Anomalous Southward Advection During 2002 in the Northern California Current: Evidence from Lagrangian Surface Drifters

Abstract

Equatorward velocities in the upwelling jet of the northern California Current were 0.05–0.06 m s−1 faster in spring and summer 2002 than on average over 1998–2002. This result is based on a five‐year data set of surface drifters released across the continental margin off central Oregon (44.65°N) during April and July of each year. At this speed, anomalous water displacements of over a degree of latitude can occur in 20–25 days. Given a source of cold, Subarctic water to the north, this anomalous southward displacement is a plausible explanation for the cold, nutrient‐rich halocline water observed off Oregon during the summer of 2002. This interannual variability in the northern California Current and its implications for the ecosystem response, i.e., increased primary productivity, may be contrasted with interannual variability of the opposite sign ‐ increased poleward velocity, warmer temperatures and decreased productivity ‐ observed in this same region during El Niño years.

Enhanced southward flow over the Oregon shelf in 2002: A conduit for subarctic water

“…Strub and James [2003] use altimeter measurements to document enhanced large-scale equatorward flow into and within the California Current, offshore of the continental shelf. Barth [2003] Concurrent observations also indicate enhanced nutrients and increased primary production from British Columbia to northern California during the summer of 2002 [Thomas et al, 2003;Wheeler et al, 2003].…”

Forcing mechanisms controlling surface and subsurface temperature anomalies along line‐p, North‐East Pacific Ocean

“…Advection anomalies for the entire California Current can lead to temperature anomalies found along Line-P, as has been suggested as an explanation for the 2002 anomalies (Barth, 2003;Kosro, 2003). Northward coastal current anomalies result in a northward displacement of the mean temperature gradient at the coast, thus leading to positive temperature anomalies at the coast in the upper layer (see Section 3c).…”

“…Strong negative temperature anomalies, never before observed despite decades of records, were found in July 2002 between 30-and 150-m depth off Oregon and Vancouver Island (Freeland et al, 2003). Southward advection of temperature anomalies in the California Current during spring and summer 2002 (Barth, 2003;Kosro, 2003), as well as zonal advection anomalies in the North Pacific Current (Strub and James, 2003), are at least part of the explanation. The current anomalies themselves seem to be caused by large-scale atmosphere-ocean processes (Murphree et al, 2003).…”

Coupling Between the Coastal Ocean and Yaquina Bay, Oregon: Importance of Oceanic Inputs Relative to Other Nitrogen Sources

“…The higher than normal nutrients resulted in increases in phytoplankton standing stock and primary productivity and concurrent decreases in dissolved oxygen over the inner shelf (Wheeler et al 2003;Grantham et al 2004). These anomalous conditions during 2002 have been attributed to the advection of a Subarctic water mass (Barth 2003;Freeland et al 2003;Kosro 2003). During 1997 and 1998, the coastal ocean and flood tide water entering the estuary was warmer than normal and there were less nutrients entering the inlet during flood tides, which corresponds to El Niño conditions in the coastal waters off Oregon (Huyer et al 2002).…”