Pelagic primary productivity and upper ocean nutrient dynamics across Subarctic and Arctic Seas

Abstract

) decreased markedly from west to east, with minima in NO 3 2 and NH 4 1 in surface BS-CB waters, but relatively invariant urea-N concentrations across the entire region. In the BS-CB domain, low uptake rates of nitrate (qNO 32 ) and ammonium (qNH 4 1 ) were exceeded by uptake of urea (qUrea-N). Whereas average qNO 3 2 was highest in the BE-CH domain, qUrea-N was maximal in BB-LS. Average depth-integrated f-ratios ranged from 0.27 in the BS-CB domain to 0.57 in BE-CH, while chlorophyll a (chl a) and primary productivity (qC) were highest in BE-CH and BB-LS, and consistently low in the BS-CB domain. The >5 mm phytoplankton fraction dominated qC and qNO 3 2 in the BE-CH and CAA domains, whereas ESNP and BS-CB were dominated by the <5 mm fraction. In the BB-LS domain, the larger cells were responsible for $50% of qC, qNO 3 2 , and qUrea-N. This study highlights the contrast in ice-corrected average new production between the BE-CH (396 mg C m 22 d 21 ) and BS-CB (5.50 mg C m 22 d 21) domains in summer, and the larger contribution of urea-N uptake to total N uptake in central and eastern regions where NO 3 2 concentrations were lower.

Resistance of Arctic phytoplankton to ocean acidification and enhanced irradiance

“…To prevent nutrient limitation, nitrate, phosphate, and silicic acid from chelexed stock solutions were added in ratios appropriate for the region (Varela et al 2013), yielding final concentrations of approx. 20 lmol L -1 NO 3 -, 2.5 lmol L -1 PO 4 3-, and 30 lmol L -1 Si(OH) 4 .…”

Functional Redundancy Facilitates Resilience of Subarctic Phytoplankton Assemblages toward Ocean Acidification and High Irradiance

“…To prevent nutrient limitation, macronutrients from chelexed stock solutions were added in ratios appropriate for the region, yielding approx. 20 µM NO and 30 µM Si(OH) 4 (Varela et al, 2013). Dilution of incubations were conducted in order to allow sufficient time for the phytoplankton assemblages to acclimate to the experimental conditions, and for shifts in the species composition to occur, while also preventing nutrient limitation and/or drifts in carbonate chemistry.…”

Food-Web Structure in Four Locations Along the European Shelf Indicates Spatial Differences in Ecosystem Functioning

“…Also, potential use of other carbon sources cannot explain this general pattern, which was only observed at higher trophic positions. Microphytobenthos needs to be considered negligible in Hola, since the euphotic zone depth (0.1% surface irradiance) has to be expected much shallower than the bottom depth (195-220 m) at such high latitudes (Varela et al, 2013). Hola is in relative close proximity to the coast, and accordingly terrestrial carbon could be another explanation for the 13 C composition of high TP.…”