Interannual variability of mixed layer depth and heat storage of upper layer in the tropical Pacific Ocean

By using the upper layer data(downloaded from the web of the Scripps Institution of Oceanography),the interannual variability of the heat storage of upper layer(from surface to 400 m depth) and the mixed layer depth in the tropical Pacific Ocean are investigated. The abnormal signal of the warm event comes from the central and west Pacific Ocean, whereas it is regarded that the abnormal signal of the warm event comes from the east Pacific Ocean in the popular viewpoint. From the viewpoint on the evolution of the interannual variability of the mixed layer depth and the heat storage of the whole upper layer, the difference between the two types of El Nino is so small that it can be neglected. During these two El Nino/La Nina events(1972/1973 and 1997/1998), other than the case of the heat storage or for the mixed layer depth, the abnormal signal propagates from the central and west Pacific Ocean to the east usually by the path along the equator whereas the abnormal signal propagates from the east to the west by the path northern to the equator. For the interannual variability, the evolution of the mixed layer depth corresponds to that of the heat storage in the upper layer very well. This is quite different from the evolution of seasonality.

Spatial and temporal variability of heat content above the thermocline in the tropical Pacific Ocean

Heat content of the upper layer above the 20℃ isotherm in the tropical Pacific Ocean isestimated by using the sea temperature data set with a resolution 2°latitude×5°longitude (1980-1993) for the water depths (every 10 m) from 0 m to 400 m, and its temporal and spatial variabilities are analyzed. (1) The temporal variability indicates that the total heat in the upper layer of the equatorial Pacific Ocean is characterized by the interannual variability. The time series of the equatorial heat anomaly 5 months lead that of the El Nino index at the best positive lag correlation between the two, and the former 13 months lag behind the latter at their best negative lag correlation. Therefore the equatorial heat content can be used as a better predictor than the El Nino index for a warm or cold event. In addition, it is also found that less heat anomaly in the equator corresponds to the stronger warm events in the period (1980- 1993) and much more heat was accumulated in the 4 years including 1992/1993 ENSO (1989-1993) than the 4 years including 1982/1983 ENSO (1980-1983); (2) The spatial variability indicates that the area with the highest lag correlation among the grids moves in an anti-clockwise circle in the northern tropical Pacific Ocean within 4 years period and in a clockwise circle in the southern tropical Pacific Ocean. This result provides scientific evidence for the quasi - cycle theory of El Nino events.

The diagnosis for the tropical Pacific Ocean conditions in 1990

In this paper, on the basis of the observational hydrographic data obtained from the eighth cruise of PRC-USA bilateral air-sea interaction program, and combined with the sea surface temperature (SST) charts provided by NOAA, the data obtained from moored thermistor chains supplied by L. J. Mangum and sea level data provided by K. Wyrtki, the ocean conditions since October, 1989 in the western tropical Pacific are exposed, which indicate that 1990 is a year with weak El Nino event similar to the 1980 El Nino event, and the North Equatorial Countercurrent (NECC) has made a good contribution to the propagation of warm water from the Western to the Central and Eastern Pacific, a characteristic similar to that of the 1976 El Nino event. The 1990 weak El Nino event will soon fall into decay.

Abnormality of thermal structure and current in the upper western tropical Pacific Ocean and its effect on subtropical high

