Distribution of dissolved oxygen and causes of maximum concentration in the Bering Sea in July 2010

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1 Act Ocenol. Sin., 214, Vol. 33, No. 6, P DOI: 1.17/s E-mil: hyxe@263.net Distriution of dissolved oxygen nd cuses of mximum concentrtion in the Bering Se in July 21 SUN Xiuwu 1, LIN Ci 1, CHEN Yong 1, ZHANG Yunio 1,2, WANG Jigng 1,2, JI Weidong 1 * 1 Third Institute of Ocenogrphy, Stte Ocenic Administrtion, Ximen 3615, Chin 2 College of Ocen nd Erth Sciences, Ximen University, Ximen 3615, Chin Received 13 Mrch 213; ccepted 25 August 213 The Chinese Society of Ocenogrphy nd Springer-Verlg Berlin Heidelerg 214 Astrct According to dt otined in the Bering Se during the 4th Chinese Ntionl Arctic Reserch Expedition, the distriution of dissolved oxygen (DO) ws studied, cuses of its mximum concentrtion were discussed, nd the reltionships etween DO nd other prmeters, such s slinity, temperture, nd chlorophyll were nlyzed. The results showed DO concentrtion rnged from.53 to 12.5 mg/l in the Bering Se sin. The upper wters contined high concentrtions nd the mximum occurred t the depth rnge from 2 to 5 m. The DO concentrtion decresed rpidly when the depth ws deeper thn 2 m nd reched the minimum t the depth rnge from 5 to 1 m, nd then incresed slowly with the depth incresing ut still kept t low level. On the shelf, the DO concentrtion rnged from 6.53 to mg/l with men vlue of 1.75 mg/l, nd showed chrcteristic of decresing from north to south. The DO concentrtion ws higher in the re etween the Bering Se nd Lwrence Islnd nd ws lower in the southest nd southwest of Lwrence Islnd t the ltitude of 62 N. The formtion of mximum DO concentrtion ws concerned with phytoplnkton photosynthesis nd formtion of the themocline. To the south of St. B7 in the Bering Se sin, the oxygen produced y photosynthesis permeted to the deeper wter nd the themocline mde it difficult to exchnge verticlly, nd to the north of St. B7, the mximum DO concentrtion occurred ove the themocline due to phytoplnkton ctivities. On the shelf, the oxygen produced y phytoplnkton photosynthesis gthered t the ottom of the thermocline nd formed the DO mximum concentrtion. In the Bering Se sin, the DO nd slinity showed wek negtive correltion (r=.4) when the slinity ws lower thn 33.1, significnt negtive correltion (r=.92) when the slinity rnged from 33.1 to 33.7, nd n irregulr reversed prol (r=.95) when the slinity ws greter thn Key words: Bering Se, dissolved oxygen, mximum concentrtion, strtifiction, chlorophyll Cittion: Sun Xiuwu, Lin Ci, Chen Yong, Zhng Yunio, Wng Jigng, Ji Weidong Distriution of dissolved oxygen nd cuses of mximum concentrtion in the Bering Se in July 21. Act Ocenologic Sinic, 33(6): 2 27, doi: 1.17/s Introduction As n importnt mrginl se of the northern Pcific Ocen, the Bering Se comprises deep wter sin nmed Aleutin sin nd continentl shelf, which is hlf of the whole se re. The southern Bering Se exchnges wter with the Pcific Ocen through wter chnnels round the Aleutin Islnds nd in the north connects with the Arctic Ocen through the Bering Strit. The Bering Se is in the surctic se re, which is one of the three high productivity se res in the world (Berger et l., 1987; Gremeier et l., 26). The Bering Se plys n importnt role in glol climte chnge due to its essentil role in current, se ice, nd ecosystem of the Arctic Ocen. As one of importnt prmeters of the mrine ecosystem, the distriution of dissolved oxygen (DO) to some extent cn reflect