• Energy Research

AbstractOceanic methane from global deep-sea sediment is largely consumed through microbially mediated sulfate-coupled oxidation, resulting in 13C-depleted cell biomass of anaerobic methanotrophic archaea (ANME). The general ecological importance of subseafloor ANME has been well recognized in the last two decades. However, the crucial biochemical pathways for the overall anaerobic oxidation of methane (AOM) still remain enigmatic. Here, methanotrophic pathways were analyzed to trace 13C-depleted amino acid biosynthesis in two clades of ANME (ANME-1 and ANME-2) from the Black Sea. Compound-specific analysis of ANME-dominated microbial mats showed a significant 13C-depletion trend in association with increasing carbon numbers in protein-derived amino acid families (e.g., the pyruvate family in the order of alanine, valine, isoleucine and leucine was down to −114‰). This result indicates a stepwise elongation of 13C-depleted carbon during amino acid biosynthesis. The overall results suggest that intracellular protein amino acids and the most 13C-depleted signature of leucine, which has a specific branched-chain structure, are potentially propagated as isoprenoid precursor molecules into archaeal biosynthesis, resulting in the extremely 13C- and 14C-depleted nature of ANME cells in the deep microbial oasis.

Poor water quality driven by increased nutrients is the main cause of coral diversity loss in southern China’s Greater Bay Area.

Although climate variations and sea level changes are often discussed interchangeably, climate change need not always result in sea level change. Perturbations in Earth’s orbit cause major climate changes, and the resulting variations in the amount and distribution of solar radiation at ground level follow cycles lasting for thousands of years. Research done in the last decade shows that climate can change on centennial or shorter time scales. These more rapid changes appear to be related to modifications in ocean circulation initiated during the last glacial period either by injections of fresh meltwater or huge ice discharges into the North Atlantic. When first detected, these rapid climate changes were characterized as episodes decoupled from any significant change in sea level. New data clearly show a direct connection between climate and sea level, and even more surprising, this link may extend to times of glacial-interglacial transitions and possibly also to interglacials. The full extent of this sea level/climate coupling is unknown and is the subject of current research.