Spatial and temporal variation of net community production and its regulating factors in the Amundsen Sea, Antarctica

Hahm, Doshik,Rhee, Tae Siek,Kim, Hae-Cheol,Park, Jisoo,Kim, Young-Nam,Shin, Hyoung Chul,Lee, SangHoon American Geophysical Union 2014 Journal of geophysical research. Oceans Vol.119 No.5

We observed O2/Ar in the surface waters of the Amundsen Sea, Antarctica, during the austral summers in 2011 and 2012 to investigate the variability of net community production (NCP). Corresponding to the typical peak phytoplankton bloom period, the O2/Ar of the Amundsen Sea Polynya (ASP) reached 30% in early January 2011 and had a strong positive correlation with the sea surface temperature (SST) and chlorophyll-a (Chl-a). In contrast, O2/Ar decreased to -10% in the sea ice zone (SIZ), which was likely associated with either net O2 consumption in the unlit area or the entrainment of deep water containing low dissolved oxygen. Near the terminal stage of the phytoplankton bloom in late February 2012, we observed the same contrasting O2/Ar features between the ASP and SIZ. However, the O2/Ar in the ASP was not >10%, which corresponded with the overall reduction in Chl-a, solar radiation, and SST compared with the corresponding values in 2011. The average net community production in the ASP was 119 +/- 79 mmol O2 m-2 d-1 in January 2011, and 23 +/- 14 mmol O2 m-2 d-1 in February 2012. The strong correlations of NCP with SST and mixed layer depth (MLD) indicate that the ASP phytoplankton bloom is likely initiated by a combination of increased light availability and SST in early summer. Low SST and variable fluorescence to maximum florescence ratio (Fv/Fm) in February indicate that decreased solar radiation and Fe availability are likely responsible for the phytoplankton bloom demise.

Tidal influence on the sea-to-air transfer of CH₄ in the coastal ocean

HAHM, DOSHIK,KIM, GUEBUEM,LEE, YONG-WOO,NAM, SUNGH-YUN,KIM, KYUNG-RYUL,KIM, KUH Munksgaard International Publishers 2006 Tellus. Series B, Chemical and physical meteorolog Vol.58 No.1

<P>ABSTRACT</P><P>We obtained real-time monitoring data of water temperature, salinity, wind, current, CH<SUB>4</SUB> and other oceanographic parameters in a coastal bay in the southern sea of Korea from July 8 to August 15, 2003, using an environmental monitoring buoy. In general, the transfer velocity of environmental gases across the air–sea interface is obtained exclusively from empirical relationships with wind speeds. However, our monitoring data demonstrate that the agitation of the aqueous boundary layer is controlled significantly by tidal turbulence, similar to the control exercised by wind stress in the coastal ocean. The sea-to-air transfer of CH<SUB>4</SUB> is enhanced significantly during spring tide due to an increase in the gas transfer velocity and vertical CH<SUB>4</SUB> transport from bottom water to the surface layer. Thus, our unique time-series results imply that the sea-to-air transfer of gases, such as CH<SUB>4</SUB>, DMS, DMHg, N<SUB>2</SUB>O, CO<SUB>2</SUB> and <SUP>222</SUP>Rn, from highly enriched coastal bottom waters, is controlled not only by episodic wind events but also by regular tidal turbulence in the coastal ocean.</P>

An overview of the volatile systematics of the Lau Basin – Resolving the effects of source variation, magmatic degassing and crustal contamination

Hahm, Doshik,Hilton, David R.,Castillo, Paterno R.,Hawkins, James W.,Hanan, Barry B.,Hauri, Erik H. Elsevier 2012 Geochimica et cosmochimica acta Vol.85 No.-

