Production of dissolved organic carbon by Arctic plankton communities:Responses to elevated carbon dioxide and the availability of light and nutrients

• Published in: Deep Sea Research Part II: Topical Studies in Oceanography
• Main Authors: Poulton, Alex J., Daniels, Chris J., Esposito, Mario, Humphreys, Matthew P., Mitchell, Elaine, Ribas-Ribas, Mariana, Russell, Benjamin C., Stinchcombe, Mark C., Tynan, Eithne, Richier, Sophie
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Arctic Ocean; Bacteria; Diatoms; Dissolved organic carbon; Ocean acidification; Phytoplankton; Arctic; Barents Sea; Greenland; Nordic Seas
• Online Access: https://pure.uhi.ac.uk/en/publications/dc5f7000-2da8-4980-9a58-b5064c112a8a; https://doi.org/10.1016/j.dsr2.2016.01.002; http://www.scopus.com/inward/record.url?scp=84955604335&partnerID=8YFLogxK; http://www.scopus.com/inward/citedby.url?scp=84955604335&partnerID=8YFLogxK

The extracellular release of dissolved organic carbon (DOC) by phytoplankton is a potentially important source of labile organic carbon for bacterioplankton in pelagic ecosystems. In the context of increasing seawater partial pressure of CO 2 (pCO 2 ), via the oceanic absorption of elevated atmospheric CO 2 (ocean acidification), several previous studies have reported increases to the relative amount of carbon fixed into particulates, via primary production (PP), and dissolved phases (DOC). During the summer of 2012 we measured DOC production by phytoplankton communities in the Nordic seas of the Arctic Ocean (Greenland, Norwegian and Barents Sea) from both in situ sampling and during three bioassay experiments where pCO 2 levels (targets ~550 μatm, ~750 μatm, ~1000 μatm) were elevated relative to ambient conditions. Measurements of DOC production and PP came from 24 h incubations and therefore represent net DOC production rates, where an unknown portion of the DOC released has potentially been utilised by heterotrophic organisms. Production of DOC (net pDOC) by in situ communities varied from 0.09 to 0.64 mmol C m -3 d -1 (average 0.25 mmol C m -3 d -1 ), with comparative rates in two of the experimental bioassays (0.04-1.23 mmol C m -3 d -1 ) and increasing dramatically in the third (up to 5.88 mmol C m -3 d -1 ). When expressed as a fraction of total carbon fixation (i.e., PP plus pDOC), percentage extracellular release (PER) was 14% on average (range 2-46%) for in situ measurements, with PER in the three bioassays having a very similar range (2-50%). A marked increase in pDOC (and PER) was only observed in one of the bioassays where nutrient levels (nitrate, silicic acid) dropped dramatically relative to starting (ambient) concentrations; no pCO 2 treatment effect on pDOC (or PER) was evident across the three experiments. Examination of in situ net pDOC (and PER) found significant correlations with decreasing silicic acid and increasing euphotic zone depth, indicating that nutrient and light availability ...