Quaternary morphology and paleoenvironmental records of carbonate islands

Abstract

Here I use a simple numerical model of reef profile evolution to show that the presentday morphology of carbonate islands has developed largely in response to late Pleistocene sea level oscillations in addition to variable vertical motion and reef accretion rates. In particular, large amplitude 'ice-house' sea-level variability resulted in long lagoonal depositional hiatuses, producing the morphology characteristic of modern-day barrier reefs. Reactivation of carbonate factories, transport of coarse reef material and rapid infilling of shallow water accommodation space since deglaciation makes these unique sites for reconstructing Holocene climate.Integration of new tropical cyclone reconstructions from both backbarrier reef (central Pacific) and carbonate bank (the Bahamas) settings with existing storm archives suggests a coordinated pattern of cyclone activity across storm basins since the late Holocene. Seesawing of intense tropical cyclone activity between the western Pacific (~0-1000 yrs BP) and North Atlantic/Central Pacific (~1000-2500 yrs BP) appears closely tied with hydrographic patterns in the tropical Pacific and El Niño-like variability. Decoupling of North Atlantic (inactive) and South Pacific (active) tropical cyclone patterns during the mid-Holocene suggests precession driven changes in storm season insolation may constrain ocean-atmosphere thermal gradients and therefore cyclone potential intensity on orbital timescales. In particular, analysis of instrumental records (e.g. Gray, 1984;Revell and Goulter, 1986) and existing reconstructions (e.g. Woodruff et al., 2009) Reproduced with permission from GSA. 13GEOLOGY | July 2013 | www.gsapubs.org 1 INTRODUCTIONCoral reefs dynamically adapt to vertical motion (uplift or subsidence), erosion, antecedent topography, and changing sea level, developing a variety of profi le forms ( Many previous studies have introduced numerical models of reef profi le development (Bosence and Waltham, 1990;Bosscher and Schlager, 1992; Chappell, 1980; Hill et al., 2009; Koelling et al., 2009; Paterson et al., 2006;Paulay and McEdward, 1990; Warrlich et al., 2002;Webster et al., 2007). In general, these models have related reef morphology at specifi c sites to rates of island subsidence, reef accretion, and sea-level rise, but do not satisfactorily explain the wide range of morphologic variability observed in modern reefs.Here we address the broad-scale controls on island reef form. First, we discuss the growth and stability of reefs as they experience island vertical motion and sea-level change. Second, we implement a profi le model of long-term reef development, systematically exploring reef evolution for a wide variety of vertical motion rates, reef accretion rates, and sea-level histories over glacial sea-level cycles. Finally, we compare the gross morphology of reef profi le forms generated by the model with those of natural reefs with known vertical motion and accretion rates. CORAL GROWTH AND SEA LEVELThe primary control on the development of coral r...