Integrative Oceanography Division

In open ocean systems, trawling with nets remains one of the most common methods for measuring animal biomass in a volume of seawater, calculated as distance traveled multiplied by net mouth area. The effective distance traveled by the net can be measured using a flowmeter, but in the absence of a flowmeter is often estimated as the distance traveled by the trawling vessel. Studies that do not use a flowmeter to quantify trawling effort assume that the rate at which water flows into the net (flow rate) is constant within and among trawls. Similarly, studies that cannot directly measure net mouth area assume its variability is negligible. However, assumptions of constant flow rate and net mouth area are rarely scrutinized and their impacts on volume estimates are poorly understood, especially across sampling depths. We tested these assumptions using a 10 m2 Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS) and observed ~ 10% variability in both flow rate and net mouth area when trawling between the surface and 2500 m. We then compared measurements of net volume and animal biomass from 160 MOCNESS nets to estimates based on six combinations of common net distance and mouth area metrics. Volume estimation methods using vessel-based estimates of distance traveled or the nominal net mouth area overestimated measured volumes by 15–42% on average, resulting in an average 12–28% underestimation of animal biomass across methods. Estimation errors increased with sampling depth and were largest at depths greater than 1000 m. Using a novel method to predict MOCNESS flow rates based on ship velocity, net depth, and other variables describing trawling conditions, estimation errors relative to measured volumes were minimized and became consistent across depths. The findings from our case study suggest trawl studies that do not directly measure flow rates likely have depth-dependent bias in volume estimates, which has broad implications for our understanding of pelagic ecology and ecosystem services.

Many of the oceans' top predatory fishes at low to mid latitudes face an uncertain future as their vulnerable larvae deal with higher environmental temperature and reduced productivity associated with climate change. However, ocean ecosystem models that predict a general decline of zooplankton prey with warming and stratification hardly ever account for complexities in pelagic food webs that might make them resilient in providing food resources for larvae. We illustrate such complexities in comparing feeding interactions of larval Southern Bluefin Tuna (SBT) between two studies conducted 35 y apart in the same spawning region off northwest Australia. In the first (1987), SBT larvae fed and grew at low rates demonstrably limited by zooplankton prey. In the second (2022), feeding and growth were significantly higher despite substantially warmer conditions. The difference reflects a realignment in larval feeding preference from copepods to appendicularians, which allows a more direct and efficient energy transfer pathway from the microbially dominated food web base to higher-level consumers. These findings reset thinking on bluefin larvae feeding preferences, demonstrate high growth on an appendicularian diet up to 30 °C, and align with predictions of appendicularians being an environmentally selected zooplankton category in warming oligotrophic waters.

Abstract Deployment of an autonomous Zooglider in the western Mediterranean Sea revealed the presence of long phytoplankton chains attaining maximum lengths of 6.4–10.4 mm suspended in situ. Elongate chains included the diatoms Guinardia , Proboscia , two other diatom morphologies, and solitary filaments of the cyanobacterium Trichodesmium . Most elongate chains were distributed in the upper 100 m of the water column, overlapping the deep chlorophyll maximum, but some extended to depths of 400 m, suggesting occasional export into deep waters. Such elongate chains appear to be an unutilizable prey resource for most mesozooplankton grazers, including planktonic copepods and appendicularians. Elongate chains are likely to be widely distributed in the ocean, but their detection requires noninvasive measurement methods that do not disrupt the fluid environment or disturb suspended phytoplankton.

Zooplankton are important prey in ocean food webs, linking primary producers to higher trophic levels; understanding their biomass is important to understanding ecosystem state and managing commercial fisheries accordingly. Due to expense and necessary processing time, there are limited indicators of zooplankton that can be produced timely enough to be useful for real-time management needs. We analyzed and compared an 18-year dataset of zooplankton biomass of 21 different species/taxa groups from net samples and acoustic backscatter from Acoustic Doppler Current Profilers (ADCPs) deployed on underwater gliders in the California Current System. Results show positive linear relationships across multiple spatial and temporal scales with greater than 50% of the variance of the total zooplankton biomass explained by the acoustic backscatter when samples were collected within 24 h and 1 km of each other. Copepod species usually dominated the total net haul biomass and there were similar relationships between copepod biomass and a) acoustic backscatter and b) total net biomass. An analysis of cross-shelf transects of the acoustic backscatter data was used to create a Glider Acoustic Backscatter Index (GAZI). The indicator shows consistent low values during El Niño periods and consistently high values during La Niña periods, conforming to our understanding of general productivity in the California Current during El Niño-Southern Oscillation (ENSO) events. These results provide a zooplankton indicator that can be rapidly produced on a sub-monthly time frame and a pathway to potentially using autonomous underwater gliders with ADCPs to monitor zooplankton in other oceanic environments.

