Oxygen is fundamental to life. Not only is it essential for the survival of individual animals, but it regulates global cycles of major nutrients and carbon. The oxygen content of the open ocean and coastal waters has been declining for at least the past half-century, largely because of human activities that have increased global temperatures and nutrients discharged to coastal waters. These changes have accelerated consumption of oxygen by microbial respiration, reduced solubility of oxygen in water, and reduced the rate of oxygen resupply from the atmosphere to the ocean interior, with a wide range of biological and ecological consequences. Further research is needed to understand and predict long-term, global- and regional-scale oxygen changes and their effects on marine and estuarine fisheries and ecosystems.

The deep sea encompasses the largest ecosystems on Earth. Although poorly known, deep seafloor ecosystems provide services that are vitally important to the entire ocean and biosphere. Rising atmospheric greenhouse gases are bringing about significant changes in the environmental properties of the ocean realm in terms of water column oxygenation, temperature, pH and food supply, with concomitant impacts on deep-sea ecosystems. Projections suggest that abyssal (3000-6000 m) ocean temperatures could increase by 1°C over the next 84 years, while abyssal seafloor habitats under areas of deep-water formation may experience reductions in water column oxygen concentrations by as much as 0.03 mL L -1 by 2100. Bathyal depths (200-3000 m) worldwide will undergo the most significant reductions in pH in all oceans by the year 2100 (0.29 to 0.37 pH units). O 2 concentrations will also decline in the bathyal NE Pacific and Southern Oceans, with losses up to 3.7% or more, especially at intermediate depths. Another important environmental parameter, the flux of particulate organic matter to the seafloor, is likely to decline significantly in most oceans, most notably in the abyssal and bathyal Indian Ocean where it is predicted to decrease by 40-55% by the end of the century. Unfortunately, how these major changes will affect deep-seafloor ecosystems is, in some cases, very poorly understood. In this paper, we provide a detailed overview of the impacts of these changing environmental parameters on deep-seafloor ecosystems that will most likely be seen by 2100 in continental margin, abyssal and polar settings. We also consider how these changes may combine with other anthropogenic stressors (e.g., fishing, mineral mining, oil and gas extraction) to further impact deep-seafloor ecosystems and discuss the possible societal implications.

Mora and colleagues show that ongoing greenhouse gas emissions are likely to have a considerable effect on several biogeochemical properties of the world's oceans, with potentially serious consequences for biodiversity and human welfare.

We develop a novel class of measures to quantify sample completeness of a biological survey. The class of measures is parameterized by an order q ≥ 0 to control for sensitivity to species relative abundances. When q = 0, species abundances are disregarded and our measure reduces to the conventional measure of completeness, that is, the ratio of the observed species richness to the true richness (observed plus undetected). When q = 1, our measure reduces to the sample coverage (the proportion of the total number of individuals in the entire assemblage that belongs to detected species), a concept developed by Alan Turing in his cryptographic analysis. The sample completeness of a general order q ≥ 0 extends Turing's sample coverage and quantifies the proportion of the assemblage's individuals belonging to detected species, with each individual being proportionally weighted by the (q − 1)th power of its abundance. We propose the use of a continuous profile depicting our proposed measures with respect to q ≥ 0 to characterize the sample completeness of a survey. An analytic estimator of the diversity profile and its sampling uncertainty based on a bootstrap method are derived and tested by simulations. To compare diversity across multiple assemblages, we propose an integrated approach based on the framework of Hill numbers to assess (a) the sample completeness profile, (b) asymptotic diversity estimates to infer true diversities of entire assemblages, (c) non‐asymptotic standardization via rarefaction and extrapolation, and (d) an evenness profile. Our framework can be extended to incidence data. Empirical data sets from several research fields are used for illustration.

The deep sea (>200 m depth) encompasses >95% of the world's ocean volume and represents the largest and least explored biome on Earth (<0.0001% of its surface). It also provides critical climate regulation and other ecosystem services. New species and ecosystems are continuously being discovered in the deep oceans, but commercial fisheries, deep-sea mining, and offshore oil and gas extractions, along with pollution and global change effects, threaten this vast under-explored frontier region. The future of both benthic and pelagic deep-sea ecosystems depends upon effective ecosystembased management strategies enhancing deep-sea conservation, yet we lack consensus on monitoring of the biological and ecological variables that reflect ecosystem status and are needed to support management and environmental decisions at a global scale. Here, we present and discuss the results of an Expert Elicitation of more than 110 deep-sea scientists to prioritize variables and parameters for the future of deep-sea monitoring. We identified five main scientific pillars that need to be further investigated for deep-ocean conservation: i) species and habitat biodiversity, ii) ecosystem function; iii) ecosystem health, impacts, and risk assessment; iv) climate change impacts, the adaptation and evolution of deep-sea life, and v) deep-sea ecosystem conservation. As observing and monitoring can provide the necessary scientific framework for scientists and policy makers to implement effective deep-sea conservation strategies at a global scale, the proposed variables should be further studied in the context of available sensor and other advanced technologies, which are becoming increasingly available.

