Production of dissolved organic carbon by Arctic plankton communities: Responses to elevated carbon dioxide and the availability of light and nutrients. (May 2016)

• Record Type: Journal Article
• 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
• Is Part Of: Deep sea research. Volume 127(2016)
• Page Start: 60
• Page End: 74
• Publication Date: 2016-05
• Subjects: Dissolved organic carbon -- Arctic Ocean -- Ocean acidification -- Phytoplankton -- Bacteria -- Diatoms; Oceanography -- Periodicals; Ocean bottom -- Periodicals; Marine biology -- Periodicals; 551.46
• DOI: 10.1016/j.dsr2.2016.01.002
• Languages: English
• ISSNs: 0967-0645

Abstract

Abstract: 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 CO2 ( p CO2 ), via the oceanic absorption of elevated atmospheric CO2 (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 p CO2 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 p DOC) 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 p DOC), 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 p DOC (and PER) was only observed in one of the bioassays where nutrient levels (nitrate, silicic acid) dropped dramatically relative to starting (ambient) concentrations; no p CO2 treatment effect on p DOC (or PER) was evident across the three experiments. Examination of in situ net p DOC (and PER) found significant correlations with decreasing silicic acid and increasing euphotic zone depth, indicating that nutrient and light availability were strong drivers of the partitioning of primary production between particulate and dissolved phases. Furthermore, the third bioassay experiment had relatively high levels of diatom biomass as well as a strong response to nitrate and silicic acid depletion, and we suggest that nutrient starved or light limited diatom communities may be strong producers of DOC in Arctic ecosystems.