Nutrient and dissolved inorganic carbon variability in the North Pacific

Abstract

A compilation of surface water nutrient (phosphate, nitrate, and silicate) and partial pressure of CO 2 (pCO 2) observations from 1961 to 2016 reveals seasonal and interannual variability in the North Pacific. Nutrients and calculated dissolved inorganic carbon (DIC) reach maximum concentrations in March and minimum in August. Nutrient and DIC variability is in-phase (anti-phase) with changes in the mixed layer depth (sea surface temperature) north of 30 °N, and it is anti-phase (in-phase) with changes in Chl-a north of 40 °N (in 30 °N-40 °N). Seasonal drawdown of nutrients and DIC is larger toward the northwest and shows a local maximum in the boundary region between the subarctic and subtropics. Stoichiometric ratios of seasonal drawdown show that, compared to nitrate, silicate drawdown is large in the northwestern subarctic including the Bering and Okhotsk seas, and drawdown of carbon is larger toward the south. Net community production in mixed layer from March to July is estimated to be more than 6 gC/m 2 /mo in the boundary region between the subarctic and subtropics, the western subarctic, the Gulf of Alaska, and the Bering Sea. Nutrient and DIC concentrations vary with the Pacific Decadal Oscillation and the North Pacific Gyre Oscillation which cause changes in horizontal advection and vertical mixing. The DIC trend is positive in all analysis area and large in the western subtropics (> 1.0 μmol/l/yr). Averaged over the analysis area, it is increasing by 0.77 ± 0.03 μmol/l/yr (0.75 ± 0.02 μmol/kg/yr).

Global distribution and variability of subsurface chlorophyll a concentration

“…Consequently, new production derived from subsurface oxygen production in the subtropics is estimated at approximately 10% of the NPP. This is consistent with the f-ratio of 15% reported at station ALOHA (23°N 158°W; Karl et al, 1996), considering small but nonzero seasonal dissolved inorganic carbon drawdown reported in the subtropical surface layer (Yasunaka et al, 2013(Yasunaka et al, , 2021. However, it should be noted that oxygen production is sometimes not associated with biomass increase in shallow layers in the subtropics (Fujiki et al, 2020).…”

A review: iron and nutrient supply in the subarctic Pacific and its impact on phytoplankton production

“…In the WSG, seasonal amplitudes in biogeochemical parameters, e.g., nutrient concentrations, and pCO 2 , were greater than those in the AG (Shiomoto et al 1998;Shiomoto and Asami 1999;Harrison et al 1999Harrison et al , 2004, even though both gyres had HNLC characteristics. Time series studies in both gyres (Whitney and Freeland 1999;Tsurushima et al 2002) and basin-scale data-mapping analyses (Whitney 2011;Yasunaka et al 2014Yasunaka et al , 2020 have demonstrated that higher nutrient concentrations accumulate in the surface water of the WSG than in the AG in winter. Yasunaka et al (2014) and Yasunaka et al (2020) indicated that higher seasonal drawdowns of nitrate, phosphate, silicate and dissolved inorganic carbon concentrations occurred in the Oyashio and Oyashio-Kuroshio transition zones than in the AG.…”

“…Time series studies in both gyres (Whitney and Freeland 1999;Tsurushima et al 2002) and basin-scale data-mapping analyses (Whitney 2011;Yasunaka et al 2014Yasunaka et al , 2020 have demonstrated that higher nutrient concentrations accumulate in the surface water of the WSG than in the AG in winter. Yasunaka et al (2014) and Yasunaka et al (2020) indicated that higher seasonal drawdowns of nitrate, phosphate, silicate and dissolved inorganic carbon concentrations occurred in the Oyashio and Oyashio-Kuroshio transition zones than in the AG. Moreover, the effect of biological drawdown on the seasonal amplitude of pCO 2 in the surface water was higher in the WSG than in the AG (Takahashi et al 2002;Chierici et al 2006).…”

“…This biological production is not like the massive spring blooms that occur in coastal currents, such as the AC, AS, and COW, in the subarctic area. The first-case, which we focus on here, is the biological production that causes the seasonal drawdown of the pCO 2 and nutrient concentrations in the open oceanic area in HNLC waters, which are especially high in the WSG (e.g., Fujiki et al 2014;Matsumoto et al 2014;Shiozaki et al 2014;Yasunaka et al 2020). This phenomenon is a regular biological production process that occurs every year at the basin-scale range in the western to central subarctic Pacific.…”

“…Therefore, the Fe and nutrient supply from intermediate water driven by ocean mixing (winter mixing and eddy diffusive mixing) possibly contribute to maintaining biological production and dissolved inorganic carbon drawdowns in area 1 in Fig. 12b (Yasunaka et al 2014(Yasunaka et al , 2020 from spring to summer in the western subarctic Pacific. Interestingly, higher continuous primary production was observed around the Aleutian and Kuril Island chains (areas 2 and 3 in Fig.…”