Skip to main content
SpringerLink
Log in

Direct measurements of deep current at 162°E south of the equator in the Melanesian Basin: a trial to detect a cross-equatorial deep western boundary current

  • Original Article
  • Published:
Journal of Oceanography Aims and scope Submit manuscript

Abstract

We conducted 1-year-long mooring observations four times below 2000 m, slightly south of the equator (2°39′ to 4°35′S) at 162°E in the Melanesian Basin in order to detect the southward deep western boundary return current crossing the equator. Contrary to our initial expectation of the deep flow scheme in the equatorial western boundary region, the observed results indicated a fairly complicated flow configuration. We analyzed the results with the help of a high-resolution model simulation. The ensemble average of the horizontal flow at each level near the deep western boundary indicates a significant westward flow at 2000 and 2250 m, with an insignificant southward component at 2500 and 2750 m. The annual mean meridional transports are very small (>1 Sv) and insignificant, with an ensemble-averaged value of 0.3 Sv (southward) ±0.4 Sv at most. Combining this with high-resolution model results, it is deduced that the southward transport of the deep western boundary current (DWBC) leaving the equator may be smaller than those obtained by low-resolution models, because of trapping of its fairly large fraction in the equatorial zone. Annual-scale flow patterns are classified into several categories, mainly based on the meridional-flow dominating or the zonal-flow dominating pattern. A case of the meridional-flow dominating patterns may possibly capture an annual-scale variability of DWBC, because its meridional transport variation, though somewhat weak, is consistent with that simulated. The zonal-flow dominating regime includes two types: long-lasting, almost steady westward flows and long-term zonal flow oscillations. The former seems to comprise well-known zonally elongated and meridionally narrow structures of the zonal flow beneath the thermocline in the equatorial region. The ensemble-averaged flow mentioned above is dominated by this type at the upper two levels 2000 and 2250 m, with total westward transport of 1.6 ± 0.7 Sv. The latter type seems to be a manifestation of the vertically propagating equatorial annual Rossby waves.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Fig. 10
Fig. 11
Fig. 12
Fig. 13
Fig. 14
Fig. 15

Similar content being viewed by others

Notes

  1. This model is similar to that of Ishizaki (1994a, b), except for the model domain (from the Pacific to the global ocean between 75°S and 75°N), vertical resolution (from 20 levels to 44), and vertical diffusivity (from constant 0.3 × 10−4 m2 s−1 to vertically structured 0.6 to 2.6 × 10−4 m2 s−1). After spin-up calculation using accelerated time integration (Bryan 1984) with an integration time of 345 years at the surface and 2800 years at the abyssal layers, normal time integration with annual mean forcings was performed for 5 model years and later that with monthly mean forcings for 15 model years.

References

  • Aoyama M et al (2010) 2008 inter-laboratory comparison study of a reference material for nutrients in seawater. Tech Rep Meteorol Res Inst No 60:134

    Google Scholar 

  • Ascani F, Firing E, Dutrieux P, McCreary JP, Ishida A (2010) Deep equatorial ocean circulation induced by a forced-dissipated Yanai beam. J Phys Oceanogr 40:1118–1142

    Article  Google Scholar 

  • Bryan K (1984) Accelerating the convergence to equilibrium of ocean climate models. J Phys Oceanogr 14:666–673

    Article  Google Scholar 

  • Cravatte S, Kessler W, Marin F (2012) Intermediate zonal jets in the tropical Pacific Ocean observed by Argo floats. J Phys Oceanogr. doi:10.1175/JPO-D-11-0206.1

  • Edwards CA, Pedlosky J (1998) Dynamics of nonlinear cross-equatorial flow. Part I: potential vorticity transformation. J Phys Oceanogr 28:2382–2406

    Article  Google Scholar 

  • Fiadeiro ME (1980) The alkalinity of the deep Pacific. Earth Planet Sci Lett 49:499–505

    Article  Google Scholar 

  • Firing E, Wijfells SE, Hacker P (1998) Equatorial subthermocline currents across the Pacific. J Geophys Res 103:21413–21423

