Marine chemistry

  • Article
    | Open Access

    Modelling and sea surface temperature proxy data from the Weddell Sea document a 3–4 °C drop coinciding with the Early Cretaceous Weissert Event. Temperature data worldwide confirm a 3.0 °C global mean surface cooling, equivalent to a ~40% drop in atmospheric pCO2, favouring local polar ice.

    • Liyenne Cavalheiro
    • , Thomas Wagner
    •  & Elisabetta Erba
  • Article
    | Open Access

    Plastics are major marine pollutants, and while research suggests that they can release potential harmful additives into seawater, how environmental conditions influence this is unknown. Here the authors determine that byproducts released from microplastics are less under deep-sea conditions versus surface.

    • Vincent Fauvelle
    • , Marc Garel
    •  & Richard Sempéré
  • Article
    | Open Access

    N2 fixation by heterotrophic bacteria has recently been found to take place on sinking marine particles, but an understanding of its regulation and importance is lacking. Here the authors develop a trait-based model for this N2 fixation, finding that this once overlooked process could have global importance.

    • Subhendu Chakraborty
    • , Ken H. Andersen
    •  & Lasse Riemann
  • Article
    | Open Access

    North Atlantic deep water (NADW) formation influences the climate and carbon cycle, but the contribution of Arctic waters is difficult to constrain. Here the authors use Pa/Th proxy measurements to determine the amount of Arctic Ocean water that flows through the Fram Strait and contributes to NADW.

    • Lauren E. Kipp
    • , Jerry F. McManus
    •  & Markus Kienast
  • Article
    | Open Access

    Primary productivity in the oligotrophic ocean sustains Earth’s ecosystems, but nutrient concentrations are vanishingly low. Here the authors measure nanomolar macronutrient concentrations in the North Pacific and find that net community production is sustained through high rates of phosphorus recycling.

    • Fuminori Hashihama
    • , Ichiro Yasuda
    •  & Masao Ishii
  • Article
    | Open Access

    The middle of the Gulf of Mexico is stratified and highly oligotrophic, yet there are anomalously high fluxes of sinking particulate matter from the euphotic zone. Here the authors show that lateral advection of organic matter supports nitrogen export in the Gulf of Mexico’s open ocean.

    • Thomas B. Kelly
    • , Angela N. Knapp
    •  & Michael R. Stukel
  • Article
    | Open Access

    The macroalgae Sargassum has grown for centuries in the oligotrophic North Atlantic supported by natural nutrient sources and cycling. Here the authors show that changes in tissue nutrient contents since the 1980s reflect global anthropogenic nitrogen enrichment, causing blooms in the wider Atlantic basin.

    • B. E. Lapointe
    • , R. A. Brewton
    •  & P. L. Morton
  • Article
    | Open Access

    A large fraction of ice sheet discharge enters the ocean subsurface from underneath large floating ice-tongues. Here the authors show that associated nutrient export may be governed by shelf circulation and, especially for Fe, particle-dissolved phase exchanges, which is largely independent from freshwater Fe content.

    • Stephan Krisch
    • , Mark James Hopwood
    •  & Eric Pieter Achterberg
  • Article
    | Open Access

    Ocean warming and changing circulation as a result of climate change are driving down oxygen levels and threatening ecosystems. Here the author shows that though immediate cessation of anthropogenic CO2 emissions would halt upper ocean oxygen loss, it would continue in the deep ocean for 100 s of years.

    • Andreas Oschlies
  • Article
    | Open Access

    Primary productivity in the Southern Ocean plays an important role in the drawdown of atmospheric CO2, but phytoplankton growth is limited by iron. Here the authors show that iron from hydrothermal vents fuels massive phytoplankton blooms in the Southern Ocean that have recurred in the same location for decades.

    • Casey M. S. Schine
    • , Anne-Carlijn Alderkamp
    •  & Kevin R. Arrigo
  • Article
    | Open Access

    The fate of ocean carbon is determined by the balance between primary productivity and heterotrophic breakdown of that photosynthate. Here the authors show that diatoms produce a polysaccharide that resists bacterial degradation, accumulates, aggregates and stores carbon during spring blooms.

    • Silvia Vidal-Melgosa
    • , Andreas Sichert
    •  & Jan-Hendrik Hehemann
  • Article
    | Open Access

    Southern Ocean productivity is a crucial component of the carbon cycle, but phytoplankton there are thought to be limited by iron. Here the authors conduct trace metal incubation experiments across the Drake Passage, finding that manganese can play an unexpected role in restricting phytoplankton growth.

