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fort point seawater sensors

Temperature, Salinity, Conductivity, Transmittance, Fluorescence

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Fort Point Seawater Observations
Seawater Temperature (deg F) 54.7
Seawater Temperature (deg C) 12.6
Seawater Salinity (PSU) 29.424
Seawater Fluorescence (raw) 0.038
Seawater Conductivity (S/m) 3.4708
Seawater Pressure (dbar) 1.74
Seawater Density (sigma-t kg/m3-1000) 22.155
Seawater Transmittance (raw) 0.053
Last update: Fri May 26 05:40:00 2017 PDT

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Seawater Conductivity

Conductivity is the measure of a material’s ability to conduct an electric current. In ocean sciences, the electrical conductivity of seawater is used as an indication of salinity. The saltier the water, the higher the conductivity will be. Seawater salinity can be calculated from measured values of conductivity and temperature.

Seawater Salinity

Salinity refers to the amount of salts dissolved in water, expressed as parts per thousand, or ppt. This corresponds to the amount of salt in grams dissolved in 1000 grams of water. However, salinity is difficult to measure directly and is generally calculated from conductivity and temperature measurements. The current accepted standard is the 1978 Practical Salinity Scale Equations and the units are Practical Salinity Units, or PSU.

Generally, salinity increases with depth. Water with higher salinity levels is denser and descends, causing a layering or stratified affect in the deeper water. At the surface, salinity is influenced by various factors, including fresh water input and evaporation. Precipitation and run off from streams and rivers cause decreased salinity levels, while heat and wind cause evaporation that tends to increase salinity levels. The area of distinct change between this dynamic surface layer and the deeper ocean is known as a halocline.

Researchers are interested in the impact salinity levels have on marine organisms. The life cycle and diversity of marine organisms in an area is dependent on the seawater characteristics. The effect of salinity is particularly noticeable in bays, estuaries and nearshore coastal areas with high salinity gradients.

Seawater Temperature

The temperature of seawater changes very gradually and its stability plays an important role in moderating global climate. Ocean current patterns move the heated water from the equator up toward the poles and move the cold polar water toward the equator thus moderating the seawater temperature.

Seawater temperature generally increases with depth. Colder water is denser and sinks, causing a layering or stratified affect in the deeper water. However, at the surface, the degree of stratification is influenced by factors including wind and tides. The area of distinct change between this dynamic surface layer and the deeper ocean is known as a thermocline.

In some coastal regions such as California, high winds cause upwelling. Strong seasonal winds drive warmer surface waters away from the coast, and this divergence draws the cold, nutrient rich water up from beneath the thermocline to the surface. Upwelling regions generally feature high productivity and therefore are of economic significance. Researchers may look at the impact of seawater temperature on marine oganisms, and use seawater temperature and wind measurements to study upwelling and climate change.

Seawater Fluorescence

Seawater fluorescence refers to the amount of Chlorophyll-a in the water. Phytoplankton uses this pigment to convert sunlight into organic compounds during photosynthesis. When excited by a certain wavelength of light, Chlorophyll-a will give off light, or fluoresce, at another wavelength and this effect can be measured.

Fluorescence is considered a good indicator of nutrient levels in the water. An increase in nutrients, such as nitrogen and phosphorous, lead to a corresponding rise in the phytoplankton population and thus Chlorophyll-a. This appears as an increase in fluorescence.

Seawater fluorescence is affected by temperature and turbidity, so these factors are generally taken into account during measurements.

Seawater Transmittance

Transmittance is a measure of water clarity. In the simplest terms, it indicates what percentage of light at a certain wavelength is transmitted through a certain distance of water. Water clarity can be affected by sediments, pollutants, and organic matter in the water. Seawater transmittance is of interest to researchers because the amount of light available beneath the sea surface can affect levels of primary productivity.

Fort Point Seawater Salinity Fort Point Seawater Conductivity Fort Point Seawater Temperature Fort Point Seawater Temperature Fort Point Seawater Pressure Fort Point Seawater Density Fort Point Seawater Transmittance Fort Point Seawater Fluorescence

Fort Point ctdInstrument Type: Sea-Bird Electronics SBE 16+ SEACAT

Description: Self contained conductivity and temperature sensor, with strain gauge pressure sensor. Pumped during sampling with SBE 5T submersible pump.

Location: Water sampled close to Fort Point pier, San Francisco.
Latitude 37° 48' 23.8674 N
Longitude 122° 27' 58.32 W

Installed: 10/8/2004

Specifications: Temperature
Range: -5 to +35 °C
Resolution: 0.0001 °C
Accuracy: 0.005 °C

Specifications: Conductivity
Range: 0 to 9 S/m
Resolution: 0.00005 S/m
Accuracy: 0.0005 S/m

Specifications: Pressure
Range: 0 to 44 psu
Resolution: 0.002 % of full scale range
Accuracy: 0.1% of full scale range

Acquisition Settings:
Sample interval = 60 seconds, 10 measurements per sample
Pumped during sample, with 10 second warm up

Fort Point transmissometer

Instrument Type: WETLabs C-Star Transmissometer

Description: The C-Star measures light transmittance at a single wavelength
over a known path. The LED light source provides light that transmits within
a narrow bandwidth. A portion of the transmitted light is monitored by a
reference detector and used in a feedback circuit to account for variations
in the LED source over time, as well as changes in the instrument’s internal
temperature. The light transits the sample volume and enters the receiver
optics, where it passes through additional focusing optics and finally
strikes a silicon photodiode detector which converts the amount of received
light to a corresponding 0–5 V analog output signal which represents the
amount of light received. The ratio of light gathered by the receiver to
the amount originating at the source is the beam transmittance.

In general, losses of light propagating through water can be attributed to
two primary causes: scattering and absorption. Suspended particles,
phytoplankton, bacteria and dissolved organic matter, as well as the
intrinsic optical properties of the water itself, all contribute to the
losses sensed by the instrument.

Location: Water sampled at Fort Point pier, San Francisco.
Latitude 37° 48' 23.8674 N
Longitude 122° 27' 58.32 W

Installed: 10/8/2004

Wavelength: 660 nm
Pathlength: 25 cm
Sensitivity: 1.25 mV
Beam Divergence: 0.8° in water
Bandwidth: ~ 20 nm

Acquisition Settings:
Sample interval: 60 seconds
Measurements per Sample: 1

Fort Point flourometerInstrument Type:  Seapoint Chlorophyll Fluorometer

Description: High performance instrument of in situ measurements of chlorophyll a.  The open sample volume has good ambient light rejection and a low temperature coefficient.

Location: Water sampled at Fort Point pier, San Francisco.
Latitude 37° 48' 23.8674 N
Longitude 122° 27' 58.32 W

Installed: 10/8/2004

Excitation Wavelength:  470 nm peak, 30 nm FBHM
Emission Wavelength:  685 nm peak, 30 nm FBHM
Sensing Volume:  340 mm3
Min. Detectable Level:  0.02 µg/l
Operating Temperature:  0 to 65 °C
Temperature Coefficient:  <0.2 % / °C

Acquisition Settings:
Gain:  3x; 0.1 V / (µg/l)
Internal low-pass filter of 0.1 second time constant
Data logged at 10 second intervals, no averaging