-Mainly on the basis of the data obtained during PRC/US bilateral TOGA cruises, abnormal variation occurred during the 1986/1987 El Nino is shown in this paper about the thermal structure and circulation of the upper western tropical Pacific Ocean. The effects of the abmormal variation on the subtropical high over the Northwest Pacific Ocean are discussed. During the El Nino: (1) In the east part of the western tropical Pacific Ocean (the subsurface temperature data on the 165° E section are taken as an example), the water wanner than 29 C in the upper layer spread on the longitudinal section and positive temperature anormalies appeared in a large area of the sea surface. (2) In the west part of the western tropical Pacific Ocean (the subsurface temperature data on the 137°E section are representative ), the cross section occupied by the upper layer warmer water ( T >28 ℃ ) became shrunk, and the sea surface temperature showed negative amomalies. (3) The eastward flows in the upper layer of the 165°E section strengthened. (4)The northward flow volume of warm water from the origin area of Kuroshio, i. e. , the tropical oceanic area south of 18?0' N and from the west of 130?E to the Philippine coast, decreased. When those kinds of abnomal variation occurred, air divergence on the low level (1 000 hPa) over the Northwest Pacific Ocean was intensified, favourable to the strengthening of subtropical high over the Northwest Pacific Ocean.

A Coupled General Circulation Model for the Tropical Pacific Ocean and Global Atmosphere

On the basis of Zeng's theorehcal design, a coupled general circulation model(CGCM) is develO￣ with itscharacteristics different from other CGCMs such as the unified vertical coordinates and subtraction of the standard stratification for both atmosphere and ocean, available energy consideration,and so on.The oceanic comPOnent is a free surface tropical Pacific Ocean GCM betWeen 30W and 30'S with horizontal grid spacing of ic in latitude and 2°in longitude,and with 14 vertical layers.The atmospheric component is a global GCM with low-resolution of 4°in lahtude and 5°in longitude,and tWo layers of equal mass in the verhcal between the surfaCe and 200 hFa.The atmospheric GCM includes comprehensive physical processes.The coupled model is subjected to seasonally-varying cycle.Several coupling experiments,ranging from straight forward coupling without flux correction to one with flux correchon,and to so-called predictor-corrector monthly coupling(PCMC),are conducted tO show the esistence and final controlling of the climate drift in the coupled system.After removing the climate drift with the PCMC SCheme,the coupled model is integrated for more than twenty years.The results show reasonable simulations of the anneal mean and its seasollal cycle of the atmospheric and￣ante circulahon.The model also ProduCeS the coherent intermnual variations of the climate system, manifesting the observed EI Nifio/Southern OSCillation(ENSO).

Physical oceanography of the Caroline M4 seamount in the tropical Western Pacific Ocean in summer 2017

Physical oceanography plays an important role in the formation of submarine sediments,and the distribution of nutriments and biocenoses in seamounts.The M4 seamount is located in the Caroline Island Ridge of the Western Pacific Ocean.The physical properties around M4 seamount are preliminarily analyzed based on the in-situ data obtained in summer 2017 in Caroline M4 seamount and open-sourced data.We found that the water in the upper 200 m is controlled by the westward North Equatorial Current(NEC),while the water between 300-1000 m is dominated by the eastward North Equatorial Undercurrent(NEUC).The current direction fluctuates significantly below 300 m at upstream stations.At the same depth of the lee sides,the current direction changes with the distance from seamount.These are likely caused by the obstacle of M4 seamount.The calculation results show that there is an anticyclonic cap above M4 seamount caused by tidal rectification.Tidal currents in M4 seamount are squeezed by the topography and amplified,and the amplified tidal currents play a dominant role in M4 seamount.First,the circulation system generated by the interaction of the amplified tidal current and M4 seamount drives the upward/downward movement of the isotherms.Secondly,the thickness of the surface turbulent layer is changed with the tidal phase.Thirdly,high turbulent diffusivities are found in the bottom of M4 seamount,and these are most likely attributed to the turbulent mixing induced by the mutual effect between semidiurnal tidal currents and steep bathymetry.This article of physical oceanography provides scientific basis for further analysis of the distribution of biological community and deposition mechanism in M4 seamount.

