Department of Oceanography 201182193 Sung-Chan Kang Hydrographically mediated patterns of photosynthetic pigment in the East/Japan Sea : Low N:P ratios and cyanobacterial dominance Department of Oceanography 201182193 Sung-Chan Kang

Introduction

동해는 남쪽의 반이 온수 북쪽의 반이 냉수 윤곽이 뚜렷한 아극전선과 많은 eddy가 특징은 다양한 해양학적 특징을 가진 곳이다

Total nitrogen : Total phosphorus DIN: DIP Approximately 11 DIN: DIP Approximately 13 Considerably lower than the Redfield ratio(16) Primary production of Phytoplankton could be limited by nitrogen

EJS has one of the most highly produtive marine environments Approximately 200gCm-2yr-1 as measured by sediment trap experiments (Hong, 1998) New production in the southern EJS was reported to be ~64gCm-2yr-1 (Hahm and Kim, 2001)

Seasonal, yearly, and decadal changes in biomass and community structure in the EJS have been found to be associated with climate variability(Lee et al.,2009) Pacific Decadal Oscillation(PDO) Enhanced by episodic dust input

Chlorophyll a concentrations and plankton abundance were also affected by meso-scale physical features Upwelling, Warm eddies, Sub-polar front in the Ulleung Basin However, basin-scale observational studies on phytoplakton composition have not yet been conducted in the EJS

Introduction They report for the first time the change in phytoplankton communities in the EJS on a basin-wide scale, including oceanographic environments using photosynthetic pigment signatures

Materials and methods

Sampling 2004sus 5dnjfdpsms 동해의 북쪽끝에서 남쪽끝가지 전체 횡단면을 조사하였고 반면에 2005냔 7월과 10월에는 각각 남쪽 반 북쪽반을 조사하였다. 해수샘플은 CTD가 탑재된 니스킨 바틀을 이용하여 수집했다.

Analyses of nutrients and pigment Filtering Frozen until the analyses Measured using an auto analyzer Extracted in 100% acetone with an internal standard Filtered through a 0.45um filter The clear extract(1ml) mixed with deionized water(0.3ml) The mixed solution(0.1mL) was injected into an HPLC system

Estimating phytoplankton community structure using a CHEMTAX program Perid 19’-But Fuco 19’-HEX Pra Viola Allo Zea Chl b Initial ratio Frasiono 0.3151 0.0616 0.9452 Pelago 0.2453 0.5849 0.5377 Cyano 0.3478 Diatom 0.7554 Final ratio 0.0528 0.0599 1.2099 0.3147 0.3904 0.1059 0.4597 0.4722 Initial pigment to chlorophyll a ratio for each marker used in the CHEMTAX calculation obtained from the southern Ocean data(Mackey et al., 1996) However the CHEMTAX results are influenced by value of the initial pigment ratio Because of function of light or nutrient conditions

Estimating phytoplankton community structure using a CHEMTAX program Compared our CHEMTAX results (using Mackey et al., 1998) obtained by using two different pigment ratio sets from Suzuki et al.(2002) and Furuya et al.(2003)

Estimating phytoplankton community structure using a CHEMTAX program The abundance of the major algal group in the EJS varied within a range of approximately 15% The horizontal and vertical distribution patterns for algal groups were almost the same(r2>0.97) for different initial values. Initial ratios were chosen

Results and discussion

Hydrographic and biogeochemical variation

Hydrographic and biogeochemical variation Nitrite(2.1um,2.3um)≥Nitrate(2.5um,0.77um) Indicating the active regeneration of nutrients from the converging surface organic matter in this warm eddy

Hydrographic and biogeochemical variation Low N:P ratio Due to the active Redfieldian comsumption N and P since the initial N:P ratio in the entire EJS was approximately 13

Hydrographic and biogeochemical variation Strongly N-limited environment 일차생산으로 추정되는 클로로필 a가 증가함에 따라 din이 급속도로 감소. 그러나 dip 완전히 소모되지 않음 이 경향은 동해는 강한 질소제한환경임을 나타냄

Hydrographic variation in phytoplankton community Prasinophyte Frontal zone, Warm<Cold

Hydrographic variation in phytoplankton community Diatom

Eddy, Warm zone (~80%)

Hydrographic variation in phytoplankton community Cyanobacteria Surface frontal zone

Surface frontal zone in 2004 Entire transect in 2005

Because of optical temperature(>10°C), low N:P ratios, nitrogen depletion favorable for the growth of cyanobacteria

Prymnesiophytes

A large contribution of prymnesiophytes was observed in the case of low N:P ratio waters

Conclusions

Unusually high growth of cyanobacteria, pelagophytes, and diatoms Very low N:P ratio conditions Several oceanographic environments with considerably varying temperatures Unusually high growth of cyanobacteria, pelagophytes, and diatoms

A warm eddy observed in the northern EJS showed relatively low nutrient concentrations but a high biomass of phytoplankton

Phytoplankton community variations induced by the hydrographical change Warm-water zone Diatoms and prasinophytes dominated the phytoplankton community in 2004 Pelagophytes, diatoms and cyanobacteria dominated community in July and October 2005 Frontal zone Cyanobacteria and pelagophytes dominated the community in both year Cold water zone Diatoms, pelagophytes, and prasinophytes dominated community in May 2004 Pelagohytes and cyanobacteria dominated the community in July and October 2005

More extensive observations of photosynthetic pigments, together with other biogeochemical parameter, are necessary to investigate the biogeochemical responses to climate changes in this very low N:P environment.