Rainfall dynamics in Barbuda during the Little Ice Age

Summary of our new research paper on effective rainfall in Barbuda, Lesser Antilles

The coring team in Barbuda
The coring team in Barbuda

Established palaeoclimate records (E.g. Haug et al., 2001; Hodell et al., 2005; Lane et al., 2011) suggest that aridity was widespread across the Caribbean during the Little Ice Age (ca. 1400 – 1850 CE). Such dry conditions are hypothesised to result from cooler tropical sea surface temperatures and a southward migration of the Atlantic ITCZ. To determine whether arid conditions were present in the northeastern Caribbean during this period, we developed a new sediment-based reconstruction of effective rainfall from Freshwater Pond in Barbuda.

Freshwater Pond, Barbuda
Freshwater Pond, Barbuda

Freshwater Pond (17°36′05″N, 61°47′28″W; ~ 6 m a.s.l.) is a permanent inland fresh- to brackish-water lake which is closed hydrologically and situated on the Codrington Limestone Group. Its late-Holocene origin is thought to be the result of rising eustatic sea level that reached its present-day maximum level ca. 3000 yr BP (Fairbanks, 1989) and the subsequent development of a rainfall-derived freshwater lens, which rests above the underlying saltwater table (Brasier and Donahue, 1985). Consequently, the pond is very sensitive to precipitation variability (Stoddart et al., 1973).

Fig 3. Comparison of proxy-based evidence from the Freshwater Pond sediment record with AMO and ENSO indices. Source: Burn et al. (2016)
Fig 3. Comparison of proxy-based evidence from the Freshwater Pond sediment record with AMO and ENSO indices. Source: Burn et al. (2016)

Results of microfossil analyses from the sediment record at Freshwater Pond (Fig 3) challenge the occurence of uniformly-dry conditions across the Caribbean Region during the Little Ice Age. Comparisons between this proxy-evidence and tree-ring based indices of the Atlantic Multidecadal Oscillation (AMO) and El Nino Southern Oscillation (ENSO) indicate that effective rainfall in Barbuda was highly variable at that time and appears to be influenced by the interplay between different Atlantic and Pacific modes of climate varibility.

Please visit the publishers website to access the paper or download a copy of the final accepted manuscript here.

References:

Brasier M and Donahue J (1985) Barbuda – An emerging reef and lagoon complex on the edge of the Lesser Antilles island arc. Journal of the Geological Society 142: 1101–1117.

Burn MJ, Holmes JA, Kennedy LM et al. (2016) A sediment-based reconstruction of Caribbean effective precipitation during the ‘Little Ice Age’ from Freshwater Pond, Barbuda. The Holocene 26(8): 1237-1247.

Fairbanks RG (1989) A 17,000-year glacio-eustatic sea level record: Influence of glacial melting rates on the Younger Dryas event and deep-ocean circulation. Nature 342: 637–642.

Haug GH, Hughen KA, Sigman DM et al. (2001) Southward migration of the intertropical convergence zone through the Holocene. Science 293: 1304–1308.

Hodell DA, Brenner M, Curtis JH et al. (2005) Climate change on the Yucatan Peninsula during the Little Ice Age. Quaternary Research 63: 109–121.

Lane CS, Horn SP, Orvis KH et al. (2011) Oxygen isotope evidence of Little Ice Age aridity on the Caribbean slope of the Cordillera Central, Dominican Republic. Quaternary Research 75: 461–470.

Stoddart D, Bryan G and Gibbs P (1973) Inland mangroves and water chemistry, Barbuda, West Indies. Journal of Natural History 7: 33–46.

Atlantic hurricane activity during the last millennium

Summary of our new research paper published in Scientific Reports

Atlantic tropical cyclones are a persistent threat to Countries surrounding the tropical Atlantic Ocean and Caribbean Sea. The recent devastation on the Island of Dominica is a case in point where Tropical Storm Erica caused flooding and landslides and killed at least 20 people and left more than 50 missing. While these storms are often perceived as a threat to the economies of the Small Island Developing States of the Caribbean Region (primarily because of their potential devastating impacts on life, agricultural productivity and food security), hurricanes also contribute significantly to the water budget across the region by replenishing water reserves and buffering national economies from the threat of drought.

Despite recent advances in our understanding of how climatic change may control tropical cyclone activity on a global scale, there is still no consensus on the extent to which activity in the Atlantic basin is influenced by human activity. Indeed, the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC; Christensen et al. 2013) concluded that there is low confidence in region-specific projections of tropical cyclone activity and that it remains uncertain whether recent changes in Atlantic tropical cyclone activity lie outside the range of natural variability. In order to determine the long-term variability of hurricane activity over the last 1000 years, we have developed an index of long-term hurricane activity known as the Extended Hurricane Activity (EHA) index.

We present the new reconstruction of hurricane activity in a recent paper published by the Nature Publishing Group in the Open Access journal Scientific Reports and show that a strong correlation exists between the EHA index (developed from the published Jamaican lake level record), the Accumulated Cyclone Energy index (ACE) and sea surface temperature variability within the Main Development Region (MDR) of tropical cyclone activity for the modern historical period (Fig. 1).

When extended further back in time (Figure 4 (original article)) hurricane activity appears muted during the Medieval Climate Anomaly (~900–1350 CE) and becomes more variable (and extreme) during the so-called Little Ice Age (~1450–1850 CE), a period of cooler temperatures recorded in the Northern Hemisphere and thought to be associated with a combination of lower solar and enhanced volcanic activity. The index supports evidence for a gradual increase in Atlantic hurricane activity during the industrial period (ca. 1870-present), however, we show that contemporary activity has not exceeded its longer-term natural variability exhibited over last 1000 years.

Please visit the Scientific Reports Website for further details or alternatively download a pdf copy of our paper here.

References:

Burn, M.J. and Palmer, S.E. (2015): Atlantic hurricane activity during the last millennium. Scientfic Reports 5, 12838; doi: 10.1038/srep12838

Christensen, J. H. et al. in Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (eds. Stocker, T.F., Qin, D., Plattner, G.-K., Tignor, M., Allen, S.K., Boschung, J., Nauels, A., Xia, Y., V., B. & P. M., M.) (Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2013) Chapter 14.