The Tropical Pacific–Indian Ocean Associated Mode Simulated by LICOM2.0

Oceanic general circulation models have become an important tool for the study of marine status and change. This paper reports a numerical simulation carried out using LICOM2.0 and the forcing field from CORE. When compared with SODA reanalysis data and ERSST.v3 b data, the patterns and variability of the tropical Pacific–Indian Ocean associated mode(PIOAM) are reproduced very well in this experiment. This indicates that, when the tropical central–western Indian Ocean and central–eastern Pacific are abnormally warmer/colder, the tropical eastern Indian Ocean and western Pacific are correspondingly colder/warmer. This further confirms that the tropical PIOAM is an important mode that is not only significant in the SST anomaly field, but also more obviously in the subsurface ocean temperature anomaly field. The surface associated mode index(SAMI) and the thermocline(i.e., subsurface) associated mode index(TAMI) calculated using the model output data are both consistent with the values of these indices derived from observation and reanalysis data. However, the model SAMI and TAMI are more closely and synchronously related to each other.

Tintinnid diversity in the tropical West Pacific Ocean

In order to investigate the tintinnid diversity, vertical distribution and latitudinal variation in the tropical West Pacific Ocean, water samples of different depths from surface to 200 m were collected along four transects. Totally 124 tintinnid species in 39 genera were detected. Most species preferred to live in the surface and subsurface waters. High tintinnid species richness, abundance and diversity index mainly occurred at depths slight shallower than the layer of deep chlorophyll maximum. Species richness, abundance and Shannon＇s diversity index were significant positive correlation with temperature and chlorophyll a in vivo fluorescence, but significant negative correlation with salinity and depth. The correlations between most dominant species and environmental factors were not significant. Tintinnid diversity was extremely high in this area, species richness ranged from 25 to 52 at each station, Shannon＇s diversity indexes were higher than 3 at most sampling positions from surface to 75 m. Proportions of redundant species were high, accounted for 87.90% of species pool and 60.38% of total abundance, indicating high capacity to response to changes in resource composition and predation pressures of tintinnid communities in the tropical West Pacific Ocean.

The bacterial diversity and community composition altered in the oxygen minimum zone of the Tropical Western Pacific Ocean

The oxygen minimum zones(OMZs)are globally expanding,yet the variation pattern of microbial communities related to dissolved oxygen levels remain unclear.Spatial variability of bacterial diversity and community composition(repre sented by 16 S rRNA)of six stations was investigated within the water column in the seamount area of Tropical Western Pacific Ocean(TWPO)in May 2019.The seawater has dissolved oxygen(DO)concentration of 3.01-6.68 mg/L and the core of the oxygen minimum zones was located between the depths of 650 m and 1750 m.The bacterial alpha-diversity showed unimodal pattern with the decreasing DO with depths and peaked in the upper oxycline(UO)of OMZs.The bacterial community structure of the mixed layer(ML)and the bottom layer clustered and separated from each other,while those of UO and the OMZ core(OM)clustered and overlapped.Overall,bacterial community composition transitioned from being Alphaproteobacteria and Gammaproteobacteria-dominant in ML to being Gammaproteobacteria and Nitrososphaeria/Deltaproteobacteria-dominant in UO and OM,and then changed to being Clostridia and unidentified Actinobacteria-dominant in the bottom layer.Moreover,both bacterial alpha-diversity and the abundant classes fitted varying sectioned functions with DO.The DO solely explained 40.37%of the variation of bacterial community composition among layers(P<0.001).The predicted function profiling showed that the water column was predominant by chemoheterotrophy,cyanobacteria,and photoautotrophy in ML,by chemoheterotrophy and nitrate/sulfide cycling in UO and OM,and by chemoheterotrophy and ferme ntation in the bottom layer.Our findings revealed the DO-associated variation in bacterial diversity and community composition,and help to clarify the potential responses of microbes and their involved biogeochemical processes to the expansion and intensification of OMZs.

