Trinidad Head Line

THL sample graphSince late 2006, ocean observing along the Trinidad Head Line has been a core element of the mission of NOAA Fisheries’ Cooperative Fisheries Oceanography Research Team (CFORT) at Humboldt State University (HSU), and serves to provide information on the state and dynamics of the coastal ocean off northern California. Data collected along the Trinidad Head Line has already contributed to efforts to develop a more holistic understanding of the California Current System and its responses to climate variability (e.g., McClatchie et al. 2008, 2009, Bjorkstedt et al. 2010).

The Trinidad Head Line lies due west of the Humboldt State University (HSU) Telonicher Marine Laboratory in Trinidad, California (Figure 1). The transect includes three stations (TH01 to TH03) located over the continental shelf, which is narrow in this region, and additional stations beyond the shelf break, of which three (TH04 to TH06) are regularly occupied during our surveys. Most surveys of the Trinidad Head Line have been carried out aboard HSU’s R/V Coral Sea, but our time series also includes data collected by colleagues and collaborators who have graciously sampled the Trinidad Head Line in the course of large scale, coast-wide surveys.

Our typical cruise plan calls for occupying the six stations (TH01 through TH06) during a 12 hour cruise. Early in our time series, we sought to conduct all of our sampling at night, but since late 2008, we have carried out our surveys so that the nearshore stations, for which the entire water column is sampled, are occupied in the late afternoon and the offshore stations, which lie in deeper water, are occupied after nightfall to facilitate capture of important taxa (e.g. euphausiids) that undergo diel vertical migrations.

At each station we conduct a hydrographic cast to 150 m depth (or to within 5-10 m of the sea floor, depending on sea state) to collect data on temperature, salinity, fluorescence (a proxy for chlorophyll a concentration), dissolved oxygen (DO) concentration, photosynthetically active radiation (PAR) and water clarity (transmissivity) through the water column. We also collect up to six discrete water samples from selected depths which are subsequently used to assay concentrations of chlorophyll a and several key macronutrients (e.g., nitrate). Hydrographic data are subsequently analyzed to construct cross-shelf vertical sections of hydrographic properties along the transect (see links below). An underway flowthrough system provides high-resolution data on near-surface temperature, salinity, fluorescence and turbidity along the ship’s track.

At each station, we also collect zooplankton samples with (1) oblique tows of a standard CalCOFI bongo net frame fitted with 505 µm mesh and 335 µm mesh nets, and (2) vertical tows of a half-meter ring net fitted with 202 µm mesh net. In both cases, nets are fished from a depth of 100 m (or within 5-10 m of the seafloor depending on sea state) and are fitted with flowmeters to provide information on the volume of water filtered in collecting each sample. Samples are preserved in either 5% buffered formalin (505 µm mesh bongo net and ring net samples) or 95% ethanol (335 µm mesh bongo samples), and are subsequently processed to extract information on copepod abundance and diversity of copepods, euphausiids, larval fishes, and other key zooplankton taxa.

Contact: SWFSC Fisheries Ecology Division, Cooperative Fisheries Oceanography Research Team (CFORT)

Hovmoller plots