Climate variability over the circum-Caribbean region during the past 1200 years from oxygen-isotope analyses of lake sediments

Lead Research Organisation: University College London
Department Name: Geography

Abstract

Variations in water availability, especially drought, on timescales of years to decades are a major concern for society. Changes in the frequency and magnitude of drought on such timescales are a likely outcome of future climate change, especially in subtropical regions. The area that encompasses the eastern part of Central America, the Gulf of Mexico and the Caribbean (hereafter the circum-Caribbean region) is likely to be especially sensitive to climate change in the future, especially in terms of the incidence and severity of drought: it is this region that is the subject of our proposed research. Meteorological records of rainfall are too short to encompass the full range of variations in past rainfall on timescales of years to decades or to indicate whether geographical patterns have changed through time and under different conditions. Natural 'archives' of past climate, including lake and marine sediments, speleothems (cave deposits) and tree rings, provide an opportunity to extend the meteorological records further back into the past and to shed light on the modes and causes of rainfall variability. In this research, we will investigate changes in rainfall over the past 1200 years using oxygen-isotope analyses of the calcite shells of ostracods preserved in lake sediments. We plan to analyse lake sediment cores that have already been collected from sites in the Yucatan Peninsula of eastern Mexico, Jamaica, Haiti and Barbuda. These sites are located on a west to east transect, along which changes in rainfall are known to have occurred over recent decades. Our reconstructions will be complemented by existing studies along a north to south transect within the circum-Caribbean region, thus allowing us to investigate changes in the geographical patterns of past rainfall. The past 1200 years is an important time period to study as it covers intervals of marked change in climate including the Medieval Climate Anomaly (MCA) of predominantly wet climate, the drier little ice age (LIA) and the terminal classic period of marked drought at the end of the MCA, which is thought to have contributed to major societal change in the Yucatan Peninsula. The broad variations in climate over this interval are quite well known, but changes in the geographical patterns in the region, despite being implied by existing data, are poorly constrained. Furthermore, links to potential causes, such as variations in ocean circulation and sea-surface temperatures, changes in solar activity and volcanic eruptions, are not well understood. By generating new reconstructions of variability in rainfall over the past 1200 years, we will provide further insights in to the nature and causes of change during this period. By extending the timespan of records beyond that of meteorological data, we will be able to show whether geographical patterns of rainfall variability have remained constant over the recent past or, as seems likely, have changed. In addition to providing important palaeoclimatic data for the circum-Caribbean region, our research will generate much-needed reconstructions of climate for archaeologists, especially those working on links between climate and society in Mexico and Barbuda.

Planned Impact

We have identified the following beneficiaries of the research described in this proposal.

1. State governments and government agencies. In Mexico, these include the governments of the States of Quintana Roo and Yucatan, which will be accessed via Universidad Autónoma de Yucatán (UADY) and ECOSUR (Centro de Investigaciones Ecologicas del Sureste). In Jamaica, the Ministry of Land, Water, Environment and Climate Change, the Water Resources Authority and the Jamaican Meteorological Office have expressed interest in our potential findings.

2. Schools and 6th form colleges in the UK and Jamaica. We have identified a number these who would welcome talks, presentations and workshops on the board themes addressed in our proposal. The precise subject matter and mode of delivery will depend on the age group of the audience, but will include general talks on climate and society to younger (e.g. UK year 6) pupils and seminars on palaeodata to High School and 6th form students. Target schools/colleges in the UK include Esher College, Hinchley Wood School and 6th Form College, Thames Ditton Junior School (all Surrey) and in Jamaica Meadowbrook High School, Wolmer's Boys and Wolmer's Girls schools, Jamaica College (all Kingston area).
 
Description Monitoring of Yaal Chac since 2009 confirms that it is highly evaporated and effectively closed, in spite of being called a 'cenote' which would imply a free connection to the regional groundwater. Monitoring of Fredshwater Pond and Wallywash Great Pond confirms that these lakes are also influenced by evaporative enrichment. The monitoring data therefore confirm our original assumption that the lake-sediment oxygen-isotope records are proxies for changing effective moisture.

