The seasonal cycle of wind stress curl and its relationship to subsurface ocean temperature in the Northeast Pacific

Murphree, Tom; Green-Jessen, Phaedra; Bograd, Steven J.

doi:10.1029/2002gl016366

Cited by 19 publications

(24 citation statements)

References 15 publications

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“…However, since the thermocline is strongly tied to the seasonal cycle of wind stress curl along the coast, it is also possible that the observed lag could be related to a slower ocean response to weaker (or negative) wind stress curl in the offshore region relative to the stronger positive curl near the coast year‐round. Wind stress curl also peaks later in the year away from the coast, and its effect on the depth of the thermocline is less clear there [ Murphree et al , 2003].…”

Section: Discussionsupporting

confidence: 86%

Long‐term and seasonal trends in stratification in the California Current, 1950–1993

et al. 2004

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[1] State-space model decomposition of subsurface temperatures from the World Ocean Database is used to detect and characterize changes in thermal stratification in the upper 200 m of the California Current System (CCS) over the period . Model results are analyzed at eight locations representing the meridional and offshore extent of the CCS between 31°N and 40°N. Thermocline strength, depth, and temperature are derived from the mean-level trend term and the seasonal component of the state-space models. Over the 44 years, the mean level of the coastal thermocline strengthened and deepened, while it weakened and shoaled offshore. These tendencies are likely the result of geostrophic adjustment to changes in basin-scale circulation, as well as to a long-term increase in upper ocean heat content of 2-9% throughout the study area. Reduction in nutrient inputs to the surface layer resulting from these climate signals are a likely explanation for the pronounced decline in biological production in CCS ecosystems observed over the same period. Substantial decadal variability superimposed on these linear tendencies may play a role in determining the response of the upper ocean to interannual events such as El Niño. The seasonal component of thermocline depth and strength exhibited a high degree of nonstationarity, with alternating periods of weakened and enhanced annual cycles lasting 3-5 years, along with changes in the phase. This changing seasonality may have implications for marine species whose life cycles are closely tuned to the seasonal cycle.

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Section: Discussionsupporting

confidence: 86%

Long‐term and seasonal trends in stratification in the California Current, 1950–1993

et al. 2004

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“…The strong seasonality seen in CCS subsurface temperatures is driven largely by the annual cycle of winds, particularly the evolution of the alongshore wind stress which drives coastal upwelling and wind stress curl [ Bakun and Nelson , 1991; Hickey , 1998; Kelly et al , 1998; Murphree et al , 2003]. Local wind‐forcing of the CCS is, in turn, linked to basin‐scale atmospheric processes [ Strub and James , 1988].…”

Section: Discussionmentioning

confidence: 99%

“…It is well known that the CCS is characterized by strong seasonality in upper ocean circulation and thermal structure [ Lynn and Simpson , 1987; Hickey , 1979, 1998], driven primarily by the seasonal cycle of large‐scale atmospheric forcing [ Strub and James , 1988; Bakun and Nelson , 1991; Winant and Dorman , 1997; Kelly et al , 1998; Murphree et al , 2003]. Thus climate variability might also be expected to affect the phase (timing and length) or amplitude of important seasonal processes, such as coastal upwelling and the “spring transition” from winter conditions [ Lynn et al , 2003].…”

Section: Introductionmentioning

confidence: 99%

Nonstationary seasonality of upper ocean temperature in the California Current

2004

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[1] State-space models are used to examine long-term changes in the seasonal amplitude and phase of upper ocean temperatures from a set of time series representing the meridional and offshore extent of the California Current System (CCS). We use global one-degree summaries from the World Ocean Database at 11 locations and 10 standard depths in the upper 200 m for the period 1950-1993. The seasonality of upper ocean temperature in the CCS is highly nonstationary, with significant interannual to decadal changes in seasonal amplitude and phase apparent over the period of study. The 1950s and early 1990s were characterized by high seasonal variability in upper ocean temperatures, while the intervening years were characterized by a reduced seasonal cycle. Long-term changes in phase were also observed, with seasonal extrema occurring 1-2 months earlier in the year by the 1990s. The leading common seasonal components, dominated by the longer (yearly, 6-month, 4-month) periodicities, explain most of the seasonal fluctuations in the temperature series and partition the variance into well-defined dynamic regions. In particular, long-term changes in seasonality at 30-75 m in the major coastal upwelling centers (34°N-38°N) differed from that observed north of Cape Mendocino, within the Southern California Bight, and farther offshore. The observed spatial patterns suggest that the changes in temperature seasonality off central California reflect a significant lowfrequency modulation of the intensity, timing, and duration of coastal upwelling in the CCS. This nonstationarity of the seasonal temperature cycle is superimposed on both a region-wide warming trend and spatially heterogeneous responses to low-frequency climate events, such as regime shifts and El Niño events. Results from this study demonstrate that the character and potential biological impacts of climate variability can only be fully realized by considering a nonstationary, nondeterministic seasonal cycle.

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“…The CRP entrains particles up to 50 km north and south of the river mouth and within this latitudinal range, increases dispersion of particles across the continental shelf by 25% (Banas et al, 2009). In central and northern California, dispersion is primarily driven by upwelling produced by Ekman Transport and wind-stress caused by cross-shelf pressure gradients between the North Pacific High and Continental Thermal Low-pressure systems (Huyer, 1983;Murphree et al, 2003). Upwelling is typically most intense from April to June and varies along the coast at the scale of topographic features that influence coastal winds (Garc ıa-Reyes and Largier, 2012).…”

Section: Introductionmentioning

confidence: 98%

Early ocean distribution of juvenile Chinook salmon in an upwelling ecosystem

Hassrick

Henderson

Huff

et al. 2016

Fisheries Oceanography

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Extreme variability in abundance of California salmon populations is often ascribed to ocean conditions, yet relatively little is known about their marine life history. To investigate which ocean conditions influence their distribution and abundance, we surveyed juvenile Chinook salmon (Oncorhynchus tshawytscha) within the California Current (central California [37°30 0 N) to Newport, Oregon (44°00 0 N]) for a 2-week period over three summers (2010)(2011)(2012). At each station, we measured chlorophyll-a as an indicator of primary productivity, acoustic-based metrics of zooplankton density as an indicator of potential prey availability and physical characteristics such as bottom depth, temperature and salinity. We also measured fork lengths and collected genetic samples from each salmon that was caught. Genetic stock identification revealed that the majority of juvenile salmon were from the Central Valley and the Klamath Basin (91-98%). We constructed generalized logistic-linear negative binomial hurdle models and chose the best model(s) using Akaike's Information Criterion (AIC) to determine which covariates influenced the salmon presence and, at locations where salmon were present, determined the variables that influenced their abundance. The probability of salmon presence was highest in shallower waters with a high chlorophyll-a concentration and close to an individual's natal river. Catch abundance was primarily influenced by year, mean fork length and proximity to natal rivers. At the scale of sampling stations, presence and abundance were not related to acoustic indices of zooplankton density. In the weeks to months after ocean entry, California's juvenile Chinook salmon population appears to be primarily constrained to coastal waters near natal river outlets.

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The seasonal cycle of wind stress curl and its relationship to subsurface ocean temperature in the Northeast Pacific

Cited by 19 publications

References 15 publications

Long‐term and seasonal trends in stratification in the California Current, 1950–1993

Long‐term and seasonal trends in stratification in the California Current, 1950–1993

Nonstationary seasonality of upper ocean temperature in the California Current

Early ocean distribution of juvenile Chinook salmon in an upwelling ecosystem

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