Our understanding of how increasing atmospheric CO2 and climate change influences the marine CO2 system and in turn ecosystems has increasingly focused on perturbations to carbonate chemistry ...variability. This variability can affect ocean‐climate feedbacks and has been shown to influence marine ecosystems. The seasonal variability of the ocean CO2 system has already changed, with enhanced seasonal variations in the surface ocean pCO2 over recent decades and further amplification projected by models over the 21st century. Mesocosm studies and CO2 vent sites indicate that diurnal variability of the CO2 system, the amplitude of which in extreme events can exceed that of mean seasonal variability, is also likely to be altered by climate change. Here, we modified a global ocean biogeochemical model to resolve physically and biologically driven diurnal variability of the ocean CO2 system. Forcing the model with 3‐h atmospheric outputs derived from an Earth system model, we explore how surface ocean diurnal variability responds to historical changes and project how it changes under two contrasting 21st‐century emission scenarios. Compared to preindustrial values, the global mean diurnal amplitude of pCO2 increases by 4.8 μatm (+226%) in the high‐emission scenario but only 1.2 μatm (+55%) in the high‐mitigation scenario. The probability of extreme diurnal amplitudes of pCO2 and H+ is also affected, with 30‐ to 60‐fold increases relative to the preindustrial under high 21st‐century emissions. The main driver of heightened pCO2 diurnal variability is the enhanced sensitivity of pCO2 to changes in temperature as the ocean absorbs atmospheric CO2. Our projections suggest that organisms in the future ocean will be exposed to enhanced diurnal variability in pCO2 and H+, with likely increases in the associated metabolic cost that such variability imposes.
Using a global ocean biogeochemical model, we project how diurnal variability of the surface ocean CO2 system responds to historical and future projections of climate change. In a high 21st‐century emission scenario, the global mean diurnal amplitude of pCO2 increases threefold compared to preindustrial values, with a dramatic increase in the probability of extreme diurnal events. The main driver of heightened pCO2 diurnal variability in the surface open ocean is the enhanced sensitivity of pCO2 to changes in temperature as the ocean absorbs anthropogenic carbon.
Long-term stress on marine organisms from ocean acidification will differ between seasons. As atmospheric carbon dioxide (CO2) increases, so do seasonal variations of ocean CO2 partial pressure ...(pCO^, causing summer and winter long-term trends to diverge1-5. Trends may be further influenced by an unexplored factor-changes in the seasonal timing of pCO. In Arctic Ocean surface waters, the observed timing is typified by a winter high and summer low6 because biological effects dominate thermal effects. Here we show that 27 Earth system models simulate similar timing under historical forcing but generally project that the summer low, relative to the annual mean, eventually becomes a high across much of the Arctic Ocean under mid-tohigh-level CO2 emissions scenarios. Often the greater increase in summer pCO , although gradual, abruptly inverses the chronological order of the annual high and low, a phenomenon not previously seen in climate-related variables. The main cause is the large summer sea surface warming7 from earlier retreat of seasonal sea ice8. Warming and changes in other drivers enhance this century's increase in extreme summer pCO by 29±9per cent compared with no change in driver seasonalities. Thus the timing change worsens summer ocean acidification, which in turn may lower the tolerance of endemic marine organisms to increasing summer temperatures.
Diurnal variability of ocean CO2 system variables is poorly constrained. Here, this variability and its drivers are assessed using 3‐h observations collected over 8–140 months at 37 stations located ...in diverse marine environments. Extreme diurnal variability, that is, when the daily amplitude exceeds the 99th percentile of diurnal variability, is comparable in magnitude to the seasonal amplitude and can surpass projected changes in mean states of pCO2 and H+ over the twenty‐first century. At coastal sites and near coral reefs, extremes in diurnal amplitudes reach 187 ± 85 and 149 ± 106 μatm for pCO2, 0.21 ± 0.08 and 0.11 ± 0.07 for pH, and 1.2 ± 0.5 and 0.8 ± 0.4 for Ωarag, respectively. Extreme diurnal variability is weaker in the open ocean, but still reaches 47 ± 18 μatm for pCO2, 0.04 ± 0.01 for pH, and 0.25 ± 0.11 for Ωarag. Diurnal variability of the ocean CO2 system is considerable and likely to respond to increasing CO2. Therefore, it should be represented in Earth system models.
Plain Language Summary
Our understanding of how ocean pH and related chemical variables vary during the day (known as diurnal variability) is not well established. Here, we use a recent data set of such observations collected every 3 h during 8–140 months from 37 buoys located across the oceans to assess these diurnal variations and what drives them. In extreme cases, observed changes over 24 h were found to be greater than those observed between seasons. Diurnal variations in these chemical variables are particularly large in coastal waters and near coral reefs and are not negligible further offshore. Along with the more gradual, long‐term acidification of the ocean from atmospheric CO2 increases year after year, diurnal and seasonal variability of ocean chemistry is also expected to change dramatically. Understanding how this diurnal variability will change in the future is important because it modulates the levels of acidification experienced by marine organisms from long‐term yearly changes.
