Winter iron supply processes fueling spring phytoplankton growth in a sub-polar marginal sea, the Sea of Okhotsk: Importance of sea ice and the East Sakhalin Current

Kanna, Naoya; Sibano, Yusuke; Toyota, Takenobu; Nishioka, Jun

doi:10.1016/j.marchem.2018.08.006

Cited by 14 publications

(9 citation statements)

References 47 publications

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“…Spring phytoplankton communities in coastal southern Okhotsk waters off Hokkaido, Japan can also be directly affected by ice melting. High Chl a concentrations of around 30 and 60 mg m −3 have been observed in the southern part of the Sea of Okhotsk and the coastal waters of Mombetsu Harbor during the ice melt season (Taguchi et al, 2000;Kanna et al, 2018). Such high Chl a concentration could be attributed to the released ice algal cells.…”

Section: Introductionmentioning

confidence: 97%

Response to Sea Ice Melt Indicates High Seeding Potential of the Ice Diatom Thalassiosira to Spring Phytoplankton Blooms: A Laboratory Study on an Ice Algal Community From the Sea of Okhotsk

et al. 2020

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Phytoplankton communities in seasonally ice-covered areas are largely affected by ice algae. The Okhotsk Sea is the southernmost sea ice zone in the northern hemisphere with a sizeable seasonal ice cover, thus ice algae of the Okhotsk sea ice have a large potential to seed the early spring bloom. Little is known about the Okhotsk ice algal communities and their seeding effects. We investigated the dynamics of the composition and the photophysiological performances of an Okhotsk ice algal community in a 6day laboratory incubation experiment that simulated the natural ice melt conditions. Centric diatoms, especially Thalassiosira spp., overwhelmingly dominated the ice algal community throughout incubation, whereas pennate diatoms, mostly Navicula and Nitzschia, showed little growth with much higher mortality. The maximum photochemical efficiency of Photosystem II (F v /F m) was the lowest at the beginning of the ice melt, suggesting a suppressed photosynthetic functioning by changes in salinity. The cellular pigment contents decreased by 30% due to osmotic stress, evidenced by deformed plastids under a microscope. The transcript level of the rbcL gene that encodes the large subunit of RubisCO was significantly higher during ice melt and decreased in the no-ice period, suggesting an urgent need for carbon fixation under the melt condition. Full recovery of photosynthesis and growth was also made after complete ice melt. Our results indicated high seeding potential of Thalassiosira to spring blooms owing to their photophysiological plasticity to dynamic salinity changes.

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Section: Introductionmentioning

confidence: 97%

Response to Sea Ice Melt Indicates High Seeding Potential of the Ice Diatom Thalassiosira to Spring Phytoplankton Blooms: A Laboratory Study on an Ice Algal Community From the Sea of Okhotsk

et al. 2020

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“…On the front's offshore boundary, there is a region with an MLD > 120 m between the isobaths at 100 and 200 m (Fig. 2c); the MLD is obtained from the water depth where the density increases by 0.125 kg/m 3 (Kanna et al 2018;Suga et al 2004;Levitus 1982) compared to that of the surface density. The MLD value at the shelf break ( x A ~ 40 km) is larger than that in the open ocean by approximately 50 m; in the open ocean, the mixed-layer base is characterized by an isopycnal surface of 1026.0 kg/m 3 .…”

Section: Along-isobath Averaged Section Of the Escmentioning

confidence: 99%

“…Although the riverine iron is primarily deposited and sedimented on the ESC upstream shelf, the deposited iron is likely to be resuspended by strong wintertime mixing and therefore mingle with the surrounding water as well as become frozen into the sea ice (Ito et al 2017) and then transported to the south. The transported mixed water and ice, which contain considerable iron (Kanna et al 2014(Kanna et al , 2018, facilitate the next spring blooms not only in the southern Sea of Okhotsk (Mustapha and Saitoh 2008) but also in the Oyashio and western North Pacific Ocean (Kuroda et al 2019).…”

