Abstract
The European Sector of the Arctic Ocean is characterized by low CO2 concentrations in seawater during spring and summer, largely due to strong biological uptake driven by extensive plankton blooms in spring. The spring plankton bloom is eventually terminated by nutrient depletion and grazing. However, low CO2 concentrations in seawater and low atmospheric resupply of CO2 can cause episodes during which the phytoplankton growth is limited by CO2. Here, we show that gross primary production (GPP) of Arctic plankton communities increases from 32 to 72 % on average with CO2 additions in spring. Enhanced GPP with CO2 additions occur during episodes of high productivity, low CO2 concentration and in the presence of dissolved inorganic nutrients. However, during summer the addition of CO2 supresses planktonic Arctic GPP. Events of CO2 limitation in spring may contribute to the termination of the Arctic spring plankton blooms. The stimulation of GPP by CO2 during the spring bloom provides a biotic feedback loop that might influence the global role played by the Arctic Ocean as a CO2 sink in the future.
Highlights
The shelf seas and the shelf edge of the European Artic Sector are characterized by strong spring plankton blooms that extend between 70 and 80◦N in the Barents Sea and the northern Svalbard shelf (Wassmann and Reigstad, 2011)
gross primary production (GPP)-O2 within the euphotic layer increased with increasing Chl a concentration (p < 0.0001, R2 = 0.81, Figure S2), resulting in low-CO2 waters
Upward CO2 supply from deeper layers was likely to be low because the seasonal stratification produced by melting sea ice in the same area leads to small upward diffusive fluxes (Randelhoff et al, 2016)
Summary
The shelf seas and the shelf edge of the European Artic Sector are characterized by strong spring plankton blooms that extend between 70 and 80◦N in the Barents Sea and the northern Svalbard shelf (Wassmann and Reigstad, 2011). These blooms support high net community production (NCP) rates and fuel the Arctic food web (Vaquer-Sunyer et al, 2013). The strength of the spring Arctic plankton bloom results from high primary productivity, and from a very low respiratory demand of the planktonic community at that time, which leads to high NCP (VaquerSunyer et al, 2013). Several regions of the Arctic Ocean such as the Eurasian shelves and the Barents Sea (Fransson et al, 2001, 2009) and the Bering-Chukchi shelves
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