The State of the Far East Seas during the 1997/98 El Niño Event

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The Stte of the Fr Est Ses during the 1997/98 El Niño Event A.S. Krovnin, 1 G. P. Vnyushin, 1 M. Yu. Kruzhlov, 1 G.V. Khen, 2 M.A. Bogdnov, 1 E.I. Ustinov, 2 V.V. Mslennikov, 1 A.M. Orlov 1 B.N. Kotenev, 1 V.

1 The Stte of the Fr Est Ses during the 1997/98 El Niño Event A.S. Krovnin, 1 G. P. Vnyushin, 1 M. Yu. Kruzhlov, 1 G.V. Khen, 2 M.A. Bogdnov, 1 E.I. Ustinov, 2 V.V. Mslennikov, 1 A.M. Orlov 1 B.N. Kotenev, 1 V.V. Bulnov 1 nd G.P. Muriy 1 1 Russin Federl Reserch Institute of Fishery nd Ocenogrphy (VNIRO) 17 V. Krsnoselsky, Moscow , Russi e-mil: krovnin@mx.iki.rssi.ru 2 Pcific Reserch Fisheries Centre (TINRO-Centre) 4, Shevchenko Alley, Vldivostok , Russi Ocenogrphic conditions, minly temperture fields, in the Bering nd Okhotsk Ses in 1997/98 re compred with those in previous, non-el Niño s ( ). The study is sed on monthly se surfce temperture (SST) mps constructed t the Russin Federl Reserch Institute of Fishery nd Ocenogrphy (VNIRO) s prt of the progrm on the use of stellite nd ship dt to monitor the dynmics of SST in vrious fishing res of the world ocen. The min purpose of the progrm is to provide the Russin fishery community with opertive nd monthly informtion on the stte of environment in regions where the Russin fleet opertes. Also, dt of severl ocenogrphic surveys conducted in the western Bering Se in re used. Figure 1 demonstrtes the vriility in men monthly SST nomlies in the Northwest Pcific for As is seen, the El Niño signl ppered in April, 1997 nd reched it mximum in Octoer, when positive SST nomlies in the centrl Se of Okhotsk nd northwestern Bering Se exceeded 3 C. Figure 2 shows differences in men winter (left pnel) nd men summer (right pnel) SST nd se level pressure (SLP) vlues etween 1996 nd 1995, 1997 nd 1996, 1998 nd The mps llow one to identify some fetures of climtic vriility in the region for The wrming strted in winter, 1996 nd ws oserved on most of the investigted region. The only exception ws the re off Kmchtk, t the northwestern prt of the Bering Se, nd the estern Figure 1. Vriility of SST nomlies in the Northwest Pcific during 1997 (y stellite dt).

Se of Okhotsk. In 1997 wrming ws oserved in the whole Northwest Pcific, including the Bering nd Okhotsk Ses. Positive differences etween 1996 nd 1997 exceeded 1.0 1.5 C.

2 Se of Okhotsk. In 1997 wrming ws oserved in the whole Northwest Pcific, including the Bering nd Okhotsk Ses. Positive differences etween 1996 nd 1997 exceeded C. Quite the opposite sitution ws noted etween the cold sesons of 1998 nd In fct, SST decresed over the whole Northwest Pcific (out 1 2 C), nd ice cover re incresed. These chnges in SST ptterns corresponded to chnges in the chrcter of the tmospheric circultion. Thus, if in 1996 the northwestern Bering Se ws ffected y the northestern periphery of the Sierin High with prevlence of the northern winds nd corresponding decrese in SST, in 1997 this prt of the se ws under influence of the estern periphery of lrge cyclonic formtion with predomintely southern winds. In 1998 the tmospheric sitution ws very similr to tht of 1996 (Figure 2, left pnel). The development of tmospheric nd ocenic processes in the summer sesons of ws somewht different from tht in winter (Figure 2, right pnel). The cler lessening of the Est Kmchtk Current ws oserved in Compred with 1995, 1996 showed positive SST differences of 1 2 C in its core. The sme sitution ws oserved in summer, Differences in men summer SST etween 1997 nd 1996 in the western Bering Se exceeded 3 C. However, cooling tht strted in the Northwest Pcific in 1998 ws more pronounced in summer thn in winter. A decrese in SST in Andyr By nd off Nvrin Cpe in the Bering Se exceeded 3 C Chnges in ice conditions during were lso considered which llowed one to identify some nomlous events occurring in the Bering nd Okhotsk Ses during the El Niño in 1997 (Figures 3 nd 4). Figure 2. Differences in men winter (left pnel) nd men summer (right pnel) SST nd SLP vlues etween (A, D) 1996 nd 1995, (B, E), 1997 nd 1996, nd (C, F) 1998 nd 1997.

