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FastOcean APD FRRf原位剖面测量

FastOcean APD原位藻类荧光仪的应用:

水下原位剖面测量、升降式浮标定时测量、水下原位定点定时测量

The RV Atlantis seawater flow through system is modified for all NAAMES field campaigns. Specifically, a Teflon lined diaphragm pump is installed prior to a given cruise just aft of the seawater intake at the bow in order to bypass the ship’s impeller pump which would otherwise impact the sampled plankton populations (Cetini′c et al., 2016). Whole seawater from the diaphragm pump is plumbed through clean tubing to multiple instruments in the laboratory, including a custom Fast Rate Repetition fluorometer (FRRf, excitation wavelength is 490 nm) for measuring initial fluorescence (Fo), maximal fluorescence (Fm), and PSII functional cross sections (sPSII) (Behrenfeld et al., 1998). Values of Fo, Fm, and sPSII reported here represent averages for 16 individual single turnover flash sequences only for nighttime measurements to eliminate variability associated with daytime NPQ. Daytime FRRf measurements (data not shown) indicated inverse changes in initial and maximal fluorescence with changes in incident sunlight that are consistent with expected protective and reversible NPQ processes in the photosynthetic pigment bed and will not be discussed further here.Buoyancy Frequency From May 22–24th a low-pressure system with wave heights estimated to be ~9m moved through the targeted study region and was subsequently replaced by a high-pressure system from the northwest (Figures 1A,B) (NOAA Ocean Prediction Center — http://www.opc.ncep.noaa.gov/Atl_tab.shtml). Deepwater entrainment during the passing storm was evidenced by the nearly homogenous profile of Brunt–Väisälä or buoyancy frequency to 200m observed during the initial CTD cast made in this watermass (Figure 2A). It is unlikely that the stormprovided the energy to mix the water column down to 200m or greater. A more probable scenario, albeit without data to confirm this, is that a shallow stratified layer was mixed into an existing deeper and actively mixing layer, thereby homogenizing properties to greater than 200m (Dr. Peter Gaube personal communication). From May 24th through May 27th, buoyancy frequency profiles indicated rapid re-stratification of the water column, with active mixing rarely penetrating below 25m (Figure 2A). Of the seven algorithms used to estimate the active mixing depth, only the density gradient approach provided a result consistent with Brunt–Väisälä frequency distributions .

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