Anaerobic ammonium-oxidizing (anammox) bacteria are one of the latest additions to the biogeochemical nitrogen cycle. These bacteria derive their energy for growth from the conversion of ammonium and nitrite into dinitrogen gas in the complete absence of oxygen. These slowly growing microorganisms belong to the order Brocadiales and are affiliated to the Planctomycetes. Anammox bacteria are characterized by a compartmentalized cell architecture featuring a central cell compartment, the "anammoxosome". Thus far unique "ladderane" lipid molecules have been identified as part of their membrane systems surrounding the different cellular compartments. Nitrogen formation seems to involve the intermediary formation of hydrazine, a very reactive and toxic compound. The genome of the anammox bacterium Kuenenia stuttgartiensis was assembled from a complex microbial community grown in a sequencing batch reactor (74% enriched in this bacterium) using a metagenomics approach. The assembled genome allowed the in silico reconstruction of the anammox metabolism and identification of genes most likely involved in the process. The present anammox pathway is the only one consistent with the available experimental data, thermodynamically and biochemically feasible, and consistent with Ockham's razor: it invokes minimum biochemical novelty and requires the fewest number of biochemical reactions. The worldwide presence of anammox bacteria has now been established in many oxygen-limited marine and freshwater systems, including oceans, seas, estuaries, marshes, rivers and large lakes. In the marine environment over 50% of the N(2) gas released may be produced by anammox bacteria. Application of the anammox process offers an attractive alternative to current wastewater treatment systems for the removal of ammonia-nitrogen. Currently, at least five full scale reactor systems are operational.

Biochemistry and molecular biology of anammox bacteria

Paleogeography and paleoenvironments of the Late Devonian Kellwasser event: A review of its sedimentological and geochemical expression

Enhanced siliceous plankton productivity in response to middle Eocene warming at Southern Ocean ODP Sites 748 and 749

Holocene temperatures and isotopes of precipitation in Northwest Greenland recorded in lacustrine organic materials

. The Paleocene–Eocene Thermal Maximum (PETM, 56 Ma) was a phase of rapid global warming associated with massive carbon input into the ocean–atmosphere system from a 13C-depleted reservoir. Many midlatitude and high-latitude sections have been studied and document changes in salinity, hydrology and sedimentation, deoxygenation, biotic overturning, and migrations, but detailed records from tropical regions are lacking. Here, we study the PETM at Ocean Drilling Program (ODP) Site 959 in the equatorial Atlantic using a range of organic and inorganic proxies and couple these with dinoflagellate cyst (dinocyst) assemblage analysis. The PETM at Site 959 was previously found to be marked by a  ∼  3.8 ‰ negative carbon isotope excursion (CIE) and a  ∼  4 °C surface ocean warming from the uppermost Paleocene to peak PETM, of which  ∼  1 °C occurs before the onset of the CIE. We record upper Paleocene dinocyst assemblages that are similar to PETM assemblages as found in extratropical regions, confirming poleward migrations of ecosystems during the PETM. The early stages of the PETM are marked by a typical acme of the tropical genus Apectodinium, which reaches abundances of up to 95 %. Subsequently, dinocyst abundances diminish greatly, as do carbonate and pyritized silicate microfossils. The combined paleoenvironmental information from Site 959 and a close-by shelf site in Nigeria implies the general absence of eukaryotic surface-dwelling microplankton during peak PETM warmth in the eastern equatorial Atlantic, most likely caused by heat stress. We hypothesize, based on a literature survey, that heat stress might have reduced calcification in more tropical regions, potentially contributing to reduced deep sea carbonate accumulation rates, and, by buffering acidification, also to biological carbonate compensation of the injected carbon during the PETM. Crucially, abundant organic benthic foraminiferal linings imply sustained export production, likely driven by prokaryotes. In sharp contrast, the recovery of the CIE yields rapid (≪ 10 kyr) fluctuations in the abundance of several dinocyst groups, suggesting extreme ecosystem and environmental variability.

/pdf/tropical-atlantic-climate-and-ecosystem-regime-shifts-during-1jufns5nqz.pdf

Tropical Atlantic climate and ecosystem regime shifts during the Paleocene–Eocene Thermal Maximum

An understanding of modern relationships between the stable oxygen isotope composition (δ18O) of lake water and aquatic invertebrates is essential for the interpretation of paleoclimate records based on δ18O of organic remains of these organisms. We analyzed δ18O of lake water and invertebrate remains, including head capsules of chironomid larvae and resting eggs (ephippia) of planktonic Cladocera, in surface sediments from 31 large, deep, and stratified lakes along a latitudinal transect through Europe. The δ18O values measured for both lake water and aquatic invertebrate remains were compared to estimated δ18O in precipitation. A strong linear relationship between mean annual air temperature and δ18O of precipitation was observed along the north–south transect (r = 0.97), whereas the relationship between precipitation δ18O and lake-water δ18O was weaker (r = 0.80). A strong positive correlation was observed between δ18O in lake water and aquatic invertebrates (r = 0.95 and 0.94 for chironomids and cladocerans, respectively). Although slopes of linear regressions between lake-water δ18O and δ18O of both aquatic invertebrate groups are similar, a systematic offset between the absolute δ18O values of chironomids and cladocerans was observed; chironomids were on average 2.4‰ heavier than Cladocera. We attribute this offset to differences in ecology, metabolism, and/or behavior between benthic chironomid larvae and planktonic Cladocera. δ18O records based on subfossil chironomid and cladoceran remains have the potential to quantitatively characterize past lake-water δ18O and, indirectly, past climatic changes.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.2011.56.6.2071

Stable oxygen isotopes in chironomid and cladoceran remains as indicators for lake-water δ18O

A Smoking Gun for Methane Hydrate Release During the Paleocene-Eocene Thermal Maximum

Modeling the influence of a reduced equator-to-pole sea surface temperature gradient on the distribution of water isotopes in the Eocene

Increasingly high resolution isotope- and novel organic geochemical proxy records have revealed that
the long-term cooling trend of the middle Eocene was interrupted by a warming phase designated the
Middle Eocene Climatic Optimum (MECO) It is suggested to represent an increase in sea surface
temperatures of about 4°C, lasting approximately 400 kyr The temperature evolution of the MECO is
notably well-documented in the Southern Ocean However, records of temperature- and biotic change
during the MECO are largely missing from the higher northern latitudes Here we document on the sea
surface temperature evolution during the MECO reconstructed using TEX86 from Ocean Drilling Program
(ODP) site 647 situated in the Labrador Sea In addition, organic walled remains of dinoflagellates (ie
dinocysts) were investigated in order to identify environmental change in response to the MECO

G. J. Reichart

Papers

Stable oxygen isotopes in chironomid and cladoceran remains as indicators for lake-water δ18O

A Smoking Gun for Methane Hydrate Release During the Paleocene-Eocene Thermal Maximum

Modeling the influence of a reduced equator-to-pole sea surface temperature gradient on the distribution of water isotopes in the Eocene

The Middle Eocene Climatic Optimum (MECO) in the high latitudes of the North Atlantic: Temperature and Biotic change

Application of ladderane lipids as a proxy for past anammox activity