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The aftermath of end-Permian mass extinction was marked by a ∼5 million year interval of poorly-understood, extreme environments that likely hindered biotic recovery. Contemporary nitrogen isotope variations are considered, using a new conceptual model, to support a scenario that shows intensive nitrate-removal processes gradually depleted the global oceanic nitrate inventory during long-lasting oceanic anoxia. Enhanced nitrogen fixation shifted the oceanic nitrogenous nutrient (nutrient-N) inventory to an ammonium-dominated state. Ammonium is toxic to animals and higher plants but fertilizes algae and bacteria. This change in ocean chemistry could account for the intense and unexplained losses of nektonic taxa and the proliferation of microbial blooms in the Early Triassic. The transition from a nitrate ocean to an ammonium ocean was accompanied by a decrease in respiration efficiency of organisms and a shrinking oceanic nutrient-N inventory, ultimately leading to generally low productivity in the Early Triassic oceans. These unappreciated nutrient changes during episodes of prolonged ocean anoxia may be the key life-limiting factor at such times.

More than 85% of the Earth's volcanism and geothermal heat release occurs underwater at mid-ocean ridges, intra-plate hotspots, and oceanic island arcs. However, we lack a clear understanding of how a submarine eruption interacts with the overlying water column, the structure of the submarine eruptive plume, and the transport of volcanic products in the ocean by these plumes. We describe here the detection of eruption-derived temperature increase and salinity decrease from the 2012 Havre submarine caldera eruption by an existing array of temperature/salinity profiling floats, known as Argo. The Argo floats observed the signal, significant at >3 sigma level with respect to the background ocean variability (noise), at ocean depths of ∼1750–2000 m deeper than the eruptive vent itself. In order to understand this signal, we develop a new conceptual submarine plume model which suggests that the sub-vent level temperature and salinity anomalies are caused by large-scale ocean mixing induced by the eruptive plume, rather than heating directly from the eruption. Using results from scaling analysis and a modified numerical plume-gravity current model, we show that submarine eruptions can efficiently advect water masses from the deep ocean closer to the surface and form multiple subsurface intrusions during the process. Consequently, the submarine eruptive plumes can initiate significant ocean mixing, a process with significant implications for both long- and short-term influence of submarine volcanism on ocean chemistry, dynamics, and ecology. Finally, our model confirms that a detectable anomaly would persist out to 100s of km from the eruption location, comparable to Argo's spatial sampling. Given the global ocean coverage and a decadal baseline, the Argo floats (and other similar datasets), in concert with hydrophone and seismic arrays, can provide significant new constraints on subaqueous volcanism, eruption dynamics, and the impact on Earth systems through enhanced ocean mixing and nutrient supply, e.g. during submarine Large Igneous Provinces.

Reconstructions of ancient ocean chemistry are largely based on geochemical proxies obtained from epicontinental seas. Mounting evidence suggests that these shallow inland seas were chemically distinct from the nearby open ocean, decoupling epicontinental records from broader ocean conditions. Here we use the isotope-enabled Community Earth System Model to evaluate the extent to which the oxygen isotopic composition of the late Carboniferous epicontinental sea, the North American Midcontinent Sea (NAMS), reflects the chemistry of its open-ocean sources and connect epicontinental isotope variability in the sea to large-scale ocean-atmosphere processes. Model results support estuarine-like circulation patterns demonstrated by past empirical studies and suggest that orographic runoff produced decreases in surface seawater δ 18 O ( δ 18 O w ) of up to ∼3‰ between the NAMS and the bordering ocean. Simulated sea surface temperatures are relatively constant across the sea and broadly reproduced from proxy-based δ 18 O paleotemperatures for which model-based values of epicontinental δ 18 O w are used, indicating that offshore-onshore variability in surface proxy δ 18 O is primarily influenced by seawater freshening. Simulated bottom water temperatures in the NAMS are also reproduced from biogenic calcite δ 18 O using model-based values of epicontinental δ 18 O w , suggesting that benthic marine fossil δ 18 O is also influenced by seawater freshening and coastal upwelling. In addition, glacial-interglacial variations in nearshore seawater freshening counteract the effects of temperature on marine biogenic δ 18 O values, suggesting that salinity effects should be considered in δ 18 O-based estimates of glacioeustatic sea level change from nearshore regions of the NAMS. Our results emphasize the importance of constraining epicontinental dynamics for interpretations of marine biogenic δ 18 O as proxies of paleotemperature, salinity, and glacioeustasy.

