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Toward an integrated pantropical ocean observing system
No full textGlobal climate is regulated by the ocean, which stores, releases, and transports large amounts of mass, heat, carbon, and oxygen. Understanding, monitoring, and predicting the exchanges of these quantities across the ocean’s surface, their interactions with the atmosphere, and their horizontal and vertical pathways through the global oceans, are key for advancing fundamental knowledge and improving forecasts and longer-term projections of climate, weather, and ocean ecosystems. The existing global observing system provides immense value for science and society in this regard by supplying the data essential for these advancements. The tropical ocean observing system in particular has been developed over decades, motivated in large part by the far-reaching and complex global impacts of tropical climate variability and change. However, changes in observing needs and priorities, new challenges associated with climate change, and advances in observing technologies demand periodic evaluations to ensure that stakeholders’ needs are met. Previous reviews and assessments of the tropical observing system have focused separately on individual basins and their associated observing needs. Here we provide a broader perspective covering the tropical observing system as a whole. Common gaps, needs, and recommendations are identified, and interbasin differences driven by socioeconomic disparities are discussed, building on the concept of an integrated pantropical observing system. Finally, recommendations for improved observations of tropical basin interactions, through oceanic and atmospheric pathways, are presented, emphasizing the benefits that can be achieved through closer interbasin coordination and international partnerships
Global Atmospheric Composition Effects from Marine Isoprene Emissions
No full textIsoprene emissions, primarily of biogenic origin, play an important role in atmospheric chemistry and climate. However, the atmospheric implications of marine isoprene emissions remain underexplored due to sparse in situ measurements and the intricate mechanisms governing isoprene in the upper ocean. This study uses 20 years of MODIS satellite observations to upscale isoprene production and loss rates derived from laboratory experiments, enabling global modeling of aqueous isoprene concentrations and emissions. Earth system model simulations with integrated marine isoprene emissions demonstrate substantial alterations in atmospheric composition over global oceanic regions. Our investigation uncovers diurnal variations in the vertical profiles of atmospheric isoprene, indicating that surface isoprene can ascend to the mid-to-upper troposphere, where nitrogen monoxide (NO) influences isoprene epoxydiol (IEPOX) production differently over selected oceanic and terrestrial regions. These findings pave the way for future studies on the role of marine isoprene in climate models and advance our understanding of its broader implications for atmospheric chemistry under a changing climate
Calcite is an efficient and low-cost material to enhance benthic weathering in shelf sediments of the Baltic Sea
No full textRecent studies have proposed calcite and dunite as possible alkaline materials for enhanced benthic weathering in shallow depocenters of the Baltic Sea as a marine carbon dioxide removal strategy. In this study, insights on calcite and dunite weathering from laboratory incubations and long-term benthocosm experiments are combined with a numerical box-model to assess the carbon dioxide uptake potential of mineral addition to organic-rich sediments in the southwest Baltic Sea. The results reveal that calcite has an up to 10-fold higher carbon dioxide uptake efficiency and is therefore the preferable material for enhanced benthic weathering as a marine carbon dioxide removal method, with costs per tonne of sequestered carbon dioxide ranging between 82 and 462 euro for calcite while reaching 558–1920 euro for dunite. These findings could be applicable to other areas in the Baltic Sea and also globally to sediments in the wider coastal shelf with similar geochemical properties
Sediment resuspension in muddy sediments enhances pyrite oxidation and carbon dioxide emissions in Kiel Bight
