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Adaptive Sampling of Phytoplankton Responses to Episodic Physical Forcing in the Nearshore Coastal Ocean: Characterizing the Significance of Convergences in Upwelling Eddies.

July 1999 - July 2003

Project Summary:

Characterizing the impact of episodic events in time and space is critical to biogeochemical processes given their disproportionately large role in structuring planktonic foodwebs.  However, our understanding of these impacts has largely been impeded by limited sampling capabilities.  In the coastal ocean, these events include frontal boundaries, upwelling areas and convergence/divergence zones.  Peak biological activity occurs in conjunction with these phenomena by stimulating planktonic growth and/or concentrating biomass by advective transport. Furthermore, these events often demarcate transitions between distinct planktonic communities.  In the nearshore coastal ocean, the scales of interest of these physical processes are on the order of meters to kilometers and from hours to days, reflecting the relevant spatial/temporal timescales for phytoplankton bloom dynamics.

  Figure 1
 

Figure 1. Offshore transects of fluorescence from July12, 2001 (A) and from July 31, 2001 (B), demonstrating the difference in phytoplankton distribution between stratified (A) and predominately downwelling conditions (B). Upper values on scale bar apply to (A) and lower values for (B).

   

During this study a number of different sampling platforms were utilized in order to examine the relationship between episodic events, physical forcing and phytoplankton community dynamics (Figure 1). Furthermore the degree to which remote sensing can be applied to examine these processes was assessed. Cross platform comparisons are being made in order to determine the optimal ground sampling scales required to adequately characterize coastal processes (Figure 2).

  Figure 1
 

Figure 2. A composite of three ocean color satellite images (A- FY1-C; B- Oceansat and C- SeaWiFs) taken simultaneously over the study site on July 31, 2001.

   

This study has made it possible to examine some of the limitations in validation of remotely sensed products.  With new sensor development, such as the PHILLS, the ground resolution of remote sensing has surpassed our ability to sufficiently characterize a given space with point measurements.  This has been especially true in coastal regions where significant variability (order of magnitude) can occur within meters. As a result of the PECASE award, we developed a new tool to spatially validate remote sensing imagery (aircraft and/or satellite) over relevant scales in coastal waters.  We have taken a platform that we developed through an ONR program and adopted it for measurement of apparent and inherent optical properties.

  Figure 1
 

Figure 3. PHILLS RGB Mosaic of the region off of the West Florida Shelf. Image shows the trackline of the REMUS AUV (white line). Red line indicates the hyperspectral data that was used in this study (A). Comparison between mean PHILLS remote sensing reflectance and estimated mean reflectance from the REMUS AUV across the transect line (B).

   

The platform is an autonomous underwater vehicle that navigates on centimeter accuracy using acoustic navigation and is equipped with multispectral upward looking Ed sensors and downward looking Lu sensors for estimation of remote sensing reflectance that can be compared with remote sensing reflectance measured by remote platforms (Figure 3). Initial efforts used constant depth missions for comparison to in situ instrumentation and airborne and satellite platforms, future efforts will focus on the ability of the vehicle to quantify vertical differences in water column properties. Quantifying the small depth differences in apparent optical properties throughout the water column, with attention to the near surface, will lead to direct estimates of nLw and Rrs for comparison with above-water data.

People Involved:

  • Dr. Mark Moline, Principal Investigator
  • Shelley Blackwell, Research Associate
  • Ian Robbins, Graduate Student
  • Matt Oliver, Graduate Student
  • Cristina Orrico, Graduate Student

Related Information:

President Honors Scientists and Engineers in Awards Ceremony

IMCS

 

Research Funded by:

NOAA