Terrence A. McCloskey

A 7000 year record of paleohurricane activity from a coastal wetland in Belize

Sedimentary paleotempestological studies have documented that tropical cyclone activity levels in the North Atlantic have been characterized by significant fluctuations since at least the mid Holocene, with activity regimes typically lasting from several centuries to > 2000 years. These activity-level estimates are based on site-specific hurricane strike histories derived from proxy records of overwash events attributed to landfalling major hurricanes. Here we present a 7000 year composite record from two adjacent wetland sites in coastal Belize, Central America that records both tropical cyclone-generated storm surges and large precipitation events. Although overall sensitivity appears to decrease over time, this record displays clear evidence of continuous oscillation between distinctly different activity regimes, with active and quiet periods each covering ~ 50% of the record. Active periods occur during ~200–600 BP, 1450–2600 BP, 3200–4200 BP, 4750–5450 BP, 5750–6050 BP, and 6700–6900 BP. This activity pattern does not match regional records from the northern Gulf of Mexico, the northern Caribbean or the Atlantic coast of the USA, thereby supporting the view that activity patterns are temporally variable throughout the North Atlantic, and that hyperactivity does not occur simultaneously across the entire basin.

Sedimentary History of Mangrove Cays in Turneffe Islands, Belize: Evidence for Sudden Environmental Reversals

ABSTRACT McCloskey, T.A. and Liu, K.-B., 2013. Sedimentary history of mangrove cays in Turneffe Islands, Belize: evidence for sudden environmental reversals. The Holocene history of the continental margin of Belize has frequently been interpreted as being very straightforward, controlled almost entirely by postglacial sea level rise. Depending upon location, the dominant depositional environment, whether coral or mangrove, is either able to keep up with the rising sea level and thereby maintain its integrity through the present, or becomes drowned. Here we present sedimentary evidence from four mangrove cays situated on Turneffe Islands that shows an unusual pattern wherein early mangrove development is replaced by carbonate sedimentation before reverting back to mangroves in the relatively recent past. The bracketed carbonate layers, up to >2 m thick and resembling lagoon-floor material, display both a rough temporal coincidence across sites and a distinctive geographic signature, thinning landward irrespective of relative elevation. The carbonate sections are often underlain by a mixed sediment layer characterized by a jumble of stratigraphically incoherent mangrove clumps intermingled with carbonates. The replacement of mangrove peat with bottom-style carbonate deposition suggests a lowering of island surface elevation. Seismic activity is identified as the most likely cause, although hurricanes cannot be excluded. In either case the elevational reduction is probably amplified by peat collapse associated with mangrove mortality. The occurrence of such activity and the resulting catastrophic ecological/geomorphic change indicate a need for incorporating these geological perturbations in risk assessment for Turneffe Islands.

Migration of the Tropical Cyclone Zone throughout the Holocene

This paper proposes that a combination of short and long term atmospheric oscillations have resulted in latitudinal movement of the tropical cyclone (TC) zone and location of landfall through the Holocene. A GIS-based approach demonstrates that currently intensity changes of the Bermuda High (BH) result in a large latitudinal spread of TC track and landfall location across the western North Atlantic (NA), while a literature-based examination of paleoclimatic evidence supports the view that long-term changes in the pole-equator temperature gradient has resulted in significant latitudinal migration of the general NA atmospheric system throughout the Holocene, with a heightened (reduced) gradient moving the entire system southward (northward). Our model suggests that the location of hurricane landfall since the mid Holocene is controlled by a millennial scale migration of the hurricane zone (paralleling latitudinal movement of the entire system), complicated by the superimposition of a higher frequency variation in track location, (controlled by intensity oscillations). The resulting millennial scale shifts in landfall location of major hurricanes are hindcast, and methods for testing this hypothesis are described.

Storm deposition induced by hurricanes in a rapidly subsiding coastal zone

ABSTRACT Naquin, J.D., Liu, K.B., McCloskey, T.A., Bianchette, T.A., 2014. Storm Deposition Induced by Hurricanes in a Subsiding Coastal Zone. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium(Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 308–313, ISSN 0749-0208. To understand the geological processes induced by tropical cyclones, geochemical and sedimentological analyses were performed on a 3 m sediment core (basal 14C date of 940 +/− 50 years BP) extracted from a marsh adjacent to a backbarrier lake along Louisianas Gulf of Mexico coast (USA). This study was conducted in order to identify the geologic changes within a subsiding coastal region in the light of coastal recession and past hurricane activity. Previous studies show that Bay Champagne, a semi-circular lake near Port Fourchon, Louisiana, is subjected to subsidence rates between 1.0 and 1.2 cm year−1, the highest rate of retreat within the entire northern Gulf of Mexico. Loss-on-ignition (LOI) and X-ray fluorescence (XRF) analyses, employed to generate lithological and geochemical core profiles, identified three distinct sand layers measuring up to 50 cm in thickness deposited by recent hurricanes. LOI shows large decreases in water, organic, and carbonate contents, indicating the occurrence of marine inundation. Within each marine incursion layer terrestrial elemental concentrations as determined by XRF display large depletions. Grain size analysis of a portion of the core (30–86 cm) indicates the presence of two series of sequential high-energy storm deposits followed by intense fluvial flooding within Bay Champagne. These events are attributed to Hurricanes Katrina/Rita in 2005 and Gustav/Ike in 2008

