Shifting to renewable energy is an important global challenge, and there are many technologies available to help reduce carbon dioxide emissions. Seawater air conditioning (SWAC) is a renewable ocean thermal energy technology that will soon be implemented in Honolulu, Hawaii, on the island of Oahu. The SWAC system will operate by using cool water from 500 m depth in a heat exchange system and then will release this nutrient-rich water back into the ocean at a shallower depth of 100–140 m. The introduction of a plume of warmed (but still relatively cool) deep seawater has unknown impacts on the tropical marine environment. Possible impacts include increases in primary production, changes in water chemistry and turbidity, and changes in the local food web. We used moored instruments and shipboard profiling to describe oceanographic parameters at the future SWAC effluent site. Parameters varied with the M2 internal tide, and denser water was correlated with higher nitrate, lower oxygen, and lower chlorophyll a (correlation coefficients 0.55, –0.58, and –0.75, respectively). The nitrate concentrations in the plume will be >30.0 µmol kg–1, while ambient concentrations range from <2.0–9.8 µmol kg–1. Irradiance levels at the effluent depth are sufficient to support net photosynthesis, and the effluent’s location in the pycnocline could lead to rapid horizontal advection of the plume and expansion of the spatial scale of impacts. These baseline data provide an understanding of pre-impact conditions at the future SWAC site and will enable a more accurate environmental assessment. A comprehensive and well-resolved environmental monitoring effort during SWAC operation will be necessary to quantify and understand these impacts.

Comfort, C.M., M.A. McManus, S.J. Clark, D.M. Karl, and C.E. Ostrander. 2015. Environmental properties of coastal waters in Mamala Bay, Oahu, Hawaii, at the future site of a seawater air conditioning outfall. Oceanography 28(2):230–239, https://doi.org/10.5670/oceanog.2015.46.

» Detailed Methodology (92 KB pdf)
Specifics of moored and profiling instruments and programming.

Alford, M.H., M.C. Gregg, and M.A. Merrifield. 2006. Structure, propagation, and mixing of energetic baroclinic tides in Mamala Bay, Oahu, Hawaii. Journal of Physical Oceanography 36:997–1,018, https://doi.org/10.1175/JPO2877.1.

Arent, D.J., A. Wise, and R. Gelman. 2011. The status and prospects of renewable energy for combating global warming. Energy Economics 33:584–593, https://doi.org/10.1016/j.eneco.2010.11.003.

Baines, P.G. 2001. Mixing in flows down gentle slopes into stratified environments. Journal of Fluid Mechanics 443:237–270, https://doi.org/10.1017/S0022112001005250.

Boehlert, G.W., and A.B. Gill. 2010. Environmental and ecological effects of ocean renewable energy development: A current synthesis. Oceanography 23(2):68–81, https://doi.org/10.5670/oceanog.2010.46.

Brillinger, D.R. 2002. John W. Tukey’s work on time series and spectrum analysis. Annals of Statistics 30:1,595–1,618, https://doi.org/10.1214/aos/1043351248.

Bogucki, D., T. Dickey, and L.G. Redekopp. 1997. Sediment resuspension and mixing by resonantly generated internal solitary waves. Journal of Physical Oceanography 27:1,181–1,196, https://doi.org/10.1175/1520-0485(1997)027<1181:SRAMBR>2.0.CO;2.

Bondur, V.G., N.N. Filatov, Y.V. Grebenyuk, Y.S. Dolotov, R.E. Zdorovennov, M.P. Petrov, and M.N. Tsidilina. 2007. Studies of hydrophysical processes during monitoring of the anthropogenic impact on coastal basins using the example of Mamala Bay of Oahu Island in Hawaii. Oceanology 47:769–787, https://doi.org/10.1134/S0001437007060033.

Comfort, C.M., and L. Vega. 2011. Environmental assessment for ocean thermal energy conversion in Hawaii: Available data and a protocol for baseline monitoring. In Proceedings of the Oceans’11 MTS/IEEE Kona Conference, September 19–22, 2011. Institute of Electrical and Electronics Engineers, Piscataway, NJ, 8 pp.

Cooley, J.W., and J.W. Tukey. 1965. An algorithm for the machine calculation of complex Fourier series. Mathematics of Computation 19:297–301, https://doi.org/10.1090/S0025-5718-1965-0178586-1.

Dale, A.C., M.D. Levine, J.A. Barth, and J.A. Austin. 2006. A dye tracer reveals cross-shelf dispersion and interleaving on the Oregon shelf. Geophysical Research Letters 33, L03604, https://doi.org/10.1029/2005GL024959.