iologicl ctivity nd physicl nd chemicl processes in se wter. Some literture (Chen, 2; Tng et l., 21; Zho, 23) indictes the Bering Se hs unique hydrologicl chrcteristics, impcting the distriution of mrine iologicl nd chemicl elements (Jin et l., 21; Zhng et l., 211). In this pper, sed on the dt of DO, chlorophyll, temperture, nd slinity otined during the 4th Chinese Ntionl Arctic Reserch Expedition, the chrcteristics of DO distriution nd cuses of its mximum vlue were discussed, providing scientific sis nd sic dt for further study on the role of the Bering Se in glol climte chnges. 2 Mterils nd methods 2.1 Smpling sttions nd sections Section B ws set in the re etween the sin nd continentl shelf; Sections BB nd NB were oth in the continentl shelf re; nd Section BS ws in the Bering Strit re in July 21 (Fig. 1). The smples in ll 46 sttions were tken on the sis of the following rules: (1) in the sin re, 12 smples were tken t depths of 3, 2, 3, 5, 75, 1, 2, 3, 5, 1, 2 m, nd the ottom; (2) in the continentl shelf, smples were normlly tken t depths of 3, 1, 2, 3, 5, 75, 1, nd 2 m, ut sometimes the smpling depth ws djusted due to the mximum lyer of chlorophyll nd temperture or the minimum lyer of temperture. Fundtion item: The Chin Progrm for Interntionl Polr Yer 27 28; the Specil Reserch Foundtion for Pulic Welfre Mrine Project Evlution of the Arctic mrine ecosystem response to rpid chnges in se ice under contrct No *Corresponding uthor, E-mil: hyssjwd@163.com

2 SUN Xiuwu et l. Act Ocenol. Sin., 214, Vol. 33, No. 6, P N Sieri Bering Strit BS11 BS1 BS1 Andyr Gulf NB12 St Iwrence B7 B12 Section BB BB1 BB7 B15 NB1 Section BS NB- NB9 NB1 NB6 Section NB NB7 Alsk 55 B1 17 Section B Aleutin E 18 W 17 Islnds 16 Fig.1. Smpling sttions nd sections. 2.2 Smpling collection nd nlysis Iodometric spectroscopy (Generl Administrtion of Qulity Supervision, Inspection nd Qurntine of the People s Repulic of Chin, 27) ws used to mesure DO while iodometric titrtion ws used when the sornce ws over 1. Brown ground-glss ottles were seled well nd mesured volume ccurtely efore smpling. When tking smples, first, the ottle ws rinsed two or three times y the smple wter. Second, the smpling tue ws put into the ottom of the ottle, mking the ottle full of smple wter, until it overflowed. During the smpling, the tue ws slowly picked up with the wter. Third, mngnese chloride nd lkline potssium iodide (including NN 3, 1 g/l) ws orderly put into the ottle nd mixed well. Fourth, the outside of the ottle ws rinsed with fresh wter nd then mesured t 25 C within 2 h. The sturtion of DO ws clculted using the formul proposed y Grci nd Gordon (1992). Fluorescence (Generl Administrtion of Qulity Supervision, Inspection nd Qurntine of the People s Repulic of Chin, 27) ws used to mesure chlorophyll. The 25 ml smple ws filtered y Whtmn GF/F. The residue in the memrne ws extrcted into liquid y 9% cetone nd then mesured with Tnner fluorescence nlyzer. 3 Results 3.1 Horizontl distriution of DO in the Bering Se continentl shelf The concentrtion of DO in the Bering Se continentl shelf rnged from mg/l nd the verge vlue ws 1.75 mg/l. The minimum DO concentrtion ws t the ottom of BB5, while the mximum ws t 3 m of NB1. Figure 2 ws the horizontl distriution of DO concentrtion nd sturtion, indicting the concentrtion nd sturtion of DO oth decresed from north to south. The concentrtion of DO ws 66 N 66 N W W Fig.2. Horizontl distriution of DO in the Bering Se continentl shelf surfce:. sturtion (%) nd. concentrtion (mg/l).

