In the past decade, two large marine heatwaves (MHWs) formed in the northeast Pacific near Ocean Station Papa (OSP), one of the oldest oceanic time series stations. Physical, biogeochemical and biological parameters observed at OSP from 2013 to 2020 are used to assess ocean response and potential impacts on marine life from the 2019 northeast Pacific MHW. The 2019 MHW was preceded by calm and stratified surface conditions, lower dissolved inorganic carbon, and higher pH of surface waters relative to the 2013-2020 period. A spike in the summertime chlorophyll followed by a decrease in surface macronutrients suggests increased productivity in the well-lit stratified upper ocean during summer 2019. More blue whale calls were recorded at OSP in 2019 compared to the prior year. Large subsurface temperature anomalies were also found, suggesting that the earlier northeast Pacific MHW (2013-2015, previously referred to as “Blob”) as well as the long-term increase in sea surface temperatures in the region contributed to the intensity of the 2019 MHW. This study shows how the utility of long-term, continuous oceanographic datasets and analysis with an interdisciplinary lens is necessary to understand the potential impact of MHWs on marine ecosystems.

The Northwest Tropical Atlantic (NWTA) is a region with complex surface ocean circulation. The most prominent feature is the North Brazil Current (NBC) and its retroflection at 8ºN that leads to the formation of numerous mesoscale eddies known as NBC rings. The NWTA also receives the outflow of the Amazon River, generating freshwater plumes that can extend up to 100,000 km2. These two processes affect the spatial variability of the region’s surface latent heat flux (LHF). First, the presence of surface freshwater modifies the vertical stratification of the ocean limiting the amount of heat that can be released to the atmosphere. Second, they create a highly heterogeneous mesoscale sea-surface temperature (SST) field that directly influences near-surface atmospheric circulation. These effects are illustrated byd from the ElUcidating the RolE of Cloud-Circulation Coupling in ClimAte - Ocean Atmosphere (EUREC4A-OA) and Atlantic Tradewind Ocean-Atmosphere Interaction Campaign (ATOMIC) experiments, satellite and reanalysis data. We decompose the LHF budget into several terms controlled by different atmospheric and oceanic processes to identify the mechanisms leading to LHF changes. We find LHF variations of up to 160 W m2, of which 100 W m2 are associated with wind speed changes and 40 W m2 with SST variations. Surface currents or stratification-change associated heat release remain as second-order contributions with LHF variations of less than 10 W m2 each. Although this study is limited by the paucity of collocated observations, it highlights the importance of considering these three components to properly characterize LHF variability at different spatial scales.

The western Arctic marginal seas undergo large seasonal variation, but are very challenging to observe directly due to sea ice and shallow depths. Deployments of several saildrone uncrewed surface vehicles (USVs) in the summers of 2018 and 2019 provided unique opportunities to validate the satellite-derived near surface currents, Ocean Surface Current Analysis Real-time (OSCAR), in the western Arctic marginal seas against in situ upper ocean current measurements. Overall, OSCAR current is biased low with significant noise. Higher vector correlation and speed difference often occur where stronger currents (often topography-steered) are observed. Such differences reveal that the dataset resolvability depends on spatial and temporal resolutions, smoothing, and latitudes, suggesting that OSCAR is able to depict the major current systems but significantly underestimates their strength. Poorer vector correlation occurs at weaker current regimes (< 10 cm/s), over the shallow Hanna Shoal, near fresher water due to ice melt and river discharge. The latter two water class regimes highlight the importance of salinity contribution to the buoyancy force which is neglected in the OSCAR formulation.