Eich, M.L., M.A. Merrifield, and M.H. Alford. 2004. Structure and variability of semidiurnal internal tides in Mamala Bay, Hawaii. Journal of Geophysical Research 109, C05010, https://doi.org/10.1029/2003JC002049.

Freeman, W. 1993. Revised Total Maximum Daily Load Estimates for Six Water Quality Limited Segments, Island of Oahu, Hawaii. Report prepared for the State of Hawaii Department of Health Environmental Planning Office, Honolulu, HI.

Gill, A.B. 2005. Offshore renewable energy: Ecological implications of generating electricity in the coastal zone. Journal of Applied Ecology 42:605–615, https://doi.org/10.1111/j.1365-2664.2005.01060.x.

Harrison, J. 1987. The 40 MWe OTEC Plant at Kahe Point, Oahu, Hawaii: A Case Study of Potential Biological Impacts. National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southwest Fisheries Center, Honolulu, HI, NOAA-TM-MNFS-SWFC-68, 105 pp., http://www.pifsc.noaa.gov/tech/NOAA_Tech_Memo_068.pdf.

Hayward, T.L. 1987. The nutrient distribution and primary production in the central North Pacific. Deep Sea Research Part A 34(9):1,593–1,627, https://doi.org/10.1016/0198-0149(87)90111-7.

Honolulu SWAC (Seawater Air Conditioning), LLC. 2014. Final Environmental Impact Statement for the Proposed Honolulu Seawater Air Conditioning Project, Honolulu, Hawai’i. Prepared by Cardno TEC, Inc., United States Army Corps of Engineers, Honolulu, HI, 834 pp.

Inall, M.E. 2009. Internal wave induced dispersion and mixing on a sloping boundary. Geophysical Research Letters 36, L05604, https://doi.org/10.1029/2008GL036849.

Ivanov, V.V., G.I. Shapiro, J.M. Huthnance, D.L. Aleynik, and P.N. Golovin. 2004. Cascades of dense water around the world ocean. Progress in Oceanography 60:47–98, https://doi.org/10.1016/j.pocean.2003.12.002.

Karl, D.M. 2014. The contemporary challenge of the sea: Science, society, and sustainability. Oceanography 27(2):208–225, https://doi.org/10.5670/oceanog.2014.57.

Karl, D.M., K.M. Björkman, J.E. Dore, L. Fujieki, D.V. Hebel, T. Houlihan, R.M. Letelier, and L.M. Tupas. 2001. Ecological nitrogen-to-phosphorus stoichiometry at station ALOHA. Deep Sea Research Part II 48:1,529–1,566, https://doi.org/10.1016/S0967-0645(00)00152-1.

Kirk, J.T.O. 1994. Light and Photosynthesis in Aquatic Ecosystems, 2nd ed. Cambridge University Press, New York, NY, 509 pp.

Laws, E.A., R.M. Letelier, and D.M. Karl. 2014. Estimating the compensation irradiance in the ocean: The importance of accounting for non-photosynthetic uptake of inorganic carbon. Deep Sea Research Part I 93:35–40, https://doi.org/10.1016/j.dsr.2014.07.011.

Laws, E.A., D. Ziemann, and D. Schulman. 1999. Coastal water quality in Hawaii: The importance of buffer zones and dilution. Marine Environmental Research 48:1–21, https://doi.org/10.1016/S0141-1136(99)00029-X.

Leichter, J.J., H.L. Stewart, and S.L. Miller. 2003. Episodic nutrient transport to Florida coral reefs. Limnology and Oceanography 48:1,394–1,407, https://doi.org/10.4319/lo.2003.48.4.1394.

Levitus, S. 1982. Climatological Atlas of the World Ocean. National Oceanic and Atmospheric Association Professional Paper 13. US Government Printing Office, Washington, DC, 173 pp.

Lilley, J., D. Konan, D. Lerner, and D. Karl. 2012. Potential Benefits, Impacts, and Public Opinion of Seawater Air Conditioning in Waikiki. Center for Sustainable Coastal Tourism. Honolulu, HI, 9 pp.

Martini, K.I., M.H. Alford, J.D. Nash, E. Kunze, and M.A. Merrifield. 2007. Diagnosing a partly standing internal wave in Mamala Bay, Oahu. Geophysical Research Letters 34, L17604, https://doi.org/10.1029/2007GL029749.

McManus, M.A., K.J. Benoit-Bird, and C.B. Woodson. 2008. Behavior exceeds physical forcing in the diel horizontal migration of a midwater sound-scattering layer in Hawaiian waters. Marine Ecology Progress Series 365:91–101, https://doi.org/10.3354/meps07491.

