Posts Tagged 'globalmodeling'

The mass impacts on chemosynthetic primary producers: potential implications on anammox communities and their consequences

The potential of a mass asteroid impact on Earth to disturb the chemosynthetic communities at global scale is discussed. Special emphasis is made on the potential influence on anammox communities and their implications in the nitrogen biogeochemical cycle. According to our preliminary estimates, anammox communities could be seriously affected as a consequence of global cooling and the large process of acidification usually associated with the occurrence of this kind of event. The scale of affectations could vary in a scenario like the Chicxulub as a function of the amount of soot, depth of the water column and the deposition rate for sulphates assumed in each case. The most severe affectations take place where the amount of soot and sulphates produced during the event is higher and the scale of time of settlements for sulphates is short, of the order of 10 h. In this extreme case, the activity of anammox is considerably reduced, a condition that may persist for several years after the impact. Furthermore, the impact of high levels of other chemical compounds like sulphates and nitrates associated with the occurrence of this kind of event are also discussed.

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Emergence of anthropogenic signals in the ocean carbon cycle

The attribution of anthropogenically forced trends in the climate system requires an understanding of when and how such signals emerge from natural variability. We applied time-of-emergence diagnostics to a large ensemble of an Earth system model, which provides both a conceptual framework for interpreting the detectability of anthropogenic impacts in the ocean carbon cycle and observational sampling strategies required to achieve detection. We found emergence timescales that ranged from less than a decade to more than a century, a consequence of the time lag between the chemical and radiative impacts of rising atmospheric CO2 on the ocean. Processes sensitive to carbonate chemical changes emerge rapidly, such as the impacts of acidification on the calcium carbonate pump (10 years for the globally integrated signal and 9–18 years for regionally integrated signals) and the invasion flux of anthropogenic CO2 into the ocean (14 years globally and 13–26 years regionally). Processes sensitive to the ocean’s physical state, such as the soft-tissue pump, which depends on nutrients supplied through circulation, emerge decades later (23 years globally and 27–85 years regionally).

Continue reading ‘Emergence of anthropogenic signals in the ocean carbon cycle’

Recent pace of change in human impact on the world’s ocean

Humans interact with the oceans in diverse and profound ways. The scope, magnitude, footprint and ultimate cumulative impacts of human activities can threaten ocean ecosystems and have changed over time, resulting in new challenges and threats to marine ecosystems. A fundamental gap in understanding how humanity is affecting the oceans is our limited knowledge about the pace of change in cumulative impact on ocean ecosystems from expanding human activities – and the patterns, locations and drivers of most significant change. To help address this, we combined high resolution, annual data on the intensity of 14 human stressors and their impact on 21 marine ecosystems over 11 years (2003–2013) to assess pace of change in cumulative impacts on global oceans, where and how much that pace differs across the ocean, and which stressors and their impacts contribute most to those changes. We found that most of the ocean (59%) is experiencing significantly increasing cumulative impact, in particular due to climate change but also from fishing, land-based pollution and shipping. Nearly all countries saw increases in cumulative impacts in their coastal waters, as did all ecosystems, with coral reefs, seagrasses and mangroves at most risk. Mitigation of stressors most contributing to increases in overall cumulative impacts is urgently needed to sustain healthy oceans.

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Marine carbonate factories: a global model of carbonate platform distribution

Platform carbonates are a major component of the Earth system, but their spatial distribution through geological times is difficult to reconstruct, due to the incompleteness of geological records, sampling heterogeneity, and their intrinsic complexity. Beyond this complexity, carbonates are not randomly distributed in the world oceans, neither in the modern nor in the past, and thus, global trends exist. In the present review, we focus on the understanding of the spatial distribution of carbonate production at a global scale. We use a deterministic approach, which focuses on discriminating components, stratigraphic architectures, and environmental features to relate shallow-water carbonate production to oceanographic parameters. The work is based on extensive literature reviews on carbonate platforms. Ecological niche modelling coupled with deep-time general circulation models is used to calibrate a predictive tool of carbonate factory distribution. A carbonate factory function is set up that is based on sea-surface oceanographic parameters (temperature, salinity, and primary productivity). The model was tested using remote-sensing and in situ oceanographic data of Modern times, while outputs of paleoceanographic models are utilized for Lower Aptian (Cretaceous) modelling. The approach allows determining four neritic carbonate factories that are called the marine biochemical, photozoan, photo-C-, and heterozoan factories. The model finely simulates the global distribution of Lower Aptian and Modern carbonate platforms. Carbonate factories appear to thrive for specific ranges along the environmental gradient of carbonate saturation. This conceptual scheme appears to be able to provide a simple, universal model of paleoclimatic zones of shallow-water marine carbonates.

