Compounding impact of severe weather events fuels marine heatwave in the coastal ocean

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Dzwonkowski, B., Coogan, J., Fournier, S., Lockridge, G., Park, K., & Lee, T. Compounding impact of severe weather events fuels marine heatwave in the coastal ocean. Nature Communications, 11(1), (2020): 4623, doi:10.1038/s41467-020-18339-2.Exposure to extreme events is a major concern in coastal regions where growing human populations and stressed natural ecosystems are at significant risk to such phenomena. However, the complex sequence of processes that transform an event from notable to extreme can be challenging to identify and hence, limit forecast abilities. Here, we show an extreme heat content event (i.e., a marine heatwave) in coastal waters of the northern Gulf of Mexico resulted from compounding effects of a tropical storm followed by an atmospheric heatwave. This newly identified process of generating extreme ocean temperatures occurred prior to landfall of Hurricane Michael during October of 2018 and, as critical contributor to storm intensity, likely contributed to the subsequent extreme hurricane. This pattern of compounding processes will also exacerbate other environmental problems in temperature-sensitive ecosystems (e.g., coral bleaching, hypoxia) and is expected to have expanding impacts under global warming predictions.This work would not have been possible without the help of the Tech Support Group at the Dauphin Island Sea Lab. A portion of this work was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. This research was made possible by the NOAA RESTORE Science Program (NA17NOS4510101 and NA19NOS4510194) and NOAA NGI NMFS Regional Collaboration Network (18-NGI3-61)

A Limnological Assessment of a Rare Lacustrine Wetland Complex: Laguna De Cube, Ramsar Site 1143, Ecuador

The goal of my project was to conduct the first limnological investigation of Laguna de Cube, Ramsar site 1143, linking hydrogeologic landscape setting to local condition (i.e., water quality and nekton composition). Laguna de Cube, a rare lacustrine wetland within the Choco Darien biodiversity hotspot, performs critical ecosystem functions and services in a region recognized for its extraordinary biodiversity, rarity, and increasing human interference. Abiotic gradients (i.e., thermocline, pH, conductivity, dissolved oxygen (DO)) and hydrochemical parameters (i.e., plant limiting nutrients, herbicides and fecal coliform threshold levels) were quantified in vertical profile and related to nekton composition and habitat utilization. Direct (i.e., flag and caste nets, unbaited fish traps) sampling utilized 20 paired sampling sites and quantified nekton richness, abundance and diversity. Acoustic sonar surveys were used to assess fish abundance, aquatic vegetation, substrate, and lake bathymetry. Nonparametric statistics (e.g., Chi2, Kruskal Wallis), with an a priori p:5 0.10, were used for comparisons Using sonar, depth at Laguna de Cube, ranged from 0.3914 to 31.72 meters (mean 14.41 m) had a total volume of 3,000,000 m3, with a distinct thermocline at 2m. Conductivity, pH, and DO concentrations were significantly different above and below the thermocline (i.e., p=0.089, 3.2e-8, 1.2e-7 respectively). DO, in vertical profile, exhibited elevated concentrations between 8-12m. Plant limiting nutrients (total N and P), fecal coliforms, herbicides (atrizine and simazine) all exceeded US EPA safe drinking water standards. Nekton sampling resulted in 228 individuals representing 5 taxa of IUCN (2012) east concern, dominated by exotic tilapia ( Oreochrontis niloticus niloticus) that represented the majority of nekton biomass. Fish assemblages preferred edge habitats (abundance p=6.1e-7, Shannon-Wiener Diversity p=0.0015) and acoustic surveys showed variations in diurnal distributions with more fish below the therrnocline during the day, and more above the thermocline at night. Likely the oldest and deepest lacustrine feature in Ecuador, the volume, exceeding poor quality, and the potential for deadly toxic algal blooms, derived from metalimnetic cyanobacteria residing in the lake, suggests eutrophication and bioaccumulation will increase, immediately threatening human health. While no historic nekton composition data are available for Laguna de Cube, the extremely low diversity I report is likely a result of the combination of anthropogenic impacts and the presence of an exotic invasive species. The ecological importance of Laguna de Cube is not manifested in conventional measures of conservation. This floodplain lake buffers human threats to biodiversity and its location at the headwaters of the Mache Chindul Ecological Reserve makes its conservation vital. Implementation of clear and transparent conservation management plans that improve water quality, halt the range expansion of tilapia and other invasive species, and promote ecologically sound sustainable agriculture at Laguna de Cube is necessary to protect the down-gradient biodiversity of the region

Cascading weather events amplify the coastal thermal conditions prior to the shelf transit of Hurricane Sally (2020)

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Dzwonkowski, B., Fournier, S., Lockridge, G., Coogan, J., Liu, Z., & Park, K. Cascading weather events amplify the coastal thermal conditions prior to the shelf transit of Hurricane Sally (2020). Journal of Geophysical Research: Oceans, 126(12), (2021): e2021JC017957, https://doi.org/10.1029/2021JC017957.Changes in tropical cyclone intensity prior to landfall represent a significant risk to human life and coastal infrastructure. Such changes can be influenced by shelf water temperatures through their role in mediating heat exchange between the ocean and atmosphere. However, the evolution of shelf sea surface temperature during a storm is dependent on the initial thermal conditions of the water column, information that is often unavailable. Here, observational data from multiple monitoring stations and satellite sensors were used to identify the sequence of events that led to the development of storm-favorable thermal conditions in the Mississippi Bight prior to the transit of Hurricane Sally (2020), a storm that rapidly intensified over the shelf. The annual peak in depth-average temperature of >29°C that occurred prior to the arrival of Hurricane Sally was the result of two distinct warming periods caused by a cascade of weather events. The event sequence transitioned the system from below average to above average thermal conditions over a 25-day period. The transition was initiated with the passage of Hurricane Marco (2020), which mixed the upper water column, transferring heat downward and minimizing the cold bottom water reserved over the shelf. The subsequent reheating of the upper ocean by surface heat flux from the atmosphere, followed by downwelling winds, effectively elevated shelf-wide thermal conditions for the subsequent storm, Hurricane Sally. The coupling of climatological downwelling winds and warm sea surface temperature suggest regions with such characteristics are at an elevated risk for storm intensification over the shelf.his paper is a result of research funded by the National Oceanic and Atmospheric Administration's RESTORE Science Program under awards NA17NOS4510101 and NA19NOS4510194 to the University of South Alabama and Dauphin Island Sea Lab and by the NASA Physical Oceanography program under award 80NSSC21K0553 and WBS 281945.02.25.04.67 to the University of South Alabama and the Jet Propulsion Laboratory. A portion of this work was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. We thank the NASA Goddard Space Flight Center, Ocean Ecology Laboratory, Ocean Biology Processing Group for the Moderate-resolution Imaging Spectroradiometer (MODIS) Terra ocean color data; 2014 Reprocessing. NASA OB.DAAC, Greenbelt, MD, USA. 10.5067/AQUA/MODIS/MODIS_OC.2014.0