Holocene coastal dune fields used as indicators of net littoral transport: West Coast, USA Curt D. Peterson a, ⁎, Errol Stock b , Roger Hart c , David Percy a , Steve W. Hostetler d , Jeffrey R. Knott e a Portland State University, Portland, Oregon, 97207-0751, USA b Griffith University, Brisbane, Queensland, 4111, Australia c Oregon State University, Newport, Oregon, 97365, USA d U.S. Geological Survey, Oregon State University, Corvallis, Oregon, 97331, USA e California State University Fullerton, Fullerton, California, 93454, USA abstract article info Article history: Received 24 September 2008 Received in revised form 12 October 2009 Accepted 18 October 2009 Available online 25 October 2009 Keywords: Coastal dunes Littoral drift West Coast USA Paleoclimate model Shoreline angle Wind-Wave forcing Between Point Grenville, Washington, and Point Conception, California (1500 km distance) 21 dune fields record longshore transport in 20 littoral cells during the late Holocene. The direction of predominant littoral transport is established by relative positions of dune fields (north, central, or south) in 17 representative littoral cells. Dune field position is north of cell midpoints in northernmost Oregon and Washington, but is south of cell midpoints in southern Oregon and California. Downdrift sand trapping occurs at significant changes in shoreline angle and/or at bounding headlands that project at least 2.5 km seaward from the general coastal trend. Sand bypassing occurs around small headlands of less than 0.5 km in projection distance. A northward shift of the winter low-pressure center in the northeast Pacific Ocean is modeled from 11 ka to 0 ka. Nearshore current forcing in southern Oregon and northern California switched from northward in earliest Holocene time to southward in late Holocene time. The late Holocene (5–0 ka) is generally characterized by net northward littoral drift in northernmost Oregon and Washington and by net southward littoral drift in southernmost Oregon and California. A regional divergence of net transport direction in central Oregon, i.e. no net drift, is consistent with modeled wind and wave forcing at the present time (0 ka). © 2009 Elsevier B.V. All rights reserved. 1. Introduction The direction(s) of net littoral drift and resulting littoral sand tran- sport to beaches of the US West Coast are addressed in this paper by using the asymmetries of coastal dune field distributions in represen- tative littoral cells. The alongshore distributions of coastal dune fields are used to constrain long-term net transport in littoral cells from Washington, Oregon, and California, totaling about 1500 km in length (Fig. 1). Nearly 50 years ago Cooper (1958, 1967) mapped dune fields along the study area, but the dune field positions were not related to littoral sand sources, nearshore wave fields, or longshore currents. Several recent studies from other wave-dominated coastlines have used Holocene development of coastal dune fields to identify sources of littoral sediment supply and downdrift littoral transport in Brazil (Barbosa and Dominguez, 2004) and southern Africa (Bluck et al., 2007). The Holocene dune fields in the US West Coast study area (dated 7– 0 ka) generally formed during marine high-stand conditions (Orme, 1990; Weidemann, 1990; Jungner et al., 2001; Erlandson et al., 2005). In this study we investigate the use of late Holocene dune fields as proxies to establish net littoral transport of beach sand in the US West Coast. The positions of 21 dune fields in 20 littoral cells from Washington to California (Fig. 1) are presented to demonstrate the net transport direction in each littoral cell. The presence or absence of dune fields is used as a proxy for sand residence time on beaches (Psuty, 1988; Hesp, 1999). Sand residence time, and corresponding coastal dune sand accumulation, should increase where beach sand is trapped against downdrift changes in shoreline angle and/or bounding headlands. The relative positions of dune fields in the study area littoral cells are com- pared to paleo-wind and wave forcing modeled at 11, 6 and 0 ka (Patrick and Hostetler, 2004). A general agreement between dune field positions within littoral cells, and the predicted direction of winter wave attack supports the use of dune field development in establishing dominant directions of longshore transport in littoral cells in this study area. The topics raised here should have direct relevance to other coastlines with sandy beaches and onshore winds. 2. Origins of coastal dune fields and study area setting Shoreward movement of shelf sand by asymmetric wave transport occurred during the Holocene transgression on many coastlines that are characterized by broad continental shelves and high wave energy, such as in southeastern Australia (Thom et al., 1981) and south Africa Geomorphology 116 (2010) 115–134 ⁎ Corresponding author. Geology Dept. Portland State University, 1721 SW Broadway, Portland, Oregon, 97207-0751, USA. Tel.: +1 503 725 3375; fax: +1 503 725 3025. E-mail addresses: Petersonc@pdx.edu (C.D. Peterson), E.Stock@ens.gu.edu.au (E. Stock), roger_hart01@mac.com (R. Hart), percyd@pdx.edu (D. Percy), steve@coas.oregonstate.edu (S.W. Hostetler), jknott@Exchange.FULLERTON.EDU (J.R. Knott). 0169-555X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2009.10.013 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph