The role that phosphorite formation, the ultimate source rock for fertilizer phosphate reserves, plays in the marine phosphorus (P) cycle has long been debated. A shift has occurred from early models that evoked strikingly different oceanic P cycling during times of widespread phosphorite deposition to current thinking that phosphorite deposits may be lucky survivors of a series of inter-relate...

The Mesoproterozoic deep ocean is thought to have been largely anoxic, dominated by ferruginous conditions. Phosphate was scavenged from the water column iron oxyhydroxides, and dissolved nitrate rapidly reduced along redoxcline. Primary productivity therefore generally low, eukaryotic life restricted oxic marine margins. This model supported new nitrogen isotope data Lower Riphean (ca. 1.55 Ga...

In this study, we investigate phosphorus (P) and iron (Fe) cycling in sediments along a depth transect from within to well below the oxygen minimum zone (OMZ) in the northern Arabian Sea (Murray Ridge). Pore-water and solid-phase analyses show that authigenic formation of calcium phosphate minerals (Ca-P) is largely restricted to where the OMZ intersects the seafloor topography, likely due to h...

A novel sedimentary transformation product of chlorophyll, purpurin-7 phytyl ester, has been identi®ed by atmospheric pressure chemical ionisation liquid chromatography mass-spectrometry in sediments from Lake Baikal, Russia, Loch Ness and Priest Pot, UK. This product of oxidative transformation is an intermediate on the transformation pathway leading to sedimentary aetioporphyrins and its occu...

The kinetics of sulfate reduction and inorganic nutrient production (~C02' ammonium, and phosphate) were examined in the sediments at five sites in the southern Chesapeake Bay, using long term (> 200 d) sediment decomposition experiments. Average first order rate constants for these processes (at 25°C) decreased from 8.2 to 3.7 yrin the surface sediments (0-2 em), to 2.1 to 0.2 yrat 12-14 em. T...

An appealing strategy for reconstructing the timing and tempo of paleoenvironmental change from sedimentary strata is to linearly interpolate between marker beds known age. This method requires significant assumptions, but more advanced age modeling methods are usually not feasible. We used experiments explore how changes in processes invalidate these assumptions affect estimates time strata. W...