[1] Decadal time series observations of hydrothermal fluid emissions from Lō'ihi volcano were initiated in 1992 using a combination of submersible and shipboard sampling strategies. Magmatic-tectonic processes associated with a spectacular seismic event in July-August 1996 led to the collapse of Pele's Vents (31°C) near the volcano summit into a new pit crater (Pele's Pit) inundated by high-temperature (T max = 198°C) focused and lower-temperature (<95°C) diffuse fluid discharge. Variations in the concentrations and relative abundances of vented Fe and Mn characterize the precollapse, summit collapse, and postcollapse periods. The precollapse plume emanating from Pele's Vents had a low rise height ($35 m) and concentration intensity (<5 nmol/L TDMn, 70 nmol/L TDFe, $1.8 km distant) and dispersed to the southwest. Plumes coeval with the 1996 summit collapse were characterized by extreme metal concentrations within Pele's Pit (up to $10,000 nmol/L DMn and 400,000 nmol/L TDFe) and nearby East Pit ($34,000 nmol/L DMn and 120,000 nmol/L TDFe). An intense hydrothermal plume dispersed predominantly to the southwest of the several hundred meter deep pits with concentration anomalies as high as 236 nmol/L DMn and 3,800 nmol/L TDFe measured 9 km distant. Iron and Mn concentrations within the pits decreased >30-to 200-fold $1.5 months postcollapse and, during the following year, decreased a further twofold to threefold at Pele's Pit and $30-fold at East Pit. While a steady concentration of $400 nmol/L TDFe prevailed throughout the remaining years of this study at Pele's Pit, a gradual and threefold decrease in the concentration of DMn to about 15 nmol/L was observed. High-temperature fluids (128-198°C 1997-1999, $90°C 2001) venting simultaneously from different orifices within Pele's Pit had distinguishable Fe/Mn ratios that can be attributed to different subseafloor origins. Fe/Mn ratios characteristic of fluids moderated by high-temperature water-rock reaction had low values in 1997-1998 (1.6 ± 0.7), increasing to about 7 in 1999. Fluids moderated by magmatic degassing of CO 2 had much higher Fe/Mn ratios, increasing from 24 ± 15 in 1997-1998 to 50 in 1999 and 63-87 in 2001. Fe/Mn values of dispersing plumes at Lō'ihi reflect an admixture of these sources and a relative Fe abundance that is consistently high compared to mid-ocean ridge systems. The pulsed injection of Mn and Fe into the surrounding ocean associated with the 1996 tectonic-magmatic event at Lō'ihi was massive. Our decadal observations confirm that Mn and Fe are useful markers of the magnitude and evolution of the effects of magmatic perturbation on hydrothermal systems influenced by chronic magmatic degassing.

No abstract

No abstract

No abstract

Two flow-injection spectrophotometric procedures have been developed for the determination of trace amounts of iron in sea-water. The first procedure is based on the iron-catalysed oxidation of p-phenetidine by periodate after in-valve separatiodpreconcentration of iron(m). The limit of detection is 0.05 pg 1-1 of iron when concentrating 6 ml of sea-water. The second procedure is based on the selective catalytic effect of iron(m) on the oxidation of N,N'-dialkyl-p-phenylenediamines by hydrogen peroxide. The limit of detection of this method is 0.03 pg 1-1 of iron with a sampling rate of 60 h-1. The utility of both flow-injection methods was demonstrated by the determination of dissolved iron in sea-water samples, with an average recovery of 98-11OY0 and an average relative standard deviation of 1.8-8.1 YO.

No abstract

No abstract

A flow injection spectrophotometric technique for the determination of cobalt in sea-water and hydrothermal sea-water solutions is described. It is based on the catalytic effect of cobalt(I1) on the oxidation of N,N'-diethyl-p-phenylenediamine by hydrogen peroxide in the presence of Tiron as an activator. The catalytic activity of cobalt(rr) was found to be significantly enhanced by the presence of sea-water matrix components, especially calcium ions, improving the sensitivity of cobalt determination in sea-water. The comparatively weak basic medium (pH 8.7-9.0) of the reaction and its relative freedom from co-existing ions allowed the direct analysis of sea-water to be conducted effectively without any preliminary steps. The sampling rate was 50 h-1. The limit of detection for cobalt was 1 ng 1-1 and the relative standard deviation at the level of 10-100 ng 1-I was 2 4 % ( n = 5). The technique was confirmed to be accurate on the basis of the analysis of the standard sea-water solutions CASS-2 and NASS-2. Artificial hydrothermal solution samples were analysed by the proposed technique and the results were in good agreement with data obtained by ICP-MS.