Posts Tagged 'North Atlantic'

Impact of ocean acidification and warming on mitochondrial enzymes and membrane lipids in two Gadoid species

Mitochondrial respiration is a multi-step pathway that involves matrix and membrane-associated enzymes and plays a key role in acclimation to variable environmental conditions, but until now it has not been clear which of these steps would be most important in acclimation to changing temperatures and CO2 levels. Considering scenarios of ocean warming and acidification we assessed the role and limitation to phenotypic plasticity in the hearts of two Gadoid species adapted to different thermal ranges: the polar cod (Boreogadus saida), an Arctic stenotherm, and the Northeast Arctic population of Atlantic cod (NEAC, Gadus morhua), a cold eurytherm. We analysed the capacity of single enzymes involved in mitochondrial respiration [citrate synthase (CS), succinate dehydrogenase (SDH), cytochrome c oxidase (CCO)], the capacity of the electron transport system and the lipid class composition of the cellular membranes. Juveniles of the two species were held for four months at four temperatures (0, 3, 6, 8 °C for polar cod and 3, 8, 12, 16 °C for NEAC), at both ambient and elevated PCO2 (400 µatm and 1170 µatm, respectively). Polar cod showed no changes in mitochondrial enzyme capacities and in the relative lipid class composition in response to altered temperature or elevated PCO2. The lack of cardiac cellular plasticity together with evidence at the whole-animal level coming from other studies is indicative of little or no ability to overcome stenothermy, in particular during acclimation to 8 °C. In contrast, eurythermal NEAC exhibited modifications of membrane composition towards a more rigid structure and altered enzyme capacities to preserve functionality at higher temperatures. Furthermore, in NEAC, the capacities of SDH, CCO and CS were increased by high levels of CO2 if combined with high temperatures (12 and 16 °C), suggesting the compensation of an inhibitory effect. These results indicate that the cold eurythermal species (NEAC) is able to alter its mitochondrial function to a far greater extent than the Arctic stenotherm (polar cod), indicating greater resilience to variable environmental conditions. This difference in plasticity may underpin differences in the resilience to climate change and affect future species distributions and, eventually, survival.

Continue reading ‘Impact of ocean acidification and warming on mitochondrial enzymes and membrane lipids in two Gadoid species’

Ocean acidification’s potential effects on keratin protein in cetacean baleen and other integumentary tissue

Marine uptake of atmospheric CO2 from increased anthropogenic carbon emissions is leading to ocean acidification, which poses a grave threat to marine life. The potential risk of acidified seawater to cetaceans (whales, dolphins, and porpoises) and other marine mammals has received little attention, but deserves close scrutiny due to their long lifespan. Cetaceans also lack the protective fur coat which protects typical mammals, and the feeding of mysticete whales depends on a filter made of a unique tissue: baleen. Like hair and other integumentary products, baleen is made of keratin, a fibrous structural protein. We submerged baleen and skin samples from bowhead whales (Balaena mysticetus) and North Atlantic right whales (Eubalaena glacialis) for 12 weeks in seawater of varying pH representing current and projected acidification. When tested for mechanical strength via loading in compression and tension, the acid-exposed specimens were slightly but not statistically different in weakness (as measured by deformation for a given stress or the force needed to fracture the sample). Other samples exposed to low pH were examined via nuclear magnetic resonance testing to search for the presence of amino acids expected if the keratin protein deteriorated due to acid exposure; even at extreme acidity these amino acids were not found, suggesting keratin is strongly resistant to acid-induced breakdown. Finally, whale skin samples exposed to acidified seawater and examined microscopically did not demonstrate notable changes in appearance, texture, or resistance to stretching. Ocean acidification can possibly harm keratin-based cetacean tissues, but no acidrelated effects were conclusively demonstrated by these tests.

