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Attribution of the ocean acidification (OA) signal in estuarine carbonate system observations is necessary for quantifying the impacts of global anthropogenic CO2 emissions on water quality, and informing managers of the efficacy of potential mitigation options. We present an analysis of observational data to characterize dynamics and drivers of seasonal carbonate system variability in two seagrass habitats of Puget Sound, WA, USA, and estimate how carbon accumulations due to anthropogenic CO2 emissions (Canth) interact with these drivers of carbonate chemistry to determine seasonally resolved rates of acidification in these habitats. Three independent simulations of Canth accumulation from 1765 to 2100 were run using two previously published methods and one novel method for Canth estimation. Our results revealed persistent seasonal differences in the magnitude of carbonate system responses to anthropogenic CO2 emissions caused by seasonal metabolic changes to the buffering capacity of estuarine waters. The seasonal variability of pHT and pCO2 is increased (while that of Ωaragonite is decreased) and acidification rates are accelerated when compared with open‐ocean estimates, highlighting how feedbacks between local metabolism and Canth can control the susceptibility of estuarine habitats to OA impacts. The changes in seasonal variability can shorten the timeline to exceedance of established physiological thresholds for endemic organisms and existing Washington State water quality criteria for pH. We highlight how Canth estimation uncertainties manifest in shallow coastal waters and limit our ability to predict impacts to coastal organisms and ecosystems from anthropogenic CO2 emissions. Plain Language Summary: Quantifying the impacts of ocean acidification on estuarine water quality is problematic due to the many natural and human processes affecting acidification of these systems. However, understanding the role of these human processes is essential in order to understand the spatial and temporal patterns of human‐driven acidification. This study combines observations and model projections to assess how seasonal acidification dynamics in two estuarine seagrass habitats will be altered by rising atmospheric CO2 levels. We characterize how the interaction of local carbon cycling and rising atmospheric CO2 controls the sensitivity of each seagrass habitat to acidification impacts. The resulting spatial and temporal variability of acidification sensitivity creates hotspots for exceedances of organismal thresholds and existing water quality criteria. Our study constrains the dynamics of anthropogenic CO2 in estuarine waters more than past studies, but we discuss how further work is necessary to improve confidence in estuarine acidification forecasts more broadly. Key Points: Estuarine metabolism heavily modifies local seasonal ocean acidification (OA) rates, revealing a potentially large biological feedback mechanismVariable estuarine carbon cycling creates OA hotspots for exceedances of species' chemical tolerances and existing water quality criteriaReducing anthropogenic CO2 estimation uncertainties in estuarine waters is needed to improve OA forecasts and inform OA management options [ABSTRACT FROM AUTHOR]

Carbonate chemistry variables such as PCO2, pH, and mineral saturation state (Ω) are commonly thought of as covarying in open‐ocean settings but have decoupled over geologic time‐scales and among modern dynamic coastal margins and estuaries. Predicting responses of vulnerable coastal organisms to past, present, and future ocean acidification (OA) scenarios requires the empirical identification of organismal sensitivity thresholds to individual carbonate chemistry parameters. Conversely, most OA experiments involve chemistry manipulations that result in covariance of carbonate system variables. We developed the Dynamic Ocean Acidification Manipulation Experimental System (DOAMES)—a feed‐forward, flow‐through carbonate chemistry control system capable of decoupling PCO2, pH, or Ω by independently manipulating total alkalinity (TAlk) and total inorganic carbon (TCO2). DOAMES proof‐of‐concept can manipulate source seawater with stable or variable carbonate chemistry and produce experimental treatments with constant and dynamic carbonate chemistry regimes. The combination of dynamic input and output allows for offset treatments that impose a ΔPCO2 on naturally variable conditions. After overcoming several operational challenges, DOAMES is capable of simultaneously generating three different experimental treatments within 1% ± 1% of TCO2 and TAlk targets. The achieved precision and accuracy resulted in the successful decoupling of pH and ΩAr in five trials. We tested the viability of sensitive bivalve embryos raised in DOAMES‐manipulated seawater and found no difference in development when compared to the control, demonstrating DOAMES suitability for organismal studies. DOAMES provides a novel tool to evaluate organismal effects of exposure to decoupled carbonate system variables and to past, current, and future carbonate chemistry scenarios. [ABSTRACT FROM AUTHOR]