    • Thomas J. Browning
    • , Eric P. Achterberg
    •  & Edward Mawji
  • Article
    | Open Access

    The expansion of oceanic anoxia during the Paleocene Eocene Thermal Maximum has important implications for faunal turnover patterns and global biogeochemical cycles. Here the authors use uranium isotopes and a biogeochemical model to suggest that the areal expansion of anoxia must have been limited to 10-fold.

    • Matthew O. Clarkson
    • , Timothy M. Lenton
    •  & Derek Vance
  • Article
    | Open Access

    Microplastics have spread across the globe and reached even the most remote locations, but an understanding of their origins remains largely elusive. Here the authors quantify and characterise microplastics across the North Pole, finding that synthetic fibers like polyester are dominant and likely sourced from the Atlantic Ocean.

    • Peter S. Ross
    • , Stephen Chastain
    •  & Bill Williams
  • Article
    | Open Access

    Groundwater discharge is a mechanism that transports chemicals from inland systems to the ocean, but it has been considered of secondary influence compared to rivers. Here the authors assess the global significance of groundwater discharge, finding that it has a unique and important contribution to ocean chemistry and Earth-system models.

    • Kimberley K. Mayfield
    • , Anton Eisenhauer
    •  & Adina Paytan
  • Article
    | Open Access

    The Arctic Ocean is influenced by carbon and nutrients from rivers and erosion, but how this affects phytoplankton productivity is not understood. Here, the authors use a spatio-temporally resolved biogeochemical model to estimate that the input of carbon and nutrients fuels 28–51% of annual Arctic Ocean productivity.

    • Jens Terhaar
    • , Ronny Lauerwald
    •  & Laurent Bopp
  • Article
    | Open Access

    The Si cycle is important to ocean productivity and nutrient cycling, however there are uncertainties in global budgets. Here the authors use a multi-isotope approach on seafloor sediments and pore fluids, finding that an unappreciated source of Si to the ocean is the degradation of seafloor serpentinites.

    • Sonja Geilert
    • , Patricia Grasse
    •  & Catriona D. Menzies
  • Article
    | Open Access

    Ocean uptake of carbon dioxide impacts the climate, but flux estimates from surface measurements have not been corrected for temperature differences between surface and water sampling depth. Making that correction, the authors find previous estimates for ocean uptake have been substantially underestimated.

    • Andrew J. Watson
    • , Ute Schuster
    •  & Lonneke Goddijn-Murphy
  • Article
    | Open Access

    Determination of 3D molecular structures remains challenging for natural products or organic compounds available in minute amounts. Here, the authors determine the structure of complex molecules, including few micrograms of briarane B-3 isolated from Briareum asbestinums, through measurement of 1H residual chemical shift anisotropy.

    • Nilamoni Nath
    • , Juan Carlos Fuentes-Monteverde
    •  & Christian Griesinger
  • Article
    | Open Access

    The risks posed by plastic contamination of the ocean cannot be assessed as their amount and location remain largely unknown. Here the authors show that large quantities of microplastics exist below the ocean surface over the entire Atlantic in quantities greater than previously estimated.

    • Katsiaryna Pabortsava
    •  & Richard S. Lampitt
  • Article
    | Open Access

    Microbial ammonia oxidation is important in marine nutrient cycling and greenhouse gas dynamics, but the responses to ocean warming are unclear. Here coast to open ocean incubations show that projected year 2100 temperatures might be too hot for these microbes in oligotrophic regions to handle, but may facilitate oxidation rates in coastal waters.

    • Zhen-Zhen Zheng
    • , Li-Wei Zheng
    •  & Shuh-Ji Kao
  • Article
    | Open Access

    Monomethylmercury is a toxin that humans can be exposed to after consumption of seafood in which it has bioaccumulated. Here the authors show that amphipods in the deepest point of the global ocean contain monomethylmercury with surface origins, suggesting rapid sinking of this toxin on particles.

    • Ruoyu Sun
    • , Jingjing Yuan
    •  & Congqiang Liu
  • Article
    | Open Access

    The authors here report tensile properties of polycrystalline methane hydrate at the micron scale by applying a contactless, thermos-induced stress to a tenuous shell of hydrate grown in a thin glass capillary. The results suggest that the cohesive strength of methane hydrate in marine settings may be an order of magnitude less than currently thought.