N2 fixation rate and diazotroph community structure in the western tropical North Pacific Ocean

In the present study, we report N2 fixation rate(15N isotope tracer assay) and the diazotroph community structure(using the molecular method) in the western tropical North Pacific Ocean(WTNP)(13°–20°N, 120°–160°E). Our independent evidence on the basis of both in situ N2 fixation activity and diazotroph community structure showed the dominance of unicellular N2 fixation over majority of the WTNP surface waters during the sampling periods.Moreover, a shift in the diazotrophic composition from unicellular cyanobacteria group B-dominated to Trichodesmium spp.-dominated toward the western boundary current(Kuroshio) was also observed in 2013. We hypothesize that nutrient availability may have played a major role in regulating the biogeography of N2 fixation.In surface waters, volumetric N2 fixation rate(calculated by nitrogen) ranged between 0.6 and 2.6 nmol/(L·d) and averaged(1.2±0.5) nmol/(L·d), with <10 μm size fraction contributed predominantly(88%±6%) to the total rate between 135°E and 160°E. Depth-integrated N2 fixation rate over the upper 200 m ranged between 150 μmol/(m^2·d)and 480 μmol/(m^2·d)average(225±105) μmol/(m^2·d). N2 fixation can account for 6.2%±3.7% of the depthintegrated primary production, suggesting that N2 fixation is a significant N source sustaining new and export production in the WTNP. The role of N2 fixation in biogeochemical cycling in this climate change-vulnerable region calls for further investigations.

Nutrient distributions and nitrogen-anomaly(N^(*))in the tropical North Pacific Ocean

Based upon cruise observations broadly covering the tropical North Pacific during July-November 2017,together with data obtained from the World Ocean Circulation Experiment Hydrographic Program,this study examined the distribution of dissolved inorganic nitrogen(DIN,nitrate(NO_(3)^(-))+nitrite(NO_(2)^(-))),dissolved inorganic phosphorus(DIP)and related N^(*)(nitrogen-anomaly,N^(*)=N-16P+2.9,where N and P are the concentrations of DIN(>1.0μmol/L)and DIP(>0.1μmol/L)),used as an index of N2fixation,in the upper 1000 m of the water column.Nutrient concentrations displayed distinct spatial variability in the upper ocean but became relatively constant at a depth of 1000 m:they were high at low latitudes and in the eastern region,with an obvious nutricline at~150 m(DIN,~32.0μmol/L;DIP,~2.4μmol/L)and then generally increased with depth;they decreased markedly(DIN,~1.2μmol/L;DIP,~0.1μmol/L;at~150 m)at high latitudes and in the western region,where a nutricline was not apparent.The N^(*)index showed significant meridional and zonal variation,with the most negative values located at low latitudes and in the eastern region(~10°N,~150°-170°E),while becoming positive towards the northwest(the north of~18°N,~160°E westward).A N^(*)concentration larger than 2.0μmol/L which often used as an indicator of N2fixation,was observed between 155°E and 165°E;N^(*)values were 2.0μmol/L to6.0μmol/L at~15°-28°N,i.e.,much higher than those in the southern sector(0-2.0μmol/L at~5°-10°N).Zonally,N^(*)decreased gradually from west(-2.0μmol/L to 4.0μmol/L,~145°-165°E)to east(-2.0μmol/L to-8.0μmol/L,~155°W)along~10°N,which was consistent with the distribution of Trichodesmium abundance and N2fixation rates.Furthermore,since such region was also supplied with aeolian deposition,high N^(*)was probably not only induced by N2fixation but also influenced by iron and/or nitrogen deposition.

Observation Research of the Turbulent Fluxes of Momentum, Sensible Heat and Latent Heat over the West Pacific Tropical Ocean Area

This paper describes results of the fluxes of momentum , sensible heat and latent heat for the West Pacific Tropical Ocean Area ( 127 ° E - 150 ° E , 5 ° N -3 ° S ). The data were collected by the small tethered balloon sounding system over this ocean area including 6 continuous stations (140 ° E. 0 ° ; 145 ° E, 0 ° ; 150 ° E, 0 ° ; 140° E, 5 ° N; 145 ° E, 5° N and 150 ° E, 5 ° N) from 11 October to 15 December, 1986 . These fluxes were calculated by the semiempirical flux-profile relationships of Monin-Obukhov similarity theory using these observed data. The results show that for this tropical ocean area the drag coefficient CD is equal to (1.53 ± 0.25) × 10 3 and the daily mean latent flux Hl is greater than its daily mean sensible flux HV by a factor of about 9.

