Invasion Of Anthropogenic CO2 Research Articles

Processes of multibathyal aragonite undersaturation in the Arctic Ocean

During three years of study (2010-2012), the western Arctic Ocean was found to have unique aragonite saturation profiles with up to three distinct aragonite undersaturation zones. This complexity is produced as inflow of Atlantic- and Pacific-derived water masses mix with Arctic-derived waters, which are further modified by physiochemical and biological processes. The shallowest aragonite undersaturation zone, from the surface to ∼ 30 m depth is characterized by relatively low alkalinity and other dissolved ions. Besides local influence of biological processes on aragonite undersaturation of shallow coastal waters, the nature of this zone is consistent with dilution by sea-ice melt and invasion of anthropogenic CO2 from the atmosphere. A second undersaturated zone at ∼ 90-220 m depth (salinity ∼31.8–35.4) occurs within the Arctic Halocline and is characterized by elevated pCO2 and nutrients. The nature of this horizon is consistent with remineralization of organic matter on shallow continental shelves bordering the Canada Basin and the input of the nutrients and CO2 entrained by currents from the Pacific Inlet. Finally, the deepest aragonite undersaturation zone is at greater than 2000 m depth and is controlled by similar processes as deep aragonite saturation horizons in the Atlantic and Pacific Oceans. The comparatively shallow depth of this deepest aragonite saturation horizon in the Arctic is maintained by relatively low temperatures, and stable chemical composition. Understanding the mechanisms controlling the distribution of these aragonite undersaturation zones, and the timescales over which they operate will be crucial to refine predictive models. This article is protected by copyright. All rights reserved.

Biologically Mediated Seasonality of Aragonite Saturation States in Jinhae Bay, Korea

Kim, D.; Choi, S.-H.; Yang, E.-J.; Kim, K.-H.; Jeong, J.-H., and Kim, Y.O., 2013. Biologically mediated seasonality of aragonite saturation states in Jinhae Bay, Korea. Aragonite saturation states (Ωarag) were estimated for the surface and bottom waters of Jinhae Bay over four seasons to assess the major controlling factors. The surface and bottom waters of Jinhae Bay were highly supersaturated with respect to aragonite in spring, autumn, and winter. In summer, however, most of the bottom waters were undersaturated, even though the surface waters were supersaturated. This can be explained by the phytoplankton–carbonate saturation state interaction; high primary production increases Ωarag in surface waters, whereas vertical export and the subsequent remineralization of organic matter decreases Ωarag in subsurface waters. A strong linear correlation between the Ωarag values and dissolved oxygen concentrations supported the idea that biological activity is a major factor controlling Ωarag in Jinhae Bay. The ocean acidification induced by the invasion of anthropogenic CO2 also considerably affected the aragonite saturation state in all seasons, particularly in winter, when the Ωarag values have been reduced by 32–35% in the surface waters and 33–37% in the bottom waters since the preindustrial era. In Jinhae Bay, the undersaturation with respect to aragonite in summer can have large impacts on the calcifying benthic organisms; mussel calcification may no longer occur, and the oyster calcification rate is probably reduced by 50%. In addition, the pH and Ωarag decreases associated with the anthropogenic CO2 increase may reduce the calcification rates of oyster and mussel in all seasons, particularly in winter.

A model study of the seasonal and long–term North Atlantic surface <i>p</i>CO<sub>2</sub> variability

