Mesopelagic particulate nitrogen dynamics in the subarctic and subtropical regions of the western North Pacific

Recently, new spatiotemporal-scale particle observations by autonomous profiling floats equipped with bio-optical sensors have revealed that, in addition to gravitational particle sinking, the downward transport of surface particles by physical mixing events, which has been overlooked, contributes to particulate organic carbon export. However, the subsequent behavior of these exported particles in the mesopelagic zone (e.g., particle fragmentation and degradation) remains unclear, although it may influence the efficiency of carbon transport to further depths. This study successfully depicted the new annual mean mesopelagic particulate nitrogen (PN) dynamics with multi-layer, steady-state suspended PN pools by reanalyzing seasonal data on the stable nitrogen isotopic compositions of both suspended and sinking particles, each with different profiles, from subarctic station K2 and subtropical station S1 in the North Pacific, which are both CO2 sinks but in different oceanic settings. As analytical conditions, we assumed that the net loss of sinking PN was entirely due to abiotic fragmentation of particle aggregates to non-sinking particles and that the apparent 15N enrichment associated with heterotrophic degradation in the suspended PN pools was vertically constant. The 15N mass balance for the PN supply to the uppermost mesopelagic pool, derived from such constraints, allowed estimating the PN export by the mixed-layer pump, which was 1.6 times greater at K2 than at S1. However, its contribution to the total export (including gravitational PN sinking) from the surface layer was approximately 20% at both stations. Moreover, the ratio of PN supplied to the uppermost pool by the mixed-layer pump and by the fragmentation of particle aggregates was also similar at both stations, approximately 1:1. Using these ratios, together with separate observations of the mixed-layer pump-driven flux, it may be possible to estimate the efficiency of the particulate organic carbon transport due to the biological gravitational pump responsible for carbon sequestration in the deep sea

Observation in the Antarctic Sea using pCO2 autonomous buoy

第2回極域科学シンポジウム　共通セッション「海氷圏の生物地球化学」 11月16日（水） 統計数理研究所 3階セミナー

Continuous Monitoring and Future Projection of Ocean Warming, Acidification, and Deoxygenation on the Subarctic Coast of Hokkaido, Japan

As the ocean absorbs excessive anthropogenic CO2 and ocean acidification proceeds, it is thought to be harder for marine calcifying organisms, such as shellfish, to form their skeletons and shells made of calcium carbonate. Recent studies have suggested that various marine organisms, both calcifiers and non-calcifiers, will be affected adversely by ocean warming and deoxygenation. However, regardless of their effects on calcifiers, the spatiotemporal variability of parameters affecting ocean acidification and deoxygenation has not been elucidated in the subarctic coasts of Japan. This study conducted the first continuous monitoring and future projection of physical and biogeochemical parameters of the subarctic coast of Hokkaido, Japan. Our results show that the seasonal change in biogeochemical parameters, with higher pH and dissolved oxygen (DO) concentration in winter than in summer, was primarily regulated by water temperature. The daily fluctuations, which were higher in the daytime than at night, were mainly affected by daytime photosynthesis by primary producers and respiration by marine organisms at night. Our projected results suggest that, without ambitious commitment to reducing CO2 and other greenhouse gas emissions, such as by following the Paris Agreement, the impact of ocean warming and acidification on calcifiers along subarctic coasts will become serious, exceeding the critical level of high temperature for 3 months in summer and being close to the critical level of low saturation state of calcium carbonate for 2 months in mid-winter, respectively, by the end of this century. The impact of deoxygenation might often be prominent assuming that the daily fluctuation in DO concentration in the future is similar to that at present. The results also suggest the importance of adaptation strategies by local coastal industries, especially fisheries, such as modifying aquaculture styles

Seasonal variations in the nitrogen isotopic composition of settling particles at station K2 in the western subarctic North Pacific

