Comparative analysis of photosynthetic properties in ice algae and phytoplankton inhabiting Franklin Bay, the Canadian Arctic, with those in mesophilic diatoms during CASES 03-04

Psychrophilic phytoplankton and ice algae were collected in Franklin Bay, the Canadian Arctic, in late May 2004, and the photosynthetic properties were measured at 4°C using a pulse amplitude modulation fluorometer (Phyto-PAM). Rapid light curve measurements allowed for the assessment of the photosynthetic efficiency (α), maximal electron transport rate (rETRmax), and minimum saturating irradiance (Ek) in the samples. The values of α in phytoplankton (0.63-0.68) were much larger than those in ice algae (0.10-0.51), and the values of rETRmax in phytoplankton (4.6-6.7) were relatively larger than those in ice algae (1.8-4.3). However, Ek showed similar values in both samples and were around 10μmol photonsm^・s^. These values were systematically compared with those obtained from mesophilic marine diatoms (a centric diatom, Chaetoceros gracilis, and a pennate diatom, Phaeodactylum tricornutum) grown under various irradiances in the laboratory. The highly shade-adapted features of ice algae and phytoplankton were disclosed through this comparative analysis. It was also found that the non-photochemical quenching was much higher in psychrophilic samples than in mesophilic diatoms grown under moderate irradiance. Furthermore, in ice algae and phytoplankton, the decrease in rETR at high irradiances was prominent, showing that they were highly susceptible to photoinhibition. Our comparative analysis using psychrophilic phytoplankton, ice algae and two strains of mesophilic diatoms also revealed that the dependency on the xanthophyll cycle for the protection mechanisms of photosystems were remarkably different between the groups, indicating that the acclimation strategies to growth irradiances were variable between species. Such variable acclimation strategies could be one of the forces that results in a diverse algal flora that enables this region around Franklin Bay to be a productive area, even though the psychrophilic phytoplankton and ice algae are highly shade-adapted

A recent new knowledge on the biological carbon pump: From an international collaboration with a Canadian research group

第3回極域科学シンポジウム/特別セッション「これからの北極研究」11月28日（水） 国立極地研究所 2階大会議

Canadian Arctic Shelf Exchange Study(CASES) ケイカク ニツイテ ノ ワークショップ ホウコク

CASES(Canadian Arctic Shelf Exchange Study)計画はカナダのラバル大学を核としてカナダ,日本,アメリカなど10数カ国の研究者が参加する国際共同研究である.CASES計画はボーフォート海南東部のアムンゼン湾に形成されるCape Bathurst polynya,更にはマッケンジー河口流域から大陸棚域,またその北方海盆域との間(69°-73°N,122°-140°W)を対象海域としている.CASES計画の目的は,これらの海域における生態系の構造と機能の解明,および物質循環過程の解明である.CASES 2003-2004航海の大きな特徴は1年間にわたり観測船を研究海域に定置させることにある.そのため極域では例を見ない冬期間や早春の大規模な海洋観測が可能となる.そこで,日本の研究グループでは,これまで研究例の少ない寒冷海域における動物プランクトンの越冬生態に注目し,その活動が年間の物質循環過程に与える影響について明らかにすることをコアプロジェクトとした.得られる観測結果は,長期的な地球規模の環境変動を評価する上でも重要な科学的知見となる.The Canadian Arctic Shelf Exchange Study (CASES) is an international scientific program led by Canadian scientists at Laval University collaborating with more than 10 countries including Canada, Japan and USA. This program is carried out to know ecological and biogeochemical processes in sea area of the Mackenzie shelf, continental margin, and Cape Bathurst polynya in Amundsen Gulf. The CASES will carry out an over-wintering cruise" for scientific observations in open polar seas from the beginning of September 2003 to the end of August 2004. The Japanese CASES team focused on specific strategies of over-wintering zooplankton and their possible role in the biogeochemical cycling and transport of biogenic material in those sea areas through the year, primarily because of insufficient information on ecological processes of overwintering zooplankton, such as copepods and microzooplankton

