Trace elements and isotopes (TEIs) are important to marine life and are essential tools for studying ocean processes1. Two different frameworks have arisen regarding marine TEI cycling: reversible scavenging favours water-column control on TEI distributions2–5, and seafloor boundary exchange emphasizes sedimentary imprints on water-column biogeochemistry6,7. These two views lead to disparate interpretations of TEI behaviours8–10. Here we use rare earth elements and neodymium isotopes as exemplar tracers of particle scavenging11 and boundary exchange6,7,12. We integrate these data with models of particle cycling and sediment diagenesis to propose a general framework for marine TEI cycling. We show that, for elements with greater affinity for manganese oxide than biogenic particles, scavenging is a net sink throughout the water column, contrary to a common assumption for reversible scavenging3,13. In this case, a benthic flux supports increasing elemental concentrations with water depth. This sedimentary source consists of two components: one recycled from elements scavenged by water-column particles, and another newly introduced to the water column through marine silicate weathering inside sediment8,14,15. Abyssal oxic diagenesis drives this benthic source, and exerts a strong influence on water-column biogeochemistry through seafloor geometry and bottom-intensified turbulent mixing16,17. Our findings affirm the role of authigenic minerals, often overshadowed by biogenic particles, in water-column cycling18, and suggest that the abyssal seafloor, often regarded as inactive, is a focus of biogeochemical transformation19,20.

Beryllium isotopes (stable 9Be and cosmogenic meteoric 10Be) enter the oceans through distinct pathways – i.e., from the continents and the atmosphere respectively – and display non-conservative behaviour in seawater. This isotope system has served as a powerful tool for quantifying a variety of processes, including geomagnetism, sedimentation, continental input, and ocean circulation. However, processes at land–ocean boundaries and within the ocean interior may either amplify or buffer the seawater isotope response to environmental changes. In the last decade, substantial effort has been invested in understanding external sources and internal cycling of Be isotopes, offering an excellent opportunity to revisit their modern oceanic cycle. Here, we investigate the controls on the modern oceanic cycling of Be isotopes using a three-dimensional ocean model, constrained by observational data on input fluxes and water-column distributions of 9Be and 10Be. In addition to modelling the previously known controls, we highlight the key role of marine benthic fluxes and scavenging onto particulate organic matter and opal in determining the mass balance and spatial distribution of Be isotopes. Inter-basin Be transport by the circulation is less important than external inputs at continent/atmosphere–ocean boundaries, except in the South Pacific. Therefore, the distribution of seawater 10Be/9Be ratios largely reflects that of the external inputs in most basins in the modern ocean. Finally, we apply our data-constrained mechanistic model to test the sensitivity of basin-wide 10Be/9Be ratios to changes of external sources and internal cycling. This analysis shows that seawater 10Be/9Be ratios are to some extent buffered against changes in continental denudation. For example, a 50 % decrease in denudation rates results in a 13–48 % increase in ocean-wide 10Be/9Be ratios. Moreover, the interplay between particle scavenging and ocean circulation can cause divergent responses in 10Be/9Be ratios in different basins. Weaker scavenging (e.g., 50 % decrease in intensity) would increase the homogenising effect of ocean circulation, making North Atlantic and North Pacific 10Be/9Be ratios converge (∼20 % change in isotope ratios). The mechanistic understanding developed from this Be cycling model provides important insights into the various applications of marine Be isotopes, and offers additional tools to assess the causes of spatio-temporal Be isotope variations. We also identify the key oceanic processes that require further constraints to achieve a complete understanding of Be cycling in the modern ocean and back through time.

