Posts Tagged 'regionalmodeling'

Sudden emergence of a shallow aragonite saturation horizon in the Southern Ocean

Models project that with current CO2 emission rates, the Southern Ocean surface will be undersaturated with respect to aragonite by the end of this century1,2,3,4. This will result in widespread impacts on biogeochemistry and ocean ecosystems5,6,7, particularly the health of aragonitic organisms, such as pteropods7, which can dominate polar surface water communities6. Here, we quantify the depth of the present-day Southern Ocean aragonite saturation horizon using hydrographic and ocean carbon chemistry observations, and use a large ensemble of simulations from the Community Earth System Model (CESM)8,9 to track its evolution. A new, shallow aragonite saturation horizon emerges in many Southern Ocean locations between now and the end of the century. While all ensemble members capture the emergence, internal climate variability may affect the year of emergence; thus, its detection may have been overlooked by ensemble average analysis in the past. The emergence of the new horizon is driven by the slow accumulation of anthropogenic CO2 in the Southern Ocean thermocline, where the carbonate ion concentration exhibits a local minimum and approaches undersaturation. The new horizon is also apparent under an emission-stabilizing scenario indicating an inevitable, sudden decrease in the volume of suitable habitat for aragonitic organisms.

Continue reading ‘Sudden emergence of a shallow aragonite saturation horizon in the Southern Ocean’

The internal consistency of the marine carbon dioxide system for high latitude shipboard and in situ monitoring

Highlights
• Best calculations from combination of T,P-dependent and non-dependent parameters

• The dissociation constants of M73 and L yielded the best internal consistency

• Monte Carlo simulation of uncertainty propagation shows combined uncertainty to be more dependent on input parameters, less on dissociation constants

• Internal consistency study for deep ocean conditions is required

Abstract
Deep convection in the Labrador Sea supplies large amounts of anthropogenic carbon to the ocean’s interior. We use measurements of all four measurable CO2 system parameters made along AR7W (across Labrador Sea) between 2013 and 2015 to assess the internal consistency of the carbonate system, including, as appropriate, conversion to in situ temperature (T) and pressure (P). The best agreement between measured and calculated values was obtained through combination of T,P-dependent (pH or pCO2) and non-dependent (TA or DIC) parameters. Use of the dissociation constants of Mehrbach et al. (1973) as refit by Dickson and Millero (1987) and Lueker et al. (2000) yielded the best internal consistency irrespective of the input parameters used. A Monte Carlo simulation demonstrated that the propagated uncertainty (i.e. combined standard uncertainty) of calculated parameters of the carbonate system is (a) always larger than the analytical precision of the measurements themselves; (b) strongly dependent on the choice of input parameters and uncertainties; (c) less dependent on choice of the specific set of constants. For calculation of other parameters of the carbonate system from TA and DIC measurements made throughout the Labrador Sea time-series, the estimated combined standard uncertainty of calculated pCO2 and pH based on the Monte Carlo simulation is ~ 13 μatm and ~ 0.012 pH units respectively, with accuracy relative to laboratory-based measurement estimated to be between −3 and − 13 μatm and 0.002 and 0.007 pH units. Internal consistency especially at in situ temperature and pressure conditions is important for rapidly developing sensor-based monitoring programs in the region, including measurement of pH and/or pCO2 from gliders, profiling floats and moorings. We highlight uncertainty associated with the large pressure effect on pH and pCO2, and recommend a study of carbonate system internal consistency under deep ocean conditions that addresses pressure effects on calculations.

Continue reading ‘The internal consistency of the marine carbon dioxide system for high latitude shipboard and in situ monitoring’

Ecological-economic sustainability of the Baltic cod fisheries under ocean warming and acidification

Highlights
• Ocean warming and acidification (OAW) will drastically decrease cod fishing opportunities in the Baltic.

• Ecological-economic modeling shows high losses in catch, and profits due to OAW.

• There is a high risk of cod stock collapse under mid-term climate change.

• Improved management could temporarily counteract OAW stressors.

• Adaptation includes a reduction in fishing mortality, and increased mesh size.

