Periodic motions of the seasonal thermocline along the southern California coast

Cairns, James; LaFond, E. C.

doi:10.1029/jz071i016p03903

Cited by 32 publications

(12 citation statements)

References 2 publications

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“…Given what has been observed at other locations (Pineda 1995, Kunze et al 2002, Hall & Carter 2011, we hypothesize that during the period of falling temperatures, temperature was driven down by cold internal tidal bores propagating up the canyon and onto the shelf. As tidal energy decreased following the spring tide, the internal waves likely became smaller, causing less disruption of the thermo cline until the thermocline reformed near neap tide (Cairns & LaFond 1966, Kropfli et al 1999, whereupon the internal waves were evident as waves of depression on the thermocline (Lee 1961). We hypothesize that these waves transported warm water up the canyon and onto the shelf, generating the warm periods in the fortnightly temperature cycle.…”

Section: Potential Transport Mechanismsmentioning

confidence: 99%

Onshore transport of plankton by internal tides and upwelling-relaxation events

Shanks¹,

Morgan²,

MacMahan³

et al. 2014

Mar. Ecol. Prog. Ser.

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Identifying biophysical mechanisms of larval transport is essential to understanding the delivery of larvae to adult habitats. In addition, harmful algal blooms (HABs) can be transported onshore from populations that form offshore. In summer 2011, we measured sea surface and bottom temperatures and daily phytoplankton abundance and intertidal cyprid (barnacle post larvae) settlement at Carmel River State Beach, California, USA. Using time-series analysis, we compared the abundance of Pseudo-nitzschia spp. and daily cyprid settlement to physical forcing mechanisms (e.g. internal tides and upwelling-relaxation events) that could generate onshore delivery. Minimum bottom water temperature was significantly cross-correlated with the spring−neap tidal cycle; minimum temperatures occurred between neap and spring tides, and maximum temperatures were recorded around neap tides. When the temperature data were transformed to remove the relationship between tides and temperature, we found significantly higher maximum sea surface temperatures during upwelling-relaxation events. We observed 4 pulses in Pseudo-nitzschia spp. abundance. Pseudo-nitzschia spp. chains were longest at the start of pulses and then decreased, suggesting that they had been transported to shore from a more productive site offshore, likely the upwelling front. Pulses occurred during periods of maximum sea surface temperature associated with upwelling-relaxation events. In contrast, cyprid settlement was significantly cross-correlated with the spring−neap tidal cycle, with settlement peaks occurring during fortnightly periods of cold bottom temperatures; onshore transport of cyprids appears to have been due to the internal tides.

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Section: Potential Transport Mechanismsmentioning

confidence: 99%

Onshore transport of plankton by internal tides and upwelling-relaxation events

Shanks¹,

Morgan²,

MacMahan³

et al. 2014

Mar. Ecol. Prog. Ser.

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“…On the other hand, wind forcing explains diurnal and lower frequency temperature variability (Cairns and LaFond, 1966;List and Koh, 1976;Dorman and Palmer, 1981). Ekman upwelling is weak in the Bight nearshore (Winant and Bratkovich, 1981;Jackson, 1986), but energetic in northern Baja California (Barton and Argote, 1980).…”

Section: Introductionmentioning

confidence: 99%

Temperature, stratification and barnacle larval settlement in two Californian sites

Pineda

López

2002

Continental Shelf Research

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Barnacle settlement was monitored in two sites 100 km apart along the coast of Alta and Baja California. In five periods of observations completed between 1991 and 1996, Chthamalus spp., Pollicipes polymerus, and Balanus glandula settlement was consistently higher in the northern site, La Jolla (LJ), than in the southern site, La Salina (LS). For Chthamalus, the most abundant settler, settlement was higher in LJ in 58 out of 60 paired dates, by a mean factor of 141. In 1996, time series of temperature in about 15 m of water showed that the stratification was 72% higher, on average, and that the thermocline was shallower in LJ than in LS. Spectra of temperature showed that internal motions of tidal and higher frequencies were more energetic and closer to the surface in LJ compared to LS. In LJ changes in settlement were positively correlated with changes in stratification. These results suggest that high-frequency internal motions are important in the onshore transport of larvae. Low-frequency cooling events recorded in LJ apparently caused the energetic semidiurnal temperature variability to migrate from the bottom towards the surface, leading to the surface manifestation of the internal tide and surface internal tidal bores, which indicates that the surface nearshore bores occur in response to the shallowing of the thermocline. Tidal and higher frequency internal motions were more energetic when the thermocline was shallow during the low-frequency cooling events, than when it was deep and relatively weak during ordinary conditions. The major cooling event in LJ correlated with the local wind, suggesting local wind-driven upwelling. On the other hand, correlation of LS temperature with LJ temperature, winds, and sea level suggest propagation from the South. These results suggest that the low-frequency drops in temperature that modulate the nearshore internal tidal bores are caused by a combination of the local wind and events that propagate poleward, possibly as coastally trapped waves. r

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“…Others, including Reid [1956), Cairns and La Fond [1966), and Cairns and Nelson [1970), have related the temperature variations to wind and ticlal motions. Recent studies by Apel et al [1975) seem to indicate that internal waves may be tidally generated, as proposed by Zeilon [1934), and that the rapid temperature changes could be caused by internal surf, as predicted by De/ant [1950].…”

Section: Introductionmentioning

confidence: 99%