Nickel (Ni) is a biologically active metal whose reactivity and isotope fractionation in the marine realm are strongly influenced by biological and redox-related processes, giving the stable isotope system potential for studying past ocean environments. Reducing, organic-rich, sediments constitute an important sink of Ni from the modern ocean. Importantly, at open ocean upwelling margins, these kinds of sediment record the isotope composition of the modern deep ocean. Thus, records of their Ni isotope composition in the past have the potential to record the past deep ocean isotope composition and the oceanic isotope mass balance. However, the detailed processes controlling the upwelling sink are not fully understood. Here, we address this issue through data for sediments, porewaters and the water column of Kiel Bight in the Western Baltic Sea. This setting preserves sediments that have similar characteristics to those of open ocean upwelling margins, allowing us to study specific controlling processes in a well constrained setting. In common with sediments from open-ocean upwelling settings, Ni is well-correlated with carbon in solid sediment, suggesting delivery of Ni via rain of organic carbon from the water column. Overall, porewaters at all sites studied show increasing Ni concentrations from around 10 nM near the sediment–water interface to as high as 50 nM at 25 cm depth. This increase is correlated with increases in ammonia concentrations, suggesting release of Ni from anaerobic respiration of organic matter. However, porewater Ni/NH4 ratios are always lower than Ni:N of water column suspended particulate matter, suggesting an additional process that removes Ni from the porewater. Porewater sulphide also increases with depth, from as low as zero at the sediment–water interface to levels as high as 3 mM at 25 cm. Overall, porewater Ni isotopes become heavier with depth, from bottom water δ60Ni around +0.5 to +1‰, to values as high as +2.3‰ at depth. All these observations strongly suggest that Ni is removed from porewater into a solid sulphide. Mass balance indicates that over 90% of the Ni delivered in organic material to the sediment–water interface is transferred from organic matter into solid sulphide. Upward diffusive fluxes lead to the loss of a small amount back to the water column via a benthic flux. Given the large proportion of Ni retained within the sediment, the loss of such Ni does not strongly impact the isotope composition of the buried pool. These data are crucial in clarifying the processes controlling the size and isotope composition of organic-rich sediments on upwelling margins.

Despite its critical role in regulating the global climate and carbon cycle, the evolution of deep Pacific circulation has not been fully deciphered during the last glacial cycle. The effect of deep Pacific hydrographic change (e.g. oxygenation and circulation) on atmospheric CO2 variation is still uncertain. Here, we study redox-sensitive elements including V-U-Mn and benthic foraminiferal δ13C at the HYIV2015-B9 site in the southern South China Sea (SCS) to reconstruct the oxygenation and δ13C signals of water masses during the last glacial cycle. The intra-basin benthic foraminiferal δ13C gradient suggests enhanced stratification of the deep Pacific during the glacial compared to the interglacial, implying sluggish abyssal Pacific overturning. This is consistent with weak Pacific Deep Water (PDW) ventilation, as indicated by high contents of authigenic V and U, and low authigenic Mn. The inferred sluggish abyssal Pacific overturning is probably associated with less transport of Lower Circumpolar Deep Water, facilitating the expansion of respired carbon storage in the glacial deep Pacific. Meanwhile, the atmospheric CO2 rise is closely related to active abyssal Pacific overturning since late MIS 5, particularly when considering the impact of Southern Ocean upwelling modulated by Earth's obliquity. Overall, our data indicate the critical role of abyssal Pacific overturning in the carbon cycle, revealing the potential pathway for deep carbon dioxide outgassing in the North Pacific.

{The rubidium (Rb) isotope system has the potential for tracing water–silicate interactions and providing information on the global Rb cycling. However, the Rb isotope compositions of modern seawater and its major inputs and outputs remain poorly understood. Here we measured Rb isotope compositions of seawaters, pelagic clay sediments and porewaters from the western and central equatorial Pacific Ocean. Our results show that the δ87Rb of modern seawater is homogeneous (0.13 ± 0.04‰; 2SD