    • Dyhia Atig
    • , Daniel Broseta
    •  & Ross Brown
  • Article
    | Open Access

    Black carbon is a recalcitrant and unique form of organic carbon formed from incomplete combustion. Here the authors use global sampling to reduce uncertainty in the flux of terrestrial black carbon to the oceans, predicting that 34% of black carbon produced by fires has an oceanic fate.

    • Matthew W. Jones
    • , Alysha I. Coppola
    •  & Timothy A. Quine
  • Article
    | Open Access

    Plastic pollution has infiltrated every ecosystem, but few studies have quantified the biogeochemical or ecological effects of plastic. Here the authors show that microplastics in ocean sediment can significantly alter microbial community structure and nitrogen cycling.

    • Meredith E. Seeley
    • , Bongkeun Song
    •  & Robert C. Hale
  • Article
    | Open Access

    Previous work suggests that marine oxygen levels and bioturbation are important factors that shape phosphorus burial and the size of the marine biosphere. Here the authors show that seawater calcium concentration is a key factor in controlling marine P burial, and thus the global oxygen cycle.

    • Mingyu Zhao
    • , Shuang Zhang
    •  & Noah Planavsky
  • Article
    | Open Access

    Estuaries are diverse and important aquatic ecosystems, yet we lack information on their response to climate change. Here, the authors show that east Australian estuaries are warming and acidifying faster than predicted by ocean or atmospheric models; a trend that is magnified in shallow estuaries.

    • Elliot Scanes
    • , Peter R. Scanes
    •  & Pauline M. Ross
  • Article
    | Open Access

    Coastal pollution degrades ecosystems, but long term impacts are unknown in Australia’s Great Barrier Reef. Using a 333 year record of coral skeleton nitrogen isotopes, Erler and colleagues show that increasing nutrient inputs since European settlement have led to unexpected feedback responses.

    • Dirk V. Erler
    • , Hanieh Tohidi Farid
    •  & Janice M. Lough
  • Article
    | Open Access

    Eddies are common ocean features that isolate large swaths of seawater, but it is unclear how they influence productivity of phytoplankton trapped inside. Here Ellwood and colleagues use stable and radiogenic isotopes to characterize a Southern Ocean eddy, finding vanishingly low iron concentrations that drive low productivity across the region.

    • Michael J. Ellwood
    • , Robert F. Strzepek
    •  & Philip W. Boyd
  • Article
    | Open Access

    The Middle East is known to emit large amounts of non-methane hydrocarbon pollutants to the atmosphere, but the sources are poorly characterized. Here the authors discover a new source—deep water in the Red Sea—and calculate that its emissions exceed rates of several high gas-production countries.

    • E. Bourtsoukidis
    • , A. Pozzer
    •  & J. Williams
  • Article
    | Open Access

    Recent recession of the Larsen Ice Shelf C has revealed that microbial alteration of illite can occur within marine sediments, a process previously thought to only occur abiotically during low-grade metamorphism. Here, the authors show that such microbial alteration of illite could provide a potential source of Fe release to Southern Ocean waters during Holocene glacial cycles.

    • Jaewoo Jung
    • , Kyu-Cheul Yoo
    •  & Jinwook Kim
  • Article
    | Open Access

    The Nd isotope composition of seawater has been used to reconstruct past changes in the various contributions of different water masses to the deep ocean, with the isotope signatures of endmember water masses generally assumed to have been stable during the Quaternary. Here, the authors show that deep water produced in the North Atlantic had a significantly more radiogenic Nd signature during the Last Glacial Maximum compared to today.

    • Ning Zhao
    • , Delia W. Oppo
    •  & Lloyd D. Keigwin
  • Article
    | Open Access

    Earth’s carbon cycle and oceanic magnesium cycle are controlled by processes such as weathering, volcanism and precipitation of carbonates, such as dolomite. Here, the authors contradict the view that modern dolomite formation is rare and suggest instead that dolomite accounts for ~40–60% of the global oceanic Mg output in the last 20 Ma.

    • Netta Shalev
    • , Tomaso R. R. Bontognali
    •  & Derek Vance
  • Article
    | Open Access

    Carbon dioxide removal technologies are often touted as a potential strategy to combat ocean acidification. However, the authors show here that these strategies are only effective when included as part of aggressive and rapid climate-action, undermining the idea of geoengineering as a panacea.