Abstract. A coupled biogeochemical-physical ocean model is used to study the seasonal and long–term variations of surface pCO2 in the North Atlantic Ocean. The model agrees well with recent underway pCO2 observations from the Surface Ocean CO2 Atlas (SOCAT) in various locations in the North Atlantic. Some of the distinct seasonal cycles observed in different parts of the North Atlantic are well reproduced by the model. In most regions except the subpolar domain, recent observed trends in pCO2 and air–sea carbon fluxes are also simulated by the model. Over the longer period between 1960–2008, the primary mode of surface pCO2 variability is dominated by the increasing trend associated with the invasion of anthropogenic CO2 into the ocean. We show that the spatial variability of this dominant increasing trend, to first order, can be explained by the surface ocean circulation and air–sea heat flux patterns. Regions with large surface mass transport and negative air–sea heat flux have the tendency to maintain lower surface pCO2. Regions of surface convergence and mean positive air–sea heat flux such as the subtropical gyre and the western subpolar gyre have a higher long–term surface pCO2 mean. The North Atlantic Oscillation (NAO) plays a major role in controlling the variability occurring at interannual to decadal time scales. The NAO predominantly influences surface pCO2 in the North Atlantic by changing the physical properties of the North Atlantic water masses, particularly by perturbing the temperature and dissolved inorganic carbon in the surface ocean. We show that present underway sea surface pCO2 observations are valuable for both calibrating the model, as well as for improving our understanding of the regionally heterogeneous variability of surface pCO2. In addition, they can be important for detecting any long term change in the regional carbon cycle due to ongoing climate change.

CO<sub>2</sub> perturbation experiments: similarities and differences between dissolved inorganic carbon and total alkalinity manipulations

Abstract. Increasing atmospheric carbon dioxide (CO2) through human activities and invasion of anthropogenic CO2 into the surface ocean alters the seawater carbonate chemistry, increasing CO2 and bicarbonate (HCO3−) at the expense of carbonate ion (CO32−) concentrations. This redistribution in the dissolved inorganic carbon (DIC) pool decreases pH and carbonate saturation state (Ω). Several components of the carbonate system are considered potential key variables influencing for instance calcium carbonate precipitation in marine calcifiers such as coccolithophores, foraminifera, corals, mollusks and echinoderms. Unravelling the sensitivities of marine organisms and ecosystems to CO2 induced ocean acidification (OA) requires well-controlled experimental setups and accurate carbonate system manipulations. Here we describe and analyse the chemical changes involved in the two basic approaches for carbonate chemistry manipulation, i.e. changing DIC at constant total alkalinity (TA) and changing TA at constant DIC. Furthermore, we briefly introduce several methods to experimentally manipulate DIC and TA. Finally, we examine responses obtained with both approaches using published results for the coccolithophore Emiliania huxleyi. We conclude that under most experimental conditions in the context of ocean acidification DIC and TA manipulations yield similar changes in all parameters of the carbonate system, which implies direct comparability of data obtained with the two basic approaches for CO2 perturbation.

Oxygen and carbon stable isotopic profiles of the fan mussel, Pinna nobilis , and reconstruction of sea surface temperatures in the Mediterranean

Stable oxygen and carbon isotope profiles (δ18Oskeletal and δ13Cskeletal), taken along the direction of growth from the umbo to the shell margin in shells of the pinnid Pinna nobilis, were used to reconstruct sea surface temperatures (SST) in the south-east Mediterranean and ontogenetic records of metabolic CO2 incorporation. Comparison of the seasonal cycle of SST, predicted from the δ18Oskeletal record of a small (young) rapidly growing pinnid and temperature measured with a continuous in situ recorder showed that P. nobilis calcifies under isotopic equilibrium with surrounding seawater, thus indicating that P. nobilis shells can be used as a reliable predictor of SST. A 10-year SST record for the south-east Mediterranean was reconstructed from the shell profiles of four pinnid shells of different sizes and ages collected in 1995 and 1996. Reliable resolution of the seasonal SST could only be achieved during the first 4 years of shell growth. As the pinnids grew older, the temperature record was poorly resolved because the shell growth had diminished with age, resulting in time-averaging of the record. The amplitude of the generated seasonal temperature cycle compared favourably (±2°C) with a long-term temperature record from northern Mediterranean waters. Clear seasonal cycles in δ13Cskeletal were observed with an amplitude of ~1.0‰, similar to the calculated seasonal changes in δ13C of seawater (0.6‰) overlying seagrass meadows. An ontogenetic trend towards less positive δ13Cskeletal values was too large to be attributed to any decrease in δ13C in seawater resulting from the invasion of anthropogenic CO2. It is suggested that the temporal changes of δ13Cskeletal are due to incorporation of respiratory CO2 into the extrapallial fluid and reflect changes in the metabolic activity of the pinnid rather than changes in the isotopic composition of dissolved inorganic carbon within the surrounding seawater.