The development of nickel isotopes as a chemical tracer of past ocean environments requires a sound understanding of the modern oceanic budget. Our current understanding of this budget implies a large elemental and isotope imbalance between inputs to and outputs from the dissolved pool of the ocean. This imbalance is mainly caused by the dominant oxic sink of Ni to Mn oxide-rich sediments. Though the Ni isotope composition of Fe-Mn crusts has previously been used as proxy for the Ni isotope composition of these sediments, crusts and nodules represent a very small part of the total Mn oxide output. Instead, Mn oxide microparticle supply to pelagic and hemi-pelagic sediments dominates the removal of Mn to sediments, but there are very few isotope data for such samples. Here we present the first extensive Ni concentration and isotope dataset from fully oxic Mn-rich pelagic sediments, from 6 different sites across the open Pacific and 10 closely-spaced sites in the Indian Ocean. We also present data for one hemi-pelagic site representing a suboxic setting on the California Margin. Abyssal Pacific and Indian Ocean sediments have a Ni/Mn ratio of 0.02 (similar to Fe-Mn crusts) and their authigenic Ni is isotopically lighter (δ60Ni = +0.26 to +1.08‰) than seawater (+1.33‰) and crusts (+1.55±0.38‰). Data presented here for organic carbon-rich suboxic sediments of the Californian margin have lower Ni/Mn ratios (0.004 to 0.014 for the oxic top of the core, where Mn oxide is present in abundance) and even lighter authigenic Ni isotope compositions (δ60Ni = -0.08±0.11‰). We show that the Ni isotopes of nearly all Mn-rich sediments and deposits analysed to date, including the new data presented here, are correlated with Co/Mn ratios, suggesting that both are controlled by accumulation rate, progressive incorporation of Ni into the metal oxide structure and isotopic re-equilibration between the solid and aqueous phase. At sites where sediments are diagenetically processed, such as the California Margin, differential diagenetic remobilisation of Mn, Ni and Co cause deviations from this correlation. We present a new mass balance calculation that recognises the importance of scavenging of oceanic Ni to Mn oxide-rich proximal hydrothermal sediments, with low Ni/Mn and light isotope compositions. The mass balance produces a budget that can be simultaneously balanced for both amounts and isotope compositions of Ni. This result provides a strong basis for the application of Ni isotopes as records of the evolution of the metal sink from the oxic oceans through Earth history.

The ratio of atmosphere-derived 10Be to continent-derived 9Be in marine sediments has been used to probe the long-term relationship between continental denudation and climate. However, its application is complicated by uncertainty in 9Be transfer through the land-ocean interface. The riverine dissolved load alone is insufficient to close the marine 9Be budget, largely due to substantial removal of riverine 9Be to continental margin sediments. We focus on the ultimate fate of this latter Be. We present sediment pore-water Be profiles from diverse continental margin environments to quantify the diagenetic Be release to the ocean. Our results suggest that pore-water Be cycling is mainly controlled by particulate supply and Mn-Fe cycling, leading to higher benthic fluxes on shelves. Benthic fluxes may help close the 9Be budget and are at least comparable to, or higher (\textasciitilde2-fold) than, the riverine dissolved input. These observations demand a revised model framework, which considers the potentially dominant benthic source, to robustly interpret marine Be isotopic records.

Trace elements and isotopes (TEIs) are important tools in studying ocean biogeochemistry. Understanding their modern ocean budgets and using their sedimentary records to reconstruct paleoceanographic conditions require a mechanistic understanding of the diagenesis of TEIs, yet the lack of appropriate modeling tools has limited our ability to perform such research. Here I introduce SedTrace, a modeling framework that can be used to generate reactive-transport code for modeling marine sediment diagenesis and assist model simulation using advanced numerical tools in Julia. SedTrace enables mechanistic TEI modeling by providing flexible tools for pH and speciation modeling, which are essential in studying TEI diagenesis. SedTrace is designed to solve one particular challenge facing users of diagenetic models: existing models are usually case-specific and not easily adaptable for new problems such that the user has to choose between modifying published code and writing their own code, both of which demand strong coding skills. To lower this barrier, SedTrace can generate diagenetic models only requiring the user to supply Excel spreadsheets containing necessary model information. The resulting code is clearly structured and readable, and it is integrated with Julia's differential equation solving ecosystems, utilizing tools such as automatic differentiation, sparse numerical methods, Newton–Krylov solvers and preconditioners. This allows efficient solution of large systems of stiff diagenetic equations. I demonstrate the capacity of SedTrace using case studies of modeling the diagenesis of pH as well as radiogenic and stable isotopes of TEIs.

