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Profiling in situ Absorption in the Monterey Bay with the ICAM

Application(s)

Absorption

On October 7th 2014, Turner Designs’ Product Specialist Luke Beatman participated in a research cruise on Monterey Bay with the cooperation of Raphael Kudela’s Biological Oceanography Laboratory at UCSC.  The intentions of the cruise were to characterize resident phytoplankton populations and make determinations as to how they are affected by the dynamics of Monterey Bay.  Cruises such as this one often visit historical ocean stations to monitor how conditions have changed over time with respect to biological variables such as chlorophyll a concentration and the relationship to physical variables such as salinity and temperature.  On this cruise, 3 stations were visited with the expectations of encountering significantly different oceanographic environments.  At each station, the ICAM was cast down the wire of the R/V John H. Martin to a depth of 50 meters.

mbari-1

mbari-data

ICAM absorption profiles for blue and red wavelengths plotted above clearly show a subsurface chlorophyll maximum (SCM), the depth at which maximum absorption occurs, for all stations.  The SCM is indicative of high algal abundance at the maximum absorption depth.   The weak signal for station 1 is expected as seen in historical data profiles, as you leave the bay, algal abundance decreases.  As you approach the near shore environment algal abundance increases as seen in the next two station profiles.  Station 2 showed a well defined profile with the strongest signal recorded for algal abundance (i.e. most of the absorption signal is due to algal absorption; very little interference from other absorbing compounds).  Station 3 also showed a strong response for absorption.  However, due to pollution and runoff into the bay and near-shore mixing, interfering materials such as dissolved organics or other compounds add to the absorption signal, making it difficult to determine how much of the absorption is due to algae.  With extreme sensitivity and indifference to scattering, the ICAM is the ideal instrument to measure absorption in near-shore environments such as Monterey Bay.

Contact

  • Author: Luke Beatman (Turner Designs) & Raphael Kudela (UCSC)

Location

Monterey Bay, CA, USA