    Article  Google Scholar 

  • Gouriou Y, Delcroix T, Eldin G (2006) Upper and intermediate circulation in the western equatorial Pacific Ocean in October 1999 and April 2000. Geophys Res Lett 33 L10603. doi:10.1029/2006GL025941

  • Hayashi K, Ishikawa K, Ishizaki H (1997) Observation of deep and bottom flows in the Melanesian Basin. Abstracts of fall meeting of Oceanogr Sci Jpn (in Japanese)

  • Ishizaki H (1994a) A simulation of the abyssal circulation in the North Pacific Ocean. Part I: flow field and comparison with observations. J Phys Oceanogr 24:1921–1939

    Article  Google Scholar 

  • Ishizaki H (1994b) A simulation of the abyssal circulation in the North Pacific Ocean. Part II: theoretical rationale. J Phys Oceanogr 24:1941–1954

    Article  Google Scholar 

  • Ishizaki H, Nakano H, Nakano T, Shikama N (2012) Evidence of deep equatorial Rossby wave propagation obtained by mooring observations at 162°E (in preparation)

  • Johnson GC, Toole JM (1993) Flow of deep and bottom waters in the Pacific at 10°N. Deep-Sea Res I 40:371–394

    Article  Google Scholar 

  • Kawabe M, Fujio S (2010) Pacific Ocean circulation based on observation. J Oceanogr 66:389–403

    Article  Google Scholar 

  • Kawabe M, Taira K (1995) Flow distribution at 165°E in the Pacific Ocean. In: Sasaki H, Nozaki Y (eds) Biogeochemical processes and ocean flux in the western Pacific. Terra Science, Tokyo, pp 629–649

    Google Scholar 

  • Kawabe M, Fujio S, Yanagimoto D (2003) Deep-water circulation at low latitudes in the western North Pacific. Deep-Sea Res I 50:631–656

    Article  Google Scholar 

  • Kawabe M, Yanagimoto D, Kitagawa S, Kuroda Y (2005) Variations of the deep western boundary current in Wake Island Passage. Deep-Sea Res I 52:1121–1137

    Article  Google Scholar 

  • Kawabe M, Yanagimoto D, Kitagawa S (2006) Variations of the deep western boundary current in the Melanesian Basin in the western North Pacific. Deep-Sea Res I 53:942–959

    Article  Google Scholar 

  • Kessler WS, McCreary JP (1993) The annual wind-driven Rossby wave in the subthermocline equatorial Pacific. J Phys Oceanogr 23:1192–1207

    Article  Google Scholar 

  • Komaki K, Kawabe M (2007) Structure of the upper deep current in the Melanesian Basin, western North Pacific. La mer 45:15–22

    Google Scholar 

  • Kroopnick P (1985) The distribution of 13C of pCO2 in the world oceans. Deep-Sea Res Part A 32:57–84

    Article  Google Scholar 

  • Lukas R, Firing E (1985) The annual Rossby wave in the central equatorial Pacific Ocean. J Phys Oceanogr 15:55–67

    Article  Google Scholar 

  • Mantyla AW (1975) On the potential temperature in the abyssal Pacific Ocean. J Mar Res 33:341–354

    Google Scholar 

  • Mantyla AW, Reid JL (1983) Abyssal characteristics of the World Ocean waters. Deep-Sea Res 30:805–833

    Article  Google Scholar 

  • Marin F, Kestenare E, Delcroix T, Durand F, Cravatte S, Eldin G, Bourdalle-Badie R (2010) Annual reversal of the equatorial intermediate current in the Pacific observations and model diagnostics. J Phys Oceanogr 40:915–933. doi:10.1175/2009JPO4318.1

    Article  Google Scholar 

  • Nakano H (2000) Modeling global abyssal circulation by incorporating bottom boundary layer parameterization. Ph. D. Thesis, University of Tokyo, pp 112

  • Nakano H, Hirabara M, Tsujino H, Motoi T (2008a) Development of a global ocean model with the resolution of 1° × 1/2° and 1/8° × 1/12°. CLIVAR Exchanges 13:11–13