Abstract
Human-induced climate change such as ocean warming and acidification, threatens marine ecosystems and associated fisheries. In the Western Baltic cod stock socio-ecological links are particularly important, with many relying on cod for their livelihoods. A series of recent experiments revealed that cod populations are negatively affected by climate change, but an ecological-economic assessment of the combined effects, and advice on optimal adaptive management are still missing. For Western Baltic cod, the increase in larval mortality due to ocean acidification has experimentally been quantified. Time-series analysis allows calculating the temperature effect on recruitment. Here, we include both processes in a stock-recruitment relationship, which is part of an ecological-economic optimization model. The goal was to quantify the effects of climate change on the triple bottom line (ecological, economic, social) of the Western Baltic cod fishery. Ocean warming has an overall negative effect on cod recruitment in the Baltic. Optimal management would react by lowering fishing mortality with increasing temperature, to create a buffer against climate change impacts. The negative effects cannot be fully compensated, but even at 3 °C warming above the 2014 level, a reduced but viable fishery would be possible. However, when accounting for combined effects of ocean warming and acidification, even optimal fisheries management cannot adapt to changes beyond a warming of +1.5° above the current level. Our results highlight the need for multi-factorial climate change research, in order to provide the best available, most realistic, and precautionary advice for conservation of exploited species as well as their connected socio-economic systems.

Continue reading ‘Ecological-economic sustainability of the Baltic cod fisheries under ocean warming and acidification’

Fates of vent CO2 and its impact on carbonate chemistry in the shallow-water hydrothermal field offshore Kueishantao Islet, NE Taiwan

Highlights

• CO2 dissolution and fluid entrainment shape carbonate chemistry in vertical plumes.
• Fluids in the near-vent area have a short flushing time (tens of minutes).
• Mixing of vent fluids with seawater acts to retain vent carbon in ocean.

Abstract

Increasing public awareness of anthropogenic CO2 emissions and consequent global change has stimulated the development of pragmatic approaches for the study of shallow-water CO2 vents and seeps as natural laboratories of CO2 perturbations. How CO2 propagates from the emission sites into surrounding environments (ocean and atmosphere), and its effects on seawater carbonate chemistry, have never been studied from a mechanistic perspective. Here, we combine experimental and modeling approaches to investigate the carbonate chemistry of a shallow-water hydrothermal field offshore Kueishantao Islet, NE Taiwan. A simple Si-based mixing model is used to trace hydrothermal fluid mixing with seawater along convection pathways. The estimated vent fluid component in the near-vent region is generally <1%. We further employed a modified bubble-plume model to examine gas bubble-aqueous phase interaction. We explain the dissolved inorganic carbon characteristics of the vertical plume as a synergistic interaction between CO2 gas dissolution and fluid entrainment. The bubble-plume model provides a conservative estimate of the flushing time (tens of minutes) for water in the near-vent region. The acidic, dissolved inorganic carbon-rich water in the lateral buoyant plume readily releases CO2, but mixing with seawater rapidly quenches its degassing potential, so that hydrothermal carbon is retained in the ocean. Ebullition, governed by initial bubble size distribution, is the key mechanism for vent CO2 to exit the seawater carbonate system.

Continue reading ‘Fates of vent CO2 and its impact on carbonate chemistry in the shallow-water hydrothermal field offshore Kueishantao Islet, NE Taiwan’

Seawater temperature and buffering capacity modulate coral calcifying pH

Scleractinian corals promote the precipitation of their carbonate skeleton by elevating the pH and dissolved inorganic carbon (DIC) concentration of their calcifying fluid above that of seawater. The fact corals actively regulate their calcifying fluid chemistry implies the potential for acclimation to ocean acidification. However, the extent to which corals can adjust their regulation mechanism in the face of decreasing ocean pH has not been rigorously tested. Here I present a numerical model simulating pH and DIC up-regulation by corals, and use it to determine the relative importance of physiological regulation versus seawater conditions in controlling coral calcifying fluid chemistry. I show that external seawater temperature and buffering capacity exert the first-order control on the extent of pH elevation in the calcifying fluid and explain most of the observed inter- and intra-species variability. Conversely, physiological regulation, represented by the interplay between enzymatic proton pumping, carbon influx and the exchange of calcifying fluid with external seawater, contributes to some variability but remain relatively constant as seawater conditions change. The model quantitatively reproduces variations of calcifying fluid pH in natural Porites colonies, and predicts an average 0.16 unit decrease in Porites calcifying fluid pH, i.e., ~43% increase in H+ concentration, by the end of this century as a combined result of projected ocean warming and acidification, highlighting the susceptibility of coral calcification to future changes in ocean conditions. In addition, my findings support the development of coral-based seawater pH proxies, but suggest the influences of physicochemical and biological factors other than seawater pH must be considered.

