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

Assessing impacts of coastal warming, acidification, and deoxygenation on Pacific oyster (Crassostrea gigas) farming: a case study in the Hinase area, Okayama Prefecture, and Shizugawa Bay, Miyagi Prefecture, Japan

Coastal warming, acidification, and deoxygenation are progressing primarily due to the increase in anthropogenic CO2. Coastal acidification has been reported to have effects that are anticipated to become more severe as acidification progresses, including inhibiting the formation of shells of calcifying organisms such as shellfish, which include Pacific oysters (Crassostrea gigas), one of the most important aquaculture resources in Japan. Moreover, there is concern regarding the combined impacts of coastal warming, acidification, and deoxygenation on Pacific oysters. However, spatiotemporal variations in acidification and deoxygenation indicators such as pH, the aragonite saturation state (Ωarag), and dissolved oxygen have not been observed and projected in oceanic Pacific oyster farms in Japan. To assess the present impacts and project future impacts of coastal warming, acidification, and deoxygenation on Pacific oysters, we performed continuous in situ monitoring, numerical modeling, and microscopic examination of Pacific oyster larvae in the Hinase area of Okayama Prefecture and Shizugawa Bay in Miyagi Prefecture, Japan, both of which are famous for their Pacific oyster farms. Our monitoring results first found Ωarag values lower than the critical level of acidification for Pacific oyster larvae in Hinase, although no impact of acidification on larvae was identified by microscopic examination. Our modeling results suggest that Pacific oyster larvae are anticipated to be affected more seriously by the combined impacts of coastal warming and acidification, with lower pH and Ωarag values and a prolonged spawning period, which may shorten the oyster shipping period and lower the quality of oysters.</p

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

表層海水中溶存酸素の高精度連続観測

大気・海洋間の二酸化炭素や酸素の交換量と，その時空間変動要因や，大気中の温室効果ガスの動態を解明するための一環として，表層海水中溶存酸素の高精度連続観測に取り組んでいる．海洋地球研究船「みらい」では，表層海水連続測定装置により，水温・塩分の測定に加え，世界中で広く利用されているAADI社製OPTODEによる溶存酸素，および，蛍光光度計によるクロロフィルaの測定が行われてきた．OPTODEは時間安定性が優れており，連続観測に適していると考えられているが，応答時間が遅い（カタログによれば67%応答時間は20℃で23秒）という問題があった．そこで，船舶CTDO観測で培った高精度溶存酸素測定技術に基づき，2012年度から表層海水連続測定装置に応答時間が早いJFE Advantech社製RINKOを追加した．溶存酸素検出膜の適切なエイジングと標準ガスを用いたセンサー出力値の線形化，および，時間ドリフト補正用の溶存酸素の分析値を取得することで，溶存酸素の高精度連続観測を実現し，北極海，ベーリング海，西部太平洋，南大洋の広範囲でデータを蓄積した．従来のOPTODEと新たに導入したRINKOの比較から，RINKOに比べてOPTODEは約8分遅れて応答していることや，北極海などでの塩分の短時間での大きな変化に対応してOPTODEが不自然に大きく応答することが明らかになった．さらに，RINKOの技術を応用し，センサーを用いた酸素法による基礎生産量の測定を試みている．これらのデータを総合的に解析し，表層海水中の溶存酸素の時空間変動特性を把握し，変動要因の解明を目指す．BE13-19講演要旨 / ブルーアース2013（2013年3月14日～15日, 東京海洋大学品川キャンパス）http://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr12-e03/

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

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/

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/