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Abstract An open question in marine carbon chemistry is if organic alkalinity (or some other unidentified species) is present in non‐negligible quantities in the open ocean. If organic alkalinity is indeed present, different methods for total alkalinity (TA) analysis with different titration endpoints could titrate different amounts depending on the dissociation constants (pK_a) of the acids present, resulting in meaningful differences or offsets between methods. Two commonly used methods, open‐cell titration with non‐linear least squares fitting and single‐step titration with spectrophotometric endpoint detection, might titrate different amounts of organic alkalinity, if present, depending on their pK_a. We test this hypothesis using paired samples collected on two cruises, one in the northwest Pacific and one in the western Arctic, and analyze the TA using both methods. We found the differences to be statistically indistinguishable (∆TA_{[Open‐Cell−Single‐Step]} = 0.5 ± 3.9 μmol kg⁻¹_swmean and standard deviationN = 206). Adjustment of the single‐step TA to certified reference material could be obscuring a difference in the methods. The good agreement between methods indicated that the analytical method is not the cause of offsets in Pacific TA identified by the Global Ocean Data Analysis Project version 2. From these results, the presence of organic alkalinity in open ocean waters remains inconclusive but suggests that if present, the concentration is either very low or both methods titrate similar amounts. 

Abstract Total alkalinity (TA) plays an important role in buffering seawater and determining how much anthropogenic carbon dioxide the oceans can absorb and mitigate the rise in atmospheric concentrations. Total alkalinity varies with location, depth, and time making it an important variable needed to quantify and monitor ocean acidification, and potentially for ocean alkalinity enhancement interventions. Currently, best practices are to use expensive high‐quality borosilicate glass bottles for collecting and storing these samples. However, unlike other carbon system variables, TA is not affected by gas exchange meaning plastic bottles may be suitable for TA sample storage. Plastic bottles are lighter, cheaper, and less prone to breakage making them easier to handle and ship. Here, we test the suitability of high‐density polyethylene (HDPE) for collection and long‐term storage of TA samples. In two sets of experiments, it was determined that HDPE is not suitable for long‐term storage of TA samples as there were large changes in TA over time and precision of duplicate samples was very poor. We hypothesize that HDPE plastic is slightly porous leading to leaching of alkalinity either into or out of the bottle over time impacting the value of the sample. Use of HDPE bottles for TA samples is not recommended for long term sample storage. 

Abstract Nitrite is a ubiquitous compound found across aquatic systems and an intermediate in both the oxidative and reductive metabolisms transforming fixed nitrogen in the environment. Yet, the abiotic cycling of nitrite is often overlooked in favor of biologically mediated reactions. Here we quantify the apparent acid dissociation constant (pK_a) between nitrous acid and its conjugate base nitrite in both freshwater and seawater systems across a range of environmentally relevant temperatures (5–35°C) using potentiometric‐based titration. In freshwater, we measured a pK_a,NBSof 3.14 at 25°C and a pK_a,Tof 2.87 for seawater at the same temperature. We quantify substantial effects of both salinity and temperature on the pK_a, with colder and fresher water manifesting higher values and thus a greater proportion of protonated nitrite at any given pH. Because nitrous acid is unstable and decomposes to nitric oxide, the implications for the nitrous acid dissociation constant on ecosystem function are broad. 

Abstract Increased oceanic uptake of CO₂due to rising anthropogenic emissions has caused lowered pH levels (ocean acidification) that are hypothesized to diminish biotic calcification and reduce the export of total alkalinity (A_T) as carbonate minerals from the surface ocean or their burial in coastal sediments. This “CO₂‐biotic calcification feedback” is a negative feedback on atmospheric CO₂, as elevated levels of surfaceA_Tincrease the ocean's capacity to uptake CO₂. We detect signatures of this feedback in the global ocean for the first time using repeat hydrographic measurements and seawater property prediction algorithms. Over the course of the past 30 years, we find an increase in global surfaceA_Tof 0.072 ± 0.023 μmol kg⁻¹ yr⁻¹, which would have caused approximately 20 Tmol of additionalA_Tto accumulate in the surface ocean. This finding suggests that anthropogenic CO₂emissions are measurably perturbing the cycling of carbon on a planetary scale by disrupting biological patterns. More observations ofA_Twould be required to understand the effects of this feedback on a regional basis and to fully characterize its potential to reduce the efficiency of marine carbon dioxide removal technology. 

Abstract Seawater carbonate chemistry observations are increasingly necessary to study a broad array of oceanographic challenges such as ocean acidification, carbon inventory tracking, and assessment of marine carbon dioxide removal strategies. The uncertainty in a seawater carbonate chemistry observation comes from unknown random variations and systematic offsets. Here, we estimate the magnitudes of these random and systematic components of uncertainty for the discrete open‐ocean carbonate chemistry measurements in the Global Ocean Data Analysis Project 2022 update (GLODAPv2.2022). We use both an uncertainty propagation approach and a carbonate chemistry measurement “inter‐consistency” approach that quantifies the disagreement between measured carbonate chemistry variables and calculations of the same variables from other carbonate chemistry measurements. Our inter‐consistency analysis reveals that the seawater carbonate chemistry measurement community has collected and released data with a random uncertainty that averages about 1.7 times the uncertainty estimated by propagating the desired “climate‐quality” random uncertainties. However, we obtain differing random uncertainty estimates for subsets of the available data, with some subsets seemingly meeting the climate‐quality criteria. We find that seawater pH measurements on the total scale do not meet the climate‐quality criteria, though the inter‐consistency of these measurements improves (by 38%) when limited to the subset of measurements made using purified indicator dyes. We show that GLODAPv2 adjustments improve inter‐consistency for some subsets of the measurements while worsening it for others. Finally, we provide general guidance for quantifying the random uncertainty that applies for common combinations of measured and calculated values. 

