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Advances in Polar Science Contents Vol.23 No.3 September 2012 Articles Characteristics and variations of the picophytoplanktoncommunity in the Arctic Ocean .................................... 133 MA Yuxin, HE Jianfeng, ZHANG Fang, LIN Ling, YANG Haizhen & CAI Minghong Factors influencing small-scale distribution of 10 macrolichens in King George Island, West Antarctica ....... 141 LIU Huajie, WU Qingfeng & FANG Shibo Comparison of the defluoridation efficiency of calcium phosphate and chitin in the exoskeleton of Antarctic krill ... .................................................................................................................................................................................... 149 WANG Zhangmin & YIN Xuebin Eco-environmental spatial characteristics of Fildes Peninsula based on TuPu models ................................... 155 PANG Xiaoping & LI Yanhong Vertical structure of low-level atmosphere over the southeast Indian Ocean fronts ....................................... 163 FENG Lin, LIU Lin, GAO Libao & YU Weidong Cognitive effects of long-term residence in the Antarctic environment ............................................................ 170 YAN Gonggu, WU Songdi, WANG Tianle, ZHANG Xuemin & SAKLOFSKE Donald H Letters Russian researchers reach subglacial Lake Vostok in Antarctica .................................................................... 176 Pavel Talalay Trend Development of the geodetic coordinate system in Antarctica ......................................................................... 181 ZHANG Shengkai & E Dongchen · Article · Advances in Polar Science doi: 10.3724/SP.J.1085.2012.00133 September 2012 Vol. 23 No. 3: 133-140 Characteristics and variations of the picophytoplankton community in the Arctic Ocean 1,2 1,2* 1 1 2 1 MA Yuxin , HE Jianfeng , ZHANG Fang , LIN Ling , YANG Haizhen & CAI Minghong 1 SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai 200136, China; 2 College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China Received 2 March 2012; accepted 14 June 2012 Abstract Picophytoplankton are responsible for much of the carbon fixation process in the Arctic Ocean, and they play an im- portant role in active microbial food webs. The climate of the Arctic Ocean has changed in recent years, and picophytoplankton, as the most vulnerable part of the high-latitude pelagic ecosystem, have been the focus of an increasing number of scientific studies. This paper reviews and summarizes research on the characteristics of picophytoplankton in the Arctic Ocean, including their abundance, biomass, spatial distribution, seasonal variation, community structure, and factors influencing their growth. The impact of climate change on the Arctic Ocean picophytoplankton community is discussed, and future research directions are considered. Keywords Arctic Ocean, picophytoplankton, climate change, review Citation: Ma Y X, He J F, Zhang F, et al. Characteristics and variations of the picophytoplankton community in the Arctic Ocean. Adv Polar Sci, 2012, 23: 133-140, doi: 10.3724/SP.J.1085.2012.00133 both total phytoplankton biomass and production in marine 0 Introduction* ecosystems, especially in oligotrophic waters where they can account for up to 90% of the total photosynthetic bio- The Arctic Ocean has been a semi-enclosed basin for [8-9] [1-2] mass and carbon production . Recent studies show that 60–100 million years , and throughout this period it has the Arctic Ocean has active microbial food webs that are slowly exchanged surface waters with other oceanic re- [10-11] [3] often dominated by cells with a diameter <3 µm , and gions . The special characteristics of physical isolation, that cells <5 µm in diameter are responsible for much of the perennially low water temperatures, and extreme cycles of carbon fixation over wide regions in the Arctic Basin[12-13]. polar day and night, mean that the Arctic Ocean provides a Picophytoplankton have a large surface-area-to-volume unique marine habitat for organisms, and is very sensitive [4] ratio, which facilitates effective acquisition of nutrient sol- to climate change . utes and photons, and provides hydrodynamic resistance to Climate change is already evident in the Arctic Ocean. sinking[14]. As climate changes, these cells could be ex- The temperature of the Arctic system has been increasing [5] pected to increase in number in a regime of lower nitrate over the past 100 years , and as a result the extent of sea supply and greater hydrodynamic stability[15]. Therefore, as ice coverage has declined[6]. Some models predict that the [7] one of the most sensitive components of high-latitude pe- Arctic Ocean will be ice-free in summer by 2040 . lagic ecosystems, picophytoplankton