Field Methods

Bottle Sampling

The tide gauge room near the end of Scripps Pier houses the La Jolla Shore Station sampling equipment: a pulley-operated bottle sampler, Niskin bottles for collecting bottom water, and a calibrated digital thermometer. A well extending through the base of the pier enables sampling bottles to be lowered in virtually any weather conditions.

Page 1 of Scripps Pier time series, beginning 22 August 1916. [click for full page view]

Page 1 of Scripps Pier time series, beginning 22 August 1916. [click for full page view]

For other stations that sample from piers, the sampling bucket is lowered outside the breaking surf or near the end of the pier. For beach stations without piers, the sampler wades out to knee high depth (in calm conditions) and uses a pole sampler or casts the bucket out to deeper water to collect the sample.

Surface Measurements

An insulated sampling bucket is used to collect surface water (approximately 0.5 meter depth) and a calibrated digital thermometer is immediately placed inside the bucket to measure SST to the nearest 0.01ºC. Temperature measurements are rounded up and reported to 0.1ºC. For salinity measurements, surface water is poured into glass bottles with airtight seals after rinsing 3x with sample water.

Near-bottom Measurements (Scripps Pier only, depth approx. 5m)

A Niskin bottle is used for the collection of bottom water at the Scripps Pier location only. The Niskin bottle is lowered to the bottom and is raised ~1 meter off the bottom. A messenger is sent down the line to trip the bottle and collect the sample at depth. Once back at the surface, a digital thermometer is immediately immersed in the Niskin bottle and the temperature is measured to the nearest 0.01ºC. Temperature measurements are rounded up and reported to 0.1ºC. Seawater is drained from the Niskin bottle into glass bottles with air tight seals, after rinsing 3x with sample water.

Instrumentation

Temperature

1916 – 2008:
Although early records on methods and instrumentation are scarce, glass mercury thermometers were the scientific standard during the late 19th century and well into the 20th century. At Scripps Pier the earliest measurements were recorded in tenths of a degree Celsius (0.1°C), but no information can be found on calibration techniques.

From 1956 on, records indicate ocean temperature measurements were taken using precision engraved stem mercury immersion thermometers with 0.1°C divisions. The primary source was Kahl Scientific Instruments Corporation, a local San Diego County manufacturer established in 1935. The instruments were calibrated against certified primary standards during the manufacturing process. Instruments used at Scripps Pier and Farallon Islands were recalibrated by the Oceanic Data Facility at SIO in a water bath with 0.01°C temperature control.

2008 – present:

In December 2008 the program switched to digital thermometers because of the mercury ban in the state of California. The thermometers read in hundredths of a degree Celsius (0.01°C) and measurements are rounded to the nearest tenth of a degree.

Salinity

Saltwater samples are analyzed at Scripps Institution of Oceanography on an inductive salinometer, Guideline Model 8410. The Guildline PortASal is calibrated before and after each group of samples with an SIO seawater standard. Periodic checks on the conductivity of the SIO seawater standard are made by comparison with IAPSO Standard Seawater. Salinity values are read to four decimal places (0.0001), and are calculated using the algorithms for the Practical Salinity Scale, 1979 (UNESCO, 1981a). Salinity values are rounded up to two decimal places (0.01) after conversion to PSU and reported to two decimal places.