Dissolved Rare Earth Elements (REE) and radiogenic neodymium (Nd) isotope composition (εNd) of seawater are widely used geochemical tools in studying marine processes, but their modern ocean budgets are poorly understood. Recent discoveries of large benthic fluxes of REE with unique εNd signatures from marine sediments, particularly in the deep-sea, have led to a “bottom-up” hypothesis, which suggests that early diagenesis below the sediment-water interface (SWI) controls the ocean's REE and εNd budgets. To investigate such sedimentary processes, we created a reactive-transport model for the biogeochemical cycling of Nd and εNd in marine sediments. Here, we attempt to quantify the roles of authigenesis, marine silicate weathering and reverse weathering in the diagenetic cycling of Nd and εNd at a deep-sea (3000 m) site on the Oregon margin. Our model predicts that, at this site, Nd carried by Fe/Mn oxides into sediments eventually transforms to authigenic Nd-phosphate, during which ∼9% of the incoming solid Nd flux is released as a dissolved benthic flux back to the overlying bottom water. We also find that the classic reversible scavenging formulation applied to Nd co-cycling with Fe/Mn oxides is inconsistent with the data. Rather, a co-precipitation formulation, assuming Nd is structurally incorporated into Fe/Mn oxides, successfully simulates the data. The model also shows that authigenesis alone cannot explain the pore water and authigenic εNd, which are both more radiogenic than bottom water at this site. However, the weathering of volcanic silicates sourced from the local subduction zone can successfully explain εNd. We suggest that, because reverse weathering by authigenic clay formation maintains the under-saturation of primary silicates in pore water, marine silicate weathering can proceed. The processes we model likely affect the sedimentary cycling of many other trace elements and isotopes, with much broader implications for the understanding of ocean biogeochemistry.

Rare earth elements (REEs) are powerful tools to track oceanic biogeochemical proc-esses. However, our understanding of REE sources is incomplete, leading to contro-versial interpretations regarding their oceanic cycling. Continental margin sediments are often assumed to be a major source, but the sediment pore water data required to understand the processes controlling that potential source are scarce. Here, we mea-sure and compile pore water and estuarine REE data from the Changjiang (Yangtze) estuary-East China Sea shelf. We show that release of REEs, from shallow pore water to overlying seawater, is coupled to Mn reduction. In contrast, REEs are removed in deep pore water, perhaps via formation of an authigenic REE-bearing phase. This sedimentary source can potentially explain REE addition in the estuary at mid-high salinity. Our calculations suggest that the benthic flux is the largest Nd source (similar to 40 %) on the East China Sea shelf. Globally, however, despite a higher benthic Nd flux on the advection-dominated shelf, the much more extensive deep ocean still domi-nates the total area-integrated benthic flux. Our results call for a more extensive investigation of the magnitude of the benthic flux of REEs to the oceans.

North Pacific deoxygenation events during the last deglaciation were sustained over millennia by high export productivity, but the triggering mechanisms and their links to deglacial warming remain uncertain1–3. Here we find that initial deoxygenation in the North Pacific immediately after the Cordilleran ice sheet (CIS) retreat4 was associated with increased volcanic ash in seafloor sediments. Timing of volcanic inputs relative to CIS retreat suggests that regional explosive volcanism was initiated by ice unloading5,6. We posit that iron fertilization by volcanic ash7–9 during CIS retreat fuelled ocean productivity in this otherwise iron-limited region, and tipped the marine system towards sustained deoxygenation. We also identify older deoxygenation events linked to CIS retreat over the past approximately 50,000 years (ref. 4). Our findings suggest that the apparent coupling between the atmosphere, ocean, cryosphere and solid-Earth systems occurs on relatively short timescales and can act as an important driver for ocean biogeochemical change.