could be viewed as Picophytoplankton are photosynthetic plankton with a both sentinels and amplifiers of global climate change[16]. diameter <2 µm, including three cell types, cyanobacteria The aim of this paper is to summarize research on the (Synechococcus), Prochlorococcus, and picoeukaryotes, characteristics and variation of picophytoplankton in the although Prochlorococcus have not been reported in the Arctic Ocean, including studies on picophytoplankton Arctic Ocean. Picophytoplankton contribute substantially to abundance, biomass, spatial distribution, seasonal variation, community structure and influencing factors, and the impact of climate change on picophytoplankton growth. We * Corresponding author (email: [email protected]) also discuss the prospects for future study in this field. It journal.polar.gov.cn 134 MA Yuxin, et al. Adv Polar Sci September(2012) Vol. 23 No. 3 should be noted that picophytoplankton are defined as and ocean forcing (e.g., through flow, upwelling, wind, and phytoplankton with a diameter <2 µm, however, some of tidal mixing)[23]. the reviewed studies focused on cells with a diameter <5 Cottrell and Kirchman[24] studied the coastal waters of µm, referred to as ultraphytoplankton. Therefore, for this the Chukchi and Beaufort Seas and found the abundance of paper, we reviewed studies on both picophytoplankton and Chl a-containing picoeukaryotes in summer was about ultraphytoplankton. 5.4×103 cells·mL-1. Not et al.[25] discovered that the picoeu- karyotic community at the boundary between the Norwe- 1 Abundance and biomass gian, Greenland, and Barents Seas, was primarily composed of photoautotrophs in late summer (75% of the cells on 1.1 Central Arctic Ocean average), and on average 44% of the Chl a biomass in this region could be attributed to picophytoplankton (including Recent studies have revealed a more dynamic carbon cycle Synechococcus and picoeukaryotes). Schloss et al.[26] found in the surface waters of the Arctic Ocean[12,17] than previ- [18] that picophytoplankton represented an average of 71% of ously estimated . Research has also shown that picophy- total cells (<20 µm) in the southeastern Beaufort Sea toplankton dominate the phytoplankton biomass and pro- [12,19] [19] (Mackenzie Shelf and Amundsen Gulf regions). The highest duction in central Arctic waters . Booth and Horner concentration of picophytoplankton cells was 13 810 cells·mL-1 discovered that picophytoplankton in the Canada and in the area influenced by the Mackenzie River, while the Makarov Basins contributed 93% to autotroph cell numbers -1 -1 lowest concentration was <1 500 cells·mL in the vicinity (1 300–10 020 cells·mL ) and 36% to autotroph biomass [26] [27] -1 [11] of the Amundsen Gulf . Wang et al. found that auto- (1.0–7.1 µg·cL ). Sherr et al. showed that autotrophic trophic picoflagellate abundance in Kongsfjorden, Svalbard, protists were numerically dominated by cells sized <5 µm, ranged from 46–35 200 cells·mL-1, while autotrophic nan- which made up 44%–99% (average 95%) of cells in the oflagellate abundance ranged from 40–4 600 cells·mL-1. phytoplankton assemblage during the growing season in the The above studies demonstrate that picophytoplankton upper water column of the central Arctic Ocean. Lee and [13] are dominant organisms in the oligotrophic, strongly strati- Whitledge found that small phytoplankton (0.7–5 µm) fied waters of the Arctic Basin, and also in the coastal re- represented about 70% of the total phytoplankton biomass gions, and areas strongly influenced by inflows of fresh in the upper mixed layer over all open-water stations during water. summer in the Canada Basin. However, the mean propor- tion decreased to 44.4% of the total biomass in the chloro- 2 Seasonal variation phyll-maximum layer, in spite of high variability[13]. There- fore, picophytoplankton are dominant organisms in the In the Arctic, all groups of pelagic microbes respond oligotrophic, strongly stratified central Arctic Ocean, espe- strongly to the large annual variation in the amplitude of cially in the upper layers. solar radiation, generally with lower biomass in spring, In the Arctic, polynyas are open water regions sur- higher biomass during the short summer growing season [20] rounded by sea ice . Polynyas have been referred to as the (June—September), and decreasing biomass during autumn oases of the Arctic because of their high productivity. and winter. Among them, phytoplankton show the largest Working on the Northeast Water Polynya, located in the variation in seasonal abundance and biomass, and there is a permanent Arctic ice pack on the North East Greenland rapid increase in phytoplankton stocks in June, after winter [21] Shelf, Pesant et al. found that small phytoplankton

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