Continue reading ‘Ocean acidification’s potential effects on keratin protein in cetacean baleen and other integumentary tissue’

High‐frequency CO2‐system variability over the winter‐to‐spring transition in a coastal plain estuary

Understanding the vulnerability of estuarine ecosystems to anthropogenic impacts requires a quantitative assessment of the dynamic drivers of change to the carbonate (CO2) system. Here we present new high‐frequency pH data from a moored sensor. These data are combined with discrete observations to create continuous time series of total inorganic carbon (TCO2), CO2 partial pressure (pCO2) and carbonate saturation state. We present two deployments over the winter‐to‐spring transition in the lower York River (where it meets the Chesapeake Bay mainstem) in 2016/17 and 2017/18. TCO2 budgets with daily resolution are constructed and contributions from circulation, air‐sea CO2 exchange, and biology are quantified. We find that TCO2 is most strongly influenced by circulation and biological processes; pCO2 and pH also respond strongly to changes in temperature. The system transitions from autotrophic to heterotrophic conditions multiple times during both deployments; the conventional view of a spring bloom and subsequent summer production followed by autumn and winter respiration may not apply to this region. Despite the dominance of respiration in winter and early spring, surface waters were undersaturated with respect to atmospheric CO2 for the majority of both deployments with mean fluxes ranging from ‐9 to ‐5 mmol C m‐2 d‐1. Deployments a year apart indicate that the seasonal transition in the CO2‐system differs significantly from one year to the next and highlights the necessity of sustained monitoring in dynamic nearshore environments.

Continue reading ‘High‐frequency CO2‐system variability over the winter‐to‐spring transition in a coastal plain estuary’

Carbon and phosphorus processing in a carbonate karst aquifer and delivery to the coastal ocean

In siliciclastic systems, submarine groundwater discharge (SGD) provides a fraction of freshwater and nutrients delivered to coastal waters, but in many carbonate karst terrains SGD represents the predominant source of terrestrial water and solutes. Water compositions may be modified by reactions in subterranean estuaries, altering chemical fluxes via SGD. In carbonate settings, feedbacks between organic carbon remineralization and calcium carbonate mineral (CaCO3) dissolution and precipitation may alter carbon dioxide (CO2) and phosphorus (P) concentrations and fluxes associated with SGD. To assess these effects, we sampled water from multiple submarine springs along the east coast of the Yucatan peninsula, as well as inland cenotes, and a coastal groundwater well. We measured ammonium (NH4), phosphate (PO4), major element, dissolved inorganic and organic carbon concentrations (DIC and DOC), fluorescent characteristics of colored dissolved organic matter (CDOM) and modeled calcite saturation indices (SIcal) and the partial pressure of dissolved CO2 (PCO2). These data indicate that reactions along a hypothetical flow path to the coast control the composition of terrestrial fresh water entering the subterranean estuary. Non-conservative mixing between brackish groundwater and lagoon water reflect changes to groundwater compositions within the subterranean estuary from CO2 produced during organic matter remineralization and CaCO3 dissolution. Although both organic matter remineralization and carbonate dissolution should liberate P, molar N:P ratios in spring discharge are higher than the Redfield Ratio of 16:1, suggesting sequestration of remineralized P through sorption to carbonate minerals within the STE. This result indicates that SGD, the primary source of water and nutrient to this coastal zone, results in P limitation in coastal water and is a source of CO2 despite buffering by CaCO3 dissolution. This result also emphasizes the importance of biogeochemical reactions within subterranean estuaries for estimates of SGD solute delivery to the oceans and impacts to the coastal carbon cycle.

Continue reading ‘Carbon and phosphorus processing in a carbonate karst aquifer and delivery to the coastal ocean’

Optimum satellite remote sensing of the marine carbonate system using empirical algorithms in the global ocean, the Greater Caribbean, the Amazon Plume and the Bay of Bengal


• Satellite salinity measurements enable estimation of surface carbonate parameters.

• Uncertainties within these observation-based estimates are well characterized.

• Monthly satellite salinity and temperature allows synoptic monitoring.

• Satellite observations allow study of seasonal, interannual and episodic variations.


