Mixing in the Samoan Passage has implications for the abyssal water properties of the entire North Pacific—nearly 20% of the global ocean’s volume. Dense bottom water formed near Antarctica encounters the passage—a gap in a ridge extending from north of Samoa eastward across the Pacific at around 10°S—and forms an energetic cascade much like a river flowing through a canyon. The 2011–2014 Samoan Passage Abyssal Mixing Experiment explored the importance of topography to the dense water flow on a wide range of scales, including (1) constraints on transport due to the overall passage shape and the heights of its multiple sills, (2) rapid changes in water properties along particular pathways at localized mixing hotspots where there is extreme topographic roughness and/or downslope flow acceleration, and (3) diversion and disturbance of flow pathways and density surfaces by small-scale seamounts and ridges. The net result is a complex but fairly steady picture of interconnected pathways with a limited number of intense mixing locations that determine the net water mass transformation. The implication of this set of circumstances is that the dominant features of Samoan Passage flow and mixing (and their responses to variations in incoming or background properties) can be described by the dynamics of a single layer of dense water flowing beneath a less-dense one, combined with mixing and transformation that is determined by the small-scale topography encountered along flow pathways.
Girton, J.B., J.B. Mickett, Z. Zhao, M.H. Alford, G. Voet, J.M. Cusack, G.S. Carter, K.A. Pearson-Potts, L.J. Pratt, S. Tan, and J.M. Klymak. 2019. Flow-topography interactions in the Samoan Passage. Oceanography 32(4):184–193, https://doi.org/10.5670/oceanog.2019.424.
Alford, M.H., J.B. Girton, G. Voet, G.S. Carter, J.B. Mickett, and J.M. Klymak. 2013. Turbulent mixing and hydraulic control of abyssal water in the Samoan Passage. Geophysical Research Letters 40:4,668–4,674, https://doi.org/10.1002/grl.50684.
Baines, P.G. 1995. Topographic Effects in Stratified Flows. Cambridge University Press.
Borenäs, K., and A. Nikolopoulos. 2000. Theoretical calculations based on real topography of the maximum deep-water flow through the Jungfern Passage. Journal of Marine Research 58:709–719, https://doi.org/10.1357/002224000321358864.
Carter, G.S., G. Voet, M.H. Alford, J.B. Girton, J.B. Mickett, J.M. Klymak, L.J. Pratt, K.A. Pearson-Potts, J.M. Cusack, and S. Tan. 2019. A spatial geography of abyssal turbulent mixing in the Samoan Passage. Oceanography 32(4):194–203, https://doi.org/10.5670/oceanog.2019.425.
Choboter, P.F., and G.E. Swaters. 2003. Two-layer models of abyssal equator-crossing flow. Journal of Physical Oceanography 33:1,401–1,415, https://doi.org/10.1175/1520-0485(2003)033<1401:TMOAEF>2.0.CO;2.
Cusack, J.M., G. Voet, M.H. Alford, J.B. Girton, G.S. Carter, L.J. Pratt, K. Pearson-Potts, and S. Tan. 2019. Persistent turbulence in the Samoan Passage. Journal of Physical Oceanography, https://doi.org/10.1175/JPO-D-19-0116.1.
Freeland, H. 2001. Observations of the flow of abyssal water through the Samoa Passage. Journal of Physical Oceanography 31:2,273–2,279, https://doi.org/10.1175/1520-0485(2001)031<2273:OOTFOA>2.0.CO;2.
Gaberšek, S., and D.R. Durran. 2004. Gap flows through idealized topography: Part I. Forcing by large-scale winds in the nonrotating limit. Journal of the Atmospheric Sciences 61:2,846–2,862, https://doi.org/10.1175/JAS-3340.1.
Gill, A.E. 1977. The hydraulics of rotating-channel flow. Journal of Fluid Mechanics 80:641–671, https://doi.org/10.1017/S0022112077002407.
Johnson, G., D. Rudnick, and B. Taft. 1994. Bottom water variability in the Samoa Passage. Journal of Marine Research 52:177–196, https://doi.org/10.1357/0022240943077118.
Killworth, P.D., and N.R. MacDonald. 1993. Maximal reduced-gravity flux in rotating hydraulics. Geophysical & Astrophysical Fluid Dynamics 70:31–40, https://doi.org/10.1080/03091929308203585.
Pearson-Potts, K.A. 2019. Deep Near-Inertial Waves in the Samoan Passage. Dissertation, University Hawai’i, Honolulu, HI, 140 pp.
Pratt, L.J., G. Voet, A. Pacini, S. Tan, M.H. Alford, G.S. Carter, J.B. Girton, and D. Menemenlis. 2019. Pacific abyssal transport and mixing: Through the Samoan Passage versus around the Manihiki Plateau. Journal of Physical Oceanography 49:1,577–1,592, https://doi.org/10.1175/JPO-D-18-0124.1.
Rabe, B., D.A. Smeed, G.F. Lane-Serff, and S.B. Dalziel. 2004. Rotating exchange flows through straits with multiple channels. Chapter 12 in International Conference: Towards a Balanced Methodology in European Hydraulic Research. Proceedings from Budapest, May 22–23, 2003.
Reid, J., and P. Lonsdale. 1974. On the flow of water through the Samoan Passage. Journal of Physical Oceanography 4:58–73, https://doi.org/10.1175/1520-0485(1974)004<0058:OTFOWT>2.0.CO;2.
Roemmich, D., S. Hautala, and D. Rudnick. 1996. Northward abyssal transport through the Samoan Passage and adjacent regions. Journal of Geophysical Research 101:14,039–14,055, https://doi.org/10.1029/96JC00797.
Rudnick, D. 1997. Direct velocity measurements in the Samoan Passage. Journal of Geophysical Research 102:3,293–3,302, https://doi.org/10.1029/96JC03286.
Thorpe, S.A., J. Malarkey, G. Voet, M.H. Alford, J.B. Girton, and G.S. Carter. 2018. Application of a model of internal hydraulic jumps. Journal of Fluid Mechanics 834:125–148, https://doi.org/10.1017/jfm.2017.646.
Voet, G., J.B. Girton, M.H. Alford, G.S. Carter, J.M. Klymak, and J.B. Mickett. 2015. Pathways, volume transport and mixing of abyssal water in the Samoan Passage. Journal of Physical Oceanography 45:562–588, https://doi.org/10.1175/JPO-D-14-0096.1.
Voet, G., M.H. Alford, J.B. Girton, G.S. Carter, J.B. Mickett, and J.M. Klymak. 2016. Warming and weakening of the abyssal flow through Samoan Passage. Journal of Physical Oceanography 46:2,389–2,401, https://doi.org/10.1175/JPO-D-16-0063.1.
Whitehead, J.A., A. Leetmaa, and R.A. Knox. 1974. Rotating hydraulics of strait and sill flows. Geophysical Fluid Dynamics 6:101–125, https://doi.org/10.1080/03091927409365790.
Whitehead, J.A. 1998. Topographic control of oceanic flows in deep passages and straits. Reviews of Geophysics 36:423–440, https://doi.org/10.1029/98RG01014.
Whitehead, J.A. 2003. Constant potential vorticity hydraulically controlled flow: Complexities from passage shape. Journal of Physical Oceanography 33:305–312, https://doi.org/10.1175/1520-0485(2003)033<0305:CPVHCF>2.0.CO;2.
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.