Characteristics of change of the SST in the tropical western Pa-cific and the tropical Indian Ocean and its response to thechange of the Antarctic ice area

In this paper, by using ocean surface temperature data(COADS), the study is made of the characteristics of the monthly and annual changes of the SST in the tropical western Pacific and Indian Oceans, which have important influences on the climate change of the whole globe and the relation between ENSO(El Nio Southern Oscillation) and the Antarctic ice area is also discussed. The result indicates that in the tropical western Pacific and the Indian Oceans the change of Sea Surface Temperture(SST) is conspicuous both monthly and annaully, and shows different change tendency between them. This result may be due to different relation in the vibration period of SST between the two Oceans. The better corresponding relationship is obvious in the annual change of SST in the tropical Indian Ocean with the occurrence El Nio and La Nia. The change of the SST in the tropical western Pacific and the tropical Indian Oceans has a close relation to the Antarctic ice area, especially to the ice areas in the eastern south Pole and Ross Sea, and its notable correlative relationship appears in 16 months when the SST of the tropical western Pacific and the Indian Oceans lag back the Antarctic ice area.

Different El Niño Flavors and Associated Atmospheric Teleconnections as Simulated in a Hybrid Coupled Model

A previously developed hybrid coupled model(HCM)is composed of an intermediate tropical Pacific Ocean model and a global atmospheric general circulation model(AGCM),denoted as HCMAGCM.In this study,different El Niño flavors,namely the Eastern-Pacific(EP)and Central-Pacific(CP)types,and the associated global atmospheric teleconnections are examined in a 1000-yr control simulation of the HCMAGCM.The HCMAGCM indicates profoundly different characteristics among EP and CP El Niño events in terms of related oceanic and atmospheric variables in the tropical Pacific,including the amplitude and spatial patterns of sea surface temperature(SST),zonal wind stress,and precipitation anomalies.An SST budget analysis indicates that the thermocline feedback and zonal advective feedback dominantly contribute to the growth of EP and CP El Niño events,respectively.Corresponding to the shifts in the tropical rainfall and deep convection during EP and CP El Niño events,the model also reproduces the differences in the extratropical atmospheric responses during the boreal winter.In particular,the EP El Niño tends to be dominant in exciting a poleward wave train pattern to the Northern Hemisphere,while the CP El Niño tends to preferably produce a wave train similar to the Pacific North American(PNA)pattern.As a result,different climatic impacts exist in North American regions,with a warm-north and cold-south pattern during an EP El Niño and a warm-northeast and cold-southwest pattern during a CP El Niño,respectively.This modeling result highlights the importance of internal natural processes within the tropical Pacific as they relate to the genesis of ENSO diversity because the active ocean–atmosphere coupling is allowed only in the tropical Pacific within the framework of the HCMAGCM.

