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This study examines carbonate chemistry variability from 2008 to 2021 in subtropical coastal waters adjacent to Honolulu, Hawai'i. We use surface seawater carbon dioxide partial pressure (pCO2sw) measurements obtained every three hours from two buoys located along the south shore of O'ahu near anthropogenically impacted fringing reefs. The Ala Wai buoy was located 200 m offshore of a canal draining most of Honolulu, while the Kilo Nalu buoy was 1.3 miles (2 km) to the northwest, at a similar distance from shore with fewer terrestrial inputs. We compare pCO2sw variability from diurnal to interannual time scales. A trend analysis reveals a statistically significant increase in pCO2sw of +1.84 ± 0.27 µatm per year over the 11-year period. This rate is slightly lower than the average atmospheric growth rate observed during the same timeframe. In contrast to a nearby open-ocean site, the coastal sites experience amplified shorter-term variability, while seasonal to inter-annual variability is comparable to the open ocean. Ala Wai exhibits greater ranges than Kilo Nalu in all carbonate system variables due to its proximity to the Ala Wai Canal outflow. We examine the drivers that may explain both the similarities and contrasts in carbon dynamics observed between the two locations. Drivers of aragonite saturation state (WAr), an important variable for quantifying ocean acidification, are isolated from the in-situ time-series. Interannual salinity variations both due to freshwater pulses and large-scale regional salinity changes have a larger impact on WAr than temperature changes, which mostly have an effect seasonally. A large biological contribution to WAr is suspected, and further investigated using TA/DIC ratios normalized to median salinity and their slopes. Observed ratios at the south shore sites are evaluated relative to expected ratios derived from an open-ocean reference. Results suggest that dissolution and respiration are the primary biogeochemical processes occurring at these coastal sites. This highlights the significance of carbonate dissolution in anthropogenically impacted coastal waters, which is likely buffering acidification due to anthropogenic CO2 and freshwater inputs at these sites. [ABSTRACT FROM AUTHOR]

One of the major challenges to assessing the impact of ocean acidification on marine life is the need to better understand the magnitude of long-term change in the context of natural variability. This study addresses this need through a global synthesis of monthly pH and aragonite saturation state (Ωarag) climatologies for 12 open ocean, coastal, and coral reef locations using 3-hourly moored observations of surface seawater partial pressure of CO2 and pH collected together since as early as 2010. Mooring observations suggest open ocean subtropical and subarctic sites experience present-day surface pH and Ωarag conditions outside the bounds of pre-industrial variability throughout most, if not all, of the year. In general, coastal mooring sites experience more natural variability and thus, more overlap with pre-industrial conditions; however, present day Ωarag conditions surpass biologically relevant thresholds associated with ocean acidification impacts on Mytilus californianus (Ωarag < 1.8) and Crassostrea gigas (Ωarag < 2.0) larvae in the California Current Ecosystem (CCE) and Mya arenaria larvae in the Gulf of Maine (Ωarag < 1.6). At the most variable mooring locations in coastal systems of the CCE, subseasonal conditions approached Ωarag = 1. Global and regional models and data syntheses of ship-based observations tended to underestimate seasonal variability compared to mooring observations. Efforts such as this to characterize all modes of pH and Ωarag variability and change at key locations are fundamental to assessing present-day biological impacts of ocean acidification, further improving experimental design to interrogate organism response under real-world conditions, and improving predictive models and vulnerability assessments seeking to quantify the broader impacts of ocean acidification. [ABSTRACT FROM AUTHOR]

Based on measureraents from the WOCE/JGOFS global CO2 survey> the CLIVAR/CO2 Repeat Hydrography Program and the Canadian Line P survey, we have observed an average decrease of 0.34% yr-1 in the saturation state of surface seawater in the Pacific Ocean with respect to aragonite and calcite. The upward migrations of the aragonite and calcite saturation horizons, averaging about 1 to 2 m yr-1, are the direct result of the uptake of anthropogenic CO2 by the oceans and regional changes in circulation and biogeochemical processes. The shoaling of the saturation horizon is regionally variable, with more rapid shoaling in the South Pacific where there is a larger uptake of anthropogenic CO2. In some locations, particularly in the North Pacific Subtropical Gyre and in the California Current, the decadal changes in circulation can be the dominant factor in controlling the migration ofthe saturation horizon. If COs emissions contimie as projected over the rest of this century, the resulting changes in the marine carbonate system would mcan that many coral reef systems in the Pacific would no longer be able to sustain a sufficiently high rate of calcification to maintain the viability of these ecosystems as a whole, and thcse changes perhaps could seriously impact the thousands of marine species that depend on them for survival [ABSTRACT FROM AUTHOR]