<P><B>Abstract</B></P><P>The Lau Basin erupts lavas with a range of geochemical features reflecting a complex history of interaction involving different mantle sources. The Valu Fa Ridge (VFR) and Mangatolu Triple Junction (MTJ) region have lavas with arc-like characteristics, Niuafo’ou Island (NV), Peggy Ridge and Central and Eastern Lau Spreading Centers (PR, CLSC and ELSC) erupt mid-ocean ridge basalt (MORB)-like volcanics, whereas the Rochambeau Bank (RB) has features akin to ocean island basalt (OIB). To characterize the volatile systematics of these various regions, we report a comprehensive study of 39 submarine lavas from these various eruptive centers encompassing analyses of the noble gases (He, Ne, and Ar) and carbon (CO<SUB>2</SUB>) – both isotopes and abundances – together with other major volatile phases (H<SUB>2</SUB>O, S, Cl, and F).</P><P>Helium isotope ratios of the NV, MTJ, CLSC, and ELSC are MORB-like for the most part except for differentiated lavas that tend to have lower, more radiogenic <SUP>3</SUP>He/<SUP>4</SUP>He values. The RB has considerably higher <SUP>3</SUP>He/<SUP>4</SUP>He ratios (up to 23 <I>R</I><SUB>A</SUB> in this work) which extend as far south as the PR. The influence of ‘plume-like’ sources in the RB is also apparent in Ne isotopes: RB samples follow a trend similar to Hawaiian basalts in 3-isotope neon space. However, RB lavas have lower <SUP>40</SUP>Ar/<SUP>36</SUP>Ar (300–730) and higher [<SUP>36</SUP>Ar] than CLSC and ELSC, suggesting greater air contamination. Elemental He/Ne ratios (<SUP>3</SUP>He/<SUP>22</SUP>Ne<SUB>S</SUB> and <SUP>4</SUP>He/<SUP>21</SUP>Ne<SUP>∗</SUP> where S=solar and *=nucleogenic) are high throughout the Lau Basin and identify the Lau mantle as one of only two high <SUP>3</SUP>He/<SUP>4</SUP>He provinces worldwide with such an enrichment of He relative to Ne.</P><P>Magmatic CO<SUB>2</SUB> and δ<SUP>13</SUP>C fall in the range 7–350ppm and −28‰ to −6‰, respectively. RB lavas have less [CO<SUB>2</SUB>] and slightly lower δ<SUP>13</SUP>C than CLSC and ELSC. The lowest values are found among MTJ lavas. These lavas also have the highest [H<SUB>2</SUB>O], [F], [Cl], and [S] whereas the PR, ELSC and CLSC have the lowest. RB has intermediate [H<SUB>2</SUB>O]. We estimate primary [CO<SUB>2</SUB>] in primary melts using [CO<SUB>2</SUB>]–δ<SUP>13</SUP>C relationships, and find that RB lavas have higher [CO<SUB>2</SUB>] (∼935±168ppm) than ELSC/CLSC (638±115ppm). They also possess higher initial δ<SUP>13</SUP>C values, consistent with observations at other hotspot-related localities. However, there are no discernible differences in primary CO<SUB>2</SUB>/Nb ratios between mantle sources characterized by high <SUP>3</SUP>He/<SUP>4</SUP>He and MORB-like ratios. On the other hand, reconstructed values are considerably higher than that envisaged for depleted MORB mantle based on olivine-hosted melt inclusions.</P>

Spatial variability of ΔO2/Ar and net community production in the surface waters of the Amundsen Sea, Antarctica

Doshik Hahm,Tae Siek Rhee,Young-Nam Kim,Hyoung Chul Shin,SangHoon Lee 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.6