Abstract The ocean carbonate system is critical to monitor because it plays a major role in regulating Earth's climate and marine ecosystems. It is monitored using a variety of measurements, and it is commonly understood that all components of seawater carbonate chemistry can be calculated when at least two carbonate system variables are measured. However, several recent studies have highlighted systematic discrepancies between calculated and directly measured carbonate chemistry variables and these discrepancies have large implications for efforts to measure and quantify the changing ocean carbon cycle. Given this, the Ocean Carbonate System Intercomparison Forum (OCSIF) was formed as a working group through the Ocean Carbon and Biogeochemistry program to coordinate and recommend research to quantify and/or reduce uncertainties and disagreements in measurable seawater carbonate system measurements and calculations, identify unknown or overlooked sources of these uncertainties, and provide recommendations for making progress on community efforts despite these uncertainties. With this paper we aim to (1) summarize recent progress toward quantifying and reducing carbonate system uncertainties; (2) advocate for research to further reduce and better quantify carbonate system measurement uncertainties; (3) present a small amount of new data, metadata, and analysis related to uncertainties in carbonate system measurements; and (4) restate and explain the rationales behind several OCSIF recommendations. We focus on open ocean carbonate chemistry, and caution that the considerations we discuss become further complicated in coastal, estuarine, and sedimentary environments. 

Evidence for the shallow cycling of calcium carbonate in the global ocean is mounting, but the mechanisms driving the dissolution of thermodynamically stable polymorphs, like aragonite and calcite, in the surface ocean remain unconstrained. Here, we quantify how microbial metabolism creates acidic microenvironments in marine particles that enhance the local dissolution of calcite despite supersaturated conditions in bulk waters. A temporal decoupling of particle deoxygenation and acidification suggests that respiration-derived carbon dioxide is not the sole driver of the observed undersaturation. Rapid dissolution occurs in particles exhibiting bacterial growth, with rates exceeding abiotic dissolution at the same bulk saturation by more than an order of magnitude. We observe the highest particle-associated dissolution rates at intermediate settling velocities, indicating that a trade-off between elevated mass transfer due to settling and bacterial respiration governs the ensuing dissolution rates. Translation of our experiments to the water column suggests that microbially driven undersaturation in marine particles may dissolve sufficient calcite in the mesopelagic ocean to extend particle transit times by eliminating this vital ballast mineral, reducing the efficiency of organic carbon sequestration. 

Abstract. The Global Ocean Data Analysis Project (GLODAP) is a synthesis effort providing regular compilations of surface to bottom ocean biogeochemical bottle data, with an emphasis on seawater inorganic carbon chemistry and related variables determined through chemical analysis of seawater samples. GLODAPv2.2023 is an update of the previous version, GLODAPv2.2022 (Lauvset et al., 2022). The major changes are as follows: data from 23 new cruises were added. In addition, a number of changes were made to the data included in GLODAPv2.2022. GLODAPv2.2023 includes measurements from more than 1.4 million water samples from the global oceans collected on 1108 cruises. The data for the now 13 GLODAP core variables (salinity, oxygen, nitrate, silicate, phosphate, dissolved inorganic carbon, total alkalinity, pH, chlorofluorocarbon-11 (CFC-11), CFC-12, CFC-113, CCl4, and SF6) have undergone extensive quality control with a focus on the systematic evaluation of bias. The data are available in two formats: (i) as submitted by the data originator but converted to World Ocean Circulation Experiment (WOCE) exchange format and (ii) as a merged data product with adjustments applied to minimize bias. For the present annual update, adjustments for the 23 new cruises were derived by comparing those data with the data from the 1085 quality-controlled cruises in the GLODAPv2.2022 data product using crossover analysis. SF6 data from all cruises were evaluated by comparison with CFC-12 data measured on the same cruises. For nutrients and ocean carbon dioxide (CO2), chemistry comparisons to estimates based on empirical algorithms provided additional context for adjustment decisions. The adjustments that we applied are intended to remove potential biases from errors related to measurement, calibration, and data-handling practices without removing known or likely time trends or variations in the variables evaluated. The compiled and adjusted data product is believed to be consistent to better than 0.005 in salinity, 1 % in oxygen, 2 % in nitrate, 2 % in silicate, 2 % in phosphate, 4 µmol kg−1 in dissolved inorganic carbon, 4 µmol kg−1 in total alkalinity, 0.01–0.02 in pH (depending on region), and 5 % in the halogenated transient tracers. The other variables included in the compilation, such as isotopic tracers and discrete CO2 fugacity (fCO2), were not subjected to bias comparison or adjustments. The original data, their documentation, and DOI codes are available at the Ocean Carbon and Acidification Data System of NOAA National Centers for Environmental Information (NCEI), which also provides access to the merged data product. This is provided as a single global file and as four regional ones – the Arctic, Atlantic, Indian, and Pacific oceans – under https://doi.org/10.25921/zyrq-ht66 (Lauvset et al., 2023). These bias-adjusted product files also include significant ancillary and approximated data, which were obtained by interpolation of, or calculation from, measured data. This living data update documents the GLODAPv2.2023 methods and provides a broad overview of the secondary quality control procedures and results.