High air–sea CO 2 uptake rates in nearshore and shelf areas of Southern Greenland: Temporal and spatial variability S. Rysgaard a, ⁎, J. Mortensen a , T. Juul-Pedersen a , L.L. Sørensen a, b , K. Lennert a , D.H. Søgaard a, c , K.E. Arendt a , M.E. Blicher a , M.K. Sejr a, b , J. Bendtsen a a Greenland Climate Research Centre, Greenland Institute of Natural Resources, Nuuk, Greenland b National Environmental Research Institute, Aarhus University, Aarhus, Denmark c University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark abstract article info Article history: Received 12 May 2011 Received in revised form 10 November 2011 Accepted 11 November 2011 Available online 27 November 2011 Keywords: Air–sea CO2 exchange Arctic shelf Greenland Primary production Vertical sinking flux Fjord Glacial meltwater The present study is based on hourly samplings of wind speed, monthly sampling sessions of temperature, salin- ity, dissolved inorganic carbon, alkalinity, nutrients, primary productivity and vertical export in the outer sill re- gion (station GF3) of a sub-arctic SW Greenland fjord (Godthåbsfjord) through 2005–2010. Air–sea CO 2 fluxes varied at GF3 from c. −20 g C m −2 month −1 (uptake from the atmosphere) to 25 g C m −2 month −1 (release to the atmosphere) during 2005–10. The average annual air–sea CO 2 flux of −83 to −108 g C m −2 yr −1 was within the range of the local gross annual primary productivity of 76–106 g C m −2 yr −1 . Furthermore, the esti- mated vertical export of phytoplankton carbon to depths below 60 m of 38–89 g C m −2 suggests that a large fraction of the mineralization (release of CO 2 ) occurs in deeper waters in the outer sill region of the fjord. How- ever, there was no statistically significant correlation between average annual gross primary production and an- nual air–sea flux during 2005–2010, which suggests that regulation of pCO 2 in the fjord is more complex. Despite three confined periods with supersaturated pCO 2 conditions in surface waters during 2005–2010, Godthåbsfjord can be considered as a strong sink (7.2 tons C month −1 km −2 ) for atmospheric CO 2 . In addition, measurements from Godthåbsfjord during the summer season showed that mixing between glacial meltwater and coastal water could explain a large part of the low pCO 2 -values observed in the innermost part of the fjord. Finally, a larger sur- vey confirmed the existence of very low pCO 2 conditions in nearshore and shelf waters around Southern Greenland. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Over the global oceans, the seasonal and geographical variation of the partial pressure of CO 2 (pCO 2 ) is much greater than that of atmo- spheric pCO 2 , and, hence, the direction and magnitude of the air–sea CO 2 flux are mainly regulated by oceanic pCO 2 . A recent synthesis of worldwide measurements of pCO 2 indicates that most open shelves in the temperate and high-latitude regions are undersaturated with respect to atmospheric CO 2 during all seasons, although the low- latitude shelves seem to be supersaturated (Chen and Borges, 2009; Takahashi et al., 2002). Basic knowledge is still needed, however, to elucidate whether coastal waters are net sources or sinks of atmo- spheric CO 2 , and whether organic carbon from primary production in coastal seas is exported or recycled (Mackenzie et al., 2000; Smith and Hollibaugh, 1993; Smith and Mackenzie, 1987; Thomas et al., 2004; Ver et al., 1999a,b). One of the arguments presented for areas with CO 2 degassing to the atmosphere is based on the imbal- ance between the total river transport of c. 0.4 Pg C yr −1 and the oce- anic organic carbon burial rate of c. 0.14 Pg C yr −1 . The difference of 0.26 Pg C yr −1 would most likely be returned to the atmosphere (Smith and Hollibaugh, 1993; Smith and Mackenzie, 1987). Further- more, there is an increasing evidence that a very large fraction of ter- restrial/riverine organic matter is degraded in nearshore areas and emitted as CO 2 to the atmosphere there without ever reaching the continental shelves (Middelburg and Herman, 2007 and references therein). Based on carbon mass-balance calculations as well as scaled estimates of pCO 2 measurements, Chen and Borges (2009) estab- lished that open shelf areas are sinks for atmospheric CO 2 , although many inner estuaries, nearshore coastal waters and intensive upwell- ing areas are supersaturated with respect to CO 2 . Although the Arctic covers c. 25% of the global coastal region (areas with water depths b 200 m, Menard and Smith, 1966) very few studies of pCO 2 uptake exist from these high-latitude nearshore areas and virtually none from Greenland waters (Anderson et al., 2000; Miller et al., 2002; Murata and Takizawa, 2003; Sejr et al., 2011; Yager et al., 1995). In addition, investigations have been restricted to short surveys and most measurements have been performed during summer. Marine Chemistry 128-129 (2012) 26–33 ⁎ Corresponding author at: Centre for Earth Observation Science, University of Manitoba, Winnipeg, Canada. E-mail address: Rysgaard@cc.umanitoba.ca (S. Rysgaard). 0304-4203/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.marchem.2011.11.002 Contents lists available at SciVerse ScienceDirect Marine Chemistry journal homepage: www.elsevier.com/locate/marchem