Improving our ability to monitor ocean carbonate chemistry has become a priority as the ocean continues to absorb carbon dioxide from the atmosphere. This long-term uptake is reducing the ocean pH; a process commonly known as ocean acidification. The use of satellite Earth Observation has not yet been thoroughly explored as an option for routinely observing surface ocean carbonate chemistry, although its potential has been highlighted. We demonstrate the suitability of using empirical algorithms to calculate total alkalinity (AT) and total dissolved inorganic carbon (CT), assessing the relative performance of satellite, interpolated in situ, and climatology datasets in reproducing the wider spatial patterns of these two variables. Both AT and CT in situ data are reproducible, both regionally and globally, using salinity and temperature datasets, with satellite observed salinity from Aquarius and SMOS providing performance comparable to other datasets for the majority of case studies. Global root mean squared difference (RMSD) between in situ validation data and satellite estimates is 17 μmol kg−1 with bias  < 5 μmol kg−1 for AT and 30 μmol kg−1 with bias  < 10 μmol kg−1 for CT. This analysis demonstrates that satellite sensors provide a credible solution for monitoring surface synoptic scale AT and CT. It also enables the first demonstration of observation-based synoptic scale AT and CT temporal mixing in the Amazon plume for 2010–2016, complete with a robust estimation of their uncertainty.

Continue reading ‘Optimum satellite remote sensing of the marine carbonate system using empirical algorithms in the global ocean, the Greater Caribbean, the Amazon Plume and the Bay of Bengal’

Quantifying the effects of nutrient enrichment and freshwater mixing on coastal ocean acidification

The US Northeast is vulnerable to ocean and coastal acidification because of low alkalinity freshwater discharge that naturally acidifies the region, and high anthropogenic nutrient loads that lead to eutrophication in many estuaries. This study describes a combined nutrient and carbonate chemistry monitoring program in 5 embayments of Buzzards Bay, Massachusetts to quantify the effects of nutrient loading and freshwater discharge on aragonite saturation state (Ω). Monitoring occurred monthly from June 2015 – September 2017 with higher frequency at two embayments (Quissett and West Falmouth Harbors) and across nitrogen loading and freshwater discharge gradients. The more eutrophic stations experienced seasonal aragonite undersaturation, and at one site, nearly every measurement collected was undersaturated. We present an analytical framework to decompose variability in aragonite Ω into components driven by temperature, salinity, freshwater endmember mixing, and biogeochemical processes. We observed strong correlations between apparent oxygen utilization and the portion of aragonite Ω variation that we attribute to biogeochemistry. The regression slopes were consistent with Redfield ratios of dissolved inorganic carbon and total alkalinity to dissolved oxygen. Total nitrogen and the contribution of biogeochemical processes to aragonite Ω were highly correlated, and this relationship was used to estimate the likely effects of nitrogen loading improvements on aragonite Ω. Under nitrogen loading reduction scenarios, aragonite Ω in the most eutrophic estuaries could be raised by nearly 0.6 units, potentially increasing several stations above the critical threshold of 1. This analysis provides a quantitative framework for incorporating ocean and coastal acidification impacts into regulatory and management discussions.

Continue reading ‘Quantifying the effects of nutrient enrichment and freshwater mixing on coastal ocean acidification’

Seasonal patterns of surface inorganic carbon system variables in the Gulf of Mexico inferred from a regional high-resolution ocean-biogeochemical model

Uncertainties in carbon chemistry variability still remain large in the Gulf of Mexico (GoM), as data gaps limit our ability to infer basin-wide patterns. Here we configure and validate a regional high-resolution ocean-biogeochemical model for the GoM to describe seasonal patterns in surface pressure of CO2 (pCO2), aragonite saturation state (ΩAr), and air-sea CO2 flux during 2005–2014. Model results indicate that seasonal changes in surface pCO2 are strongly controlled by temperature across most of the GoM basin, except in the vicinity of the Mississippi-Atchafalaya River System delta, where runoff largely controls dissolved inorganic carbon (DIC) and total alkalinity (TA) changes. Our model results also show that seasonal patterns of surface ΩAr are driven by seasonal changes in DIC and TA, and reinforced by the seasonal changes in temperature. Simulated air-sea CO2 fluxes are consistent with previous observation-based estimates that show CO2 uptake during winter-spring, and CO2 outgassing during summer-fall. Annually, our model indicates a basin-wide mean CO2 uptake of 0.35 mol m−2 yr−1, and a northern GoM shelf (< 200 m) uptake of 0.93 mol m−2 yr−1. The observation and model-derived patterns of surface pCO2 and CO2 fluxes show good correspondence, thus contributing to improved constraints of the carbon budget in the region.

Continue reading ‘Seasonal patterns of surface inorganic carbon system variables in the Gulf of Mexico inferred from a regional high-resolution ocean-biogeochemical model’

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Ocean acidification in the IPCC AR5 WG II

OUP book