Key Points
Multi‐year 3‐h observations of CO2 system variables are used to assess diurnal and seasonal variability across marine environments
Amplitudes of extreme diurnal variations in pCO2, pH, and Ωarag are often comparable to those of seasonal cycles
The balance between different drivers of diurnal and seasonal CO2 system variability differs across timescales and environments
Pairs of marine carbonate system variables are often used to calculate others, but those results are seldom reported with estimates of uncertainties. Although the procedure to propagate these ...uncertainties is well known, it has not been offered in public packages that compute marine carbonate chemistry, fundamental tools that are relied on by the community. To remedy this shortcoming, four of these packages were expanded to calculate sensitivities of computed variables with respect to each input variable and to use those sensitivities along with user-specified estimates of input uncertainties (standard uncertainties) to propagate uncertainties of calculated variables (combined standard uncertainties). Sensitivities from these packages agree with one another and with analytical solutions to within 0.01%; similar agreement among packages was found for the combined standard uncertainties. One package was used to quantify how propagated uncertainties vary among computed variables, seawater conditions, and the chosen pair of carbonate system variables that is used as input. The relative contributions to propagated uncertainties from the standard uncertainties of the input pair of measurements and various other input data (equilibrium constants etc) were explored with a new type of diagram. These error-space diagrams illustrate that further improvement beyond today's state-of-the-art measurement uncertainties for the input pair would generally be ineffective at reducing the combined standard uncertainties because the contribution from the constants is larger. Likewise, using much more uncertain measurements of the input pair does not always substantially worsen combined standard uncertainty. The constants that contribute most to combined standard uncertainties are generally K1 and K2, as expected. Yet more of the propagated uncertainty in the computed saturation states of aragonite and calcite comes from their solubility products. Thus percent relative combined standard uncertainties for the saturation states are larger than for the carbonate ion concentration. Routine propagation of these uncertainties should become standard practice.
•Uncertainty propagation added to four public software packages that make CO2 system calculations•New type of diagram helps to assess how propagated uncertainty changes with different input uncertainties•Uncertainties from the constants often dominate propagated uncertainty, so that measurement uncertainty plays little role•Relative uncertainties are larger for CaCO3 saturation states than for CO32- because of uncertainties in solubility products
Fabry, V. J., Seibel, B. A., Feely, R. A., and Orr, J. C. 2008. Impacts of ocean acidification on marine fauna and ecosystem processes. – ICES Journal of Marine Science, 65: 414–432. Oceanic uptake ...of anthropogenic carbon dioxide (CO2) is altering the seawater chemistry of the world’s oceans with consequences for marine biota. Elevated partial pressure of CO2 (pCO2) is causing the calcium carbonate saturation horizon to shoal in many regions, particularly in high latitudes and regions that intersect with pronounced hypoxic zones. The ability of marine animals, most importantly pteropod molluscs, foraminifera, and some benthic invertebrates, to produce calcareous skeletal structures is directly affected by seawater CO2 chemistry. CO2 influences the physiology of marine organisms as well through acid-base imbalance and reduced oxygen transport capacity. The few studies at relevant pCO2 levels impede our ability to predict future impacts on foodweb dynamics and other ecosystem processes. Here we present new observations, review available data, and identify priorities for future research, based on regions, ecosystems, taxa, and physiological processes believed to be most vulnerable to ocean acidification. We conclude that ocean acidification and the synergistic impacts of other anthropogenic stressors provide great potential for widespread changes to marine ecosystems.
Our understanding of how increasing atmospheric CO
and climate change influences the marine CO
system and in turn ecosystems has increasingly focused on perturbations to carbonate chemistry ...variability. This variability can affect ocean-climate feedbacks and has been shown to influence marine ecosystems. The seasonal variability of the ocean CO
system has already changed, with enhanced seasonal variations in the surface ocean pCO
over recent decades and further amplification projected by models over the 21st century. Mesocosm studies and CO
vent sites indicate that diurnal variability of the CO
system, the amplitude of which in extreme events can exceed that of mean seasonal variability, is also likely to be altered by climate change. Here, we modified a global ocean biogeochemical model to resolve physically and biologically driven diurnal variability of the ocean CO
system. Forcing the model with 3-h atmospheric outputs derived from an Earth system model, we explore how surface ocean diurnal variability responds to historical changes and project how it changes under two contrasting 21st-century emission scenarios. Compared to preindustrial values, the global mean diurnal amplitude of pCO
increases by 4.8 μatm (+226%) in the high-emission scenario but only 1.2 μatm (+55%) in the high-mitigation scenario. The probability of extreme diurnal amplitudes of pCO
and H
is also affected, with 30- to 60-fold increases relative to the preindustrial under high 21st-century emissions. The main driver of heightened pCO
diurnal variability is the enhanced sensitivity of pCO
to changes in temperature as the ocean absorbs atmospheric CO
. Our projections suggest that organisms in the future ocean will be exposed to enhanced diurnal variability in pCO
and H
, with likely increases in the associated metabolic cost that such variability imposes.
