Seasonal cycles of currents, temperatures, winds, and sea level over the northeast Pacific continental shelf: 35°N to 48°N

Abstract

Seasonal cycles of coastal wind stress, adjusted sea level (ASL), shelf currents, and water temperatures off the west coast of North America (35øN to 48øN) are estimated by fitting annual and semiannual harmonics to data from 1981-1983. Longer records (9-34 years) of monthly ASL indicate that these two harmonics adequately represent the long-term monthly average seasonal cycle and that the current measurement period is long enough to estimate the seasonal cycles. We characterize the differences between fall/winter and spring/summer as follows: For fall/winter, monthly mean winds north of 35øN are northward for 3-6 months (longer in the north than in the south); south of 35øN, the mean winds are near zero or weakly southward; monthly mean alongshore currents are northward over midshelf and shelf break at all locations sampled at depths of 35 m and deeper and are associated with high coastal sea levels and relatively warm water temperatures. For spring/summer, monthly mean wind stresses are southward at all latitudes for 3-6 months (longer in the south than in the north), sea levels are low, and water temperatures are relatively cool; monthly mean currents at 35 m depth over the shelf are southward for 1-6 months (longer at the shelf break than over midshelf and longer in the north than in the south), while the deeper currents are less southward or northward. The magnitudes of the seasonal cycles of all variables are maximum between approximately 38øN and 43øN, generally decreasing slightly to the north and greatly to the south. At each location the seasonal cycle of the alongshore current from 35 m depth at midshelf leads the sea level slightly and both lead the wind stress and temperatures by 1-2 months. The seasonal cycles of all variables show a south-to-north progression (south leads north by 1-2 months). At 48øN, annual mean currents at 50 m depth over the shelf break oppose the annual mean wind (northward wind and southward current). Similarly, at 35øN, annual mean currents at 35 m depth over both midshelf and shelf break are opposed to the annual mean wind (southward wind and northward current). From 35øN to 43øN, both summer and winter regimes are dominated by strongly fluctuating currents. 1507 1508 STRUB ET AL.: SEASONAL CYCLES OVER THE WESTERN U.S. CONTINENTAL SHELF

An eddy-stimulated hotspot for fixed nitrogen-loss from the Peru oxygen minimum zone

“…1a) consistent with prior observations (Codispoti and Christensen, 1985). Southward intensification of the OMZ along its northern boundary is associated with the poleward flow of the Peru Undercurrent (PUC) partly sourced in the lower equatorial undercurrent (Strub et al, 1987), comprising both the OMZ's core and the primary source of upwelled waters in this region. Onset of dissimilatory NO (1)…”

Nearshore circulation during upwelling inferred from the distribution of dissolved cadmium off the Oregon coast

“…4a), followed by increases in all upwelling tracer concentrations. Throughout the year, sustained periods of either poleward or equatorward winds were interrupted by wind relaxation or reversal events, which occur frequently at the Oregon coast (Peterson et al 1979;Huyer 1983;Strub et al 1987b;Barth and Smith 1998). Following brief wind relaxation events, surfzone P concentrations tended to decline rapidly while Cd concentrations and salinity remained relatively constant (e.g., August 1994, Fig.…”

“…6d). Along the western U.S. coast, the composition of the water column typically shifts to that of upwelling conditions in late spring, following several days of equatorward wind stress in excess of 2 dynes cm Ϫ2 (Strub et al 1987a). Increasing Cd and P concentrations in the surfzone indicate that this transition occurred in May in 1994 and 1995 (Fig.…”

Quantifying 20th Century Glacier Change in the Sierra Nevada, California

“…8). Winter air temperatures in this region are mild because of the moderating effect of the Pacific Ocean, and sea surface temperatures vary only a few degrees from an average of about 10 °C (Strub et al, 1987). Consequently, the low-elevation G&PS are increasingly subject to winter precipitation occurring as rain rather than snow as air temperatures approach 0 °C (Mote et al, 2005;Nolin and Daly, 2006;McCabe et al, 2007).…”