Towards radiocarbon calibration beyond 28ka using speleothems from the Bahamas

We present a new speleothem record of atmospheric Δ14C between 28 and 44 ka that offers considerable promise for resolving some of the uncertainty associated with existing radiocarbon calibration curves for this time period. The record is based on a comprehensive suite of AMS 14C ages, using new low-blank protocols, and U–Th ages using high precision MC-ICPMS procedures. Atmospheric Δ14C was calculated by correcting 14C ages with a constant dead carbon fraction (DCF) of 22.7 ± 5.9%, based on a comparison of stalagmite 14C ages with the IntCal04 (Reimer et al., 2004) calibration curve between 15 and 11 ka. The new Δ14C speleothem record shows similar structure and amplitude to that derived from Cariaco Basin foraminifera (Hughen et al., 2004, 2006), and the match is further improved if the latter is tied to the most recent Greenland ice core chronology (Svensson et al., 2008). These data are however in conflict with a previously published 14C data set for a stalagmite record from the Bahamas — GB-89-24-1 (Beck et al., 2001), which likely suffered from 14C analytical blank subtraction issues in the older part of the record. The new Bahamas speleothem ∆14C data do not show the extreme shifts between 44 and 40 ka reported in the previous study (Beck et al., 2001). Causes for the observed structure in derived atmospheric Δ14C variation based on the new speleothem data are investigated with a suite of simulations using an earth system model of intermediate complexity. Data-model comparison indicates that major fluctuations in atmospheric ∆14C during marine isotope stage 3 is primarily a function of changes in geomagnetic field intensity, although ocean–atmosphere system reorganisation also played a supporting role.

The organization of statistics in Bahamas, Barbados, Belize and Trinidad and Tobago

Includes bibliography

Hurricanes Frances and Jeanne in 2004: their impact in the Commonwealth of the Bahamas: preliminary version

Includes bibliography

The impact of immigration on Caribbean microstates: Bahamas, British Virgin Islands, Saint Maarten, United States Virgin Islands

Includes bibliography

Selected information on the Bahamas

Includes bibliography

An assessment of the economic impact of climate change on the tourism sector in the Bahamas

The Bahamas is at great risk and vulnerability given its geographical features as a low-lying, sea encircled country. If projected sea level rise is reached by 2050, between 10-12% of territory will be lost, especially in coastal zones where the main tourism assets are located. Vulnerability could also be manifested if flight carbon emission taxes are established in the main source markets, representing an economic threat to the tourism sector for the islands. The impact of climate change on main tourism demand variables will cause some losses to the country‟s income and government revenues. This would be acting conjointly with some local threats to tourism assets and trends in future global tourism demand. The second and no less important threat is tropical cyclones, which may be associated with raising sea level. Estimations posited the amount of losses in excess of 2400 million US$ for the four decades under examination. It is to be pointed out that there is still a lack of comparatively accurate data collection and analysis on this subject, a point deserving more attention in order to deepen the understanding of, and to extract better lessons from these extreme events. In the same period, total estimated impacts of progressive climate change are between 17 and 19 billions of B$ with estimated discount rates applied. The Bahamas is a Small Island Developing State with low growth on GHG emissions (second in Latin America), as well as a relative short capacity to lower emissions in the future. The country has a relative delay in the application of renewable energy systems, a solution that, provided documented studies on-site, might turn out to be fundamental in the country‟s efforts to establish mitigation related policies. The Bahamas currently has institutions and organizations that deal with climate change-related issues and an important number of measures and courses of action have been set up by the government. Nevertheless, more coordination among them is needed and should include international institutions. This coordination is essential even for the first steps, i.e. to conduct studies with a bottom-up approach in order to draw more accurate programs on adaptation and mitigation. It is fundamental for tourism to keep track of potential losses in tourist attractions (and to act accordingly), related to correspondent losses in biodiversity, water resources and coastal erosion. Also, actions to fight climate change impacts might improve the islands security standards, quality of living and protect cultural and heritage assets. These elements may definitely shape the future of the country‟s competitiveness as a tourism destination. It is possible and necessary to decide about the options with good cost-benefit ratio and reasonable payback periods, notwithstanding that cost-benefit analysis requires more refined and accurate data to provide precise and locally adapted options.

