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The Guayas estuary in Ecuador is the largest estuarine ecosystem on the Pacific coast of South America. This estuary provides nurseryand fisheries habitats, as well as filtering and detoxification services provided by suspension feeders, vegetation, and wetlands. Weused oceanographic and meteorological observations to understand the hydrodynamic variability of two areas in the inner part ofthe estuary, Manglares de Churute and Estero Salado, from February 2016 to February 2017. Churute has less anthropogenic impacts thanEstero Salado, which is currently uncoupled from river flow and highly influenced by Guayaquil, the second largest city in Ecuador, andadjacent shrimp pond effluents. The influences from the ocean and river on Churute include higher dissolved oxygen (DO) and lower salinity,temperature and phosphates than in Estero Salado, particularly during the wet season when the river is the dominant mode of forcing inthose warm and rainy first months of the year. Hypoxic levels (DO below 2 mg L-1) were found in Estero Salado in several stations duringthe hot, rainy season. These data suggest seasonal variability (dry/rainy season) influences the hydrographic conditions in the inner Guayasestuary mostly, adding variability to salinity, turbidity, nutrients and DO of the whole water column.

Subtidal water temperatures in estuaries influence where organisms can survive and are determined by oceanic, atmospheric and riverine heat fluxes, modulated by the distinct geometry and bathymetry of the system. Here, we use 14 years of data from the Coos Estuary, in southwest Oregon, USA, to explore the impact of anomalously warm oceanic and atmospheric conditions during 2014-2016 on the estuary temperature. The arrival of a marine heatwave in September 2014 increased water temperature in the greater Pacific Northwest region until March 2015, and again from July to August 2015. Additionally, in 2014-2016, the Equatorial Pacific showed increased temperatures due to El Niño events. In the Coos Estuary, this warming was observed at all the water quality stations, producing more than 100 days with temperatures at least 1.5°C warmer than normal, and notably, a higher prevalence during Fall and Winter seasons. Larger temperature variations occurred at shallower stations located further away from the mouth of the estuary, changing the along-estuary temperature gradient and potentially the advection of heat through the estuary. After the onset of these increased temperatures, eelgrass declined sharply, but only in certain stations in the shallow estuary South Slough and has not yet returned to long term average values. As global temperatures continue rising due to climate change, increased numbers of marine heatwaves and El Niño events are expected, leading to higher temperature stress on the marine ecosystem within estuaries.

Time series spanning 22 years of monthly conductivity-temperature-depth profiles are used to examine upper water column temperature interannual variability near the Ecuador coastline. The sampling program began in 1992 (and continues) by Ecuador's National Institute of Oceanography of the Navy and National Fisheries Institute. The five coastal stations are located 8 NM away from the coast and extend from 2°S to 1°N. The anomaly data show marked interannual variations with distinct characteristics associated with El Niño Southern Oscillation (ENSO) indices. Heat content and the 20°C isotherm depth are both largest during El Niño periods and weakest during La Niña periods. The first mode empirical orthogonal function (EOF) decomposition of the anomaly coastal station data represents bulk variations of the thermocline depth and has temporal variability coupled to Niño 3.4 and 1+2 indices. Coastal observations are compared with observations obtained from the offshore TAO/Triton buoys located along 95°W from 2°S to 2°N. The EOF decomposition of TAO buoy time series shows similar spatial EOF structure. The first EOF amplitude time series from coastal and TAO station decomposition is correlated, showing that the dominant variability of the upper water column near the coast is coupled to variations along the equator and seaward of the Galápagos. Coupling between ENSO indices and ERA-1 zonal wind stress from the central Pacific (Niño 4) with observed coastal temperature structure shows that effects of El Niño forcing are strongly influencing the Ecuadorian Sea eastward of the Galápagos Islands.