The deep ocean below 200 m water depth is the least observed, but largest habitat on our planet by volume and area. Over 150 years of exploration has revealed that this dynamic system provides critical climate regulation, houses a wealth of energy, mineral, and biological resources, and represents a vast repository of biological diversity. A long history of deep-ocean exploration and observation led to the initial concept for the Deep-Ocean Observing Strategy (DOOS), under the auspices of the Global Ocean Observing System (GOOS). Here we discuss the scientific need for globally integrated deep-ocean observing, its status, and the key scientific questions and societal mandates driving observing requirements over the next decade. We consider the Essential Ocean Variables (EOVs) needed to address deep-ocean challenges within the physical, biogeochemical, and biological/ecosystem sciences according to the Framework for Ocean Observing (FOO), and map these onto scientific questions. Opportunities for new and expanded synergies among deep-ocean stakeholders are discussed, including academic-industry partnerships with the oil and gas, mining, cable and fishing industries, the ocean exploration and mapping community, and biodiversity conservation initiatives. Future deep-ocean observing will benefit from the greater integration across traditional disciplines and sectors, achieved through demonstration projects and facilitated reuse and repurposing of existing deep-sea data efforts. We highlight examples of existing and emerging deep-sea methods and technologies, noting key challenges associated with data volume, preservation, standardization, and accessibility. Emerging technologies relevant to deep-ocean sustainability and the blue economy include novel genomics approaches, imaging technologies, and ultra-deep hydrographic measurements. Capacity building will be necessary to integrate capabilities into programs and projects at a global scale. Progress can be facilitated by Open Science and Findable, Accessible, Interoperable, Reusable (FAIR) data principles and converge on agreed to data standards, practices, vocabularies, and registries. We envision expansion of the deep-ocean observing community to embrace the participation of academia, industry, NGOs, national governments, international governmental organizations, and the public at large in order to unlock critical knowledge contained in the deep ocean over coming decades, and to realize the mutual benefits of thoughtful deep-ocean observing for all elements of a sustainable ocean.
Deep-sea ecosystems and hydrothermal vents
The natural capital of the vast deep ocean is significant yet not well quantified. The ecosystem services provided by the deep sea provide a wide range of benefits to humanity. Proposed deep-sea economic activities such as fishing, deep-sea mining and bioprospecting therefore need to be assessed in this context. In addition to quantifying the economic benefits and costs of such activities on their own, their potential impact on the deep-sea natural capital also needs to be considered.
This article describes such a natural capital approach, identifies relevant ecosystem services and looks at how a range of proposed commercial activities could be assessed in this context. It suggests a methodology for such analysis and suggests an approach to a sustainable blue deep-sea economy that is consistent with environmental precaution. It will close with suggestions of how potential risks can best be handled.
The article aims to show that modern environmental economics based on natural capital can provide a useful framework for deciding future deep-sea efforts.
Climate and environmental conditions are determinant for coral distribution and their very existence. When changes in such conditions occur, their effects on distribution can be predicted through species distribution models, anticipating suitable habitats for the subsistence of species. Mussismilia harttii is one of the most endangered Brazilian endemic reef-building corals, and in increasing risk of extinction. Herein, species distribution models were used to determine the present and future potential habitats for M. harttii. Estimations were made through the maximum entropy approach, predicting suitable habitat losses and gains by the end of the 21st century. For this purpose, species records published in the last 20 years and current and future environmental variables were correlated. The best models were chosen according to the Akaike information criterion (AIC) and evaluated through the partial ROC (AUCratio), a new approach which uses independent occurrence data. Both approaches showed that the models performed satisfactorily in predicting potential habitat areas for the species. Future projections were made using the International Panel on Climate Change (IPCC) scenarios for 2100, with different levels of greenhouse gas emission. Representative Concentration Pathways (RCPs) were used to model the Future Potential Habitat (FPH) of M. harttii in two different scenarios: stabilization of emissions (RCP 4.5) and increase of emissions (RCP 8.5). According to the results, shallow waters to the south of the study area concentrate most of the current potential habitats for the species. However, in future scenarios, there was a loss of suitable areas in relation to the Current Potential Habitat (RCP 4.5 46% and RCP 8.5 59%), whereas there is a southward shift of the suitable areas. In all scenarios of FPH, the temperature was the variable with the greatest contribution to the models (> 35%), followed by the current velocity (> 33%) and bathymetry (>29%). In contrast, there is an increase of deep (50–75 m) suitable areas FPH scenarios, mainly in the southern portion of its distribution, at Abrolhos Bank (off Espirito Santo State). These deeper sites might serve as refugia for the species in global warming scenarios. Coral communities at such depths would be less susceptible to impacts of climate change on temperature and salinity. However, the deep sea is not free from human impacts and measures to protect deeper ecosystems should be prioritized in environmental policies for Brazilian marine conservation, especially the Abrolhos Bank, due to its importance for M. harttii.
