Spatial variability of photophysiology and primary production rates of the phytoplankton communities across the western Antarctic Peninsula in late summer 2013

Primary production measurements in the Southern Ocean are generally carried out during phytoplankton blooms in the Antarctic summer, whereas information from late summer is scarcer, especially in the northernmost part of the western Antarctic Peninsula (wAP). Here, we present data on phytoplankton photophysiology, chlorophyll-a concentration (Chl a), phytoplankton communities and primary productivity for 3 sub-regions, as follows: Transitional Water with Bellingshausen Sea influence (TBW-dominated sub-region), Transitional Water with Weddell Sea influence (TWW-dominated sub-region), both occupying the Bransfield Strait (BS), and a mixture of both transitional waters in the Gerlache Strait (Gerlache sub-region). Comparisons between these sub-regions have shown that, on average, Chl a, (0.65 mg m−3) was lower and upper mixed layer depth (ZUMLD = 52.62 m) was deeper in TWW-dominated waters, whereas intermediate Chl a (1.22 mg m−3) and moderate ZUMLD (36.46 m) values were found in the TBW-dominated sub-region and the lowest ZUMLD (22.33 m) and highest Chl a values (1.58 mg m−3) were found in the Gerlache sub-region. However, similar values of Fv/Fm were found in the 3 sub-regions, which indicate a high physiological plasticity, even considering different phytoplankton communities. A canonical correspondence analysis highlighted the association between the TBW-dominated sub-region and the dominance of diatoms, coupled with higher photosynthetic carotenoids (especially fucoxanthin), contrasting with the Gerlache sub-region, mainly associated with photoprotective carotenoids (particularly alloxanthin from cryptophytes) and relative lower ZUMLD. Primary production rates estimated from the PAM (Pulse-Amplitude Modulate) fluorometric technique agreed very well with 14C measurements (r2=0.91, n=5, p=0.01). Although higher maximum chlorophyll a specific primary production rates were found in the TWW sub-region (1.91 ± 1.22 mgC mg Chl a−1 h−1), the other two areas also showed relatively high assimilation numbers as compared to previous works in the region. In short, despite the large spatial variability of physical water column features, adequate photophysiological traits allowed high primary production rates by those late summer phytoplankton communities in the northern wAP region.