Coastal and estuarine systems play an important role in the global carbon cycle and often have complex carbonate chemistry dynamics due to a multitude of biogeochemical and physical drivers. Compared to classic estuaries, mechanisms driving the distribution of carbonate parameters in low-inflow estuaries are understudied. The spatial distribution of carbonate chemistry and hydrodynamic parameters were characterized in Morro Bay, a short and seasonally hypersaline estuary on the Central California Coast, during the dry, low-inflow season to better understand in situ modifications. Sampling transects were completed in the main channel in June, August, and September of 2018, bracketing both a high and low tide on each date. Temperature, salinity, total alkalinity, and dissolved inorganic carbon all increased from the mouth to the back of the estuary, with larger values observed during the low tide. pH values decreased towards the back of the bay, and had little variation between high and low tide for June and August transects. Flushing times (estimated using a salt-budget model approach) also increased toward the back of the bay which led to hypersaline conditions. Salinity alone only explained 20–33% of observed changes in total alkalinity and 13–22% of observed changes in dissolved inorganic carbon throughout the bay. The remaining changes in total alkalinity and dissolved inorganic carbon were likely driven by biogeochemical modifications enhanced by extended flushing times, particularly in the back bay. Prior to this project, Morro Bay experienced a recent, rapid collapse of eelgrass, the major biogenic habitat. In the last four years eelgrass in Morro Bay appears to be on a recovery trajectory; therefore, this study provides a baseline whereby future studies can evaluate carbonate chemistry changes associated with potential eelgrass recovery and expansion. This study highlights the unique hydrodynamic exchange in seasonally low-inflow estuaries and its potentially large role in influencing local carbonate chemistry and ocean acidification.

Spectrophotometric pH measurements of seawater (pH(spec)) are routinely made by the oceanographic community for a wide variety of studies. However, obtaining consistent measurements between laboratories that meet stringent thresholds such as the "weather" (+/- 0.02) and "climate" (+/- 0.003) standards, has been a challenge. One of the main sources of error for pH(spec) measurements is gas exchange of carbon dioxide during sample handling. Here, we present a simple method where pH(spec) measurements on the total scale are made directly in the sampling bottle, which minimizes sample handling errors because the solution is not transferred during analysis. We compared the performance of this method to a standard automated benchtop system on a hydrography cruise, and the two methods were consistent to 0.003 +/- 0.0033 (1 sigma). This demonstrates that this simple method can produce pH(spec) that approaches climate quality, and comfortably meets weather quality standards. Additional benefits include high sample throughput, and the ability to rapidly quantify dye perturbation effects for each sample. The latter should be particularly useful for low salinity samples such as those taken from estuaries, insofar as modifications specific to the pH(spec) measurements of estuarine waters are employed.

In the last two decades, the need for seawater pH control methodologies paralleled the rise in attention to the biological impacts of ocean acidification. Many effective and high-performing systems have been created, but they are often expensive, complex, and difficult to establish. We developed a system that is similarly high performing, but at a low cost and with a simple and accessible design. This system is controlled by an Arduino Nano, an open-source electronics platform, which regulates the flow of CO2 gas through electric solenoid valves. The Arduino and other inexpensive materials total ∼$150 (plus CO2 gas and regulator), and a new treatment can be added for less than $35. Easy-to-learn code and simple wire-to-connect hardware make the design extremely accessible, requiring little time and expertise to establish. The system functions with a variety of pH probes and can be adapted to fit a variety of experimental designs and organisms. Using this set up, we were able to constrain seawater pH within a range of 0.07 pH units. Our system thus maintains the performance and adaptability of existing systems but expands their accessibility by reducing cost and complexity.

Per the Statement of Work, the following tasks were outlined for completion in Year 2: 1). Testing, modification, and optimization of the system. 2). Addition of oxygen manipulation and monitoring. 3). Expansion of CO2 bubbling/pH reduction system to include oxygen addition/removal and temperature control. 4). Investigate alkalinity modification by the microbial cultures and its impact on the carbonate chemistry control of the system. 5).Deliverable: Seawater chemistry and temperature control and monitoring system for microbial culture studies under present and future ocean conditions.

