The biogeochemical cycling in oxygen-minimum zones (OMZs) is dominated by the interactions of microbial nitrogen transformations and, as recently observed in the Chilean upwelling system, also through the energetically less favorable remineralization of sulfate reduction. The latter process is masked, however, by rapid sulfide oxidation, most likely through nitrate reduction. Thus, the cryptic ...

The Toarcian oceanic anoxic event (T-OAE; ∼ 183 million y ago) is possibly the most extreme episode of widespread ocean oxygen deficiency in the Phanerozoic, coinciding with rapid atmospheric pCO2 increase and significant loss of biodiversity in marine faunas. The event is a unique past tipping point in the Earth system, where rapid and massive release of isotopically light carbon led to a majo...

17 Nitrogen cycling has been evaluated across a depth transect in the late Paleoproterozoic 18 Animikie Basin, spanning the end of Earth’s final period of global iron precipitation and a major 19 transition to euxinic conditions in areas of high productivity. Sediments from near shore where 20 productivity was highest have N compositions up to ~3‰ higher than at more distal sites. 21 This sugg...

Seasonal and interannual variabilities in the partial pressure of CO 2 ( p ), pH, calcium carbonate saturation state (?) were investigated highly eutrophicated Tokyo Bay, Japan, based on monthly observations that conducted from 2011 to 2017. There large these parameters for surface bottom waters due photosynthesis respiration, respectively. Warming/cooling freshwater input also altered ?. Durin...

Ancient rocks record the redox conditions of the oceanatmosphere system through the distribution of iron (Fe) between oxidised and reduced minerals, which can be formulated into a suite of Fe palaeoredox proxies. The balance between Fe and S in a given system reflects the variance in a range of highand low-temperature sources and sinks. Iron can be delivered by hydrothermal, diagenetic or clast...

An unexpected increase of phototrophic and heterotrophic picoand nanoplankton under anoxic conditions was encountered in the central Baltic Sea below 120 m depth in August 1991 and 135 m depth in July 1992, respectively. Cell abundances in anoxic layers were up to 10 times higher for chroococcoid cyanobacteria, 6 to 8 times for phototrophic nanoflagellates and 3 to 4 times for bacteria, as comp...

In modern marine sediments, the anoxic decomposition of organic matter generates a significant flux of methane that is oxidized microbially with sulphate under the seafloor and never reaches the atmosphere. In contrast, prior to ca 2.4Gyr ago, the ocean had little sulphate to support anaerobic oxidation of methane (AOM) and the ocean should have been an important methane source. As atmospheric ...

Life originated in Archaean oceans, almost 4 billion years ago, in the absence of oxygen and the presence of high dissolved iron concentrations. Early Earth oxidation is marked globally by extensive banded iron formations but the contributing processes and timing remain controversial. Very few aquatic habitats have been discovered that match key physico-chemical parameters of the early Archaean...

The Cenomanian-Turonian period recorded one of the largest disruptions to oxygen and carbon cycles, Oceanic Anoxic Event 2 (OAE2, 94 Ma). This event is global, yet paleo-reconstructions document heterogeneous ocean oxygenation states sedimentary contents, temporally spatially, suggesting that several mechanisms are at play. To better understand long-term controls on oceanic initial conditions p...

The Devonian is characterized by major changes in ocean-atmosphere O 2 concentrations, colonialization of continents plants and animals, widespread marine anoxic events associated with rapid δ 13 C excursions biotic crises. However, the long-term upper ocean redox trend for still not well understood. This study presents new I/Ca data from well-dated Lower through Upper limestone sections Great ...