O₂/Ar 관측에 기반한 순군집생산량 추정 연구 동향

함도식,이인희,HAHM, DOSHIK,LEE, INHEE 한국해양학회 2018 바다 Vol.23 No.1

순일차생산량과 종속 영양 생물의 호흡량의 차이로 정의되는 순군집생산량(net community production; NCP)은 해양 생물펌프의 척도로 활용되고 있다. 이 논문에서 소개하는 $O_2/Ar$ 관측에 기반한 NCP 추정법($O_2/Ar-NCP$)은 연구선의 이동 중에도 1분 미만의 고빈도로 $O_2/Ar$를 연속적으로 측정할 수 있어, 신생산량 혹은 방출생산량 등 전통적인 생물펌프 척도가 갖는 시간 혹은 공간 해상도의 제한을 혁신적으로 개선한 것이다. 논문에서는 $O_2/Ar-NCP$ 방법의 이론적 배경과 실험 장치의 구성에 대해 설명하였다. 또한 기존 생물펌프 척도와 $O_2/Ar-NCP$의 비교, 대양의 해역별 NCP 분포, 현장 관측 결과와 기계학습을 결합한 전 대양 NCP의 추정, 식물 플랑크톤 군집 구조와 NCP 연관성 등에 관한 주요 연구 사례들을 소개하였다. Net community production (NCP), defined as the difference between net primary production and respiration of heterotrophs, has been used as a measure of oceanic biological carbon pump. This paper summarizes the theoretical background and experimental methods for the estimation of NCP based on $O_2/Ar$ measurements ($O_2/Ar-NCP$). The high frequency measurements of $O_2/Ar-NCP$ (<1 min) is a significant enhancement over the conventional measures of biological pump, such as new production and export production. This paper also introduces some of important works as to the comparison between $O_2/Ar-NCP$ and other measures of biological pump, the distributions of $O_2/Ar-NCP$ in the oceans, and the correlation of $O_2/Ar-NCP$ with various oceanic parameters, including community structures.

Characteristics of the horizontal and vertical distributions of dimethyl sulfide throughout the Amundsen Sea Polynya

Kim, Intae,Hahm, Doshik,Park, Keyhong,Lee, Youngju,Choi, Jung-Ok,Zhang, Miming,Chen, Liqi,Kim, Hyun-Cheol,Lee, SangHoon Elsevier 2017 The Science of the total environment Vol.584 No.-

<P><B>Abstract</B></P> <P>We investigated horizontal and vertical distributions of DMS in the upper water column of the Amundsen Sea Polynya and Pine Island Polynya during the austral summer (January–February) of 2016 using a membrane inlet mass spectrometer (MIMS) onboard the Korean icebreaker R/V <I>Araon</I>. The surface water concentrations of DMS varied from <1 to 400nM. The highest DMS (up to 300nM) were observed in sea ice–polynya transition zones and near the Getz ice shelf, where both the first local ice melting and high plankton productivity were observed. In other regions, high DMS concentration was generally accompanied by higher chlorophyll and ΔO<SUB>2</SUB>/Ar. The large spatial variability of DMS and primary productivity in the surface water of the Amundsen Sea seems to be attributed to melting conditions of sea ice, relative dominance of <I>Phaeocystis Antarctica</I> as a DMS producer, and timing differences between bloom and subsequent DMS productions. The depth profiles of DMS and ΔO<SUB>2</SUB>/Ar were consistent with the horizontal surface data, showing noticeable spatial variability. However, despite the large spatial variability, in contrast to the previous results from 2009, DMS concentrations and ΔO<SUB>2</SUB>/Ar in the surface water were indistinct between the two major domains: the sea ice zone and polynya region. The discrepancy may be associated with inter-annual variations of phytoplankton assemblages superimposed on differences in sea-ice conditions, blooming period, and spatial coverage along the vast surface area of the Amundsen Sea.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Recent distributions of DMS were investigated throughout the Amundsen Sea. </LI> <LI> DMS hotspots (>150nM) in the polynya were observed during the austral summer. </LI> <LI> Trends of DMS and ΔO<SUB>2</SUB>/Ar were indistinct between the sea ice zone and polynya. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Bacterial community of sediments from the Australian-Antarctic ridge

Lee, Yung Mi,Hahm, Doshik,Jung, You-Jung,Park, Sung Hyun,Chun, Jongsik,Hong, Soon Gyu Springer-Verlag 2014 Polar biology Vol.37 No.4