Our understanding of past ocean-climate dynamics is informed by multiple paleocirculation proxies including δ13C, 231Pa/230Th, and radiogenic neodymium isotopes (εNd). Of these, the εNd signature of marine authigenic phases is of particular importance as it is considered a robust circulation proxy applicable across timescales, permitting circulation reconstructions during periods of rapid, climatically-induced biological or chemical change (e.g. productivity, pH). However, growing evidence of non-conservative behavior and a widespread sedimentary source (benthic flux via pore water) of Nd to the global ocean suggests that authigenic εNd records do not strictly record a water mass signature, highlighting the need to reconsider interpretations of the authigenic record. To examine the impact of a sedimentary influence on the authigenic record, here we compile paired authigenic and detrital neodymium records from every major ocean basin and from 80 Ma to present. We then focus on just the North Atlantic Ocean basin to examine if this relationship holds up regionally and how authigenic εNd changes relate to sediment composition changes from two scientific ocean drill cores spanning the past 25 ka. We present a new conceptual framework to guide our discussion that examines the coupling or decoupling of authigenic and detrital εNd in terms of the relative importance of each of the three major potential controls as defined in the existing literature (bottom water, pore water, sediments) on the authigenic record. Our compilation reveals a strong linear relationship between detrital εNd and authigenic εNd (correlation coefficient = 0.86, n = 871), demonstrating a widespread influence of lithogenically sourced neodymium on authigenic εNd. We find the same is true within the North Atlantic, with the authigenic records at both locations strongly influenced by the sediments and likely not recording bottom water neodymium values. Emerging evidence for a lithogenic or benthic flux influence on the budgets of a wide range of trace elements suggests that our interpretative framework will be broadly useful for understanding the behavior of trace elements and their isotopes at the sediment-water interface.

The role of nickel (Ni) in ocean biogeochemical cycles is both under-studied and controversial. Strong correlations between Ni and organic carbon in modern and ancient marine sediments suggest a prominent biogeochemical role over a substantial portion of Earth history. Addition of Ni to culturing and seawater incubation experiments produces strong responses in terms of cell growth, particularly of nitrogen-fixing organisms. But the implied limiting role for phytoplankton growth is inconsistent with observations in the real ocean, specifically that photic zone Ni concentrations never descend to the very low values that characterise other bioactive, and often bio-limiting, metals like iron. These two observations can be reconciled if a large portion of the total dissolved Ni present in open-ocean surface waters is not bio-available on short timescales. Here we present new Ni concentration and stable isotope data from the GEOVIDE transect in the North Atlantic. We interpret these new data in the light of the growing database for Ni stable isotopes in the modern ocean, with implications for the biogeochemical importance of Ni. In the new North Atlantic dataset, the lowest Ni concentrations (1.8-2.6 nmol/L) and highest δ60Ni (up to +1.67‰) are associated with low nitrate, south of the subarctic front (SAF). By contrast, stations at latitudes north of the SAF, with higher surface nitrate, show very subdued variation in Ni concentrations throughout the entire depth of the water column (3.6±0.3 nmol/L, mean and 2SD), and no variation in δ60Ni beyond the narrow global deep-ocean range (+1.33±0.13 ‰). These North Atlantic Ni isotope data also show relationships with nitrogen isotope effects, observed in the same samples, that are suggestive of a link between Ni utilisation, isotope fractionation and nitrogen fixation. The global dataset, including the new data presented here, reveals a biogeochemical divide with Ni isotope fractionation only occurring in low latitude surface waters. A simple observationally constrained three-dimensional model of Ni cycling suggests that the creation of this isotopically heavy, Ni-poor, end-member, together with the physical circulation and remineralisation at depth, can explain the global Ni-δ60Ni systematics. Taken together, these findings hint at Ni-N co-limitation in the modern ocean. We advocate for more extensive and detailed culturing/incubation studies of this neglected metal in order to elucidate its potentially crucial biogeochemical role.