A multiparameter linear regression model (MLR) of aragonite saturation state (ΩARG) as a function of temperature, pressure and O2 concentration in the upper 1,000 m of the Sea of Japan (East Sea) was derived with an uncertainty of ±0.020 (1σ). The ΩARG data (n = 1,482) used to derive the basin-wide ΩARG prediction model were collected during a field survey in 1999 and were corrected for anthropogenic CO2. Some biases were resolved by addition of a pressure and O2 concentration interaction term to the proposed model. Correlation between the two predictor terms, caused by addition of this term, was minimized by centering the data for the three variables (thus subtracting the mean from each individual data point). Validation of the model against data sets obtained in 1992 and 2007 yielded correlation coefficients of 0.995 ± 0.013 for 1992 (n = 64, p ⪡ 0.001) and 0.995 ± 0.009 for 2007 (n = 137, p ⪡ 0.001) and root mean square errors of ±0.064 for 1992 and ±0.050 for 2007: The strong correlation between measurements and predictions suggests that the model can be used to estimate the distribution of ΩARG in the Sea of Japan (East Sea) (including dynamic coastal waters) on varying time scales when basic hydrographic data on temperature, pressure and O2 concentration are available. Application of the model to past measurements for the Sea of Japan (East Sea) indicated that interdecadal variability (2σ from the mean) in ΩARG corrected for anthropogenic CO2 was generally high (0.1-0.7) in the upper water layer (<200 m depth), and decreased (0.05-0.2) with depth for waters deeper than 500 m. The interdecadal variability is largely controlled by variations in the degree of water column ventilation. Superimposed on this natural variability, the input of CO2 derived from fossil fuels has markedly acidified the upper water layers during the anthropocene and thereby moved the aragonite saturation horizon upward by 50-250 m. The impact of CO2 derived from fossil fuels on upper ocean acidification will increase in the future. The present study indicates that, in combination with other easily measurable parameters, a multifunctional model can be a powerful tool for predicting the temporal evolution Of ΩARG in the ocean, including coastal waters that are highly likely to be susceptible to ocean acidification in the future. [ABSTRACT FROM AUTHOR]

Rising atmospheric carbon dioxide (CO[sub 2]) concentrations over the past two centuries have led to greater CO[sub 2] uptake by the oceans. This acidification process has changed the saturation state of the oceans with respect to calcium carbonate (CaCO[sub 3]) particles. Here we estimate the in situ CaCO[sub 3] dissolution rates for the global oceans from total alkalinity and chlorofluorocarbon data, and we also discuss the future impacts of anthropogenic CO[sub 2] on CaCO[sub 3] shellforming species. CaCO[sub 3] dissolution rates, ranging from 0.003 to 1.2 micromoles per kilogram per year, are observed beginning near the aragonite saturation horizon. The total water column CaCO[sub 3] dissolution rate for the global oceans is approximately 0.5 ± 0.2 petagrams of CaCO[sub 3]-C per year, which is approximately 45 to 65% of the export production of CaCO[sub 3]. [ABSTRACT FROM AUTHOR]

The dissolution of aragonite particles in the ocean primarily depends on the degree of undersaturation of seawater with respect to that mineral. Most of the upper Atlantic Ocean, particularly north of 30°S and at depths of less than 2000 m, is supersaturated with respect to aragonite, whereas much of the deep Atlantic is undersaturated. Here we report, for the first time, shallow layers of aragonite-undersaturated water between 20°S and 15°N in the eastern tropical Atlantic. These layers are centered at 800 m and are surrounded by aragonite-supersaturated water above and below. This feature most likely results from a combination of chemical and biological processes including the uptake of anthropogenic CO2, and the oxidation of organic matter falling from the highly productive overlying surface water. Reaction with protons resulting from these processes decreases the carbonate ion concentration and consequently the saturation state of the waters with respect to aragonite. The oceanic uptake of anthropogenic CO2 during the industrial era has caused a significant increase in the size of the undersaturated layers. Future expansion will likely occur laterally to the west and south, where the degree of supersaturation is low compared to waters to the north. This expansion of the undersaturated layers is a prime example of how human activity during the industrial era has altered the upper ocean chemistry by injecting fossil fuel CO2 into the ocean. [ABSTRACT FROM AUTHOR]