동해 남서부해역의 표층 용존 기체 분포: 여름철 연안과 울릉분지의 일차생산력과 CO₂ 흡수 비교

이인희,함도식,LEE, INHEE,HAHM, DOSHIK 한국해양학회 2021 바다 Vol.26 No.4

연안은 전 지구 관점에서 대기 이산화탄소를 흡수하는 것으로 평가된다. 그동안 동해의 탄소 순환에 관한 연구들이 울릉분지에 집중되어 있어서 동해 연안이 탄소 순환에 기여하는 역할에 대한 이해는 제한적이다. 본 연구에서는 표층의 생물학적 과포화도(𝚫O₂/Ar)와 이산화탄소 분압(fCO₂)의 변화를 관측하여 울릉분지와 연안의 생물 펌프 세기 및 탄소 흡수력을 비교하였다. 연안은 저온 저염한 환경으로 고온 고염한 울릉분지와 대비되었다. 삼척과 포항 연안에서는 울릉분지에 비해 높은 생물량과 𝚫O₂/Ar, 낮은 fCO₂ 분포를 보여 연안에서 더 많은 일차 생산이 일어나 용존 CO₂ 흡수를 촉진한 것으로 나타났다. 삼척과 포항 연안에서 𝚫O₂/Ar을 기반으로 추정된 순군집생산(net community production)은 각각 19 ± 6과 60 ± 9 mmol O₂ m^-2d^-1로 울릉분지의 8 ± 4 mmol O₂ m^-2d^-1에 비하여 약 2-7배 가량 활발하게 생물 펌프가 작동하고 있었다. 삼척과 포항 연안의 CO₂ 교환율은 각각 -17.1 ± 8.9와 -25.8 ± 13.2 mmol C m^-2d^-1로, 울릉분지의 -4.7 ± 2.5 mmol C m^-2d^-1보다 약 4배에서 5배 가량 높았다. 삼척과 포항 연안에서는 울릉분지에 비하여 질소포화도가 최대 3% 낮게 나타나 일차생산자에 의한 질소 고정이 일어났을 가능성을 제시하였다. The global coastal region is considered as a sink for atmospheric CO₂. Since most of the studies in the East Sea focused on the Ulleung Basin, the importance of coastal region for carbon cycle has been overlooked. In this study, we compared the biological pump and CO₂ absorption between the Ulleung Basin and coastal region by surface measurements of biological O₂ supersaturation (𝚫O₂/Ar) and partial pressure of CO₂ (fCO₂). Cold and less saline waters in the coastal regions were in contrast with a warm and saline water in the Ulleung Basin. The coastal waters near Samcheok and Pohang showed higher fluorescence, 𝚫O₂/Ar, and lower fCO₂ than those in the Ulleung Basin, indicating higher primary production and CO₂ absorption in the areas. The average net community production estimated by 𝚫O₂/Ar were 19 ± 6 and 60 ± 9 mmol O₂ m^-2d^-1 in the Samcheok and Pohang, respectively, 2-7 times higher than that of 8 ± 4 mmol O₂ m^-2d^-1 in the Ulleung Basin. Similarly, the average CO₂ flux between the seawater and atmosphere were -17.1 ± 8.9 and -25.8 ± 13.2 mmol C m^-2d^-1 in the Samcheok and Pohang, respectively, 4-5 times higher than that of -4.7 ± 2.5 mmol C m^-2d^-1 in the Ulleung Basin. In the Samcheok and Pohang, degrees of N₂ saturation were lower by 3% than that the ambient waters, suggesting the possibility of nitrogen fixation by primary producers.