The “Cambrian Explosion” is known for rapid increases in the morphological disparity and taxonomic diversity of metazoans. It has been widely proposed that this biological event was a consequence of oxygenation of the global ocean, but this hypothesis is still under debate. Here, we present high-resolution Fe–S–C–Al-trace element geochemical records from the Jinsha (outer shelf) and Weng'an (outer shelf) sections of the early Cambrian Yangtze Platform, integrating these results with previously published data from six correlative sections representing a range of water depths (Xiaotan, Shatan, Dingtai, Yangjiaping, Songtao, and Longbizui). The integrated iron chemistry and redox-sensitive trace element data suggest that euxinic mid-depth waters dynamically coexisted with oxic surface waters and ferruginous deep waters during the earliest Cambrian, but that stepwise expansion of oxic waters commenced during Cambrian Stage 3 ( ∼ 521 – 514 Ma ). Combined with data from lower Cambrian sections elsewhere, including Oman, Iran and Canada, we infer that the global ocean exhibited a high degree of redox heterogeneity during the early Cambrian, consistent with low atmospheric oxygen levels ( ∼ 10 – 40 % of present atmospheric level, or PAL). A large spatial gradient in pyrite sulfur isotopic compositions (δ34Spy), which vary from a mean of − 12.0 ‰ in nearshore areas to + 22.5 ‰ in distal deepwater sections in lower Cambrian marine units of South China imply low concentrations and spatial heterogeneity of seawater sulfate, which is consistent with a limited oceanic sulfate reservoir globally. By comparing our reconstructed redox chemistry with fossil records from the lower Cambrian of South China, we infer that a stepwise oxygenation of shelf and slope environments occurred concurrently with a gradual increase in ecosystem complexity. However, deep waters remained anoxic and ferruginous even as macrozooplankton and suspension-feeding mesozooplankton appeared during Cambrian Stage 3. These findings suggest that the “Cambrian Explosion” in South China may have been primarily a consequence of locally improved oxygenation of the ocean-surface layer rather than of the full global ocean. Our observations are inconsistent with predicted changes in ocean chemistry driven by early Cambrian animals, suggesting that the influence of early Cambrian animals on contemporaneous ocean chemistry, as proposed in previous studies, may be overly exaggerated.

The boron isotopic composition of calcium carbonate skeletons is a promising proxy method for reconstructing paleo-ocean pH and atmospheric CO2 from the geological record. Although the boron isotope methodology has been used extensively over the past two decades to determine ancient ocean-pH, the actual value of the boron isotope fractionation factor ( e B ) between the two main dissolved boron species, 11B(OH)3 and 10B(OH)−4, has remained uncertain. Initially, e B values were theoretically computed from vibrational frequencies of boron species, resulting in a value of ∼ 19 ‰ . Later, spectrophotometric pH measurements on artificial seawater suggested a higher value of ∼ 27 ‰ . A few independent theoretical models also pointed to a higher e B value. Here we provide, for the first time, an independent empirical fractionation factor ( e B = 26.0 ± 1.0 ‰ ; 25 °C ), determined by direct measurements of B(OH)3 in seawater and other solutions. Boric acid was isolated by preferential passage through a reverse osmosis membrane under controlled pH conditions. We further demonstrate that applying the Pitzer ion-interaction approach, combined with ion-pairing calculations, results in a more accurate determination of species distribution in aquatic solutions of different chemical composition, relative to the traditional two-species boron-system approach. We show that using the revised approach reduces both the error in simulating ancient atmospheric CO2 (by up to 21%) and the overall uncertainty of applying boron isotopes for paleo-pH reconstruction. Combined, this revised methodology lays the foundation for a more accurate determination of ocean paleo-pH through time.

Recognising variations in the carbon isotope compositions of marine organic-rich sedimentary rocks can provide insight into changes in ocean chemistry throughout geological time. Further, identification of global excursions in the carbon isotope record has proved to be valuable as a chronostratigraphic correlation tool. This investigation presents new high-resolution organic carbon isotope data ( δ C org 13 ) for marine sediments from 2 regions in North America (Last Creek, British Columbia, Canada and Five Card Draw, Nevada, USA). The carbon isotope profiles demonstrate that there were significant differences between the carbon reservoirs at Five Card Draw and Last Creek, notably in the upper part of the Leslei Zone. The δ C org 13 values show a gradual positive CIE ( ∼ 2 ‰ ) at Last Creek in the upper part of the Leslei Zone. This corresponds to a coeval positive CIE of similar duration in Dorset, UK (upper Turneri Zone; Jenkyns and Weedon, 2013 ), suggesting that this may be a global marine carbon isotope signature, and likely reflects a widespread increase in primary productivity during the Early Sinemurian. In addition, a brief negative CIE is observed in the uppermost Lower Sinemurian at Last Creek. This negative excursion is not recorded in the Dorset section, suggesting localised upwelling of 12C-rich bottom-waters at Last Creek. Further, the signals identified at Last Creek are not present in coeval sections at Five Card Draw, thus highlighting a significant difference between these localities. Osmium (Os) isotope data (initial 187Os/188Os values) provide a quantitative determination of the contrasting depositional environments of Five Card Draw and Last Creek (at least partially restricted with high levels of continental inundation and open-ocean, respectively). This demonstrates that basinal restriction may act as a major factor that controls isotopic stratigraphic signatures, thus preventing the identification of global or widespread regional excursions.