Research assessing the biological impacts of global ocean change often requires a burdensome characterization of seawater carbonate chemistry. For laboratory-based ocean acidification research, this impedes the scope of experimental design. Honeywell Durafet (R) Ill pH electrodes provide precise and continuous seawater pH measurements. In addition to use in oceanographic sensor packages, Durafets can also be used in the laboratory to track and control seawater treatments via Honeywell Universal Dual Analyzers (UDAs). Here we provide performance data, instructions, and step-by-step recommendations for use of multiple UDA-Durafets. Durafet pH measurements were within +/-0.005 units pH(T) of spectrophotometric measurements and agreement among eight Durafets was better than +/-0.005 units pH(T). These results indicate equal performance to Durafets in oceanographic sensor packages, but methods for calibration and quality control differ. Use of UDA-Durafets vastly improves time-course documentation of experimental conditions and reduces person-hours dedicated to this activity. Due to the versatility of integrating Durafets in laboratory seawater systems, this technology opens the door to advance the scale of questions that the ocean acidification research community aims to address.

Seawater CO2 measurements are being made with increasing frequency as interest grows in the ocean's response to changing atmospheric CO2 levels and to climate change. The ultimate usefulness of these measurements depends on the data quality and consistency. An inter-laboratory comparison was undertaken to help evaluate and understand the current reliability of seawater CO2 measurements. Two seawater test samples of different CO2 content were prepared according to the usual method for the creation of seawater reference materials in the Dickson Laboratory at Scripps Institution of Oceanography. These two test samples were distributed in duplicate to more than 60 laboratories around the world. The laboratories returned their measurement results for one or more of the following parameters: total alkalinity (AT), total dissolved inorganic carbon (CT), and pH, together with information about the methods used and the expected uncertainty of the measurements. The majority of laboratories reported AT and CT values for all their measurements that were within 10μmolkg−1 of the assigned values (i.e. within ±0.5%), however few achieved results within 2μmolkg−1 (i.e. within ±0.1%), especially for CT. Results for the analysis of pH were quite scattered, with little suggestion of a consensus value. The high-CO2 test sample produced results for both CT and pH that suggested in many cases that CO2 was lost during analysis of these parameters. This study thus documents the current quality of seawater CO2 measurements in the various participating laboratories, and helps provide a better understanding of the likely magnitude of uncertainties in these measurements within the marine science community at the present time. Further improvements will necessarily hinge on adoption of an improved level of training in both measurement technique and of suitable quality control procedures for these measurements.

Spawning market squid lay embryo capsules on the seafloor of the continental shelf of the California Current System (CCS), where ocean acidification, deoxygenation and intensified upwelling lower the pH and [O2]. Squid statolith geochemistry has been shown to reflect the squid’s environment (e.g., seawater temperature and elemental concentration). We used real-world environmental levels of pH and [O2] observed on squid-embryo beds to test in the laboratory whether or not squid statolith geochemistry reflects environmental pH and [O2]. We asked whether pH and [O2] levels might affect the incorporation of element ratios (B:Ca, Mg:Ca, Sr:Ca, Ba:Ca, Pb:Ca, U:Ca) into squid embryonic statoliths as (1) individual elements and/or (2) multivariate elemental signatures, and consider future applications as proxies for pH and [O2] exposure. Embryo exposure to high and low pH and [O2] alone and together during development over four weeks only moderately affected elemental concentrations of the statoliths, and uranium was an important element driving these differences. Uranium:Ca was eight-times higher in statoliths exposed to low pHT (7.57–7.58) and low [O2] (79–82 µmol·kg−1) than those exposed to higher ambient pHT (7.92–7.94) and [O2] (241–243 µmol·kg−1). In a separate experiment, exposure to low pHT (7.55–7.56) or low [O2] (83–86 µmol·kg−1) yielded elevated U:Ca and Sr:Ca in the low [O2] treatment only. We found capsular effects on multiple elements in statoliths of all treatments. The multivariate elemental signatures of embryonic statoliths were distinct among capsules, but did not reflect environmental factors (pH and/or [O2]). We show that statoliths of squid embryos developing inside capsules have the potential to reflect environmental pH and [O2], but that these “signals” are generated in concert with the physiological effects of the capsules and embryos themselves.