Holocene and Pleistocene marine sediment records in the North Pacific record multiple dysoxic events proximal to continental margins and oxygen minimum zones (OMZs). High-resolution paleoenvironmental studies in the Gulf of Alaska (GoA) were previously restricted to the last ∼17,000 years, limiting our knowledge of oxygenation in the high latitude North Pacific. Here we develop a ∼54,000-year-long record of co-registered benthic foraminiferal assemblages and redox sensitive metal concentrations (Mo/Al and U/Al) at Site U1419 in the upper OMZ of GoA to reconstruct the history of OMZ extent and intensity at multi-centennial resolution. Using multivariate analyses of total benthic foraminiferal assemblages, we develop quantitative dissolved oxygen estimates that are robust to differences in the benthic foraminiferal size fraction analyzed, replicate modern oxygenation patterns in the GoA, and are cross-validated by redox sensitive metal concentrations. We identify dysoxic events in the early Holocene and in the Bølling-Allerød (B/A), consistent with previous studies, as well as two dysoxic events during MIS 3 that are comparable in severity to the B/A event and lower in oxygen than the modern GoA OMZ. We further record short-duration (\textless300 years) dysoxic events during glacial times similar to those recorded at more southern latitudes. Rates of oxygenation change can be abrupt with transitions exceeding 1 ml/L O2 in 100 years. Quantitative estimates of paleo-oxygenation, such as those possible with benthic foraminiferal assemblages, are important for forecasting future oxygenation changes in OMZs and their potential impacts on the marine ecosystems.

Deep-sea ecosystems are highly sensitive to changes in organic matter export and oxygenation driven by climate change. Here we document past ecological changes in benthic foraminiferal assemblages indicative of deglacial changes in deep-sea oxygenation and the character of organic matter fluxes from sedimentary records retrieved at intermediate (692 m) and abyssal (3667m) depths in the Gulf of Alaska. Constrained multivariate ordination combining faunal and geochemical data over the past \textasciitilde22,000 years distinguishes the impacts of pulsed productivity, which exports carbon to the abyss, from extreme dysoxia across the deglacial warming transition. At both depths, opportunistic species are more prevalent in interglacial conditions, reflecting higher pulsed organic matter export to the seafloor developed in response to warming and reduced sea-ice cover. Benthic foraminiferal species tolerant of low-oxygen conditions increased in abundance during the deglacial transition at both intermediate and abyssal depths. Authigenic trace metals reveal sulfidic sedimentary conditions indicative intermittent anoxia, but only at intermediate-depths. Benthic foraminiferal richness and evenness are also highest during this deglacial low-oxygen interval, likely due to high food availability. Last Glacial Maximum faunas were distinctly different at the two sites, consistent with a more stratified deep Pacific, but the faunas become more similar during Holocene time, suggesting destratification of the abyss during deglaciation. These ecosystem responses support that carbon fluxes increased during warm intervals in subpolar regions and underscores the importance of considering the effects of transient biological blooms on paleoceanographic interpretations and in model projections of future deep carbon export.

Calving cousins Walczak et al. report that increases in Pacific Ocean ventilation and periods of rapid production of icebergs from the Cordilleran Ice Sheet during the last glacial period preceded episodic iceberg discharges into the Atlantic Ocean (see the Perspective by Jaeger and Shevenell). Marine sediments from the Gulf of Alaska show that increases in vertical mixing of the ocean there correspond with intense iceberg calving from the ice sheet that covered much of high-latitude western North America and that these changes occurred before the analogous Heinrich events in the North Atlantic. Thus, these Pacific climate system reorganizations may have been an early part of a cascade of dynamic climate events with global repercussions. Science, this issue p. 716; see also p. 662 New radiocarbon and sedimentological results from the Gulf of Alaska document recurrent millennial-scale episodes of reorganized Pacific Ocean ventilation synchronous with rapid Cordilleran Ice Sheet discharge, indicating close coupling of ice-ocean dynamics spanning the past 42,000 years. Ventilation of the intermediate-depth North Pacific tracks strength of the Asian monsoon, supporting a role for moisture and heat transport from low latitudes in North Pacific paleoclimate. Changes in carbon-14 age of intermediate waters are in phase with peaks in Cordilleran ice-rafted debris delivery, and both consistently precede ice discharge events from the Laurentide Ice Sheet, known as Heinrich events. This timing precludes an Atlantic trigger for Cordilleran Ice Sheet retreat and instead implicates the Pacific as an early part of a cascade of dynamic climate events with global impact. Pacific iceberg discharge events preceded their Atlantic counterparts during the last glacial period. Pacific iceberg discharge events preceded their Atlantic counterparts during the last glacial period.