No full textSediment resuspension of blue carbon ecosystems (e.g., seagrass beds) and muddy sediments exposes buried particulate organic carbon to oxygenated waters and remineralization, potentially enhancing carbon dioxide fluxes. However, the kinetics of carbon degradation under oxic and anoxic conditions are poorly constrained. We report the results of incubation experiments with sediments from Kiel Bight to simulate sediment resuspension events induced by natural and anthropogenic resuspension in this area. A numerical model determined that oxic carbon remineralization rates were up to two-fold higher than those under anoxic conditions. A coupled sediment-water column model demonstrated that pyrite oxidation, rather than carbon oxidation, has the potential to induce large carbon dioxide emissions to the atmosphere following anthropogenic sediment disturbance by trawling. Upscaling to muddy areas of Kiel Bight suggests an annual emission of up to ~14 k tonnes of carbon dioxide per year. Pyrite oxidation may contribute to a weakening of the carbon shelf pump and a reduction of anthropogenic carbon dioxide uptake
Ice core evidence for the Los Chocoyos supereruption disputes millennial-scale climate impact
No full textVolcanic supereruptions are considered among the few drivers of global and existential catastrophes, with recent hypotheses suggesting massive volcanic stratospheric sulfate injection could instigate major shifts in global climate. The absence of supereruptions during recent history as well as large uncertainties on eruption ages limits understanding of the climatic risk they impose. Polar ice cores have well-resolved continuous age models, record past temperature, and contain volcanic sulfate and cryptotephra deposits which can be geochemically fingerprinted to determine eruption timing and improve stratospheric sulfur loading estimates. Here, we provide an age of 79,500 years for the Atitlán Los Chocoyos supereruption, one of the largest Quaternary eruptions, by identifying tephra shards in ice cores from both Greenland and Antarctica. This ice core age is supported by a revised marine sediment core stratigraphy age for the Los Chocoyos ash layer. Through comparison with well-dated ice-core temperature proxy records, our study suggests that despite being one of the largest sulfur emissions recorded in ice cores, the Los Chocoyos supereruption did not trigger a millennial-scale cold period
Trace metal evolution of the Late Cretaceous Ocean
No full textThe Cenomanian-Turonian boundary (Late Cretaceous) witnessed the last spectacular manifestation of Mesozoic Anoxic Events (OAE 2, ∼94 Ma), marked by a prominent carbon isotope excursion (CIE) and burial of organic-matter-rich sediments under high atmospheric CO2 concentrations. But the Late Cretaceous generally was a time of profound environmental change. OAE 2 was preceded by other CIEs, including the Mid-Cenomanian Event (MCE), and was punctuated by a short re‑oxygenation and cooling event (the Plenus Cold Event, PCE). Extensive previous studies, including many trace metal studies, have focused on OAE 2, but there is still debate concerning the degree of drawdown of oceanic trace metal reservoirs during OAE 2, whether this drawdown is global or local, its causes and consequences for ocean ecology. Here, we present records of eight trace metals, over about 5 Myr of the Late Cretaceous, from the Tarfaya Basin in the proto-North Atlantic. The long records from a core preserving a continuous sedimentary succession allow us to set changes occurring across OAE 2 in the broader context of Late Cretaceous, including the lead up to OAE 2. Moreover, the multiple trace metal dataset allows us to broadly investigate the oceanographic setting in the context of recent studies of multiple trace metals in modern organic-rich sediments aimed at refining the proxies. Trace metal enrichments in these organic-rich sediments are discussed on three different timescales. Firstly, comparison of these Late Cretaceous sediments with modern organic-rich sediments are consistent with deposition in an open ocean upwelling margin in the Late Cretaceous, very like the modern Peru or Namibian Margin, although the deep proto-North Atlantic was probably partially restricted. Secondly, in common with previous studies, metal/TOC ratios often show sharp drops in the early part of OAE 2. Thirdly, however, this sharp drop occurs within a framework of pseudo-cyclical variations in metal/TOC, with a period of about 143 ±19 kyr (1 SD), that is a feature of these long records well before OAE 2, including across the MCE. Different metals respond differently to the perturbation in the early part of OAE 2 itself. Simple mass balance considerations suggest that trace metal drawdown with organic carbon must be at least partially compensated by changes in the rate of chemical weathering on the continents, as previously inferred from Li and Ca isotopes. Moreover, changes in the patterns of variation between different metals, as well as covariation of metal/TOC ratios and Os isotopes, hint at changes in the pattern of chemical weathering, most prominently in the contribution of mafic rocks to the chemical weathering flux
Boron isotopes identify deep-slab serpentinite in the source of Aleutian arc magma
