Assessing controls on cross‐shelf phytoplankton and suspended particle distributions using repeated bio‐optical glider surveys

Abstract

Characterizing the space/time variability of bio‐optical properties is essential to understand the mechanisms that control cross‐shelf phytoplankton and suspended particle distributions in coastal waters. Approximately 400 high‐resolution cross‐shelf sections of bio‐optical properties collected with an oceanographic glider in the coastal Santa Barbara Channel, California, revealed complex relationships among optical properties and environmental conditions. Surface waves were found as a proximate control on suspended sediment variability for both inner and midshelves. Increases in phytoplankton abundances attributed to horizontal advection and upwelling events were observed only on episodic time scales. The lack of all‐encompassing linear relationships between environmental forcings and changes in cross‐shelf phytoplankton highlights the challenge of decoupling bio‐optical signals from their controlling processes in coastal zones where phytoplankton distributions are patchy, and where nearshore and offshore phytoplankton populations and suspended sediments often occupy the same portion of the water column. Clear relationships between runoff and productivity were not observed. Temporal variability of suspended particles and phytoplankton distributions were roughly independent from each other during stratified conditions. Synchronous increases in phytoplankton and suspended sediments were observed when associated with strong upwelling events that may induce mixing and promote productivity. The repeated glider sections illustrated many processes regulating phytoplankton and particle transport in the innershelf and showed the difficulty in establishing general connections between high‐frequency changes in optical properties and potential environmental forcings in a complex coastal environment.

A Time Series of Water Column Distributions and Sinking Particle Flux of Pseudo-Nitzschia and Domoic Acid in the Santa Barbara Basin, California

“…In order to examine the role of upwelling on Pseudo-nitzschia abundance and DA toxicity, upwelling events were defined as the shoaling of the 12 °C isotherm above 30 m at Station 4 ( Figure 2 ). During the study period, the mixed layer depth ranged from 5 m to 60 m. Note that the specific mechanisms that induce upwelling, e.g., wind direction and strength as well as mesoscale eddies, require a more detailed analysis of basin physics, such as cross-shelf transport and eddy strength [ 60 ]. These analyses are beyond the scope of the present study.…”

Global Perspectives on Observing Ocean Boundary Current Systems

“…Measurements of pressure, temperature (Figure 1D), conductivity, and depth-average currents are standard, enabling estimates of absolute geostrophic transport and other physical parameters at relevant scales in boundary currents. Measurements of biooptical (e.g., Niewiadomska et al, 2008;Henderikx Freitas et al, 2016) and bio-acoustic properties (e.g., Baumgartner and Fratantoni, 2008;Van Uffelen et al, 2017), dissolved oxygen (e.g., Figure 1E; Perry et al, 2008), nitrate, turbulent microstructure (St. Laurent and Merrifield, 2017), and velocity profiles ( Figure 1F; are becoming increasingly common. The main constraints on sensors for gliders are the requirements for small-size, low-power consumption and multimonth stability.…”

Temporal and Spatial Dynamics of Physical and Biological Properties along the Endurance Array of the California Current Ecosystem

“…The similarities and differences between chl and b bp spatial and temporal distributions indicate variability in the types of materials dominating optical properties at the different moorings. Biogenic particles typical of productive pelagic oceanic environments have large chl and low-to-moderate b bp values, whereas waters dominated by minerogenic particles have high b bp and low chl concentrations (Henderikx Freitas et al, 2016). Thus, the relationships between b bp and chl in Figure 4b for samples collected between May and September at both lines indicate that nearshore b bp estimates are more likely (e-l): cross-shore salinity profiles along the WA (e-h) and OR (i-l) lines where the white contours are the 32 and 32.5 psu isohalines; (m-t): cross-shore CDOM profiles along the WA (m-p) and OR (q-t) lines, where the white lines are the 0.75 and 1.25 ppb contours.…”