Abstract
Long-term stress on marine organisms from ocean acidification will differ between seasons. As atmospheric carbon dioxide (CO
2
) increases, so do seasonal variations of ocean CO
2
partial ...pressure (
$${p}_{{{\rm{CO}}}_{2}}$$
p
CO
2
), causing summer and winter long-term trends to diverge
1–5
. Trends may be further influenced by an unexplored factor—changes in the seasonal timing of
$${p}_{{{\rm{CO}}}_{2}}$$
p
CO
2
. In Arctic Ocean surface waters, the observed timing is typified by a winter high and summer low
6
because biological effects dominate thermal effects. Here we show that 27 Earth system models simulate similar timing under historical forcing but generally project that the summer low, relative to the annual mean, eventually becomes a high across much of the Arctic Ocean under mid-to-high-level CO
2
emissions scenarios. Often the greater increase in summer
$${p}_{{{\rm{CO}}}_{2}}$$
p
CO
2
, although gradual, abruptly inverses the chronological order of the annual high and low, a phenomenon not previously seen in climate-related variables. The main cause is the large summer sea surface warming
7
from earlier retreat of seasonal sea ice
8
. Warming and changes in other drivers enhance this century’s increase in extreme summer
$${p}_{{{\rm{CO}}}_{2}}$$
p
CO
2
by 29 ± 9 per cent compared with no change in driver seasonalities. Thus the timing change worsens summer ocean acidification, which in turn may lower the tolerance of endemic marine organisms to increasing summer temperatures.
The Mediterranean region is a climate change
hotspot. Increasing greenhouse gas emissions are projected to lead to a
substantial warming of the Mediterranean Sea as well as major changes in its
...circulation, but the subsequent effects of such changes on marine
biogeochemistry are poorly understood. Here, our aim is to investigate how
climate change will affect nutrient concentrations and biological
productivity in the Mediterranean Sea. To do so, we perform transient
simulations with the coupled high-resolution model NEMOMED8-PISCES using the
high-emission IPCC Special Report on Emissions
Scenarios (SRES) A2 socioeconomic scenario and corresponding
Atlantic, Black Sea, and riverine nutrient inputs. Our results indicate that
nitrate is accumulating in the Mediterranean Sea over the 21st century, while
phosphorus shows no tendency. These contrasting changes result from an
unbalanced nitrogen-to-phosphorus input from riverine discharge and fluxes
via the Strait of Gibraltar, which lead to an expansion of phosphorus-limited
regions across the Mediterranean. In addition, phytoplankton net primary
productivity is reduced by 10 % in the 2090s in comparison to the present
state, with reductions of up to 50 % in some regions such as the Aegean
Sea as a result of nutrient limitation and vertical stratification. We also
perform sensitivity tests to separately study the effects of climate and
biogeochemical input changes on the future state of the Mediterranean Sea.
Our results show that changes in nutrient supply from the Strait of Gibraltar
and from rivers and circulation changes linked to climate change may have
antagonistic or synergistic effects on nutrient concentrations and surface
primary productivity. In some regions such as the Adriatic Sea, half of the
biogeochemical changes simulated during the 21st century are linked with
external changes in nutrient input, while the other half are linked to climate
change. This study is the first to simulate future transient climate change
effects on Mediterranean Sea biogeochemistry but calls for further work to
characterize effects from atmospheric deposition and to assess the various
sources of uncertainty.
During the fifth phase of the Coupled Model Intercomparison Project (CMIP5) substantial efforts were made to systematically assess the skill of Earth system models. One goal was to check how ...realistically representative marine biogeochemical tracer distributions could be reproduced by models. In routine assessments model historical hindcasts were compared with available modern biogeochemical observations. However, these assessments considered neither how close modeled biogeochemical reservoirs were to equilibrium nor the sensitivity of model performance to initial conditions or to the spin-up protocols. Here, we explore how the large diversity in spin-up protocols used for marine biogeochemistry in CMIP5 Earth system models (ESMs) contributes to model-to-model differences in the simulated fields. We take advantage of a 500-year spin-up simulation of IPSL-CM5A-LR to quantify the influence of the spin-up protocol on model ability to reproduce relevant data fields. Amplification of biases in selected biogeochemical fields (O2, NO3, Alk-DIC) is assessed as a function of spin-up duration. We demonstrate that a relationship between spin-up duration and assessment metrics emerges from our model results and holds when confronted with a larger ensemble of CMIP5 models. This shows that drift has implications for performance assessment in addition to possibly aliasing estimates of climate change impact. Our study suggests that differences in spin-up protocols could explain a substantial part of model disparities, constituting a source of model-to-model uncertainty. This requires more attention in future model intercomparison exercises in order to provide quantitatively more correct ESM results on marine biogeochemistry and carbon cycle feedbacks.
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