Section: Introductionmentioning

confidence: 99%

“…Considering the difficulty of wintertime hydrographic observations off the Sakhalin, observations of the ESC by an ice breaker off Hokkaido in the south of the Sea of Okhotsk were suggestive, and similar well-mixed water masses were observed at the shelf break (Ohshima et al 2005(Ohshima et al , 2001Mizuta et al 2004). The mixed water mass has a thickness larger than 200 m and contains sea-ice melting water as well as riverine discharge water from the far-eastern Eurasian Continent (Kanna et al 2018), while the water over the shallower shelf was stratified. This deep mixed water is characterized by high nutrient and iron concentrations, and it flows out from the Sea of Okhotsk as the Coastal Oyashio and fertilizes the western North Pacific (Kuroda et al 2019).…”

Section: Introductionmentioning

confidence: 99%

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Cross-shelf overturning in geostrophic-stress-dominant coastal fronts

Yuan

Mitsudera

2022

J Oceanogr

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Compared to the dynamics of the predominantly geostrophic along-shelf current, our understanding of the cross-shelf dynamics in the Sea of Okhotsk is inadequate despite their importance in water mixing and nutrient entrainment. We investigated the cross-shelf overturning circulation along the East Sakhalin Current, which is a source of nutrients such as iron for the western North Pacific. Here, we reveal that the cross-shelf circulation during winter is characterised by a nearshore upwelling and a shelf-break downwelling under a downwelling-favourable monsoon wind, contrary to a classical Ekman overturning (EOT). This reverse EOT is driven by the internal water stress, which is caused by intensive vertical mixing and geostrophic vertical shear in the shelf-break front produced by riverine discharges from the far-eastern Eurasian Continent. The EOT blocks the Ekman onshore transport from the open ocean, thereby producing a deep mixed layer at the shelf break. Scaling analyses indicate the applicability of this mechanism to various other shelf-break fronts.

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“…11b), lower salinities (Nishioka et al 2011;Kuroda et al 2019) and higher Fe concentrations (Fig. 11c) than the surrounding waters (Nakayama et al 2010;Nishioka et al 2011), which are probably influenced by the winter surface ESC (including the influence of the Amur River discharge) and by sea ice melt water from the Sea of Okhotsk, which contains high amounts of Fe (Kanna et al 2014(Kanna et al , 2018) (Fig. 11c).…”

Section: Impact On the Phytoplankton Ecosystemmentioning

confidence: 99%

A review: iron and nutrient supply in the subarctic Pacific and its impact on phytoplankton production

et al. 2021

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One of the most important breakthroughs in oceanography in the last 30 years was the discovery that iron (Fe) controls biological production as a micronutrient, and our understanding of Fe and nutrient biogeochemical dynamics in the ocean has significantly advanced. In this review, we looked back both previous and updated knowledge of the natural Fe supply processes and nutrient dynamics in the subarctic Pacific and its impact on biological production. Although atmospheric dust has been considered to be the most important source of Fe affecting biological production in the subarctic Pacific, other oceanic sources of Fe have been discovered. We propose a coherent explanation for the biological response in subarctic Pacific high nutrient low chlorophyll (HNLC) waters that incorporates knowledge of both the atmospheric Fe supplies and the oceanic Fe supplies. Finally, we extract future directions for Fe oceanographic research in the subarctic Pacific and summarize the uncertain issues identified thus far.

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Winter iron supply processes fueling spring phytoplankton growth in a sub-polar marginal sea, the Sea of Okhotsk: Importance of sea ice and the East Sakhalin Current

Cited by 14 publications

References 47 publications

Response to Sea Ice Melt Indicates High Seeding Potential of the Ice Diatom Thalassiosira to Spring Phytoplankton Blooms: A Laboratory Study on an Ice Algal Community From the Sea of Okhotsk

Response to Sea Ice Melt Indicates High Seeding Potential of the Ice Diatom Thalassiosira to Spring Phytoplankton Blooms: A Laboratory Study on an Ice Algal Community From the Sea of Okhotsk

Cross-shelf overturning in geostrophic-stress-dominant coastal fronts

A review: iron and nutrient supply in the subarctic Pacific and its impact on phytoplankton production

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