The amphipod Hirondellea gigas inhabits the deepest regions of the oceans in extreme high-pressure conditions. However, the mechanisms by which this amphipod adapts to its high-pressure environment remain unknown. In this study, we investigated the elemental content of the exoskeleton of H. gigas specimens captured from the deepest points of the Mariana Trench. The H. gigas exoskeleton contained aluminum, as well as a major amount of calcium carbonate. Unlike other (accumulated) metals, aluminum was distributed on the surface of the exoskeleton. To investigate how H. gigas obtains aluminum, we conducted a metabolome analysis and found that gluconic acid/gluconolactone was capable of extracting metals from the sediment under the habitat conditions of H. gigas. The extracted aluminum ions are transformed into the gel state of aluminum hydroxide in alkaline seawater, and this gel covers the body to protect the amphipod. This aluminum gel is a good material for adaptation to such high-pressure environments.
Deepwater exploration has been developed for more than 40 years since 1975; generally, its exploration history can be divided into the beginning stage (1975–1984), the early stage (1985–1995) and the rapid development stage (1996-now). Currently, deepwater areas have become the hotspot of global oil and gas exploration, and they are also one of the most important fields of oil and gas increase in reserves and production all over the world. In 40 years, global deepwater oil and gas discoveries are mainly distributed along five deepwater basin groups which are characterized by “three vertical and two horizontal” groups: (1) In deepwater basins of the Atlantic Ocean, giant discoveries of oil are mainly concentrated in Brazil, West Africa and the Gulf of Mexico, and significant discoveries of natural gas are mainly on the west coast of Norway in the northern part of the Atlantic Ocean; (2) In deepwater basins of the East African continental margin, a group of giant gas fields has been found in the Rovuma Basin and Tanzania Basin; (3) In deepwater basins of the West Pacific Ocean, giant discoveries of oil and gas are mainly concentrated in the South China Sea and Southeast Asian waters; (4) The deepwater basins of the Neo-Tethys Region are rich in gas, and the most important gas discoveries are mainly distributed in the northwest shelf of Australia and the eastern Mediterranean; and (5) In deepwater basins around the Arctic Pole, major discoveries of oil and gas have been only found in deepwater areas of the Barents sea. Global deepwater oil resources are mainly concentrated in the middle and south sections of the Atlantic Ocean. Deepwater gas resources are relatively widely spread and mainly distributed in the northern part of Atlantic Ocean deepwater basins, the deepwater basins of East Africa, the deepwater basins of the Neo-Tethys region and the deepwater basins around the Arctic Pole. There will be six domains for future oil-gas exploration of global deepwater basins which are characterized by “two old and four new” domains; specifically, “two old” domains referring to the Atlantic offshore deepwater basins and offshore deepwater basins of the Neo-Tethys structural domain, where the exploration degree is relatively high, and the potential is still great. While the “four new” domains stand for pre-salt and ultra deepwater basin formations, offshore deepwater basins surrounding the North Pole area and West Pacific offshore deepwater basins and the new fields will be the main fields of deepwater oil and gas exploration in the future.
In just four decades, hundreds of hydrothermal vent fields have been discovered, widely distributed along tectonic plate boundaries on the ocean floor. Vent invertebrate biomass reaching up to tens of kilograms per square meter has attracted attention as a potential contributor to the organic carbon pool available in the resource-limited deep sea. But the rate of chemosynthetic production of organic carbon at deep-sea hydrothermal vents is highly variable and still poorly constrained. Despite the advent of molecular techniques and in situ sensing technologies, the factors that control the capacity of vent communities to exploit the available chemical energy resources remain largely unknown. Here, we review key drivers of hydrothermal ecosystem productivity, including (a) the diverse mechanisms governing energy transfer among biotic and abiotic processes; (b) the tight linkages among these processes; and (c) the nature and extent of spatial and temporal diversity within a variety of geological settings; and (d) the influence of these and other factors on the turnover of microbial primary producers, including those associated with megafauna. This review proposes a revised consideration of the pathways leading to the biological conversion of inorganic energy sources into biomass in different hydrothermal habitats on the seafloor. We propose a conceptual model that departs from the canonical conservative mixing-continuum paradigm by distinguishing low-temperature diffuse flows (LT-diffuse flows) derived from seawater and high-temperature fluids (HT-diffuse flow) derived from end-member fluids. We further discuss the potential for sustained organic matter production at vent-field scale, accounting for the natural instability of hydrothermal ecosystems, from the climax vent communities of exceptional productivity to the long-term lower-activity assemblages. The parameterization of such a model crucially needs assessment of in situ rates and of the largely unrecognized natural variability on relevant temporal scales. Beyond the diversity of hydrothermal settings, the depth range and water mass distribution over oceanic ridge crests, volcanic arcs and back-arc systems are expected to significantly influence biomass production rates. A particular challenge is to develop observing strategies that will account for the full range of environmental variables while attempting to derive global or regional estimates.
