Synthesis of primary production in the Arctic Ocean: III. Nitrate and phosphate based estimates of net community production

Abstract

Combining nitrate, nitrite and phosphate data from several sources with additional quality control produced a database that eliminates many questionable values. This database, in turn, facilitated estimation of net community production (NCP) in the Arctic Marine System (AMS). In some regions, the new database enabled quantitative calculation of NCP over the vegetative season from changes in nutrient concentrations. In others, useful inferences were possible based on nutrient concentration patterns. This analysis demonstrates that it is possible to estimate NCP from seasonal changes in nutrients in many parts of the Arctic, however, the data were so sparse that most of our estimates for 14 sub-regions of the AMS are attended by uncertainties >50%. Nevertheless, the wide regional variation of NCP within the AMS (∼two orders of magnitude) may make the results useful.NCP for the entire AMS was estimated as 345±72TgC over the vegetative season. Converting this value to annual primary production (PP) as determined by typical 14C incubations suggests an annual primary production rate for the AMS of ∼1000TgC.We divided the AMS and its marginal seas into the same 13 sub-regions employed in the companion studies of Matrai et al. (2012) and Hill et al. (2013) and estimated NCP for each. We also made separate estimates for the Eurasian and Amerasian portions of the Arctic Basin.Significant findings include:1.NCP in the Arctic Basin is low, but there are regional variations in the controls and in rates. In the Amerasian Basin (particularly in the Canada sub-basin), nitrate concentrations from 0 to ∼50m are very low (∼0μM) even in winter. Thus, nutrient limitation suppresses NCP in this region. In the Eurasian Basin, light or grazing or both may be important limiting factors since significant surface layer nutrient concentrations persist during summer.2.Low wintertime nitrate concentrations in the upper layers of the Amerasian Basin and Northern Beaufort Sea suggest that NCP in these sub-regions may be insensitive to changes in the ice and light regimes.3.Although tentative because of limitations in the data, we group NCP in the 14 sub-regions as follows:a.Very high NCP (∼70–100gCm−2) in the Bering and Southern Chukchi sub-regions.b.High NCP (∼30–40Cm−2) in the Nordic and Barents seas and the Canadian Archipelago.c.Moderate NCP (>10 to ∼15gCm−2) in the Eurasian Basin, Southern Beaufort, Southern East Siberian Sea+Laptev, Kara Sea and Greenland Shelf sub-regions.d.Low (NCP∼10gCm−2) in Northern East Siberian Sea+Laptev and Northern Chukchi sub-regions.e.Extremely low NCP (∼1–5gCm−2) in the Northern Beaufort and Amerasian Basin sub-regions.