Mara Freilich’s research while affiliated with Brown University and other places

The Sub-Mesoscale Ocean Dynamics Experiment (S-MODE) is a NASA Earth Ventures Suborbital investigation designed to test the hypothesis that oceanic frontogenesis and the kilometer-scale (“submesoscale”) instabilities that accompany it make important contributions to vertical exchange of climate and biological variables in the upper ocean. These processes have been difficult to resolve in observations, making model validation challenging. A necessary step toward testing the hypothesis was to make accurate measurements of upper-ocean velocity fields over a broad range of scales and to relate them to the observed variability of vertical transport and surface forcing. A further goal was to examine the relationship between surface velocity, temperature and chlorophyll measured by remote sensing, and their depth-dependent distributions, within and beneath the surface boundary layer. To achieve these goals, we used aircraft-based remote sensing, satellite remote sensing, ships, drifter deployments, and a fleet of autonomous vehicles. The observational component of S-MODE consisted of three campaigns, all conducted in the Pacific Ocean approximately 100 km west of San Francisco during 2021-2023 fall and spring. S-MODE was enabled by recent developments in remote sensing technology that allowed operational airborne observation of ocean surface velocity fields and by advances in autonomous instrumentation that allowed coordinated sampling with dozens of uncrewed vehicles at sea. The coordinated use of remote sensing measurements from three aircraft with arrays of remotely operated vehicles and other in situ measurements is a major novelty of S-MODE. All S-MODE data is freely available, and its use is encouraged.

Many geoscience departments in the United States (US) are working to recruit faculty from underrepresented groups. However, there is little information about how hiring practices are perceived by candidates. Here we address this gap by interviewing 19 geoscientists who identify as an underrepresented race, ethnicity, or gender who recently declined a tenure-track faculty job offer in the US about their faculty job searches, with an emphasis on their decisions to accept or decline an offer. We find that many participants experienced hiring practices inconsistent with existing recommendations to increase faculty diversity, and some participants were subject to uncivilized, even potentially discriminatory, practices. Therefore, we leverage our results to provide actionable recommendations for improving faculty recruitment efforts. We highlight that departments may doubly benefit from improving their culture: in addition to benefiting current members, it may also help with recruitment. Overall, our findings emphasize the need for continued evaluation of faculty hiring practices.

The Salton Sea, California’s largest lake, is undergoing significant environmental degradation, which has adverse health effects on nearby rural communities, who are primarily Latinx and Torres Martinez Desert Cahuilla Indian. Over the past two decades, the lake’s water levels have steadily dropped. Water conditions in the Sea, characterized by low oxygen and high nutrient levels, favor the production of H2S. This study investigates the connection between the Sea’s changing conditions, particularly the worsening water quality, and hydrogen sulfide (H2S) emissions using air quality and water quality data collected since 2013 and 2004, respectively. H2S concentrations often exceed California’s air quality standards, particularly in areas near the Sea during summer months. Wind patterns substantially impact detection of H2S. When wind is blowing from the sea towards communities with sensors, which are located to the northwest of the sea, H2S is detected significantly more often. Current monitoring efforts underestimate the frequency and distribution of H2S that exceeds air quality standards. An air sensor deployed in shallow water over the Salton Sea by a community science program detected substantially higher concentrations of H2S, particularly when wind was blowing over exposed sediment and shallow water, suggesting that these are a significant and overlooked H2S source at the Salton Sea. These findings highlight the need for improved air quality monitoring and more effective environmental management policies to protect public health in the region. The study emphasizes the importance of community-led solutions and provides insights relevant to other regions experiencing similar environmental crises.

Submesoscale eddies (those smaller than 50 km) are ubiquitous throughout the ocean, as revealed by satellite infrared images. Diagnosing their impact on ocean energetics from observations remains a challenge. This study analyzes a turbulent field of submesoscale eddies using airborne observations of surface currents and sea surface temperature, with high spatial resolution, collected during the S‐MODE experiment in October 2022. Assuming surface current divergence and temperature are homogeneous down to 30 m depth, we show that more than 80% of the upward vertical heat fluxes, reaching ∼ ${\sim}$227 W m−2 ${\mathrm{m}}^{-2}$, is explained by the smallest resolved eddies, with a size smaller than 15 km. This result emphasizes the contribution of small‐scale eddies, poorly represented in numerical models, to the ocean heat budget and, therefore, to the climate system.

The Salton Sea (SS), California’s largest inland lake at 816 square kilometers, formed in 1905 from a levee breach in an area historically characterized by natural wet-dry cycles as Lake Cahuilla. Despite more than a century of untreated agricultural drainage inputs, there has not been a systematic assessment of nutrient loading, cycling, and associated ecological impacts at this iconic waterbody. The lake is now experiencing unprecedented degradation, particularly following the 2003 Quantification Settlement Agreement—the largest agricultural-to-urban water transfer in the United States. Combined with high evaporation rates, reduced inflows have led to rapid lake shrinkage, with current maximum depths of only 10 m. Here we report distinct temporal and spatial patterns for nutrient dynamics at the SS for two decades spanning the period before and after major water transfer agreement. While external nutrient loading remains relatively consistent year-round, internal cycling varies seasonally. Winter exhibits high total phosphates and nitrate levels due to reduced primary productivity, with lower ammonium concentrations from increased oxygenation. Summer conditions shift to decreased phosphate and nitrate levels from enhanced primary production, sustained partly by internal phosphorus release from sediments during anoxic periods. Although N:P molar ratios can exceed 50:1 to 100:1 (far above the Redfield ratio of 16:1), phosphorus consistently remains at hypereutrophic levels (> 0.05 mg/L) challenging previous assumptions of phosphorus limitation. Post-2020 data show disrupted stratification patterns. Despite higher oxygen levels in bottom waters compared to 2004–2009, overall water column oxygenation has declined, reflecting altered hydrodynamics in the shallowing lake. These changes have intensified environmental challenges stemming from cultural eutrophication including harmful algal blooms, threatening both ecosystem and public health. Effective remediation will require significant reduction in external nutrient loading through constructed wetlands and/or treatment facilities at tributary mouths to reduce the lake’s overall nutrient inventory over time.

