Geoscience Reference
In-Depth Information
and recover from rapid and extreme biasing (interferences) causing photo-detector/sensor
output saturation. Choosing the proper sensor design and deployment platform can be chal-
lenging in these systems. Questions must be raised regarding instrument gain, whether or
not the sensor will be submerged during the entire deployment time (e.g., drought-prone
or tidal rivers/estuaries), and if the optical system is strong enough to tolerate the physical
energy of the environment (e.g., crashing waves or corrosion in acidified lakes). Analysts
want to ensure not only high-data quality of fluorescence measurements, but also that their
sensors will remain securely in place during extended deployments (e.g., moorings or on
vertical profilers).
6.6 Revolutionizing NOM Studies via High-Resolution
Fluorescence Measurements
The development of
in situ
fluorometers has led to the ability to examine NOM on spatial
and temporal scales of traditional hydrographic parameters such as temperature and salinity.
This has enhanced biogeochemical studies in a manner similar to how chlorophyll fluorom-
eters have impacted biological oceanography (Geiskes et al.,
1978
). As a result, improved
understanding of processes such as tidal flushing and DOM outwelling from mangroves
and salt marshes; groundwater DOM sources to coastal and fresh waters; photochemical
and biodegradation pathways that affect NOM distributions and quality; and benthic fluxes
of sedimentary OM and hydrocarbon seeps have taken place. Continued understanding of
OM cycling over varying spatial or temporal scales at land-ocean interfaces, sediment-
water interfaces, or during episodic events will be made possible by deploying small, low-
power, high-sensitivity, robust fluorescence sensors via a variety of sensor platforms.
6.6.1 Deployment Platforms
Scientists and engineers never cease to develop new and clever means of obtaining optical
measurements, thereby increasing the ways field sensors are deployed in natural waters.
Novel sensor platforms and deployment strategies have revolutionized the community's
ability to obtain NOM measurements and understand the NOM pool (Twardowski et al.,
2005
). Just like with sensor choice, analysts must choose a platform that aligns well with
sampling design. Hence consideration must be given to length of deployment, spatial and
temporal variability of environment, power requirements, sensor size and stability, data
logging methods, and optimal sampling rates. In addition, one must ensure that sensor
placement and orientation on a platform does not interfere with its performance (e.g.,
objects within the optical path or altered water circulation near sensor).
6.6.1.1 Spatial Resolution
Common tethered platforms utilized from ship deck include vertical profilers, towed vehi-
cles, and pumped flow-through systems, which can accommodate most commercially
