Abstract
Abstract. Small phytoplankton are anticipated to be more important in a recently warming and freshening ocean condition. However, little information on the contribution of small phytoplankton to overall phytoplankton production is currently available in the Amundsen Sea. To determine the contributions of small phytoplankton to total biomass and primary production, carbon and nitrogen uptake rates of total and small phytoplankton were obtained from 12 productivity stations in the Amundsen Sea. The daily carbon uptake rates of total phytoplankton averaged in this study were 0.42 g C m−2 d−1 (SD = ± 0.30 g C m−2 d−1) and 0.84 g C m−2 d−1 (SD = ± 0.18 g C m−2 d−1) for non-polynya and polynya regions, respectively, whereas the daily total nitrogen (nitrate and ammonium) uptake rates were 0.12 g N m−2 d−1 (SD = ± 0.09 g N m−2 d−1) and 0.21 g N m−2 d−1 (SD = ± 0.11 g N m−2 d−1), respectively, for non-polynya and polynya regions, all of which were within the ranges reported previously. Small phytoplankton contributed 26.9 and 27.7 % to the total carbon and nitrogen uptake rates of phytoplankton in this study, respectively, which were relatively higher than the chlorophyll a contribution (19.4 %) of small phytoplankton. For a comparison of different regions, the contributions for chlorophyll a concentration and primary production of small phytoplankton averaged from all the non-polynya stations were 42.4 and 50.8 %, which were significantly higher than those (7.9 and 14.9 %, respectively) in the polynya region. A strong negative correlation (r2 = 0. 790, p<0. 05) was found between the contributions of small phytoplankton and the total daily primary production of phytoplankton in this study. This finding implies that daily primary production decreases as small phytoplankton contribution increases, which is mainly due to the lower carbon uptake rate of small phytoplankton than large phytoplankton.
Highlights
The Amundsen Sea is located in West Antarctica between the Ross Sea and Bellingshausen Sea (Fig. 1), which is one of the least biologically studied regions in the Southern Ocean
Field-measurement data revealed that annual primary production of phytoplankton reaching to 220 g C m−2 yr−1 in the Amundsen Sea polynya is as high as that of Ross Sea polynya (200 g C m−2 yr−1) which was previously known for the highest productivity region in the Southern Ocean (Lee et al, 2012)
Over the past several decades, a rapid climate change has been detected and subsequently physical changes have occurred in the marine ecosystem in the western Antarctic Peninsula (WAP), which was mainly based on the results from Palmer Antarctic Long-Term Ecological Research project focusing on the north of ∼ 69◦ S (Ducklow et al, 2007; Montes-Hugo et al, 2009)
Summary
The Amundsen Sea is located in West Antarctica between the Ross Sea and Bellingshausen Sea (Fig. 1), which is one of the least biologically studied regions in the Southern Ocean. Field-measurement data revealed that annual primary production of phytoplankton reaching to 220 g C m−2 yr−1 in the Amundsen Sea polynya is as high as that of Ross Sea polynya (200 g C m−2 yr−1) which was previously known for the highest productivity region in the Southern Ocean (Lee et al, 2012). Given the fact that the chlorophyll a concentration averaged from all the chlorophyll a measured stations was twice as high as that of the only productivity-measured stations, Lee et al (2012) argued that the annual production in the Amundsen Sea polynya could be even 2 times higher than that of Ross Sea polynya.
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