Zooplankton diel vertical migration (DVM) is a globally ubiquitous phenomenon and a critical component of the ocean's biological pump. During DVM, zooplankton metabolism leads to carbon and nutrient export to mesopelagic depths, where carbon can be sequestered for decades to millennia, while also introducing labile, energy-rich food sources to midwater ecosystems. Three pervasive metabolic pathways allow zooplankton to sequester carbon: fecal pellet egestion, dissolved organic matter excretion, and respiration. Additionally, there are several less well-parameterized sources of DVM transport associated with growth, feeding, reproduction, and mortality. These processes are challenging to measure in situ and difficult to extrapolate from laboratory experiments, making them some of the most poorly constrained factors in assessments and models of the biological pump. In this review, we evaluate and compare observational and modeling approaches to estimate zooplankton DVM and the resulting active carbon flux, highlighting major discrepancies and proposing directions for future research.

Built infrastructure, such as seawalls and levees, has long been used to reduce shoreline erosion and protect coastal properties from flood impacts. In contrast, natural and nature-based features (NNBF), including marshes, mangroves, oyster reefs, coral reefs, and seagrasses, offer not only coastal protection but also a range of valuable ecosystem services. There is no clear understanding of the capacity of either natural habitats or NNBF integrated with traditional engineered infrastructure to withstand extreme events, nor are there well-defined breakpoints at which these habitats fail to provide coastal protection. Evaluating existing NNBF strategies using a standardized set of metrics can help to assess their effectiveness to better inform design criteria. This review identifies a selection of NNBF projects with long-term monitoring programs and synthesizes the monitoring data to provide a literature-based performance assessment. It also explores the integration of NNBF with existing gray infrastructure to enhance overall effectiveness.

The Atlantic Ocean circulation, in particular its zonally averaged north-south volume transport indicated by the Atlantic Meridional Overturning Circulation (AMOC), is sensitive to surface buoyancy anomalies. It may undergo a transition to a climate-disrupting state within a century under continuing greenhouse gas emissions. The potential climate and societal impacts are expected to be large, and therefore reliable estimates of the probability of the onset of such a collapse before the year 2100 are crucial for policymakers. This article addresses whether current Earth system models are fit for purpose to capture present-day AMOC stability and presents the current status of estimates of collapse onset probabilities.

For over 50 years I have studied corals, coral reefs, and reef-associated animals. Although much of my work was underpinned by genetics and I have dabbled in theory, I am a natural historian at heart. The many topics I pursued reflect in part what sparked my fancy but were also greatly shaped by a series of chance events, unexpected data, and unplanned opportunities. Many of the findings and ideas for which I am now known were initially met with skepticism and rejection-success required stubborn faith in my intuitions and convictions and the support of many assistants, collaborators, mentors, and leaders. Watching the sudden loss of the reefs that dazzled me as a graduate student and the subsequent steady decline of ocean life around the world has driven my interests in conservation and communication, and in the end, perhaps surprisingly, made me focus on the positive.

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.

Sediments covering Arctic continental shelves are uniquely impacted by ice processes. Delivery of sediments is generally limited to the summer, when rivers are ice free, permafrost bluffs are thawing, and sea ice is undergoing its seasonal retreat. Once delivered to the coastal zone, sediments follow complex pathways to their final depocenters-for example, fluvial sediments may experience enhanced seaward advection in the spring due to routing under nearshore sea ice; during the open-water season, boundary-layer transport may be altered by strong stratification in the ocean due to ice melt; during the fall storm season, sediments may be entrained into sea ice through the production of anchor ice and frazil; and in the winter, large ice keels more than 20 m tall plow the seafloor (sometimes to seabed depths of 1-2 m), creating a type of physical mixing that dwarfs the decimeter-scale mixing from bioturbation observed in lower-latitude shelf systems. This review summarizes the work done on subtidal sediment dynamics over the last 50 years in Arctic shelf systems backed by soft-sediment coastlines and suggests directions for future sediment studies in a changing Arctic. Reduced sea ice, increased wave energy, and increased sediment supply from bluffs (and possibly rivers) will likely alter marine sediment dynamics in the Arctic now and into the future.

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 linked to 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.

Understanding the long-term effects of ongoing global environmental change on marine ecosystems requires a cross-disciplinary approach. Deep-time and recent fossil records can contribute by identifying traits and environmental conditions associated with elevated extinction risk during analogous events in the geologic past and by providing baseline data that can be used to assess historical change and set management and restoration targets and benchmarks. Here, we review the ecological and environmental information available in the marine fossil record and discuss how these archives can be used to inform current extinction risk assessments as well as marine conservation strategies and decision-making at global to local scales. As we consider future research directions in deep-time and conservationpaleobiology, we emphasize the need for coproduced research that unites researchers, conservation practitioners, and policymakers with the communities for whom the impacts of climate and global change are most imminent.

Fine-scale currents, O(1-100 km, days-months), are actively involved in the transport and transformation of biogeochemical tracers in the ocean. However, their overall impact on large-scale biogeochemical cycling on the timescale of years remains poorly understood due to the multiscale nature of the problem. Here, we summarize these impacts and critically review current estimates. We examine how eddy fluxes and upscale connections enter into the large-scale balance of biogeochemical tracers. We show that the overall contribution of eddy fluxes to primary production and carbon export may not be as large as it is for oxygen ventilation. We highlight the importance of fine scales to low-frequency natural variability through upscale connections and show that they may also buffer the negative effects of climate change on the functioning of biogeochemical cycles. Significant interdisciplinary efforts are needed to properly account for the cross-scale effects of fine scales on biogeochemical cycles in climate projections.

I am a child of Sputnik, the satellite launched by the Soviet Union in 1957. That event created opportunities for me to escape the horrors of apartheid by emigrating from South Africa to the United States. There, fortuitously, I was given excellent ...Read More