For the first time we can track long-term changes. More heat is being transported into northerly waters, for instance.⁵ Currents are changing,⁶ with some slowing down or speeding up,⁷ and vast “gyres” shifting position.⁸ Ocean chemistry is also in flux: dangerous low-oxygen zones are growing.⁹ Researchers are now watching for evidence of tipping points,¹⁰,¹¹ such as a slowdown or collapse of the Atlantic Meridional Overturning Circulation (AMOC),¹² although timescales remain difficult to determine.

There is an urgent need for more data on the physical characteristics of the ocean, especially in the deep sea, which is constrained by gaps in our ability to gather data, whether using survey vessels, moored buoys, Argo floats or instruments tied to animals. If this situation can be improved by more scientific research as well as acquisition of data from commercial and military vessels (and through geochemical proxies that provide historical data, sometimes over million-year timescales), it may be possible (though this is still a subject of debate) to create a “digital twin” of the global ocean that is detailed enough to be useful in oceanographic prediction and intervention modelling.¹³

Technologies like eDNA and metagenomics are revealing unprecedented diversity in the “ocean genome”,¹⁴ aided by sampling programmes such as Tara Oceans.¹⁵ Bio-logging enables remote tracking of animal behaviour,¹⁶ while acoustic sensors are increasingly contributing to biodiversity assessments.¹⁷ Furthermore, machine learning can be used to make sense of vast datasets, for example characterising the functional traits of plankton.¹⁸ There remains a need for consistent identifiers across different kinds of biodiversity data so researchers can make links between databases.

The immense variety of microbial marine life¹⁹ is only now coming to light²⁰ — as are the complex ecosystems found in deep-sea water, as well as on and In the deep seabed.²¹,²²,²³,²⁴ As the climate warms, some species are moving to new areas, creating an urgent need to understand which ones are becoming invasive.²⁵ More broadly, there is a need for more tracking of biodiversity, both to establish baselines and to follow trends as climate change²⁶ and other human impacts mount up.²⁷ Although warming is slower in the deep ocean, research suggests that its biodiversity is no less exposed than that of surface waters because of free-drifting (pelagic) larval stages in many deep-ocean organism life cycles and because of most deep-sea organisms’ adaptation to cold and stable conditions. Indeed, projections indicate that, while mitigation could limit threats to surface biodiversity, deep-ocean biodiversity will face an unavoidable escalation in threat.²⁸ The ongoing threats to ocean biodiversity will limit the potential of marine genetic resource use.

For instance, in recent years ecologists have realised the critical importance of wetlands, mangroves, seagrass beds and coral reefs, often operating as a single unit which supports the recovery of entire ecosystems and their services,³¹ and even traps marine plastics.³² Similarly, the scale of ecosystem services provided by plankton continues to expand under examination.³³

Increasing exploration of the deep-sea water column and seafloor substrate — by submersibles, robotic vehicles and other methods — is revealing complex ecosystems unlike anything at the surface. Hydrothermal vents are emerging as major contributors to the overall marine ecosystem.³⁴ Researchers are finally able to explore the microbes living in oceanic crust,³⁵ revealing hidden ecosystems shaped by magmatism and water-rock interactions.³⁶ Some marine microbes perform metabolic processes such as degrading petrochemicals,³⁷ and genetic information from deep-sea microbes and from sponges has aided the development of antiviral drugs and rapid testing for COVID-19.³⁸ Marine genetic resources represent a large, and mostly untapped, source of potentially useful substances.³⁹ However, the open-water pelagic zone (including the dark ecosystem), the largest habitat on Earth, remains under-explored.

A key challenge is to determine the fluxes of carbon and other nutrients through marine ecosystems, enabling us to track the carbon budget of the oceans,⁴⁰ including the deep ocean,⁴¹ and the oceans’ ability to remove carbon from the atmosphere.⁴² Autonomous platforms can help monitor these biogeochemical processes.⁴³ Behaviours such as deep diving by large predators like sperm whales are crucial to these fluxes.⁴⁴

Available data on ecosystem function covers less than the past 25 years. Attention has mostly focused on a handful of charismatic groups, notably shallow-water corals, the decline of which is fairly well-documented.⁴⁵ Expanding this longitudinal tracking to other species, including in the deep sea, will be crucial for tracking ecosystem responses to climate-driven changes such as ice-shelf collapses.⁴⁶ It will also be key for planning how we use and conserve marine ecosystems.⁴⁷

⁴⁸ Climate change is deoxygenating, acidifying and warming the oceans, pollution such as fertiliser run-off from farms threatens many ecosystems, and overfishing is also destabilising many. There are emerging impacts, too, such as the nascent deep-sea mining industry⁴⁹ and initiatives to remove carbon dioxide to the ocean to mitigate climate change. These impacts intersect in numerous ways:⁵⁰,⁵¹ for instance, ocean biodiversity affecting climate.⁵² However, with effective knowledge-gathering and policy-making, it should be possible to minimise harms and create a sustainable future for the oceans.⁵³ AI may have roles to play here, for instance in modelling the impacts of interventions.⁵⁴

Better understanding of our impacts will come from improvements in monitoring, for instance by robotic surface vehicles,⁵⁵ and in expanding our observations to the remote deeps.⁵⁶ There is great potential for citizen scientists to contribute⁵⁷ both to ocean observations and to conservation.⁵⁸ New “blue” industries like marine aquaculture may have key roles both in our economies and in marine conservation.⁵⁹ Capacity-building and knowledge transfer will be crucial to understanding all parts of the ocean from the south to north and shallow to deep.

Managing the oceans is a major geopolitical challenge.⁶⁰ A key issue is to determine, by leveraging scientific expertise and co-design, which kinds of policy interventions will be the most beneficial and have the fewest unintended consequences. The UN BBNJ (biodiversity of areas beyond national jurisdiction) treaty,⁶¹ once ratified, will regulate the sustainable use of marine genetic resources, environmental-impact assessments and area‑based management tools such as marine protected areas in the ocean outside national boundaries.⁶² Successes in ocean diplomacy, such as with the adoption of the BBNJ treaty, will need to be built upon to assist future ocean-science and conservation efforts.⁶³ Conservationists are increasingly exploring radical ideas such as granting legal rights to nature.⁶⁴