The Republic of Palau, a group of islands in the western tropical Pacific Ocean, is located between the westward-​flowing North Equatorial Current (NEC) to the north and the eastward-flowing North Equatorial Countercurrent (NECC) to the south, and the Mindanao Eddy (ME) lies to the west. This unique geographical location may make Palau an oceanographically sensitive region due to strong equatorial zonal flows encountering steep island topography. We investigate the effect Palau has on the regional ocean circulation through numerical model simulations with identical forcing but differing bathymetry: one with Palau and the other without it. The simulations use realistic initial conditions—monthly climatological atmospheric forcing, open-ocean boundary conditions, and runoff fluxes—and were run for up to 37 years to distinguish between model intrinsic variability and deterministic differences. The significant differences between the two solutions show that Palau’s effect on circulation is localized and small. The model state differences, quantified as percentage of model variability near Palau from the 37-year solution, are about 20% for sea surface height, 25% for surface velocities, and <1% for surface temperature and salinity. The subsurface velocity fields around Palau show a two-layered flow, as previously reported by other authors, with upper layer flow from the surface to 300 m, and a lower layer flow from 300 m to 3,000 m. The topographic form stress on Palau is <10% of the vertically integrated total form stress in the 5°N–10°N latitudinal band, and when the island is removed from model simulations, the stress is redistributed within the region. Although these results are restricted to model resolution scales and physics, they provide an estimate of the influence of Palau on the large-scale northwestern tropical Pacific Ocean circulation.

Gopalakrishnan, G., and B.D. Cornuelle. 2019. Palau’s effects on regional-scale ocean circulation. Oceanography 32(4):126–135, https://doi.org/10.5670/oceanog.2019.418.

Chassignet, E., H. Hurlburt, O. Smedstad, G. Halliwell, P. Hogan, A. Wallcraft, R. Baraille, and R. Bleck. 2007. The HYCOM (HYbrid Coordinate Ocean Model) data assimilative system. Journal of Marine Systems 65(1–4):60–83, https://doi.org/10.1016/​j.jmarsys.2005.09.016.

Cummings, J.A. 2005. Operational multivariate ocean data assimilation. Quarterly Journal of the Royal Meteorological Society 131(613):3,583–3,604, https://doi.org/10.1256/qj.05.105.

Dee, D.P., S.M. Uppala, A.J. Simmons, P. Berrisford, P. Poli, S. Kobayshi, U. Andrae, M.A. Balmaseda, G. Balsamo, P. Bauer, and others. 2011. The ERA-Interim reanalysis: Configuration and performance of the data assimilation system. Quarterly Journal of the Royal Meteorological Society 137(656):553–597, https://doi.org/10.1002/qj.828.

Ducet, N., P.-Y. Le Traon, and G. Reverdin. 2000. Global high-resolution mapping of ocean circulation from TOPEX/Poseidon and ERS-1 and -2. Journal of Geophysical Research 105(C8):19,477–19,498, https://doi.org/​10.1029/2000JC900063.

Edwards, C., T. Fake, and P. Bogden. 2004a. Spring-summer frontogenesis at the mouth of Block Island Sound: Part 1. A numerical investigation into tidal and buoyancy-forced motion. Journal of Geophysical Research 109(C12), https://doi.org/​10.1029/2003JC002132.

Edwards, C., T. Fake, D. Codiga, and P. Bogden. 2004b. Spring-summer frontogenesis at the mouth of Block Island Sound: Part 2. Combining acoustic Doppler current profiler records with a general circulation model to investigate the impact of subtidal forcing. Journal of Geophysical Research 109(C12), https://doi.org/10.1029/2003JC002133.

Fekete, B.M., C.J. Vörösmarty, and W. Grabs. 2002. High-resolution fields of global runoff combining observed river discharge and simulated water balances. Global Biogeochemical Cycles 16(3):15-1–15-10, https://doi.org/​10.1029/​1999GB001254.

