments [nationally determined contributions or NDCS] are more likely to be met than those imposed by the global community”.

Continue reading ‘Ocean acidification post-Paris: Gauging law and policy responses in light of evolving scientific knowledge’

Physiological effects of climate change on the American lobster, Homarus americanus

Increases in anthropogenic input of carbon dioxide into the atmosphere have caused widespread patterns of ocean warming and ocean acidification. Both processes will likely have major impacts on commercial fisheries and aquaculture, with acidification posing a particular threat to many marine calcifying invertebrates. In the State of Maine, commercial fisheries landings and a growing aquaculture industry have a combined value in excess of $600 million, 75% of which is sustained by marine calcifiers. Moreover, the American lobster (Homarus americanus) supports the most economically valuable fishery in the Gulf of Maine and Atlantic Canada. Previous research has documented a strong link between lobster biology and ocean temperature, but it is unclear how H. americanuswill respond to a rapidly changing environment. Additionally, previous efforts have focused primarily on the direct effects of a changing climate on lobsters (i.e., changes in growth, survival, and calcification), with little emphasis placed on the potential for sublethal effects to impact the population.

In this dissertation, I explore the effects of increasing ocean temperatures and acidification on H. americanus to understand how environmental changes can alter the health and physiology in multiple life stages of marine calcifying invertebrates. In Chapter 1, I introduce the global patterns and effects of climate change on marine calcifiers and review the current state of knowledge of my study species. In Chapter 2, I discuss how exposure to warming conditions impacts larval development, with a focus on potential trade-offs between enhanced growth and developmental instability. In Chapter 3, I continue to explore the sublethal impacts of warming on larval lobsters by examining changes in gene expression patterns in postlarvae exposed to varying temperatures during development. Chapter 4 explores how short-term exposure to acidified conditions impacts subadult (50 – 65 mm carapace length) lobster thermal physiology, hemolymph chemistry, and stress levels, a relatively understudied yet crucial life history stage. Finally, Chapter 5 summarizes the overarching themes of the dissertation, and concludes by providing suggestions for future research efforts.

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Salish sea response to global climate change, sea level rise, and future nutrient loads

Given annual occurrences of hypoxia, harmful algal blooms, and evidence of coastal acidification, the potential impacts of climate change on water quality are of increasing concern in the U.S. Pacific Northwest estuaries such as the Salish Sea. While large‐scale global climate projections are well documented, our understanding of the nearshore estuarine‐scale response is not as well developed. In this study, the future response within the Salish Sea fjord‐like environment was examined using the Salish Sea Model driven by downscaled outputs from the NCAR climate model CESM. We simulated a single projection of 95‐year change under the RCP 8.5 greenhouse gas emissions scenario. Results indicate that higher temperatures, lower pH, and decreased dissolved oxygen levels in the upwelled shelf waters in the future would propagate into the Salish Sea. Results point to potential changes in average Salish Sea temperature (≈+1.51°C), dissolved oxygen (≈‐0.77 mg/L), and pH (acidification ‐0.18 units) in the Y2095 relative to historical Y2000. The algal biomass in the Salish Sea could increase by ≈23% with a potential species shift from diatoms towards dinoflagellates. The region of annually recurring hypoxia could increase from <1% today to ≈16% in the future. The results suggest that the future response in the Salish Sea is less severe relative to the change predicted near the continental shelf boundary. This resilience of the Salish Sea may be attributed to the existence of strong vertical circulation cells that provide mitigation and serve as a physical buffer, thus keeping waters cooler, more oxygenated, and less acidic.

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Combined effects of simulated acidification and hypoxia on the harmful dinoflagellate Amphidinium carterae

Hypoxia and acidification frequently co-occur in coastal marine ecosystems, and will likely become more intense and persistent with anthropogenic climate change. Although the separate effects of these stressors have previously been described, their combined effects on marine phytoplankton are currently unknown. In this novel study, multi-stressor incubation experiments using the harmful dinoflagellate, Amphidinium carterae, examined the effects of acidification and hypoxia both individually and in combination. Long-term (7 days) and short-term (6 h) experiments under controlled carbon dioxide (CO2) and oxygen (O2) conditions examined the interactive effects of the stressors and the physiological mechanisms driving their interaction. In the long-term experiment, synergistically negative effects were observed for A. carterae growth, photosynthesis, carbon fixation, nitrate uptake, and photosynthetic efficiency (Fv/Fm) under combined high CO2 (low pH) and low O2 conditions. In the short-term experiment, delayed recovery of photosystem II (PSII) reaction centers was observed following photoinhibition, suggesting that high CO2 and low O2 conditions negatively affect photosynthesis in A. carterae even after relatively short exposures. Although high CO2, low O2 conditions should decrease photorespiration and favor carbon fixation by the key photosynthetic enzyme ribulose-1,5-bisphosphate-carboxylase/oxygenase (RuBisCO), these findings demonstrate that the affinity of RuBisCO for CO2 relative to O2 alone does not predict phytoplankton responses to CO2 and O2 conditions in vivo, complicating predictions of phytoplankton community responses to hypoxia and acidification. Results of these experiments suggest that the combination of low pH and O2 concentrations may negatively impact the growth of some harmful dinoflagellates in coastal marine ecosystems.

Continue reading ‘Combined effects of simulated acidification and hypoxia on the harmful dinoflagellate Amphidinium carterae’

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Ocean acidification in the IPCC AR5 WG II

OUP book