Total- and Monomethyl-Mercury and Major Ions in Coastal California Fog Water: Results from Two Years of Sampling on Land and at Sea

Marine fog water samples were collected over two summers (2014–2015) with active strand collectors (CASCC) at eight coastal sites from Humboldt to Monterey counties in California, USA, and on four ocean cruises along the California coastline in order to investigate mercury (Hg) cycling at the ocean-atmosphere-land interface. The mean concentration of monomethylmercury (MMHg) in fog water across terrestrial sites for both years was 1.6 ± 1.9 ng L-1 (\u3c0.01–10.4 ng L-1, N = 149), which corresponds to 5.7% (2.0–10.8%) of total Hg (HgT) in fog. Rain water samples from three sites had mean MMHg concentrations of 0.20 ± 0.12 ng L-1 (N = 5) corresponding to 1.4% of HgT. Fog water samples collected at sea had MMHg concentrations of 0.08 ± 0.15 ng L-1 (N = 14) corresponding to 0.4% of HgT. Significantly higher MMHg concentrations in fog were observed at terrestrial sites next to the ocean relative to a site 40 kilometers inland, and the mean difference was 1.6 ng L-1. Using a rate constant for photo-demethylation of MMHg of -0.022 h-1 based on previous demethylation experiments and a coastal-inland fog transport time of 12 hours, a mean difference of only 0.5 ng L-1 of MMHg was predicted between coastal and inland sites, indicating other unknown source and/or sink pathways are important for MMHg in fog. Fog water deposition to a standard passive 1.00 m2 fog collector at six terrestrial sites averaged 0.10 ± 0.07 L m-2 d-1, which was ∼2% of typical rainwater deposition in this area. Mean air-surface fog water fluxes of MMHg and HgT were then calculated to be 34 ± 40 ng m-2 y-1 and 546 ± 581 ng m-2 y-1, respectively. These correspond to 33% and 13% of the rain fluxes, respectively

Influence of synoptic weather events on the isotopic composition of atmospheric moisture in a coastal city of the western United States

Synoptic weather events are known to strongly influence the isotope composition ofprecipitation in continental locations. In this study, we present hourly values of water vaporisotopologues (HDO and H218O) measured over a 30 day period in locally extreme weatherconditions, including Santa Ana winds and winter rainstorms, in San Diego, California,USA. We investigate how atmospheric and hydrological processes influence HDO andH218O using an isotope-enabled GCM model (IsoGSM). Combining measurements andIsoGSM simulation, we demonstrate that convective mixing of marine and continental airmasses are responsible for the isotopic variation of near-surface water vapor in this coastallocation. The isotopic variability is most pronounced during Santa Ana winds. The SantaAna winds represent a unique boundary layer condition in which atmospheric mixingbecomes the process that dominantly controls the changes in the isotopic compositionrelative to air humidity. We demonstrate that a two-source mixing approach (Keeling plot)can reliably be used to estimate the isotopic composition of the source moisture, and fromthat, to infer the location of the moisture origin that contributes to the atmospheric moisturecontent in southern California. The present study is unique because it combines large-scaleisotope GCM modeling with a robust and high-resolution isotope data set to disentangle thecontrol of atmospheric and hydrologic processes on the atmospheric humidity in anextratropical climate. Our results demonstrate the utility of using single-point, ground-basedisotope observations as a complementary resource to existing satellite isotopemeasurements for constraining isotope-enabled GCMs in future investigation ofatmospheric water cycle

Seawater carbonate chemistry and growth and survival of native and commercial oysters

The effects of climate change, including ocean acidification and ocean heatwaves, on biological communities in estuaries are often uncertain. Part of the uncertainty is due to the complex suite of environmental factors in addition to acidification and warming that influence the growth of shells and skeletons of many estuarine organisms. The goal of this study was to document spatial and temporal variation in water column properties and to measure the in situ effects on larval and recently settled stages of ecologically important Olympia oysters (Ostrea lurida) and commercially important Pacific oysters (Crassostrea gigas) in a low‐inflow estuary with a Mediterranean climate in Northern California. Our results reveal that seasonal inputs of upwelled or riverine water create important and predictable gradients of carbonate system parameters, temperature, salinity, dissolved oxygen (DO), and other variables that influence oyster performance, and that the influence of these gradients is contingent upon the location in the estuary as well as seasonal timing. During upwelling events (dry season), temperature, carbonate chemistry, and DO had the greatest impact on oyster performance. During runoff events (wet season), gradients in salinity, nutrient concentrations, and total alkalinity driven by river discharge were comparatively more important. These results suggest that the spatial importance of carbonate chemistry and temperature are seasonally variable and are two of several other factors that determine oyster performance. We use these results to discuss future impacts on oysters given projected regional changes in the frequency and magnitude of upwelling and precipitation‐driven runoff events

Influence of synoptic weather events on the isotopic composition of atmospheric moisture in a coastal city of the western United States

Synoptic weather events are known to strongly influence the isotope composition ofprecipitation in continental locations. In this study, we present hourly values of water vaporisotopologues (HDO and H218O) measured over a 30 day period in locally extreme weatherconditions, including Santa Ana winds and winter rainstorms, in San Diego, California,USA. We investigate how atmospheric and hydrological processes influence HDO andH218O using an isotope-enabled GCM model (IsoGSM). Combining measurements andIsoGSM simulation, we demonstrate that convective mixing of marine and continental airmasses are responsible for the isotopic variation of near-surface water vapor in this coastallocation. The isotopic variability is most pronounced during Santa Ana winds. The SantaAna winds represent a unique boundary layer condition in which atmospheric mixingbecomes the process that dominantly controls the changes in the isotopic compositionrelative to air humidity. We demonstrate that a two-source mixing approach (Keeling plot)can reliably be used to estimate the isotopic composition of the source moisture, and fromthat, to infer the location of the moisture origin that contributes to the atmospheric moisturecontent in southern California. The present study is unique because it combines large-scaleisotope GCM modeling with a robust and high-resolution isotope data set to disentangle thecontrol of atmospheric and hydrologic processes on the atmospheric humidity in anextratropical climate. Our results demonstrate the utility of using single-point, ground-basedisotope observations as a complementary resource to existing satellite isotopemeasurements for constraining isotope-enabled GCMs in future investigation ofatmospheric water cycle