Hurricane Isaac storm surge deposition in a coastal wetland along Lake Pontchartrain, southern Louisiana

ABSTRACT Liu, K.., McCloskey, T.A., Bianchette, T.A., Keller, G., Lam, N.S.N., Cable, J.E., Arriola, J. 2014. Hurricane Isaac Storm Surge Deposition in a Coastal Wetland along Lake Pontchartrain, Southern Louisiana. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 266–271, ISSN 0749-0208. Hurricanes play an important role in shaping the coast of Louisiana. Although the sedimentary signatures of hurricane deposits have been documented in several different coastal environments along the northern Gulf coast, no studies have as yet documented the signatures in wetlands adjacent to large, inland brackish water bodies. In this paper we present results of a case study documenting the distribution and characteristics of storm surge deposits related to Hurricane Isaac (2012) in a wetland on the western shore of Lake Pontchartrain, Louisiana. Hurricane Isaac, a category1 storm, made landfall near the mouth of the Mississippi River on August 28, 2012. Due to its large size and slow movement, Isaac generated strong easterly winds across Lake Pontchartrain, producing a large storm surge along the west shore of the lake and unprecedented flooding in the surrounding lowlands. Loss-on-ignition, XRF, radioisotopic, and grain-size analyses conducted on sediment cores and surface samples from the area identify two distinct sedimentary signatures for the Hurricane Isaac deposits. Near the lake shore the signature is characterized by a laminated silty sand with a geochemical profile closely resembling that of lake bed material. Storm deposits located in a brackish swamp ~ 1km inland consist of a dark, low-organic mud with low concentrations of terrestrial metals and elevated concentrations of Br, S, and Cl. Differences in the storm signal are explained by the differing effect of topographical features on the depositional and transportation processes occurring at the two sites. Utilizing the geochemical/compositional signatures as a hurricane-generated storm surge proxy indicates the possible occurrence of a similar event predating the historical record.

Re-Evaluating the Geological Evidence for Late Holocene Marine Incursion Events along the Guerrero Seismic Gap on the Pacific Coast of Mexico

Despite the large number of tsunamis that impact Mexico’s Pacific coast, stratigraphic studies focusing on geological impacts are scanty, making it difficult to assess the long-term risks for this vulnerable region. Surface samples and six cores were taken from Laguna Mitla near Acapulco to examine sedimentological and geochemical evidence for marine incursion events. Sediment cores collected from behind the beach barrier are dominated by intercalated layers of peat and inorganic sediments, mostly silt and clay, with little or no sand. Sand- and shell-rich clastic layers with high levels of sulfur, calcium, and strontium only occur adjacent to the relict beach ridge remnants near the center of the lagoon. With the exception of one thin fine sand layer, the absence of sand in the near-shore cores and the predominance of the terrigenous element titanium in the inorganic layers, evidently eroded from the surrounding hillslopes, suggests that these large-grained intervals do not represent episodic marine incursions, but rather were likely formed by the erosion and redeposition of older marine deposits derived from the beach ridge remnants when water levels were high. These results do not support the occurrence of a large tsunami event at Laguna Mitla during the Late Holocene.

A 7000-year history of coastal environmental changes from Mexico’s Pacific coast: A multi-proxy record from Laguna Mitla, Guerrero:

The lack of multi-millennial multi-proxy paleoenvironmental reconstructions from Mexico’s Pacific coast has limited our understanding of the regional response to climate change and sea-level rise. A 479-cm core covering the last 6900 years was extracted from Laguna Mitla in the state of Guerrero on Mexico’s Pacific coast. Beginning as a Rhizophora-dominated salt pan ~6900 yr BP, at ~6500 yr BP, the site transitioned to a mangrove swamp dominated by Laguncularia, which lasted about 300 years. The beach barrier formed from ~6200 to 5200 yr BP, during which time, the site existed as an intermittently sheltered bay, the result of large, rapid changes in wave energy associated with the shifting barrier location and changes in stability. After the beach barrier was stabilized at ~5200 yr BP, water level at the coring site became a function of precipitation rather than sea level. Since that time, deposition has alternated between peat, laid down in a mangrove swamp, and clay intervals characterized by high concentrations of titanium and a predominantly regional pollen signal, representing open-water lagoon phases. Seven periods of increased water level, varying in duration, occurred during the backbarrier period, with El Niño-Southern Oscillation (ENSO) likely the main climatic mechanism causing these periodic shifts in the paleo-precipitation levels. We suggest that the deepest water levels detected over the last ~3200 years correlate with periods of increased ENSO activity. The spatial distribution of tropical cyclone rainfall, which represents a significant percentage of total annual precipitation along Mexico’s Pacific coast, may explain the inconsistencies between our record and paleoclimatic records from Mexico’s interior, but more work is needed to test this hypothesis.