Abstract: Calcifying organisms face increasing stress from the changing carbonate chemistry of an acidifying ocean, particularly bivalve larvae that live in upwelling regions of the world, such as the coastal and estuarine waters of Oregon (USA). Arguably the first and most significant developmental hurdle faced by larval oysters is formation of their initial prodissoconch I (PDI) shell, upon which further ontological development depends. We measured the minor metal compositions (Sr/Ca, Mg/Ca) of this aragonitic PDI shell and of post‐PDI larval Crassostrea gigas shell, as well as the water they were reared in, over ∼20 days for a May and an August cohort in 2011, during which time there was no period of carbonate under‐saturation. After testing various methods, we successfully isolated the shell from organic tissue using a 5% active chlorine bleach solution. Elemental compositions (Sr, Mg, C, N) of the shells post‐treatment showed that shell Sr/Ca ranged from 1.55 to 1.82 mmol/mol; Mg/Ca from 0.60 to 1.11 mmol/mol, similar to the few comparable published data for larval oyster aragonite compositions. We compare these data in light of possible biomineralization mechanisms: an amorphous calcium carbonate (ACC) path, an intercellular path, and a direct‐from‐seawater path to shell formation via biologically induced inorganic precipitation of aragonite. The last option provides a mechanistic explanation for: (1) the accelerated precipitation rates of biogenic calcification in the absence of a calcifying fluid; (2) consistently elevated precipitation rates at varying ambient‐water saturation states; and (3) the high Ca‐selectivity of the early larval calcification despite rapid precipitation rates. [ABSTRACT FROM AUTHOR]

Increasing anthropogenic carbon dioxide is altering marine carbonate chemistry through a process called ocean acidification. Many calcium carbonate forming organisms are sensitive to changes in marine carbonate chemistry, especially mollusk bivalve larvae at the initial shell building stage. Rapid calcification, limited energy reserves, and more exposed calcification surfaces, are traits at this stage that increase vulnerability to ocean acidification through our previously argued kinetic-energetic hypothesis. These developmental traits are common to broadcast spawning bivalve species that are the focus of most ocean acidification studies to date. Some oyster species brood their young, which results in slower development of the embryos through the initial shell formation stage. We examined the responses of the brooding Olympia oyster, Ostrea lurida, during their initial shell building stage. We extracted fertilized eggs from, O. lurida, prior to shell development, then exposed developing embryos to a wide range of marine carbonate chemistry conditions. Surprisingly, O. lurida showed no acute negative response to any ocean acidification treatments. Compared to the broadcast spawning Pacific oyster, Crassostrea gigas, calcification rate and standardized endogenous energy lipid consumption rate were nearly 10 and 50 times slower, respectively. Our results suggest that slow shell building may lessen the energetic burden of acidification at this stage and provides additional support for our kinetic-energetic hypothesis. Furthermore, these results may represent an example of exaptation; fitness conveyed by a coopted trait that evolved for another purpose, a concept largely lacking in the current perspective of adaptation and global climate change. [ABSTRACT FROM AUTHOR]

We assess the global balance of calcite export through the water column and burial in sediments as it varies regionally. We first drive a comprehensive 1-D model for sediment calcite preservation with globally gridded field observations and satellite-based syntheses. We then reformulate this model into a simpler five-parameter box model, and combine it with algorithms for surface calcite export and water column dissolution for a single expression for the vertical calcite balance. The resulting metamodel is optimized to fit the observed distributions of calcite burial flux. We quantify the degree to which calcite export, saturation state, organic carbon respiration, and lithogenic sedimentation modulate the burial of calcite. We find that 46% of burial and 88% of dissolution occurs in sediments overlain by undersaturated bottom water with sediment calcite burial strongly modulated by surface export. Relative to organic carbon export, we find surface calcite export skewed geographically toward relatively warm, oligotrophic areas dominated by small, prokaryotic phytoplankton. We assess century-scale projected impacts of warming and acidification on calcite export, finding high sensitive to inferred saturation state controls. With respect to long-term glacial cycling, our analysis supports the hypothesis that strong glacial abyssal stratification drives the lysocline toward much closer correspondence with the saturation horizon. Our analysis suggests that, over the transition from interglacial to glacial ocean, a resulting ∼0.029 PgC a-1 decrease in deep Atlantic, Indian and Southern Ocean calcite burial leads to slow increase in ocean alkalinity until Pacific mid-depth calcite burial increases to compensate [ABSTRACT FROM AUTHOR]

