Long term trend of chemical oxygen demand in Saroma-ko Lagoon, Japan; possible effects of climatic warming

A trend of shortening duration of ice coverage has been reported in many rivers, ponds and lakes around the world due to climatic warming. The shortening will have much influence on organic production due to the greater supply of light intensity and hence on water quality. Chemical Oxygen Demand (COD), a useful measure of water quality, has been monitored over the past thirty years in Saroma-ko Lagoon, a boreal lake in Japan characterized by wintertime ice coverage. Here the data set of water quality in the lagoon is analyzed to reveal long-term trends in COD and the influence of climatic warming on such trends. There has been a significant increasing trend, caused primarily by an abrupt increase in the early 1990s. However, the increase could not be explained by the increased load of organic matter on the lagoon from the river basin and organic production in the lagoon. On the other hand, periods of freezing of the entire surface have tended to be shorter with inevitable thinning of ice over the past forty years, probably due to climatic warming. Ice and planktonic algae are exposed to the low light intensity in situ, which is not optimum for the algal production of organic matter. The shortening and thinning should thus bring an improvement in ambient light conditions for algae, resulting in an increase of organic matter in winter. Most of the organic matter possibly remains even after spring because of the low water temperature. It is highly possible that climatic warming promotes deterioration in water quality in ice-covered lakes

Subsurface chlorophyll a maximum in the coastal front around St. Paul Island

Size-fractionated primary productivity and chlorophyll a (Chl a) concentration were measured in the middle domain of the southeastern Bering Sea shelf in summer 2004. A subsurface Chl a maximum of 7.9 μg l^(-1) was observed at 20 m depth, around the pycnocline in the coastal front around St. Paul Island. Large phytoplankton exceeding 10 μm in size accounted for about 80% of the primary productivity and Chl a concentration at the subsurface Chl a maximum. The growth rate of the large phytoplankton was estimated to be 0.09 d^(-1), which is low compared to previously reported growth rates as well as other rates obtained in this study (0.06-0.56 d^(-1)). More abundant nutrient supply from deeper to upper layers due to the topography of the area is considered the leading factor producing the subsurface Chl a maximum. Moreover, ineffective grazing of the large phytoplankton in the middle shelf domain and their accumulation around the pycnocline are thought to be advantageous factors maintaining the subsurface Chl a maximum

Distribution of biogenic particulate matter in the surface waters of the Bering Sea basin, winter 1993

Biogenic silica (BSi), particulate organic carbon (POC) and nitrogen (PON) and chlorophyll α (Chl α) of surface waters were measured in the Bering Sea basin from January through March 1993. BSi concentration varied extraordinarily among stations (0.01-0.59μM) and was relatively high in the central region. POC and PON concentrations showed variations of several fold among stations (2.28-11.38μM for POC and 0.36-2.11μM for PON), and were relatively high in the eastern region. The regional variations of POC and PON concentrations reflected that of Chl α concentration, whereas the same results were not found for the BSi concentration. Extraordinary variation was found in the BSi/POC atomic ratio (0.070) were observed in the central region. Values higher than 0.13,the typical atomic ratio of cellular silicon to cellular carbon for culture diatoms, were also found. In contrast, POC/PON atomic ratios were roughly uniform (mostly 4-10) and the average was 6. 7. The present results show a possibility that diatoms with high silicon demand occur in the Bering Sea basin in winter. In addition, I also compared the characteristics of biogenic particulate matter with those in the summertime Bering Sea basin and in the wintertime Antarctic Ocean

Seasonal variations in abundance of pico- and nano-plankton in Lagoon Notoro-ko adjacent to the southwestern Okhotsk Sea

第6回極域科学シンポジウム[OB] 極域生物圏11月16日（月）　国立極地研究所１階交流アトリウ

Population dynamics of Pseudocalanus newmani in the coastal area of southwestern Okhotsk Sea

第6回極域科学シンポジウム[OB] 極域生物圏11月16日（月）　国立極地研究所１階交流アトリウ

オホーツクエンガン カイセキコ ノトロコ ニ オケル イチジセイサントクセイ -サイズベツ クロロフィル a ト ヨウゾンタイムキチッソ ノ ドウタイ-

オホーツク海と湖口部でつながり,潮汐変動により湖水交換が行われる能取湖にて2007-2009年,一次生産の特性を把握することを目的に調査研究を実施し,サイズ別クロロフィルaと溶存態無機窒素に着目し検討した。本研究の結果,能取湖のクロロフィルaは,基本的には10m以上の大型の画分により構成され,特に春季の底層で高い値を示した。しかし,春季に高濃度のクロロフィルaが観測された後(5,6月)や冬季には小型の画分のクロロフィルa濃度が高くなる現象もみられた。溶存態無機窒素は,調査期間中,アンモニア態窒素が優占し,特に成層期の底層で高濃度に分布していた。このことは,能取湖はアンモニア態窒素が硝酸態窒素へと酸化される前に植物プランクトンが利用する環境にあることが推察された。一方,冬季には外海水の影響と推察される硝酸態窒素が優占する現象も確認された。これらの変動は,湖口でつながるオホーツク海から流入する外海水の勢力による変動,気象の変化にともなう表面加熱・表面冷却による水柱の成層と対流による変動,そして半閉鎖的環境による集積効果,これらが複雑に組み合わされることによりもたらされていることが示唆された。Lagoon Notoroko is connected to the Okhotsk Sea by an artificial channel so the water mass of this lagoon has been exchanged by tidal movement and little river water flows into this lagoon. Therefore, the lagoon is assumed to be a saltwater lagoon and seasonal change of environmental conditions in the lagoon have been affected by the coastal waters of the Okhotsk Sea. Size-fractionated chlorophyll a and dissolved inorganic Nitrogen were measured in this lagoon from 2007 through 2009. The chlorophyll a was basically comprised by large-sized phytoplankton (more than 10m). However, the small-sized phytoplankton (<2 and 2-10m fraction) might be found at high concentrations after spring bloom and/or in the winter season so the influence of open-sea water might be strongly seen. It was notable that ammonium nitrogen concentration existed most in dissolved inorganic nitrogen (DIN). Especially, concentrated ammonium has been distributed in the bottom water. Ammonium was an easily assimilable nutrients for phyotoplankton which was the primary producer in the marine ecosystem. It was suggested that these changes of concentrations of size-fractionated chlorophyll a and DIN were constructed by the variation of the inflow of water mass from Okhotsk Sea, the change of the stratification and convection of the water column with the change of the temperature and the cumulus effect of semi-enclosed environment