Chemical Mapping Results From RV Point Sur

The underway mapping system on the RV Point Sur continuously measured pCO2, NO3, and other species as the ship traced out a grid in the study area. pCO2 was measured once per minute, and NO3 every 30 seconds.

Figures 1 and 2 show NO3 concentration and pCO2 overlaid on AVHRR SST image #4 (acquired on April 21). The grid data was acquired between April 19 and April 26. Although the SST image is but a "snapshot" of a dynamic situation, correlations between chemistry and surface temperature are apparent.

Figure 1: NO3 and Sea Surface Temperature

Highest NO3 concentrations (>25 uM) are associated with the coldest SSTs north and west of Monterey Bay, and off Point Sur. Lowest values occur offshore outside of the most intense upwelling, and in the warm Monterey Bay water.

Figure 2: pCO2 and Sea Surface Temperature

Measured pCO2 values are positively correlated with NO3. Freshly upwelled water to the northwest of Monterey Bay shows pCO2 in excess of 770 uatm (present atmospheric values are about 360 uatm). The lowest values (~240 uatm) occur in the warm Monterey Bay water.

Figure 3: pCO2 versus Chlorophyll

Figure 3 is a scatter plot of near-surface chlorophyll and pCO2 for the grid. The low chlorophyll, high pCO2 samples are at the upwelling center. As chlorophyll increases, pCO2 decreases until values well below atmospheric levels are reached. As water warms offshore, pCO2 increases again.

Back to introduction