Continue reading ‘Seawater temperature and buffering capacity modulate coral calcifying pH’

Ecosystem metabolism drives pH variability and modulates long-term ocean acidification in the Northeast Pacific coastal ocean

Ocean acidification poses serious threats to coastal ecosystem services, yet few empirical studies have investigated how local ecological processes may modulate global changes of pH from rising atmospheric CO2. We quantified patterns of pH variability as a function of atmospheric CO2 and local physical and biological processes at 83 sites over 25 years in the Salish Sea and two NE Pacific estuaries. Mean seawater pH decreased significantly at −0.009 ± 0.0005 pH yr−1 (0.22 pH over 25 years), with spatially variable rates ranging up to 10 times greater than atmospheric CO2-driven ocean acidification. Dissolved oxygen saturation (%DO) decreased by −0.24 ± 0.036% yr−1, with site-specific trends similar to pH. Mean pH shifted from 8.0 in summer concomitant to the seasonal shift from heterotrophy (%DO  100) and dramatic shifts in aragonite saturation state critical to shell-forming organisms (probability of undersaturation was >80% in winter, but <20% in summer). %DO overwhelmed the influence of atmospheric CO2, temperature and salinity on pH across scales. Collectively, these observations provide evidence that local ecosystem processes modulate ocean acidification, and support the adoption of an ecosystem perspective to ocean acidification and multiple stressors in productive aquatic habitats.

Continue reading ‘Ecosystem metabolism drives pH variability and modulates long-term ocean acidification in the Northeast Pacific coastal ocean’

Sedimentary alkalinity generation and long-term alkalinity development in the Baltic Sea

Enhanced release of alkalinity from the seafloor, principally driven by anaerobic degradation of organic matter under low-oxygen conditions and associated secondary redox reactions, can increase the carbon dioxide (CO2) buffering capacity of seawater and therefore oceanic CO2 uptake. The Baltic Sea has undergone severe changes in oxygenation state and total alkalinity (TA) over the past decades. The link between these concurrent changes has not yet been investigated in detail. A recent system-wide TA budget constructed for the past 50 years using BALTSEM, a coupled physical–biogeochemical model for the whole Baltic Sea area revealed an unknown TA source. Here we use BALTSEM in combination with observational data and one-dimensional reactive-transport modeling of sedimentary processes in the Fårö Deep, a deep Baltic Sea basin, to test whether sulfate (SO2−4) reduction coupled to iron (Fe) sulfide burial can explain the missing TA source in the Baltic Proper. We calculated that this burial can account for up to 26 % of the missing source in this basin, with the remaining TA possibly originating from unknown river inputs or submarine groundwater discharge. We also show that temporal variability in the input of Fe to the sediments since the 1970s drives changes in sulfur (S) burial in the Fårö Deep, suggesting that Fe availability is the ultimate limiting factor for TA generation under anoxic conditions. The implementation of projected climate change and two nutrient load scenarios for the 21st century in BALTSEM shows that reducing nutrient loads will improve deep water oxygen conditions, but at the expense of lower surface water TA concentrations, CO2 buffering capacities and faster acidification. When these changes additionally lead to a decrease in Fe inputs to the sediment of the deep basins, anaerobic TA generation will be reduced even further, thus exacerbating acidification. This work highlights that Fe dynamics plays a key role in the release of TA from sediments where Fe sulfide formation is limited by Fe availability, as exemplified by the Baltic Sea. Moreover, it demonstrates that burial of Fe sulfides should be included in TA budgets of low-oxygen basins.

Continue reading ‘Sedimentary alkalinity generation and long-term alkalinity development in the Baltic Sea’


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Ocean acidification in the IPCC AR5 WG II

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