Ocean Indicators Summary for 2020

Summary of ocean ecosystem indicators used to characterize juvenile marine salmon survival in the Northern California Current.

West Coast

Summary of Ocean Indicators for 2020

The early onset of upwelling led to cool ocean conditions during the winter and early spring. This winter, 'pre-conditioning' was likely the cause of the highest annual biomass of northern copepods observed in our 24-year time series. The nearshore winter ichthyoplankton index also pointed towards productive ocean conditions, likely for the same reason.

Therefore, although summer temperatures were warmer than average, our biological indices point towards a productive year for higher trophic levels.

Pacific Decadal Oscillation and Ocean Nino Index

The PDO turned negative (cool phase) in January 2020 and remained negative throughout 2020. This trend was the longest stretch of negative PDO values since 2013. The Ocean Niño Index turned negative in May 2020 and has been in La Niña conditions (values less than or equal to -0.5 °C) for four consecutive months, one month shy of being declared a La Niña event from the National Weather Service Climate Prediction Center.

Time series of shifts in sign of the Pacific Decadal Oscillation (PDO; bars) and the Ocean Niño Index (ONI; line) from 1996 to present. Red bars indicate positive (warm) years; blue bars negative (cool) years.

Upwelling Index at 45°N

At the Newport Hydrographic Line, the onset of upwelling began quite early. Periods of upwelling-favorable winds occurred during the winter in mid-February through mid-April 2020. Persistent but weak upwelling followed from early May until mid-June, and upwelling strength was similar to the long term mean from mid-June until September. Upwelling-favorable winds became weak in September, followed by an early storm in late September that brought strong downwelling and heavy precipitation to the region.

Sea Surface Temperatures from NOAA Buoys

Negative temperature anomalies occurred in the winter from November-December 2019, followed by positive SST anomalies from January – mid-February 2020. Early upwelling in February through mid-April resulted in negative sea surface temperatures during this time. Following the early onset of upwelling, sea surface temperature anomalies followed a cyclical pattern of positive and negative anomalies following upwelling and relaxation cycles. After the fall transition in September, sea surface temperature anomalies became strongly positive (+2°C) through mid-October. In 2020, we tracked a large marine heatwave in the NE Pacific. That warm water inundated the Oregon shelf in September, but localized east winds produced negative sea surface temperatures at the end of October.

Daily sea surface temperature anomalies from 2019 (top panel) and 2020 (bottom panel) measured at seven NOAA Buoys located off coastal Oregon and Washington.

Water Temperatures on the Shelf and Slope

At the Newport Hydrographic Line, the near-bottom water temperature on the continental shelf (50 m) became cooler than average from late 2019 to early 2020 for the first time since the spring of 2014, before returning to positive anomalies in summer. Anomalies on the continental slope (150 m) at the NHL briefly became weakly negative in early 2020 but returned to weakly positive through summer 2020.

Water temperature anomalies at 150m water depth at station NH-25 (top panel) located on the continental slope (25 nm from shore in 300m water depth; top panel) and in the near bottom waters at station NH-5 (bottom panel) located on the continental shelf in 60m water depth.

Hypoxia

We measured hypoxic oxygen concentrations below 1.4 ml/L on the shelf (50-m depth) during each sampling occurrence in July and August 2020. Although hypoxic conditions occurred in summer during most years since 1999, the summers of 2018-2020 have been the most hypoxic since 2000 - 2001.

Zooplankton

Throughout 2020, northern copepods continued an overall increasing trend since the extreme lows during the 2014-2016 heatwave. The biomass anomalies remained positive throughout the year, with the spring-summer anomalies among the highest of the time series.

Southern copepods were below-average for much of 2020, continuing a decline since the heatwave. These values suggest above-average feeding conditions for pelagic fishes off central Oregon in 2020, with late-spring/summer northern copepod biomass the most favorable since before the 2014-2016 heatwave.

The transition from a warm-water lipid-deplete winter copepod community to a cold-water summer community occurred on March 15 in 2020, the third earliest year in our 24-year time series. This transition occurred on May 7 in 2019, which is near the 24-year average, and the transition was very late in 2017 and 2018 and did not happen at all in 2015 or 2016.

Monthly biomass anomalies of the northern (top panel) and southern (lower panel) copepod taxa from 1996 to present. Biomass values are log base-10 in units of mg carbon m–3.

Pyrosomes

While colonial tunicates called pyrosomes were common in our plankton nets from fall 2016 through midsummer 2018, they have been absent over the past couple of years. They were present throughout California in 2020, and we collected hundreds of small pyrosomes averaging about 4 cm in length in plankton nets off the Oregon/California border (41.8°N) in September 2020. We also collected a few colonies collected off Newport on December 23, 2020. Strong winter storms likely transported these animals to our region from southern locales.

Winter Ichthyoplankton

The Index of Coastal Prey Biomass (ICPB) was greater in 2020 than the long-term mean and the 7th highest in the 23-year time series. The ICPB importance to juvenile salmon had been relatively low since 2013. The relatively high ICPB in 2020 and the ichthyoplankton community composition in 2020, which included similar proportions of both coastal and offshore taxa, suggests that average to good prey conditions existed for piscivorous juvenile salmon that out-migrated in 2020.