Columbia River megafloods occurred repeatedly during the last deglaciation, but the impacts of this fresh water on Pacific hydrography are largely unknown. To reconstruct changes in ocean circulation during this period, we used a numerical model to simulate the flow trajectory of Columbia River megafloods and compiled records of sea surface temperature, paleo-salinity, and deep-water radiocarbon from marine sediment cores in the Northeast Pacific. The North Pacific sea surface cooled and freshened during the early deglacial (19.0-16.5 ka) and Younger Dryas (12.9-11.7 ka) intervals, coincident with the appearance of subsurface water masses depleted in radiocarbon relative to the sea surface. We infer that Pacific meltwater fluxes contributed to net Northern Hemisphere cooling prior to North Atlantic Heinrich Events, and again during the Younger Dryas stadial. Abrupt warming in the Northeast Pacific similarly contributed to hemispheric warming during the Bølling and Holocene transitions. These findings underscore the importance of changes in North Pacific freshwater fluxes and circulation in deglacial climate events. Deglacial meltwater input to the North Pacific contributed to abrupt Northern Hemisphere climate events. Deglacial meltwater input to the North Pacific contributed to abrupt Northern Hemisphere climate events.

The Global Overturning Circulation is linked to climate change on glacial-interglacial and multi-millennial timescales. The understanding of past climate-circulation links remains hindered by apparent conflicts among proxy measures of circulation. Here we reconstruct circulation changes since the Last Glacial Maximum (LGM) based on a global synthesis of authigenic neodymium isotope records (εNd). We propose the bottom-up framework of interpreting seawater and authigenic εNd considering not only conservative watermass mixing, but also the preformed properties and the non-conservative behavior of εNd, both subject to sedimentary influences. We extract the major spatial-temporal modes of authigenic εNd using Principal Component Analysis, and make a first-order circulation reconstruction with budget-constrained box model simulations. We show that during the LGM, the source region of North Atlantic overturning shifted southward, which led to more radiogenic preformed εNd of glacial Northern Source Water (NSW). Considering this preformed effect, we infer that glacial deep Atlantic had a similar proportion of NSW as today, although the overall strength of glacial circulation appears reduced from both North Atlantic and Southern Ocean sources, which increased the relative importance of non-conservative behavior of εNd and may have facilitated accumulation of respired carbon in the deep ocean. During the deglaciation, we find that Southern Ocean overturning increased, which offset suppressed North Atlantic overturning and resulted in a net stronger global abyssal circulation. Faster global scale deglacial circulation reduced the relative importance of non-conservative effects, resulting in Atlantic-Pacific convergence of abyssal εNd signatures. Variations of Southern Ocean overturning likely drove a significant fraction of deglacial changes in atmospheric CO2 and oceanic heat budget.

The progress of science is tied to the standardization of measurements, instruments, and data. This is especially true in the Big Data age, where analyzing large data volumes critically hinges on the data being standardized. Accordingly, the lack of community-sanctioned data standards in paleoclimatology has largely precluded the benefits of Big Data advances in the field. Building upon recent efforts to standardize the format and terminology of paleoclimate data, this article describes the Paleoclimate Community reporTing Standard (PaCTS), a crowdsourced reporting standard for such data. PaCTS captures which information should be included when reporting paleoclimate data, with the goal of maximizing the reuse value of paleoclimate data sets, particularly for synthesis work and comparison to climate model simulations. Initiated by the LinkedEarth project, the process to elicit a reporting standard involved an international workshop in 2016, various forms of digital community engagement over the next few years, and grassroots working groups. Participants in this process identified important properties across paleoclimate archives, in addition to the reporting of uncertainties and chronologies; they also identified archive-specific properties and distinguished reporting standards for new versus legacy data sets. This work shows that at least 135 respondents overwhelmingly support a drastic increase in the amount of metadata accompanying paleoclimate data sets. Since such goals are at odds with present practices, we discuss a transparent path toward implementing or revising these recommendations in the near future, using both bottom-up and top-down approaches.

Enhanced overturning in the Pacific Ocean flushed carbon from the abyssal ocean to the atmosphere during the last deglaciation, according to authigenic neodymium isotope data.