Abstract Oxygen is critical for nearly all life on Earth, including aquatic species that breathe dissolved oxygen in both freshwater and marine systems. The rapid, global, and anthropogenic loss of dissolved oxygen known as “aquatic deoxygenation” threatens life in these environments, the human communities that depend on them, and Earth system stability long‐term. Recognizing the important and increasingly widespread effects of aquatic deoxygenation, scientists have proposed that it be added to the planetary boundary framework, which is designed to capture the wider envelope of Earth‐system conditions that support a “safe operating space for humanity.” Here, we argue that the planetary boundary framework should include maintenance of Earth's aquatic ecosystems and thus dissolved oxygen conditions. We synthesize important, in some cases poorly understood, interactions and feedbacks that exist between deoxygenation and all nine of the established planetary boundaries. We find that aquatic deoxygenation interacts with and extensively modulates other boundary processes, including climate change, nutrient loading, biodiversity loss, and aerosol loading. Subsequently, we identify and describe four indicators that can be used to assess the status of aquatic deoxygenation and eventually define a global boundary for it within the framework. Given these interactions and current rates of oxygen loss, we argue that aquatic deoxygenation is approaching an “unsafe space,” with Earth‐system impacts that are likely to be irreversible in our lifetimes. We discuss the wider societal significance of this research, including applications to the framework, future analyses, policy‐making, and management.

The seafloor is recognized as a major sink for marine debris, while deep-sea litter remains poorly investigated due to the logistical and economic constraints associated with seabed exploration. This study reports for the first time the occurrence of marine debris found on the Argentine deep seafloor using the SOI’s Remotely Operated Vehicle (ROV), providing the first documented evidence for this region. A total of 29 litter items were recorded across 55.6 km of surveyed seafloor. The highest debris abundance was recorded in submarine canyon areas (1.4 items/km), whereas the Malvinas Basin showed the lowest levels (0.1 items/km), likely associated with hydrodynamic conditions. In addition, plastic items, fishing ropes, and nets were the most frequently recorded types of debris. These findings establish a baseline of the current status of deep-sea marine debris and propose future directions for the region.

Sporadic mass strandings of the hydrozoan, Velella velella, along the US West Coast fascinate beachcombers and perplex oceanographers. Velella often arrive to the coast in the spring concurrent with a shift in onshore winds and after winters with warmer water temperatures. Understanding the factors that bring Velella to coastal waters provides new information about the ecological impacts of local and basin-scale environmental variability in the northeast Pacific. We summarize several compelling, non-exclusive hypotheses that could explain the recent increase in Velella, including increased population size, larger surface patches and enhanced coastward transport. We compiled a comprehensive dataset spanning planktonic larval to colonial adult life stages from 10 sources covering ~1900-2025. We highlight pulses of Velella and an unprecedented number of strandings and at-sea observations since 2014. We found that wind patterns in the central-east Pacific favor transport toward the coast during years of Velella presence. However, we found no clear relationship between surface frontal features and Velella abundance, nor a consistent association with El Niño. We also identified phalarope abundance as a potential seabird proxy for increased Velella abundance at-sea. Finally, we provide recommendations for future monitoring efforts to improve long-term assessments, given the current inability to clearly distinguish among hypotheses.

This paper presents a comprehensive overview of the Coupled Model Intercomparison Project Phase 7 (CMIP7) request for data pertaining to Earth systems science, and provides justification for the resources needed to produce this data. Topics within the CMIP7 Earth System (CMIP7-ES) theme centre around tracking of flows of energy, carbon, water and other fluxes across domains, and constraining feedbacks between these cycles and the climate system. These topics are summarized in this paper as scientific “opportunities” describing specific model intercomparison experiments and use cases for next-generation Earth System Model (ESM) output. These opportunities were submitted by modelling groups and scientific consortia following an extended public consultation process. Contained within each opportunity are requests for groups of Climate & Forecasting (CF) variables, which are bundled into variable groups representing all data required to address the opportunities' needs. Novel opportunities in CMIP7 compared with previous phases will include running `emissions-driven' simulations that integrate carbon emissions and removal scenarios with updated representations of the global carbon cycle, expanded variable groups needed to model marine trophic interactions and biogeochemistry, and data needed to understand the risk of global tipping points, among others. The production of these variables will close key gaps and uncertainties identified during previous rounds of CMIP, and support the 7th Intergovernmental Panel on Climate Change Assessment Report (AR7). We argue that CMIP7-ES data will be broadly used by scientific, policy, governmental, industry, and other communities that rely on climate model projections for research and decision making. As an author group we also reflect on the evolution of the CMIP7-ES data request as a part of a deliberative process in support of the global CMIP program.

Deep-sea hydrothermal vents form small, unique, and fragile ecosystems that are widely recognized as sites in need of protection. Deep-seabed mining (DSM) is a future threat to hydrothermal ecosystem integrity. In most areas within, and in all areas beyond national jurisdiction, currently proposed protection measures from DSM are unlikely to be sufficient, as only the known active venting sites on the seafloor are intended to be protected from DSM impacts. To ensure effective protection, we propose protecting not only the active vent sites but the entire hydrothermal ecosystems and their transition zones, embracing the seafloor, subseafloor and overlying water column. We discuss how ecological knowledge supports the proposed three-dimensional (3-D) protection. We suggest no DSM extraction or indirect impacts on the seafloor and entire subseafloor within a minimum 50 km diameter (25 km radius) around visible active vents. This will ensure the maintenance of subseafloor connections that are key for ecosystem integrity, as changes in vent fluid conditions can alter all ecosystem functions and services linked to venting activity. In the water column, protection from pollution from the seafloor to surface is suggested to protect vent larvae. This extent spans the entire length of ridges or back-arc basins, with a cross-axial extent of 80 km. We further discuss how international law can contribute to the effective protection of vent ecosystems and transition zones in international waters, and provide guidance for coastal States to safeguard these ecosystems and transition zones within their own maritime areas.