Fukumori, I., T. Lee, B. Cheng, and D. Menemenlis. 2004. The origin, pathway, and destination of Niño-3 water estimated by a simulated passive tracer and its adjoint. Journal of Physical Oceanography 34:582–604, https://doi.org/​10.1175/2515.1.

Godfrey, J. 1989. A Sverdrup model of the depth-​integrated flow for the world ocean allowing for island circulations. Geophysical & Astrophysical Fluid Dynamics 45(1–2):89–112, https://doi.org/​10.1080/03091928908208894.

Gopalakrishnan, G., B.D. Cornuelle, and I. Hoteit. 2013a. Adjoint sensitivity studies of loop current and eddy shedding in the Gulf of Mexico. Journal of Geophysical Research 118(7):3,315–3,335, https://doi.org/10.1002/jgrc.20240.

Gopalakrishnan, G., B.D. Cornuelle, I. Hoteit, D.L. Rudnick, and W.B. Owens. 2013b. State estimates and forecasts of the Loop Current in the Gulf of Mexico using the MITgcm and its adjoint. Journal of Geophysical Research 118(7):3,292–3,314, https://doi.org/10.1002/jgrc.20239.

Gopalakrishnan, G., B.D. Cornuelle, G. Gawarkiewicz, and J.L. McClean. 2013c. Structure and evolution of the cold dome off northeastern Taiwan: A numerical study. Oceanography 26(1):66–79, https://doi.org/​10.5670/oceanog.2013.06.

Hoteit, I., B. Cornuelle, S.Y. Kim, G. Forget, A. Kohl, and E. Terrill. 2009. Assessing 4D-VAR for dynamical mapping of coastal high-frequency radar in San Diego. Dynamics of Atmospheres and Oceans 48(1–3):175–197, https://doi.org/10.1016/​j.dynatmoce.2008.11.005.

Hoteit, I., B. Cornuelle, and P. Heimbach. 2010. An eddy-permitting, dynamically consistent adjoint-based assimilation system for the tropical Pacific: Hindcast experiments in 2000. Journal of Geophysical Research 115(C3), https://doi.org/​10.1029/2009JC005437.

Karnauskas, K.B., R. Murtugudde, and A.J. Busalacchi. 2007. The effect of the Galápagos Islands on the equatorial Pacific cold tongue. Journal of Physical Oceanography 37(5):1,266–1,281, https://doi.org/​10.1175/JPO3048.1.

Kashino, Y., A. Ishida, and S. Hosoda. 2011. Observed ocean variability in the Mindanao Dome region. Journal of Physical Oceanography 41(2):287–302, https://doi.org/10.1175/2010JPO4329.1.

Kashino, Y., A. Atmadipoera, and Y. Kuroda. 2013. Observed features of the Halmahera and Mindanao eddies. Journal of Geophysical Research 118(12):6,543–6,560, https://doi.org/​10.1002/2013JC009207.

Kim, S.Y., G. Gopalakrishnan, and A. Ponte. 2015. Interpretation of coastal wind transfer functions with momentum balances derived from idealized numerical model simulations. Ocean Dynamics 65(1):115–141, https://doi.org/10.1007/s10236-014-0766-x.

Kohl, A., D. Stammer, and B. Cornuelle. 2007. Interannual to decadal changes in the ECCO global synthesis. Journal of Physical Oceanography 37(2):313–337, https://doi.org/​10.1175/JPO3014.1.

Large, W., and S. Pond. 1981. Open ocean momentum flux measurements in moderate to strong winds. Journal of Physical Oceanography 11(3):324–336, https://doi.org/10.1175/1520-0485(1981)011​<0324:​OOMFMI>2.0.CO;2.

Large, W.G., J.C. McWilliams, and S.C. Doney. 1994. Oceanic vertical mixing: A review and a model with a nonlocal boundary layer parameterization. Reviews of Geophysics 32(4):363–403, https://doi.org/​10.1029/94RG01872.