Submesoscale dynamics, operating at spatial scales of O(1−10 km) and temporal scales of O(1 day), are particularly important for marine ecosystems as they occur on similar timescales as phytoplankton growth, enabling biophysical feedbacks. While submesoscale dynamics are known to impact biological fluxes by modifying nutrient upwelling, horizontal transport has traditionally been assumed to only redistribute phytoplankton without altering concentrations. However, variations in submesoscale dispersion may significantly impact total biogeochemical flux if biological reactions occur during dispersal. By parameterizing the effects of dispersion due to lateral stirring on flux, within an eastern boundary current region, we show that enhanced dispersion yields a near-linear increase in offshore flux, with the magnitude modulated by phytoplankton growth rates and ambient nutrient availability. These findings identify a pathway for improving parameterizations of biogeochemical fluxes, while revealing a source of uncertainty in their prediction by climate models.

Pycnocline stratification is increasing across multiple ocean basins due to a warming surface ocean and increasing sea ice melt. Pycnocline stratification plays a leading order role in tracer transport, shaping capacity for heat and carbon uptake, making it a key parameter of interest on timescales ranging from paleoclimate to plankton blooms. Part of the challenge in assessing the role of pycnocline stratification in global models is the two-way connection between physical processes at the (sub)mesoscale and stratification with important implications for tracer subduction. Using a suite of numerical simulations of an idealized front, we find that the strength of pycnocline stratification influences the formation and evolution of submesoscale structure and the resulting tracer transport. The impact of changing stratification on tracer flux strongly depends on whether frontal strength is also changed correspondingly by holding the isopycnal slope fixed. When a constant isopycnal slope is initialized, tracers get efficiently transferred across the base of the mixed layer and get trapped in anticyclonic submesoscale vortices below the mixed layer. This leads to tracer concentrations below the mixed layer and fluxes through it to be stronger under decreased stratification conditions. In contrast, when frontal lateral buoyancy gradient is held fixed while stratification changes, the vertical flux of tracers and the concentrations at depth stay constant across all examined stratification conditions. Understanding the relationship between pycnocline stratification and fine-scale physical motions is necessary to diagnose and predict trends in carbon uptake and storage, particularly in the Southern Ocean.

Introduction A defining aspect of the Intergovernmental Panel on Climate Change (IPCC) assessment reports (AR) is a formal uncertainty language framework that emphasizes higher certainty issues across the reports, especially in the executive summaries and short summaries for policymakers. As a result, potentially significant risks involving understudied components of the climate system are shielded from view. Methods Here we seek to address this in the latest, sixth assessment report (AR6) for one such component—the deep ocean—by summarizing major uncertainties (based on discussions of low confidence issues or gaps) regarding its role in our changing climate system. The goal is to identify key research priorities to improve IPCC confidence levels in deep ocean systems and facilitate the dissemination of IPCC results regarding potentially high impact deep ocean processes to decision-makers. This will accelerate improvement of global climate projections and aid in informing efforts to mitigate climate change impacts. An analysis of 3,000 pages across the six selected AR6 reports revealed 219 major science gaps related to the deep ocean. These were categorized by climate stressor and nature of impacts. Results Half of these are biological science gaps, primarily surrounding our understanding of changes in ocean ecosystems, fisheries, and primary productivity. The remaining science gaps are related to uncertainties in the physical (32%) and biogeochemical (15%) ocean states and processes. Model deficiencies are the leading cited cause of low certainty in the physical ocean and ice states, whereas causes of biological uncertainties are most often attributed to limited studies and observations or conflicting results. Discussion Key areas for coordinated effort within the deep ocean observing and modeling community have emerged, which will improve confidence in the deep ocean state and its ongoing changes for the next assessment report. This list of key “known unknowns” includes meridional overturning circulation, ocean deoxygenation and acidification, primary production, food supply and the ocean carbon cycle, climate change impacts on ocean ecosystems and fisheries, and ocean-based climate interventions. From these findings, we offer recommendations for AR7 to avoid omitting low confidence-high risk changes in the climate system.

Frontal zones within the Western Alboran Gyre (WAG) are characterized by a density gradient resulting from the convergence of Atlantic and Mediterranean waters. Subduction along isopycnals at the WAG periphery can play a crucial role in upper ocean ventilation and influences its stratification and biogeochemical cycles. In 2019, physical parameters (comprising temperature, salinity, turbulent kinetic energy dissipation rates) and biogeochemical data (oxygen and chlorophyll-a) profiles were collected in transects along the northern edge of the WAG. Several intrusions of subducted water with elevated oxygen, chlorophyll-a and spice anomaly were identified towards the center of the anticyclone. These features had elevated kinetic energy dissipation rates on both their upper and lower boundaries. Analysis of the turbulent fluxes involving heat, salt, oxygen, and chlorophyll-a demonstrated a net flux of physical and biogeochemical properties from the intrusions to the surrounding ocean. Either the turbulent or diffusive convection mixing contributed to the observed dilution of the intrusion. Other factors (e.g., water column density stability, variability of the photic layer depth, and organic matter degradation) likely played a role in these dynamics. Enhanced comprehension of the persistence and extent of these features might lead to an improved quantitative parametrization of relevant physical and biogeochemical properties involved in subduction within the study zone.