3 22 SUN Xiuwu et l. Act Ocenol. Sin., 214, Vol. 33, No. 6, P high in the re etween the Bering Strit nd Lwrence Islnd, while low in the southest nd southwest of Lwrence Islnd t 61 N ltitude due to the upwelling in the sin nd input from the Yukon River. The surfce sturtion of DO ws etween 15% 12%, indicting the unlnced sttue of oxygen in sewter nd ir. The concentrtion of DO ws lso high t depths of 1 m in the Bering Strit, 2 m t N ltitude, nd 3 m in the western Lwrence Islnd, while the highest sturtion ws 139%. The chlorophyll concentrtion ws lso high in this re, indicting high influence of phytoplnkton ctivities on DO concentrtion nd occurrence of looms in some res. 3.2 Verticl distriution Section B Section B ws locted in the res mong the Aleutin Islnds nd sin nd continentl shelf of the Bering Se. The verticl distriution of DO sturtion nd concentrtion in this section ws shown in Fig. 3. The DO concentrtion in this section vried slightly nd sturtion ws higher thn 9% from the surfce to 1 m. The DO ws sturted or supersturted within 5 m. In the sin, the concentrtion of DO rnged from.53 to mg/l with n verge vlue of 7.27 mg/l. The DO concentrtion rnged from 8.15 to mg/l from the surfce to 2 m, decresed quickly from 2 to 5 m, reched the lowest vlue of.53 mg/l from 5 to 1 m, nd then incresed with depth. Sttion B1 ws locted out of the Aleutin Islnds with the depth of 5 m. In the re from Sts B1 to B8, the DO concentrtion decresed quickly from 15 to 25 m. The depth with the sme DO concentrtion from Sts B8 to B12 ws deeper thn tht from Sts B1 to B8, indicting the depth of hypoxi ws deeper from south to north due to the cyclonic vortex ner St. B8. The southern Section B exchnged wters with the northern Pcific wter through the Ner Strit nd the northern section ws influenced y the Bering Slope Current (Clement et l., 25), so the vortex formed ner St. B8. The distriution of DO sturtion ws the sme s DO concentrtion Section NB nd Section BB Figure 4 showed how the sturtion nd concentrtion of DO distriuted in Section NB nd Section BB. Locted in the B1 B B B Fig.3. Distriution of DO in Section B:. sturtion (%) nd. concentrtion (mg/l).

4 SUN Xiuwu et l. Act Ocenol. Sin., 214, Vol. 33, No. 6, P B15 NB1 NB B15 NB1 NB BB1 BB c BB1 BB d Fig.4. Distriution of DO in Sections NB nd BB: nd c. sturtion (%) nd nd d. concentrtion (mg/l). north-centrl Bering Se continentl shelf nd south of Lwrence Islnd, Section NB wound its wy estwrds. The DO concentrtion vried from 8.1 to 14. mg/l with n verge vlue of 1.5 mg/l. The DO concentrtion ws higher thn 1.5 mg/l nd sturtion ws over 1% within 4 m. The highest DO concentrtion ws t 2 m t St. NB1 with sturtion of 128% nd the lowest ws t the ottom of St. B15 with sturtion of 72%. The DO sturtion vried oviously within 5 m nd slightly from 5 m to the ottom. Locted west of the Bering Se shelf nd est of the Andyr Gulf, Section BB extended from southwest to northest, the sme s Section B. The DO concentrtion rnged from 6.53 to mg/l with n verge vlue of 1.24 mg/l. Sme s Section NB, the DO concentrtion ws over 1. mg/l nd sturtion over 1%. The sturtion of DO ws highest t 2 m nd over 12% in some res ut not sturted from 4 m to the ottom.