Legg, S., R. Hallberg, and J. Girton. 2006. Comparison of entrainment in overflows simulated by z-coordinate, isopycnal and non-hydrostatic models. Ocean Modelling 11:69–97, https://doi.org/​10.1016/​j.ocemod.2004.11.006.

Lien, R.-C., B. Ma, C.M. Lee, T.B. Sanford, V. Mensah, L.R. Centurioni, B.D. Cornuelle, G. Gopalakrishnan, A.L. Gordon, M.-H. Chang, and others. 2015. The Kuroshio and Luzon Undercurrent east of Luzon Island. Oceanography 28(4):54–63, https://doi.org/​10.5670/oceanog.2015.81.

Marshall, J., A. Adcroft, C. Hill, L. Perelman, and C. Heisey. 1997. A finite-volume, incompressible Navier Stokes model for studies of the ocean on parallel computers. Journal of Geophysical Research 102(C3):5,753–5,766, https://doi.org/​10.1029/96JC02775.

Masich, J., T.K. Chereskin, and M.R. Mazloff. 2015. Topographic form stress in the Southern Ocean state estimate. Journal of Geophysical Research 120(12):7,919–7,933, https://doi.org/​10.1002/2015JC011143.

Masumoto, Y., and T. Yamagata. 1991. Response of the western tropical Pacific to the Asian winter monsoon: The generation of the Mindanao Dome. Journal of Physical Oceanography 21(9):1,386–1,398, https://doi.org/​10.1175/​1520-​0485​(1991)​021​<1386:​ROTWTP>​2.0.CO;2.

Mazloff, M., P. Heimbach, and C. Wunsch. 2010. An eddy-permitting Southern Ocean state estimate. Journal of Physical Oceanography 40:880–899, https://doi.org/10.1175/2009JPO4236.1.

Menemenlis, D., I. Fukumori, and T. Lee. 2005. Using Green’s functions to calibrate an ocean general circulation model. Monthly Weather Review 133(5):1,224–1,240, https://doi.org/10.1175/MWR2912.1.

Munk, W.H., and E. Palmén.1951. Note on the dynamics of the Antarctic Circumpolar Current. Tellus 3(1):53–55, https://doi.org/10.3402/tellusa.v3i1.8609.

Musgrave, R., and T. Peacock. 2016. The momentum balance of steady flow past an island. Paper presented at the VIII^th International Symposium on Stratified Flows, August 29–September 1, 2016, San Diego, California.

Nitani, H. 1972. Beginning of the Kuroshio. Pp. 129–163 in Kuroshio, its Physical Aspects. H. Stommel and K. Yoshida, eds, University of Tokyo Press.

Qiu, B. 1999. Seasonal eddy field modulation of the North Pacific Subtropical Countercurrent: TOPEX/Poseidon observations and theory. Journal of Physical Oceanography 29(10):2,471–2,486, https://doi.org/10.1175/1520-0485(1999)029​<2471:SEFMOT>2.0.CO;2.

Qiu, B., and S. Chen. 2010. Interannual variability of the North Pacific Subtropical Countercurrent and its associated mesoscale eddy field. Journal of Physical Oceanography 40(1):213–225, https://doi.org/​10.1175/2009JPO4285.1.

Qiu, B., D.L. Rudnick, S. Chen, and Y. Kashino. 2013. Quasi-stationary North Equatorial Undercurrent jets across the tropical North Pacific Ocean. Geophysical Research Letters 40(10):2,183–2,187, https://doi.org/10.1002/grl.50394.

Qiu, B., D.L. Rudnick, I. Cerovecki, B.D. Cornuelle, S. Chen, M.C. Schönau, J.L. McClean, and G. Gopalakrishnan. 2015. The Pacific North Equatorial Current: New insights from the Origins of the Kuroshio and Mindanao Currents (OKMC) Project. Oceanography 28:24–33, https://doi.org/​10.5670/oceanog.2015.78.

