Quantifying temporal and spatial variability of nearshore processes around a nearshore kelp forest rocky reef with the KFA cabled observatory

Oceanographic data from the Kelp Forest Array (KFA) cabled observatory is used to determine the frequency, intensity, duration and seasonal variation of low-pH and low-DO events, and relate them to temperature and density variability associated with internal waves and upwelling. We employ standard time series analyses, to determine the frequency distributions of variance in pH, DO, and T and coherence analysis to identify frequency dependent co-variability among the three variables. Statistical analysis is used to identify the probability of a hypoxic event of given strength (e.g., DO < 4.5 mg/l17) lasting for a given duration and compare this between habitats. Joint probability distribution functions of low-pH and low-DO are computed from the data in the same way. This approach can be used to identify the likelihood of extreme events with respect to specific DO and pH thresholds of physiological relevance for species of interest in MPAs.

The time scales and vertical structure of velocities, temperature, and dissolved oxygen associated with low-DO events are analyzed to determine the dominant transport mechanisms for these events and how they are tied to internal shoaling waves prevalent in the southern part of Monterey Bay.

Our work in 2015 is contextualized by multi-year data sets from the three previous years which contain observations of both upwelling and non-upwelling periods. Long-term instrumentation attached to the KFA main node include a 1200 KHz ADCP, a CTD with transmissometer, oxygen optode, and fluorometer (Chla), a Satlantic SeaFET pH sensor, and a PME temperature and dissolved oxygen string (DO/T chain).