Year-round observations of sea-ice drift and near-inertial internal waves in the Northwind Abyssal Plain, Arctic Ocean

The Tenth Symposium on Polar Science/Ordinary sessions: [OM] Polar Meteorology and Glaciology, Thu. 5 Dec. / 2F Auditorium , National Institute of Polar Researc

Nutrient supply and biological response to wind-induced mixing, inertial motion, internal waves, and currents in the northern Chukchi Sea

A fixed-point observation station was set up in the northern Chukchi Sea during autumn 2013, and for about 2 weeks conductivity-temperature-depth (CTD)/water samplings (6-hourly) and microstructure turbulence measurements (two to three times a day) were performed. This enabled us to estimate vertical nutrient fluxes and the impact of different types of turbulent mixing on biological activity. There have been no such fixed-point observations in this region, where incoming low-salinity water from the Pacific Ocean, river water, and sea-ice meltwater promote a strong pycnocline (halocline) that stabilizes the water column. Previous studies have suggested that because of the strong pycnocline wind-induced ocean mixing could not change the stratification to impact biological activity. However, the present study indicates that a combined effect of an uplifted pycnocline accompanied by wind-induced inertial motion and turbulent mixing caused by intense gale-force winds (>10 m s-1) did result in increases in upward nutrient fluxes, primary productivity, and phytoplankton biomass, particularly large phytoplankton such as diatoms. Convective mixing associated with internal waves around the pycnocline also increased the upward nutrient fluxes and might have an impact on biological activity there. For diatom production at the fixed-point observation station, it was essential that silicate was supplied from a subsurface silicate maximum, a new feature that we identified during autumn in the northern Chukchi Sea. Water mass distributions obtained from wide-area observations suggest that the subsurface silicate maximum water was possibly derived from the ventilated halocline in the Canada Basin

シベリア側北極海の沿岸-陸棚-海盆域に及ぶ生物地球化学過程の変化

北極海の中でもシベリア側北極海は、地球温暖化に伴う海底永久凍土の融解や海岸浸食、そして海氷激減が引き金となり生物地球化学的な変化が最もダイナミックに起きている海域である。海底永久凍土の融解は温暖化ガスであるメタンを大気中に放出させ (Shakhova et al., 2010a, b)、さらなる温暖化を招く恐れがある。海岸浸食は炭素・栄養塩・微量金属・粒子態及び溶存態有機物等を北極海に供給し (e.g., Semiletov et al., 2011, 2012, 2013)、CO2の大気への放出や基礎生産、微生物生産の増減を左右する可能性がある。また、海氷減少は水塊構造や海洋循環の変化を伴い栄養塩分布を変化させ (Nishino et al., 2011, 2013)、その結果、基礎生産や生物ポンプにも影響すると考えられる。しかし、この海域はロシアEEZ内、或いはそれに近接しているため、利用できるデータが非常に限られており、生物地球化学的な変化の定量的な評価はもちろん、基本的な物質循環像さえ、ほとんど分かっていない。 　本研究では、ロシアEEZ海域を含むシベリア側北極海の船舶観測を中心として、氷上キャンプやセジメントトラップ・係留系による観測、さらに衛星データや数値モデルを駆使して、シベリア側北極海で起きているダイナミックな生物地球化学的変化を把握するとともに、それが環北極海域、そして全球の生態系・気候システムに与える影響について評価する。発表資料, 北極環境研究コンソーシアム (JCAR) 長期計画ワークショッ

Abundances and ebridian skeleton contents from IODP Exp302

Abundant and diversified ebridians recovered during IODP Expedition 302 (ACEX) have been identified and counted in order to establish their taxonomy and to decipher the biostratigraphic potential of ebridians in the central Arctic Ocean. In the ACEX samples these fossils are preserved in Lithologic Units 1/6 and 2, which consist mainly of dark silty clay and biosiliceous ooze, respectively. Thirty taxa have been distinguished, three of which are described as new species (Ammmodochium lomonosovense, Pseudammodochium karyon, and pseudammodochium psichion). The most dominant ebridian species is Pseudammodochium dictyoides throughout the biosiliceous section. The second dominant species varies alternately throughout the section. Based on the characteristic occurrences of major ebridian taxa, the ebridian assemblageswere divided into GroupsAtoDin stratigraphic order. The ebridian assemblages in piston core USGS Fl-422 from the Alpha Ridge probably correlate to our assemblage Group A of early middle Eocene age, although rare younger taxa are irregularly included

Abundances and contents of major silicoflagellates from IODP Holes of Exp302

The silicoflagellate taxa obtained in IODP Expedition 302 (ACEX) were identified and counted in order to establish the silicoflagellate biostratigraphy in the central Arctic Ocean. These microfossils in the ACEX samples were preserved in the Lithology Units 1/6 and 2, which are dark silty clay and biosiliceous ooze, respectively. The silicoflagellate skeletons in the ACEX samples are assigned to 56 taxa. Seven taxa were described as new species, which were abundant in Lithology Unit 2. Comparison with several study cases outside the Eocene Arctic Ocean suggested that the silicoflagellate assemblages in ACEX were unique in Lithology Unit 2. The dominance of silicoflagellate taxa varied throughout the lithological section. Based on the cluster analysis by Morishita similarity index C(Lambda), the silicoflagellate assemblageswere divided into nine assemblage groups. The silicoflagellate datum event of the first occurrence of Corbisema hexacantha in the lower part of Lithology Unit 1/6 is regarded. Based on the datum events for silicoflagellate and palynomorphs, the assigned epoch of Lithology Units 1/6 and 2 is the middle Eocene

(Table 2) Similarity Indexes (Pearson's correlation coefficient) of the silicoflagellate assemblages of IODP Exp302

The silicoflagellate and ebridian assemblages in early middle Eocene Arctic cores obtained by IODP Expedition 302 (ACEX) were studied in order to decipher the paleoceanography of the upper water column. The assemblages in Lithologic Unit 2 (49.7-45.1 Ma), one of the biosiliceous intervals, were usually endemic as compared to the assemblages that occurred outside of the Arctic Ocean. The presence of these endemic assemblages is probably due to a unique environmental setting, controlled by the degree of mixing between the low-salinity Arctic waters and relatively high salinity waters supplied from outside the Arctic Ocean, such as the Atlantic and possibly the Western Siberian Sea. Using the basin-to-basin fractionation model, the early middle Eocene Arctic Ocean corresponds to an estuarine circulation type, which includes the modern-day Black Sea. The abundant down-core occurrence of ebridians strongly suggests the past presence of low-salinity waters, and may indicate that low oxygen concentrations prevailed in the euphotic layer, on the basis of the ecology of the modern ebridian Hermesinum adriaticum