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A model for integrating the effects of multiple simultaneous stressors on marine systems

While much has been learnt about the impacts of specific stressors on individual marine organisms, considerable debate exists over the nature and impact of multiple simultaneous stressors on both individual species and marine ecosystems. We describe a modelling tool (OSIRIS) for integrating the effects of multiple simultaneous stressors. The model is relatively computationally light, and demonstrated using a coarse-grained, non-spatial and simplified representation of a temperate marine ecosystem. This version is capable of reproducing a wide range of dynamic responses.Results indicate the degree to which interactions are synergistic is crucial in determining sensitivity to forcing, particularly for the higher trophic levels, which can respond non-linearly to stronger forcing. Stronger synergistic interactions sensitize the system to variability in forcing, and combinations of stronger forcing, noise and synergies between effects are particularly potent. This work also underlines the significant potential risk incurred in treating stressors on ecosystems as individual and additive.

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Time‐of‐detection as a metric for prioritizing between climate observation quality, frequency, and duration

We advance a simple framework based on “time‐of‐detection” for estimating the observational needs of studies assessing climate changes amidst natural variability, and apply it to several examples related to ocean acidification. This approach aims to connect the Global Ocean Acidification Observing Network “weather” and “climate” data quality thresholds with a single dynamic threshold appropriate for a range of potential ocean signals and environments. A key implication of the framework is that measurement frequency can be as important as measurement accuracy, particularly in highly variable environments. Pragmatic cost‐benefit analyses based on this framework can be performed to quantitatively determine which observing strategy will accomplish a given detection goal soonest and resolve a signal with the greatest confidence, and to assess how the tradeoffs between measurement frequency and accuracy vary regionally.

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Insights from GO-SHIP hydrography data into the thermodynamic consistency of CO2 system measurements in seawater

Highlights
• The thermodynamic consistency of CO2 system measurements was investigated.

• Errors in CO2 measurements are unlikely to be the main cause of inconsistencies.

• There are likely systematic errors in K1, K2, and the total boron-salinity ratio.

• An unaccounted source of alkalinity may be present in the open ocean.

Abstract
Due to advances in technology, routine seawater pH measurements of excellent repeatability are becoming increasingly common for studying the ocean CO2 system. However, the accuracy of pH measurements has come into question due to a widespread observation, from a large number of carefully calibrated state-of-the-art CO2 measurements on various cruises, of there being a significant pH-dependent discrepancy between pH that was measured spectrophotometrically and pH calculated from concurrent measurements of total dissolved inorganic carbon (CT) and total alkalinity (AT), using a thermodynamic model of seawater

acid-base systems. From an analysis of four recent GO-SHIP repeat hydrography datasets, we show that a combination of small systematic errors in the dissociation constants of carbonic acid (K1 and K2), the total boron-salinity ratio, and in CT and AT measurements are likely responsible for some, but not all of the observed pH-dependent discrepancy. The residual discrepancy can only be fully accounted for if there exists a small, but meaningful amount (~4 μmol kg–1) of an unidentified and typically neglected contribution to measured AT, likely from organic bases, that is widespread in the open ocean. A combination of these errors could achieve consistency between measured and calculated pH, without requiring that any of the shipboard measurements be significantly in error. Future research should focus on establishing the existence of organic alkalinity in the open ocean and constraining the uncertainty in both CO2 measurements and in the constants used in CO2 calculations.

Continue reading ‘Insights from GO-SHIP hydrography data into the thermodynamic consistency of CO2 system measurements in seawater’


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Ocean acidification in the IPCC AR5 WG II

OUP book