기계학습법을 이용한 동해 남서부해역의 표층 이산화탄소분압(fCO₂) 추정

함도식,박소예나,최상화,강동진,노태근,이동섭,HAHM, DOSHIK,PARK, SOYEONA,CHOI, SANG-HWA,KANG, DONG-JIN,RHO, TAEKEUN,LEE, TONGSUP 한국해양학회 2019 바다 Vol.24 No.3

지구의 탄소순환을 이해하고 미래 대기 $CO_2$의 농도와 기후 변화를 예측하기 위해서는 해양과 대기 사이 $CO_2$ 교환율(sea-to-air $CO_2$ flux)의 시공간 변화를 정확하게 추정하는 것이 필요하다. 연구선을 이용한 현장 관측이 갖고 있는 시공간 제약으로 인해 동해에는 매우 제한적인 표층 이산화탄소분압($fCO_2$) 자료만 존재한다. 이 연구에서는 위성 및 수치모형에서 얻은 수온, 염분, 엽록소, 혼합층 자료를 세 종류의 기계학습 모형에 입력하여 동해 남서부해역의 고해상도 표층 $fCO_2$ 시계열 자료를 산출하였다. 세 모형 중 현장 관측 자료를 가장 잘 재현하는 Random Forest (RF) 모형의 평균제곱근오차는 $7.1{\mu}atm$이었다. RF 모형을 이용한 $fCO_2$ 예측에 중요한 역할을 하는 변수는 수온, 염분과 시간 정보였으며, 엽록소와 혼합층 깊이는 $fCO_2$ 예측에 미미한 역할을 하였다. RF 모형에서 예측한 표층 $fCO_2$를 이용하여 계산한 동해 남서부해역의 $CO_2$ 교환율은 $-0.76{\pm}1.15mol\;m^{-2}yr^{-1}$로 이전 현장 관측 연구에서 제시한 교환율( $-0.66{\sim}-2.47mol\;m^{-2}yr^{-1}$) 범위 중 작은 값에 해당한다. RF 모형의 표층 $fCO_2$ 시계열 자료는 1주일 내외의 짧은 시간 사이에도 $CO_2$ 교환율이 상당히 변할 수 있음을 보여주었다. 앞으로 보다 정확한 $CO_2$ 교환율 산출을 위해서는 $fCO_2$가 급격하게 변화하는 봄철에 높은 해상도의 현장 관측을 수행할 필요가 있다. Accurate evaluation of sea-to-air $CO_2$ flux and its variability is crucial information to the understanding of global carbon cycle and the prediction of atmospheric $CO_2$ concentration. $fCO_2$ observations are sparse in space and time in the East Sea. In this study, we derived high resolution time series of surface $fCO_2$ values in the southwest East Sea, by feeding sea surface temperature (SST), salinity (SSS), chlorophyll-a (CHL), and mixed layer depth (MLD) values, from either satellite-observations or numerical model outputs, to three machine learning models. The root mean square error of the best performing model, a Random Forest (RF) model, was $7.1{\mu}atm$. Important parameters in predicting $fCO_2$ in the RF model were SST and SSS along with time information; CHL and MLD were much less important than the other parameters. The net $CO_2$ flux in the southwest East Sea, calculated from the $fCO_2$ predicted by the RF model, was $-0.76{\pm}1.15mol\;m^{-2}yr^{-1}$, close to the lower bound of the previous estimates in the range of $-0.66{\sim}-2.47mol\;m^{-2}yr^{-1}$. The time series of $fCO_2$ predicted by the RF model showed a significant variation even in a short time interval of a week. For accurate evaluation of the $CO_2$ flux in the Ulleung Basin, it is necessary to conduct high resolution in situ observations in spring when $fCO_2$ changes rapidly.

An Investigation of Gas Exchange and Water Circulation in the Amundsen Sea Based On Dissolved Inorganic Radiocarbon

Kim, Bumsoo,Lee, SangHoon,Kim, Minkyoung,Hahm, Doshik,Rhee, Tae Siek,Hwang, Jeomshik American Geophysical Union 2018 Geophysical research letters Vol.45 No.22