5 24 SUN Xiuwu et l. Act Ocenol. Sin., 214, Vol. 33, No. 6, P Section BS Section BS wound its wy estwrds to the whole Bering Strit with the depth of less thn 5 m. The verticl distriution of DO sturtion nd concentrtion in this section ws shown in Fig. 5. The DO concentrtion rnged from 9.25 to 13.3 mg/l with n verge vlue of mg/l. Most of the re in this section ws supersturted nd the most sturted in the middle from surfce to 2 m. From Sts BS1 to BS3, which were ll locted in the western strit, the DO concentrtion ws the sme from surfce to ottom nd incresed from west to est due to the mixing of three wter msses (Woodgte nd Agrd, 25; Li et l., 211). In the western Bering Strit, the Andyr Current hd high slinity, low temperture, nd high nutrients. In the estern Bering Strit, opposite to the Andyr Current, the Alsk BS1 BS BS BS Fig.5. Distriution of DO in Section BS:. sturtion (%) nd. concentrtion (mg/l). Costl Current hd low slinity, high temperture, nd low nutrients. The Bering Se shelf flow ws locted in the middle. The vrition of temperture, slinity, nd nutrients of these ove three msses contriuted to the distriution of DO concentrtion nd sturtion in this re. 4 Discussion 4.1 Cuses of mximum DO concentrtion According to the dt, the mximum DO concentrtion in upper wter of the Bering Se sin ws from 2 to 5 m nd through the whole thermocline in July 21. Reid (1962) thought tht in the northern Pcific Ocen, the mximum concentrtion of DO ws usully t the ottom of the mixing lyer in winter nd ws totlly influenced y temperture in summer. Gu (198) elieved it ws common phenomenon tht the mximum DO concentrtion ws mintined y tht in winter. However, Wng (1996) thought tht in the Hunghe River, the mximum concentrtion of DO ws ffected y photosynthesis nd the thermocline ut not mintined y them in winter. Thompson et l. (1934) elieved the mximum DO concentrtion from 15 to 5 m in the northern nd northestern Pcific Ocen dpted to the photosynthesis elt. In the Bering Se sin, cooling nd freezing of surfce se wter led to n increse of density, verticl mixture from surfce to 2 m or 3 m, nd low temperture down to 1 C or 3 C in winter (Khen, 1988). However, in summer, endothermic wrming of surfce se wter contriutes to preservtion of hypothermi nd formtion of cold wter lyer. In this survey, n ovious cold wter lyer existed in the upper wter lyer in the sin with depths from 25 to 3 m (Fig. 6). Insted of DO concentrtion, the concentrtion of sturted DO in the winter upper wter lyer clculted y temperture nd slinity of cold nucler in cold wter lyer ws higher thn the mximum concentrtion of DO in summer, indicting the mximum DO concentrtion ws mintined y tht in winter. To the south of St. B7 in the sin, the mximum DO concentrtion ws t the ottom of the thermocline t depths from 4 to 5 m nd different with the depth of mximum chlorophyll (Fig. 6). The oxygen generted y phytoplnkton photosynthesis penetrted into deeper wter with formtion of the thermocline nd ws then preserved due to difficult exchnge, so the mximum DO concentrtion ws cused y phytoplnkton photosynthesis,

6 SUN Xiuwu et l. Act Ocenol. Sin., 214, Vol. 33, No. 6, P B1 B B1 B B15 NB1 NB c BB1 BB d Mximum concentrtion of DO, mximum concentrtion of chlorophyll Fig.6. Distriution of temperture: nd. Section B, c. Section NB nd d. Section BB.