3 N 58 N 1 April 1 My 1 57 N 130 dfrs dys 60 dys Figure 3. Durtion of the ice period in the estern Se of Okhotsk ( estern chnnel ) t () different ltitudes nd () numers of 1 1 squres covered y ice on April 1 nd My 1 nd their differences for For exmple, in 1997 the northern oundry of the so clled estern chnnel (qutory permnently free of ice during the cold seson in the estern Se of Okhotsk) did not cross 57 N, while in 1998 the oundry ws locted south of this ltitude for 80 dys (Figure 3). The rte of decresing ice re in the se ws highest in compred with , s is demonstrted y differences in the numer of 1 1 squres covered y ice etween April 1 nd My 1 (Figure 3). Durtion of the ice period round St. Mtthew Islnd in the Bering Se decresed eginning in 1996, nd in 1998 it equled 48 dys compred with 138 dys in 1996 (Figure 4) ws lso chrcterized y the erly retret of the ice oundry to the north of 63 N in oth the western nd estern Bering Se. If, in 1996, ice oundry crossed the western Bering Se t 63 N in mid-june, in 1998 this occurred in the third ten-dy period of April (Figure 4). Thus, the difference ws out 55 dys. Also, in the western region of the se decrese in the ice cover re in 1997 strted on Ferury 17, while in 1996 it egn on April 15, nd in 1998, on Mrch 15 (Figure 4c). Results of joint Russin Jpnese surveys conducted in June nd Septemer, 1997 onord of Jpnese trwler Tenyo Mru 78 in the northwestern Bering Se showed some significnt nomlies in the development of ocenogrphic conditions. First, the core of Wrm Intermedite Lyer (WIL), in oth June nd Septemer, ws locted t depths of m which ws y m shllower thn tht found from Arsenyev s dt (1967) nd y 100 m shllower compred with vlues given in the tls prepred y Syles et l. (1978). Along with the rising of the core, n increse in WIL temperture nd decrese in its slinity were oserved. The vlues of se wter temperture in the WIL core long the 180 meridin were C, while in previous s the tempertures did not exceed C. Slinity decresed y 0.05 psu nd greter. The men long-term slinity in the region is psu. In 1997 its men vlues were only psu. Such decrese in slinity is possily ssocited with the chnge in the chrcter of WIL trnsformtion in the Olutorsky-Nvrinsky region. Ocenogrphic prmeters in this region re similr to those for the Priyloff-Mtthew continentl slope. In ll, positive se wter temperture nomlies in 1997 were out C in the surfce lyer, C in the core of Cold Intermedite Lyer, nd C in the Wrm Intermedite Lyer. El Niño effects were pprently oserved in the western Bering Se in 1998 s well. Despite the sur-

4 fce therml conditions in this region eing close to norml, temperture vlues in WIL remined high. Along the continentl slope off the Koryksky cost nd Nvrin re vlues exceeded 3.80 C. As in 1997, the loction of the WIL core ws exclusively shllow, m (cruise of R/V Professor Kgnovsky, August Novemer, 1998). In 1998 the significnt lessening of the Kmchtk Current ws lso oserved. There ws negtive wter exchnge lnce vi the Kmchtk Strit etween the Bering Se nd North Pcific: in the m lyer outflow equled 0.97 Sv, while inflow ws 1.52 Sv, nd the resulting flow ws 0.55 Sv. Even tking into ccount the sesonl lessening of the Kmchtk Current, the result is mzing. We consider tht one of the 1997/98 El Niño effects ws n ppernce of typiclly Americn fish species to the Asin cost. In 1997, rex sole (Errex zchirus) which ws recorded there only once (Kulikov, 1964) spred over lmost the entire sin (Figure 5). Compred with previous s, lrgesized (men length 54.8 cm) rrowtooth flounder (Aterestes stomis) lso ecme widely common species in the western Bering Se (Figure 5c). According to similrity of the size composition of oth the species with tht in the estern Bering Se, we could ssume tht the wrming ssocited with the El Niño event led to n extension of these species westwrds. In , lrge record numer of northern rockfish (Sestes polyspinis) (Figure 5) nd dusky rockfish (Sestes cilitus) (Sheiko nd Trenkov, 1998) occurred in Pcific wters off the northern Kurils; these wters lso reveled juvenile rrowtooth flounder (Figure 5d) nd slefish. Erlier, ll the four species were never registered, or were ccidentlly cught there. Becuse these species hve pelgic lrve nd juveniles, one cn suppose their lrve or juveniles were trnsported from the Aleutin re to the North Kurils y currents in previous s. However, they were not recorded off the Kurils erlier. The similrity in size composition of cptured fish with those off the Aleutin Islnds my indicte their Aleutin genesis. c dys dt west est dt west est Figure 4. () Durtion of the ice period round St. Mtthew Islnd; () dtes when the ice oundry crossed 63 N; (c) dtes when the ice cover strted to decrese, in the Bering Se.

5 S I B E R I A SEA OF OKHOTSK BERING SEA PACIFIC OCEAN W c d S I B E R I A SEA OF OKHOTSK BERING SEA PACIFIC OCEAN W Figure 5. Records sites (tringles) of () rex sole nd (c) rrowtooth flounder in the western Bering Se in 1997, nd () northern rockfish nd (d) rrowtooth flounder in Pcific wters off the North Kurils nd southest Kmchtk in The continuous line shows the 1000-m isoth. References Arsenyev, V.S Currents nd Wter Msses. Nuk, Moscow, 133 pp. (in Russin) Kulikov, M.Yu The First Record of Rex Sole Errex zchirus (Lock) off the Asin Cost of the Bering Se. Izvestiy TINRO, vol. 55, p (in Russin) Syles, M.A., Agrd, K. nd Cochmn, L.A Ocenogrphic Atls of the Bering Se Bsin. Univ. of Wshington, 158 pp. Sheiko, B.A., nd Trenkov, A.G New for Russin fun nd rre mrine fishes from Kmchtk, Kuril nd Commnder Islnds. pp in Actul prolems of fish txonomy. Astrcts of conference St. Petersurg, Zoologicl Institute of Russin Acdemy of Science.

Journal of the Meteorological Society of Japan, Vol. 75, No. 6, pp ,

Journal of the Meteorological Society of Japan, Vol. 75, No. 6, pp , Journl of the Meteorologicl Society of Jpn, Vol. 75, No. 6, pp. 1109-1123, 1997 1109 Internnul nd Interdecdl Vritions of the Western North Pcific Monsoon nd Biu Rinfll nd their Reltionship to the ENSO