Qu, T., H. Mitsudera, and T. Yamagata. 1998. On the western boundary currents in the Philippine Sea. Journal of Geophysical Research 103(C4):7,537–7,548, https://doi.org/​10.1029/98JC00263.

Qu, T., and R. Lukas. 2003. The bifurcation of the North Equatorial Current in the Pacific. Journal of Physical Oceanography 33(1):5–18, https://doi.org/10.1175/1520-0485(2003)033​<0005:TBOTNE>2.0.CO;2.

Sarkisyan, A., and V. Ivanov. 1971. The combined effect of baroclinicity and bottom relief as an important factor in the dynamics of ocean currents. (AGU translation) Izvestiya, Academy of Sciences, USSR, Atmospheric and Oceanic Physics 2:173–188.

Schönau, M.C., D.L. Rudnick, I. Cerovecki, G. Gopalakrishnan, B.D. Cornuelle, J.L. McClean, and B. Qiu. 2015. The Mindanao Current: Mean structure and connectivity. Oceanography 28(4):34–45, https://doi.org/​10.5670/oceanog.2015.79.

Schönau, M.C., and D.L. Rudnick. 2017. Mindanao Current and Undercurrent: Thermohaline structure and transport from repeat glider observations. Journal of Physical Oceanography 47(8):2,055–2,075, https://doi.org/10.1175/JPO-D-16-0274.1.

Schönau, M.C., H.W. Wijesekera, W.J. Teague, P.L. Colin, G. Gopalakrishnan, D.L. Rudnick, B.D. Cornuelle, Z.R. Hallock, and D.W. Wang. 2019. The end of an El Niño: A view from Palau. Oceanography 32(4):32–45, https://doi.org/​10.5670/oceanog.2019.409.

Schramek, T.A., B.D. Cornuelle, G. Gopalakrishnan, P.L. Colin, S.J. Rowley, M.A. Merrifield, and E.J. Terrill. 2019. Tropical western Pacific thermal structure and its relationship to ocean surface variables: A numerical state estimate and forereef temperature records. Oceanography 32(4):156–163, https://doi.org/10.5670/oceanog.2019.421.

Stammer, D., C. Wunsch, R. Giering, C. Eckert, P. Heimbach, J. Marotzke, A. Adcroft, C. Hill, and J. Marshall. 2002. Global ocean circulation during 1992–1997, estimated from ocean observations and a general circulation model. Journal of Geophysical Research 107(C9), 1-1–1-27, https://doi.org/​10.1029/​2001JC000888.

Wajsowicz, R.C. 1993. The circulation of the depth-​integrated flow around an island with application to the Indonesian throughflow. Journal of Physical Oceanography 23(7):1,470–1,484, https://doi.org/10.1175/1520-0485(1993)023​<1470:TCOTDI>2.0.CO;2.

Wang, J., M.R. Mazloff, and S.T. Gille. 2016. The effect of the Kerguelen Plateau on the ocean circulation. Journal of Physical Oceanography 46(11):3,385–3,396, https://doi.org/10.1175/JPO-D-15-0216.1.

Zhang, X., B. Cornuelle, and D. Roemmich. 2012. Sensitivity of western boundary transport at the mean North Equatorial Current bifurcation latitude to wind forcing. Journal of Physical Oceanography 42:2,056–2,072, https://doi.org/​10.1175/JPO-D-11-0229.1.

This is an open access article made available under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format as long as users cite the materials appropriately, provide a link to the Creative Commons license, and indicate the changes that were made to the original content. Images, animations, videos, or other third-party material used in articles are included in the Creative Commons license unless indicated otherwise in a credit line to the material. If the material is not included in the article’s Creative Commons license, users will need to obtain permission directly from the license holder to reproduce the material.