Dynamics and Origin of Transparent Exopolymer Particles in the Oyashio Region of the Western Subarctic Pacific during the Spring Diatom Bloom

Abstract

The seasonal biological drawdown of the partial pressure of CO 2 (pCO 2 ) in the surface waters of the Oyashio region of the western subarctic Pacific is one of the greatest among the world's oceans. This is attributable to spring diatom blooms. Transparent exopolymer particles (TEPs) are known to affect efficiency of the biological carbon pump, and higher TEP levels are frequently associated with massive diatom blooms. However, TEP dynamics in the Oyashio region remain unclear. We investigated the TEP distribution from three cruises during the spring diatom bloom periods in 2010 and 2011. TEP concentrations varied from < 15 to 196 ± 71 µg xanthan gum equiv. L −1 above 300 m and generally declined with depth. Vertical TEP concentrations were significantly related not only to chlorophyll a concentrations but also to bacterial abundance. Average TEP concentrations within the mixed layer (> 30 m) were significantly higher during the bloom (155 ± 12 µg xanthan gum equiv. L −1 ) than in the post-bloom phase (90 ± 32 µg xanthan gum equiv. L −1 ). In contrast, bacteria abundance within the mixed layer changed little during the bloom to post-bloom phases. These results suggest that the abundance of phytoplankton greatly contributed to dynamics of the TEP distribution. To evaluate the ability of the phytoplankton to produce TEP, an axenic strain of the diatom Thalassiosira nordenskioeldii, which is a representative species of Oyashio blooms, was examined within a batch culture system. Cell abundance-normalized TEP and dissolved organic carbon (DOC) production rates changed simultaneously with growth of the strain. Although these production rates were significantly higher in the stationary phase than in the exponential growth period, values of the TEP/DOC ratio changed little throughout incubation. These findings suggest that TEP production in the Oyashio region may be enhanced by an increase in DOC production from spring diatoms.

Responses of phytoplankton assemblages to iron availability and mixing water masses during the spring bloom in the Oyashio region, NW Pacific

“…The diatom species identified by SEM consisted of a mixture of Thalassiosira and Chaetoceros species. Previous studies also showed that these species were co‐dominant during the spring bloom in the Oyashio region (Chiba et al ; Tsuda et al ; Hattori‐Saito et al ; Suzuki et al ; Nosaka et al ). However, our high‐frequency observations revealed diatom taxa succession from Thalassiosira spp.…”

“…The phytoplankton assemblages during the spring bloom in the Oyashio region possess higher light utilization efficiency of photosynthesis and primary productivity (Shiomoto ; Isada et al , ), which contributes to the highest biological utilization effect on seawater p CO 2 in the world ocean (Takahashi et al ; Chierici et al ) and high biological production (Taniguchi ; Sakurai ; Ikeda et al ; FAO ). Nosaka et al () reported that diatoms during the spring bloom in the Oyashio region are the main producer of transparent exopolymer particles (TEPs) that affect the efficiency of the biological carbon pump. Therefore, understanding the spatiotemporal changes in spring bloom dynamics is essential for better characterizing the biogeochemical and ecosystem processes in the Oyashio region.…”

“…(Takahashi et al 2002;Chierici et al 2006) and high biological production (Taniguchi 1999;Sakurai 2007;Ikeda et al 2008;FAO 2016). Nosaka et al (2017) reported that diatoms during the spring bloom in the Oyashio region are the main producer of transparent exopolymer particles (TEPs) that affect the efficiency of the biological carbon pump. Therefore, understanding the spatiotemporal changes in spring bloom dynamics is essential for better characterizing the biogeochemical and ecosystem processes in the Oyashio region.…”

Community Composition and Photosynthetic Physiology of Phytoplankton in the Western Subarctic Pacific Near the Kuril Islands With Special Reference to Iron Availability

“…According to Sarthou et al (), the half‐saturation constant values of silicate for the growth of diatoms are <3.9 μM. The silicate deficiency could be crucial in Oyashio waters because diatoms primarily contribute to spring blooms and the most significant phytoplankton group in the WSP (Hattori‐Saito et al, ; Mochizuki et al, ; Nosaka et al, ; Suzuki et al, ; Yoshida et al, ). It should be noted that nitrate was also depleted at Station PS1.…”

Editorial: Microbial Exopolymers: Sources, Chemico-Physiological Properties, and Ecosystem Effects in the Marine Environment

“…They serve as a labile source of carbon and energy to micro- and macro-heterotrophs, and are thus important in food webs. The article by Nosaka et al ( 2017 ) focuses on TEP distribution and its potential correlation to diatom-derived chlorophyll- a biomass and DOC productivity during the spring bloom periods in 2010 and 2011 in surface waters of the Oyashio region of the western subarctic Pacific, where seasonal biological drawdown of the partial pressure of CO 2 is one of the greatest in the world's oceans. The article by Ortega-Retuerta et al describes TEP distributions in the northwest Mediterranean Sea during late spring 2012, along perpendicular and parallel transects to the Catalan coast, and its correlation with chlorophyll- a , O 2 (as a proxy of primary production) and bacterial production.…”