Temperature is considered to be a fundamental factor controlling biodiversity in marine ecosystems, but precisely what role temperature plays in modulating diversity is still not clear. The deep ocean, lacking light and in situ photosynthetic primary production, is an ideal model system to test the effects of temperature changes on biodiversity. Here we synthesize current knowledge on temperature-diversity relationships in the deep sea. Our results from both present and past deep-sea assemblages suggest that, when a wide range of deep-sea bottom-water temperatures is considered, a unimodal relationship exists between temperature and diversity (that may be right skewed). It is possible that temperature is important only when at relatively high and low levels but does not play a major role in the intermediate temperature range. Possible mechanisms explaining the temperature-biodiversity relationship include the physiological-tolerance hypothesis, the metabolic hypothesis, island biogeography theory, or some combination of these. The possible unimodal relationship discussed here may allow us to identify tipping points at which on-going global change and deep-water warming may increase or decrease deep-sea biodiversity. Predicted changes in deep-sea temperatures due to human-induced climate change may have more adverse consequences than expected considering the sensitivity of deep-sea ecosystems to temperature changes.

High tropical and low polar biodiversity is one of the most fundamental patterns characterising marine ecosystems, and the influence of temperature on such marine latitudinal diversity gradients is increasingly well documented. However, the temporal stability of quantitative relationships among diversity, latitude and temperature is largely unknown. Herein we document marine zooplankton species diversity patterns at four time slices [modern, Last Glacial Maximum (18 000 years ago), last interglacial (120 000 years ago), and Pliocene (~3.3-3.0 million years ago)] and show that, although the diversity-latitude relationship has been dynamic, diversity-temperature relationships are remarkably constant over the past three million years. These results suggest that species diversity is rapidly reorganised as species' ranges respond to temperature change on ecological time scales, and that the ecological impact of future human-induced temperature change may be partly predictable from fossil and paleoclimatological records.

A benthic microfaunal record from the equatorial Atlantic Ocean over the past four glacial-interglacial cycles was investigated to understand temporal dynamics of deep-sea latitudinal species diversity gradients (LSDGs). The results demonstrate unexpected instability and high amplitude fluctuations of species diversity in the tropical deep ocean that are correlated with orbital-scale oscillations in global climate: Species diversity is low during glacial and high during interglacial periods. This implies that climate severely influences deep-sea diversity, even at tropical latitudes, and that deep-sea LSDGs, while generally present for the last 36 million years, were weakened or absent during glacial periods. Temporally dynamic LSDGs and unstable tropical diversity require reconsideration of current ecological hypotheses about the generation and maintenance of biodiversity as they apply to the deep sea, and underscore the potential vulnerability and conservation importance of tropical deep-sea ecosystems.deep-sea Ostracoda ͉ global climate change ͉ latitudinal species diversity gradients ͉ macroecology ͉ Quaternary paleoceanography L atitudinal species diversity gradients (LSDGs), the patterns in which tropical regions contain more species than high latitudes, are one of the most basic ecological patterns on the earth (1). In the modern ocean, deep-sea bivalves, gastropods, isopods, cumaceans, and foraminifera all show strong LSDGs (2-6), and studies of benthic foraminifera assemblages indicate that the deep-sea gradients were established Ϸ36 million years ago (7). The environmental stability hypothesis holds that stability in tropical (1,8), and deep-sea (9, 10) environments might enhance species diversity, but there is now evidence for highly fluctuating high-latitude deep-sea diversity during Quaternary climatic cycles (11)(12)(13)(14)(15)(16). Surprisingly little attention has been given to understanding low-latitude deepsea diversity and the temporal dynamics of the LSDGs. Although pollen records suggest a persistent latitudinal diversity gradient existed in terrestrial ecosystems over the last 13,000 years (17, 18), we know of no studies of species-level temporal dynamics of LSDGs based on fossil assemblages from marine environments, despite the sensitivity of marine ecosystems to climatic change (12,13,(19)(20)(21)(22)(23)(24).The Ostracoda (Crustacea) are an important component of the deep-sea benthos (25)(26)(27), and the only commonly fossilized metazoan group in deep-sea sediments (12,13,28). Their various habitats and ecological preferences represent a wide range of deep-sea benthic niches, and their fossil record is considered representative of the benthic community (12,13,28). Furthermore, large (Ϸ130 m) glacial-interglacial sea-level changes (29), which drastically altered shallow-marine environments, had negligible effects on deep-sea habitats (e.g., Ͼ1,000 m water depth). Here, we examine low-latitude Quaternary records of deep-sea ostracods and temporal changes in LSDGs in the North Atlantic Oc...