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We have measured Cd/Ca ratios of several benthic foraminiferal species and studied benthic foraminiferal assemblages on two cores from the northern Indian Ocean (Arabian Sea and northern Bay of Bengal, BoB), in order to reconstruct variations in intermediate-water circulation and paleo-nutrient content since the last deglaciation. Intermediate water Cdw records estimated from the benthic Cd/Ca reflect past changes in surface productivity and/or intermediate–bottom-water ventilation. The benthic foraminiferal assemblages are consistent with the geochemical data. These results suggest that during the last deglaciation, Cdw variability was primarily driven by changes in intermediate-water properties, indicating an enhanced ventilation of intermediate–bottom water masses during both Heinrich Stadial 1 and the Younger Dryas (HS1 and YD, respectively). During the Holocene, however, surface primary productivity appears to have influenced Cdw more than intermediate water mass properties. This is evident during the early Holocene (from 10 to 6 cal ka) when benthic foraminiferal assemblages indicate that surface primary productivity was low, resulting in low intermediate-water Cdw at both sites. Then, from ∼ 5.2 to 2.4 cal ka, surface productivity increased markedly, causing a significant increase in the intermediate-water Cdw in the southeastern Arabian Sea and the northeastern BoB. The comparison of intermediate-water Cdw records with previous reconstructions of past Indian monsoon evolution during the Holocene suggests a direct control of intermediate-water Cdw by monsoon-induced changes in upper-water stratification and surface primary productivity.

We present a global atlas of downcore foraminiferal oxygen and carbon isotope ratios available at https://doi.pangaea.de/10.1594/PANGAEA.936747 (Mulitza et al., 2021). The database contains 2,108 published and previously unpublished stable isotope downcore records with 362,067 stable isotope values of various planktonic and benthic species of foraminifera from 1,265 sediment cores. Age constraints are provided by 6,153 uncalibrated radiocarbon ages from 598 (47 %) of the cores. Each stable isotope and radiocarbon series is provided in a separate netCDF file containing fundamental meta data as attributes. The data set can be managed and explored with the free software tool PaleoDataView. The atlas will provide important data for paleoceanographic analyses and compilations, site surveys, or for teaching marine stratigraphy. The database can be updated with new records as they are generated, providing a live ongoing resource into the future.

The Fezouata Shale in Morocco is the most diverse Lower Ordovician unit yielding soft-tissue preservation. Iron played a crucial role in the preservation of soft parts in this formation through the damage of bacterial membranes under oxic conditions and the pyritization of soft parts under the activity of bacterial sulphate reduction. However, the origin of Fe in this formation remains largely speculative. Herein, trace and rare earth elements were investigated in drilled-core sediments from the Fezouata Shale. It is shown that a correlation exists between Fe and Al suggesting that most Fe has a detrital source. Elemental concentrations in the Fezouata Shale are most comparable to rivers and are the least similar to loess and sediments deposited near active island arcs. In this sense, continental weathering and its related Fe in river fluxes dictated occurrences of exceptional fossil preservation in the Fezouata Shale.

Abstract. Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (EFOS) are based on energy statistics and cement production data, while emissions from land-use change (ELUC), mainly deforestation, are based on land-use and land-use change data and bookkeeping models. Atmospheric CO2 concentration is measured directly, and its growth rate (GATM) is computed from the annual changes in concentration. The ocean CO2 sink (SOCEAN) is estimated with global ocean biogeochemistry models and observation-based data-products. The terrestrial CO2 sink (SLAND) is estimated with dynamic global vegetation models. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ. For the first time, an approach is shown to reconcile the difference in our ELUC estimate with the one from national greenhouse gases inventories, supporting the assessment of collective countries’ climate progress. For the year 2020, EFOS declined by 5.4 % relative to 2019, with fossil emissions at 9.5 ± 0.5 GtC yr−1 (9.3 ± 0.5 GtC yr−1 when the cement carbonation sink is included), ELUC was 0.9 ± 0.7 GtC yr−1, for a total anthropogenic CO2 emission of 10.2 ± 0.8 GtC yr−1 (37.4 ± 2.9 GtCO2). Also, for 2020, GATM was 5.0 ± 0.2 GtC yr−1 (2.4 ± 0.1 ppm yr−1), SOCEAN was 3.0 ± 0.4 GtC yr−1 and SLAND was 2.9 ± 1 GtC yr−1, with a BIM of −0.8 GtC yr−1. The global atmospheric CO2 concentration averaged over 2020 reached 412.45 ± 0.1 ppm. Preliminary data for 2021, suggest a rebound in EFOS relative to 2020 of +4.9 % (4.1 % to 5.7 %) globally. Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959–2020, but discrepancies of up to 1 GtC yr−1 persist for the representation of annual to semi-decadal variability in CO2 fluxes. Comparison of estimates from multiple approaches and observations shows: (1) a persistent large uncertainty in the estimate of land-use changes emissions, (2) a low agreement between the different methods on the magnitude of the land CO2 flux in the northern extra- tropics, and (3) a discrepancy between the different methods on the strength of the ocean sink over the last decade. This living data update documents changes in the methods and data sets used in this new global carbon budget and the progress in understanding of the global carbon cycle compared with previous publications of this data set (Friedlingstein et al., 2020; Friedlingstein et al., 2019; Le Quéré et al., 2018b, 2018a, 2016, 2015b, 2015a, 2014, 2013). The data presented in this work are available at https://doi.org/10.18160/gcp-2021 (Friedlingstein et al., 2021).

