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Plankton Community Respiration and Particulate Organic Carbon in the Kuroshio East of Taiwan - PubMed

  • ️Sat Jan 01 2022

Plankton Community Respiration and Particulate Organic Carbon in the Kuroshio East of Taiwan

Chung-Chi Chen et al. Plants (Basel). 2022.

Abstract

Biological organic carbon production and consumption play a fundamental role in the understanding of organic carbon cycling in oceans. However, studies on them in the Kuroshio, the western boundary current in the North Pacific Ocean, are scarce. To better understand the variations of plankton community respiration (CR) and particulate organic carbon (POC), eight cruises. which covered four seasons over a 2-year period, were surveyed across the Kuroshio at the KTV1 transect east of Taiwan. Spatially, a coastal uplift of isotherms (i.e., onshore lifting and offshore deepening) was observed along the KTV1 transect. During the uplift, the cold and nutrient-rich deep waters shoal to shallow water and enhance phytoplankton growth, resulting in higher values of phytoplankton, POC, and plankton CR on the onshore side. In this study, phytoplankton was dominated by picophytoplankton including Prochlorococcus, Synechococcus, and picoeukaryotes. Plankton CR was low, and its mean depth-normalized integrated rate (the upper 100 m water depth) ranged from 7.07 to 22.27 mg C m-3 d-1, to which the picophytoplankton and heterotrophic bacteria contributed the most. The mean depth-normalized integrated value of POC ranged from 12.7 to 21.6 μg C L-1. POC is mainly associated with phytoplankton biomass with a mean carbon ratio of chlorophyll a/POC ≈ 1.03. All results suggest that plankton CR and POC variations may be associated with picoplankton dynamics in the Kuroshio.

Keywords: Prochlorococcus; Synechococcus; dissolved inorganic nutrients; particulate organic carbon; picoeukaryotes; picoplankton; plankton community respiration; the Kuroshio.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1

Sampling stations (K101–K108) along the KTV1 transect of the Kuroshio east of Taiwan. The climatological current velocity (gray arrows) at a depth of 30 m was computed from the historical ADCP dataset available from Taiwan’s Ocean Data Bank. The bold black line indicates the maximum velocity axis at 15 m depth obtained from the surface drifter data. The solid yellow line indicates the 0.2 m s−1 isotach at 30 m depth obtained from the historical ADCP dataset [28]. The path of the Kuroshio with velocity >1 m s−1 is indicated by surface drifter trajectories and speeds (data available at

http://www.coriolis.eu.org/Data-Products/Data-Delivery/Data-selection

; accessed on 27 February 2018) in the lower right inset, where the black dotted rectangle marks the map area. (Modified from Figure 1 of Chen et al. [15]).

Figure 2
Figure 2

Typical depth profile contour plots of (a) temperature (Temp; °C), (b) nitrate (NO3−; µM), (c) chlorophyll a (Chl a; µg Chl L−1), and (d) particulate organic carbon (POC; µg C L−1) within 250 m water depth along the KTV1 transect in September 2015. Contour lines in white bold are guidelines, including temperature (21 °C), nitrate (1 µM), Chl a (0.3 µg Chl L−1), and POC (30 µg C L−1). The inverse triangles at the top of each panel indicate the locations of stations k101–k108 along the KTV1 transect. Corresponding distance (=0) start from St. k101. For reference, the depths of mixed layer (+) and euphotic zone (×) are also marked.

Figure 3
Figure 3

Temporal and spatial variations of the mean values of nitrate (NO3−; (a,b)) and phosphate (PO43−; (c,d)) across the KTV1 transect of the Kuroshio. The depth-normalized integrated value over 100 m water column of each variable at each sampling station was used for the mean values. The mean values were averaged across all stations of the KTV1 transect for each sampling period or across each station of the KTV1 transect for all sampling periods. The standard deviations are illustrated as vertical white lines with caps.

Figure 4
Figure 4

Temporal and spatial variations of the mean values of chlorophyll a (Chl a; (a,b)), particulate organic carbon (POC; (c,d)), and plankton community respiration (Plankton CR; (e,f)) across the KTV1 transect of the Kuroshio. The depth-normalized integrated value over 100 m water column of each variable at each sampling station was used for the mean values. The mean values were averaged across all stations of the KTV1 transect for each sampling period or across each station of the KTV1 transect for all sampling periods. The standard deviations are illustrated as vertical white lines with caps.

Figure 5
Figure 5

Relationships between concentration of plankton community respiration (plankton CR) and (a) particulate organic carbon (POC), (b) chlorophyll a (Chl a), (c) heterotrophic bacterioplankton, and (d) all picophytoplankton (i.e., Prochlorococcus + Synechococcus + picoeukaryotes) for all pooled data. Note that the variables are in carbon units. The r2 and p values of linear relationships are shown.

Figure 6
Figure 6

Relationships between concentration of particulate organic carbon (POC) and (a) chlorophyll a (Chl a) and (b) picophytoplankton for all pooled data. The r2 and p values of linear relationships are shown.

Figure 7
Figure 7

Temporal and spatial variations of the mean values of picophytoplankton (i.e., Prochlorococcus [Proch] + Synechococcus [Syne] + picoeukaryotes [PicoEuk]) in terms of abundance (a,b) and biomass (c,d) across the KTV1 transect of the Kuroshio. The depth-normalized integrated value over 100 m water column of each variable at each sampling station was used for the mean values. The mean values were averaged across all stations of the KTV1 transect for each sampling period or across each station of the KTV1 transect for all the sampling periods. The standard deviations are illustrated as vertical white lines with caps.

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