Niche construction by non-diazotrophs for N2 fixers in the eastern tropical North Atlantic Ocean
"Diazotrophic dinitrogen (N2) fixation contributes ~76% to “new” nitrogen inputs to the sunlit open ocean, but environmental factors determining N2 fixation rates are not well constrained. Excess phosphate (phosphate–nitrate/16 > 0) and iron availability control N2 fixation rates in the eastern tropical North Atlantic (ETNA), but it remains an open question how excess phosphate is generated within or supplied to the phosphate-depleted sunlit layer. [...]"
Source: Geophysical Research Letters
Authors: Arvind Singh et al.
Historical records of coastal eutrophication-induced hypoxia
"Under certain conditions, sediment cores from coastal settings subject to hypoxia can yield records of environmental changes over time scales ranging from decades to millennia, sometimes with a resolution of as little as a few years. A variety of biological and geochemical indicators (proxies) derived from such cores have been used to reconstruct the development of eutrophication and hypoxic conditions over time. [...]"
Authors: A. J. Gooday et al.
U.N. Moved to Protect 60% of the Ocean and the World Hardly Noticed
"After years of talks, the U.N. has taken a major step toward an international treaty to preserve the biodiversity of the high seas to combat climate change, overfishing and plastic pollution.
[...] The move, which ended two weeks of sometimes contentious talks to hash out the major elements of the treaty, could result in far-reaching protections for marine life through the creation of reserves and other actions designed to blunt threats to ocean health from climate change, over-fishing and pollution. The high seas constitute the nearly 60 percent of the ocean beyond any nation’s jurisdiction. They play a crucial role in the global climate, food supply and economy, yet are largely beyond the reach of the law. [...]"
Biological nitrogen fixation in the oxygen-minimum region of the eastern tropical North Pacific ocean
"Biological nitrogen fixation (BNF) was investigated above and within the oxygen-depleted waters of the oxygen-minimum zone of the Eastern Tropical North Pacific Ocean. BNF rates were estimated using an isotope tracer method that overcame the uncertainty of the conventional bubble method by directly measuring the tracer enrichment during the incubations. Highest rates of BNF (~4 nM day−1) occurred in coastal surface waters and lowest detectable rates (~0.2 nM day−1) were found in the anoxic region of offshore stations. [...]"
Source: The ISME Journal
Authors: Amal Jayakuma et al.
Oceanic nitrogen cycling and N2O flux perturbations in the Anthropocene
"There is currently no consensus on how humans are affecting the marine nitrogen (N) cycle, which limits marine biological production and CO2 uptake. Anthropogenic changes in ocean warming, deoxygenation, and atmospheric N deposition can all individually affect the marine N cycle and the oceanic production of the greenhouse gas nitrous oxide (N2O). However, the combined effect of these perturbations on marine N cycling, ocean productivity, and marine N2O production is poorly understood. Here we use an Earth system model of intermediate complexity to investigate the combined effects of estimated 21st century CO2 atmospheric forcing and atmospheric N deposition. [...]"
Source: Global Biogeochemical Cycles
Authors: A. Landolfi, C. Somes, W. Koeve, L. M. Zamora, A. Oschlies
Influence of seaway changes during the Pliocene on tropical Pacific climate in the Kiel climate model
Mean state, annual cycle, ENSO, and their interactions
"The El Niño/Southern Oscillation (ENSO) is the leading mode of tropical Pacific interannual variability in the present-day climate. Available proxy evidence suggests that ENSO also existed during past climates, for example during the Pliocene extending from about 5.3 million to about 2.6 million years BP. Here we investigate the influences of the Panama Seaway closing and Indonesian Passages narrowing, and also of atmospheric carbon dioxide (CO2) on the tropical Pacific mean climate and annual cycle, and their combined impact on ENSO during the Pliocene. [...]"
Source: Climate Dynamics
Authors: Zhaoyang Song, Mojib Latif, Wonsun Park, Uta Krebs-Kanzow, Birgit Schneider
Deep-ocean dissolved organic matter reactivity along the Mediterranean Sea: does size matter?
"Despite of the major role ascribed to marine dissolved organic matter (DOM) in the global carbon cycle, the reactivity of this pool in the dark ocean is still poorly understood. Present hypotheses, posed within the size-reactivity continuum (SRC) and the microbial carbon pump (MCP) conceptual frameworks, need further empirical support. Here, we provide field evidence of the soundness of the SRC model. We sampled the high salinity core-of-flow of the Levantine Intermediate Water along its westward route through the entire Mediterranean Sea. At selected sites, DOM was size-fractionated in apparent high (aHMW) and low (aLMW) molecular weight fractions using an efficient ultrafiltration cell. [...]"
Source: Scientific Reports
Authors: Alba María Martínez-Pérez, Xosé Antón Álvarez-Salgado, Javier Arístegui & Mar Nieto-Cid
Cryptic oxygen cycling in anoxic marine zones
"Oxygen availability drives changes in microbial diversity and biogeochemical cycling between the aerobic surface layer and the anaerobic core in nitrite-rich anoxic marine zones (AMZs), which constitute huge oxygen-depleted regions in the tropical oceans. The current paradigm is that primary production and nitrification within the oxic surface layer fuel anaerobic processes in the anoxic core of AMZs, where 30–50% of global marine nitrogen loss takes place. Here we demonstrate that oxygenic photosynthesis in the secondary chlorophyll maximum (SCM) releases significant amounts of O2 to the otherwise anoxic environment. [...] "
Source: Proceedings of the National Academy of Sciences of the United States of America (PNAS)
Authors: Emilio Garcia-Robledo et al.
Fossil site shows impact of early Jurassic's low oxygen oceans
Using a combination of fossils and chemical markers, scientists have tracked how a period of globally low ocean-oxygen turned an Early Jurassic marine ecosystem into a stressed community inhabited by only a few species.
Source: Science Daily
Function of the High Seas and Anthropogenic Impacts Science Update 2012 - 2017
The Zoological Department of Oxford University has reviewed and synthesised major marine science findings which have been published since Rio+20 in 2012.
The purpose of this synthesis is to determine how our understanding of the ocean at an Earth System level, with a particular focus on the role of the high seas, has changed in the last five years.
"During the last five years scientists have utilised novel technologies and methods to explore new locations and investigate both the fundamental processes of the ocean and the mounting anthropogenic impacts on the marine environment. Studies have highlighted the important functions that the high seas perform for the planet and have often focused on the complexity and interconnected nature of these processes."
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