One of the most persistent questions regarding the phase equilibria of mid-ocean ridge basalts (MORB) pertains to the petrogenesis of the anorthitic plagioclase phenocrysts (>An₉₀) that are characteristic of the more primitive members of such suites. Anorthitic phenocrysts are present in many if not most MORB suites in spite of...
Steepland valleys subject to debris flows incise bedrock even as episodic deposition typically covers valley bottoms. This paper’s hypothesis is that, while continual fluvial processes evacuate deposits, storage of episodic deposition drives valley widening and, thereby, creation of accommodation space for sediment storage on the valley floor. Data from three...
We used an in situ steady state ¹⁵N-labeled nitrate (¹⁵NO₃⁻) and acetate (AcO⁻) well-to-wells injection experiment to determine how the availability of labile dissolved organic carbon (DOC) as AcO⁻ influences microbial denitrification in the hyporheic zone of an upland (third-order) agricultural stream. The experimental wells receiving conservative (Cl⁻ and Br)...
We undertook an interlaboratory comparison of techniques used to extract and analyze trapped gases in ice cores. The intercomparison included analyses of standard reference gases and samples of ice from the Greenland Ice Sheet Project 2 (GISP2) site. Concentrations of CO₂, CH₄, the δ¹⁸O of O₂, the δ¹⁵N of N₂,...
Empirical algorithms for the total absorption coefficient and absorption
coefficient by pigments for surface waters at 440 nm were developed by applying a quadratic formula that combines two spectral ratios of remote-sensing reflectance. For
total absorption coefficients ranging from 0.02 to 2.0 m⁻¹, a goodness of fit was achieved
between...
The propagation of downwelling irradiance at wavelength l from surface to a depth (z) in the ocean is governed by the diffuse attenuation coefficient, K𝒹(λ). There are two standard methods for the derivation of K𝒹(λ) in remote sensing, which both are based on empirical relationships involving the blue-to-green ratio of...
Biogenic opal, organic carbon, organic matter stable isotope, and trace metal data from
a well-dated, high-resolution jumbo piston core (EW0408–85JC; 59° 33.3′N, 144° 9.21′W,
682 m water depth) recovered from the northern Gulf of Alaska continental slope reveal
changes in productivity and nutrient utilization over the last 17,000 years. Maximum...
We investigated the late-time (asymptotic) behavior of tracer test breakthrough
curves (BTCs) with rate-limited mass transfer( e.g., in dual-porosity or multiporosity
systems) and found that the late-time concentration c is given by the simple expression
C = tₐ𝒹{C₀g-- [m₀(∂g/∂t)]}, for t >> tₐ𝒹 and tα >> tₐ𝒹, where tad is...
Biogeochemical reactions associated with stream nitrogen cycling, such as
nitrification and denitrification, can be strongly controlled by water and solute residence
times in the hyporheic zone (HZ). We used a whole‐stream steady state ¹⁵N‐labeled
nitrate (¹⁵NO₃⁻) and conservative tracer (Cl⁻) addition to investigate the spatial and
temporal physiochemical conditions controlling...
We have measured cosmic ray produced ¹⁰Be (t₁/₂ = 1.5 My) and ²⁶Al (t₁/₂ = 0.72 My) as functions of depth in a core of quartz sandstone bedrock collected in South Victoria Land, Antarctica. These data were used to place limits on the exposure age and erosion rate of the...