Coral reefs host exceptionally diverse and abundant marine life. Connecting coasts and sheltered lagoons to the open ocean, reef passages are important yet poorly studied components of these ecosystems. Abiotic and biotic elements ‘pass’ through these reef passages, supporting critical ecological processes (e.g. fish spawning). Reef passages provide multiple social and ecological benefits for islands and their peoples, but are so far neither characterized nor recognized for their multifaceted significance. This study investigated 113 reef passages across nine Pacific islands (Fiji, New Caledonia, Vanuatu). GIS-based visual interpretations of satellite imagery were used to develop criteria to define three distinct types, mainly based on distance to coastline and presence/absence of an enclosed water body. The discussion identifies ways to refine and augment this preliminary typology as part of a research agenda for reef passages. With these next steps, this typology will be extendable to other regions to better document reef passages and their various roles, supporting biodiversity conservation and sustainable fisheries management.

Nutrients limiting phytoplankton growth in the ocean are a critical control on ocean productivity and can underpin predicted responses to climate change. The extensive western subtropical North Pacific is assumed to be under strong nitrogen limitation, but this is not well supported by experimental evidence. Here, we report the results of 14 factorial nitrogen–phosphorus–iron addition experiments through the Philippine Sea, which demonstrate a gradient from nitrogen limitation in the north to nitrogen–iron co‐limitation in the south. While nitrogen limited sites responded weakly to nutrient supply, co‐limited sites bloomed with up to ~60‐fold increases in chlorophyll a biomass that was dominated by initially undetectable diatoms. The transition in limiting nutrients and phytoplankton growth capacity was driven by a gradient in deep water nutrient supply, which was undetectable in surface concentration fields. We hypothesize that this large‐scale phytoplankton response gradient is both climate sensitive and potentially important for regulating the distribution of predatory fish. National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809

Predicted intensified climate warming will likely alter the ecosystem net carbon (C) uptake of the Qinghai–Tibetan Plateau (QTP). Variations in C sink–source responses to climate warming have been linked to water availability; however, the mechanisms by which net C uptake responds to soil water content in saturated swamp meadow ecosystems remain unclear. To explore how soil moisture and other environmental drivers modulate net C uptake in the QTP, field measurements were conducted using the eddy covariance technique in 2014, 2015, 2017, and 2018. The alpine swamp meadow presented in this study was a persistent and strong C sink of CO2 (−168.0 ± 62.5 g C m−2 yr−1, average ± standard deviation) across the entire 4-year study period. A random forest machine-learning analysis suggested that the diurnal and seasonal variations of net ecosystem exchange (NEE) and gross primary productivity (GPP) were regulated by temperature and net radiation. Ecosystem respiration (Re), however, was found mainly regulated by the variability of soil water content (SWC) at different temporal aggregations, followed by temperature, the second contributing driver. We further explored how Re is controlled by nearly saturated soil moisture and temperature comparing two different periods featuring almost identical temperatures and significant differences on SWC and vice versa. Our data suggest that, despite the relatively abundant water supply, periods with a substantial decrease in SWC or increase in temperature produced higher Re and therefore weakened the C sink strength. Our results reveal that nearly saturated soil conditions during the growing seasons can help maintain lower ecosystem respiration rates and thus enhance the overall C sequestration capacity in this alpine swamp meadow. We argue that soil respiration and subsequent ecosystem C sink magnitude in alpine swamp meadows could likely be affected by future changes in soil hydrological conditions caused by permafrost degradation or accelerated thawing–freezing cycling due to climate warming.