We report an annual cycle of surface seawater aragonite mineral saturation state (Ω arag ) during 2006–2007 at the Gray's Reef time-series site off Georgia, USA, calculated based on three-hourly observations of carbon dioxide partial pressure ( p CO 2 ) and salinity-derived total alkalinity. Ω arag varied between 2.30 and 4.39 with low values (< 3.00) mainly during February–April 2007 and high values (> 3.50) during July–October 2006 and July–September 2007 as well as during two biological production spikes (April–June 2007). We first present a qualitative analysis of the drivers of Ω arag variability based on property regressions with surface temperature, salinity and apparent oxygen utilization, and then quantify the contributions of temperature, air-sea exchange, mixing, and biological processes to monthly Ω arag net changes using a simple 1-D mass budget model. Our analyses suggest that river inputs played the most important role in the seasonal variation of surface Ω arag , in contrast to temperature control on p CO 2 . Nevertheless, the primary processes controlling monthly Ω arag net change varied with time of year. Furthermore, river inputs lowered Ω arag by 0.28 and 0.48 in July–August and September–October 2007 relative to the equivalent periods of 2006. This implies that interannual Ω arag variability at this location may be greater than that due to the influence of increased atmospheric CO 2 over the past few decades, making efforts to discern decadal coastal ocean acidification trends particularly challenging. In addition, although sea surface salinity varies substantially in coastal waters, our analysis suggests that similar to the open ocean Ω arag is essentially determined by carbonate ion concentration ([CO 3 2 − ]), not calcium ion concentration ([Ca 2 + ]) or the stoichiometric solubility product (K′ sp ), both varying substantially with salinity. Finally, we show that the difference between total alkalinity (TA) and dissolved inorganic carbon (DIC) is a better proxy for [CO 3 2 − ] and Ω arag compared with the ratio (TA/DIC) and helps to better elucidate processes affecting Ω arag in coastal oceans. [ABSTRACT FROM AUTHOR]

The continental shelf region off the west coast of North America is seasonally exposed to water with a low aragonite saturation state by coastal upwelling of CO 2 -rich waters. To date, the spatial and temporal distribution of anthropogenic CO 2 (C anth ) within the CO 2 -rich waters is largely unknown. Here we adapt the multiple linear regression approach to utilize the GO-SHIP Repeat Hydrography data from the northeast Pacific to establish an annually updated relationship between C anth and potential density. This relationship was then used with the NOAA Ocean Acidification Program West Coast Ocean Acidification (WCOA) cruise data sets from 2007, 2011, 2012, and 2013 to determine the spatial variations of C anth in the upwelled water. Our results show large spatial differences in C anth in surface waters along the coast, with the lowest values (37–55 μmol kg −1 ) in strong upwelling regions off southern Oregon and northern California and higher values (51–63 μmol kg −1 ) to the north and south of this region. Coastal dissolved inorganic carbon concentrations are also elevated due to a natural remineralized component (C bio ), which represents carbon accumulated through net respiration in the seawater that has not yet degassed to the atmosphere. Average surface C anth is almost twice the surface remineralized component. In contrast, C anth is only about one third and one fifth of the remineralized component at 50 m and 100 m depth, respectively. Uptake of C anth has caused the aragonite saturation horizon to shoal by approximately 30–50 m since the preindustrial period so that undersaturated waters are well within the regions of the continental shelf that affect the shell dissolution of living pteropods. Our data show that the most severe biological impacts occur in the nearshore waters, where corrosive waters are closest to the surface. Since the pre-industrial times, pteropod shell dissolution has, on average, increased approximately 19–26% in both nearshore and offshore waters. [ABSTRACT FROM AUTHOR]

The dissolution of aragonite particles in the ocean primarily depends on the degree of undersaturation of seawater with respect to that mineral. Most of the upper Atlantic Ocean, particularly north of 30°S and at depths of less than 2000 m, is supersaturated with respect to aragonite, whereas much of the deep Atlantic is undersaturated. Here we report, for the first time, shallow layers of aragonite-undersaturated water between 20°S and 15°N in the eastern tropical Atlantic. These layers are centered at 800 m and are surrounded by aragonite-supersaturated water above and below. This feature most likely results from a combination of chemical and biological processes including the uptake of anthropogenic CO2, and the oxidation of organic matter falling from the highly productive overlying surface water. Reaction with protons resulting from these processes decreases the carbonate ion concentration and consequently the saturation state of the waters with respect to aragonite. The oceanic uptake of anthropogenic CO2 during the industrial era has caused a significant increase in the size of the undersaturated layers. Future expansion will likely occur laterally to the west and south, where the degree of supersaturation is low compared to waters to the north. This expansion of the undersaturated layers is a prime example of how human activity during the industrial era has altered the upper ocean chemistry by injecting fossil fuel CO2 into the ocean. [ABSTRACT FROM AUTHOR]