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Paulsen, ML, Andersson AJ, Aluwihare L, Cyronak T, D'Angelo S, Davidson C, Elwany H, Giddings SN, Page HN, Porrachia M, Schroeter S.  2018.  Temporal changes in seawater carbonate chemistry and carbon export from a Southern California estuary. Estuaries and Coasts. 41:1050-1068.   10.1007/s12237-017-0345-8   AbstractWebsite

Estuaries are important subcomponents of the coastal ocean, but knowledge about the temporal and spatial variability of their carbonate chemistry, as well as their contribution to coastal and global carbon fluxes, are limited. In the present study, we measured the temporal and spatial variability of biogeochemical parameters in a saltmarsh estuary in Southern California, the San Dieguito Lagoon (SDL). We also estimated the flux of dissolved inorganic carbon (DIC) and total organic carbon (TOC) to the adjacent coastal ocean over diel and seasonal timescales. The combined net flux of DIC and TOC (FDIC + TOC) to the ocean during outgoing tides ranged from - 1.8 +/- 0.5 x 10(3) to 9.5 +/- 0.7 x 10(3) mol C h(-1) during baseline conditions. Based on these fluxes, a rough estimate of the net annual export of DIC and TOC totaled 10 +/- 4 x 10(6) mol C year(-1). Following a major rain event (36 mm rain in 3 days), FDIC + TOC increased and reached values as high as 29.0 +/- 0.7 x 10(3) mol C h(-1). Assuming a hypothetical scenario of three similar storm events in a year, our annual net flux estimate more than doubled to 25 +/- 4 x 10(6) mol C year(-1). These findings highlight the importance of assessing coastal carbon fluxes on different timescales and incorporating event scale variations in these assessments. Furthermore, for most of the observations elevated levels of total alkalinity (TA) and pH were observed at the estuary mouth relative to the coastal ocean. This suggests that SDL partly buffers against acidification of adjacent coastal surface waters, although the spatial extent of this buffering is likely small.

Pedler, BE, Aluwihare LI, Azam F.  2014.  Single bacterial strain capable of significant contribution to carbon cycling in the surface ocean. Proceedings of the National Academy of Sciences of the United States of America. 111:7202-7207.   10.1073/pnas.1401887111   AbstractWebsite

Marine dissolved organic carbon (DOC) encompasses one of the largest reservoirs of carbon on Earth. Heterotrophic bacteria are the primary biotic force regulating the fate of this material, yet the capacity of individual strains to significantly contribute to carbon cycling is unknown. Here we quantified the ability of a single Alteromonas strain [Alteromonas sp. strain Scripps Institution of Oceanography (AltSIO)] to drawdown ambient DOC in a coastal ecosystem. In three experiments, AltSIO alone consumed the entire pool of labile DOC, defined here as the quantity consumed by the submicron size fraction of ambient microbial assemblages within 5 d. These findings demonstrate that complete removal of the labile DOC pool in coastal surface seawater can be achieved by a single taxon. During long-term incubations (>1 y) testing semilabile DOC consumption, AltSIO entered dormancy but remained viable, while the diverse assemblages continued to consume carbon. Given that AltSIO is a large bacterium and thus subject to increased grazing pressure, we sought to determine the ecological relevance of this phenotype. Growth dynamics in natural seawater revealed that AltSIO rapidly outgrew the native bacteria, and despite intense grazing pressure, was never eliminated from the population. A survey in the California Current Ecosystem revealed that large bacteria (>= 40 fg C.cell(-1)) were persistent, accounting for up to 12% of total bacterial abundance and 24% of total bacterial biomass. We conclude that large, rapidly growing bacteria have the potential to disproportionately alter the fate of carbon in the mesotrophic ocean and play an important role in ecosystem function.

Prather, KA, Bertram TH, Grassian VH, Deane GB, Stokes MD, DeMott PJ, Aluwihare LI, Palenik BP, Azam F, Seinfeld JH, Moffet RC, Molina MJ, Cappa CD, Geiger FM, Roberts GC, Russell LM, Ault AP, Baltrusaitis J, Collins DB, Corrigan CE, Cuadra-Rodriguez LA, Ebben CJ, Forestieri SD, Guasco TL, Hersey SP, Kim MJ, Lambert WF, Modini RL, Mui W, Pedler BE, Ruppel MJ, Ryder OS, Schoepp NG, Sullivan RC, Zhao DF.  2013.  Bringing the ocean into the laboratory to probe the chemical complexity of sea spray aerosol. Proceedings of the National Academy of Sciences of the United States of America. 110:7550-7555.   10.1073/pnas.1300262110   AbstractWebsite

The production, size, and chemical composition of sea spray aerosol (SSA) particles strongly depend on seawater chemistry, which is controlled by physical, chemical, and biological processes. Despite decades of studies in marine environments, a direct relationship has yet to be established between ocean biology and the physicochemical properties of SSA. The ability to establish such relationships is hindered by the fact that SSA measurements are typically dominated by overwhelming background aerosol concentrations even in remote marine environments. Herein, we describe a newly developed approach for reproducing the chemical complexity of SSA in a laboratory setting, comprising a unique ocean-atmosphere facility equipped with actual breaking waves. A mesocosm experiment was performed in natural seawater, using controlled phytoplankton and heterotrophic bacteria concentrations, which showed SSA size and chemical mixing state are acutely sensitive to the aerosol production mechanism, as well as to the type of biological species present. The largest reduction in the hygroscopicity of SSA occurred as heterotrophic bacteria concentrations increased, whereas phytoplankton and chlorophyll-a concentrations decreased, directly corresponding to a change in mixing state in the smallest (60-180 nm) size range. Using this newly developed approach to generate realistic SSA, systematic studies can now be performed to advance our fundamental understanding of the impact of ocean biology on SSA chemical mixing state, heterogeneous reactivity, and the resulting climate-relevant properties.