Abstract
Abstract. Present and future levels of primary production (PP) in the Arctic Ocean (AO) depend on nutrient inputs to the photic zone via vertical mixing, upwelling and external sources. In this regard, the importance of horizontal river supply relative to oceanic processes is poorly constrained at the pan-Arctic scale. We compiled extensive historical (1954–2012) data on discharge and nutrient concentrations to estimate fluxes of nitrate, soluble reactive phosphate (SRP), silicate, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), particulate organic nitrogen (PON) and particulate organic carbon (POC) from 9 large Arctic rivers and assess their potential impact on the biogeochemistry of shelf waters. Several key points can be emphasized from this analysis. The contribution of riverine nitrate to new PP (PPnew) is very small at the regional scale (< 1% to 6.7%) and negligible at the pan-Arctic scale (< 0.83%), in agreement with recent studies. By consuming all this nitrate, oceanic phytoplankton would be able to use only 14.3% and 8.7–24.5% of the river supply of silicate at the pan-Arctic and regional scales, respectively. Corresponding figures for SRP are 28.9% and 18.6–46%. On the Beaufort and Bering shelves, riverine SRP cannot fulfil phytoplankton requirements. On a seasonal basis, the removal of riverine nitrate, silicate and SRP would be the highest in spring and not in summer when AO shelf waters are nitrogen-limited. Riverine DON is potentially an important nitrogen source for the planktonic ecosystem in summer, when ammonium supplied through the photoammonification of refractory DON (3.9 × 109 mol N) may exceed the combined riverine supply of nitrate and ammonium (3.4 × 109 mol N). Nevertheless, overall nitrogen limitation of AO phytoplankton is expected to persist even when projected increases of riverine DON and nitrate supply are taken into account. This analysis underscores the need to better contrast oceanic nutrient supply processes with the composition and fate of changing riverine nutrient deliveries in future scenarios of plankton community structure, function and production in the coastal AO.
Highlights
Earth System SciencesFifty years ago, the Arctic Ocean (AO) was perceived as a small contributor to the global carbon cycle because of its extensive sea-ice cover and the relatively low light levels experienced by phytoplanOktcone(aEnnglSishc,i1e9n61c)e
The Arctic Ocean (AO) was perceived as a small contributor to the global carbon cycle because of its extensive sea-ice cover and the relatively low light levels experienced by phytoplanOktcone(aEnnglSishc,i1e9n61c)e
The earlier and longer exposure of surface waters to sunlight triSggoerlisdeaErliaerrtvhernal blooms in some parts of the Arctic Ocean (Kahru et al, 2011). It has been suggested based on ocean colour remote sensing data that annual primary production (PP) is increasing (Arrigo et al, 2008)
Summary
Earth System SciencesFifty years ago, the Arctic Ocean (AO) was perceived as a small contributor to the global carbon cycle because of its extensive sea-ice cover and the relatively low light levels experienced by phytoplanOktcone(aEnnglSishc,i1e9n61c)e. The earlier and longer exposure of surface waters to sunlight triSggoerlisdeaErliaerrtvhernal blooms in some parts of the Arctic Ocean (Kahru et al, 2011). It has been suggested based on ocean colour remote sensing data that annual primary production (PP) is increasing (Arrigo et al, 2008). Recent observations show that the density out the ysteraarti(fiTcraetmiobnlTa(yi.hee.etpayClc.,nr2oy0co0li8ns)ep)anihsdepsertrreesinsgtethnetntihnrgouagsharesult of increasing river discharge (Li et al, 2009). These conditions limit the vertical supply of nutrients offshore and favour small phytoplankton cells at the expense of large ones (Li et al, 2009)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