7 26 SUN Xiuwu et l. Act Ocenol. Sin., 214, Vol. 33, No. 6, P which ws consistent with the view of Богоявленский (1953). In the re from Sts B9 to B12, the mximum DO concentrtion ws t depth of 2 m, which ws the thermocline surfce, nd lso the depth of mximum chlorophyll (1.79 mg/m 3 ), so the mximum DO concentrtion ws cused y plnkton ctivities. In the continentl shelf, typicl strtifiction strts from My nd is minly ffected y temperture in summer (Ldd nd Steno, 212), which ws oviously expressed in Sections BB nd NB. In this re, the thermocline ws from 15 to 3 m in July 21 (Figs 6c nd d). In the sttion deeper thn 5 m, the mximum DO concentrtion ws usully t the ottom of the thermocline, which ws from 2 to 3 m. At the sme time, the mximum chlorophyll ws from 3 to 47 m. Therefore, the depth of mximum DO concentrtion ws the sme or lower thn tht of chlorophyll, which ws different from tht in the sin. In the continentl shelf, the wter ws frozen in winter nd strtifiction formed quickly due to endothermic ctivity with melting in spring nd summer. The strtifiction would e stle without disturnce y strong wind. Aundnt nutrients rought y tides, upwelling, nd costl current were exchnged to the photosynthetic lyer tht ws under the thermocline ecuse of shllow depth. The undnt oxygen generted y photosynthesis penetrted to the thermocline, nd then ccumulted t the ottom of the thermocline due to strtifiction, indicting the mximum DO concentrtion ws influenced y phytoplnkton ctivities in the continentl shelf. 4.2 Reltionship etween DO nd slinity The DO concentrtion ws not correlted with slinity in the continentl shelf, ut in the sin, the reltionship etween these two cn e divided into three prts, shown in Fig. 7 nd Tle 1. (1) When slinity ws from 32.6 to 33.1, the DO concentrtion ws slightly negtively correlted with slinity nd influenced y tmospheric exchnge nd photosynthesis. (2) When slinity ws from 33.1 to 33.7, DO concentrtion ws oviously correlted with slinity. These sttions were through the whole hlocline of upper wter nd some were locted in the DO/mg L Slinity Fig.7. Reltionship etween DO nd slinity in the Bering Se sin. Tle 1. Correlted curves etween DO nd slinity in the Bering Se Are Slinity (S) Curve eqution Curve type Coefficient Shelf 25.9<S<33.1 y=.79x liner r=.4 Bsin 32.6<S<33.1 y= 1.325x liner r=.4 Bsin 33.1<S<33.7 y= x liner r=.92 Bsin 33.7<S<34.7 y=12.748x x prolic r=.95 lower prt of the photosynthetic zone. The DO concentrtions in these sttions were ffected y photosynthesis, iologicl respirtion, nd physicl diffusion. (3) When slinity ws from 33.7 to 34.7, DO concentrtion ws n irregulr reversed prol with slinity nd lowest when slinity ws The DO concentrtion incresed when slinity ws higher thn 34.2 due to supplement of oxygen from ir. 5 Conclusions (1) The distriution of DO concentrtion in the Bering Se sin hd typicl ocenic chrcteristics. The DO concentrtion ws highest from 2 to 5 m, decresed quickly from 2 m down to the lowest etween 5 nd 1 m, nd then incresed with depth. In the sin, the DO concentrtion rnged from.53 to 12.5 mg/l. (2) The DO concentrtion in the continentl shelf ws from 6.53 to mg/l with n verge vlue of 1.75 mg/l. It decresed from north to south, tht ws, high in the re from the Bering Se to Lwrence Islnd nd low in southestern nd southwestern Lwrence Islnd t out 62 N. (3) The mximum DO concentrtion ws relted with phytoplnkton photosynthesis nd thermocline formtion. To the south of St. B7 in the sin, the oxygen generted y phytoplnkton photosynthesis penetrted deeper wter nd reched the mximum DO concentrtion due to hrd verticl exchnge cused y the thermocline. However, to the north of St. B7, the mximum DO concentrtion ws formed y phytoplnkton ctivities. In the continentl shelf, it ws lso formed y phytoplnkton ctivities under the thermocline. (4) In upper wter of the Bering Se, the DO concentrtion ws not correlted with slinity when slinity ws lower thn 33.1, oviously negtively correlted with slinity when it ws etween 33.1 nd 33.7 in the sin with coefficient of.94, nd n irregulr reversed prol with slinity when it ws higher thn 33.7 with the lowest vlue s Acknowledgements Thnks to ll tem memers of the 4th Chinese Ntionl Arctic Reserch Expedition for their support nd help.