McPhee-Shaw, E. 2006. Boundary–interior exchange: Reviewing the idea that internal-wave mixing enhances lateral dispersal near continental margins. Deep Sea Research Part II 53:42–59, https://doi.org/10.1016/j.dsr2.2005.10.018.

Merrifield, M.A., P.E. Holloway, and T.M. Johnston. 2001. The generation of internal tides at the Hawaiian Ridge. Geophysical Research Letters 28:559–562, https://doi.org/10.1029/2000GL011749.

Myers, E.P., D. Hoss, W. Matsumoto, D. Peters, M. Seki, R. Uchida, J. Ditmars, and R. Paddock. 1986. The Potential Impact of Ocean Thermal Energy Conversion (OTEC) on Fisheries. NOAA Technical Report NMFS 40, US Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Washington, DC, 39 pp., http://spo.nwr.noaa.gov/tr40opt.pdf.

Nash, J.D., E. Kunze, C. Lee, and T. Sanford. 2006. Structure of the baroclinic tide generated at Kaena Ridge, Hawaii. Journal of Physical Oceanography 36:1,123–1,135, https://doi.org/10.1175/JPO2883.1.

NOAA (National Oceanic and Atmospheric Administration). 1981. Ocean Thermal Energy Conversion Cinal Environmental Impact Statement. United States Department of Commerce, National Oceanic and Atmospheric Administration, Office of Ocean Minerals and Energy, Charleston, SC, 284 pp., http://coastalmanagement.noaa.gov/programs/media/otec1981feis.pdf.

NOAA. 2010. Ocean Thermal Energy Conversion: Assessing Potential Physical, Chemical, and Biological Impacts and Risks. Prepared by Coastal Response Research Center, University of New Hampshire, Durham, NH, 39 pp., http://coast.noaa.gov/czm/media/otecjun10wkshp.pdf.

Pelc, R., and R. Fujita. 2002. Renewable energy from the ocean. Marine Policy 26:471–479, https://doi.org/10.1016/S0308-597X(02)00045-3.

Petrenko, A.A., B.H. Jones, and T.D. Dickey. 1998. Shape and initial dilution of Sand Island, Hawaii sewage plume. Journal of Hydraulic Engineering 124:565–571, https://doi.org/10.1061/(ASCE)0733-9429(1998)124:6(565).

Petrenko, A.A., B.H. Jones, T.D. Dickey, and P. Hamilton. 2000. Internal tide effects on a sewage plume at Sand Island, Hawaii. Continental Shelf Research 20:1–13, https://doi.org/10.1016/S0278-4343(99)00060-6.

Petrenko, A.A., B.A. Jones, T.D. Dickey, M. LeHaitre, and C. Moore. 1997. Effects of a sewage plume on the biology, optical characteristics, and particle size distributions of coastal waters. Journal of Geophysical Research 102(C11):25,061–25,071, https://doi.org/10.1029/97JC02082.

Sevadjian, J.C. 2008. The effects of physical structure and processes on thin zooplankton layers in Mamala Bay, Hawaii. MS thesis, University of Hawaii at Manoa, HI.

Sevadjian, J.C., M.A. McManus, K.J. Benoit-Bird, and K.E. Selph. 2012. Shoreward advection of phytoplankton and vertical re-distribution of zooplankton by episodic near-bottom water pulses on an insular shelf: Oahu, Hawaii. Continental Shelf Research 50:1–15, https://doi.org/10.1016/j.csr.2012.09.006.

Sevadjian, J.C., M.A. McManus, and G. Pawlak. 2010. Effects of physical structure and processes on thin zooplankton layers in Mamala Bay, Hawaii. Marine Ecology Progress Series 409:95–106, https://doi.org/10.3354/meps08614.

Shastna, M., and W.R. Peltier. 2005. On the resonant generation of large-amplitude internal solitary and solitary-like waves. Journal of Fluid Mechanics 543:267–292, https://doi.org/10.1017/S002211200500652X.

Stevenson, M., J. O’Connor, and J. Aldrich. 1996. Mamala Bay Study: Pollutant Source Identification. Mamala Bay Study Commission, Pacific Islands Ocean Observing System, MB-3, Honolulu, HI, 83 pp.

War, J.C. 2011. Seawater Air Conditioning (SWAC): A renewable energy alternative. In Proceedings of the Oceans’11 MTS/IEEE Kona Conference, September 19–22, 2011. Institute of Electrical and Electronics Engineers, Piscataway, NJ, 9 pp.

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.