Intensive observations using hydrographical cruises and moored sediment trap deployments during 2010 and 2012 at station K2 in the North Pacific western subarctic gyre (WSG) revealed seasonal changes in δ15N of both suspended and settling particles. Suspended particles (SUS) were collected from depths between the surface and 200 m; settling particles by drifting traps (DST; 100-200 m) and moored traps (MST; 200 and 500 m). All particles showed higher δ15N values in winter and lower in summer, contrary to the expected by isotopic fractionation during phytoplankton nitrate consumption. We suggest that these observed isotopic patterns are due to ammonium consumption via light-controlled nitrification, which could induce variations in δ15N(SUS) of 0.4-3.1 ‰ in the euphotic zone (EZ). The δ15N(SUS) signature was reflected by δ15 N(DST) despite modifications during biogenic transformation from suspended particles in the EZ. δ15 N enrichment (average: 3.6 ‰) and the increase in C:N ratio (by 1.6) in settling particles suggests year-round contributions of metabolites from herbivorous zooplankton as well as TEPs produced by diatoms. Accordingly, seasonal δ15 N(DST) variations of 2.4-7.0 ‰ showed a significant correlation with primary productivity (PP) at K2. By applying the observed δ15 N(DST) vs. PP regression to δ15 N(MST) of 1.9-8.0 ‰, we constructed the first annual time-series of PP changes in the WSG. Moreover, the monthly export ratio at 500 m was calculated using both estimated PP and measured organic carbon fluxes. Results suggest a 1.6 to 1.8 times more efficient transport of photosynthetically-fixed carbon to the intermediate layers occurs in summer/autumn rather than winter/spring

西部北太平洋亜寒帯域と津軽海峡の海洋環境変化 -海が変わって、水産資源にも影響!?-

http://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr13-04/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr11-03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr11-02/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr10-06/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr08-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr07-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr05-04/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr05-01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-06/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-04/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt04-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-02/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt03-07/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr03-k01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr01-k03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr07-01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr00-k03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr00-k01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr99-k02/

Seawater carbonate chemistry and elemental composition of the particulate and dissolved organic matter of marine diatoms

Although the dissolved inorganic carbon concentration, pH, and nutrient regimes of seawater dramatically change in coastal regions, the synergistic effects of changes in the CO2 and nutrient levels on the elemental dynamics of the particulate and dissolved organic matters (DOMs) produced by diatoms are rarely investigated. Here, we investigated the impacts of four different CO2 levels (180, 380, 600, and 1000 μatm partial pressure of CO2 : pCO2) on the allocation of carbon, nitrogen, phosphorus, and silicon between the particulate matter (PM) and DOM in two cosmopolitan coastal diatoms, Chaetoceros affinis and Ditylum brightwellii, under nutrient‐replete and nitrate‐depleted conditions. Under nutrient‐replete conditions, the specific growth rates of both species were positively correlated with pCO2 levels. The elemental compositions of the exponentially growing diatoms were stable under the different pCO2 conditions. After nitrate depletion, the particulate organic carbon to particulate nitrogen ratio and biogenic silica content per unit biomass in both species were positively correlated with the pCO2 value. Factors affecting the pCO2 dependent change in elemental composition were the variations in the partitioning of organic carbon between PM and DOM in C. affinis, and the physiological uncoupling of intracellular carbon and nitrogen and the intracellular silicon and nitrogen, as well as resting spore formation in D. brightwellii. Under high‐CO2 conditions, the faster growth rates of both diatom species could lead to their dominance in a phytoplankton community; their blooms could modify the first‐order processes in the biogeochemical cycling of bioelements after nitrate depletion

西部北太平洋亜寒帯域と津軽海峡域の酸性化モニタリング

http://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr98-k01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr99-k02/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr00-k01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr00-k03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr01-k03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr03-k01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt03-07/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt04-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-02/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-04/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-06/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr05-01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr05-04/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr07-01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr07-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr08-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr10-06/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr11-02/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr13-04/

北の海でおきている海洋酸性化！ ?その進行と影響?

http://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr98-k01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr99-k02/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr00-k01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr00-k03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr01-k03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr03-k01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt03-07/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt04-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-04/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-06/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr05-01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr05-04/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr07-01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr07-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr08-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr10-06/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr11-02/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr11-03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr13-04/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-02/

西部北太平洋亜寒帯域と津軽海峡の酸性化進行とその影響

http://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr98-k01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr99-k02/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr00-k01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr00-k03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr01-k03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr03-k01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt03-07/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt04-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-04/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-06/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr05-01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr05-04/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr07-01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr07-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr08-05/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr10-06/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr11-02/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr11-03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr13-04/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-02/