Why is Trichodesmium abundant in the Kuroshio?

The genus Trichodesmium is recognized as an abundant and major diazotroph in the Kuroshio, but the reason for this remains unclear. The present study investigated the abundance of Trichodesmium spp. and nitrogen fixation together with concentrations of dissolved iron and phosphate in the Kuroshio and its marginal seas. We performed the observations near the Miyako Islands, which form part of the RyGBRyu Islands, situated along the Kuroshio, since our satellite analysis suggested that material transport could occur from the islands to the Kuroshio. Trichodesmium spp. bloomed (> 20 000 filaments L-1) near the Miyako Islands, abundance was high in the Kuroshio and the Kuroshio bifurcation region of the East China Sea, but was low in the Philippine Sea. The abundance of Trichodesmium spp. was significantly correlated with the total nitrogen fixation activity. The surface concentrations of dissolved iron (0.19-0.89 nM) and phosphate (< 3-36 nM) were similar for all of the study areas, indicating that the nutrient distribution could not explain the spatial differences in Trichodesmium spp. abundance and nitrogen fixation. Numerical particle-tracking experiments simulated the transportation of water around the RyGBRyu Islands to the Kuroshio. Our results indicate that Trichodesmium growing around the RyGBRyu Islands could be advected into the Kuroshio

R/V SHINSEI MARU Cruise Report KS-21-15

調査海域: 駿河湾, 南海トラフ北縁部, 四国南方海域, 九州南方海域, 沖縄北東海域, 熊野灘 / Area: Southern waters of Shikoku, Southern waters of Kyushu, Northeast water of Okinawa ; 期間: 2021年7月25日～2021年7月31日 / Operation Period: July 25, 2021～July 31, 2021http://www.godac.jamstec.go.jp/darwin/cruise/shinsei_maru/ks-21-15/

RV Shinsei maru "Cruise Report" KS-20-15_leg1

調査海域: 三陸沿岸 / Area: Sanriku coastal area ; 期間: 2020年9月26日～2020年9月30日 / Operation Period: September 26, 2020～September 30, 2020http://www.godac.jamstec.go.jp/darwin/cruise/shinsei_maru/ks-20-15_leg1/

R/V SHINSEI MARU Cruise Report KS-21-8

調査海域: 房総, 常磐沖, 相模湾 / Area: Off Boso, Joban coasts, Sagami Bay ; 期間: 2021年5月13日～2021年5月18日 / Operation Period: May 13, 2021～May 18, 2021http://www.godac.jamstec.go.jp/darwin/cruise/shinsei_maru/ks-21-8/

R/V Shinsei-maru Cruise Report KS-19-19

調査海域: 本州東方沖 / Area: East of Honshu ; 期間: 2019年9月27日～2019年10月4日 / Operation Period: September 27, 2019～October 4, 2019http://www.godac.jamstec.go.jp/darwin/cruise/shinsei_maru/ks-19-19/

R/V SHINSEI MARU Cruise Report KS-21-3

調査海域: 東北沿岸域 / Area: Coastal areas off Tohoku ; 期間: 2021年3月23日～2021年3月30日 / Operation Period: March 23, 2021～March 30, 2021http://www.godac.jamstec.go.jp/darwin/cruise/shinsei_maru/ks-21-3/

Methyl halides in surface seawater and marine boundary layer of the northwest Pacific

The partial pressures of methyl halides (CH3X; X = Cl, Br, or I) and of CHClF2 (HCFC‐22), which are all volatile organic compounds (VOCs), were measured in the air of the marine boundary layer (pVOCair) and in surface seawater (pVOCwater) during a cruise from the subarctic to subtropical regions of the northwest Pacific in summer of 2008. In the northern transition water (TWN) with high biological activity, high levels of the three CH3Xs in surface seawater were frequently observed, probably owing to their enhanced production by phytoplankton. Supersaturation of CH3Br was only present in TWN water, with a saturation anomaly (SCH3Br) of 0.95 [SCH3X = (pCH3Xwater − pCH3Xair)/pCH3Xair]. The highest saturation anomalies for CH3Cl (SCH3Cl = 1.6) and CH3I (SCH3I = 91) were found in the southern subtropical water (STS) with low biological production south of the subtropical front. We found that the molar concentrations of CH3Cl (CCH3Cl) and CH3I (CCH3I) sharply increased with increasing sea surface temperature (SST) in the subtropical waters. The maximum CCH3Cl (144 pmol l−1) was present in STS water at SST = 30°C and is 1.5 times the value extrapolated from the previously reported relationship between CCH3Cl and SST. Photochemical production might have contributed to the production of CH3Cl and CH3I in STS water