Mangrove creeks have extremely large carbonate chemistry parameters (partial pressure of carbon dioxide (pCO2), dissolved inorganic carbon (DIC), and total alkalinity (TA)) owing to the porewater export by tidal pumping. In this study, the relationship between tidal oscillations and carbonate chemistry parameters was clarified, and CO2 emissions from mangrove creeks and swamps were evaluated in a mangrove forest in Japan, where the duration of swamp inundation was longer during neap tides owing tidal asymmetry. The pCO2 values in the mangrove creek ranged between 307 and 6036 µatm, with maximum values recorded at 4583 µatm during the spring tide (symmetric tide) and 6036 µatm during the neap tide (asymmetric tide). Spatiotemporal water sampling over a spring-neap tidal cycle revealed that the increase in the mangrove-derived DIC and TA varied between the inundated and exposed periods of the swamps, with DIC being produced more than TA during the inundated period. This suggests that the increase in the DIC/TA ratio as the duration of the swamp inundation increases controls the CO2 variations over a spring-neap tidal cycle in this region. Although high pCO2 values were recorded in the mangrove creeks, water-air CO2 emissions (integrating flux by inundated area) were limited to approximately 3.3% of the fate of the sequestered carbon, suggesting that approximately 94.6% of the DIC outwelled to the ocean was stored therein.

Carbon export from mangrove forests to the oceans partly acts as a sink for atmospheric CO₂, exceeding the rate of carbon burial in mangrove soils. Primary production in ecosystems adjacent to mangroves may prevent degassing and enhance further carbon export from mangroves to the oceans. In this study, we continuously monitored carbonate chemistry parameters (pCO₂, dissolved inorganic carbon (DIC), total alkalinity (TA)) and dissolved organic carbon (DOC) in a tidal flat adjacent to a fringe mangrove forest over a spring-neap tidal cycle. Mean pCO₂ during the entire period was 923 ± 318 μatm, and the export of TA, DIC, and DOC from the mangroves to the ocean was 36 ± 26 mmol m⁻² d⁻¹, 42 ± 39 mmol m⁻² d⁻¹, and 10 ± 9 mmol m⁻² d⁻¹, respectively. Semi-monthly pCO₂ variations in the mangrove front were controlled by the tidal level during spring tide and by photosynthesis and respiration on the tidal flat during neap tide. This means that during neap tide, photosynthesis on the tidal flat offset the increase in pCO₂ caused by the porewater export from the mangrove soil. The DIC/TA export ratio in this study was 1.17 ± 0.08, which was lower than the global average of 1.41 ± 1.39, indicating that the tidal flat adjacent to the mangrove forest may act as a buffer zone to mitigate the increase in pCO₂, resulting in much of the exported DIC being stored in the ocean.

大気海水間のCO₂交換と海水中のpCO₂の鉛直分布構造の関係を明らかにするため，大阪湾の湾奥部で海水中のDICと水質の鉛直分布と大気中のCO₂を通年にわたって測定するとともに，台風通過前後に同様の調査を実施し気象攪乱の影響を検討した．季節変動調査の結果，生物活性が高くなる高水温期に海水中のpCO₂は高くなるが，平常時のpCO₂は年間を通して大気のほうが表層水より大きく大気から海域へCO₂が吸収されていた．しかし，雨天時は表層水のpHが低下するため炭酸種におけるpCO₂の存在比が大きくなり，大気へCO₂が放出されることが明らかとなった．また，攪乱前後の調査から，湧昇時や台風による攪乱時には海域から大気へCO₂が放出されること，さらに，平常時でも成層期に底層で増加したCO₂が成層の緩和に伴って全水深へと拡がり，大気へ放出されることが確認された．

To understand oxygen consumption characteristics of sediment for the case of oxygen supply to the bottom of sea under the hypoxic condition, we carried out a laboratory experiment by using sediment and artificial-seawater. It is found that the oxygen consumption pattern of sediment is changing while sediment consumes oxygen. Immediately after oxygen supplying, dissolved oxygen of seawater was consumed by the chemical reaction in the sediment. And then dissolved oxygen consumed by the biological reaction.

大阪南港野鳥園北池の炭素収支における植物プランクトンの寄与を評価するため，現地海水を用いた光合成実験と植物プランクトンの炭素吸収量と海域内の炭素動態の現地調査を実施した．明暗瓶実験の結果，Chal.aあたりの光合成量を光量子量と水温の関数で，水中内の呼吸・分解量を水温に依存する関数で定式化した．また，植物プランクトンの現存量と表層水のDICの通年調査から北池内の炭素吸収量と大気海水間の炭素交換量を推定した結果，大気からの取り込み量は植物プランクトンの吸収量に比べて小さく，両者の空間分布や季節変化には相関がみられなかった．最後に，大気海水間および海水交換による炭素収支，植物プランクトンの吸収量，水中内の排出量の日変化を比較した結果，湿地の炭素収支における植物プランクトンの炭素吸収効果は1～3割程度であった．

Mangrove creeks adjoining typical riverine mangrove forests is known to be a net source of CO2 and dissolved inorganic carbon (DIC) to the ocean due to the decomposition of rich organic carbon in the soil; such information is limited in fringe mangroves. This study aims to clarify the difference in carbonate processes between the two types of mangrove forests. We conducted continuous monitoring of the partial pressure of carbon dioxide (pCO2) and measured carbonate chemistry parameters (total alkalinity (TA) and DIC) in two types of mangrove areas located in Okinawa, Japan. The result showed that the maximum pCO2 reached 5242 µatm in the Fukido River estuary (a riverine mangrove), whereas it was only 765 µatm on the Yubu coast (a fringe mangrove). The measured maximum TA and DIC values were 3285 µM and 3283 µM in the Fukido River estuary and 3162 µM and 2977 µM on the Yubu coast. These indicate that pCO2 on the Yubu coast was maintained at low values by the carbonate buffering capacity even when TA and DIC increased rapidly. The mangroves on the Yubu coast grow on dead corals and coral soils. It was suggested that the DIC/TA ratio was constantly kept at approximately 0.9 due to TA production by the dissolution of calcium carbonate (CaCO3), which resulted in lower pCO2.