Observation of physical oceanography at the Y3 seamount (Yap Arc) in winter 2014

Seamounts aff ect the surrounding physical oceanography and form unique dynamic processes.The infl uences of these processes on biological and sedimentary distributions are quite diff erent in seamount areas at diff erent depths.The Y3 seamount is located in the Yap Arc of the tropical Western Pacifi c Ocean.The water depth of its summit is~280 m.Based on fi eld data obtained in December 2014 and other open-access data,the physical oceanography around the Y3 seamount was preliminarily analyzed.The results show that the upper layer(0-150 m)was under the infl uence of the westward-fl owing North Equatorial Current(NEC),while the eastward-fl owing North Equatorial Undercurrent(NEUC)controlled the water between 200-800 m.The NEC was strong and steady,but the NEUC was disturbed by the Y3 seamount.The cold dome above the Y3 seamount was not caused by a Taylor cap or tidal rectifi cation but probably by upwelling during the survey time.Tidal currents were squeezed against topography and greatly amplifi ed in the Y3 seamount.The thicknesses of the surface turbulent layers were greatly infl uenced by the spring-neap tidal cycle.The turbulent diff usivities in the sea surface layer above the Y3 seamount were much larger than those in the open ocean.Calculations showed that the surface wind stress greatly aff ected the turbulent mixing in the surface layer of the Y3 seamount.The reciprocal action between the amplifi ed tidal currents and topography was the most likely cause of the turbulent mixing near the bottom of the Y3 seamount.This study can provide a scientifi c basis for further study of biological and depositional characteristics at the Y3 seamount.

Two new species of the genus Munidopsis Whiteaves,1874(Crustacea:Anomura:Munidopsidae)from the Caroline Ridge,South of the Mariana Trench

The genus Munidopsis has high biodiversity in seamount habitats.In this study,two new Munidopsis species,Munidopsis ahyongi sp.nov.and Munidopsis carolinensis sp.nov.from the Caroline Ridge in the tropical western Pacific Ocean were described.M.ahyongi sp.nov.is very similar to a group of species in the M.serricornis complex,but can be readily distinguished from the related species in having the oblique posterior orbital margins,2 spines on the lateral carapace margin,and a relatively longer rostral median spine.M.carolinensis sp.nov.is different from two related species primarily in having oblique frontal margins,blunt outer orbital angles,straight lateral margins of the rostrum,scale-like rugae on sternites 5-7,and less spinose pereopod 1(chelipeds,P1)merus and carpus.Aside from the morphological comparisons,DNA barcode analysis and phylogenetic analysis based on the cytochrome c oxidase subunit I gene(COI)were employed for the identification of these new species.

STUDY ON THE AMPLITUDE AND PHASE VARIATION OF EQUATORIAL WARMING BY USING COMPLEX EOF(CEOF) ANALYSIS

In order to understand the mechanism of equatorial warming during El Nio and to search for its prediction methods, the complex EOF analysis is used in this article to study the time-space structure of SST variation in the tropical Pacific

Intensified Impact of the Equatorial QBO in August–September on the Northern Stratospheric Polar Vortex in December–January since the Late 1990s

This study reveals an intensified impact of the equatorial quasi-biennial oscillation(QBO)in August–September(QBO_AS)on the northern stratospheric polar vortex(SPV)in December–January(SPV_DJ)since the late 1990s.The unstable relationship may be related to the differences in the deep convection anomaly over the tropical western Pacific and Indian Oceans in October–November(ON)related to the QBO_AS prior to and after the late 1990s.During 1998–2017,the easterly phase of the QBO_AS is accompanied by a colder tropical tropopause in ON,which enhances the deep convective activity over the tropical western Pacific and suppresses it over the Indian Ocean.The deep convection anomaly generates anomalous Rossby waves that propagate into the northern mid-to-high latitudes to constructively interfere with the climatological wavenumber-1 and wavenumber-2 components,thereby resulting in enhanced upward-propagating tropospheric planetary-scale waves and a weakened SPV_DJ anomaly.During1979–1997,however,the deep convection anomaly over the tropical western Pacific and Indian Oceans in ON related to the easterly phase of the QBO_AS is weaker and shifts eastward,which excites the anomalous Rossby waves to constructively/destructively interfere with the climatological wavenumber-1 component in the midlatitudes/high latitudes,thereby weakening the upward-propagating planetary-scale waves and leading to a weaker linkage with the SPV_DJ.Further analyses reveal that the unstable relationship may be associated with the interdecadal differences in deep convection over the tropical western Pacific and Indian Oceans and the upward-propagating tropospheric planetary-scale waves in ON.