Difficulties in quantifying the value of an ecosystem have prompted efforts to emphasize how human well-being depends on the physical, chemical and biological properties of an ecosystem (i.e., ecosystem structure) as well as ecosystem functioning. Incorporating ecosystem structure and function into discussions of value is important for deep-sea ecosystems because many deep-sea ecosystem services indirectly benefit humans and are more difficult to quantify. This study uses an ecosystem principles approach to illustrate a broader definition of value for deep-sea hydrothermal vents. Expert opinion, solicited using an iterative survey approach, was used to develop principles that describe hydrothermal vent processes and their links to human well-being. Survey participants established 28 principles relating to ecosystem structure (n = 12), function (n = 6), cultural services (n = 8) and provisioning services (n = 2), namely the provision of mineral deposits and genetic resources. Principles relating to cultural services emphasized the inspirational value of hydrothermal vents for the arts and ocean education, as well as their importance as a frontier in scientific research. The prevalence of principles relating to ecosystem structure and function (n = 18) highlights the need to understand subsequent links to ecosystem services. For example, principles relating to regulating services were not established by the expert group but links between ecosystem function and regulating services can be made. The ecosystem principles presented here emphasize a more holistic concept of value that will be important to consider as regulations are developed for the exploitation of minerals associated with deep-sea hydrothermal vents.
The offshore and deep-sea marine environment provides many ecosystem services (i.e., benefits to humans), for example: climate regulation, exploitable resources, processes that enable life on Earth, and waste removal. Unfortunately, the remote nature of this environment makes it difficult to estimate the values of these services. One service in particular, waste removal, was examined in the context of the Deepwater Horizon oil spill. Nearly 5 million barrels of oil were released into the offshore Gulf of Mexico, and 14 billion dollars were spent removing about 25% of the oil spilled. Using values for oil spill cleanup efforts, which included capping the wellhead and collecting oil, surface combustion, and surface skimming, it was calculated that waste removal, i.e., natural removal of spilled oil, saved BP over $35 billion. This large amount demonstrates the costs of offshore disasters, the importance of the offshore environment to humans, as well as the large monetary values associated with ecosystem services provided.
Resolutions of the United Nations General Assembly (UNGA) require states and competent authorities to protect vulnerable marine ecosystems (VMEs), ecologically important habitats in the deep sea that are considered to be especially at risk from anthropogenic disturbances such as fishing. The lack of data concerning the location and extent of VMEs poses a significant obstacle to their protection. Habitat suitability modeling is increasingly used in spatial management planning due to its ability to predict the distribution and niche of marine organisms based on limited input data. We generated broad-scale, medium-resolution (1 km2) ensemble models for ten VME indicator taxa within the New Zealand Exclusive Economic Zone and a portion of the South Pacific Regional Fishery Management Organisation (SPRFMO) convention area. Ensemble models were constructed using a weighted average of three habitat suitability model types: Boosted Regression Trees, Maximum Entropy, and Random Forest. All models performed well, with area under the curve scores above 0.9, and ensemble models marginally outperformed any of the individual modeling approaches. Highly suitable habitat for each VME indicator taxa was predicted to occur in relatively small areas throughout the region, typically associated with elevated seafloor features with steep slopes. Determining the spatial distribution of VME indicator taxa is critical for assessing the current and historical extent of bottom trawling impacts on benthic communities, and for supporting the improved spatial management of fisheries in the South Pacific Ocean. Given the additional threats of climate change and ocean acidification to VME indicator taxa throughout the deep sea, habitat suitability modeling is likely to play an increasing role in designing effective, long-term protection measures for cumulative impacts on VMEs.
Pollution of the marine environment by large and microscopic plastic fragments and their potential impacts on organisms has stimulated considerable research interest and has received widespread publicity. However, relatively little attention has been paid to the fate and effects of microplastic particles that are fibrous in shape, also referred as microfibres, which are mostly shed from synthetic textiles during production or washing. Here we assess composition and abundance of microfibres in seafloor sediments in southern European seas, filling gaps in the limited understanding of the long-range transport and magnitude of this type of microplastic pollution. We report abundances of 10–70 microfibres in 50 ml of sediment, including both natural and regenerated cellulose, and synthetic plastic (polyester, acrylic, polyamide, polyethylene, and polypropylene) fibres. Following a shelf-slope-deep basin continuum approach, based on the relative abundance of fibres it would appear that coastal seas retain around 33% of the sea floor microfibres, but greater quantities of the fibres are exported to the open sea, where they accumulate in sediments. Submarine canyons act as preferential conduits for downslope transport of microfibres, with 29% of the seafloor microfibres compared to 18% found on the open slope. Around 20% of the microfibres found had accumulated in the deep open sea beyond 2000m of water depth. The remoteness of the deep sea does not prevent the accumulation of microfibres, being available to become integrated into deep sea organisms.