We examined high-resolution cross-shelf distributions of particulate organic carbon (POC) and dissolved O2 during the upwelling season off the Oregon coast. Oxygen concentrations were supersaturated in surface waters, and hypoxic in near-bottom waters, with greatly expanded hypoxic conditions late in the season. Simplified time- dependent mass balances on cross-shelf integrated concentrations of these two parameters, found the following: (1) The average net rate of photosynthesis generated 2.1 mmol O2 m-3 d-1 and (2) essentially none of the corresponding net carbon fixation of 1.4 mmol m-3 d-1 could be accounted for in the observed standing stocks of POC. After examining other possible sinks for carbon, we conclude that most of the net production is being exported to the adjacent deep ocean. A simplified POC budget suggests that about a quarter of the export is via alongshore advection, and the remainder is due to some other process. We propose a simplistic conceptual model of across-shelf transport in which POC sinks to the bottom boundary layer where it comes into contact with mineral ballast material but is kept in suspension by high turbulence. When upwelling conditions ease, the BBL waters move seaward, carrying the suspended, ballasted POC with it where it sinks rapidly into the deep ocean at the shelf break. This suggests a mechanism whereby the duration and frequency of upwelling events and relaxations can determine the extent to which new carbon produced by photosynthesis in the coastal ocean is exported to depth rather than being respired on the shelf. [ABSTRACT FROM AUTHOR]

A biological pump for transferring atmospheric CO2 to deep ocean regimes has been identified in the upwelling zone of the U.S. Pacific coast off Oregon using high-resolution measurements of PCO2 and nutrient concentrations that were made in May through August 2001. Surface water over most of the shelf was a strong sink for atmospheric CO2, while a narrow nearshore strip was an intense source. The dominance of the low-CO2 waters over the shelf area makes the region a net sink during upwelling season. This is due to (1) upwelled water that carries abundant preformed nutrients, (2) complete photosynthetic uptake of these excess nutrients and a stoichiometric proportion of CO2, and (3) moderate warming of upwelled waters. If the remaining North Pacific's eastern boundary area is assumed to have similar conditions, this area should represent a sink of atmospheric CO2 that is 5% of the annual North Pacific CO2 uptake, and roughly equivalent to the North Pacific's uptake in the summer season. By mid-August, PCO2 in subsurface waters increased 20-60%, corresponding to a 1.0-2.3% TCO2 increase, due to respiration of settling biogenic debris. This water would be transported off the shelf to depth by winter downwelling flow, providing an important mechanism for sequestering atmospheric CO2 into the oceans' interior. [ABSTRACT FROM AUTHOR]

We report results from an oyster hatchery on the Oregon coast, where intake waters experienced variable carbonate chemistry (aragonite saturation state < 0.8 to > 3.2; pH < 7.6 to > 8.2) in the early summer of 2009. Both larval production and midstage growth (∼ 120 to ∼ 150µm) of the oyster Crassostrea gigas were significantly negatively correlated with the aragonite saturation state of waters in which larval oysters were spawned and reared for the first 48h of life. The effects of the initial spawning conditions did not have a significant effect on early-stage growth (growth from D-hinge stage to ∼ 120 µm), suggesting a delayed effect of water chemistry on larval development. [ABSTRACT FROM AUTHOR]

Three cross-shelf transects were conducted off northern Oregon in February, 2003, coincident with flooding of Coast Range rivers, to assess the riverine impact on coastal ocean biogeochemistry. During downwelling conditions, low salinity river-influenced water was located in a narrow band near the coast and contained elevated macronutrient, iron, and organic carbon concentrations. Wind relaxation allowed the river-influenced water to spread out at the surface across the shelf. Nutrients supplied by the rivers could result in winter carbon fixation equating to ~20% of the summer upwelling carbon fixation if conditions are suitable for phytoplankton growth, which is likely on the basis of recent studies. This implies that wintertime production may be significant and requires further study. Iron supplied by the rivers is sufficient to support the entire summer upwelling production and because downwelling conditions prevail during the winter and minimize cross-shelf transport, this iron may be retained on the shelf to support the summer phytoplankton blooms. Of the major eastern boundary current systems, the northern California Current (including Oregon) and Portugal Current (i.e., Iberian Peninsula) have the highest riverine discharge rates normalized to coastline length. In contrast, riverine inputs to the central California, Canary (i.e., northwest Africa), Benguela and Peruvian Current systems averaged only 3-35% of that in Oregon. This patchy riverine input (and narrower shelves) might explain why iron limitation is more widespread off California and Peru than Oregon. These results show that small coastal rivers, characteristic of the U.S. Pacific Northwest, can significantly alter coastal biogeochemical cycles and influence ecosystem structure. [ABSTRACT FROM AUTHOR]