Ecosystem fragmentation drives increased diet variation in an endemic livebearing fish of the Bahamas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Cenozoic radiolarians from the Bahamas

Radiolarians from two sites north of Little Bahama Bank (Sites 627 and 628) are correlated with assemblages from sites on the southeastern U.S. coastal plain and continental shelf and from DSDP Sites 391 and 534 in the Blake-Bahama Basin. Results show that deposition of biogenic silica-rich sediments occurred in this region from the late Oligocene through middle Miocene, although the record is interrupted by unconformities. Radiolarians help constrain the age of a mass-transported deposit at Site 627 that appears to be coeval with the Great Abaco Member of the Blake Ridge Formation.

Chronostratigraphy of sediments from the Bahamas

Continuous cores drilled during the Bahamas Drilling Project (BDP) and the Ocean Drilling Program (ODP) Leg 166 along a transect from the top of Great Bahama Bank to the basin in the Straits of Florida provide a unique data set to test the assumption in seismic stratigraphy that seismic reflections are time lines and, thus, have a chronostratigraphic significance. Seismic reflections that are identified as seismic sequence boundaries (SSBs) were dated by means of biostratigraphy in the five ODP sites and by a combination of biostratigraphy, magnetostratigraphy and Sr isotope stratigraphy in the two BDP sites. The seismic reflection horizons are carried across a variety of facies belts from shallow-water carbonates over slope carbonates to drift deposits in the Straits of Florida. Within this system 17 SSBs were identified and dated. Despite the fact that the seismic reflections cross several facies belts, their ages remain remarkably constant. The average offset in all sites is 0.38 Myr. In no cases do the seismic reflections cut across time lines. The age differences are the combined result of the biostratigraphic sampling frequency, the spacing of marker species that required extrapolation of ages, and the resolution of the seismic data. In addition, uncertainties of age determination in the proximal sites where age-diagnostic fauna are rare add to the age differences between sites. Therefore, it can be concluded that the seismic reflections, which mark the SSBs along the Bahamas Transect, are time lines and can be used as stratigraphic markers. This finding implies that depositional surfaces are preferentially imaged by reflected seismic waves and that an impedance contrast exists across these surfaces. Facies successions across the sequence boundaries indicate that the sequence boundaries coincide with the change of deposition from times of high to low sea level. In the carbonate setting of Great Bahama Bank, sea-level changes produce changes in sediment composition, sedimentation rate and diagenesis from the platform top to the basin. The combination of these factors generates differences in sonic velocity and, thus, in impedance that cause the seismic reflection. The impedance contrasts decrease from the proximal to the distal sites, which is reflected in the seismic data by a decrease of the seismic amplitude in the basinal area.

U-Th dating of marine sediments from the Bahamas slope

In order to understand the driving forces for Pleistocene climate change more fully we need to compare the timing of climate events with their possible forcing. In contrast to the last interglacial (marine isotope stage (MIS) 5) the timing of the penultimate interglacial (MIS 7) is poorly constrained. This study constrains its timing and structure by precise U-Th dating of high-resolution delta18O records from aragonite-rich Bahamian slope sediments of ODP Leg 166 (Sites 1008 and 1009). The major glacial-interglacial cycles in delta18O are distinct within these cores and some MIS 7 substages can be identified. These sediments are well suited for U-Th dating because they have uranium concentrations of up to 12 ppm and very low initial 230Th contributions with most samples showing 230Th/232Th activity ratio of >75. U and Th concentrations and isotope ratios were measured by thermal ionisation mass spectrometry and multiple collector inductively coupled plasma mass spectrometry, with the latter providing dramatically better precision. Twenty-nine of the 41 samples measured have a delta234U value close to modern seawater suggesting that they have experienced little diagenesis. Ages from 27 of the 41 samples were deemed reliable on the basis of both their U and their Th isotope ratios. Ages generally increase with depth, although we see a repeated section of stratigraphy in one core. Extrapolation of constant sedimentation rate through each substage suggests that the peak of MIS 7e lasted from ~237 to 228 ka and that 7c began at 215 ka. This timing is consistent with existing low precision radiometric dates from speleothem deposits. The beginning of both these substages appears to be slightly later than in orbitally tuned timescales. The end of MIS 7 is complex, but also appears to be somewhat later than is suggested by orbitally tuned timescales, although this event is not particularly well defined in these cores.