The threat that ocean acidification (OA) poses to marine ecosystems is now recognized and U.S. funding agencies have designated specific funding for the study of OA. We present a research framework for studying OA that describes it as a biogeochemical event that impacts individual species and ecosystems in potentially unexpected ways. We draw upon specific lessons learned about ecosystem responses from research on acid rain, carbon dioxide enrichment in terrestrial plant communities, and nitrogen deposition. We further characterize the links between carbon chemistry changes and effects on individuals and ecosystems, and enumerate key hypotheses for testing. Finally, we quantify how U.S. research funding has been distributed among these linkages, concluding that there is an urgent need for research programs designed to anticipate how the effects of OA will reverberate throughout assemblages of species.

High biomass and heavy particle loads may interfere with carbonate chemistry analyses of samples from experimental aquaria and cultures used to investigate the impact of ocean acidification on organisms, as well as from biologically productive coastal regions. For such samples, a filtration method is needed that does not change the dissolved CO2 content, and consequently does not alter the total dissolved inorganic carbon and pH of the sample. Here, a filtration method is presented in which the sample seawater is pumped by a peristaltic pump through a replaceable 0.45 µm filter in a 50 mm polycarbonate filter holder and then into the sample bottle. Seawater samples of known carbonate composition were filtered to confirm that the filtration method did not alter the CO2 content, and compromise the subsequent sample analysis and data usefulness. Seawater samples with added phytoplankton concentrations in the range of 1–5 × 105 cells mL−1 were also filtered successfully. Finally, seawater with added biogenic CaCO3 was tested to prove that the method could successfully filter out such particles and produce dependable results. This approach will help to ensure more consistent and reliable carbonate chemistry measurements in coastal environments and from ocean acidification aquaria and cultures, by providing a well‐tested method for sample filtration.

Natural variation and changing climate in coastal oceans subject meroplanktonic organisms to broad ranges of pH and oxygen ([O2]) levels. In controlled‐laboratory experiments we explored the interactive effects of pH, [O2], and semidiurnal pH fluctuations on the survivorship, development, and size of early life stages of two mytilid mussels, Mytilus californianus and M. galloprovincialis. Survivorship of larvae was unaffected by low pH, low [O2], or semidiurnal fluctuations for both mytilid species. Low pH (<7.6) resulted in delayed transition from the trochophore to veliger stage, but this effect of low pH was absent when incorporating semidiurnal fluctuations in both species. Also at low pH, larval shells were smaller and had greater variance; this effect was absent when semidiurnal fluctuations of 0.3 units were incorporated at low pH for M. galloprovincialis but not for M. californianus. Low [O2] in combination with low pH had no effect on larval development and size, indicating that early life stages of mytilid mussels are largely tolerant to a broad range of [O2] reflective of their environment (80–260 μmol kg−1). The role of pH variability should be recognized as an important feature in coastal oceans that has the capacity to modulate the effects of ocean acidification on biological responses.

As the field of ocean acidification has grown, researchers have increasingly turned to laboratory experiments to understand the impacts of increased CO2 on marine organisms. However, other changes such as ocean warming and deoxygenation are occurring concurrently with the increasing CO2 concentrations, complicating the understanding of the impacts of anthropogenic changes on organisms. This experimental aquarium design allows for independent regulation of CO2 concentration, O2 levels, and temperature in a controlled environment to study the impacts of multiple stressors. The system has the flexibility for a wide range of treatment chemistry, seawater volumes, and study organisms. Control of the seawater chemistry is achieved by equilibration of a chosen gas mixture with seawater using a Liqui-Cel® membrane contactor. Included as examples, two experiments performed using the system have shown control of CO2 at values between approximately 500 and 1400 μatm and O2 at values from 80 to 240 μmol kg−1. Temperature has been maintained to 0.5 °C or better in the range of 10–17 °C. On a weeklong timescale, the system has achieved variability in pH of less than 0.007 pH units and in oxygen concentration of less than 3.5 μmol kg−1. Longer experiments, over a month in duration, have been completed with control to better than 0.08 pH units and 13 μmol kg−1 O2. The ability to study the impacts of multiple stressors in the laboratory simultaneously, as well as independently, will be an important part of understanding the response of marine organisms to a high-CO2 world.