In marine sediments, the Sr content and isotope composition (87Sr/86Sr) of the terrigenous detrital component are widely used to track changes in provenance and related transport and weathering processes. Accurately separating detrital-Sr from other sedimentary Sr-phases is a prerequisite for such studies. Conventionally, it is assumed that Sr in the carbonate-free residue corresponds to detrital Sr alone. However, the decarbonated residue may contain barite with significant Sr content and a non-detrital 87Sr/86Sr composition; this may substantially affect the measured Sr signal. To examine this chronically overlooked phenomenon, the Mediterranean Sea is an ideal area because 1) detailed provenance studies have been done using Sr and 87Sr/86Sr of the residual fraction, and 2) enhanced levels of barite repeatedly occurred in association with distinct, organic-rich sapropel sediments. Here, we use the most-recent sapropel S1 interval to evaluate the effect of barite-bound Sr in the residual fraction after decarbonation. A total of 130 samples were taken from 10 cores in the eastern Mediterranean Sea (EMS) and 1 core in the western Mediterranean Sea. This selection represents a geographic and bathymetric coverage of the EMS and permits the basin-wide comparison between organic-rich and -lean sediments. After decarbonation using 1 M HCl solution, the residual sediments were subject to NH4Cl extraction (2 M, pH 7), known to selectively dissolve barite. Our results demonstrate the presence of Sr-bearing barite after traditional carbonate removal and its effect on the derived “detrital” Sr signature. This barite-Sr effect is considerable for samples with barite-Ba >400 μg/g in bulk sediment. The impact of barite is prominent if accompanied by a detrital provenance background of high 87Sr/86Sr (>0.713) or low Sr/Al (<1.0 mg/g). In such cases, removal of remaining barite is required to obtain an unbiased detrital Sr signal. We recommend an improved procedure for detrital Sr separation in marine sediments, with an additional NH4Cl leaching step to eliminate any remaining barite after decarbonation. This approach is particularly important for areas/times of high biological productivity, where sediments are often characterized by abundant barite content.

The COVID-19 global pandemic has had severe, unpredictable and synchronous impacts on all levels of perishable food supply chains (PFSC), across multiple sectors and spatial scales. Aquaculture plays a vital and rapidly expanding role in food security, in some cases overtaking wild caught fisheries in the production of high-quality animal protein in this PFSC. We performed a rapid global assessment to evaluate the effects of the COVID-19 pandemic and related emerging control measures on the aquaculture supply chain. Socio-economic effects of the pandemic were analysed by surveying the perceptions of stakeholders, who were asked to describe potential supply-side disruption, vulnerabilities and resilience patterns along the production pipeline with four main supply chain components: a) hatchery, b) production/processing, c) distribution/logistics and d) market. We also assessed different farming strategies, comparing land- vs. sea-based systems; extensive vs. intensive methods; and with and without integrated multi-trophic aquaculture, IMTA. In addition to evaluating levels and sources of economic distress, interviewees were asked to identify mitigation solutions adopted at local / internal (i.e., farm-site) scales, and to express their preference on national / external scale mitigation measures among a set of a priori options. Survey responses identified the potential causes of disruption, ripple effects, sources of food insecurity, and socio-economic conflicts. They also pointed to various levels of mitigation strategies. The collated evidence represents a first baseline useful to address future disaster-driven responses, to reinforce the resilience of the sector and to facilitate the design reconstruction plans and mitigation measures, such as financial aid strategies M.C.M.'s research activity was supported by the European Union's Horizon 2020 Research and Innovation programme under the Marie Skłodowska-Curie Action (Grant agreement no. 835589, MIRROR Project). People at the Laboratory of Ecology have been funded by the PRIN-MAHRES project (Ministry of Italian Research; MUR - 017MHHWBN_003 Linea C) and by the Interreg Italia-Malta HARMONY 2016 (Grant C1-3.1-31). C. Pita and A. Nogueira would like to thank FCT/MCTES for the financial support to CESAM (UIDP/50017/2020+UIDB/50017/2020), through national funds. J.M.F. Babarro thanks project PID2019-106008RB-C21 for support through Spanish Government funds. The authors would like to thank also the ERASMUS+-FISHAQU project (No. 610071-EPP-1-2019-1-PT-EPPKA2-CBHE-JP) 13 pages, 3 tables, 5 figures Peer reviewed

Few fishes have evolved elevated body temperatures compared with ambient temperatures, and only in opah (Lampris spp) is the entire body affected. To understand the molecular basis of endothermy, we analyzed the opah genome and identified 23 genes with convergent amino acid substitutions across fish, birds, and mammals, including slc8b1, which encodes the mitochondrial Na+/Ca2+ exchanger and is essential for heart function and metabolic heat production. Among endothermic fishes, 44 convergent genes with suggestive metabolic functions were identified, such as glrx3, encoding a crucial protein for hemoglobin maturation. Numerous genes involved in the production and retention of metabolic heat were also found to be under positive selection. Analyses of opah's unique inner-heat-producing pectoral muscle layer (PMI), an evolutionary key innovation, revealed that many proteins were co-opted from dorsal swimming muscles for thermogenesis and oxidative phosphorylation. Thus, the opah genome provides valuable resources and opportunities to uncover the genetic basis of thermal adaptations in fish. Public summary • Endothermy has evolved multiple times in fishes (teleosts and chondrichthyans) • Opah genome explaining genetic changes in heat production and the sensory and immune system • Convergent evolution of genes in endothermic vertebrate lineages was investigated • Analyses of the pectoral muscle of opah revealed numerous highly expressed genes for thermogenesis Graphical abstract