Decoupling between bacterial production and primary production over multiple time scales in the North Pacific Subtropical Gyre

摘要

We measured rates of H-3-leucine (3H-Leu) incorporation, as a proxy for bacterial production, at Station ALOHA (22 45'N, 158 W) in the oligotrophic North Pacific Subtropical Gyre (NPSG). We report measurements conducted between January 2011 and April 2013, examining variability in H-3-Leu incorporation over diel, daily, and monthly time scales. Rates of 3H-Leu were evaluated in the context of contemporaneous C-14-based primary productivity (C-14 -PP) to identify potential temporal coupling between these measures of productivity. Throughout the upper ocean (0-125 m), rates of H-3-Leu incorporation measured in the light (H-3-Leuught) were stimulated (1.5 -fold, on average) relative to measurements in the dark (H-3-Leupark). At monthly scales, rates of H-3-Leuught and H-3-Leunark varied 4.9 -fold and 3.8 -fold, respectively, while rates of C-14-PP varied 1.7 -fold. Rates of C-14 -PP were often elevated during summer months (May through August) when incident light flux was greatest, while rates of both H-3-Letiught and H-3-Leunark often peaked in early fall (August through October) when seawater temperatures were maximal. Near -daily measurements of H-3-Leu incorporation and C-14 -PP conducted over a 62 -day period in the summer of 2012 revealed that rates of H-3-Leuught and H-3-Leunark varied 2.5 and 2.0 -fold, respectively, similar to similar to 1.8 -fold daily variability observed in rates of C-14 -PP. Over diel time scales, rates of H-3-Leulight and 3H-Leupark demonstrated different patterns, with rates of H-3-Leuught elevated at mid -day and rates of H-3-Leupark greatest in the early evening. Together, these results suggest that in this oligotrophic ecosystem, photosynthetic production of organic matter and bacterial production can be temporally uncoupled across daily to seasonal scales.