Seawater CO2-Chemistry Variability in the Near-Shore Environment of the Southern California Bight

Seawater CO2-chemistry in the Southern California Bight (SCB) has been well characterized at seasonal resolution over the past several decades by multiple research expeditions. However, the near-shore environment (0-2 km) has largely been absent from these surveys and the drivers of seawater CO2-chemistry variability in this region remain to be fully characterized. In particular, the role of variable upwelling intensity is poorly known, and could have important implications for near-shore habitats sensitive to low pH and ΩAr conditions. Here, I present near-shore seawater CO2-chemistry data based on monthly transects between March 2017 and September 2018 at four stations extending from the Scripps Pier to the 60 m depth contour (~2 km offshore). Seawater samples were analyzed for seawater CO2-chemistry parameters and were paired with autonomous sensors deployed at 18 m depth. The results showed that during fall and winter, pH and ΩAr values ranged from 7.9-8.1 and 1.8-2.9 along the transect, respectively. During spring and summer, intensified upwelling transported low pH and ΩAr seawater to the near-shore region reaching values as low as 7.69 and 0.95, respectively, at depths less than 20 m and within 1 km of the shoreline. The low pH and ΩAr conditions typically persisted for several months from April to July. The magnitude of change in pH and ΩAr was correlated with the density of the water, i.e., the higher the density the lower the pH and ΩAr, but did not show direct correlation with the total amount of water that was upwelled

Monthly cross-shore transects of biogeochemical properties in La Jolla, CA

Dataset: La Jolla Nearshore BiogeochemistryThese data result from monthly cross-shore transects of biogeochemical properties in La Jolla, CA. In this study, discrete seawater samples were collected between 0-40m on a monthly transect extending from the coastline to ~2km offshore in La Jolla, CA. Seawater samples were collected for analysis of dissolved inorganic carbon chemistry parameters and dissolved inorganic nutrient concentrations. The study was designed to characterize the biogeochemical near-shore spatiotemporal variability in the Southern California Bight, and in particular, the influence of seasonal upwelling. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/839175NSF Division of Ocean Sciences (NSF OCE) OCE-125504

Spatial surveys of carbonate chemistry in Heron Reef, Great Barrier Reef, Australia

Dataset: Heron Reef Carbonate ChemistrySeawater samples and environmental measurements were collected across the Heron Island coral reef during three reef-scale surveys in the morning and evening in October of 2015. Seawater samples were analyzed for dissolved inorganic carbon chemistry parameters. The study was designed to characterize the natural spatio-temporal variability of carbonate chemistry and environmental parameters across the entire coral reef system. The spatial surveys were complemented with autonomous sensors making high frequency measurements at three locations. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/839261NSF Division of Ocean Sciences (NSF OCE) OCE-125504

Seasonal nearshore ocean acidification and deoxygenation in the Southern California Bight

The California Current System experiences seasonal ocean acidification and hypoxia (OAH) owing to wind-driven upwelling, but little is known about the intensity, frequency, and depth distribution of OAH in the shallow nearshore environment. Here we present observations of OAH and dissolved inorganic carbon and nutrient parameters based on monthly transects from March 2017 to September 2018 extending from the surf zone to the ~ 40 m depth contour in La Jolla, California. Biologically concerning OAH conditions were observed at depths as shallow as 10 m and as close as 700 m to the shoreline. Below 20 m depth, 8% of observations were undersaturated with respect to aragonite, 28% of observations had a pHT less than 7.85, and 19% of observations were below the sublethal oxygen threshold of 157 µmol kg-1. These observations raise important questions about the impacts of OAH on coastal organisms and ecosystems and how future intensified upwelling may exacerbate these conditions

Temporal and Spatial Variabilities of Chemical and Physical Parameters on the Heron Island Coral Reef Platform

Globally, coral reefs are threatened by ocean warming and acidification. The degree to which acidification will impact reefs is dependent on the local hydrodynamics, benthic community composition, and biogeochemical processes, all of which vary on different temporal and spatial scales. Characterizing the natural spatiotemporal variability of sea- water carbonate chemistry across different reefs is critical for elucidating future impacts on coral reefs. To date, most studies have focused on select habitats, whereas fewer studies have focused on reef scale variability. Here, we investigate the temporal and spatial seawa- ter physicochemical variability across the entire Heron Island coral reef platform, Great Barrier Reef, Australia, for a limited duration of six days. Autonomous sensor measure- ments at three sites across the platform were complemented by reef-wide boat surveys and discrete sampling of seawater carbonate chemistry during the morning and evening. Vari- ability in both temporal and spatial physicochemical properties were predominantly driven by solar irradiance (and its effect on biological activity) and the semidiurnal tidal cycles but were influenced by the local geomorphology resulting in isolation of the platform dur- ing low tide and rapid flooding during rising tides. As a result, seawater from previous tidal cycles was sometimes trapped in different parts of the reef leading to unexpected bio- geochemical trends in space and time. This study illustrates the differences and limitations of data obtained from high-frequency measurements in a few locations compared to low- frequency measurements at high spatial resolution and coverage, showing the need for a combined approach to develop predictive capability of seawater physicochemical proper- ties on coral reefs

Temporal and Spatial Variabilities of Chemical and Physical Parameters on the Heron Island Coral Reef Platform

Globally, coral reefs are threatened by ocean warming and acidification. The degree to which acidification will impact reefs is dependent on the local hydrodynamics, benthic community composition, and biogeochemical processes, all of which vary on different temporal and spatial scales. Characterizing the natural spatiotemporal variability of seawater carbonate chemistry across different reefs is critical for elucidating future impacts on coral reefs. To date, most studies have focused on select habitats, whereas fewer studies have focused on reef scale variability. Here, we investigate the temporal and spatial seawater physicochemical variability across the entire Heron Island coral reef platform, Great Barrier Reef, Australia, for a limited duration of six days. Autonomous sensor measurements at three sites across the platform were complemented by reef-wide boat surveys and discrete sampling of seawater carbonate chemistry during the morning and evening. Variability in both temporal and spatial physicochemical properties were predominantly driven by solar irradiance (and its effect on biological activity) and the semidiurnal tidal cycles but were influenced by the local geomorphology resulting in isolation of the platform during low tide and rapid flooding during rising tides. As a result, seawater from previous tidal cycles was sometimes trapped in different parts of the reef leading to unexpected biogeochemical trends in space and time. This study illustrates the differences and limitations of data obtained from high-frequency measurements in a few locations compared to low-frequency measurements at high spatial resolution and coverage, showing the need for a combined approach to develop predictive capability of seawater physicochemical properties on coral reefs

Short-term acidification promotes diverse iron acquisition and conservation mechanisms in upwelling-associated phytoplankton

Coastal upwelling regions are among the most productive marine ecosystems but may be threatened by amplified ocean acidification. Increased acidification is hypothesized to reduce iron bioavailability for phytoplankton thereby expanding iron limitation and impacting primary production. Here we show from community to molecular levels that phytoplankton in an upwelling region respond to short-term acidification exposure with iron uptake pathways and strategies that reduce cellular iron demand. A combined physiological and multi-omics approach was applied to trace metal clean incubations that introduced 1200 ppm CO2 for up to four days. Although variable, molecular-level responses indicate a prioritization of iron uptake pathways that are less hindered by acidification and reductions in iron utilization. Growth, nutrient uptake, and community compositions remained largely unaffected suggesting that these mechanisms may confer short-term resistance to acidification; however, we speculate that cellular iron demand is only temporarily satisfied, and longer-term acidification exposure without increased iron inputs may result in increased iron stress