Changing abundant ecotypes during the warm anomaly period
We further investigated the interannual turnover during the periods of highest POC flux in spring and summer of some of the abundant OTUs and their correlation with the temperature changes observed in Fram Strait during the period 2003 - 2011. One of the interesting patterns that emerged was the alternating abundances between some of the most abundant phytoplankton OTUs. For example, chlorophyte OTUs in the Wolf938 dataset showed that the temperate Clade C represented by OTU 2 had higher read counts (t-test, p <0.05) in both spring and summer from 2005-2008, while the cold adapted Clade Ea represented by OTU 268 dominated the chlorophyte communities in the other years (Figures 5A and 5C). The same general pattern was observed in the OTUs identified from the Stoeck dataset, where Clade C was more dominant among the Chlorophyta in the years 2006-2009 for both seasons (t-test,p <0.05), while Clade Ea was prominent in the other years. Similar observation however was not apparent in any of the OTUs in the Wolf964 dataset.
Interestingly, alternating dominance of some OTUs was also observed in the haptophytes based on the Wolf964, but was not observed in the Stoeck and Wolf964 datasets. Specifically, Emiliania sp. (OTU 36) andPhaeocystis sp. (OTU 29) followed that of the chlorophytes where the former becoming more prominent in 2006-2008 and the latter in both seasons for the other years (Figure 5B and 5D). No similar pattern was observed for the diatoms at the OTU level. However, their abundances were generally higher before 2004 and after 2008 when haptophytes and chlorophytes were more dominant.