    Google Scholar 

  • Nakano T, Ishizaki H, Shikama N (2008b) Comparison of data from four current meters obtained by long-term deep-sea moorings. Tech Rep Meteorol Res Inst No 55:22

    Google Scholar 

  • Ostlund HG, Stuiver M (1980) GEOSECS Pacific radiocarbon. Radiocarbon 22:25–53

    Google Scholar 

  • Reid JL (1986) On the total geostrophic circulation of the South Pacific Ocean: flow patterns, tracers and transports. Prog Oceanogr 16:1–61

    Article  Google Scholar 

  • Reid JL (1997) On the total geostrophic circulation of the Pacific Ocean: flow patterns, tracers and transports. Prog Oceanogr 39:263–352

    Article  Google Scholar 

  • Richardson PL, Fratantoni DM (1999) Float trajectories in the deep western boundary current and deep equatorial jets of the tropical Atlantic. Deep-Sea Res II 46:305–333

    Article  Google Scholar 

  • Richardson PL, Schmitz WJ Jr (1993) Deep cross-equatorial flow in the Atlantic measured with SOFAR floats. J Geophys Res 98:8371–8387

    Article  Google Scholar 

  • Schmitz WJ Jr (1996) On the world ocean circulation: the Pacific and Indian Oceans/A global update, vol. II. Woods Hole Oceanographic Institution, Tech. Rep., HHOI-96-08, pp 237

  • Siedler G, Holfort J, Zenk W, Müller TJ, Csernók T (2004) Deep-water flow in the Mariana and Caroline Basins. J Phys Oceanogr 34:566–581

    Article  Google Scholar 

  • Talley LD (2007) Hydrographic atlas of the World Ocean Circulation Experiment (WOCE). Volume 2: Pacific Ocean. International WOCE Project Office, Southampton

  • Warren BA (1973) Transpacific hydrographic sections at Lats. 43°S and 28°S: the SCORPIO Expedition-II. Deep water. Deep-Sea Res 20:9–38

    Google Scholar 

  • Whitworth T III, Warren BA, Nowlin WD Jr, Rutz SB, Pillsbury RD, Moore MI (1999) On the deep western-boundary current in the Southwest Pacific Basin. Prog Oceanogr 43:1–54

    Article  Google Scholar 

  • Wunsch C, Hu D, Grant B (1983) Mass, heat, salt and nutrient fluxes in the South Pacific Ocean. J Phys Oceanogr 13:725–753

    Article  Google Scholar 

Download references

Acknowledgments

The authors express their gratitude to Mr. K. Ishikawa, and the officers and crew of the R/V Ryofu-maru and R/V Keifu-maru, Japan Meteorological Agency, for their help in planning the mooring system and their onboard work of setting and recovering the system. The authors thank Dr. K. Hayashi for conducting the hydrographic survey prior to the moorings. The authors also thank the members of the Oceanographic Research Department, Meteorological Research Institute (MRI), for their helpful suggestions and discussion on data analyses. Finally the authors thank the reviewers for their critical and constructive comments and suggestions, which significantly improved this article. This study was funded by the ordinary budget of MRI.

Author information

Authors and Affiliations

  1. Department of Oceanographic Research, Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Japan

    Hiroshi Ishizaki, Toshiya Nakano, Hideyuki Nakano & Nobuyuki Shikama

  2. Global Environment and Marine Department, Japan Meteorological Agency, Tokyo, Japan

    Toshiya Nakano

Authors
  1. Hiroshi Ishizaki
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Toshiya Nakano
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Hideyuki Nakano
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Nobuyuki Shikama
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Hiroshi Ishizaki.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Ishizaki, H., Nakano, T., Nakano, H. et al. Direct measurements of deep current at 162°E south of the equator in the Melanesian Basin: a trial to detect a cross-equatorial deep western boundary current. J Oceanogr 68, 929–957 (2012). https://doi.org/10.1007/s10872-012-0145-5

Download citation

  • Received:

  • Revised:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1007/s10872-012-0145-5

Keywords

Search

Navigation