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by cassandra21 » Fri Jan 20, 2023 2:34 pm America/New_York
Usually PIC algorithms are related with coccolitophores. However, some species of zooplankton also incorporate CaCO3 in their skeleton so how can we be sure that the concentrations and/or variability of PIC that we observe in the satellite imagery (MODIS) reflect only phytoplankton (coccoliths) and not other zoo species?
The PIC algorithms are based on the light scattering properties of coccolithophorids, primarily Emiliania huxleyi. Because of their larger size and generally lower population density in the water column, calcareous zooplankton are unlikely to significantly influence the ocean optical characteristics of surface waters. The PIC algorithm was refined by experiments in which an overpass coincided with the release of chalk from a ship, in experiments called "Chalk-Ex", so the algorithm is specifically attuned to the light scattering and reflective properties of coccolithophorids and coccoliths.
by cassandra21 » Fri Jul 07, 2023 1:35 pm America/New_York
Thank you so much! This is now a lot more enlightening to me. But I still have a doubt: on my data whenever I have high values of PIC, usually they are associated with low values of chlorophyll a. I see that in different regions of the oceans, namely Azores and Cape Verde, for example. So, shouldn't we expect high values of Chl a in the satellite images when we have a strong bloom of Ehux (high PIC) in the same region?
That's a good question. As I recall, the high reflectivity of the coccolithophores makes it difficult to properly estimate chlorophyll in cocco blooms. I think (though I can be corrected) that chl-a processing includes a coccolithophore bloom mask because of that interference. I.e., so much light is being reflected that it's difficult to detect any absorption.
by cassandra21 » Fri Jul 07, 2023 1:57 pm America/New_York
Thank you so much because this is a doubt we had for some time! If I may ask you one more question: what about the PFT (phytoplankton functional type) products? Does this mean what you said is taken into consideration for deriving the PFT products? And also, I should interpret the chl a product does not represent at all the Ehux?
At this point you have gone beyond my basic understanding of the PIC algorithm, so I would recommend further correspondence with the OBDAAC staff. I will add the "OBDAAC" tag to this thread. It is my expectation that the chl-a product does not provide a good estimate of chlorophyll in Ehux.