8 SUN Xiuwu et l. Act Ocenol. Sin., 214, Vol. 33, No. 6, P References Berger W H, Fischer K, Li C, et l Ocen productivity nd orgnic cron flux: prt I. overview nd mp of primry production nd export production. Scripps Institution of Ocenogrphy SIO Reference, 87(3): 67 Chen Juf. 2. The distriution of thermocline nd middle cold wter in the Bering Se in summer. Chinese Mrine Fisheries Reserch (in Chinese), 21(2): Clement J L, Mslowski W, Cooper L W, et l. 25. Ocen circultion nd exchnges through the nothern Bering Se : model results. Deep-Se Reserch II, 52(17): Grci H E, Gordon L I Oxygen soluility in se wter: Better fitting equtions. Limnology nd Ocenogrphy, 37: Generl Administrtion of Qulity Supervision, Inspection nd Qurntine of the People s Repulic of Chin. 27. GB/T Specifictions for Ocenogrphic Survey Survey of Chemicl Prmeters in Se Wter (in Chinese). Beijing: Chin Stndrd Press Gremeier J M, Cooper L W, Feder H M, et l. 26. Ecosystem dynmics of the Pcific influenced northern Bering nd Chkchi Ses in the Amersin Arctic. Progress in Ocenogrphy, 71: Gu Hongkn The mximum vlue of dissolved oxygen in its verticl distriution in yellow se. Act Ocenologic Sinic (in Chinese), 2(2): 7 8 Jin Mingming, Lin Yi n, Lu Yong. 21. Verticl fetures of nutrient nd dissolved oxygen of the Bering sin in July1999. Chinese Mrine Fisheries Reserch (in Chinese), 13(4): Khen G V Ocenogrphic conditions nd Bering Se iologicl productivity. In: Proceedings of the Interntionl Symposium on the Biology nd Mngement of Wlleye Pollock. Ancorge, AK: Alsk Se Grnt Rep, 89 1 Ldd C, Steno P J Strtifiction on the Estern Bering Se shelf revisited. Deep-Se Reserch II, 65 7: Li Hongling, Chen Jinfng, Go Shengqun, et l Nutrients vrition of the Pcific inflow in the western Arctic Ocen. Act Ocenologic Sinic (in Chinese), 33(2): Reid J L Jr Distriution of dissolved oxygen in the summer thermocline. Journl of Mrine Reserch, 29(2): Tng Yuxing, Jio Yutin, Zou Emei. 21. A preliminry nlysis of the hydrogrphic fetures nd wter msses in the Bering Se nd the Chukchi Se. Chinese Journl of Polr Reserch (in Chinese), 16(1): Thompson T, Toms B, Brnes C Distriution of dissolved oxygen in North Pcific Ocen. In: Jmes Johnston Memoril Volume. Liverpool: University Press of Liverpool: Wng Bodong Formtion mechnism of mximum vlue in verticl distriution of dissolved oxygen in the Yellow Se. Journl of Ocenogrphy of Hunghi & Bohi Ses (in Chinese), 15(3): 1 15 Woodgte R A, Agrd K. 25. Revising the Bering Strit fresh wter flux into the Arctic Ocen. Geophysicl Reserch Letters, 32: L262, doi: 1 129/24GL21747 Zhng Fng, He Jinfeng, Lin Ling, et l Distriution of picophytoplnkton nd environmentl correltion nlysis in Bering Se shelf during the summer of 28. Act Ocenologic Sinic (in Chinese), 33(2): Zho Jinping. 23. Temperture structure of Chukchi Se nd its exchnge with Bering Se wter. In: Chen Liqi, ed. Mrine Enviroment nd Air-Se Interction in the Arctic Region. Beijing: Chin Ocen Press, Богоявленский A H Происожцение Максимума кислорода в море. Рукопись Фонды инта Океанол AH CCCP