南極海酸性化の長期観測用指標としての隔離フラックス測定

第6回極域科学シンポジウム分野横断セッション：[IB1] 海氷域における生物地球化学的研究11月17日（火）　統計数理研究所 セミナー室1（D305

南大洋インド洋区における植物プランクトン群集の光保護応答

第6回極域科学シンポジウム分野横断セッション：[IB1] 海氷域における生物地球化学的研究11月17日（火）　国立極地研究所１階交流アトリウ

南極海インド洋区における粒状物質（全粒子、炭素、窒素）の鉛直フラックスの3年間に渡る変動

第6回極域科学シンポジウム分野横断セッション：[IB1] 海氷域における生物地球化学的研究11月17日（火）　統計数理研究所 セミナー室1（D305

Variations in contributions of dead copepods to vertical fluxes of particulate organic carbon in the Beaufort Sea

Dead zooplankton, including crustaceans, are increasingly recognized as important agents of vertical carbon export from surface waters and in marine food webs. Quantifying the contribution of passively sinking copepods (PSCs) to vertical fluxes of total particulate organic carbon (POC) is important for understanding marine ecosystem carbon budgets. Information on this is limited because identifying PSCs in sediment trap samples is difficult. Generally, swimmers (undecomposed metazoans, including PSCs, caught in sediment traps) are removed from a trap sample before the POC content is measured, although ignoring PSCs causes the total POC flux to be significantly underestimated. We quantified temporal and regional variability in PSC flux and contribution of PSCs to total POC flux (PSCs + detrital sinking particles, generally analyzed to estimate detrital POC flux) at the Mackenzie Shelf margins in the Beaufort Sea. Six datasets were used to examine PSC flux variability at ~100 m depth, which is deeper than the winter pycnocline depth (30-50 m), at the continental margin. The average (±SD) annual PSC flux (1378 ± 662 mg C m-2 yr-1, n = 6 [datasets]) and PSC contribution to the total POC flux (21 ± 10%, n = 6) suggested that PSCs, especially Pareuchaeta glacialis, were important agents of POC export from the surface layer (~100 m) to deeper water at the inter-regional and multiyear scales. We propose a hypothesis that processes controlling PSC flux variability may vary seasonally, perhaps relating to life cycle (reproduction) in winter (February) and osmotic stress in July-October when the PSC flux is relatively high

Sediment-Associated Phytoplankton Release From the Seafloor in Response to Wind-Induced Barotropic Currents in the Bering Strait

Bering Strait is the single gateway between the Arctic and Pacific Oceans, and has localized strong currents, which can exceed 100 cm s^-1. Although massive spring phytoplankton blooms and the subsequent production of particulate organic matter that sinks to the seafloor are observed in the surrounding regions of the Bering Strait, the impact of the locally strong current on the horizontal and vertical transport of the particles remains unclear. Therefore, we conducted year-round mooring measurements from 2016 to 2017 by focusing on near-bottom processes associated with ocean currents. Our time-series analysis showed that high-turbidity events, triggered by strong barotropic currents, occurred near the seafloor in all seasons. Consequently, the fluorescence sensor detected highly concentrated chlorophyll a in the resuspended sediment; however, the amount of chlorophyll a release was seasonal, with large and small amounts being released during the warm and cold seasons, respectively. The small amounts of chlorophyll a may be attributed to small amounts of phytoplankton in the sediment owing to less input of fresh phytoplankton from the overlaying water column and organic matter decomposition in the sediments under no-light conditions. The barotropic currents were modulated by surface winds associated with an intercontinental atmospheric pattern having a 5000-km spatial scale on a timescale of 6 days. The locally strong ocean current in the Bering Strait, driving the upward transport of sediment and the subsequent horizontal transport, may play a vital role in supplying particulate organic matter/phytoplankton/nutrients to the downstream region of the southern Chukchi Sea where the formation of biological hotspots is reported

A report on workshop of Canadian Arctic Shelf Exchange Study (CASES)

The Canadian Arctic Shelf Exchange Study (CASES) is an international scientific program led by Canadian scientists at Laval University collaborating with more than 10 countries including Canada, Japan and USA. This program is carried out to know ecological and biogeochemical processes in sea area of the Mackenzie shelf, continental margin, and Cape Bathurst polynya in Amundsen Gulf. The CASES will carry out an over-wintering cruise" for scientific observations in open polar seas from the beginning of September 2003 to the end of August 2004. The Japanese CASES team focused on specific strategies of over-wintering zooplankton and their possible role in the biogeochemical cycling and transport of biogenic material in those sea areas through the year, primarily because of insufficient information on ecological processes of overwintering zooplankton, such as copepods and microzooplankton