Annual Review of Marine Science - Early Publication

Ocean metabolism constitutes a complex, multiscale ensemble of biochemical reaction networks harbored within and between the boundaries of a myriad of organisms. Gaining a quantitative understanding of how these networks operate requires mathematical tools capable of solving in silico the resource allocation problem each cell faces in real life. Toward this goal, stoichiometric modeling of metabolism, such as flux balance analysis, has emerged as a powerful computational tool for unraveling the intricacies of metabolic processes in microbes, microbial communities, and multicellular organisms. Here, we provide an overview of this approach and its applications, future prospects, and practical considerations in the context of marine sciences. We explore how flux balance analysis has been employed to study marine organisms, help elucidate nutrient cycling, and predict metabolic capabilities within diverse marine environments, and highlight future prospects for this field in advancing our knowledge of marine ecosystems and their sustainability.

Across the natural sciences, humans are typically conceptualized as external disruptors of nature rather than adaptable components of it. Historical evidence, however, challenges this dominant schema. Here, we describe the broad repertoire of ecological functions performed by people in place-based societies across the Pacific Ocean over millennia, illustrating their roles as ecosystem engineers, dispersers, bioturbators, nutrient cyclers, predators, and herbivores. By considering the reciprocal relationships between people and the ecosystems within which they are embedded, evidence of humanity's ability to experiment, learn, adapt, innovate, and sustain diverse and resilient social–ecological relationships emerges. Therefore, recognizing people as inseparable components of marine ecosystems and their millennia of engagement with coastal ocean spaces is critical to both understanding marine ecosystems and devising resilient and equitable ocean policies.

The present-day state and future of the Antarctic Ice Sheet depend on the rate at which the ocean melts its fringing ice shelves. Ocean heat must cross many physical and dynamical barriers to melt ice shelves, with the last of these being the ice–ocean boundary layer. This review summarizes the current understanding of ice–ocean boundary-layer dynamics, focusing on recent progress from laboratory experiments, turbulence-resolving numerical simulations, novel observations, and the application to large-scale simulations. The complex interplay between buoyant meltwater and external processes such as current shear leads to the emergence of several melting regimes that we describe, as well as freezing processes. The remaining challenges include developing new parameterizations for large-scale ice–ocean models based on recent advances and understanding the coevolution of melt and basal topography.

Advancements in space-based ocean observation and computational data processing techniques have demonstrated transformative value for managing living resources, biodiversity, and ecosystems of the ocean. We synthesize advancements in leveraging satellite-derived insights to better understand and manage fishing, an emerging revolution of marine industrialization, ocean hazards, sea surface dynamics, benthic ecosystems, wildlife via electronic tracking, and direct observations of ocean megafauna. We consider how diverse space-based data sources can be better coupled to modernize and improve ocean management. We also highlight examples of how data from space can be developed into tools that can aid marine decision-makers managing subjects from whales to algae. Thoughtful and prospective engagement with such technologies from those inside and outside the marine remote sensing community is, however, essential to ensure that these tools meet their full potential to strengthen the effectiveness of ocean management.

According to some authors, the Messinian salinity crisis was ended by a giant waterfall or megaflood 5.33 million years ago, when the Atlantic Ocean reconnected in a catastrophic way with the desiccated Mediterranean, creating the Strait of Gibraltar. An erosional surface deeply cutting upper Miocene or older rocks and sealed by lower Pliocene sediments is the geological feature that inspired this fascinating hypothesis. The hypothesis, which recalls several ancient myths, is well established in the scientific community and often considered to be a fact. However, several studies are suggesting that the Atlantic–Mediterranean connection through the Strait of Gibraltar was probably active before and during the entire Messinian salinity crisis. This allows us to consider the possibility that long-lived, more gradual physical processes were responsible for the evolution of the strait, opening the idea of a nondesiccated Mediterranean Sea.

In recent years, our view of coastal ecosystems has expanded and come into greater focus. We are currently making more types of observations over larger areas and at higher frequencies than ever before. These advances are timely, as coastal ecosystems are facing increasing pressures from climate change and anthropogenic stressors. This article synthesizes recent literature on emerging technologies for coastal ecosystem monitoring, including satellite monitoring, aerial and underwater drones, in situ sensor networks, fiber optic systems, and community science observatories. We also describe how advances in artificial intelligence and deep learning underpin all these technologies by enabling insights to be drawn from increasingly large data volumes. Even with these recent advances, there are still major gaps in coastal ecosystem monitoring that must be addressed to manage coastal ecosystems during a period of accelerating global change.

Oyster reef loss represents one of the most dramatic declines of a foundation species worldwide. Oysters provide valuable ecosystem services (ES), including habitat provisioning, water filtration, and shoreline protection. Since the 1990s, a global community of science and practice has organized around oyster restoration with the goal of restoring these valuable services. We highlight ES-based approaches throughout the restoration process, consider applications of emerging technologies, and review knowledge gaps about the life histories and ES provisioning of underrepresented species. Climate change will increasingly affect oyster populations, and we assess how restoration practices can adapt to these changes. Considering ES throughout the restoration process supports adaptive management. For a rapidly growing restoration practice, we highlight the importance of early community engagement, long-term monitoring, and adapting actions to local conditions to achieve desired outcomes.

The relationship between climate and human evolution is complex, and the causal mechanisms remain unknown. Here, we review and synthesize what is currently known about climate forcings on African landscapes, focusing mainly on the last 4 million years. We use information derived from marine sediment archives and data-numerical climate model comparisons and integration. There exists a heterogeneity in pan-African hydroclimate changes, forced by a combination of orbitally paced, low-latitude fluctuations in insolation; polar ice volume changes; tropical sea surface temperature gradients; the Walker circulation; and possibly greenhouse gases. Pan-African vegetation changes do not follow the same pattern, which is suggestive of additional influences, such as CO2 and temperature. We caution against reliance on temporal correlations between global or regional climate, environmental changes, and human evolution and briefly proffer some ideas on how pan-African climate trends could help create novel conceptual frameworks to determine the causal mechanisms of associations between climate/habitat change and hominin evolution.

Scenarios to stabilize global climate and meet international climate agreements require rapid reductions in human carbon dioxide (CO2) emissions, often augmented by substantial carbon dioxide removal (CDR) from the atmosphere. While some ocean-based removal techniques show potential promise as part of a broader CDR and decarbonization portfolio, no marine approach is ready yet for deployment at scale because of gaps in both scientific and engineering knowledge. Marine CDR spans a wide range of biotic and abiotic methods, with both common and technique-specific limitations. Further targeted research is needed on CDR efficacy, permanence, and additionality as well as on robust validation methods—measurement, monitoring, reporting, and verification—that are essential to demonstrate the safe removal and long-term storage of CO2. Engineering studies are needed on constraints including scalability, costs, resource inputs, energy demands, and technical readiness. Research on possible co-benefits, ocean acidification effects, environmental and social impacts, and governance is also required.

One major conundrum of modern microbiology is the large pangenome (gene pool) present in microbes, which is much larger than those found in complex organisms such as humans. Here, we argue that this diversity of gene pools carried by different strains is maintained largely due to the control exercised by viral predation. Viruses maintain a high strain diversity through time that we describe as constant-diversity equilibrium, preventing the hoarding of resources by specific clones. Thus, viruses facilitate the release and degradation of dissolved organic matter in the ocean, which may lead to better ecosystem functioning by linking top-down to bottom-up control. By maintaining this equilibrium, viruses act as a key element of the adaptation of marine microbes to their environment and likely evolve as a single evolutionary unit.