The quantification of the sources and sinks of elements to the oceans forms the basis of our understanding of global geochemical cycles and the chemical evolution of the Earth's surface. There is, however, a large imbalance in the current best estimates of the global fluxes to the oceans for many elements. In the case of strontium (Sr), balancing the input from rivers would require a much greater mantle-derived component than is possible from hydrothermal water flux estimates at mid-ocean ridges. Current estimates of riverine fluxes are based entirely on measurements of dissolved metal concentrations, and neglect the impact of riverine particulate dissolution in seawater. Here we present 87Sr/86Sr isotope data from an Icelandic estuary, which demonstrate rapid Sr release from the riverine particulates. We calculate that this Sr release is 1.1–7.5 times greater than the corresponding dissolved riverine flux. If such behaviour is typical of volcanic particulates worldwide, this release could account for 6–45% of the perceived marine Sr budget imbalance, with continued element release over longer timescales further reducing the deficit. Similar release from particulate material will greatly affect the marine budgets of many other elements, changing our understanding of coastal productivity, and anthropogenic effects such as soil erosion and the damming of rivers.

High-temperature hydrothermal systems at mid-ocean ridges play a critical role in global geochemical cycles. Most of the magmatic heat driving hydrothermal circulation along the global mid-ocean ridge system is released into basalt-hosted systems exemplified by intermediate- to fast-spreading ridges. Constraints on the fluid and chemical fluxes associated with these systems come from the compositions of high-temperature hydrothermal vent fluids and the compositions of altered sheeted dikes. Global data compilations of both of these data types, including 20 mineral components, 10 major fluid species, 13 trace elements and 6 isotope ratios, have been jointly fit using a numerical Bayesian inversion procedure. This new approach provides the first internally consistent estimates of fluid and chemical fluxes, with rigorously quantified uncertainties, for a broad suite of elements. The resulting global fluid flux is 8.0 ± 2.1 × 1012 kg yr− 1, at a water-dike mass ratio of 0.92, sufficient to cool the sheeted dike complex from magmatic to hydrothermal temperatures and remove ~ 50% of the latent heat of crystallization of the plutonic complex. For conservative elements, the fluxes represent inputs into the ocean and should allow more accurate models of the controls on modern and paleo-seawater chemistry to be developed.

Multiple observations have revealed that environmental disturbances may have been linked to the end-Permian mass extinction and delayed biotic recovery. Biogeochemical constraints on the temporal and spatial changes of oceanic redox chemistry during the Permian–Triassic interval are essential to evaluate global significance of previous hypotheses and to improve our understanding of extinction and recovery processes. To investigate redox ocean chemistry change associated with the end-Permian extinction and subsequent delayed biotic recovery, we examine framboidal pyrites as well as sulfur isotopic compositions of pyrites from the East Greenland Basin. The size distributions of framboidal pyrites in sediments from a continuous section across the Permian–Triassic boundary reveal that sulfidic conditions in water columns were established about 0.7 m above the extinction event in the East Greenland Basin. Our detailed examination of framboidal pyrites challenges a leading hypothesis that euxinia in the photic zone caused the end-Permian ecosystem collapse. We identify several positive and negative S-isotopic shifts before and after the extinction event and demonstrate that a positive S-isotopic shift is not indicative of an abrupt change of redox chemistry in water columns, in contrast to previous claims. The integration of isotope and framboidal pyrite data provides a nearly continuous record of ocean chemistry evolution and new insights into the end-Permian extinction and delayed biotic recovery in the East Greenland Basin.

Variations in Earth's rates of seafloor generation and recycling have far-reaching consequences for sea level, ocean chemistry, and climate. However, there is little agreement on the correct parameterization for the time-dependent evolution of plate motions. A strong constraint is given by seafloor age distributions, which are affected by variations in average spreading rate, ridge length, and the age distribution of seafloor being removed by subduction. Using a simplified evolution model, we explore which physical parameterizations of these quantities are compatible with broad trends in the area per seafloor age statistics for the present-day and back to 140 Ma from paleo-age reconstructions. We show that a probability of subduction based on plate buoyancy (slab-pull, or “sqrt(age)”) and a time-varying spreading rate fits the observed age distributions as well as, or better than, a subduction probability consistent with an unvarying “triangular” age distribution and age-independent destruction of ocean floor. Instead, we interpret the present near-triangular distribution of ages as a snapshot of a transient state of the evolving oceanic plate system. Current seafloor ages still contain hints of a ∼ 60 Myr periodicity in seafloor production, and using paleoages, we find that a ∼ 250 Myr period variation is consistent with geologically-based reconstructions of production rate variations. These long-period variations also imply a decrease of oceanic heat flow by ∼ − 0.25%/Ma during the last 140 Ma, caused by a 25–50% decrease in the rate of seafloor production. Our study offers an improved understanding of the non-uniformitarian evolution of plate tectonics and the interplay between continental cycles and the self-organization of the oceanic plates.