The oxygen-isotope records from lake sediments show large and systematic changes over the course of the records. In low latitude lakes such as the ones in our study, time series of oxygen-isotopes in lacustrine carbonates are controlled primarily by the isotopic composition of lake water, which in turn is determined by the degree of evaporative concentration and ultimately effective rainfall, as confirmed by the monitoring data referred to above. Our data from Freshwater Pond, Barbuda, provide a record that covers the period from the 16th century to present. Episodes of strong El Niño-like activity that occurred during the 18th, early 19th and late 20th centuries were associated with inferred drier conditions in Barbuda whereas inferred wetter periods in the late 18th and the late 19th century correspond with La Niña-like conditions. Further dating of the Yaal Chac core YC2011 sequence has shown that there is no hardwater effect influencing the most recent sediments (NERC Radiocarbon allocation1724.0713), but may have been more significant earlier in the record with an offset of 471 years recorded between bulk sediment and plant macrofossil ages at 389 cm (NERC Radiocarbon 1943.1015).Dating now confirms that the core sequence covers much of the Holocene. The downcore d18O record indicates reduced evaporative concentration in the mid Holocene, with two major drying events since 471 ± 37 yr BP. Data from Wallywash Great Pond also shows marked variability, which we interpret to represent shifts in effective moisture. However, until the age models for these sites have been fully developed (see below), the synchronicity or lack thereof between changes in Jamaica and the other sites will remain unclear.
Exploitation Route Once the age models have been fully developed, our time series of oxygen-isotope analyses will be of interest to others working on the palaeoclimate of the northern neotropics, to archaeologists working in this region and to climate modellers.
Sectors Environment

 
Description Some of the data from the project have fed into undergraduate and postgraduate teaching, including field-based teaching, at UCL and the University of Nottingham
First Year Of Impact 2015
Sector Education
 
Description Envision DTP
Amount £71,257 (GBP)
Funding ID NE/L002604/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 10/2014 
End 04/2018
 
Description NERC Isotope Geosciences Facilities Steering Committee
Amount £7,500 (GBP)
Funding ID IP-1394-1113 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 02/2014 
End 02/2015
 
Description NERC Isotope Geosciences Laboratory
Amount £29,200 (GBP)
Funding ID IP1671-1116 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 11/2016 
End 07/2017
 
Title Ostracod carbonate isotope data, Freshwater Pond, Barbuda 
Description Ostracod carbonate isotope data, Freshwater Pond, Barbuda supplied to database held at National Geoscience Data Centre - British Geological Survey 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact None yet 
 
Description Analysis of tephra from Jamaican lake sediments 
Organisation Royal Holloway, University of London
Department Department of Geography
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution Lake sediments provided for tephra analysis
Collaborator Contribution Partners at Royal Holloway have successfully screened the sediments for tephra with a view to undertaking further work
Impact None yet - work is ongoing
Start Year 2015
 
Description Evolution of the isotope composition of precipitation during the passage of Hurricane Matthew over Jamaica 
Organisation University of Cambridge
Department Department of Engineering
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution Provision of water samples for isotope analysis
Collaborator Contribution Oxygen and hydrogen isotope analyses of rainwater samples
Impact None to date
Start Year 2016
 
Description Scanning XRF analysis of sediment cores from Jamaica and Barbuda 
Organisation University of Exeter
Department College of Life and Environmental Sciences
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution Cores provided for XRF analysis
Collaborator Contribution XRF analysis of sediment cores
Impact Scanning XRF data
Start Year 2015
 
Description Synthesising regional climate records from N. Neotropics 
Organisation University of North Carolina at Chapel Hill
Country United States of America 
Sector Academic/University 
PI Contribution Collaborative work on synthesis of climate records
Collaborator Contribution Collaborative work on synthesis of climate records
Impact Presentation at forthcoming PAGES conference in Zaragoza, Spain (2017)
Start Year 2016
 
Description Synthesising regional climate records from N. Neotropics 
Organisation University of Tennessee
Country United States of America 
Sector Academic/University 
PI Contribution Collaborative work on synthesis of climate records
Collaborator Contribution Collaborative work on synthesis of climate records
Impact Presentation at forthcoming PAGES conference in Zaragoza, Spain (2017)
Start Year 2016
 
Description 6th Form Talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Talk to 6th form geography and politics students reported in college newsletter, which is circulated to all staff and parents of this large (almost 1800 on roll) 6th form college
Year(s) Of Engagement Activity 2016