No full textSeafloor lavas of the Western Aleutian arc have isotopically heavy boron (delta B-11 to +13.4%(0)) that is negatively correlated with B content (ppm). Endmember samples are primitive dacites and rhyodacites (delta B-11 > +10%(0), SiO2 = 63%-70%, Mg# > 0.60) with adakitic trace-element and isotopic characteristics that require roles for residual garnet and rutile in their formation. The source of isotopically heavy B is likely serpentinite in the mantle section of the subducting plate, which dewaters into an inverted geothermal gradient and drives melting within the overlying volcanic section at depths where prior effects of seawater alteration were minimal. Most volcanic rocks from the Aleutian Island locations have 10-30 ppm B with an average delta B-11 of similar to+1.0%(0) +/- 1.3%(0), reflecting a mixed source dominated by subducted sediment. A subset of island samples has B that is isotopically light (delta B-11 < -2.4%0) and at low concentrations (<11.0 ppm), which is typical of arc lavas globally from rear-arc settings where depth-to-slab is high, and where delta B-11 may be interpreted to reflect a source in dehydrated (isotopically light) altered oceanic crust. Mass balance modeling indicates that isotopically heavy B from deep-slab serpentinite is present in the Aleutian source arc-wide but is typically masked by sediment-derived B at volcanic centers outside of the westernmost segment of the arc
Deposition, deformation, and flexure in a transpressional trough, Queen Charlotte fault, offshore Haida Gwaii (British Columbia, Canada)
No full textTranspressional deformation along the Pacific–North American plate boundary off British Columbia (Canada) generates interactions between tectonic and depositional processes; first-order deformation is creation of a bathymetric trough by flexure of the Pacific plate. Interpretation of a suite of single-channel seismic reflection data in the central and southern trough shows second-order internal structure and depositional systems within the trough. Much of these sediments originated from Quaternary slope fans, although the age of the underlying oceanic crust is 8–13 Ma. These turbidite deposits overlie hemipelagic deposits. Two distinct layers of turbidite deposits in the trough can be explained by sediment deposition systems rather than tectonic events. We infer that the most recent flat-lying deposits, which have been previously interpreted in the northern trough as indicating a lack of compressive deformation, consist, in fact, of along-axis flows based on the general geomorphology of the margin. Second-order deformation consists of small-offset extensional and compressive structures common within 15 km of the foot of the continental slope. A few normal faults are observed tens of kilometers further out on the flexural bulge. Recent faults that cut the seafloor are observed offshore from the rupture plane of the 2012 M7.8 earthquake and match an area of extensional aftershocks. These faults may not be from bending of the entire bulge, which is 30–40 km wide, but from the plate being pulled into the underthrust zone. Maximum depression of the Pacific plate is also offshore from the region of recent rupture, indicating that this rupture is representative of long-term geologic processes
Seasonal productivity of the equatorial Atlantic shaped by distinct wind-driven processes
No full textThe eastern equatorial Atlantic hosts a productive marine ecosystem that depends on upward supply of nitrate, the primary limiting nutrient in this region. The annual productivity peak, indicated by elevated surface chlorophyll levels, occurs in the Northern Hemisphere summer, roughly coinciding with strengthened easterly winds. For enhanced productivity in the equatorial Atlantic, nitrate-rich water must rise into the turbulent layer above the Equatorial Undercurrent. Using data from two trans-Atlantic equatorial surveys, along with extended time series from equatorial moorings, we demonstrate how three independent wind-driven processes shape the seasonality of equatorial Atlantic productivity: (1) the nitracline shoals in response to intensifying easterly winds; (2) the depth of the Equatorial Undercurrent core, defined by maximum eastward velocity, is controlled by an annual oscillation of basin-scale standing equatorial waves; and (3) mixing intensity in the shear zone above the Equatorial Undercurrent core is governed by local and instantaneous winds. The interplay of these three mechanisms shapes a unique seasonal cycle of nutrient supply and productivity in the equatorial Atlantic, with a productivity minimum in April due to a shallow Equatorial Undercurrent and a productivity maximum in July resulting from a shallow nitracline coupled with enhanced mixing