Future warming is predicted to shift the Earth system into a mode with progressive increase and vigour of extreme climate events possibly stimulating other mechanisms that invigorate global warming. This study provides new data and modelling investigating climatic consequences and biogeochemical feedbacks that happened in a warmer world not, vert, similar 112 Myr ago. Our study focuses on the Cretaceous Oceanic Anoxic Event (OAE) 1b and explores how the Earth system responded to a moderate not, vert, similar 25,000 yr lasting climate perturbation that is modelled to be less than 1 °C in global average temperature. Using a new chronological model for OAE 1b we present high-resolution elemental and bulk carbon isotope records from DSDP Site 545 from Mazagan Plateau off NW Africa and combine this information with a coupled atmosphere–land–ocean model. The simulations suggest that a perturbation at the onset of OAE 1b caused almost instantaneous warming of the atmosphere on the order of 0.3 °C followed by a longer (not, vert, similar 45,000 yr) period of not, vert, similar 0.8 °C cooling. The marine records from DSDP Site 545 support that these moderate swings in global climate had immediate consequences for African continental supply of mineral matter and nutrients (phosphorous), subsequent oxygen availability, and organic carbon burial in the eastern subtropical Atlantic, however, without turning the ocean anoxic. The match between modelling results and stratigraphic isotopic data support previous studies [summarized in Jenkyns, H.C., 2003. Evidence for rapid climate change in the Mesozoic–Palaeogene greenhouse world. The Royal Society, 361: 1885–1916.] in that methane emission from marine hydrates, albeit moderate in dimension, may have been the trigger for OAE 1b, though we can not finally rule out alternative mechanisms. Following the hydrate mechanism a total of 1.15 × 1018 g methane carbon (δ13C = − 60 ‰), equivalent to about 10% to the total modern gas hydrate inventory, generated the δ13Ccarb profile recorded in the section. Modelling suggests a combination of moderate-scale methane pulses supplemented by continuous methane emission at elevated levels over not, vert, similar 25,000 yr. The proposed mechanism, though difficult to finally confirm in the geological past, is arguably more likely to occur in a warmer world and apparently perturbs global climate and ocean chemistry almost instantaneously. This study shows that, once set-off, this mechanism can maintain Earth's climate in a perturbed mode over geological time leading to pronounced changes in regional climate.

We review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the Earth system has evolved through time—that of calcium carbonate (CaCO3). In particular, we highlight a Mid-Mesozoic Revolution in the nature and location of carbonate deposition in the marine environment, driven by the ecological success of calcareous plankton. This drove the creation of a responsive deep-sea sedimentary sink of CaCO3. The result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric CO2 in the modern system. However, the same calcifying organisms that under-pin the deep-sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel CO2 and increasing acidity of the surface ocean. We are not yet in a position to predict what the impact on CaCO3 production will be, or how the uptake of fossil fuel CO2 by the ocean will be affected. This uncertainty in the future trajectory of atmospheric CO2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern.

We collected 19 samples of bottom sea water (including 8 samples of shimmering fluid), using the Japanese submersible Shinkai 2000, in the bathyal Calyptogena community area (the Hatsushima area) along Sagami Trough, at the northern end of the Philippine Sea plate, in order to clarify the source of fluid seepage. Shimmering fluid samples showed a maximum temperature of 11.6°C, which is about 9°C higher than the ambient sea water. The fluid chemistry of these samples is summarized as follows: (1) alkalinity, H2S, SiO2, NH4, ΣCO2 and CH4 show enrichment and Cl, SO4, K, Na, Mg and Ca show depletion compared with ambient sea water; (2) Cl depletion is about 20%; and (3) the content and 3He4He ratio of dissolved helium show little anomaly compared with ambient sea water. The observed chemical composition and temperature of the fluid is well explained by mixing of sea water, pore water and land-derived groundwater with a temperature of about 40°C and a seeping flux of about 400 m3 per day. A preliminary estimation of the global chemical flux implies that groundwater discharge to the ocean (including pore water recycling) is an important factor in controlling ocean chemistry.