    • M. Hofmann
    • , S. Mathesius
    •  & H. J. Schellnhuber
  • Article
    | Open Access

    Deciphering the origin, age, and composition of deep marine organic carbon remains a challenge for understanding the dynamics of the marine carbon cycle. Here, the authors identify (sub)micron-sized graphite emanating from both high and low temperature hydrothermal vents along the East Pacific Rise, and suggest graphite is a source of old carbon in the deep ocean.

    • Emily R. Estes
    • , Debora Berti
    •  & George W. Luther III
  • Article
    | Open Access

    Rivers are thought to be the largest source of the recalcitrant and abundant black carbon in the ocean. Here, Wagner and colleagues find distinct pools of black carbon between rivers and the open ocean, challenging the long-held assumption that marine black carbon is of terrestrial origin.

    • Sasha Wagner
    • , Jay Brandes
    •  & Aron Stubbins
  • Article
    | Open Access

    Iron is crucial for marine photosynthesis, but observational constraints on the magnitude of key iron cycle processes are lacking. Here the authors use a range of observational data sets to demonstrate that the balance between iron re-supply and removal in the subsurface controls upper ocean iron limitation.

    • Alessandro Tagliabue
    • , Andrew R. Bowie
    •  & Philip W. Boyd
  • Article
    | Open Access

    The loss of anomalous sulfur isotope compositions from sedimentary rocks has been considered a symptom of permanent atmospheric oxygenation. Here the authors show sulfur and oxygen isotope evidence from < 2.31 Ga sedimentary barium sulphates (barites) from the Turee Creek Basin, W. Australia, demonstrating the influence of local non-atmospheric processes on anomalous sulfur isotope signals.

    • B. A. Killingsworth
    • , P. Sansjofre
    •  & S. V. Lalonde
  • Article
    | Open Access

    Iron fertilisation of the high latitude oceans is a well-established biological mechanism to explain the ice age drawdown of atmospheric CO2, yet modelling has so far struggled to account for a sufficient drawdown via this mechanism. Here, the authors propose that N2 fixers, which inhabit the lower latitude ocean, made a significant contribution to CO2 drawdown and so amplified the global response to iron fertilisation during ice ages.

    • Pearse J. Buchanan
    • , Zanna Chase
    •  & Nathaniel L. Bindoff
  • Article
    | Open Access

    The ocean emits the greenhouse gas methane, but its vastness renders estimations challenging. Here the authors use machine learning to map global ocean methane fluxes, finding a disproportionate contribution from shallow coastal waters, and a link between primary production and methane cycling.

    • Thomas Weber
    • , Nicola A. Wiseman
    •  & Annette Kock
  • Article
    | Open Access

    Marine chemistry during the Early Earth (over 2.7 billion years ago) is commonly inferred to have been inorganically sulfate-reducing. Here, the authors argue that organic sulfur cycling may have played a previously unrecognized, yet important, role in the formation of ancient Archean marine sulfides.

    • Mojtaba Fakhraee
    •  & Sergei Katsev
  • Article
    | Open Access

    The oceanic magnesium cycle is closely linked to Earth’s carbon cycle and long-term climate change, due to processes such as continental weathering and authigenic mineral formation. Here, the authors update the global oceanic magnesium budget by quantifying the flux of magnesium from oceans to marine sediments and the associated isotopic fractionation.

    • Richard D. Berg
    • , Evan A. Solomon
    •  & Fang-Zhen Teng
  • Review Article
    | Open Access

    Subseafloor microbial activities are central to global biogeochemical cycles, affecting Earth’s surface oxidation, ocean chemistry, and climate. Here the authors review present understanding of subseafloor microbes and their activities, identify research gaps, and recommend approaches to fill those gaps.

    • Steven D’Hondt
    • , Robert Pockalny
    •  & Arthur J. Spivack
  • Article
    | Open Access

    The relative importance of crustal vs. anthropogenic dust deposition for iron cycling in the surface ocean is unclear. Based on analysis of iron isotope data from North Atlantic aerosol samples, the authors can reveal the relative importance of anthropogenic iron emissions and its impact on marine biogeochemistry.

    • Tim M. Conway
    • , Douglas S. Hamilton
    •  & Seth G. John