Response of marine bacterioplankton to a massive under-ice phytoplankton bloom in the Chukchi Sea (Western Arctic Ocean)

Special issue The Phytoplankton Megabloom beneath Arctic Sea Ice: Results from the ICESCAPE Program.-- 11 pages, 6 figures, 5 tables, 1 appendix supplementary data https://doi.org/10.1016/j.dsr2.2014.03.015The activity of heterotrophic bacterioplankton and their response to changes in primary production in the Arctic Ocean is essential to understand biogenic carbon flows in the area. In this study, we explored the patterns of bacterial abundance (BA) and bacterial production (BP) in waters coinciding with a massive under-ice phytoplankton bloom in the Chukchi Sea in summer 2011, where chlorophyll a (chl a) concentrations were up to 38.9mgm-3. Contrary to our expectations, BA and BP did not show their highest values coinciding with the bloom. In fact, bacterial biomass was only 3.5% of phytoplankton biomass. Similarly, average DOC values were similar inside (average 57.2±3.1μM) and outside (average 64.3±4.8μM) the bloom patch. Regression analyses showed relatively weak couplings, in terms of slope values, between chl a or primary production and BA or BP. Multiple regression analyses indicated that both temperature and chl a explained BA and BP variability in the Chukchi Sea. This temperature dependence was confirmed experimentally, as higher incubation temperatures (6.6°C vs. 2.2°C) enhanced BA and BP, with Q10 values of BP up to 20.0. Together, these results indicate that low temperatures in conjunction with low dissolved organic matter release can preclude bacteria to efficiently process a higher proportion of carbon fixed by phytoplankton, with further consequences on the carbon cycling in the area. © 2014 Elsevier Ltd.This work was supported by the Ocean Biology and Biogeochemistry Program and the Cryosphere Science Program of the National Aeronautic and Space Administration (NNX10AF42G to K. Arrigo) and by the French National Research Agency, under the Grant no. ANR-BLAN08-1 310980 to the MALINA project, the LEFE-CYBER and CNES TOSCA programmes, ArcticNet, and the European Space AgencyPeer Reviewe