Effects of basin-scale climate modes and upwelling on nearshore marine heatwaves and cold spells in the California Current.

Marine heatwaves and cold spells (MHWs/MCSs) have been observed to be increasing globally in frequency and intensity based on satellite remote sensing and continue to pose a major threat to marine ecosystems worldwide. Despite this, there are limited in-situ based observational studies in the very shallow nearshore region, particularly in Eastern Boundary Current Upwelling Systems (EBUS). We analyzed a unique dataset collected in shallow waters along central California spanning more than four decades (1978-2020) and assessed links with basin-scale climate modes [Pacific Decadal Oscillation (PDO) and El Niño (MEI)] and regional-scale wind-driven upwelling. We found no significant increase/decrease in MHW/MCS frequency, duration, or intensity over the last four decades, but did observe considerable interannual variability linked with basin-scale climate modes. Additionally, there was a decrease in both MHW/MCS occurrence during the upwelling season, and the initiation of individual MHWs/MCSs coincided with anomalous upwelling. Most notably, the co-occurrence of warm (cold) phases of the PDO and MEI with negative (positive) upwelling anomalies strongly enhanced the relative frequency of positive (negative) temperature anomalies and MHW (MCS) days. Collectively, both basin-scale variability and upwelling forcing play a key role in predicting extreme events and shaping nearshore resilience in EBUS.

Modeling changes in baleen whale seasonal abundance, timing of migration, and environmental variables to explain the sudden rise in entanglements in California.

We document changes in the number of sightings and timing of humpback (Megaptera novaeangliae), blue (Balaenoptera musculus), and gray (Eschrichtius robustus) whale migratory phases in the vicinity of the Farallon Islands, California. We hypothesized that changes in the timing of migration off central California were driven by local oceanography, regional upwelling, and basin-scale climate conditions. Using 24 years of daily whale counts collected from Southeast Farallon Island, we developed negative binomial regression models to evaluate trends in local whale sightings over time. We then used linear models to assess trends in the timing of migration, and to identify potential environmental drivers. These drivers included local, regional and basin-scale patterns; the latter included the El Niño Southern Oscillation, the Pacific Decadal Oscillation, and the North Pacific Gyre Oscillation, which influence, wind-driven upwelling, and overall productivity in the California Current System. We then created a forecast model to predict the timing of migration. Humpback whale sightings significantly increased over the study period, but blue and gray whale counts did not, though there was variability across the time series. Date of breeding migration (departure) for all species showed little to no change, whereas date of migration towards feeding areas (arrival) occurred earlier for humpback and blue whales. Timing was significantly influenced by a mix of local oceanography, regional, and basin-scale climate variables. Earlier arrival time without concomitant earlier departure time results in longer periods when blue and humpback whales are at risk of entanglement in the Gulf of the Farallones. We maintain that these changes have increased whale exposure to pot and trap fishery gear off the central California coast during the spring, elevating the risk of entanglements. Humpback entanglement rates were significantly associated with increased counts and early arrival in central California. Actions to decrease the temporal overlap between whales and pot/trap fishing gear, particularly when whales arrive earlier in warm water years, would likely decrease the risk of entanglements.

Anomalous Near-Surface Low-Salinity Pulses off the Central Oregon Coast.

From mid-May to August 2011, extreme runoff in the Columbia River ranged from 14,000 to over 17,000 m(3)/s, more than two standard deviations above the mean for this period. The extreme runoff was the direct result of both melting of anomalously high snowpack and rainfall associated with the 2010-2011 La Niña. The effects of this increased freshwater discharge were observed off Newport, Oregon, 180 km south of the Columbia River mouth. Salinity values as low as 22, nine standard deviations below the climatological value for this period, were registered at the mid-shelf. Using a network of ocean observing sensors and platforms, it was possible to capture the onshore advection of the Columbia River plume from the mid-shelf, 20 km offshore, to the coast and eventually into Yaquina Bay (Newport) during a sustained wind reversal event. Increased freshwater delivery can influence coastal ocean ecosystems and delivery of offshore, river-influenced water may influence estuarine biogeochemistry.