Confocal Fluorescence Microscopy of the Morphology and Composition of Interstitial Fluids in Freezing Electrolyte Solutions

Ice rheology, the integrity of polar ice core records, and ice−atmosphere interactions are among the phenomena controlled by the morphology and composition of interstitial fluids threading polycrystalline ice. Herein, we investigate how ionic impurities affect such features via time-resolved confocal fluorescence microscopy of freezing electrolyte solutions doped with a pH probe. We find that the 10 μM probe accumulates into 12 μm thick glassy channels in frozen water, but it is incorporated into randomly distributed <1 μm diameter inclusions in freezing 1 mM NaCl. We infer that morphology is largely determined by the dynamic instabilities generated upon advancing ice by the rejected solute, rather than by thermodynamics. The protracted alkalinization of the fluid inclusions reveals that the excess negative charge generated by the preferential incorporation of Cl^− over Na^+ in ice is neutralized by the seepage of the OH^− slowly produced via H_2O → H^+ + OH^− thermal dissociation

Confocal Fluorescence Microscopy of the Morphology and Composition of Interstitial Fluids in Freezing Electrolyte Solutions

Ice rheology, the integrity of polar ice core records, and ice−atmosphere interactions are among the phenomena controlled by the morphology and composition of interstitial fluids threading polycrystalline ice. Herein, we investigate how ionic impurities affect such features via time-resolved confocal fluorescence microscopy of freezing electrolyte solutions doped with a pH probe. We find that the 10 μM probe accumulates into 12 μm thick glassy channels in frozen water, but it is incorporated into randomly distributed <1 μm diameter inclusions in freezing 1 mM NaCl. We infer that morphology is largely determined by the dynamic instabilities generated upon advancing ice by the rejected solute, rather than by thermodynamics. The protracted alkalinization of the fluid inclusions reveals that the excess negative charge generated by the preferential incorporation of Cl⁻ over Na⁺ in ice is neutralized by the seepage of the OH⁻ slowly produced via H₂O → H⁺ + OH⁻ thermal dissociation

A Coupled Modeling and Molecular Biology Approach to Microbial Source Tracking at Cowell Beach, Santa Cruz, CA, United States

Consistently high levels of bacterial indicators of fecal pollution rank Cowell Beach as the most polluted beach in California. High levels of fecal indicator bacteria (FIB), <i>E. coli</i> and enterococci, are measured throughout the summer, resulting in beach advisories with social and economic consequences. The source of FIB, however, is unknown. Speculations have been made that the wrack accumulating on the beach is a major source of FIB to the surf zone. The present study uses spatial and temporal sampling coupled with process-modeling to investigate potential FIB sources and the relative contributions of those sources. Temporal sampling showed consistently high FIB concentrations in the surf zone, sand, and wrack at Cowell Beach, and ruled out the storm drain, the river, the harbor, and the adjacent wharf as the sources of the high concentrations observed in the surf zone. Spatial sampling confirmed that the source of FIB to the beach is terrestrial rather than marine. Modeling results showed two dominant FIB sources to the surf zone: sand for enterococci and groundwater for <i>E. coli</i>. FIB from wrack represented a minor contribution to bacterial levels in the water. Molecular source tracking methods indicate the FIB at the beach is of human and bird origin. The microbial source tracking (MST) approach presented here provides a framework for future efforts